Tag Archives: Calibration & Accuracy

Precision Gas Flow Control is Key to R&D Instrumentation

If you’re a scientific researcher, few things are as important as your ability to accurately control experimental research variables. Data – more specifically, precise data – is king! When you need gas flow rate measurement and control instrumentation, the ability to derive statistically sound and repeatable data is the key driver.

Over the past several years, it’s been a privilege to develop a good working relationship with the Monterey Bay Aquarium Research Institute (MBARI), which is just a short drive from our facilities here in Monterey, Calif. In the past, we’ve helped Jim Barry, Ph.D., a researcher and Benthic Ecologist, accurately simulate past, present, and future atmospheres and their effects on ocean chemistry.

In his early experiments, Dr. Barry wasted countless hours recalibrating his mass flow controllers to account for his ever changing flow rates to his experiments. In 2005, with the application expertise of our product manager, Dr. Barry and his team installed nine of Sierra’s digital Smart-Trak 2 Model C100 gas mass flow controllers to control mixtures of O2, N2 and CO2 to his aquarium tanks. The O2 levels varied from 1 – 20%, N2 from 80 – 99% and C02 levels from 180 to 1500 ppm, depending on the desired atmosphere or ocean condition Dr. Barry wanted to create.

Dr. Barry says “accuracy is essential” for these experiments. If his CO2 readings are off by just 0.1%, the acidity of his simulated oceanic environment will change drastically, requiring many hours of work to reset conditions and restart the experiment. Now Dr. Barry can rely on his gas control instrumentation to deliver the precise gas flow rate to his control his various atmospheres.

For Dr. Barry, data is king! All his findings and discoveries – basically, his life’s work – hinge on the accuracy of his data. He wants gas control equipment he can set and forget.

We look forward to years of invaluable research from MBARI. We have learned that Dr. Barry’s findings have led to more in-depth research on how acidification and rising levels of carbon dioxide may upset the ocean’s delicate geochemical balance, as well as ongoing study of greenhouse gases and ocean chemistry. These ramifications are just now being explored.

Benefits of Precise Gas Flow Control for Researchers

We recognize that gas flow control is only one small part of what you want to accomplish. In the end, you want to present sound research to colleagues and other influencers in your field of scientific study.

Thanks to researchers like Dr. Barry, who have told us what they need, our Smart Trak 2 can provide your with:

  • Stability and accuracy
  • User-friendly design
  • Ability to adjust for 10 different gases independently

Do you have a story about gas flow control instrumentation or equipment? Please share it with us in the comments below!

Chemical Engineering Magazine Article By Sierra’s Founder

Chemical Engineering Flow Meters

Sierra’s Founder, Dr. John G. Olin, looks at the Principles of Operation, Installation, Calibration and Best Applications for Thermal Mass Flow Meters…

Read the full article in Chemical Engineering Magazine.

Primary Standard Gas Flow Calibration—The Only Guarantee of Accuracy


Calibration facility

At Sierra, we have a saying: “An instrument’s accuracy is only as good as its calibration.”

The accuracy of your mass flow controller (MFC) is essential in assuring the efficiency, performance, and quality of your flow meter. In many cases, if your instrumentation is not calibrated, then a decline in performance is possible due to sensor drift from the factory calibration. Various things cause drift: dirt buildup, aging of the electronics, physical changes in the sensor, etc.

To make sure your MFC is reading at the accuracy you specified at purchase, many users recalibrate or validate flow meter or MFC  annually. In some industries, assuring your flow meter’s accuracy is required by either corporate policy or government regulations like EPA, FDA, MACT mandates. There are many ways to calibrate MFCs to assure accuracy including transfer standards, but the best way is a primary standard calibration.

Primary Standard = Precision Calibration

Only primary standard gas flow calibration systems deliver world-class levels of accuracy and traceability.

Here is what to look for in mass flow meter primary standard calibration:

  1. Primary standards are characterized by the basic quantities of time and distance, while transfer or secondary standards, such as laminar flow elements, are calibrated against another device, generally another flow meter. Primary standards can also be verified by every national laboratory.
  2. The calibration standard should be NIST traceable standard accuracy, better than 1% of full scale.
  3. The most accurate primary standards adhere to the NIST “rule of four.” This means the gas flow primary standards are required to be four times more accurate than the device under test. This “rule of four” needs to be a requirement for any factory calibration or calibration house.
  4. Flow meter calibration is both a science and an art–look for expertise in flow meter manufacturing or flow meter calibration. In reality, the manufacturing factory not a third party calibration house, will give the very best flow meter calibration due to the flow calibration core competency and working knowledge of the meter.
  5. Facilities should be ISO 9001 certified and/or ISA 17025 & NAVLAP compliant.

Sierra is one of few manufacturers today that performs a detailed 10-point calibration across the entire mass flow range. We strictly adhere to using primary standards and the NIST “rule of four.”  Sierra’s SmartTrak mass flow controller is a prime example of this. SmartTrak’s NIST-traceable standard accuracy is better than 1% of full scale. We offer even better accuracy–as good as half a percent of full scale upon request.

Learn more about utilizing Sierra’s SmartTrak mass flow controller for your next project. Over 100,000 installed SmartTrak mass flow controllers can’t be wrong. And SmartTrak’s unmatched accuracy and performance is guaranteed with a lifetime warranty.

Discover The Swiss Army Knife of Mass Flow Controllers

SmartTrak® 140 Ultra-Low ΔP Mass Flow Controllers

Get Incredible 4.5 psid (310 mBard) at Flows up to 500 slpm. When you need precision gas mass flow control of expensive process gases, where minimal pressure drop is a key consideration for cost savings and efficiency, the SmartTrak® 140 flow meter controls up to 500 slpm with an ultra-low ΔP of 4.5 psid (310 mBard) much better than typical ΔP values of 25 psid (1700 mBard) for equivalent mass flow controllers on the market.

  • Control 10 sccm to 500 slpm (nlpm) with 4.5 psid (310 mBard)
  • Competitively priced compared to other high flow controllers
  • Controls up to 500 slpm (nlpm) with an ultra-low ΔP of 4.5 psid (310 mBard)
  • Control valve with large flow coefficient (Cv) for precise digital PID control at low ΔP
  • Dial-A-Gas® Technology allows control of 10 pre-programmed gases in one instrument; substitute any gas
  • Pilot Module gives the customer a remote or local display and ability to change gas, engineering units, output signal, full-scale, set point, zero, span
  • All 316 stainless steel construction for increased durability
  • Patented, inherently linear Laminar Flow Element (LFE) for true linear performance

Learn More…

Best Practices for Mass Flow Controller Selection & Installation

Mass Flow Controller Best PracticesAs scientists, facilities managers and manufacturing engineers, specifying equipment is a part of our daily work life. What product do I need? What’s the best price for the value? How do I install the product once I get it? The more information about best practice principles, the easier the job is of specifying and buying equipment. Through our years of experience of specifying, installing, and servicing mass flow controllers, we have compiled a comprehensive list of best practices by users for the selection, safety, installation, and operation of their thermal mass flow meters and controllers are as follows:

Best Practices-Product Selection
1. Select only those mass flow meters and flow controllers where the manufacturer’s specifications meet the conditions of the application, such as maximum and minimum flow rate, pressure and temperature. Some manufacturers have software programs that recommend the instrument model best suited for your application.

2. To minimize pressure drop and flow non-uniformities, you should select the instrument with the largest inlet fittings compatible with the size of the process line. In the case of corrosive gases, the instrument selected should have materials of construction that provide protection against corrosion.

3. Size the instrument so it operates in the upper two-thirds of its full scale mass flow rate range.

Installation and Set-Up

4. Install the instrument only in process lines that meet the manufacture’s pressure and temperature ratings. A margin of safety should be provided if spikes and surges exist in the process. Proper pressure relief valves and burst plates should be installed in high pressure applications.

5. To avoid obstructions in the sensor tube and the narrow flow channels in the laminar flow element, you should install the instrument in process lines that have clean gases. Upstream particulate filters properly sized for the flow rate, with a minimum rating of 5 microns are recommended for all applications.

6. To avoid thermal siphoning (or, the so-called, “chimney effect”), you should install the instrument in the process line with the axis of the flow body oriented horizontally, not vertically. At zero flow, if the axis is vertical, the gas heated by the sensor tube rises upward through the sensor tube and creates a closed flow loop in the flow body that causes the instrument to read a flow rate when there is none. This effect is significant only in the very lowest portion of the full scale range. If system constraints require vertical mounting, then the instrument should be re-zeroed in the field. Vertical mounting requirements should be communicated to the manufacturer upon order so the instrument can be adjusted to meet these special requirements.

7. To avoid stress on the springs in the control valve, particularly in medium- and high-flow mass flow controllers, you should install the instrument in the process line with the axis of the flow body oriented horizontally as required above and, additionally, with the control valve located on top of the flow body, not on the bottom or the side. If system constraints require a different instrument orientation, you should communicate this requirement to the manufacturer upon order so that adjustments can be made.

8. After turning on the instrument, you should allow the instrument to warm up for the time period specified by the manufacturer. A warm-up time of about 10 to 30 minutes typically is required for the instrument to reach full accuracy.

9. Be sure to zero your mass flow meters and controllers prior to first use and periodically afterward on a schedule based on the manufacturer’s recommendations or your own experience. The zero flow output signal should be averaged over a sufficient time interval. Preferably, zeroing should be performed with the actual gas to be measured at the same pressure and temperature of the application, or close to it. If there is a change of gas, the instrument should be flushed with the new gas before being zeroed. Obviously, for proper zeroing, the flow rate must be zero. This is best accomplished, in the case of controllers, by commanding the control valve to be shut, and, in the case of both mass flow meters and controllers, by closing shut-off valves installed just upstream and downstream of the instrument. In the absence of these valves, the process line must have other means to insure that the flow is zero.

Following these best practices are sure to result in the most accurate measurement outcome with your new mass flow meter or controller. Have any other tips we didn’t mention or questions about mass flow control? Please leave them in the comments section below.

Direct Mass Flow or Volumetric: The Thermal Flow Meter Technology Advantage!

In today’s world where everyone is watching the bottom line, you need high performance, cost-effective instrumentation—and capillary thermal mass flow meters and controllers have been proven to meet this criteria in a wide range of process applications.

Thermal mass flow technology is an industry standard for mass flow control of gases because it measures flow directly, at the molecular level.  In most processes flowing gases like Air,  Argon, CO2, N2, Etc., it is gas mass, not gas volume, which is the critical variable of most interest.

Volumetric flow measurements are less reliable than mass flow measurements because changes in gas temperature and pressure effect measurement performance.  You lose accuracy and you lose reliability and in many cases even money due to process inefficiency and waste.  Volumetric flow meters need additional temperature and pressure compensation to convert the volumetric flow rate into mass flow rate.

Gas flow measurement and steady control of mass flow rate with capillary thermal technology is the cleanest choice.

No messy calculations or T & P compensation, just pure physics at work for you.

Check out our infographic below to see the thermal mass flow advantage for yourself.

Do You Have the Thermal Mass Flow Advantage?
Capillary Thermal Principal of Operation is the Core Technology for Thermal Mass Flow.
How has capillary thermal mass flow been used? Gas Mixing for laboratory research.
beverage manufacturing
SmartTrak 100 is the Swiss Army knife of MFCs. Watch Video.
Learn More

Need more info? Find out more about Sierra’s gas mass flow meters and controllers with application flexibility and proven performance for lab researcherssystem integrators and more.

Under Pressure, Part 3: How to Avoid ‘Droop’ (Hysteresis) with Flowmeters

If you’ve been reading my series on pressure regulation, you know my goal is to help you achieve the best possible gas mass flow control with your flowmeter. Previously, I’ve discussed undersizing and seat-drop lock. Now I want to move onto something that can really get you down – “droop.”

Pressure Regulation with Flow Meters, how to avoid droopRegulators may exhibit hysteresis, also known as droop. Droop is a function of the loss in max outlet pressure with regard to flow rate and is often characterized as the ‘range’ of change in outlet pressure across normal operating conditions (before asymptotically approaching choked flow). So, the hysteresis of a regulator is the difference in outlet pressure for a given amount of diaphragm depression between approaching the setpoint from a higher outlet pressure or from a lower outlet pressure. In short, there will be a slight difference in the actual output for a given amount of depression pending climb or fall to setpoint. Or there will be a slight difference in post ride height on the regulator for a given outlet pressure setpoint if you approach from the top or from the bottom. This means that the more up and down you go, the more you should pay attention to whether the setpoint is at the top or the bottom of the meniscus, so to speak.

Proper line regulation, be it supply pressure regulation or back pressure regulation, is fundamentally key to a properly tuned flow system process. All instruments operate most accurately under steady-state conditions, so awareness of regulator behavior and proper tuning will save you time and money during transient conditions.

At Sierra, we are always happy to help you with your application. Feel free to contact us with any questions you may have about pressure regulation in flowmeters, gas mass flow control applications or other topics.

Best Practices for Mass Flow Controller Manufacturing

In Part 1 of our mass flow controller best practices series, Best Practices for Mass Flow Controller Selection and Installation,  Sierra’s Chief Engineer John Smitherman compiled a comprehensive list of best practices for the selection, installation and operation of mass flow meters and controllers. With so many flow measurement products and technologies on the market, it’s important to also be able to assess the manufacturer:

  • What is the company’s expertise?
  • Is it focused on just one flow measurement product or many?
  • Does its manufacturing procedures drive product safety and accuracy?

Since we have been manufacturing flow meter solutions for more than 40 years, we have learned and adhere to best practices to create the highest quality product possible. When assessing your flow measurement equipment, you should consider the following best practices.

Sierra’s Standards for Mass Flow Controller Manufacturing

In the design and production of mass flow controllers and meters, manufacturers should:

1.  Design and manufacture instruments to have a burst pressure sufficiently above their specified pressure rating of the instrument. The instrument must meet applicable pressure vessel codes, and these codes should be cited in the specifications of the instrument.

2. Pressure test every instrument at a pressure sufficiently above its pressure rating to insure safety when in use. However, the test pressure should be sufficiently less than the burst pressure so that the integrity of the instrument is not compromised during the pressure test.

3.  Comply with the hazardous-area and electrical-safety codes and other standards and codes cited in the specifications of the instruments.

4. Provide to users only those instruments that have a leak integrity specification that insures safe use with the gas of the application. Manufacturers shall leak test their instruments. Leak testing equipment should have sufficient sensitivity to insure compliance with the leak integrity specification of the instrument.

5. Burn-in their instruments using a protocol that insures compliance with their long-term drift and accuracy specifications.

6. Flow calibrate every instrument. The flow calibration standard used should have an accuracy that is at least factor of 2, and preferably a factor of 4, better than the accuracy specification of the instrument under test.

Following these best practices are sure to result in the most accurate measurement outcome with your new mass flow meter or controller. Have any other tips we didn’t mention? Please leave them in the comments section below.

Overcoming Natural Gas Sampling Challenges in Oil & Gas Applications

It is a fact that in order to comply with various government rules and regulations, oil and gas companies have to continually take natural gas samples to prove the gas composition and amount of gas flowing in their oil fields.

The challenge comes in trying to actually take an adequate gas sample representative of the gas flow.

  • First, engineers must carefully consider where the “representative” gas sample will be taken from in the source stream all the while maintaining chain of custody to avoid contact with contaminants.
  • Then engineers must also reduce and control the pressure to the analytical tool, stabilize and control the flow, all the while protecting the analytical instrument from particulates, moisture, and pressure/flow excursions.
  • Add to that, engineers must take the gas sample in as real time as possible, so that it correlates with the actual process flow.

hydrocarbon-engineering-cover-1116_highThe goal for oil and gas engineers is to take the most accurate gas flow sample, as quickly as possible, with the lowest incurred cost. This may seem impossible, but advances in flow meter technology are tackling the challenges of natural gas sampling – head on.

In our technical article in Hydrocarbon Engineering, learn how flow meter technology advancements solve all the inherent challenges in gas sampling applications like:

  • Accuracy at low flow rates
  • Metering accuracy in changing gas compositions
  • Managing changes in varying pressure
  • And more…

The article is an informative look into natural gas sampling and how to overcome those challenges. Read the article today.

Under Pressure, Part 2: Don’t Run a Flowmeter Regulator into the Mud!

Proper line regulation, be it supply pressure regulation, or back pressure regulation, is fundamentally key to a properly tuned flow system process. All instruments operate most accurately under steady-state conditions, so awareness of regulator behavior and proper tuning will save you time and money on avoiding waste during transient conditions.

In my continuing tutorial on mass flow controllers and pressure regulators (for my intro, see Pressure Regulation Can Be a Sticky Wicket with Flow Meters), I want to point out a seemingly obvious but often overlooked phenomenon with gas mass flow control: seat-drop lock. I know you’ll get this concept right away.

SmartTrak flow meters for optimal gas mass flow control

Outlet pressure and flow rate are directly proportional, so it’s important to remember that regulators need some flow to properly maintain a setpoint. This can be particularly obvious with a back pressure regulator vs. a line regulator. In short, if you cut the flow significantly, the droop slope spikes. Then, the relationship between outlet pressure and a given flow rate is nonlinear and entirely more drastic at fractions of full-scale flow rate. So, don’t run a regulator down into the mud and expect it to work right!

If you’re having problems with controlling gas mass and need some advice on flowmeter settings, contact us. We’re always happy to help improve your flow!