Emerson Rosemount5081 Instruction Manual page 67

Instruction Manual
c. For Rosemount PLUS (+) and TUpH sensors that do not have an integral
preamplifier, attach the blue solution ground wire to TB-8 or, better, leave
the blue wire unattached and jumper TB-7 to TB-8.
d. If the sensor does not have a blue solution ground wire, jumper terminals
TB-7 and TB-8.
- If the wiring was correct and the glass impedance is still too high, go
on to Step b.
- If correcting wiring errors causes the diagnostic message to disappear,
the sensor is in good condition.
- If after correcting wiring errors, the glass impedance is still high, go on
to Step b.
b. Inspect and clean the sensor. After cleaning the sensor, calibrate it. Be sure to
note the sensor slope.
- If cleaning the sensor lowers the impedance below 800 megohms...
a. The sensor is in good condition.
b. Return the calibrated sensor to service.
- If cleaning does not lower the glass impedance and the sensor can be
calibrated...
a. The sensor is probably in good condition; however, it may be nearing
the end of its life. The electrode slope is a good indicator of remaining
life.
Slope
54-60 mV/unit pH
48-50 mV/unit pH
b. The Glass Fail High (GFH) limit is probably set too low for the sensor.
Set the GFH limit to about 150 megohms greater than the measured
glass impedance.
c. If the GLASSWArn message was also flashing, raise the GWH limit from
its former value by the same amount the GFH was raised from its
former value.
- If cleaning does not lower the glass impedance and the sensor cannot be
calibrated, the sensor has failed and should be replaced.
• if the glass impedance is moderate (between 40 and 800 megohms)...
a. The sensor may be dirty, in which case cleaning it will lower the impedance
reading. The sensor may also be in good condition. The warning and fail limits
are simply set too low.
b. Inspect and clean the sensor. After cleaning the sensor, calibrate it. Be sure to
note the sensor slope.
Condition of sensor
Sensor is in good condition.
Sensor is nearing the end of its life. Once the slope
drops below 48 mV/unit pH, the sensor can no longer
be calibrated.
Diagnostics and troubleshooting
57