What could cause the display on the GLI pH controller to remain at pH 7 no matter what solution the pH probe is placed in?

Document ID

Document ID TE2061

Version

Version 5.0

Status

Status Published

Published Date

Published Date 05/23/2018
Question
What could cause the display on the GLI pH controller to remain at pH 7 no matter what solution the pH probe is placed in?
Summary
pH/ORP sensor troubleshooting
Answer
No change in a pH reading is likely due to a problem with the wiring or with the calibration of the sensor itself. If the pH probe is wired into a junction box, then attached to the controller using an interconnect cable, disconnect the probe from the junction box and connect it directly to the controller to eliminate the extension cable as a variable.

If the pH probe is connected directly to the controller and the problem remains, check the calibration as follows:

Press the Diag button on the display unit, select CALIBRATION RECORD and press Enter. Check the buffer values shown for the last calibration. If the buffer values are incorrect, recalibrate the probe. Choose Yes when asked IS THIS PROBE BEING CALIBRATED FOR THE FIRST TIME? Make sure that the displayed pH buffer value matches the value that the probe is placed in.

If the probe is still unable to pass calibration then checking the signals from the sensor can determine if the probe is faulty or the controller is faulty:
Disconnect the red and green wires from the controller while all others are still connected. Connect a multimeter (red on red, black on green) to the loose leads of the sensor. While in a 7 pH buffer the DC mV reading should be 0 +/- 50 mV. If this is good then move the probe to either a 4 pH or 10 pH buffer. There should be a change in the mV reading of at least 160 mV . If not then the probe will need maintenance or replacement.
 

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