Frequently asked questions about Thermal Electronic Mass Flow Meters and Controllers .

1. Can these meters also be used with gases other than N2?
2. Can these meters be used with flammable gases?
3. Can these meters be used where the flow is pulsating?
4. Why don't Mass Flow Meter companies use flow units ingrams per minute g/m?
5. Why is a Thermal Mass Flow meter better than a Pressure Based Flow Transducer?
6. How does Sierra calibrate these meters?
7. What are your wetted materials?
8. Do I need a special power supply?
9. Can I use this meter for a gas mixture?
10. How do I select a meter specific for my application?
11. What is your warranty?
12. What are your terms?
13. I am using Rotameters, Why should I switch?
14. Who do I contact if my meter breaks or needs calibration?
15. Who do I contact if I have technical questions?
16. Who do I contact if I have delivery questions?
17. How do I contact you via e-mail?
18. How do I talk to you on your cell phone?
19. Why don't I just buy directly from Sierra?
20. How do I know my transaction is safe with you?
21. Do you have a BLOG?
22. Have a suggestion for additions to our FAQ or website?
23. What is the difference between SLPM and NLPM?

1. Can these meters also be used with gases other than N2?
All Sierra flow meters are calibrated with N2 unless otherwise specified. The reason is the “K-Factor” for other gases is nearly linear when one goes from N2 to almost any other gas. Other gases scale the signal and generate a slight offset. For each type of gas, this effect can be calculated and compensated by using a relatively simple "K-Factor". The math is clearly shown, with examples, in the instruction manual available online in our Technical Tab always visible on the left.
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2. Can these meters be used with flammable gases?
Sierra mass flow systems without the FM approval are not designed for use in hazardous or explosive environments. Do not confuse a “hazardous environment” with flowing gas inside a closed system, such as your plumbing, into pressure and flow measuring instruments. Customers regularly use the 800 series flow meters with flammable gases such as CH4, C2H6, C3H8, and H2 that is plumbed in accordance with proper safety measures. It is important to note the Sierra 800 series sensor is a long hollow tube more than 90 times it's diameter in length. As such this sensor is essentially a "flame arrestor". Having the heated part, or the "thermal" part, of the sensor within a long hollow tube explains why these Mass Flow Meters are chosen above ANY other flow measuring methodology in nearly EVERY semiconductor facility on the planet. These applications require the use of flammable gases for the production of wafers. The Sierra 800 series sensor can reach a temperature of about 50°C above room temperature on less.23 mm^2 in the middle of the sensor tube.
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3. Can these meters be used in pulsating flow conditions?
The Sierra flow meters are regularly used in these conditions without noticeable problems. This is because the design of the flow meter is such that conditioning elements within the flow meter virtually eliminate the sensitivity to such pulsations. Many other flow technologies, such as "Delta Pressure" devices suffer from sensitivity to pulsations because the flow is not conditioned prior to measurement. The Sierra Flow Meters are essentially "Laminar Flow Meters" with a thermal laminar flow sensing element in parallel with the "main" flow. Many customers have tried using these other devices and end up coming back to the Sierra 800 series time tested mass flow measuring technology.
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4. Why don't Mass Flow Meter companies use flow units in grams per minute (g/m)?
Tradition and it is not a good one. SCCM and SLPM refer to an "implied" density, the S in SCCM, which is determined by the calibration conditions chosen for your meter. Using air as an example, we know the density of air at the STP conditions (Standard Temperature, and Pressure) of 0 Degrees C and one atmosphere is1.293 g/cc. Knowing this we can convert SCCM to g/m. An example: If our meter uses air at the STP conditions of 0 Degrees C then a 1000 SCCM mass flow meter is really a 1293 g/m device. The math: 1000 cc/m*1.293 g/cc = 1293 g/m.
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5. Why is a Thermal Mass Flow meter better than a Pressure Based Flow Transducer?
Great question! We hear this all the time and it is why the Sierra meter is such a popular a choice by scientists and technicians “in the know”. Sometimes the pressure based flow transducers are called Volumetric or Mass Flow Meters. A pressure based meter is essentially a "Volumetric" device with the addition of the corrections required to compensate for the flowing gas, pressure, temperature and other second and third order effects. Once the temperature, pressure, and other gas properties are known an on-board computer can manipulate the variables to indicate any of the desired parameters. One of the leading problems is these meters are difficult to properly "correlate" because the mechanical construction of the orifice, or pressure creating means, requires VERY CRITICAL dimensions and fabrication techniques in order to properly follow the theory that dictates their operation. As such some companies invoke "K-Factors" that attempt to overcome these difficult and costly manufacturing procedural shortcomings. Once one invokes a "K factor" to correct the basic operation of a meter we expose the difficulties in matching Primary Flow calibration checks. The Sierra Thermal Mass Flowmeter line has illustrated an extraordinary ability to follow the theory dictating it's principle of operation. It is also EXTREMELY important to note that no other company, on the planet, calibrates EVERY SINGLE flow meter with Primary Standards. This is because Sierra invented the first Automated Primary Standard Calibration system that was sold for more than 15 years and is installed in nearly every standards lab as well as the standard at the Swiss Metrology Laboratory in Switzerland .
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6. How does Sierra calibrate mass flow meters?
Every single 800 Series Sierra Flow meter is calibrated on a Primary Standard. Sierra does NOT use transfer standards. We can not stress how beneficial this is to YOU as the end user! The reason nobody else calibrates EVERY meter on a Primary Standards because the cost to calibrate Flow Meters with Primary Standards is IMMENSE however it is TRULY the ONLY way any company manufacturing Mass Flow Meters with accuracies of 1% or better could justifiably make such claims of accuracy. Sierra has been around for more than 30 years and has made substantial investments in the calibration facility that makes your flow meters. Sierra strictly maintains the classic four-to-one ratio of propagated transducer uncertainties at every calibration step. That is, in a calibration uncertainty propagation chain, the subject mass flow transducer (unit under test) can only be calibrated by a "standard transducer" that itself has an uncertainty approaching one-fourth that of the unit-under-test. This level of commitment to flow measurement accuracy requires that Sierra base their laboratory Flow measurement standards upon Primary Piston Provers that have been calibrated using NIST traceable measurements of EVERY parameter involved. Sierra does this in order to drive the initial uncertainties to the minimum possible level. The ONLY way to do this, it turns out, for measuring gas flow in the ranges you are looking at, is to utilize a Primary Standard Piston prover. NIST refers to these systems as a PVTt system, meaning Pressure, Volume Temperature and time. As such the Sierra "standard transducer" happens to be a Primary Piston Prover. Sierra does NOT use nozzles, laminar flow elements or "secondary standards" as the justification of the uncertainty would not support the claim of anything better than 1% uncertainty or "accuracy" as we so incorrectly refer to it. What YOU get is a flow meter calibrated using the best calibration system in the world. The reference to the classic four-to-one can be found many places in the NIST website at:NIST Home Page Please forgive our industries incorrect use of the term "accuracy" (as well as using units such as SCCM for mass instead of g/m). We all really know the term is an abstract one and should be replaced with the term "uncertainty". Indeed, it makes more sense to describe the uncertainty of an instrument rather than the accuracy. I recall lessons given to me by Dr. George Mattingly, Deputy Division Chief of the Process Measurements Division of NIST, goes something like this: So you have an instrument that carries an accuracy of 1%? So, does that means it is 99% inaccurate? I am guessing it will take another 40 years for this industry to "abandon" the incorrect use of the term accuracy, till then we have what we have, right along with SCCM. Please take advantage of our calibration and maintenance packages that give you from 1 to 3 future calibrations at very reasonable prices. Click on the “About Us & Terms” button at the left.
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7. What are your wetted materials?
Nylon 6/6, 316 SS, and Viton. nothing more. When you check the materials of competing flow meters you will se materials such as brass, aluminum, and epoxy.
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8. Do I need a special power supply?
No, the 810 and 820 series meters operate in using a "single ended supply" meaning you only need between 9 and 25 VDC to operate them. We sell very reasonably priced power supplies that accomplish this in a very economical manner.
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9. Can I use this meter for a gas mixture?
Yes, you can use any number of gases in your mixture. The instruction manual gives simple math to determine the linear "k-Factor" to apply to the reading if you purchased your meter for air and use it for a mixture of Nitrogen and Argon as an example. Feel free to click the Technical tab on the left to download the instruction manual that gives very good examples.
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10. How do I select a meter specific for my application?
First, you need to ensure that the flow is clean and dry in order to use the Sierra 800 series flow meters. If you have a 1/16" to ½” line that has a pressure between 15 to 100 PSIG then all you have to do is get an estimate of the flow you expect you want to monitor. Some folks time how long it takes to fill a plastic bag of a known volume and then calculate the flow rate. As an example let’s say you are using air and it takes 1 minute to fill up a 17 liter bag at your nominal flow rate. Using that number, we have 17 liters in one minute which yields a flow of 17 SLPM. Given we want to size the meter such that this nominal flow would represent about 60% of the full scale. Given a meter with 60% full scale of 17 SLPM yields the range you wish to order is 17/.6= 28 SLPM. Therefore I would order a 30 SLPM meter.
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11. What is your warranty?
Your warranty is the standard Sierra warranty. All Sierra products are warranted for ONE (1) YEAR to be free from defects in material and workmanship and will be repaired or replaced at no charge to Buyer, provided return or rejection of product is made within a reasonable period. This does not include routine maintenance, such as cleaning and calibration. See "Terms & Conditions of Sale " for a more detailed description of Sierra's Factory Warranty. Please take advantage of the extended warranties that give you a choice to extend your warranty to either 2 or 3 years at a very reasonable price. Click on the “About Us & Terms” button at the left.
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12. What are your terms?
Please click our “About Us & Terms” tab to the left to view our complete terms and conditions.
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13. I am using Rotameters, Why should I switch?
If you want an electronic output: then you can obviously not use a rotameter. Switching is an easy choice here. Try this experiment with your rotameter: Hook your rotameter inlet to the outlet of a variable valve with a pressure of at least 30 PSIG. Adjust the indicated flow of the rotameter so that the ball is at about 60% of the scale height. Once the ball is steady, gently hold your finger over the OUTLET of the rotameter and watch the ball drop to less than 40% of what it was. Remove your finger to ensure the flow is still at 60% of the height. Do this a few times to satisfy yourself that the mass flow is really constant. We know the flow did not decrease 20% because your finger can not decrease the flow created by the 30 PSIG supply and valve combination. If you had a mass flow meter in SERIES with this arrangement you would see the mass flow will remain constant while the rotameter flow would drop more than 20% by nothing more than a little back pressure. Note too that the units on the rotameter are most likely in SCCM, and on some high quality rotameters will print a stated reference temperature and pressure stated on the tube or body. Your test just illustrated that the rotameter is really a volumetric device. It is important to note that nearly EVERY process requires knowing the mass flow over the volume flow. As such you most likely NEED a mass flow meter and not a volume flow meter.
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14. Who do I contact if my meter breaks or needs calibration?
Sierra Instruments at 800-866-0200.
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15. Who do I contact if I have technical questions?
Sierra Instruments at 800-866-0200 (email: service@sierrainstruments.com)
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16. Who do I contact if I have delivery questions?
Sierra Instruments at 800-866-0200 (email: service@sierrainstruments.com)
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17. How do I contact you via e-mail?
You may e-mail me at Dave@MassFlowMetersAndControllers.Com . All of our contact info is also in About Us as well as many other locations.
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18. How do I contact to you on the phone?
Call Dave Korpi's cell phone at 831-594-6138. YOu may also call the 888-252-0007 or 831-455-0419 in Pacific time.
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19. Why don't I just buy directly from Sierra?
We offer a very narrow offering based on best of class performance, delivery and price.  We are able to purchase at wholesale volumes and leverage the cost savings into competitive prices, rapid delivery and free shipping.
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20. How do I know my transaction is safe with you?
Our secure e-commerce website uses redundant Sun Microsystems Enterprise 3500 payment-dedicated network servers with four Ultra Sparc™ processors with at least 1 gigabyte of RAM per unit. These servers are running the industry standard enterprise UNIX operating system and the most recent version of Solaris™. This means the basic UNIX system is virtually impenetrable by Windows type virus and worm threats. Our system also features symmetrical failover using Veritas Firstwatch™ and HA for Oracle, the entire system sits behind a Cisco PIX Firewall which also has redundant failover.

Our payment servers are housed at Level (3) facilities in New York City consisting of a state-of-the-art global network that sets new standards for the industry (http://www.level3.com). Physical access is protected with biometric (palm scan) identification. Uninterruptible Power Supplies (UPS) are employed as well as utilizing auto-starting generator back-up systems. We boast 24/7 worldwide network monitoring of all of the servers. Access to servers is protected via cardkey, palm print, and key lock.

All credit card numbers are stored on our Oracle-dedicated Sun E3500 database server. All credit card numbers are encrypted in real-time within the database using 512 bit RSA Crypto-C technology. RSA Security submits its Crypto-C products for FIPS 140 testing and certification. FIPS 140-1 and the forthcoming FIPS 140-2 are the US Government's standards that specify the security requirements to be satisfied by a cryptographic module. RSA Security supports PNP Security with over 20 years of experience in the security industry. It is important to compare our security to the widely known Verisign product that utilizes 128 bit encryption (as of April 2006), compare this to our 512 bit RSA Crypto-C technology utilized by the US Government. We anticipate Verisign to improve their system soon.
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21. Do you have a BLOG?
Yes. It is on the browser bar to the left. Please feel free to post any messages you wish to share!
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22. Have a suggestion for additions to our FAQ or website?
Please feel free to submit suggestions and come back soon to see your suggestion here!
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23. What is the difference between SLPM and NLPM?
NLPM is used in Europe and refers to the standard temperature of 0 Deg C where SLPM refers to the standard temperature of 70 Deg F or 21.1 Deg C
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