Using Flowstream With Different Gases; Reference Conditions For Mass Flow Measurement - Universal Flow Monitors FlowStream OFS User Manual

The internal temperature sensor is located above the inlet port, very close to where the gas enters
the meter. This ensures accurate measurement of the gas temperature. However, because the
temperature sensor is embedded inside the flowmeter body, if ambient temperature is different
from gas temperature, there would be a discrepancy between what the sensor reads and the true
gas temperature. The flowmeter body would track ambient temperature while gas temperature
would heat/cool the body at a different rate.
Likewise, if temperature variation is rapid, the flowmeter body may not follow it quickly enough
due to the mass of the metal flow chamber, which in turn would result in inaccurate
measurement of gas temperature.
For optimal performance, always allow two to four hours from the time the ambient and gas
temperatures are stabilized to when the first flowmeter reading is taken.

Using FlowStream with Different Gases

FlowStream flowmeters can easily be used to measure the flow rate of other gases, as long as
the gas compatibility criteria are observed. For example, a flowmeter that is factory-calibrated
for air can be used to measure the flow of Argon. (Consult Factory for additional information.)

Reference Conditions for Mass Flow Measurement

Although the correct units for mass are expressed in grams, kilograms, etc., it has become
somewhat standard that mass flow rate is specified in SLPM (standard liters per minute), SCFH
(standard cubic feet per hour) or other similar units.
This means that the mass flow rate is calculated by normalizing the volumetric flow rate to some
standard temperature and pressure (STP). By knowing the gas density at that STP, one can
determine the mass flow rate in grams per minute, kilograms per hour, etc. STP is usually
specified at sea level conditions; however, no single standard exists for this convention. UFM
uses STP of 70° F and 14.7 PSIA.
Note: If used outside the parameters specified in this manual, the proper operation of the
flowmeter cannot be guaranteed.
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