Troubleshooting The System; Calibration Failures; Calibration Or Slope Drift - Siemens RAPIDLAB 248 Operator's Manual

4 Troubleshooting the System

The 248 continually performs self-diagnostic tests to maintain integrity of
results. If the instrument detects an abnormality, setup options may be
reset to default and the 248 will display Check Setup. You can still use the
248 but the data relating to the result will be default (factory set) values.
If Check Setup is displayed check the setup options in Operating
Setup, Page 5-1, System Setup, Page 5-4 and Service Setup, Page 5-7.
You will also need to check the barometer calibration setting, Page 2-9.
When you have checked all the setup options, exit to the Ready screen
and press * to clear the Check Setup message.
If the 248 does not respond to any user input refer to Page 4-14, Using
the Status Indicators, and check status indicator 1, microprocessor.
If the roll printer is off, select On and Results + Cals (Page 5-3) as the
printout may give further details of the problem.

Calibration Failures

The possible causes for standardization failure have been grouped
together under the following headings: calibration or slope drift (↑, ↓ on
display and printout), calibration or slope no endpoint (* on display
and printout), calibration or slope outside range (! on display and
printout), fluidics failures.

Calibration or Slope Drift

New Sensors Installed
If a new sensor has been installed, allow up to 90 minutes for it to
stabilize. If the calibration still fails after this time either wait a
further 90 minutes or run 10 samples using the Measurement Block -
Run Test Sample routine to promote stability, Page 4-11. (This
diagnostic routine has to be used to measure as the 248 has not
calibrated successfully - do not use the results.)
Reference Sensor (pH drift)
Bubble in reference sensor
Nafion inner is dry due to a large bubble, or not screwed down properly,
or poorly fitting
Sensor is clogged with crystals caused by poor filling, or bubbles
creating crystal growth
Vent hole blocked
Failed membrane
See Page 3-19.
De-bubble the sensor.
Replace Nafion inner if dry, or refit correctly.
Empty sensor cassette and refill carefully with reference sensor fill
solution.
Unblock the vent hole in the reservoir cap.
Replace sensor cassette.
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