Hach 900 MAX manual Appendix C pH Troubleshooting

Appendix C

pH Troubleshooting

Symptom	Possible Cause	Solution
		•	Inspect the cable and connector of the faulty electrode for evidence of
			a crushed or broken cable jacket or brittleness of the cable due to
Meter continuously	Open circuit in either		exposure to heat. Discard the electrode if damage is present.
		•	Manipulate meter/electrode connections to check for intermittent
reads pH 14 or drifts	glass or reference
			continuity. Replace if faulty.
above 14.	electrode.
		•	Inspect the bulb, making sure it is filled with solution. If not, shake
			down (like a clinical thermometer) to displace air in the pH bulb. Retest.
		•	Inspect the bulb for signs of coating.
	Interface is wired	Check interface wiring.
Temperature is	wrong.
constant or incorrect.	Thermistor is open.	Check interface wiring. Check for open at electrode RTD wire. Disconnect
		to make measurement. (Should read approximately 100–110 ohms.)
		•	Ensure that solutions are fresh and labeled properly.
		•	Confirm that electrode and buffer temperatures have stabilized.
Electrode won’t	Gain or offset error.	•	Confirm that the wetting cap is removed.
calibrate.		•	Check bulb for cracks or other damage.
		•	Confirm that interface wires are connected properly.
		•	Check interface connections for corrosion.
		•	Inspect the pH bulb for coating or clogging. If present, clean
			thoroughly.
		•	Keep the electrode wet at all times. If it dries out, the impedance will
			increase dramatically. To restore performance, soak in 0.1 N HCI
			(Cat. No. 1481253) for 30 minutes and rinse well with distilled water.
		•	Chemical degradation of pH glass can occur rapidly in a high
	Very high impedance		temperature or high pH environment, yielding sluggish response. Low
	in either glass or		temperature environments can double the impedance for every 8 °C
	reference electrode.		drop below 25°C.
Slow response and/or		•	A high impedance electrode is extremely sensitive to electrical noise,
			e.g., oscillating electrical fields generated by motors, generators or
erratic readings.			discharges from electrical thermostats. A free-hanging cable swinging
			due to air currents will also generate erratic signals.
		•	Manipulate electrode cable and connections to check for intermittent
			continuity. Replace as necessary.
		•	Check to see if the ground wire is connected properly at the pre-amp
	Ground loop problem.		junction box.
		•	Check for continuity between the stainless steel lug on the electrode
			and the ground wire at the interface.
	Temperature is	See “Temperature” symptom in this table.
	incorrect.
	Cracked glass bulb.	If the electrode gives readings between 5.8 and 6.2 pH in all solutions,
		inspect the glass bulb. If damaged, discard.
		If a constant reading of 7.0 pH or 0.0 mV is obtained, inspect the cable. If
No response to pH	Short Circuit.	no visible damage exists, remove the connector and test for a short circuit.
change.		Replace if faulty.
	High impedance	Inspect the connector for moisture or corrosion. If wet, rinse well with
		distilled water and dry thoroughly. Determine the cause of wetness and
	bridge.
		correct it.

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8990apdx_tbl.fm	Troubleshooting and Error Messages