Thermal Mass Flow Controllers and Thermal Mass Flow Meters; Standard Flow vs. Actual Flow
Thermal mass flow controllers and thermal mass flow meters are used to measure and control the flows of gases. The measuring terminology usually includes words like “standard” or “normal” flow. A standard cubic foot of gas is the same as an actual cubic foot of gas only if the measurements are taken at some standard set of conditions (STP); like 70 degrees F and one atmosphere ambient pressure. If the ambient conditions change, you may never know how much gas you have in a volumetric measuring chamber, but, if you use a device that measures standard cubic feet of gas, you will always know the flow.
Thermal mass flow controllers and meters use a sensor that measures standard units. If you are measuring 30 psi nitrogen at 100 degrees F, the device will indicate the amount of standard cubic feet per minute (SCFM) flowing or it could indicate in standard liters per minute (SLPM). Either way, you can change the actual temperature and the actual pressure and the measuring device will still indicate flow in standard units.
83% of all instruments used in the chemical process industries (CPI) are being talked to using analog communications. By analog communications, we mean 4-20 milliAmp mainly. But we see 3-15 psi air and 0-5 volt control systems also. Why wouldn’t you use some of those 1’s and 0’s?
