Type 2390 and 2390B Table 4. Troubleshooting Guide Symptom
Possible Cause
Check
Corrective Action
1. No output
Incorrectly wired
Wiring
Wire correctly
2. Output is below 3.2 mA dc
Incorrect supply voltage or excessive field wiring resistance
Voltage at field terminals should be between 11 and 45 volts dc Sensor assembly by performing the Checking Transmitter Sensor Assembly procedure Sensor assembly by performing the Checking Transmitter Sensor Assembly procedure Confirm resistance for zero and span potentiometers (20K ohms), continuity, solder joints, and connector crimps of harness
Check power supply voltage and total field wiring resistance against figure 3. Replace sensor assembly
Sensor assembly by performing the Checking Transmitter Sensor Assembly procedure Sensor assembly checks OK and magnet has not been demagnetized. Replace parts successively to isolate problem
Replace sensor assembly
Sensor assembly failure
3. Output is constant at 3.2 or 30 mA dc
Sensor assembly failure
Open zero or span potentiometer or wiring harness
4. Lever assembly magnet movement across Hall sensor does not change output signal
Sensor assembly failure
Printed wiring board failure
5. Output drifting or erratic on bench at constant temperature
Printed wiring board failure or sensor failure
After any disconnection or troubleshooting, recalibrate the transmitter using the Matching the Transmitter to a 249 Series Sensor procedure before putting it back into operation.
Checking Transmitter Hall-Effect Sensor Assembly Key numbers are shown in figure 21 or 22 unless otherwise indicated. 1. Remove the printed wiring board housing cover (key 2) from the transmitter. 2. Remove the analog output meter (key 16), if installed, as described in the Removing the Analog Output meter procedure. 3. Apply +24 volts dc to transmitter (via field wiring). 4. Disconnect the Hall-effect sensor assembly plug P2 (figure 7) from the printed wiring board and connect it to the DVM [+ to yellow (pin 1) and ! to green (pin 2)] . 5. Center the dry span scale in its slip range per step 7 of the Matching the Transmitter to a 249 Series Sensor, Setup procedure. 6. Move the spring wire to the R holding position (figure 13).
20
Replace sensor assembly
Replace potentiometers or repair wiring harness
Replace printed wiring board
Replace faulty part
7. Observe the output of the sensor on the DVM while slowly rotating the dry span knob from 0 to 100 percent on the R scale. The DVM reading should be proportional to rotation, as follows: +47 !8 mV at the 0% extreme 0 !7 mV at the 50% position, and !47 !8 mV at the 100% position 8. If the output does not change with rotation, the sensor assembly is not functioning properly. Proceed to step 10. 9. If the output varies but is not within the above specifications, the lever assembly may be damaged or out of alignment. Inspect the lever assembly for damaged or loose flexures, failed bonds on bellows joints, magnet damage, etc. Make any required repairs, or replace with a lever assembly that is known to be in good condition. Perform the Reinstalling the Lever Assembly procedure in the “Maintenance� section of this manual. Then repeat the troubleshooting tests. If the output is still not within specification, proceed to step 10. If the output is within specification, proceed to step 12. 10. Turn the power supply off and measure the resistance between pins 1 and 2 of the sensor output plug P2. If the reading is not between 900 and 1200 ohms, replace the sensor assembly (key 11). If the resistance is within specification, proceed to step 11. 11. Disconnect plug P1 (figure 7) from the printed wiring board and measure between its pins (blue and red wires). If the reading is not between 900 and 1200