Metrohm 781 pH/Ion Meter - Manual (Page 124)

8.1 Troubleshooting
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780/781 pH/Ion Meter, Manual
Problem Possible cause Remedy
Measuring signal absent
or very variable Electrode not connected
• Connect electrode
Air in or in front of the dia-
phragm
• Remove air
Faulty electrode
• Replace electrode
Measured value remains
unstable and does not
fulfill drift criterion Dirty pH or ISE membrane or
diaphragm
• Clean membrane or diaphragm
pH or temperature of the solu-
tion is not stable
• Measure under exclusion of air
• Thermostat the solution
Unsuitable electrode:
• Conductivity too low
• Organic solution
• Use suitable electrode
Electrode not connected
• Connect electrode
Faulty electrode
• Replace electrode
Measured value reached
slowly Dirty pH or ISE membrane or
diaphragm
• Clean membrane or diaphragm
Slope too small on cali-
bration pH or ISE membrane or dia-
phragm is dirty
• Clean membrane or diaphragm
Glass membrane dehydrated
after measurement in non-
aqueous solution
• Immerse electrode in water between
measurements
Poor buffer/standard solutions
• Replace buffers or standards
Electrode "used up"
• Replace electrode
Measured value obvious-
ly incorrect Incorrect calibration
• Check / Repeat calibration
• Check / Replace buffer/standard so-
lutions
Manual temperature input incor-
rect
• Enter correct temperature of the solu-
tion
Dirty pH or ISE membrane or
diaphragm
• Clean membrane or diaphragm
Electrolyte or electrode too old
• Refill electrolyte or replace electrode
Faulty electrode
• Replace electrode