Kistler-Morse KM Load Stand II - Manual (Page 26)

97-1100-01 Rev. H
22
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SYMPTOM POSSIBLE CAUSE SOLUTION
(Continued from
previous page)
Small Amplitude
Changes or Erratic
Fluctuations in
Display Readings
(Continued from previous page)
Fluctuations can be caused by
damaged Load Stand sensor.
Problem likely to be noticed
shortly after initial installation
or on system that previously
functioned correctly.
7. Identify damaged sensor at Load Stand identified in Step 3, 4, or 5:
a. Remove one sensors’s wires from junction box terminal TB3.
b. Put one DMM lead on sensor’s white wire and other lead on red wire.
Record resistance, and verify it is 7,660 ± 200 ohms. If resistance is
outside this range, sensor is damaged and must be replaced.
c. Put one DMM lead on sensor’s white wire and other lead on black
wire. Record resistance, and verify it is 7,660 ± 200 ohms. If
resistance is outside this range, sensor is damaged and must be
replaced.
d. Verify readings from Steps B and C are within 200 ohms of each
other. If not, sensor is damaged and must be replaced.
e. Repeat Steps A through D for each sensor, until damaged sensor is
located and replaced.
Fluctuations in readings can be
caused by short to ground.
Problem likely to be noticed
shortly after initial installation
or on system that previously
functioned correctly.
Using a Digital Multimeter (DMM) or ohmmeter, check for shorts to ground
as follows:
1. Set meter resistance scale to accommodate maximum measured range.
2. Disconnect junction box wires of suspect vessel from signal processor.
3. With one lead to earth ground and other lead to white wire, check
resistance on disconnected wires:
• If reading is less than infinite (i.e., there is resistance), a short is
indicated; proceed to Step 4 to identify location.
• If no short is indicated, investigate other explanations for problem.
4. Starting with junction box closest to signal processor in daisy chain,
disconnect wires connecting junction box to other junction boxes. With
one lead to earth ground and other lead to white terminal on TB3, check
resistance on wires leading from junction box:
• If the reading is less than infinite (i.e., there is resistance), short is
indicated; proceed to Step 5 to identify location.
• If no short is indicated, proceed to next junction box in daisy chain,
disconnecting wires connecting it to other junction boxes and
checking resistance. Perform for each junction box down chain until
short is located; proceed to Step 5 to identify location.
Note: Sun shield or junction box mounting bolts are good locations for
connecting probe to ground.
5. Disconnect wires for one sensor from above-identified junction box. With
one lead to earth ground and other lead to white wire, check resistance
on disconnected sensor wires:
• If reading is less than infinite (i.e.,there is resistance), short is
indicated. Replace shorted sensor.
• If no short is indicated, disconnect next sensor’s wires from junction
box and check resistances. Repeat for each sensor wired to junction
box until short is located. Replace shorted sensor.
Fluctuations in readings can be
caused by problems with signal
processor.
Problem likely to be noticed
shortly after initial installation
or on system that previously
functioned correctly.
Check signal processor excitation voltage and incoming AC voltage for
accuracy and stability (refer to signal processor manual).