Dwyer GFC - Manual (Page 20)

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7. CALIBRATION PROCEDURES
NOTE: Removal of the factory installed calibration seals and/or any
adjustments made to the meter, as described in this section, will void
any calibration warranty applicable.
7.1 Flow Calibration
Dwyer Instruments' Flow Calibration Laboratory offers professional calibration
support for mass flow meters and Controllers, using precision calibrators under
strictly controlled conditions. NIST traceable calibrations are available.
Calibrations can also be performed at customers' site using available standards.
Factory calibrations are performed using NIST traceable precision volumetric cal-
ibrators incorporating liquid sealed frictionless actuators.
Generally, calibrations are performed using dry nitrogen gas. The calibration can
then be corrected to the appropriate gas desired based on relative correction [K]
factors shown in the gas factor table - see Appendix 2. A reference gas, other than
nitrogen, may be used to closer approximate the flow characteristics of certain
gases. This practice is recommended when a reference gas is found with ther-
modynamic properties similar to the actual gas under consideration. The appro-
priate relative correction factor should be recalculated - see section (9).
It is standard practice to calibrate mass flow meters/controllers with dry nitrogen
gas at 70
0 F (21.1 0 C), 20 psig (1.4 bars) [25 psig (1.7 bars) for GFC47] inlet pres-
sure and 0 psig (0 bar) outlet pressure. It is best to calibrate the GFC transducers
to actual operating conditions. Specific gas calibrations of non-toxic and non-cor-
rosive gases are available at specific conditions. Please contact your distributor or
Dwyer for a price quotation.
It is recommended that a flow calibrator of at least four times better collective
accuracy than that of the mass flow meter/controller to be calibrated be used.
Equipment required for calibration includes a flow calibration standard and a cer-
tified high sensitivity multimeter (which together have a collective accuracy of
±0.25% or better), an insulated (plastic) screwdriver, a flow regulator (example:
metering needle valve) installed upstream from the Mass Flow Controller and a
pressure regulated source of dry filtered nitrogen gas (or other suitable reference
gas).
The gas and ambient temperature, as well as inlet and outlet pressure conditions
should be set up in accordance with actual operating conditions.
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