Mass flow control requires precision. When poor lighting prevents you from being able to monitor your process, you cannot maintain optimal accuracy and efficiency. At Alicat, we’re with you…even in the dark.

Illuminated displays and tactile interfaces allow you to monitor and adjust mass flow control processes effectively, even under poor lighting conditions.

Backlit color TFT display

The most straightforward solution to mass flow control in poorly lit lab environments is to use a mass flow controller that has an illuminated display. Our color TFT display shows mass flow rate, volumetric flow rate, pressure, temperature, setpoint and an optional totalizer simultaneously on a large 2.1″ diagonal backlit display. The adjustable backlight has 12 levels of variable brightness to achieve the optimal lighting balance for your environment. Like our standard monochrome displays, the buttons on our color displays are raised so you can fully operate the mass flow controller in absolute darkness. There is also a backlight toggle button to turn the backlight off while leaving the device in operation.

Backlit color TFT remote display

Our backlit color TFT displays are also available in a remote display configuration. Here, the TFT is mounted inside a bezel with four mounting holes and connected to the mass flow controller by up to 12 feet of shielded ribbon cable. This affords convenient viewing of the display when the controller body is mounted in a place that is difficult to access.

LED-illuminated Local SetPoint Module

LSPM Local SetPoint Module for controllers

If you already have a mass flow controller without an illuminated display, a convenient way to monitor and control your process in poor lighting is to connect it to Alicat’s Local SetPoint Module (LSPM). This add-on accessory provides a simple red LED-illuminated digital display and a control dial for easy analog setpoint control. The seven-segment LED display can show either the flow rate or the commanded setpoint via a recessed mode button. A tracking indicator turns red if the actual mass flow rate deviates from the setpoint by more than 2%. This is a simple solution for controlling and monitoring gas flow processes in poorly lit environments.

What are other ways that you have found to be effective in illuminating dark mass flow control environments? Let us know in the comments below!

Alicat portable mass flow calibrator with optional backlit color display

Verification, validation and calibration are different but interrelated processes that are at times conflated with each other and interpreted as synonymous. Furthermore, their interpretation and application vary from industry to industry. Ask three people what these terms mean, and you will get three different answers. Please feel free to chime in with your own perspective by leaving us a comment below.

At a basic level, the three terms may be defined as follows:

• Calibration ensures the measurement accuracy of an instrument compared to an known standard;
• Verification ensures the correct operation of equipment or a process according to its stated operating specifications; and
• Validation ensures that a system satisfies the stated functional intent of the system.

Calibration: Is it accurate?

Flow calibration is a two-fold process of measuring and adjusting the accuracy of an instrument relative to a known measurement standard called a calibration standard. This process begins with comparing the measured flow of a meter or controller to that of the calibration standard. Following this assessment, the meter or controller is then made to conform to the readings of the calibration standard within the stated accuracy specifications.

Alicat portable calibration unit with three flow meter ranges and integrated battery

A primary calibration standard is directly measured against a reference standard provided by a bureau of standards, such as NIST. These standards tend to be very expensive. A secondary, or transfer, calibration standard is directly measured against this primary calibration standard in the lab and then serves in lieu of the primary standard in the field. Alicat mass flow meters and pressure gauges purchased with the “HC” (High-accuracy Calibration) option can serve as NIST-traceable secondary calibration standards in the field. An Alicat portable that is calibrated as a transfer standard becomes a portable rapid calibration lab.

We apply this same concept to our line of Portable Calibration Units (PCU), which combine three battery-powered flow meters of complimentary ranges in a single case, all with High-accuracy Calibration. This instrument is the big brother of a single portable meter, able to calibrate flow devices across a very broad array of flow ranges.

Verification: Is it working correctly?

Alicat Whisper Series mass flow meter, with optional color display

Flow verification is a procedure designed to ensure that your equipment or process is still doing what it was designed to do from the beginning. In the context of the automotive industry, you might use a flow meter to verify that the total consumption of air per minute in automated painting robots is still what it was when you bought them. This is often an internal process that focuses on maintaining the performance of a device or process over time, as opposed to a mandate or regulation coming from an outside source.

Our series of mass flow meters, both wired and portable, are excellent choices for in-line verification of process flow rates and absolute pressure readings. For volumetric measurements, the low pressure drop of our Whisper Series provides an unobtrusive way to measure volumetric flow rates with minimal affect on the flow rate being measured.

Validation: Is its system function satisfactory?

A validation process ensures that the components of a system function together to meet the need or intent of a customer or regulating body. The aim of validation is to ensure that the components of a system work together to produce the intended result for which the system was designed. Whereas verification focuses on the right operation of a process (or product) itself, validation tends to focus on the right output of the process.

For example, the EPA closely regulates the output of stack gases at power plants and refineries. Whereas flow verification might be used to confirm the maximum flow rate of a valve in the analyzer system, flow validation would be used to ensure that the analyzer system as a whole delivers a throughput that allows a level of gas analysis that meets or exceed the EPA requirements. The emphasis in validation is on the functioning of a process or whole system to meet the needs within a larger system.

Please call 888-290-6060 or email us at info@alicat.com to discuss your calibration, verification and validation needs with an Alicat applications engineer today!

Multiple unit calibration setup, including the three-meter portable calibration unit (PCU)

Flow calibration, verification and validation processes can look rather similar but in fact have differing objectives, as we outlined in a previous article. The ability of Alicat mass flow meters and mass flow controllers to provide instant flow readings and switch to different calibration gases at the touch of a button makes these processes much faster and easier. Most of our mass flow instruments now ship with up to 130 preloaded pure and mixed gas calibrations to simplify flow calibration tasks involving multiple gases.

Gas mixing flow validation setup, including mass flow meter equipped with COMPOSER™

Now, what happens when your mixed gas composition changes? Let’s say you’re analyzing stack gases for the EPA, and the relative concentrations of CO2, O2 and NOx in the stack gas changes from day to day. Your analyzer knows what today’s composition is, but your flow meter does not. When it comes time to validate the flow rates of the gas being analyzed, you have some unsatisfactory options:

1. Calibrate your mass flow meter at the factory to an estimated typical gas composition for all verifications. This will produce inaccurate results most of the time, except when your actual mix happens to reflect the ideal composition used as the basis of verification. Achieving higher accuracy by this method requires complex calculations of the differential viscosities and compressibilities of the actual gas mix at the actual validation pressure and temperature.
2. Calibrate your mass flow meter for nitrogen or air as a default, and then apply K-factors to estimate the actual gas flow. This method again introduces inaccuracies through the K-factors, which are valid for certain temperatures, pressures and flow rates. Outside of this sweet spot, K-factors inaccuracy increases. K-factors that do not match your specific gas mixture introduce even greater inaccuracy.
3. Conduct validation with volumetric flow measurement using a bubble meter or piston prover. Conversion to mass flow then requires the use of complex tables and calculations that derive total gas mix viscosity and compressibility for the temperature and pressure conditions used for validation. This process can take a long time for the volumetric flow measurement itself, and then much greater time for the back-calculation of mass flow rates.

Gas Select COMPOSER™ gas mix calibration firmware, shown on optional color display

Alicat’s COMPOSER™ gas composition builder makes possible a faster and easier method. Included on most new Alicat mass flow meters and controllers at no additional cost, COMPOSER™ allows you to create your own custom gas mixture calibration right on the instrument. Simply select a gas constituent from the onboard Gas Select menu, and define its relative concentration to 0.01% of the total molar mix. You can do this for up to 5 constituent gases, and you can create and store 20 COMPOSER™ mixes on the instrument at a time. When it is time for flow validation simply select the mix that matches your current gas composition. If no mix matches, you can create another one in just 2 minutes or less, without ever needing a computer. Take a look at the video below to see what COMPOSER™ can do for you!

Gas Select COMPOSER™ – Accurate Mixed Gas Flow Measurement

When your gas composition changes, will your flow readings still be accurate? Alicat Scientific presents COMPOSER™, the world’s first on-the-fly mixed gas composition builder, for mass flow meters and mass flow controllers.

Whispers Win Halma Product Innovation Award

Alicat’s Whisper™ series of mass flow meters and controllers with low pressure drop received Halma’s Product Innovation Award last week at the Halma Innovation and Technology Exposition (HITE) in Barcelona, Spain. This annual award recognizes new products that have made a significant impact on our industries, including flow verification, environmental monitoring, atmospheric research, leak testing and natural gas control. Alicat also received the Company of the Year Award for the Environmental & Analysis Sector within Alicat’s parent company, Halma plc.

Whisper-series mass flow meter, shown with optional color display

We developed the Whisper series in order to meet the needs of customers whose processes were too sensitive for traditional flow measurement and control instruments. Having very little pressure drop, a Whisper can be added to a system without inducing backpressure or significantly affecting volumetric flow measurement. Running a pressure-based flow meter on very little line pressure–and still expecting laboratory-class accuracy and repeatability from it–is much like asking a Grand Prix race car to win a race on fumes.

“Invisible” Flow Measurement

Whispers solve a long-standing problem for customers with low pressure flow requirements: Flow measurement technologies change the very flow conditions they are designed to measure. This is especially apparent when working with volumetric flows, whose rates change as the line pressure increases or decreases. Adding a flow meter consumes some of the line pressure, thus changing the actual volumetric flow rate as it is being measured.

Employing both a flow path that virtually eliminates pressure drop (consumption of line pressure) and a custom sensor that is powerful enough to measure the little differential pressure that remains, Whisper flow meters operate with minimal impact to flowing processes. Whispers are nearly invisible to the flow stream and therefore able to monitor flow rates without changing the rates. This is especially noticeable when measuring volumetric flows or calibrating volumetric flow instruments such as variable area meters, making Whispers ideal for these applications.

Flow Management at Atmospheric Pressures

Alicat Whisper portable mass flow meter, shown with optional color display

Beyond the impacts upon flow measurement, adding a meter to a gas stream can affect the process itself by inducing unwanted backpressure. This added backpressure can constrict or halt flows that begin with little line pressure. In the case of process analysis, added backpressure can also interfere with the measurement accuracy of in-line process analyzers. Portable Whisper meters are ideal for validating the flow in these applications with minimal impact to the actual process.

The very low pressure drop of Whisper mass flow instruments also allows them to monitor or control flows just above or below atmospheric pressures. Where most flow controllers would be unable to achieve full-scale flows, Whisper mass flow controllers can reach flows as high as 500 slpm with less than 50 mbar of pressure drop. A gas analysis system for environmental monitoring can employ a Whisper flow controller to draw air through the analyzer using very soft vacuum. Likewise, atmospheric research conducted at high altitudes can make use of the very low pressure drop of the Whisper series to negate the limitations of decreased atmospheric pressure.

Responsive Flow Measurement and Control for Leak Testing

Alicat high-flow Whisper mass flow controller, shown with downstream valve

A special application for Whisper mass flow controllers is leak testing, as well as flow characterization. The typical setup for the mass air flow method of leak testing requires a pressure controller to maintain leak test pressures and a mass flow meter to monitor leak rates. Because Alicat pressure-based flow controllers have the capability to control pressure while monitoring mass flow rates, a single Whisper-series flow controller can single-handedly accomplish the task of leak testing.The minimal internal restrictions of the Whisper controller give it exceptionally fast response in reading leak rates while maintaining leak test pressures. The same characteristics make flow characterization processes very easy and efficient.

Pressure drop is an important physical and financial consideration when working with subatmospheric and vacuum applications. Pressure drop is the loss of line pressure caused by frictional resistance in the flow path. Everything causes some degree of frictional resistance on the fluid flowing, such as a valve, fittings and tubing, and this results in the loss of pressure. By determining how much pressure drop each part causes, you can calculate how much pressure you need to run your process. The lower the total pressure drop of the system, the less gas is needed to run it, which saves you money.

How Pressure Drop Works

Static pressure affects the amount of pressure drop across an Alicat mass flow meter, and this is important to consider when choosing a device for use in sub-atmospheric pressures. Alicat devices calculate flow rates by measuring the differential pressure across a laminar flow stack. Since the flow is laminar, we can use the Hagen-Poiseuille equation to calculate the pressure drop caused by an Alicat device. The equation is notated as follows:

∆P= 8μLQ/(πr^4)

Where:
ΔP = pressure drop
L = length of pipe
η = viscosity of the fluid
Q = volumetric flow rate
r = radius of pipe
π = mathematical constant Pi

Since Alicat mass flow meters measure the pressure drop internally, L and r are constant for each flow device. Assuming the gas viscosity (η) remains the same, the pressure drop increases proportionally to the volumetric flow rate.

ΔP ∝ Qη

In a previous blog post, we explained that decreasing your static line pressure increases the volume of gas flowing through your system and therefore your volumetric flow rate. With this thought in mind, the relationship above shows that increasing volumetric flow (as a result of our decrease in static pressure) also increases pressure drop.

For the sake of simplifying this concept, I am going to pretend temperature remains constant or does not exist in the following example. Say I fill up a balloon that has been blown up to perfectly fit through a tube. I then make a road trip up into the mountains with the same balloon and tube, and attempt to fit the balloon through the tube. Since I am at higher elevation, there is less pressure compressing the molecules in the balloon, resulting in the balloon increasing in size and volume. I can still fit the balloon through the tube, but I have to apply more force since it now takes up more volume and generates more resistance against the tube walls. Pressure drop increases as static pressure decreases.

Sizing Flow Meters for Subatmospheric Applications

Understanding this relationship between static pressure and pressure drop will help you select the appropriate mass flow device for your subatmospheric application. The product specification sheets on our website provide the pressure drops for Alicat mass flow meters and controllers at atmospheric pressures. Let’s say we need to find a mass flow meter that can measure a maximum of 500 sccm at half an atmosphere (½ atm) of pressure (about 7.4 psia). In our previous post, we saw that 500 sccm becomes 1000 ccm at ½ atm. Since our devices by default are sized for the mass flow rate and not the volumetric flow rate, you will need to increase the size of the device to accommodate the increased volume of the gas.

The solution is to choose a 1000-sccm device (Alicat part number M-1SLPM-D) instead of a 500-sccm device (M-500SCCM-D), and then requesting a custom range of 500 sccm for the mass flow and 1000 ccm for the volumetric flow. Both of these instruments have full-scale pressure drops of 1 psid at 1 atm. At ½ atm, the M-500SCCM-D mass flow meter’s pressure drop would theoretically double to 2 psid at full scale, since the volume of the gas has doubled. However, using the larger M-1SLPM-D meter at ½ atm results in the full-scale pressure drop of 1 psid. Essentially, we are doubling the tube size to fit a balloon that has doubled in size. At ¼ atm, you would need the M-2SLPM-D meter with a range of 500 SCCM for mass flow and 2000 for volumetric flow, since the volumetric flow is now 4 times the mass flow.

Mass Flow Meters with Low Pressure Drop

Now, this works if you have enough pressure in your subatmospheric system to lose a whole psi through the flow meter. If we look at the available pressure at ½ atm, the pressure drop across the oversized M-1SLPM-D meter restricts 1 psid, or around 14% of your available pressure. It gets even tighter working at ¼ atm, where the oversized M-2SLPM-D meter again induces 1 psid of pressure drop, which is now 27% of your available pressure. This is not optimal, especially when you are limited in your available pressure.

Whisper-series mass flow meter, shown with optional color display

Ah-ha! Alicat has a solution: Our “Whisper” series of low pressure drop mass flow meters are perfect for this type of scenario, since their pressure drops are very low compared to our standard M-series meters. An oversized MW-1SLPM-D Whisper meter has a pressure drop of only 0.07 psid at ½ atm and 500 sccm, which is now just 1% of your available pressure. Both the standard mass flow meter and the Whisper meter will perform with the same accuracy under these conditions, but using a low pressure drop Whisper will give you a lot more breathing room in terms of pressure loss as you design your subatmospheric system.

If you have questions about your subatmospheric or vacuum application, please contact Alicat (info@alicat.com or 888-290-6060) so one of our applications engineers can help you find the right solution.

Whether you are giving your new Alicat mass flow controller a setpoint for the first time or putting a trusted Alicat pressure controller into a new system, your device sometimes may need a few adjustments to achieve the highest degree of control stability. This is done through PID tuning, which adjusts a set of values that control how fast a controller will get to the setpoint and how stable it will be at that setpoint. Alicat sends out controllers with a standard set of PID values that will work for most applications, if no user specific parameters are provided at the time of order. However, as all applications are unique, these PID terms can require some adjustments. The values assigned to each parameter can seem arbitrary and therefore make PID tuning frustrating and seem like random guessing. In this post, we will demystify some of the principles behind PID tuning and offer some tips for tuning in the field.

Proportional, Integral, Derivative

Let’s start with some formal definitions. PID stands for Proportional, Integral, Derivative, the three components of the control algorithm.

Proportional. One of the principle inputs to the valve drive is the proportional error. The proportional error is the difference between the process reading and the set point. This difference is multiplied by the P gain and is added to the summation register. From this, you can see that if there is a large difference between the present reading and the setpoint, the controller will move its valve quickly to try to reach the setpoint. We can think of this as the gas pedal in a car.

Derivative. From calculus, we know that the derivative is the change in x over the change in time (t). In this case, x is our flow rate. The PID loop takes this dx/dt, multiplies it by the D gain and subtracts it from the summation register to create a damping term. In this way, we can think of D as the brake pedal in the car. Here is a link to a video explaining the car analogy of P and D further.

Integral. An integral, in calculus, is the area under a defined curve between two points, usually a start and stop time. In more practical terms, it is the sum of previous readings from time zero, or the sum of errors. While the P and D terms only take into account the present measurement and the one immediately preceding it, the I term uses many previous readings to correct the process value to setpoint. In most Alicat devices, the I term is given a zero value, reducing the tuning to just the P and D terms. In this case the results of the P and D values are incorporated into a summation register, as noted above, which is updated a thousand times a second and eliminates the need for user input to an I term. The summation register is scaled to provide the valve drive command.

PD2I. Our dual valve controllers, the MCD and PCD series, do still use the I term, but they use it differently than in a traditional PID algorithm. We use a special PD2I algorithm created by Alicat that incorporates a predictive function into the algorithm. This is why standard methods of PID tuning will not work for these devices. The PD2I algorithm is more complex, and single-valve controllers typically don’t benefit from it. If you are having trouble with tuning a MCD or PCD device, please give us a call and we can help out!

Achieving Responsive and Stable Valve Control

These definitions are pretty useless if we can’t figure out how to apply them to an application. The most common problem users experience is oscillations about the setpoint. What’s happening is that the P and D terms are overcorrecting. The typical fix is to leave the D term alone and decrease the P term. If the two terms are well balanced, the process variable will converge to setpoint quickly. On the other hand, you can also decrease P too far and send the system back into oscillations, where P and D are again out of balance. The oscilloscope plots in this post show what a properly tuned valve looks like in its response curves.

So, why do controllers sometimes work perfectly well in one set up but not another? For that, we have to look at the application. The trouble spots for tuning often occur when there is a high inlet pressure. This tends to be difficult because they use only a small portion of the valve’s range of motion. With high inlet pressure the valve only has to open slightly to achieve the unit’s full scale flow rate, so there is a limited amount of space to make adjustments. If you can decrease the inlet pressure of the system, the valve has to open more, leaving more room for fine adjustments. Switching gases can also affect the tuning on the device. Argon and Helium, for example, have very different characteristics and may require some P gain adjustments to achieve optimal control.

If you know your operating conditions before ordering, tell us! We can spec out the right size valve and factory set the tuning parameters to fit your set-up before the unit gets to you. This is also why we ask for the inlet and outlet pressures, and the process volume, on all dual-valve PCD and MCD orders. We can replicate these conditions in our calibration lab and send your unit out, ready for use right out of the box
Please contact an Alicat applications engineer (info@alicat.com or 888-290-6060) to talk about your valve tuning needs. We’ll be happy to help you get the most out of your instrument!

The post Achieving Responsive and Stable Valve Control with PID Tuning appeared first on Alicat Scientific.

One of the Alicat Mass Flow Controllers at a water treatment plant which solved a big failure problem.

A regional water treatment plant feeds ammonia gas into their water system—in precise doses with chlorine—to sanitize 60 million gallons of drinking water per day. But their controllers (not from Alicat) were breaking due to an ingress of liquid ammonia. The problem was the thermal differential sensors inside the meters. The sensors in ordinary thermal MFC’s are programmed to raise the gas temperatures to a specific range. Liquids conduct heat better than gases, and the presence of even a small amount of liquid rapidly cools the elements inside. Detecting the drop, the temperature regulator will draw more and more power to heat them back up—quickly frying the electronics.

Accidental liquid in a gas flow controller can happen from many causes. Environmental monitoring stations take measurements in all kinds of weather. Rain, condensation, and melting snow are all potential sources. Fuel cell systems produce moisture by mixing oxygen and hydrogen in their process, a situation fraught with risks for accidental exposure. Or, a fluid tank that’s getting gas sparging may have a backflow event.

There is a cure

Getting liquids inside an Alicat leaves you in a far better state. Unlike thermally-based instruments, Alicat flow meters and flow controllers operate on the principle of differential pressure. Inside the instrument, gas flow turbulence is eliminated by a structure that creates laminar flow, and the difference in pressure between the two ends of the laminar stack is measured.

The water treatment plant got tired of buying new meters every time fluid got into their devices. They replaced their thermal instruments with Alicat meters. Now, when the liquid ammonia gets into their meters, they simply purge the system with a high-pressure flush of ammonia gas, then resume their sanitizing process.

Dry it out

If your Alicat meter/controller gets liquid into it, don’t delay. Liquids may cause the dissimilar metals to interact if left inside too long. If you can, put the assembly under vacuum conditions. We recommend a hard vacuum (0.25 psi or less) and some gentle heat (50° to 60° C). Together, they will encourage the liquid to evaporate out of the small channels in your instrument.

If the liquid has suspended solids, drying the liquid may leave grit, and solutions can leave a residue. There’s a small chance that the contamination is heavy enough to interfere with the laminar flow conditions needed for accurate measurements. In that case, the instrument can be flushed with isopropyl alcohol. Our service department can disassemble, clean and recalibrate for you. If you need service, you can request a return authorization, or call our customer service experts to make arrangements.

If you have one of our controllers with 316L stainless steel components—selected for their resistance to corrosion—you’re in the best possible situation. They are virtually identical, physically, to our liquid flow meters and have the highest degree of tolerance for liquids. [This might be a good time to ask: Did you know we make liquid flow meters and controllers?]

Customers—like the water treatment plant and air quality monitoring companies—have switched from ordinary thermal controllers to Alicat’s differential pressure controllers because they had run into problems. It’s one of the lesser-known benefits of our products, but if you are at risk, it’s a good reason to choose Alicat mass flow controllers and meters.

The post Liquid in a gas flow controller: How bad is it, Doc? appeared first on Alicat Scientific.

You know one problem with anodizing and bluing? While it prevents corrosion, it can scratch off. Most anodizing doesn’t strengthen a surface much. Chrome plating has been an alternative, but chrome-6 is toxic, and can still wear, pit and spall. Duralar, a vacuum deposition system manufacturer, wanted to develop a fast, diamond-like coating process using physical vapor deposition that’s harder and more durable than either. It would have applications in prevention of corrosion, erosion and wear on metal parts.

Suppose, like Duralar, you’re a physical vapor deposition innovator. And just to make life interesting, let’s pretend that you don’t have unlimited time, and that money doesn’t grow on trees(!). R&D means testing, allowing for new formulations of barrier and reactive gases. You’ll need to change flow ratios and gases—all the while maintaining accurate flow, so success will be reproducible. You can’t keep buying new vacuum flow controllers for every test, and you can’t afford the downtime to have them recalibrated for each new recipe. You get the picture.

Duralar started with a generic vacuum deposition system, but none of the six built-in thermal controllers were calibrated for their special gas, tetramethylsilane (TMS), a vaporized liquid. The fact is, those controllers couldn’t change gases accurately, without downtime for a recalibration. So Duralar called Alicat. Although TMS isn’t on our standard list, with a bit of engineering we provided them with a corrosion resistant flow controller with a custom gas calibration for TMS.

After the diamond-hard PVD vacuum coating, plain steel shows as black.

They retrofitted their system using the Alicat controller—it’s a drop-in replacement—and they are now assured that the accuracy of their TMS flow will remain high, whether flowing full scale or turned down to 0.5% of full scale. That’s because Alicat’s gas selection isn’t just a k-factor offset for a single point, it’s a complete performance curve based on NIST’s viscosity tables. Going forward, Duralar needn’t worry about inaccuracy due to changing temperatures or pressures in their factory, since the closed-loop sensor in the controller compensates for volumetric changes—unlike those original thermal controllers.

Soon, Duralar was producing coated parts by pumping down the chamber to a vacuum, flowing in just the right amount of gases, adding material vapor and turning it to a plasma which bonds to the parts. In physical vapor deposition, the vacuum is needed because the chemistry won’t work in the presence of atmospheric gases.

A vacuum pump and three mass flow controllers for prototyping.

Next, they wanted to develop a process to deposit this thin coating inside tubes and pipes. With the inside of the pipe coated, you could reduce abrasive wear and corrosion—perfect for flowing abrasive liquids in a pipe, or protecting the inside of a rifle barrel from rust. The technique is clever: seal the ends of the tubes, and the interior of the tube becomes the vacuum chamber. The catch is, you need to be able to vary the location of the plasma-producing electrical discharge inside a narrow tube to get a complete coating. So, more prototyping, more experimentation, and Alicat to the rescue again.

By using an MCS flow controller for the corrosive TMS and just two more Alicat MC mass flow controllers, they were able to change gases at will, selecting from up to 98 built-in types and 20 user-customizable mixes—even more on the corrosion-resistant controller.

Alicat’s LabVIEW downloads customized to run a prototype system

Then, they used our downloadable LabVIEW drivers to build the vacuum process steps, controlling the MFCs and their shut-off solenoids from a remote laptop. In due time, they had perfected the process and begun building coating systems to order. Now, you can order diamond-like coatings for your metal parts—or the systems to provide the service for others—and the vacuum coating is more durable than anodizing, while quicker and harder than chrome plating. Thanks to Alicat’s flow controller adaptability, physical vapor deposition gets better and better.

Have questions?

Manufacturers of electrical power systems love Sulfur Hexafluoride (SF6): it’s a colorless, odorless gas which is chemically non-toxic to humans and animals, and has great usefulness in electrical insulation and arc prevention. Fill an electrical distribution switch box with SF6 and seal it, and you’ve increased the safety and longevity of the equipment.
Environmentally, though, SF6 has a drawback: while it doesn’t deplete ozone, it is the strongest greenhouse gas identified by the Intergovernmental Panel on Climate Change—by mass, it’s more than 22,000 times more potent in contributing to global warming than carbon dioxide! So, SF6 is tightly controlled around the world by environmental protection regulations.
As a power generation/distribution company using SF6, when you decommission a switch box, it’s critical to show regulators that you removed the same amount of SF6 as you put in years ago. That means accurate reclamation measurements—and it’s where totalizers, like the ones offered by Alicat on our meters and flow controllers, come in. A totalizer helps our electrical equipment manufacturing customers verify that they’re not venting this potent greenhouse contributor into the atmosphere… Using the totalizer, they keep the planet safe, and avoid a possible penalty.

With totalizing, a simple procedure sets up your batch dispensing.

How a totalizer works

A flow meter or controller reports a flow rate such as standard liters per minute (SLPM)—that is, the amount of standard volumes of mass passing through per unit of time. Supposing you have a 5 liter switching box, and you fill the box at 5 SLPM for 1 minute. You’ve now got 5 standard liters inside. A totalizer would tally up that flow, providing a running total, not just a reading of the rate. On a meter, you could periodically check the total on the front panel, or poll it electronically. On a mass flow controller, a totalizer becomes a precision dispensing instrument which saves you work and improves precision: you might set your totalizer to dispense 5 liters into the switch box, and start the totalizer. The controller then starts flow, counts down the liters until the 5 liters have been delivered (at your chosen setpoint rate) then it closes the control valve, and you’re ready to move on to the next step in your process. You don’t need to watch the flow rate on the display for spikes, and you don’t need a stopwatch.

Transformers, using SF6 for insulation, at a power substation.

Who else uses totalizers?

Gas totalizers are everywhere — the gas meter in your house has a totalizer (although it probably is only a volumetric total, calibrated to line pressure), and so does the gas pump for your car.
In industry, gas totalizers are used in:

• Beer brewing: for aeration of yeast mashes
• Gas blanketing: using nitrogen to fill the volume in tanks to avoid the emission of toxic or combustible fumes
• Pharmaceutical manufacturing: to dispense hydrogen in hydrogenation reactors
• Packaging: to fill each potato chip bag with non-reactive gas, keeping it plump without bursting.
• Custody transfer: whether filling a propane tank for commercial sale, or metering gas flows inter-departmentally at a research lab
• High altitude ballooning: by filling balloons with a precisely measured mass of buoyant gas, you can optimize altitude.
• Bio-reactors: regulating gases going in, or being siphoned off to control reactions.

Things to consider when choosing a totalizer

Does the totalizer allow batch processing?

This would be a programming option allowing a totalizing loop to be triggered from the memory of the device. Alicat totalizers offer batch loops. Another way to handle triggering is through remote software, such as our FlowVision application.

Is the valve tuned for your dispensing rates?

The tricky part about dispensing is getting the valve to shut just when you want to, in the way you want to. You may want a very quick valve snap at the end of the delivery, for the convenience of being able to move onto the next step quickly, but for high flow rates, it may be preferable to taper off flow as the total approaches, and then close at the most precise moment.
Either way, you will need tuning of the PID values to optimize the valve behavior. Alicat works to understand your particular situation so that the instrument is shipped from the factory with the right PID tuning. But we also provide the means for you to customize it in the field. Since our MFC’s all include 100 or more selectable gases, it’s not unusual for our customers to change the gases and processes the device is used with–we want you to be able to optimize your controller in each situation.

Which is better for your application: an integrated totalizer and valve (in an MFC), or a flow meter and remote valve wired together?

With a totalizer inside an MFC, the closed-loop relationship between the meter and the valve offers efficiency and precision. Plus, you don’t have to do the programming yourself! It reduces the number of devices you will need to connect to and maintain.
On the other hand, some customers have an existing valve, and just need to totalize flow, or they need the two elements to be physically separated for other reasons.

Do I need volumetric totals, standard mass totals or true mass dispensing?

Generally, each of these types of measurement would be handled by a different kind of flow measurement device. Our flow meters and controllers report volumetric as well as temperature, absolute pressure, and the standard mass flow. Any Alicat with a totalizer can totalize on volume or standard mass. By knowing the density of the gas flowing, we can program in true mass measurements. True mass is expressed in terms of mass per unit of time (e.g., kg/hr). If you’d like true mass data built into your Alicat meter or MFC, contact our applications engineers.

Whether you’re dispensing and reclaiming greenhouse gases, or if you need to calibrate a monitoring sampler (using a totalizer to provide average flow rate over time), or you need to measure grams per minute of oxygen going into a bioreactor for alternative fuel production, a totalizer from Alicat can enable and optimize your process.

Have questions about this article?

Volumetric vs. standard volumetric vs. true mass

“Measuring flow rates” of gases and other fluids means different things, depending:

• volumetric rate: the space the material consumes, seen as “volume unit per unit of time” (e.g., liters per minute)
• molar mass flow rate: widely abbreviated to “mass flow” this is the number of molecules per volume under specific conditions, expressed as “standardized volume units per unit of time—under normalized conditions” (e.g., standard liters per minute, or liters normal per minute)
• true mass flow: measuring the mass of the molecules in the flow, which is reported as units of mass per unit of time (e.g., grams per minute).

Each of these types have their applications, but each is more technically challenging than the one before, because of added levels of complexity in the measurements. The most difficult one, resulting in the priciest solutions, is true mass flow.

So it’ll come as a significant advantage to our customers that Alicat now offers selectable engineering units on our instruments, including true mass, standard (molar) mass, and volumetric flow units—essentially extending our multivariate instruments into multi-purpose measurement and control devices.

Why doesn’t everyone offer true mass?

Measuring mass itself is always an indirect process. It means measuring momentum, weight or thermal capacity…there are several means. Some methods work with flowing fluids—for example, coriolis devices use a vibrating channel, and measure the variation on that vibrational momentum, which is caused by mass flow of gas or liquids through the channel. They are unaffected by changes in the fluid, or even chunky and dirty flows. The catch is, they’re expensive—several times the price of an Alicat instrument. And they will give you mass, but not any information about how many molecules are flowing, because they are ignorant about the media that’s flowing. (Find out more about measurement technologies in the “Types of Gas Mass Flow Meters” section of the How it Works page).

With updated firmware, an Alicat flow meter or controller can now measure true mass for your fluids—in units of your choosing—for any of the fluids on the unit’s Gas Select list, or any custom mix you build from those fluids. It’s true, you can order other mass flow metering instruments that have been programmed to provide true mass flow data for a single, known, pre-determined fluid. They’re programmed in the factory before shipment, but that fluid type can not be changed without a factory reprogram because the instrument is not capable of adjusting for changes in viscosity. The unit loses its traceable ties between its calibration and changed conditions.

With Alicat instruments, when you change gas types, you change the viscosity look-up of the gas itself — effectively re-calibrating the instrument to the new gas—all the necessary information is present to calculate true mass flow. For the same reason, we don’t have an accuracy modifier, which is common to other instruments, on our measurements when you change gases in our selection table. You can decide in the field to measure true mass, then change gas types (changing your selected gas setting, too), and stay as accurate as ever. You get true mass measurements, without paying the coriolis price.

Who needs true mass flow measurements?

In bioreactors like the one pictured at the top, systems engineers may be interested in measuring out-gas mass (for example, a fuel gas like methane) from the biomass. Metering this in kilograms can be more useful than liters. Conversely, regulating reactions in a chamber may be best measured in mass terms, for calculating consumption rates and predicting production output. Hypothetically, “I’ve got 4 kg of biomass, and it will require 2 kg of CO2 in the nutrient mix to keep it productive over the next 24 hours.”

In pharmaceuticals, gases and fluids are used in many reactions. A common process is hydrogenation, especially to provide coatings. Knowing the intended thickness, density, mass and area of coverage, one can calculate the required mass that would be added, and therefore using true mass dispensing of reactive gases into the process would be easier to calculate than converting standard volume into mass.

Measuring mass per unit of time is a powerful new capability, especially if you are dispensing or totalizing mass, as can happen with bioreactors or in pharmaceutical production.

The point is, it’s easy

While some users will benefit from true mass units, others will find an advantage in the volumetric, standard volume or pressure control capabilities that are already built into our instrument’s smart sensing. Nearly any flow system can benefit from the fact that the change between units is easy—a few clicks through the display menus, or a few instructions through the serial connection. This capability allows for easy repurposing of the flow instrument, or realigning units to correlate better with other calculations.

Have questions about this article?

Knowing the correct flow range for your application will help you select the best meter or controller for your system.

The flow or pressure device’s full scale should match the largest flow rate that you need to be able to measure. If your device has a higher or lower range than is required by your system, you will be unable to acquire a proper measurement.

In some applications the flow range is too wide for one device to handle. This is less frequently an issue with Alicat devices, thanks to a turndown ratio of 200:1. This is 4 times larger than industry standard devices at 50:1.

As an example, imagine you require a 50 SLPM (Standard Liter per Minute) mass flow meter to measure your highest flow rates. However, your application also requires you to measure a flow rate of 0.30 SLPM (300 SCCM) on the low end. This would mean that the device would need to measure a flow rate that is 150 times smaller than its full scale range. Below (or above) the specified flow range, your device may still detect flow, but since it is outside of specification, there is no scientific certainty to the numbers.

For the 50:1 turndown of typical devices, you’d have to buy two flow meters in this application. A 200:1 Alicat can handle both flow rates and remain within specification. The standard accuracy specification for an Alicat gas flow device is ± (0.8% of reading + 0.2% of full scale). A high accuracy calibration is also available. Both accuracy ranges offer 200:1 turn down capability, saving set-up time and money.

If you need an even higher turn-down ratio, such as 1000:1, two or three Alicat meters can be daisy-chained to fully cover the range of flows you are measuring.

Need to figure out your flow rate?

If you’d like some guidance on calculating a flow rate in your system, you can find pointers in the article “How to optimize flow systems“.

The post Flow range matters: it’s the speed limit appeared first on Alicat Scientific.

Compact, versatile and accurate BASIS mass flow controllers are ideal for original equipment manufacturing and process integration applications buying in volume. Now the product line includes ranges of 100 sccm, 1000 sccm and the new 20 SLPM model, each with digital communications options.

With the expanded range the new model provides, BASIS can now fit into more applications, such as sample dilution, sparging into liquids, and additional gas mixing systems.

The BASIS mass flow controller family was specifically designed to provide a fast, accurate, and economical package to OEM and process integration engineers. With its rapid control response speed of 100 ms, BASIS will react in real time to upstream fluctuations, producing a smoothly controlled flow downstream. Its accuracy is an impressive NIST-traceable, +/-(1.5% of the reading + 0.5% full scale).

The controllers offer a good flexibility of fluid type, with built-in calibrations for Air, Ar, CO2, N2, O2, N2O. He and H2 are available as single-gas units. This flexibility means integrators can use BASIS in a broad range of end-user products, selecting their gas type through any of multiple communications options—RS-485, RS-232, Modbus Serial and 0-5 Vdc analog. PLC and PC control are therefore also available, and the instrument provides either digital or analog feedback.

You can get specifications and learn more about BASIS MFCs on the product page, or by contacting your regional Alicat distributor.

Have a question about BASIS mass flow controllers?

Talking to your Alicat products digitally has just gotten easier. Whether you’re integrating an Alicat into a LabVIEW dashboard, or you’re using our Flow Vision software to log, control or optimize your flows and mixes, the new updates available on the download pages are compatible with our new Gas Select™ 6v0 firmware update.

Alicat Scientific has released updated LabVIEW instrument drivers for its mass flow meters, flow controllers, and pressure controllers. These drivers are backwards compatible for older Alicat instruments, and one version works for all Alicat instruments except BASIS—which takes a separate download.

In addition to the LabVIEW dashboard, which presents the full set of controls and reporting, the suite also offers dozens of simplified virtual interfaces—if you just want to do one thing through LabVIEW, you only need to include one of the simplified interfaces in your LabVIEW dashboard.The virtual interfaces are individualized panels for controlling a smaller set of features. For example, there are simplified interfaces for functions like taring, assigning a setpoint, and datalogging.

Available for free download at http://www.alicat.com/labview, the new device drivers enable users to more easily develop control interfaces to Alicat instruments or integrate Alicat devices into existing LabVIEW programs. LabVIEW provides data collection from Alicat instruments, instrument control capabilities, and integration with other process instruments. Common functions include evaluating data in order to trigger events such as changes to set points or flow rates, gas selection, validation, and monitoring ongoing process data.

Flow Vision software updated

If you have a new instrument, with the Gas Select version 6 software installed at the factory, or you recently sent an instrument in for calibration and the software was upgraded by the service department, and you have a license for Flow Vision, you’ll want to download the latest software update at the web site.

Since the Flow Vision software is backwards compatible, you’ll only need the one application for all instruments old and new.

Flow Vision is our proprietary software interface for communicating with Alicat Instruments. You can use it to adjust PID settings, change or poll registers, program scripts for various instruments in a system, or log and plot data.

There are two versions of Flow Vision: Flow Vision SC communicates directly with multiple Alicat devices, and provides direct control of them. Flow Vision MX configures up to six mass flow controllers within a gas mixing system.

Need more information about digital communications to Alicat products?

Use this form to contact our customer support Applications Engineers, or check out the software/drivers page for options.

Alicat devices are available in thousands of possible configurations to ensure that the instrument you receive is the right fit for your application. In this first of a new series of blog posts centered on our available instrument options, we will be taking you through the main product categories in greater detail.

Gas Flow Measurement and Control

If you are looking for precision gas flow instrumentation, then we’ve got you covered. Our mass flow devices output the mass flow (standardized volumetric flow), volumetric flow (also referred to as “actual flow”), temperature and pressure. This means that you can sometimes replace multiple sensor components with a single Alicat instrument. Alicat uses a differential pressure-based flow measurement technology to calculate the volumetric flow rates, which are also converted to a mass flow rates using the temperature and pressure readings from inside the gas stream. These instruments can be configured as either a meter or a controller, which can control based on the mass flow, the volumetric flow or the pressure. All Alicat differential pressure-based mass flow instruments have a part number beginning with “M”.

Gas Flow – Low Pressure Drop

Would pressure drop or a potential flow restriction due to a mass flow meter be a problem for your system? If so, you may be able to overcome this issue by using our Whisper series mass flow devices. Whisper series devices are configured with an over-sized flow body and laminar flow stack for a significantly lower pressure drop, and make use of a much more sensitive pressure sensor to maintain accuracy. The greater sensitivity to differential pressures results in a lower maximum pressure threshold for the Whisper series. Whisper series devices will have a “W” in the first block of characters in the Alicat part number (such as MW, MWB, MCW, MCRW, etc.)

Liquid Flow Measurement and Control

If you are working with liquids and need to measure or control the flow rates, our liquid devices may be right for you. Our liquid series instruments use the same principle of operation as our gas flow meters and controllers, and work best with pure filtered DI water. That said, we are sometimes able to customize them for metering or controlling different liquids (such as some alcohols) depending on the viscosity and materials compatibility (contact our application engineers at Alicat to learn more). All liquid devices have a part number beginning with “L”, and include bleed ports to remove trapped gas from the flow body (which can negatively impact the readings if left in the unit).

Pressure Instrumentation

Though our mass flow series devices can both output and control on pressure, you may not be interested in the other variables (mass flow, volumetric flow, and temperature) or you may have pressure requirements that lie outside their range, accuracy or pressure reference (gauge, differential or absolute). If this is the case, our pressure devices may be the option you are looking for. We offer pressure controllers and gauges with full scales ranging from 2 inches of water column up to 1500 PSI. We can do a variety of configurations, and can build devices that output gauge pressure, absolute pressure, or differential pressure. All Alicat pressure devices have a part number beginning with “P”. Additionally, in the section of the part number containing the range of the sensor used, there will be an indication of whether the device is using a gauge, differential, or absolute pressure sensor (denoted by a “G”, “D”, or “A”, respectively).

Anti-Corrosive Option for Flow or Pressure Instruments

Are you using a corrosive gas, or have potentially condensing liquids in your gas stream? If so, you should configure your Alicat device as an anti-corrosive “S” series unit. The anti-corrosive series Alicat devices are built with a 316L Stainless steel sensor and FFKM (Kalrez/Markez) that are more resistant to the aggressive gases and water condensation (though you should still dry a mass flow device out to prevent water droplets from impacting your flow measurement). Anti-corrosive Alicat devices have an “S” in the first block of characters in the part number (such as MS, MCS, MBS, MCRS, MCHS, PS, PCS, PCHS, PCRS, etc.).

Portable (Rechargeable) Meters – Flow or Pressure

Do you need to use your device where there is no access to power sources? All of our meters can be ordered as rechargeable battery powered portable devices with built-in lithium-ion batteries. In this configuration, they will include a micro USB cable and a wall plug for charging the battery. With a battery life of up to 18 hours on units with the monochrome LCD display (5-6 hours for the backlit color TFT display), you can measure the flow or pressure in the field away from local power supplies. Any portable device will have a “B” in the first block of characters in the part number (MB, MWB, MBS, PB, PBS, LB, etc.)

If you are looking for a very wide flow range in a single convenient case, then our Portable Calibration Unit (PCU) series may be a good fit. The PCU case contains three panel-mounted, battery-powered Alicat mass flow meters (standard or Whisper series) side by side with push-to-connect fittings. Each of the three meters can have a different range and comes with high-accuracy calibration and totalizer functionality. PCU part numbers begin with either “PCU” or “PCUW” (with Whisper meters) and include each of the three meter ranges (e.g. PCU-50SCCM-5SLPM-500SLPM-D).

That covers our main product categories. Stay tuned for the next installment, which will go over some of our controller-specific options in more depth. Would you like to know more? Explore our product pages and application notes to view more of what Alicat has to offer and how our devices can be implemented in common applications.

Have questions? Let us help.

Use the form below, try our Online Chat, email us at info@alicat.com, or call and talk to our expert apps engineers: Tel: 520-290-6060

The post How to choose meters and controllers for pressure or flow appeared first on Alicat Scientific.

Alicat’s “Whisper” series portable flow meters reduce the time it takes to conduct flow calibrations and audits of gas analyzers and gas dilution calibrators used in ambient air monitoring and other applications.

Auditing Gas Analyzers and Gas Dilution Calibrators

Gas analyzers and gas dilution calibrators in a typical ambient air monitoring shed. Alicat Whisper flow calibrator pictured at bottom left.

Flow calibrating a gas analyzer can consume your entire day. Most dreaded are low flow calibrations, which can take an hour or two alone. You watch the bubble or piston slowly rise to the top of the positive displacement tube at a pace of 10 sccm over the course of several minutes, and cheer when it finally reaches the top. Do that another nine times for a single averaged data point, unless the bubble sticks or the piston stutters along the way. There must be a better way.

Every analyzer technician knows that maintaining a constant sample gas flow rate is critical to ensuring the measurement accuracy of the analyzer. Gas analyzers are used in ambient air monitoring to identify the concentrations of greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) that are found in the air around us. Process analyzers are used to monitor the concentrations of such gases in smokestack emissions. Unfortunately, the flow controllers that are built into these analyzers often do not live up to our expectations, and this necessitates the use of regular flow check, calibration and audit cycles to ensure the quality of the data.

Gas dilution calibrator, showing its program of calibration flow rates.

Analyzer flow rates can be checked and calibrated directly using high-accuracy flow meters. When it comes to testing the compositional analyses of the gas analyzers, gas dilution calibrators are used, which themselves use two or three mass flow controllers to control the composition of their outlet gas streams. Gas dilution calibrators combine a large flow rate of unpolluted air with a smaller flow rate of the greenhouse gas being analyzed, for example CO2, to provide the CO2 gas analyzer with a sample of the pollutant gas at the desired concentration.The presence of flow controllers within these dilution calibrators again requires the use of high-accuracy flow meters to ensure their correct operation.

Faster Flow Calibration with Laminar Differential Pressure

Calibrations and audits of gas analyzer and dilution calibrator flow controllers have often been performed using positive displacement flow meters. “Wet” positive displacement flow meters measure the time it takes for air bubbles to pass through a tube coated in a soapy solution. “Dry” positive displacement meters measure the time it takes for air to push a piston up a tube. In both cases, a single flow measurement data point can take as little as a few seconds up to many minutes to complete, depending on the flow rate. Calibrating all the analyzers in an ambient air monitoring shed can easily take a full day with these slow measurement methods.

Alicat Whisper-series portable mass flow meter.

Alicat Scientific’s “Whisper” series flow meters measure extremely low differential pressure through a laminar flow element to present live readings of both actual volumetric flow and standardized mass flow. Flow readings are calculated a thousand times each second (1000 Hz), so even the lowest flow rates are visible instantly. Streaming and recording this data over RS-232 can reveal cyclical flow inconsistencies and help identify underperforming mass flow controllers. The wide flow ranges of Alicat’s NIST-traceable mass flow meters (200:1, or 0.5% to 100% of full scale) means you can calibrate analyzer mass flow controllers down to the bottoms of their ranges with confidence in the accuracy of their calibration. Using a Whisper, calibrations at the bottom of a mass flow controller’s flow range take just seconds instead of hours to obtain a robust average of flow measurements. Portable Whispers (MWB series) integrate a rechargeable battery for even greater convenience and efficiency while you are conducting your flow audits.

Whisper-series mass flow meters are available in common analyzer flow controller ranges of 20 slpm, 10 slpm, 200 sccm, 100 sccm and 5 sccm, or any other range of your choosing between 0.5 sccm and 1000 slpm. These flow meters are also well-suited to other applications, including:

• Auditing the flow rates of indoor air sampling instruments used in industrial hygiene applications,
• Setting the mechanical flow controllers used with air sampling canisters, and
• Calibrating the flow controllers used in gas chromatographs and other analytical instruments.

Explore the Whisper product page to learn more about these fast flow meters.

Have questions? Let us help.

Use the form below, try our Online Chat, email us at info@alicat.com, or call and talk to our expert apps engineers: Tel: 520-290-6060

The post Faster Flow Calibration for Gas Analyzer Audits appeared first on Alicat Scientific.

A few flow measurement principles dominate the flow technology landscape, but there’s a rich variety of ways to measure flow that might not make themselves apparent without a bit of research. Anyone who works with flow is likely to be familiar with thermal flow meters, differential pressure-based flow instruments, and rotameters, so here is a look at a few flow technologies you may hear less about, depending on your specialization.

Ultrasonic:

Ultrasonic flow meters can be an excellent option if you need to measure flow, but can’t install an invasive, new fixture to your flow path; some meters’ transducers can be strapped or clamped directly to the exterior of a pipe! The two methods used by ultrasonic flow meters are Doppler and transit time. Both types of meters emit an ultrasonic beam into the fluid medium. Doppler meters measure the change in frequency of the beam caused by the Doppler effect, and use the known speed of sound of the fluid to determine flow. Transit time flow meters emit two beams which reflect back into receiving transducers in the meter. The transmit times of the two beams can be used to find both the average fluid velocity and the speed of sound of the fluid.

Magnetic flow meters:

Magnetic flow meters can be used for measuring liquid flows so long as they are sufficiently conductive, and can be tolerant of corrosive or aggressive liquids.  Magnetic flow meters utilize Faraday’s Law to measure the velocity of conductive fluids. According to Faraday’s Law, any conductor moving at a 90° angle to a magnetic field experiences an induced voltage proportional to the conductor’s velocity. The meter creates a magnetic field in the fluid path and uses electrodes in contact with the conductive fluid to measure the induced voltage. The meter calculates the fluid velocity using the measured voltage, the known strength of the emitted magnetic field, and the distance between the electrodes.

Optical:

Lasers have penetrated so many different technologies, so of course they can be applied to flow measurement too! Optical flow meters are used for fluids containing small solid particles—which could cause a clogging problem for other techniques that may rely on capillary bypasses or other restrictions to flow. A laser shines perpendicular to the flow stream and collides with a particle. The light scattered by the particle is picked up by a photodetector, which generates an electric pulse signal. A second laser positioned further downstream of the first laser repeats this process with a second photodetector, and the velocity of the flowing gas is calculated as the distance the particle travelled over time.

Venturi:

Venturi devices have the advantage of being very low cost, but at the expense of flexibility. The Venturi effect is a reduction in pressure caused by a constriction in a fluid’s flow path. Pressure sensors measure the pressure before and inside the length of constriction, and the meter calculates fluid velocity using Bernoulli’s Equation; Bournoulli’s principle states that the a fluid’s speed is inversely proportional to its pressure, so decreasing the pressure of the gas with a known constriction and measuring the differential pressure yields a flow measurement. Without strict control of system pressure and temperature, though, the result is volumetric, not mass flow, so one’s results may vary by environmental conditions.

Laminar Differential Pressure Flow:

For high accuracy, rapid response and a great turndown ratio metering clean dry gases, many experts turn to LDP techniques. Alicat instruments measure differential pressure, similarly to Venturi products, the type of restriction is a bit different, in a way that makes a huge difference. In an Alicat flow instrument, a stack of plates and spacers is used to laminarize the flow and create a pressure drop; that stack is called a laminar flow element. Laminarizing the flow lowers the Reynolds number of the fluid, and allows calculation of the mass flow rate using known temperature vs viscosity data and the Reynolds number of the fluid. A sensor measures the differential pressure across a section of the laminar flow element with known pressure drop, another measures the absolute pressure of the fluid and a temperature sensor measures the temperature of the gas. All of these parameters, combined with the fluid’s physical constants programmed into the instrument, give the Alicat meter everything it needs to calculate volumetric and mass flow.

Because Alicat flow meters don’t just collect but also report pressure, volumetric and mass flow measurements, they are multivariate devices: you can use the data that matters most to you in your application. For many Alicat fans, this versatility is one of the best reasons to use Alicat flow meters and controllers. Measuring both pressure and mass flow means that users can control flow based on either one, using a controlled loop function built into Alicat mass flow controllers. It means being able to measure mass flow while controlling on pressure, or controlling mass flow while knowing pressure. The benefit is saved time, improved precision, and reduced complexity in your system designs.

Questions about meter technology?

The post Mass flow measurement techniques across the spectrum appeared first on Alicat Scientific.

There are times when a high operating pressure is needed, and now you can use an Alicat for that high pressure system. It means you can take advantage of all the Alicat benefits you love so much: changing gas types on the fly, multivariate displays, and the controls and speed you depend on for a stable, repeatable process.

You can take a look at the new MQ meters and MCQ controllers for high pressure flow systems on the respective Alicat meter and controller pages. They handle pressures up to 320 PSIA (22 bar), a new upper limit on Alicat flow instrument performance. Minimum operating pressures are 15 PSIA for the meters and 30 PSIA for the controllers.

Like our standard instruments, the MQs and MCQs come equipped with our COMPOSER software, which lets you save up to 20 custom gas mixes (in 0.1% increments), composed from up to five of the 98 standard on-board gas calibrations. And the devices can be ordered in the same full scale ranges as the standard products, so it doesn’t matter if you are flowing less than 0.5 sccm or as high as 5000 SLPM. You can get a meter or controller for your application.

To ensure the highest possible measurement resolution and fastest possible control response times, MCQ high pressure controllers feature valves and sensors ranged to your application. Our standard control response time is less than 100 ms, and with custom tuning you can see performance under 50 ms (ask your application engineer for help with this). With Alicat’s industry-leading control response time, you can be assured that your process will be rock steady, regardless of the disturbances.

Full PDF specifications for high pressure flow controllers and high pressure flow meters can be easily downloaded.

Questions about high pressure applications?

The post Flow metering and control for high pressure flow systems appeared first on Alicat Scientific.

A pressure decay test can take a while, and waiting time is wasted time.

In this video, we demonstrate Alicat’s mass flow controller simultaneously controlling the pressure in the device under test, and monitoring leak rates as low as 2.5 sμlm. The result is an instant quantification of a leak rate, as soon as your system is settled at the target pressure. Nor do you need to do a lot of math to find an average leak rate—you’ll know the leak rate at any pressure you want tested.

Here are some ideas for optimizing this test:

• For testing larger volumes, a bypass fill-valve can be used to rapidly pressurize the DUT, reducing the wait between tests.
• An integrated bleed valve can be configured into the MFC for testing non-leaking parts… or you can include a bleed valve in your setup, as shown in the video.
• Using a low pressure drop Whisper controller will reduce stabilization times and ensures accuracy of real-time readings.

We have other configurations for measuring leaks, including those described in these papers from our Applications page:

• Faster Leak Checking
• High Efficiency Helium Leak Check

Leak check quickly using an MFC – without the delay of pressure decay tests

Questions about leak checking applications?

The post Even faster leak checking using pressure control loop on MFC appeared first on Alicat Scientific.

Gas mixing is a science that can present new challenges, even if you think you’ve seen everything. Having the right equipment alleviates many problems, since the end product can suffer if the mixing setup is subpar. It helps to understand the role of each component in a mixing system and how it can improve your process. Starting at the beginning of the process, here are some of the challenges that may arise, and suggestions to help make your gas mixing setup better.

Gas Supply

Many processors mix gases on site, since buying a custom mixture from a gas supplier can be expensive. Having a supply of the pure gases reduces costs, while allowing the user to adjust the concentration of a constituent for a different end result. Also, when a custom mixture is purchased it typically is delivered in a special canister that cannot be discarded, or even returned to the gas supplier. Where are you going to put all of those empty bottles? Stratification of the gases will occur if a bottle is left unused for a while, so that the denser gases will settle on the bottom and less dense gases will settle on top. Using a pure gas supply will mean not having to roll your gas bottle across the floor of your lab before you can use it.
Having an Alicat mass flow controller for each gas in your process provides fast and accurate control of your mixture. If you need to measure a mixture, whether pre-mixed or mixed on site, the mixed gas recipe can be programmed into the mass flow controller using the COMPOSER firmware on the Alicat.

Controlling the Mix

In a dynamic system, your mixture may not always be 75% Gas 1 + 25% Gas 2. What do you do if your mixture changes to 25% Gas 1 + 75% Gas 2 the next day, and then 50% Gas 2 + 50% Gas 3 the next? Careful consideration of your potential mixes is very important when selecting flow controllers for a mixing setup. Alicat mass flow controllers are calibrated for 98 gases (128 gases for the anti-corrosion S series) that can be changed on the fly. A 200:1 turndown ratio means you get more usable flow range per controller. These features will reduce the number of flow controllers required for a setup.
After the gas flow has been controlled, the gases in the stream needs to be mixed properly. If you can’t afford to lay out a bunch of right angles in your piping, a static mixing tube is recommended. Right angles and mixing tubes induce turbulence to create a homogenous mixture, and can be installed downstream of the flow controllers.
Many mixing systems have an analyzer that will provide real time updates on the mixture. If the mixture is not correct, the analyzer triggers a light or horn alarm so the technician is alerted that the mix is not within specification. Analyzers are viable options if you know which gases you are flowing, since they are typically calibrated for one specific gas. Otherwise, a mass spectrometer can determine everything in the gas sample—if you can afford it.

Pressure Feedback

In some real-time mixing applications continuous pressure is important. For example, in welding, pressure loss in the shield gas can result in a bad weld, since the shield gas is protecting the weld from atmospheric gases. Pressure loss occurs because gas mixing systems aren’t on 100% of the time, and because multiple stations coming on or offline change demand. A pressure feedback system, incorporating a pressure controller, a pressure gage, or using the pressure control loop on an Alicat mass flow controller, will responsively increase or decrease flow rates based on pressure readings at each station.
A surge tank or stabilization volume can help mitigate pressure loss. They act as a gas reservoir until you need the mixed gas. The issue of pressure control also goes back to sizing your flow controllers properly, since you want to guarantee that they can handle the maximum and minimum flow rates required to operate in all likely conditions.

Software

While having an adequate source, precise mass flow control and good pressure sensing will provide a system that delivers gas accurately and fast, you probably will need something to control all of the elements together. In most cases, a software programmer at the mixing site will write something up to integrate everything together. Alicat has a couple of options that can make this task easier. For one, our gas mixing software Flow Vision MX, can be used with up to ten Alicat devices to control a mixing process, and will integrate an Alicat pressure gauge for pressure responsiveness. If the set-up incorporates other devices that aren’t compatible with Flow Vision MX, we have LabVIEW drivers on our website that can integrate Alicat devices into a LabVIEW interface to control the mixing system.
However you put your gas mixing system together, Alicat’s applications engineers are ready to help you get extraordinarily good results. Contact an Application Engineer using our online chat system, call in, send us a question on a web form, or email info@alicat.com.

Have questions about gas mixing or Flow Vision MX?

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A Rotameter is a variable area flowmeter (VAF). It provides a flow measurement by using the pressure of a flow stream to float a ball within a conically shaped tube and provides the mass flow measurement of a gas or liquid, when operating in its standard fluid, temperature and pressure environment.

When ordering a Rotameter, one must choose a specific gas, standard temperature, and pressure that it will be specifically calibrated for. If one parameter deviates from these specifications in actual operating conditions, the accuracy will suffer. The Rotameter will not automatically adjust its readings and is virtually blind to any sort of changing conditions. Even though the Rotameter is marked in “standard” flow (for example “Standard Cubic Feet per Minute”), you must remember that the measurement lines are a fixed distance apart, and if your operating conditions deviate from the STP (or you are running a different species of gas), the scale doesn’t adjust. You’re no longer measuring SCFM!

By contrast, Alicat mass flow meters are multi parameter devices that provide standard and volumetric flow readings, while reading process pressure and temperature conditions. Because the Alicat is measuring all the variables, it is able to adjust in real time to changes in operating conditions. Alicats always give the standard mass flow reading. It’s NIST-traceable.

Customers who have Rotameters and receive Mass Flow Meters from Alicat often ask how they can calibrate their Rotameter using an Alicat. We have to resort to the old saw, “comparing apples to oranges,” when looking for correlation between these two different types of flow meters. Although similar in purpose, they are different technology, measuring with different underlying assumptions about conditions. Correlation is not impossible, just difficult—you can compare apples with apples, if the variables are aligned.

A Rotameter calibrated to three gases: 0xygen, N20 and Air.

The conditions within the Rotameter must be controlled to the calibration conditions it was built for, to converge on a correlation. In a calibration lab, the tech will flow the specified gas, bring the test bench to the proper temperature, and use a pressure control system to put the Rotameter in its STP conditions. This requires some significant investment in equipment. Once the Rotameter is in its STP environment, the meter can be adjusted to read the same as the calibration standard, thus calibrating the Rotameter.

I don’t have a calibration lab. How do I match a Rotameter to an Alicat?

Temperature has some effect on the flow reading, but pressure changes, whether caused by process conditions, barometric or altitude differences will have a stronger effect (unless the temperature change is large). Try to adjust internal temperature and pressure to match the Rotameter’s STP. This will require some sensors. In the field, you could use an Alicat as near as possible to the Rotameter in the process, to give you some readings. If internal pressure can be controlled within the Rotameter to match the fixed STP values, then there is cause for a legitimate comparison from the Alicat to VAF.

Ensure that the Rotameter is flowing out to its intended pressure. Let’s assume venting pressure is 30 PSIA for this example. Then, plumb an Alicat Mass Flow Controller with a downstream valve configuration inline and downstream of the Rotameter. Set it to our “Closed Loop Pressure” control mode. If the ranges and gases allow, use an Alicat Whisper product, so that the pressure drop induced by the Alicat doesn’t skew the Rotameter conditions. Ensure the gas selection and the STP setting on the Alicat are identical to the Rotameter’s. (Gas selection and STP are adjustable on Alicats.)

Then set a backpressure control point to equal the rotameter’s calibrated venting pressure, let’s say 30 PSIA. This means the Alicat is controlling the most important condition within the Rotameter, pressure. Now that you have standardized the Alicat to the Rotameter conditions, introduce a flow, and they should be comparable.

We now have apples all around. (Eat fruit, it’s good for you.)

Have questions about calibrating using Alicat devices?

The post Why is my variable area flow meter not matching up with the Alicat? appeared first on Alicat Scientific.