American Magnetics 135 & 136 Liquid Helium Level Instruments (CE-Marked) - Manual (Page 61)

Rev. 3 49
Service Guide
Erratic or erroneous level reading
Warning
This procedure is to be performed only when the instrument is
completely de-energized by removing the power-cord from the power
receptacle. Failure to do so could result in personnel coming in
contact with high voltages capable of producing life-threatening
electrical shock.
a. Ensure the instrument is de-energized by disconnecting the
power cord from the power source. Disconnect the power cord
from the connector located on the rear panel of the instrument.
b. Remove the instrument top cover and check the fuse F2 for
continuity.
c. If the fuse is bad, replace with a 500 mA IEC 127-2 Type F
Sheet II 5x20mm fuse.
Warning
Installing fuses of incorrect values and ratings could result in
damage to the instrument in the event of component failure and/or
a safety hazard.
d. Replace the fuse(s) and securely fasten the instrument top
cover. Reconnect the power-cord.
6.1.2 Erratic or erroneous level reading
1. Ensure that the sensor is connected properly to the rear panel
SENSOR connector, J1 (see the Rear Panel Layout on page 4 and
the pinout diagram in the Appendix on page 56).
Note
A significant number of trouble calls are the result of the sensor not
properly connected to J1 on the rear panel. The proper positioning of
the sensor wires and proper solder connections are critical to the
proper operation of the Model 135/136.
2. Ensure there are no ice formations on the sensor. Ice formations on
the sensor inhibit sensing element thermal propagation thereby
producing incorrect readings. If ice formation has occurred, the ice
must be removed. If ice formation of the sensor is likely to reoccur,
refer to the operation section of the manual under dirty sensor
operation.