YSI PRO20 - Instrument readings are inaccurate.; Dissolved Oxygen values display Over or Undr on run screen.; Temperature values display Over or Undr on run screen.

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Symptom Possible Solution
Instrument readings
are inaccurate.
1. Verify correct sensor/membrane type
selection in the System Setup menu.
2. Verify calibration, barometer reading, and
salinity settings are correct and recalibrate.
3. Verify accurate temperature readings.
4. Sample temperature is over 45 ºC, the
temperature compensation range.
5. Probe may not have been in 100%
water saturated air during calibration
procedure. Moisten sponge in
calibration sleeve and recalibrate.
6. Replace membrane and
electrolyte, recalibrate.
7. Clean sensor electrodes.
8. Return system for service.
Dissolved Oxygen
values display Over or
Undr on run screen.
1. Verify correct sensor/membrane type
selection in the System Setup menu.
2. If using a polarographic sensor,
allow instrument to warm up for
5 – 15 minutes before use.
3. Sample O
2
concentration is more
than 50 mg/L or 500%, or less
than –0.02 mg/L or -0.3%.
4. Verify barometer and salinity settings
are correct and recalibrate.
5. Verify accurate temperature readings.
6. Replace membrane and
electrolyte. Recalibrate.
7. Clean sensor electrodes.
8. Return system for service.
Temperature values
display Over or Undr
on run screen.
1. Sample temperature is less than -5º
C or more than +55
o
C . Increase or
decrease the sample temperature to
bring within the allowable range.
2. Return system for service.