Metex 8760CLP Total Free Chlorine & pH Analyzer - Manual (Page 57)

AQUAMETRIX INC.
1-800-742-1413 www.aquametrix.com
57
pH Sensor
AquaMetrix carries a portable pH analyzer and pH calibrator, model AM-659, for this purpose. The
calibrator can be used to prove the portable pH analyzer before use, or it can be used to prove the
process pH analyzer, in this case the 8760CL, where a problem has been exhibited.
Before testing the pH sensor, be sure the test analyzer is known to be good.
FIRST: Inspect electrodes and if dirty or scaled:
| Clean with a soft cloth.
| Acid clean to remove scale as per Chemical Clean procedure.
SECOND: Run buffer tests in (but do not adjust analyzer):
| pH 7 buffer; write down reading and response time
| pH 4 buffer; write down reading and response time
Slow response? Clean again or acid clean overnight in electrode wash solution, P/N AM-A1100091.
Make sure that after cleaning, response is not longer than 3 minutes.
REFERENCE: If pH 7 reads between 6 pH and 8 pH then the reference is good. If pH reading is
outside pH 6 or pH 8, then the reference is poor or has failed.
pH GLASS: Subtract pH 4 reading from pH 7 reading.
| if result is 2.5 to 3, the glass is good.
| if result is less than 2.5, then pH electrode is failing and should be replaced.
Less responsive pH electrodes can sometimes be regenerated with P/N AM-A1100092, electrode renew
solution. Refer to Restoring Electrode Response.
THIRD: If pH sensor passes the above tests, then it is good.
Place electrode back in the loop and then run a 2 buffer calibration following the instructions in this
manual.
FOURTH: If the sensor fails tests:
| Replace the pH sensor.
Troubleshooting Tips for pH
Reading spike – characteristic of bubbles in the sample line passing through the sensor or sticking to
the pH sensor. Also characteristic of pickup from interference pulses generated from AC lines, when
AC loads go off-line.
Readings gradually drifting away – the pH sensor can no longer be calibrated. This problem is typical
of scale or sludge/slime deposits on the pH glass. The sensor may need to be cleaned.
Readings at maximum – under all conditions.
Either the sensor is in air or there is a problem with the wiring/analyzer setup. Test for shorts by
disconnecting BNC and checking impedance between center pin and outside housing with sensor in air.
Insulation value should exceed 100 MΩ.
If the sensor is OK, use the model AM-659 portable calibrator/analyzer to test the preamp, wiring and
the analyzer. If the problem persists with the AM-659 in place then it is an analyzer problem.