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Best Flow Blogs of 2018

best of 2018 facebook

2018 is now in the history books, and 2019 has begun with gusto. Can you feel the electric energy of a fresh start in the air?

This time of year is a perfect time to reflect on the previous year and to set goals building on the success of the previous year to ensure an even better year ahead.  So here’s a look at the most read blogs by you, our customers and fellow flow measurement enthusiasts!


Top Blogs of 2018

Understanding the iSeries Totalizer for Gas Mass Flow Rate

The number one most read “How to” blog addressed questions regarding flow meter totalizers, specifically, Sierra’s iSeries flow meter Totalizer App that comes standard with every QuadraTherm 640i/780i Thermal Mass Flow Meter. Discover how to correctly use flow meter totalizers and understand the power of the iSeries flow meter totalizer in this top read blog.   



social-image-how-waterflow-meter-works-110817How Does a Water Flow Meter Work?

Water measurement is one of the most common applications and biggest market, so it doesn’t surprise us that so many want to learn how liquid flow meters work and the benefits of the varying measurement technologies. This blog discusses the four types of flow meter technologies for water application and how they work.


ammonia-blog-image-1200-630-012218Flow Meter Do’s and Don’ts with Ammonia
Ammonia measurement is a tough measurement to make, but possible.  And you have consistently wanted to know more about the “do’s and don’ts”. We have updated this blog to reflect the changes in flow measurement technology while keeping the original spirit and content of the piece – measuring ammonia flow correctly. 


suspended-animation-facebook-1200-by-630-030818Turning Science Fiction into Reality
When you mix sci-fi and flow measurement innovation, you have a winning story. This is case study of how one scientist uses Sierra’s flow controllers for a cool and innovative gas mixing application to achieve suspended animation in mice. Now, this breakthrough is used by NASA. Learn about suspended animation and how it’s used to save lives.


Blog-image-1Flow Energy Management Applications-Installation Tips & Tricks
Proper installation is key! Often times when your flow meter “doesn’t work,” it could just be that your flow meter is not installed properly.  Part 2 of our 3 part Flow Energy Management Applications blog series offers insightful tips and tricks to consider for successful installation of your flow meter.



Oldies, but Goodies …Still

Since their first appearance on our blog, these older posts remain some of the most read and popular content by our readers:

Tuning Your Boiler for Energy Efficiency
Improving energy efficiency and cost savings will forever be a popular topic. This blog describes 3 ways to tune your boilers to meet government BoilerMact regulations and details the various boiler applications.

Insertion Flow Meter Straight Run Requirements
A flowmeter is only as good as its installation and, in this blog, Sierra offers expert advice on straight run requirements for the best installation.  

Challenges with Submetering Natural Gas (Part 1)
Who doesn’t want to save money on their natural gas bill? Learn how to save on natural gas billing by analyzing sub-metering in your facility or campus.

More To Come In 2019

This year, you can expect even more in-depth content from Sierra Instruments that focuses on “how to” content to achieve accurate flow measurement, increase energy efficiency, and save money on energy costs. 

Welcome to 2019! Let’s make it a great one.

Complete Guide to Gas Mixing and Blending | Sierra Instruments


Gas mixing sounds simple enough. You simply mix a number of pure gasses to create a new mixture. Unfortunately, it’s not usually as simple as it sounds. There are many variables and factors that play a role. 

In this post, we’ll dissect this challenging application and discuss how to obtain perfect gas mixing and blending with capillary thermal mass flow controller technology.

Why It’s Important

There are many applications and industries that rely on gas mixing and blending. In a laboratory environment, our customers need gas mixtures to test catalysts to see the effect of certain concentrations of pollutants on gasses. The food industry needs a mixture of gasses to prevent oxidation of food. The semiconductor industry needs accurate gas mixing to generate certain atmospheres in their ovens. Hospitals mix gases to create O2 rich air or narcotic gasses. 

There are hundreds of other applications that utilize gas mixing like welding, dilution, chemical reactions, testing of gas analyzers, filling light bulbs, and double glazing windows.  The most common gas blending applications, however, are related to burning and combustion.

Do you remember the basics of combustion? You need fuel, oxygen, and ignition. If the fuel and the oxygen are both gasses, it is ideal to mix them in the perfect ratio to get optimum and clean combustion. 

We can name several applications for this type of gas mixing: Your car, big boilers, small flames used in the glass industry, big power plants, Waste burning plants, etc.

Why Mass Flow Meters?

In gas mixing and blending, direct gas mass flow control provided by a mass flow controller (MFC) not volumetric flow control, is very important. Proper mixing and blending saves money and increases repeatability of the end product and improves quality.

Combustion or burning applications have their own set of challenges. Combustion or burning is a chemical process, a reaction between molecules. To quantify the gas used, then, we should count those gas molecules and not the space between these gas molecules. We do that by measuring the gas mass flow, the weight of the gas (molecules), and not the volume (molecules + space between molecules).

The nice thing about Mass Flow Controllers is that they do just that: They measure and/or control the gas mass flow. They are molecule counters! 

Accuracy in Gas Mixing & Blending

Mass flow controllers are devices that have an accuracy of % of full scale (%FS). That means that the uncertainty of a 1% device is 1% of the maximum flow range of the instrument.

For example, if you purchase a mass flow controller with a range of 0-500 SLPM and the unit has an uncertainty 1% of full scale, the uncertainty is 1% of 500 = 5 SLPM. So, when you control a mass flow rate of 500 SLPM, the flow can be between 495 to 505 SLPM. However, if you control mass flow rate at 10 SLPM using the same 500 SLPM instrument, the uncertainty is still +/-5 SLPM.  As a result, the controlled flow could be anywhere between 5 SLPM up to 15 SLPM. Pretty bad!

The good news is that the newest generation of high-performance Thermal Mass Flow Controllers has drastically improved with the aid of advanced electronics, sensor, and laminar flow element design and linearization mathematics are getting closer to being % of measured value devices. And for a gas mixing and blending application requiring multiple mass flow controllers, the price of the instrument matters.

You’re probably wondering what all this means for gas mixing and blending applications? The lesson learned is that the absolute accuracy is not as good when you operate the mass flow controller at the bottom of the maximum flow range of the instrument, so size your instrument correctly. 

This sizing of mass flow controllers in a gas mixing system is critical. You should be very clear what the purpose and the operational range of each mass flow controller in your gas mix system should be. Ask the manufacturer of the instrument to assist you as they probably have many customers faced with the same challenge.

‘Kwik Kalucations’ with K-Factors

‘Kwik Kalucations’ with K-factors make gas mixing with a single gas mass flow meter simple.

If you’re looking to improve flexibility and save money when it comes to gas mixing and blending applications, consider applying a “K-Factor.” A dimensionless numerical relation of a specific gas vs. air or nitrogen, a gas K-factor never changes. If K-factors will work in your application, you can use one gas mass flow controller calibrated on air or nitrogen for several gasses by simply applying the K-factor.

K-factors, in general, do not change and are used for measurement and control of mass flow rate in units of SCCM and SLPM.  For example, if you calibrate your capillary-sensor gas mass flow controller with air for 0-100 SLPM, but intend to run 100 SLPM of argon through it, you will only get an output of 69 SLPM for the instrument. That’s because the physical properties of argon that affect heat transfer (the standard gas density and specific heat) are different than air.

Furthermore, when you run enough argon through the instrument so that it indicates 100 SLPM, you will actually find the flow of argon is 145 SLPM. Thus, the K-factor of Argon is always 145/100 = 1.45.

Every gas has its own K-factor, but there can be slight differences across various brands of instruments. Is the K-factor a perfect linear function? Well, we assume so, but in reality that is not always true, especially with lower-cost flow sensors and flow meters for gas on the market today. Errors can be up to 7% on very specific light gasses like hydrogen or helium for these lower performing instruments. 

In contrast, the SmartTrak 100 digital mass flow controller is a premium instrument with a high level of reliability with K-factor behavior enabling such technologies as Dial-A-Gas, multi-gas capability. This makes the SmartTrak 100, together with the advanced digital communication possibilities of the Compod, an ideal choice in gas mixing and blending applications.

Dilution in Gas Mixing

Dilution is a special application in the world of gas mixing. Basically, you are diluting a concentration of gas in an already existing gas mixture. Let’s say you have a gas mixture of 10% Ar / 90% N2 and you really need 5 Ar / 95% N2 for your application. The solution is to add more N2 to the mix, but how much? 

To answer the question of ‘how much,’ we first need to know if the gas mix ratio is in % mass or % volume. Let’s assume it is % mass. In that case, we need to generate a new mix of 50% of the original 10% Ar / 90% N2 mix and dilute (or mix in) that with 50% N2. The result is a new mix of 5% Ar / 95% N2 mix.

Most concentrations, however, are much smaller, more in the 0.0001% region. In general, one expresses this in ppm values (ppm = parts per million). This means that 10000 ppm = 1%.

Wouldn’t it be nice to have an automated gas mix system that calculates this all for you? Sierra can provide this for you, contact us to learn more about our SmartTrak® 100 Digital Mass Flow Controllers for Gas Mixing & Blending

Benefits of Capillary Thermal Mass Flow Controllers

  • Direct mass flow with +/- 0.5 percent full-scale accuracy
  • Patented, inherently linear laminar flow element design
  • Mass flow rates up to 1,000 slpm and down to 0 to 0.1 sccm
  • Pressure to 5,000 psig (345 barg) with low pressure drop of 4.5 psid (310 mBard)
  • Provides smooth and flexible valve performance, even at low flows
  • True multigas digital mass flow controller—up to 10 pre-programmed gases
  • 10-point NIST calibration on primary standard


Watch this video to learn more about SmartTrak®: Master of All Flows.

Core Technology Series: Capillary Tube Thermal Mass Flow Meters and Controllers

Understanding Capillary Tube Thermal Mass Flow Meters & Controllers:  

Flow meters and controllers are used every day in general purpose industrial and laboratory applications and in the semiconductor industry.  Have you ever wondered how capillary tube flow meters work?  or How to specify the perfect flow meter for your application? I am excited to present this ongoing core technology series based on excerpts from Sierra’s Founder and Chairman (Also my Father), Dr. John G. Olin’s, white paper entitled, “Capillary Tube Thermal Mass Flow Meters & Controllers- A User’s Guide.”  This “User’s Guide” is designed to educate both flow beginners and experts in the most common types of direct mass flow thermal flow meters, typical applications, principle of operation of capillary tube thermal flow meters, best practices for users, including the selection, installation, and operation of the instruments.   Now let’s start at the beginning.

What is a Capillary Tube Thermal Mass Flow Meter or Controller?

Capillary tube thermal mass flow meters directly measure the mass flow rate of clean gases and gas mixtures in lower flow ranges. A capillary tube thermal mass flow controller adds an integrally mounted flow control valve to the flow body of the mass flow meter and both monitors the mass flow rate and controls it to be equal to a set-point value selected by the user.

History of Capillary Tube Thermal Mass Flow Meter and Controllers

SmartTrak 100 flowmeter for highly accurate gas mass flow control

Capillary tube thermal mass flow meters and controllers were first commercialized in the early 1960’s. The space industry was one of the first users, but before long the industry that fabricated solid state semiconductor devices recognized their usefulness. When integrated circuit semiconductor devices began their long and continuing period of exceptional growth, the market for capillary tube thermal mass flow controllers grew with it. In the 1970’s and 1980’s, general industry recognized the advantages of using capillary tube mass flow meters and controllers in a broad range of applications, and several new companies were formed to serve this growing market. The advantages of accuracy, compactness, reliability, and cost-effectiveness continue to make capillary tube thermal instruments the choice for monitoring and controlling smaller mass flow rates of clean gases in general industry and in the fabrication of semiconductor devices.

The primary virtue, and the source of their prominence, is the fact that capillary tube thermal instruments directly measure mass flow rate, as opposed to, for example, volumetric flow rate. This is important because most industries need to measure and control the flow of the molecules, i.e., the mass, of the gas entering their process.

Types of Direct Mass Flow Meters & Applications

Figure 1: Classifications of Mass Flow Meters

There are two kinds of flow meters that directly measure the mass flow rate of fluids—Coriolis mass flow meters and thermal mass flow meters. Coriolis mass flow meters directly measure the mass flow rate of most fluids, both liquids and gases, and do not require knowledge of the identity, or composition, of the fluid. Thermal mass flow meters directly measure the mass flow rate of gases, and do require knowledge of its composition. Coriolis mass flow meters have high accuracy, high pressure drop, work best with liquids, and are relatively expensive. Thermal mass flow meters have medium to high accuracy, low pressure drops, work best with gases, and are relatively inexpensive.

For the purposes of this blog series we will focus on thermal mass flow meters. Specially, capillary tube flow meters and controllers. Capillary tube thermal mass flow meters and controllers have two broad fields of application: general purpose industrial and laboratory applications and semiconductor manufacturing and other high purity vacuum processes. More MFCs are manufactured than MFMs because most users want to control the mass flow rate of the gas in their process rather than just monitor it. Capillary tube thermal MFCs offer a cost-effective solution for controlling the flow of gases because they are compact, require only one penetration of the process line, and have a built-in optimized control system.

Principle of Operation: How Capillary Tube Mass Flow Meters & Controller Work

Figure 2: Typical general purpose mass flow controller

In the case of the capillary tube type of thermal mass flow meter (MFM) described in this blog, the flow enters the flow body and splits into two internal flow paths. One path flows through a heated capillary sensor tube that has a small diameter and relatively long length. The second parallel path inside the flow body passes through a split-flow bypass consisting of a laminar flow element that shunts the bulk of the flow around the sensor tube. The ratio of the flows through the bypass and the sensor tube is a constant. The capillary sensor tube measures its internal mass flow rate by means of the heat capacity of the gas that carries heat from an upstream resistance-temperature-detector winding to a downstream winding, both  on outside of the sensor tube. The difference in the electrical resistances of the two windings provides the measurement of the mass flow rate through the sensor tube, and thereby the total mass flow rate in the flow conduit.

A capillary tube thermal mass flow controller (MFC) adds an integrally mounted flow control valve to the flow body of the MFM and both monitors the mass flow rate and controls it to be equal to a set-point value selected by the user either remotely or on the MFC itself. To learn more about Capillary Thermal Mass Flow Controller & Meter technology, watch this video that follows a molecule of gas through a typical capillary thermal flow controller.


Next up in the “Capillary Tube Thermal Mass Flow Meters & Controllers- User’s Guide” series, Dr. Olin describes the mechanical components of mass flow meters and controllers and the operation of these components.

Get more information on Capillary Tube Mass Flow Meters and Controllers:

Download Dr. Olin’s Complete White Paper “Capillary Tube Thermal Mass Flow Meters & Controllers- A User’s Guide.”

Read more about the History & Evolution of Mass Flow Controllers

Read Core Technology: Capillary & Immersible


The Challenges of Measuring Flare Gas

flare gas measurement

The associated gas generated from oil production has received a lot of attention recently.   In many areas, the lack of gas collection infrastructure requires this gas to be flared off.  Many jurisdictions now require the flow rate of gas to the flare to be monitored in order to reduce emissions and to allocate taxes, fines and other fees.

Measuring the flow rate of flare gas is challenging because a flare is not a pure gas, but a mixture of many different gases.  In order to correctly measure the flow rate of the constituent gases, the composition of the flare must be known.  This is typically determined by taking a sample (a cut) and processing it through a gas chromatograph (GC).  This composition coupled with the total measured flow rate allows the flow rate of the individual component gases to be calculated.

Once the gas begins to flow from a well, operators need to account for this associated gas from day 1.  This of course requires a flow meter calibrated to measure the flow rate of the flare gas.  Virtually all current flow measurement technology requires a known composition for calibration.  This presents a “chicken or egg” problem, since the composition may not be known at start-up and will change over time, thus rendering the flow meter inaccurate at best and inoperable at worst.

Achieving Flare Gas Measurement Accuracy Regardless of Changing Gas Composition

Recent innovations in immersible thermal flow meter technology provide a solution to this “what came first” problem.  Sierra’s QuadraTherm flow meter can accurately measure the mass flow of gases over a very wide turn-down.  Most importantly, users can change the meter’s calibration in the field to reflect the actual gas composition.  This is made possible by an industry first algorithm called qMix, which uses the NIST RefProp database of gases to calculate the heat transfer properties of complex gas mixtures and thus maintains meter accuracy.

qMix Mathematical Model – How It Works*

QuadraTherm’s advanced mathematical model operates a microprocessor-based system that provides the foundation for making in-the-field compositional compensation. In a thermal mass flow meter, a velocity sensor measures the heat removed from a heated sensor by the flowing gas, while additional sensors measure other heat losses, such as those caused by natural convection, radiation, stem and end loss. The heat removed by the flowing gas is proportional to the mass flow.   In operation, the four-temperature microprocessor-based system measures the resistance of each of four RTD sensors along with the current in the velocity sensor. The resistance values are converted to their four corresponding temperature values, and the current to the velocity sensor is converted to electrical power, or wattage. The four temperatures, the wattage, and the gas composition are the inputs to the system. The gas property algorithms calculate the updated properties of the gas (mass density, dynamic viscosity, thermal conductivity, and heat capacity). The system then computes the total mass flow rate in the pipe line – the desired output.

QuadraTherm meters can thus be stocked on the shelf, so that when a spare or new meter is needed, they can be installed, and the sample gas composition programmed in upon start-up of the well, thus ensuring day 1 flow measurement accuracy.

Download “New Developments in Thermal Dispersion Mass Flow Meters: In-The-Field Compensation for Changes in Natural Gas Composition” for more information on advances of QuadraTherm with qMix.

*Reference: Blog copy reprinted from Olin, J. G. 2014. New Developments in Thermal Dispersion Mass Flow Meters: In-The-Field Compensation for Changes in Natural Gas Composition. Presented at 2014 American Gas Association Operations Conference, Pittsburgh, PA, May 20-23, 2014.

Dissecting a Mass Flow Meter Spec Sheet

7 Need to Know Terms for Successful Specification of a Mass Flow Meter or Controller

Whether you have been on the job for decades or just starting to purchase or specify a mass flow meter or controller to measure fluid flow in your application, there is key terminology to understand. Here are seven terms you should know to assure you are getting what you need to measure or control flow in your process effectively.

1. Flow Ranges (Mass Flow Rate)

The amount of fluid a mass flow meter or controller is best suited to measure flow for.

Example: the table below shows mass flow ranges of three typical flow body sizes of general purpose mass flow meters (MFM) and mass flow controllers (MFCs) for air at 0°C and 1 atmosphere pressure:

Flow Body Size Maximum Mass Flow Rate Range (slpm)
Low Flow 0 to 50
Medium Flow 0 to 300
High Flow 0 to 1500

NOTE: Most manufacturers make no distinction between mass flow meters and controllers and published specifications may vary from manufacturer to manufacturer.

2. Accuracy
The accuracy statement on any spec sheet indicates how precise the flow meter/controller will measure flow within its flow ranges.

Officially, the American Society of Mechanical Engineers (ASME) defines the “accuracy” of flow meters as: the degree of freedom from error, or the degree of conformity of the indicated value of the instrument to the true value of the measured quantity [1].

An accuracy specification includes errors due to: (a) uncertainty in the flow calibration standard; (b) any non-repeatability of the MFM or MFC under test; (c) disagreement between the curve-fitting function and the actual flow response curve; and (d) inability of the flow calibration facility to deliver a sufficiently constant flow rate.

Typically, the accuracy of most general purpose MFMs and MFCs in measuring gas mass flow rate is 1% of full scale, including linearity, and at flow calibration conditions.

These are some examples of how manufacturers express the accuracy of their MFCs and MFMs in measuring mass flow rate:

  • Percent of full scale: X % of full scale
  • Combination: X % of reading + X % of full scale
  • Divided range: X % of reading (≥ Y % of full scale) and X % of full scale (< Y % of full scale)
  • Calibrated Span (%CS)
  • Upper Range Limit (%URL)

3. Repeatability
The flow meter or controller’s ability to produce the same results/readings multiple times with no change in conditions (same flow rate, same operator/engineer, same laboratory, and short intervals of time, etc.).

Typically, the repeatability of general purpose MFMs and MFCs is +/-0.2% of full scale.  Some manufacturers specify a repeatability of +/-0.2% of reading.

4. Reproducibility
The flowmeter’s ability to produce similar results/readings when the conditions of measurement differ. Example: different operators/engineers, facilities, time intervals, laboratories, etc.

5. Rangeability / Turn Down
Turndown or Rangeability is the range of flow (maximum to minimum flow rate) that a flow meter is able to measure in its specified accuracy.

6. Response Time
The time it takes the flow meter to settle on the new flow rate after a sudden change in flow.

7. Leak Integrity
The amount of gas leakage you can expect from seals on your mass flow meter or mass flow co

General purpose instruments with elastomeric seals have maximum leak-rate specifications ranging from about 1 x 10-9 to 5 x 10-9 atmosphere cubic centimeters per second of helium. Semiconductor MFCs and general purpose metal sealed MFMs and MFCs intended for vacuum processes have lower maximum leak rates of about 1 x 10-11 to 1 x  10-10 atmosphere cubic centimeters per second of helium.

This blog, as part of our ongoing core technology series based on excerpts from Sierra’s Founder and Chairman, Dr. John G. Olin’s, white paper entitled, “Capillary Tube Thermal Mass Flow Meters & Controllers – A User’s Guide,”  dives “under the hood” and takes a closer look at the flow body, flow rates & sizing, and how flow conditioning works. Referenced material from ASME MFC-1M-2003(R2008), “Glossary of Terms Used in The Measurement of Fluid Flow in Pipes,” American Society of Mechanical Engineers, 3 Park Avenue, New York, NY.

Get more information on Capillary Tube Mass Flow Meters and Controllers:

Download Dr. Olin’s Complete White Paper “Capillary Tube Thermal Mass Flow Meters & Controllers- A User’s Guide

View Sierra’s Mass Flow Meter and Controllers.

How to Specify the Best Mass Flow Meter or Controller for Your Application

A question we get a lot from our customers is how to determine which Sierra mass flow meter or mass flow controller is best for their application.  Followed up by: What’s the difference between an economical mass flow controller and a premium mass flow controller. Our new video explains the differences between Sierra’s economical and premium mass flow meters and gas controllers (our SmartTrak 50 and 100 product lines) and offers you a simple checklist you can use to purchase the best mass flow meter or controller for your application.


Differences Between an Economical Premium Mass Flow Meter or Controller

SmartTrak 50 is an economical mass flow meter or controller which offers a single gas flow calibration with no local touchpad or control. Maximum flow range of this device is 200 slpm. It’s ideal for single gas and OEM applications. SmartTrak 100 is the premium mass flow meter for you, if you need to measure/control multiple gases and have the ability to change your application parameters in the field. SmartTrak comes pre-programmed with 10 standard custom gases or mixes, with or without a touchpad display, and has a flow range of 4 sccm-1000 slpm.  The SmartTrak 100 is ideal for applications that need flexibility like universities or laboratories. Add an optional Compod™ to the SmartTrak 100 for gas mixing blending/batch control/ratio control applications.

50/100 table

How to Order A Mass Flow Meter or Controller

Using our SmartTrak 50 (economical version) and 100 (premium) as an example, we’ve created a short checklist that will help you specify the right flow meter or controller for gas applications (with most flow meter manufacturers).

  1. Decide if you want to meter or control the gas flow.
  2. Determine your application conditions.
    • What is your application gas?
    • How many gases does your application have? Decide if your application requires the economical (single gas) or premium meter (single/multiple gases with wider flow range).
    • What is your maximum flow rate?
  3. Determine the required body size of your device which is based on your application flow rate. For SmartTraks:
    • Flow rates up to 50 slpm Air equivalent, choose low flow (L) 50 Series
    • Flow rates up to 200 slpm, choose the medium flow (M) 50 Series controller
    • Higher than 200 slpm (up to 1000 slpm) choose high flow (H) flow device. In this case, SmartTrak 100.
  4. Choose flow body material, either aluminum or stainless steel.
  5. Decide on a display option.
    Digital display or no display.
  6. Choose your inlet/outlet fittings depending on the line size and flow rate.
  7. Decide on an output signal/and set point (controller).
  8. Choose the accessory or power supply needed. For the SmartTrak 50 & 100, you can use our purchasing guide to determine the right one for your meter or watch the cabling guide video.

Have an application you need help with? Contact us today.

Understanding the Mass Flow Meter and Mass Flow Controller Flow Body – Why it Matters.

When it comes to mass flow meters and controllers size matters.

Not all flow meters are the same. It’s like choosing a car. All cars are designed to move you from point A to B. However, if you live high up in the mountains you might want a truck or a tougher built car to handle your specific terrain.

The same applies when choosing a flow measurement device. If you need to measure water or steam you wouldn’t want to purchase a general purpose mass flow meter (MFM) or mass flow controller (MFC), you would want to look at an ultrasonic or vortex flow meter. If you need to measure gas for laboratory or research and development, you would look at mass flow meters and gas controllers.

However, like purchasing a car not all mass flow meters and controllers are built the same. It’s important to know how the MFC and MFM  are built to know if it can handle your flow measurement application. In this part of the Core Technology Series, we will focus on the construct of an MFC or MFM flow body.

Flow Body

General purpose MFMs and MFCs typically have only three flow body sizes covering the entire flow range of the instruments—low flow, medium flow, and high flow. The type of flow device or flow controller you choose depends on your gas and the flow range.

Flow Body Size Maximum Mass Flow Rate Range (slpm)
Low flow

0 to 50

Medium flow

0 to 300

High flow

0 to 1500


SmartTrak 100 flowmeter for highly accurate gas mass flow control










Low flow bodies often are machined out of a single piece of stainless steel bar stock. To get an idea of their relatively compact size, MFCs have the following approximate widths and lengths (not including inlet and outlet fittings): low flow—1.0 W x 3.0 L inches (25 W x 76 L mm); medium flow—1.5 W x 4.5 L inches (38 W x 114 L mm); and high flow—3.0 W x 9.0 L inches (76 W x 229 L  mm). MFMs usually have the same widths but have about two-thirds the length in the medium and high flow sizes.

The flow body has inlet and outlet flow conduit fittings and houses the flow conditioning section, the sensor tube, the bypass/laminar flow element, and, in the case of MFCs, the control valve. The electronics are mounted in their enclosure on the top of the flow body. The wetted parts of a typical flow body and its internal components are made of corrosion resistant materials. Typical wetted materials for the flow bodies of general purpose MFMs and MFCs are: 316 L stainless steel; ferromagnetic stainless steel in the valve; and “O” rings and valve seats of fluoroelastomers and other advanced elastomeric materials. Some lower cost instruments intended for light duty and lower accuracy applications have flow bodies made of plastic or aluminum.

Instruments with elastomeric seals throughout the flow body have relatively low rates of leakage in and out of the flow body. MFMs and MFCs used in vacuum processes use metal seals at all locations in the flow body to further reduce leak rates. Manufacturers should subject every instrument to a helium leak check using a mass spectrometer leak detector, or equivalent instrument. Additionally,  all instruments  should comply with applicable pressurized equipment standards and codes, and manufacturers should pressure test all instruments to ensure compliance.

Process lines typically are tubes with outside diameters of 1/8, 1/4, 3/8, 1/2, 3/4, and 1 inche (6, 10, 12, and 20 mm). The 1/4 inch (6 mm) tubing size is most common. Some MFMs operated at very high flow rates are available in wafer and flange pipe sizes. Manufacturers offer a broad selection of process tube fittings, including compression fittings, elastomeric “O”-ring face seal fittings, and metal gasket face seal fittings. Since the inlet and outlet fittings contribute to the pressure drop in the instruments, the size of the fittings should be as large as practicable within constraints imposed by the size of the process line.

Semiconductor MFCs

Semiconductor MFCs often have a particulate filter, pressure regulator, and a positive shut-off valve installed upstream of the instrument and may have a positive shut-off valve and pressure regulator installed downstream. General purpose instruments also may include ancillary flow components in their installation.

Semiconductor MFCs used in the fabrication of high-end semiconductor devices have several special requirements to ensure that: (1) no particulates or other contaminants enter the fabrication process; (2) no toxic process gases escape the MFC; and (3) no ambient air enters the process. Typical specifications are: wetted surfaces must have high purity and be highly polished (surface roughness in the range of  about 4 to 10 microinches Ra (0.1 to 0.25 micrometers Ra); leak rates must be extremely low; and internal flow paths, as shown in Fig. 3, must have no sharp corners, cavities, or dead spaces where particles can form. Semiconductor MFCs are available in both in-line and down- port configurations. Down-port versions reduce the axial dimensions of the MFC and its ancillary flow components, thereby facilitating the compactness required by manufacturers of semiconductor equipment.

This blog, as part of our ongoing core technology series based on excerpts from Sierra’s Founder and Chairman, Dr. John G. Olin’s, white paper entitled, “Capillary Tube Thermal Mass Flow Meters & Controllers – A User’s Guide,”  dives “under the hood” and takes a closer look at the flow body, flow rates & sizing, and how flow conditioning works. Referenced material from ASME MFC-1M-2003(R2008), “Glossary of Terms Used in The Measurement of Fluid Flow in Pipes,” American Society of Mechanical Engineers, 3 Park Avenue, New York, NY.

Get more information on Capillary Tube Mass Flow Meters and Controllers:

Download Dr. Olin’s Complete White Paper “Capillary Tube Thermal Mass Flow Meters & Controllers- A User’s Guide

View Sierra’s Mass Flow Meter and Controllers.


Top Blogs of 2020

Even though 2020 has come and gone, we would like to take a minute to recognize our Top Blogs from 2020.  As with most things in 2020, the theme of  “get back to the basics” resonated with our readers.

The winning blogs of 2020 all answered foundational questions like: “How does this work?” or “How do I do this?” Enjoy getting back to the flow basics.

Top Blogs of 2020 – Answering Your Top Questions

  1. What Is a Flow Rate Totalizer & How Does It Work?
    Discover how to correctly use flow meter totalizers and understand the power of the iSeries flow meter totalizer in the number one read blog of 2020.
  2. How do Ultrasonic Flow Meters Work?
    Get an in-depth understanding of how ultrasonic flow meters work and why you might choose one for your application.
  3. How a Vortex Flow Meter Works?
    This blog gives explains how vortex flow meters work and the various vortex sensor technology available for steam flow measurement.
  4. Tips & Tricks to Installing Your Flow Energy Meter
    Get practical hands-on advice on how to properly install your flow energy flow meters in this blog. To get an accurate measurement, proper installation is key. Most of the time when your flow meter “doesn’t work,” it could be that your flow meter is not installed properly.
  5. How do Water Flow Meters work?
    One of the most common applications and biggest markets out there is water measurement so it’s no wonder that our blog on how water flow meters work was a top read. Discover the four types of flow meter technologies for water applications and how they work today.
  6. How to obtain perfect gas mixing and blending?
    Offering a complete Guide to Gas Mixing and Blending, this blog dissects this challenging application and discusses how to obtain perfect gas mixing and blending with capillary thermal mass flow controller technology.
  7. Why mass flow instead of volumetric flow?
    Watch this quick tip-video blog to find out the difference between direct mass flow and volumetric flow technology and discover the advantages of direct mass flow.

More To Come In 2021

In 2021, you can expect in-depth content from Sierra Instruments that focuses on “how-to” content to achieve accurate flow measurement, increase energy efficiency, and save money on energy costs.

Welcome to 2021! Let’s make it an amazing year.

How Do MEMS Mass Flow Controllers Work?

Not All MFC Sensor Technology is Created Equal

Mass flow controllers offer precision gas flow control to many critical industries including biopharm, semicon, food & beverage, manufacturing, and R&D. As the technology demands increase in these sectors, so does the demand for precision gas flow control systems. The more accurate and repeatable the gas flow control the better the yield, the higher the product quality and the lower the cost in wasted materials.

So what mass flow control technology offers the highest accuracy and repeatability over time? MEMS (Micro-Electro Mechanical Systems) sensors offer the most stable and accurate gas flow control in the industry. Mass flow controllers and meters based on MEMS technology don’t drift like other technologies, offering OEMs and bioprocessing applications a mass flow controller that is accurate over the lifetime of the device-no yearly recalibration or process shutdown necessary.

How does MEMS technology work to ensure a “no-drift” mass flow controller?

MEMS Principle of Operation

MEMS technology utilizes an advanced, ultra-stable, no-drift CMOS (Complementary Metal Oxide Semiconductor) sensor. The CMOS sensor houses both the electronic circuits and mechanical elements on a silicon chip, similar to the process used for integrated circuits.

Sierra’s RedySmart MFC – MEMS Sensor at 50x Amplification view

MEMS technology is based on the thermal principle of operation. MEMS sensors consist of two or three temperature sensors and a heater. Through vapor deposition, an extremely small molecular layer is deposited on a thin membrane. MEMS-based mass flow controllers have a bypass that pushes a defined percentage of the total gas flow through the sensor. The bore of the sensor is fairly large, so that the pressure drop is relatively low. In the presence of flow, the MEMS chip introduces heat into the medium with a constant heating output. The two temperature sensors are arranged symmetrically before and after the heating element to detect a shift in the temperature profile towards the downstream sensor of the heating element. If there is no flow, both sensing elements measure the same temperature. Because the sensor is part of the MEMS electronic circuit, the measured signal is immediately digitized giving direct mass flow readings.

Why Mass Flow is Critical

Measuring mass flow is important since most processes are more directly related to mass flow rather than to volumetric flow. For respiration, fermentation or any chemical process, it is that number of oxygen molecules that are critical, mass not volume that is critical. Unlike turbine meters, ultrasonic, pressure differential, pitot tubes and many other devices, thermal flow meters measure mass flow. Direct mass flow meters are unaffected by fluctuations in both temperature and pressure which make them inherently more accurate than volumetric technologies.

Benefits of MEMS Mass Flow Controllers

The biggest advantage of the MEMs sensor is that there is no (measurable) drift. Drift is a slow shift of the zero and the measured value at a given flow. Drift affects the accuracy. MEMS sensors are also compatible with its electromagnetic (EM) environment and don’t emit levels of EM energy that cause electromagnetic interference (EMI) distorting the signal. This along with the fact that the sensors are free of mechanical and thermal stress enables a no drift sensor and long-term device accuracy.

Mass flow controllers based on MEMs technology do not have a linear output, so they must be calibrated with the actual gas that is being used in the application. The output is a complex curve that can only be accurately curve-fit with a spline or a polynomial. And every sensor construction varies, so there is no repeatability from sensor to sensor. That means that every flow meter and controller needs to be calibrated individually on actual gas which increases their accuracy.

MEMS sensors are also very fast with a 50 msec response time with virtually no warm-up time. The instrument does not need the zero to be adjusted on regular basis. A MEMS sensor is also a lot more sensitive and due to that a turndown of 1000 : 1 is obtainable.

Benefits of MEMS Sensors

  • No-drift sensor-Long term stability over a long period of use
  • Wide turndown of 100:1. (Higher possible)
  • Less sensitive to pollution due to big ID sensor
  • Excellent temperature coefficient
  • High accuracy due to real gas calibration
  • Low-pressure drop (2.5 mbar at low flow)
  • Built-in flexibility
  • Low power consumption

RedySmart Mass Flow Controller with Lifetime No-Drift Sensor Warranty

Sierra’s RedySmart thermal mass flow meters & mass controllers are based on MEMS-based (Micro-Electro Mechanical System) technology to complement our SmartTrak® capillary-based mass flow meters & gas controllers. RedySmart thermal mass flow devices contain no moving parts and are unaffected by upstream temperature and pressure fluctuations, resulting in exceptional accuracy and repeatability.

RedySmart Proven & Stable Mass Flow Controllers offer OEMS:

  • Lifetime no-drift sensor warranty – if drift occurs, instrument will be repaired or replaced free of charge
  • High Accuracy up to ± 0.3% of full scale ±0.5% of reading
  • Repeatability of +/- 0.2% of full scale
  • Air, N2, O2 are standard. Other non-toxic, non-corrosive gases available upon request.
  • Custom and compact gas mixing blocks
  • MEMS (Micro-Electro Mechanical Systems) with ultra-stable no-drift CMOS (Complementary Metal Oxide Semiconductor) sensor
  • Ideal for OEM Applications-optimized for BioPharm/Burner Control
  • Modular-customize to needs. An easy-connect communication and power cable system has been designed for ultimate flexibility

Learn more about MEMS Sensor technology and RedySmart products.

Discover how MEMS sensor technology is providing edge to accelerate bioprocessing from pilot to production.

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.