Fluke 875 manual Troubleshooting

Maintenance, Calibration, and Troubleshooting

Troubleshooting 5

5.3 Troubleshooting

The 875 High-Range Containment Monitor is safety-related equipment. The monitor has been assembled by techniques and with parts selected for the reliability required in a nuclear application. Any repairs made to the detector or readout (other than replacement of parts listed in Section 5) may void the safety-related rating. The troubleshooting procedure that follows is a guide to isolating a fault in the system.

Replacement of parts is at the printed circuit board level only. Printed circuit boards must be returned to Fluke Biomedical for service.

There are two self-contained system tests available in Containment Monitor 875, the Channel Test and the ECS Test. In both cases, the procedure is to put a known input into the system, and to look for the desired output.

There is an important difference between the Channel Test and the ECS Test: the former applies an input to the readout module (that is, to the first electronic circuit in the Containment Monitor); however, it does not test the detector or the cables connecting the detector to the readout module. In addition, the Channel Test applies a DC voltage, whereas the ECS Test applies a ramp voltage to the detector plates, monitoring the resultant current into the readout module.

The digital multimeter mentioned in Table 5-1 of the calibration section is also recommended for troubleshooting.

If the ECS Test gives a favorable result, the following conditions exist:

1.The detector cannot have any appreciable malfunction.

2.The cables must have continuity.

3.The ECS board and power supply board must be operative.

4.It is highly improbable that any malfunction exists in the fail/safe circuitry.

5.The amplifier, meter and alarm circuitry must be operative.

Essentially, the Channel Test verifies only #5 of the above. However, in doing so, it incidentally verifies all of the power supplies except the high voltage power supply.

For clarity, troubleshooting is divided into six divisions:

1.Power supplies

2.Input circuit

3.Meter circuit

4.Alarm circuits

5.ECS board

6.Overall fail circuitry

NOTE

Disconnect Detector 877-1 from Readout Module 876A-1 by removing cables from J1 and J2 before starting troubleshooting of readout module. The user will probably wish to disconnect the external alarms as well. It is the responsibility of the user to see that the alarms are not set off by disconnection.

5-3