Calibration Failure - Walchem WDSW100 Instruction Manual

Calibration Failure

For WebMaster
The controller will display a calibration failure if the offset calculated in the
Zero Calibration is outside of the range –20 to 40 mV or the slope
(mV/ppm) calculated in the One Point Process Calibration is outside of the
range of the nominal mV per 0.1 to 2.0 ppm.
For WDIS:
The acceptable range for the slope (mV/ppm) is the nominal mV per 0.5 to
2.0 ppm. The range of mV for a Zero Calibration is –100 mV to 100 mV.
For W100 or W600 or 900:
The calibration will fail if the adjustment to the gain is outside of 0.2 to
10.0, or if the calculated offset is outside of -40 to 40 mV.
To calculate the nominal slope for your sensor, divide the high end of the
nominal range by -2000. For example, for a 0-20 ppm sensor, the nominal
slope is -2000/20 = -100 mV/ppm.
Possible Causes
Insufficient conditioning
Insufficient sample flow
Air bubbles on membrane
Dirty membrane
Faulty membrane
High Pressure
No electrolyte fill solution in
membrane cap
Faulty sensor
Faulty analysis equipment or
reagents
Sample contaminated with
interfering molecule (refer to
Sensitivity specification in
section 6.0)
Faulty wiring
Faulty controller sensor input
Corrective Actions
Wait for the appropriate amount of time
before attempting a calibration.
Increase flow rate to between 30 and 100
liters per hour
Dislodge bubbles. Adjust flow rate higher
if necessary.
Clean membrane
Replace membrane cap.
Reduce pressure to below 1 atmosphere and
refill cap with electrolyte
Fill membrane cap with electrolyte.
Replace membrane cap if it will not hold
solution.
Replace sensor
Consult test equipment instructions
Remove source of contamination
Check wiring
Go to the Sensor Input Page and perform a
self test. If this passes, then the problem is
with the sensor or its wiring. If it fails, then
disconnect the sensor from the circuit board
and try the self test again. If it still fails,
replace the circuit board.
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