Hach 900 MAX ユーザーズマニュアル

8990apdx_tbl.fm

Meter continuously 
reads pH 14 or drifts 
above 14.

Open circuit in either 
glass or reference 
electrode.

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 
exposure to heat. Discard the electrode if damage is present.

Manipulate meter/electrode connections to check for intermittent 
continuity. Replace if faulty.

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.

Temperature is 
constant or incorrect.

Interface is wired 
wrong.

Check interface wiring.

Thermistor is open.

Check interface wiring. Check for open at electrode RTD wire. Disconnect 
to make measurement. (Should read approximately 100–110 ohms.)

Electrode won’t 
calibrate.

Gain or offset error.

Ensure that solutions are fresh and labeled properly.

Confirm that electrode and buffer temperatures have stabilized.

Confirm that the wetting cap is removed.

Check bulb for cracks or other damage.

Confirm that interface wires are connected properly.

Check interface connections for corrosion.

Slow response and/or 
erratic readings.

Very high impedance 
in either glass or 
reference electrode.

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 
temperature or high pH environment, yielding sluggish response. Low 
temperature environments can double the impedance for every 8 °C 
drop below 25°C.

A high impedance electrode is extremely sensitive to electrical noise, 
e.g., oscillating electrical fields generated by motors, generators or 
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. 

Ground loop problem.

Check to see if the ground wire is connected properly at the pre-amp 
junction box.

Check for continuity between the stainless steel lug on the electrode 
and the ground wire at the interface.

Temperature is 
incorrect. 

See “Temperature” symptom in this table.

No response to pH 
change.

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.

Short Circuit.

If a constant reading of 7.0 pH or 0.0 mV is obtained, inspect the cable. If 
no visible damage exists, remove the connector and test for a short circuit. 
Replace if faulty.

High impedance 
bridge.

Inspect the connector for moisture or corrosion. If wet, rinse well with 
distilled water and dry thoroughly. Determine the cause of wetness and 
correct it.