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Instruction Sheet
ECDOGEN-S / ECDOTPII-S
Submersible Galvanic Dissolved Oxygen Sensor
Copyright © 2006 All rights reserved.
Eutech Instruments Pte Ltd
Blk 55, Ayer Rajah
Crescent, #04-16/24
Singapore 139949
+65 6778 6876
+65 67730836 fax
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HOW DISSOLVED OXYGEN SENSORS WORK
Your Dissolved Oxygen (DO) Probe is a galvanic electrochemistry device; i.e. it does not require power
from your meter or controller to generate its signal. The Sensorex DO Probe will provide a millivolt signal
proportional to the concentration of oxygen in the water. DO probes do not measure oxygen directly.
They measure the partial pressure of oxygen in the water, which is directly proportional to the percent
saturation of oxygen in the water. The concentration (mg/L or ppm) can be calculated based upon the
oxygen solubility, temperature, salinity, and total atmospheric pressure. Your Dissolved Oxygen Probe
consists of a cathode, anode, and an electrolyte separated from your process fluid by an oxygen
permeable membrane. The oxygen passing through the membrane reacts with the cathode, giving up
electrons, which produce an electrical current. A Pt 100 RTD temperature sensor is also included.
Electrical Connections
First connect the sensor to the DO instrument as follows:
DO + Red
DO - Yellow
TC+ Red, White
TC – Black
GETTING YOUR DO SENSOR READY TO USE
Remove clear wire and label from vent hole on top of DO sensor as shown in FIG 1. Discard these parts
after removing.
CALIBRATION
The simplest method to calibrate your DO sensor is in air, since air is saturated with oxygen. You may also
bubble oxygen or air. The sensor is pre-calibrated at the factory (see Specifications Section for calibration
range). If you want a 2-point calibration, a saturated solution of sodium sulfite (Na2SO3) is suggested.
17g Sodium sulfite in 125mL DI water is more than enough. Sodium sulfite will not reach a true zero
output but it should reach less than 1 mV (see Specifications Section for range).
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MEMBRANE TYPE
Two types of membrane materials are offered for DO sensors, either PTFE or HDPE. Teflon offers excellent
durability and moderate speed of response. HDPE offers fast response but less mechanical strength. The
PTFE membrane also has less membrane permeability error with temperature as compared to HDPE.
Spare membranes are available is 5 or 25 counts, or in maintenance kits.
MOUNTING YOUR DO SENSOR
Submersion mounting of the sensor is recommended. To prevent air bubbles from becoming trapped on
the membrane and producing falsely high DO readings, it is recommended that the sensor be mounted
with the membrane pointing slightly upward (not horizontal) as shown in FIG. 2.
SENSOR RE-CONDITIONING
1. Unscrew the lower body from the upper body(FIG. 3)
2. Safely dispose of the electrolyte that is a special molarity, reagent grade Sodium Chloride
solution (salt water) as shown in FIG. 4
3. Using the Membrane Tool, unscrew the Membrane Lock in the lower body as shown in FIG. 5
4. Remove and dispose of the membrane and its O-Ring as show in FIG 6
5. Using a toothbrush, dishwashing powder and clean water, clean the cathode, anode, and plastic
between them. Rinse all components thoroughly. Household Ammonia may be used to clean
the silver anode overnight If Ammonium Hydroxide is used, expose it for no more than 3
minutes (it is very strong). See FIG. 7.
6. Install a new O-Ring into the lower body membrane cavity then a new membrane into the lower
body. Using the Membrane Tool, screw the Membrane Lock on top of the membrane as shown
in FIG. 8.
7. Inspect the membrane for wrinkles--replace if it is wrinkled.
8. Pour some water into the lower body and look for leakage around the membrane--replace it if
there is leakage. If no leakage, dispose of the water.
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9. Fill the lower body to its rim with fresh Electrolyte as shown in FIG. 9.
10. Inspect the large O-Ring between the upper and lower body. Replace it if it appears
deteriorated. See FIG. 10.
11. Screw the lower body onto the upper body. Excess Electrolyte will squirt out of a small pressure
balance hole atop the upper body. If no electrolyte squirts out, clear the hole of its blockage
before installing the lower body.
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SENSOR STORAGE
If long-term storage of probes is required, empty electrolyte out of probe leaving only a little solution on
the membrane to keep it wet. Leaving a full volume of electrolyte in DO probe long-term without use will
deplete the probes’ anode. See section “Sensor RE-CONDITIONING ” for steps on how to open and close
probe housing.
SENSOR SPECIFICATIONS
Output at 100% saturation
PTFE membrane 24-42 mV
HDPE membrane 36-54 mV
Output at 0% saturation
PTFE membrane <1mV <1mV
HDPE membrane <1mV <1mV
Temperature Range
Max 50 °C
Min 0 °C
Accuracy +2% when measuring temp equal cal temp.
Response Time
PTFE membrane 2 minutes to reach 90% of final reading
HDPE membrane 1 minute to reach 95% of final reading
Water Flow Rate Min 2 inch/second across membrane
Wetted Materials
Body Delrin
Membrane Teflon, HDPE
Wiring
DO + Red
DO – Yellow
TC + Red, White
TC – Black
Teflon and Delrin are registered trademarks of E.I. DuPont.
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WARRANTY
This electrode is supplied with a six-month warranty against significant deviations in material and
workmanship.
Exclusions
The warranty on your instrument shall not apply to defects resulting from:
Improper or inadequate maintenance by customer
Unauthorised modification or misuse
Operation outside of the environment specifications of the products
RETURN POLICY
Please obtain authorisation from our Customer Service Department or authorised distributor before
returning items for any reason. A “Return Goods Authorisation” (RGA) form is available through our
authorised distributor. Please include data regarding the reason the items are to be returned. Items
must be carefully packed to prevent damage in shipment and insured against possible damage or loss.
Eutech Instruments/ Oakton Instruments will not be held responsible for damage resulting from careless
or insufficient packing. A restocking charge will be made on all unauthorised returns.
NOTE: Eutech Instruments Pte Ltd reserves the right to make improvements in design, construction, and
appearance of products without notice.
As of the date of preparation of this document, the foregoing information is believed to be accurate.
However, no warranty or representation with respect to such information is intended or given.
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