Dwyer GFC User Manual

Page 22

7.2.2 ZERO Adjustment

Shut off the flow of gas into the Mass Flow Controller. 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 poten-
tiometer [R34] through the access window for 0 VDC (or 4 mA respectively) at
zero flow.

7.2.3 SPAN Adjustment

Reconnect the gas source. Adjust the control setpoint to 100% of full scale flow.
Check the flow rate indicated against the flow calibrator. If the deviation is less
than ±10% of full scale reading, correct the SPAN potentiometer [R33] setting by
using the insulated screwdriver through the access window, to eliminate any devi-
ation. If the deviation is larger than ±10% of full scale reading, a defective condi-
tion may be present.

LIKELY REASONS FOR A MALFUNCTIONING SIGNAL MAY BE:

Occluded or contaminated sensor tube.

Leaking condition in the GFC transducer or the gas line and fittings.

For gases other than nitrogen, recheck appropriate "K" factor from Gas Factor Table.

Temperature and/or pressure correction errors.

See also section (8) TROUBLESHOOTING. If after attempting to remedy the above con-
ditions, a malfunction still persists, return the meter for factory service, see section (1).

At this point the calibration is complete. However, it is advisable that several addi-
tional points between 0 and 100%, such as 25%, 50%, and 75% flow be checked.
If discrepancies are found, proceed to step 7.3 for Linearity Adjustment.

7.3 Linearity Adjustment

All adjustments in this section are made from the outside of the meter, there is no
need to disassemble any part of the instrument.

7.3.1.1 Disable Solenoid Valve in GFC-110/111/113/114 Models

Set the valve into PURGE mode. This step essentially bypasses the flow control
properties of the transducer. The unit will now act as a mass flow meter.

7.3.1.2 Open Motorized Valve in GFC-1143/1144/1145 Models
Set the valve to PURGE mode by connecting pin 4 to pin 3 (ground), on 15pin
D-connector.

CAUTION: FOR GFC-110/111/113/114-If the valve is left in the AUTO
(control) or OPEN mode for an extended period of time, it may become
warm or even hot to the touch. Use care in avoiding direct contact with
the valve during operation.