American Magnetics 135 & 136 Liquid Helium Level Instruments (CE-Marked) - Manual (Page 62)

50 Rev. 3
Service Guide
Erratic or erroneous level reading
3. Check for a dirty sensor. If the sensor collects oil, water, etc., the
sensor could possibly not operate correctly. Refer to page 20 for a
discussion of the optional dirty sensor operational mode.
4. Ensure the sensor is not installed in a restricted area which
prohibits the level of helium around the area of the sensor to be an
accurate representation of the level to be measured. The gas
produced by the sensor when the sensor current is on can depress
the liquid level.
5. Ensure the sensor is installed with lead wires at the top. Due to the
physical construction of the AMI LHe sensor, a reading of 100% will
always result if the sensor is installed upside down.
6.1.3 Controller output does not energize
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.
1. Verify continuity of controller output fuses, F1 and F3, located on
the instrument printed circuit board.
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 fuses F1 and F3
for continuity.
c. If the fuse is bad, replace with a 1.25 A IEC 127-2 Type F Sheet
II 5x20mm fuse.
d. Check your connected equipment for compliance with the
output receptacle rating.
Caution
Installing fuses of incorrect values and ratings could result in
damage to the instrument in the event of component failure.
2. Replace the fuse and securely fasten the instrument top cover.
Reconnect the power-cord.
0RGHO