7.2.5
Connections and Initial Warm Up
Connect the multimeter to output pins [1] and [2] for 0 to 5 VDC (or pins [9] and
[14] for 4 to 20 mA) of the 15-pin “D” connector - (see Figure 2-1).
If calibration to a new flow range or different gas is being performed, it may be
necessary to remove any jumpers at J1A, J1B, J1C and J1D before beginning lin-
earizing procedure.
Power up the Mass Flow Controller for at least 30 minutes prior to commencing
the calibration procedure.
7.2.6
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 LCD read-
ing and 0 Vdc (or 4 mA respectively) analog output reading at zero flow by adjust-
ing the zero potentiometer [R34] through the access window.
7.2.7
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 a flow calibrator. Adjust the
setting for potentiometer [R33] by using the insulated screwdriver through the
access window, until the output of the flow meter reads 1.25VDC ±63mV (or 8mA
±0.25mA).
Using the flow regulator, adjust the flow rate until the output of the flow meter
reads 0.5 Vdc (or 5.6mA). Check the flow rate against the flow calibrator. If the
flow rate indicated by the calibrator is within 10% ± 1.0% of F.S. then skip para-
graphs 7.2.8, 7.2.9 and proceed directly to paragraph 7.2.10, if not, perform 10%
flow adjustment according to paragraph 7.2.8.
21
CAUTION: The minimum voltage on 0-5 Vdc output can be in the
range of 7 to 25 mV. Trying to reduce voltage below this level may
increase negative zero shift. This shift may be invisible on devices with-
out LCD display. Stop R34 zero potentiometer adjustment if voltage on
0-5 Vdc output is in the range from 7 to 25 mV and does not decrease
any lower.
