Instruction manual

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MODEL XMT-A-FF/FI SECTION 15.0
TROUBLESHOOTING
15.2.2 Broken pH Glass and pH Glass Z High
These messages mean that the pH sensor glass impedance is outside the programmed limits. To read the impedance go
to the main display and press

until Glass Imp appears in the display. The default lower limit is 10 MΩ. The default upper
limit is 1000 MΩ. Low glass impedance means the glass membrane — the sensing element in a pH sensor — is cracked
or broken. High glass impedance means the membrane is aging and nearing the end of its useful life. High impedance can
also mean the pH sensor is not completely submerged in the process liquid.
1. Check the sensor wiring, including connections in a junction box.
2. Verify that the sensor is completely submerged in the process liquid.
3. Verify that the software switch identifying the position of the preamplifier is properly set. See Section 7.3.3, step 7b.
4. Check the sensor response in buffers. If the sensor can be calibrated, it is in satisfactory condition. To disable the fault
message, reprogram the glass impedance limits to include the measured impedance. If the sensor cannot be cali-
brated, it has failed and must be replaced.
15.2.3 ADC Read Error
The analog to digital converter has probably failed.
1. Verify that sensor wiring is correct and connections are tight. Be sure to check connections at the junction box if one
is being used. See Section 3.1 for wiring information.
2. Disconnect the sensor(s) and simulate temperature and sensor input.
3. If the transmitter does not respond to simulate signals, call the factory for assistance.
15.2.4 PV>DisplayLimit, Sensor Curr High, Sensor Curr Low.
The first two messages imply that the amperometric sensor current is very high (greater than 210 µA) or the sensor cur-
rent has a very large negative number. Normally, excessive current or negative current implies that the amperometric sen-
sor is miswired or has failed. Occasionally, these messages may appear when a new sensor is first placed in service.
1. Verify that wiring is correct and connections are tight. Be sure to check connections at the junction box if one is being
used. Pay particular attention the anode and cathode connections.
2. Verify that the transmitter is configured for the correct measurement. See Section 7.3.3. Configuring the measurements
sets (among other things) the polarizing voltage. Applying the wrong polarizing voltage to the sensor can cause a large
negative current.
3. If the sensor was just placed in service, put the sensor in the zero solution and observe the sensor current. It should
be moving fairly quickly toward zero. To view the sensor current go to the main display and press

until Input Current
appears. Note the units: nA is nanoamps, µA is microamps.
4. Replace the sensor membrane and electrolyte solution and clean the cathode if necessary. See the sensor instruction
sheet for details.
5. Replace the sensor.
To simulate See Section
Dissolved oxygen 15.11
Ozone, monochloramine, chlorine 15.12
pH 15.13
Temperature 15.14