Position Switch Circuit - Emerson Fisher 4200 Instruction Manual

4200 Transmitters
March 2011
1. Verify that the instrument is receiving power, and verify that the receiving device(s) are operating correctly.
2. If the transmitter is the problem, maintenance can be performed by either sending the entire instrument to the
factory for repair, by replacing the printed wiring board(s), or by replacing the pot/bushing assembly (key 3,
figures 11 and 14) depending on which is defective.
3. Troubleshoot the transmitter circuit by measuring the voltages.
4. Location of test voltage designated by V1 (table 9) is shown on the printed wiring board assembly (figure 12).
Table 9. Test Procedure (also refer to figure 12)
CONNECT DVM TO
STEP
(+) Lead
1 V1
2 V2
3 V3
5. Check the voltage at V1 as described in table 9.
6. If the voltage is not present, field repair of the instrument is not recommended. Either replace the printed wiring
board or return the instrument to the factory for repair.
7. If this voltage is present, the potentiometer may be the source of trouble.
8. Check the voltage between TP3 (+) and TP4 (-) as the position of the potentiometer is varied. For 4212 and 4222
transmitters, check the voltage between TP5 and TP6 as the position of the potentiometer is varied.
a . If the voltage does not vary with position, perform the potentiometer alignment. If the problem remains, replace
the pot/bushing assembly (key 3, figure 11 or 14).
b . If the potentiometer wiper voltage checks good, but the transmitter output is constant or non‐linear, the
problem may be due to improper potentiometer alignment. Perform the potentiometer alignment procedures;
then repeat step 8 above.
c . If the potentiometer voltage is present but the transmitter output current does not change linearly as the
position of the potentiometer changes, replace the transmitter printed wiring board, or return the transmitter to
the factory for repair.

Position Switch Circuit

1. Ensure that the position switch circuit is connected correctly, and that the terminal marked (R) on the field circuit
printed wiring board is returned to the negative terminal of the supply. Refer to figure 4 for wiring connections.
2. Ensure that the power supply voltage is between 20 and 30 volts DC.
3. Check voltages V2 and V3 as described in table 9:
a . If either or both of the voltages are not present, field repair of the instrument is not recommended. Return the
instrument to the factory for repair.
b . If V2 and V3 are correct, continue with the following steps:
4. Perform the high and low position switch calibration procedures in the Calibration section.
5. If the position switches cannot be set, replace the field circuit printed wiring board (figure 11) or return the
instrument to the factory for repair.
Printed Wiring Board Removal and Replacement
WARNING
Refer to the Maintenance WARNING at the beginning of this section.
28
DVM READS
(-) Lead
TP4 2.46 to 2.54 VDC (VREF)
TP6 14.1 to 16.1 VDC (+15)
TP6 2.46 to 2.54 VDC (VREF2)
Instruction Manual
D200354X012