DO Sensor Information Sheet

This DO Sensor information sheet was put together to help Waltron customers properly maintain and care for their DO sensors. Proper maintenance and care of DO sensors will help extend the life of DO sensors and ensure that DO analyzers run properly.

The DO sensor operates as a battery. It puts out more current when exposed to high concentrations of DO thus draining its charge. If the probe handle connection is corroded, the full micro-amp output from the sensor cannot reach the electronic section.

• Avoid exposing DO sensors to high ambient and/or sample temperatures. Higher temperatures increase the rate of the chemical reaction that takes place at the sensor membrane thus reducing the life of the sensor. (For every 10C above 30C, sensor life is cut in half.)Use a chiller to reduce sample temperature so it remains constant in the range 20-30C

• If DO sensor is used to monitor high (ppm) level sample concentrations the life of the sensor will be reduced. High sample concentrations increase the rate of the chemical reaction that takes place at the sensor membrane thus reducing the life of the sensor.

• Remove sensor if sample is shut off or disconnected for more than 3 days. When sensor is exposed to AIR or stagnant sample a more rapid chemical reaction takes place and the life of the sensor is reduced. If a sensor is left exposed to AIR for one or two days the life of the sensor will be reduced considerably. If flow is stopped sample will remain in the flow cell for some period of time but evaporation will occur and eventually the flow cell will be dry. NOTE: If the analyzer is set to perform an automatic calibration the solenoid will activate and drain the water in the flowcell thus exposing the sensor to AIR.

• Do not over-tighten clamping screw when installing probe handle assembly into the flowcell.  Over-tightening of clamping screw will damage sensor pins. Only finger-tighten the clamping screw when installing into the flowcell.

• Do not touch sensor membrane with your hands.

Please follow these steps for proper storage of DO sensors:

1. Store the sensor in its original canister making sure that membrane is kept moist.  Make sure that sponge at the bottom of canister is wetted with DI water and that the membrane is in contact with the sponge pad.  When storing the canister should be kept vertical so that the sensor pins are not exposed to fluid and more prone to corrosion.
   
   
2. Dry the probe handle assembly and the interior of the flow cell with a tissue or soft cloth.
   
   
3. Store sensor is a cool dry place such as a refrigerator.
   
   
4. If you do not have the original sensor container then store the sensor in a cool dry place making sure the membrane remains moist and the pins are not exposed to moisture.

Proper placement of o-rings is essential to the successful operation of dissolved oxygen analyzers. Please see the pictures below showing the proper location of both the small and large o-rings. Neither of these o-rings goes on the sensor.

Incorrect installation of o-rings will lead to analyzer problems such as failing calibration and/or incorrect sample readings.  Misplacement of o-rings will cause corrosion of DO sensor pins and probe handle pin holes.

** Important Note - A corroded probe handle assembly means frequent DO sensor replacement.  Increased resistance due to corrosion causes increased drain on the sensor shortening its life. If the resistance is significant the micro amp output from the sensor will not reach the electronics.

1. Inspect probe handle assembly pins for corrosion. The pins on the probe handle should have a shiny gold color.(See pictures below) If you notice corrosion (discoloration) on the probe handle pins please contact Waltron to order a new probe handle assembly.
   
   

   DO Sensor Good

   DO Sensor Bad

2. Do not allow probe handle pins or sensor pins to get wet or moist. Moisture will cause corrosion (see #1)and this will affect analyzer performance.
   
3. Higher temperature and/or higher DO sample concentrations significantly reduce the life of a DO sensor.  Please monitor and know sample concentration and sample temperatures. (For every 10C above 30C, sensor life is cut in half.)
   
   
4. Check the temperature readout on the analyzer display. If displayed temperature is not within 3-4C of the true sample temperature then analyzer thermistor needs to be replaced. Please contact Waltron to order a new thermistor.
   
   
5. Check to make sure sample flowrate is steady and constant. Depending on severity of sample flowrate fluctuation – readings may change and sensor life may be affected.