Aalborg GFM - Manual (Page 16)

12
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 better approximate the flow
characteristics of certain gases. This practice is recommended when a reference
gas is found with thermodynamic properties similar to the actual gas under con-
sideration. The appropriate relative correction factor should be recalculated - see
section 9.
It is standard practice to calibrate Mass Flow Meters with dry nitrogen gas at 70 0
F (21.1 F C), 20 psig (1.4 bars) inlet pressure and 0 psig (0 bar) outlet pressure.
It is best to calibrate the GFM transducers to actual operating conditions. Specific
gas calibrations of non-toxic and non-corrosive gases are available at specific
conditions. Please contact your distributor or Aalborg
7 for a price quotation. It is
recommended that a flow calibrator of at least four times better collective accu-
racy than that of the Mass Flow Meter to be calibrated be used. Equipment
required for calibration includes a flow calibration standard and a certified 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 Meter and a pressure reg-
ulated 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.
R52-25%
(IF ENABLED)
R1
J1A (R52) J1B (R38) J1C (R39) J1D (R40)
R33-SPAN
(25% or 10%)
R34-ZERO
R38-50% R39-75% R40-100%
POWER JACK
D-CONNECTOR
MODULAR JACK
INCREASE
DECREASE
FIGURE 7.a - CALIBRATION POTENTIOMETER AND JUMPER LOCATIONS