Aalborg AFC - Manual (Page 21)

7.3.2 ZERO Adjustment
Shut off the flow of gas into the Mass Flow Meter. To ensure that no seepage or
leak occurs into the meter, it is good practice to temporarily disconnect the gas
source. Using the multimeter and the insulated screwdriver, adjust the ZERO
potentiometer [R29] through the access window for 0 VDC (or 4 mA respectively)
at zero flow.
7.3.3 25% Flow Adjustment
Reconnect the gas source. Using the flow regulator, adjust the flow rate to 25% of
full scale flow. Check the flow rate indicated against the flow calibrator. Adjust the set-
ting for potentiometer [R21] by using the insulated screwdriver through the access
window, until the output of the flow meter reads 1.25VDC +37mV (or 8mA +0.12mA).
7.3.4 50% Flow Adjustment
Using the flow regulator, increase the flow rate to 50% of full scale flow. Check the
flow rate indicated against the flow calibrator. Adjust the setting for potentiometer
[R45] by using the insulated screwdriver through the access window, until the out-
put of the flow meter reads 2.50VDC +37mV (or 12mA +0.12mA).
7.3.5 75% Flow Adjustment
Increase the flow rate to 75% of full scale flow. Check the flow rate indicated
against the flow calibrator. Adjust the setting for potentiometer [R44] by using the
insulated screwdriver through the access window, until the output of the flow
meter reads 3.75VDC +37mV (or 16mA +0.12mA).
7.3.6 100% Flow Adjustment
Increase the flow rate to 100% of full scale flow. Check the flow rate indicated
against the flow calibrator. Adjust the setting for potentiometer [R43] by using the
insulated screwdriver through the access window, until the output of the flow
meter reads 5.00VDC +37mV (or 20mA +0.12mA).
Repeat steps 7.3.3 to 7.3.6 at least once more.
7.4 Calibration of AFC Mass Flow Controllers
All adjustments in this section are made from the outside of the meter, there is no
need to disassemble any part of the instrument.
AFC Mass Flow Controllers may be field recalibrated/checked for the same range
they were originally factory calibrated for.
7.4.1 Disable Solenoid Valve
Remove the round plastic cap on top of the solenoid valve. Turn the set screw on
top of the valve counterclockwise until it stops, to open the valve. Set the valve
into PURGE mode. This step essentially bypasses the flow control properties of
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