PART FOUR - SERVICE AND MAINTENANCE
SECTION 3 - TROUBLESHOOTING
Rev. 6-1100
Model P33 pH/ORP Analyzer (panel-mount 1/4 DIN)
87
S
ECTION
3
3.1 Ground Loops
Determining if
Ground Loop Exists
The analyzer may be affected by a “ground loop” problem
(two or more electrically grounded points at different poten-
tials).
Symptoms Indicating a Possible Ground Loop
•
Analyzer reading is offset from the actual value by a
consistent amount, or ....
•
Analyzer reading is frozen on one value, or ....
•
Analyzer reading is “off scale” (upscale or downscale).
Although the source of a ground loop is difficult to deter-
mine, there are several common causes.
Common Causes of a Ground Loop
•
Components, such as recorders or computers, are
connected to non-isolated analog outputs.
•
Not using shielded cabling or failure to properly connect
all cable shields.
•
Moisture or corrosion in a junction box.
The following simple test can help to determine if there is a
ground loop:
1. With the pH MEASURE screen displayed, put the sen-
sor in a non-conductive container (plastic or glass) filled
with a known value pH buffer. Note the analyzer read-
ing for this solution.
2. Connect one end of a wire to a known earth ground,
such as the analyzer ground terminal on TB1 or a metal
water pipe. Place the other end of this wire into the
buffer next to the sensor.
3. Note the analyzer reading now and compare it with the
reading taken in step 1. If the reading changed, a
ground loop exists.
TROUBLESHOOTING
