YSI PRO20 - TROUBLESHOOTING; Instrument will not calibrate; instrument displays Calibration Over, Calibration Under, or Unstable Reading during calibration.; Instrument will not turn on, a battery symbol appears, or Critical Shutdown displays on the screen.; Barometer reads over;under, Dissolved Oxygen and Temperature display Over;Undr, and pressing Cal key results in a Barometric Pressure Over;Undr message.

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to air dry completely. Use a clean, dry new membrane cap to screw
over the sensor to keep it dry and to protect the anode and cathode.
After storing the sensor for a long period of time it is necessary to
“condition” the sensor by putting a new membrane with electrolyte
solution on the sensor.
Long Term Storage Temperature: -5 to 70°C (23 to 158°F)
TROUBLESHOOTING
Symptom Possible Solution
Instrument will not
calibrate; instrument
displays “Calibration
Over”, “Calibration
Under”, or “Unstable
Reading” during
calibration.
1. Verify barometer reading.
2. Verify correct sensor and membrane type
selection in the System Setup menu.
3. Calibration sleeve may not be 100% water
saturated, ensure sponge is moisten.
4. Ensure adequate sample movement if
performing mg/L or ppm calibration.
5. Allow sufficient stabilization time for
dissolved oxygen and temperature AND
wait at least 3 seconds before confirming
a DO % or DO %Local calibration.
6. Replace membrane and electrolyte.
7. Clean sensor electrodes.
8. Return system for service.
Instrument will
not turn on, a
battery symbol
appears, or “Critical
Shutdown” displays
on the screen.
1. Low battery voltage, replace batteries.
2. Batteries installed incorrectly, check battery
polarity.
3. Return system for service.
Barometer reads
over/under,
Dissolved Oxygen
and Temperature
display Over/Undr,
and pressing Cal
key results in a
Barometric Pressure
Over/Undr message.
1. Barometer failure, return system for service.