Frequently Asked Questions (FAQ)
Before you spend time writing us an email, you might find your question has already been answered. Look at the list below to find out. You also may want to check our glossary page. If you still want more information, please use this feedback link.
Q sccm, ln/min or other Mass Flow units, where do they stand for?
A Mass flow should actually be expressed in units of weight such as g/h, mg/s, etc. Most users, however, think and work in units of volume. No problem, provided conditions are agreed upon, under which the mass is converted to volume.
Our STP or standard temperature and pressure conditions used are stated here:
Normal conditions (ln/min): a temperature of 32 °F (or 0° C) and a pressure of 14.69 psi (or 1.013 bar) are selected, and these reference conditions are indicated by the underlying letter “n” in the unit of volume used. The direct thermal mass flow measurement method is always based on these reference conditions unless otherwise requested.
Standard conditions (ls/min): here the reference conditions are based on 68 °F (20 °C) instead of 32 °F (0 °C). Please be aware of this difference, because mixing up these reference conditions causes an error of 7%!
|Typical flow unit||Reference conditions for gas temperature||Reference conditions for gas pressure|
|mln/min (milliliter normal per minute)||0 °C / 32 °F||1.013 bar / 1 atm / 14.69 psi|
|ln/min (liter normal per minute)||0 °C / 32 °F||1.013 bar / 1 atm / 14.69 psi|
|sccm (standard cubic centimeter per minute)||0 °C / 32 °F||1.013 bar / 1 atm / 14.69 psi|
|slm (standard liter per minute)||0 °C / 32 °F||1.013 bar / 1 atm / 14.69 psi|
|mls/min (milliliter standard per minute)||20 °C / 68 °F||1.013 bar / 1 atm / 14.69 psi|
|ls/min (liter standard per minute)||20 °C / 68 °F||1.013 bar / 1 atm / 14.69 psi|
Q How do I calculate a conversion factor?
developed a unique database, consisting of fluid data of over 600 fluids.
Using application software routines various calculations can be made on-line
at our internet site www.fluidat.com
We invite our customers to visit this site for a free registration. Upon receipt of your login deatails you will be able to calculate conversion factors/tables for Bronkhorst thermal gas & liquids flow meters, calculate Kv-values and orifice sizes for Bronkhorst control valves, calculate the pressure drop accross in-line filters and perform calculations relevant to our CEM evaporation system.
A IP is an acronym for Ingress Protection. NEMA stands for National Electrical Manufacturers Association. Both IP and NEMA ratings determine how well enclosures for electronic components resist the infiltration of dust and moisture. Read more.
Q What are the "wetted parts" of Bronkhorst's gas / liquid mass flow meters & controllers constructed of?
A Standard materials of construction for all instruments is Stainless Steel 316 or equivalent. On request some wetted parts are available in Monel or Hastelloy. Contact factory for more information. Standard seals are Viton® for a gas mass flow meter / controller and Kalrez® for a liquid mass flow meter / controller.
A The selection of elastomeric sealing material for our instruments must be based on chemical resistance at operating conditions. Bronkhorst has gathered a lot of information about the compatibility of various compounds and we can advise our customers accordingly. However, our recommendations must be considered as guidelines for which no guarantees can be given.
Q Which supply voltage and I/O signals are available for Bronkhorst High-Tech gas / liquid mass flow meters & controllers?
A Bronkhorst offers a wide variety of possibilities for electrical hook-up and communication. As a standard all mass flow and pressure meters & controllers can be fed with 15 or 24 Vdc. The options for analog input/output are 0-5 Vdc, 0-10 Vdc, 0-20 mA and 4-20 mA (other on request). Digital communication of virtually all product lines are: RS232, PROFIBUS DP, PROFINET, DeviceNet™, Modbus, EtherCAT and FLOW-BUS (Bronkhorst fieldbus).
Q How to interpret the data and terminology on Bronkhorst calibration certificates?
A For a better understanding of the contents of Bronkhorst calibration certificates, please click here.
Q How often should I perform a calibration check on my mass flow devices?
A Mass flow instruments, in fact all process instruments, experience wear from the conditions of the process in which they are installed. Temperature, electronic component tolerance shift, contamination build up over time (even very slight), plus other factors will all contribute to affecting the accuracy of an instrument. Your instruments should regularly undergo, at a minimum, a calibration check if not a recalibration. But how often? Because the nature of each application is different (conditions, running time, etc.) a calibration can last three years or three months. Bronkhorst instruments do not have specified due dates for calibration. Bronkhorst suggests that our instruments be calibrated every year. However based on the application conditions, and perhaps company quality procedures, each customer must determine when they need to send in an instrument for recalibration. Properly calibrated instruments will be more accurate, more reliable, help ensure consistency, and help improve production yields.
Q Which pipe fittings does Bronkhorst recommend for their instruments?
A As a standard, Bronkhorst use compression type or face seal (VCR/VCO) fittings with BSPP thread on their instruments. BSPP (British Standard Pipe Parallel) is, as the name suggests, a parallel fitting. The threads are used to hold the two pieces together and not to create a seal. The sealing is done by an elastomeric seal external to the thread. Because the seal is external to the thread there is no danger of debris in the threads being forced into the flow path of the gas. For this reason we do not recommend NPT fittings with PTFE (Teflon) tape sealing.
Q What do you mean by turndown ratio?
ratio is also commonly referred to as rangeability. It indicates the range
in which a flow meter or controller can accurately measure the fluid. In
other words, it's simply the high end of a measurement range compared to
the low end, expressed in a ratio and is calculated using a simple formula:
Turndown Ratio = maximum flow / minimum flow
For example, if a given flow meter has a 50:1 turndown ratio the flow meter is capable of accurately measuring down to 1/50th of the maximum flow. So, suppose a flow meter has a full scale rating of 20 slm the flow meter will measure down to 0.4 slm of flow.
Keep in mind that the maximum and minimum flow capability of a meter or controller is likely to be a greater span than the measurable and controllable range. For example, a mass flow controller with a 50:1 turndown ratio may have the capability of measuring as high as 25 slm or as low as 0.16 slm but the turndown ratio will govern the actual measurable range. In this example if the calibrated high flow is 25 slm, then the lowest that can be measured is 0.5 slm (1/50th of 25). If the application requires that the calibrated minimum flow is 0.1 slm, then the maximum flow that can be measured is 5 slm (50 times 0.1).