Xylem WQ-FDO Sensor and GL500-7-2 Data Logger - Manual (Page 32)

Global Water
800-876-1172
• globalw.com
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XVII. Maintenance:
a. There are no user-serviceable parts inside the Data Logger.
b. Global Water recommends checking the battery on a regular basis, the
period depending on the number of sensors, sample interval,
temperature and the type of battery used.
c. Consult the WQ-FDO Sensor manual for information on the dissolved
oxygen sensor maintenance.
XVIII. Troubleshooting:
Issue: Logger is reading incorrectly.
a. Verify the power source is supplying enough voltage. The data logger
requires about 5 volts to operate. Consult the power requirements for
the individual sensors. The Global Water WQ-FDO sensor requires a
minimum of 10 volts between the red and black leads.
b. The WQ-FDO sensor cap has a limited lifespan of approximately one
year, depending on use. If the sensor is not operating properly,
replace the membrane cap. Calibration of the WQ-FDO sensor should
not be necessary when replacing the cap. All calibration information
for each sensor cap is stored in a memory chip inside the cap itself.
This information is used to recalibrate the sensor each time the cap is
replaced.
c. The WQ-FDO sensor partial pressure output has been factory
calibrated for an output of 4.00-20.00mA over the range of 0-400mbar;
and for the temperature output 4.00-20.00mA over 0-50ºC. Because
dissolved oxygen levels vary with temperature, atmospheric pressure
and salinity; an exact calibration can be difficult using the sensor
alone. A current loop meter is the best way to recalibrate the DO
sensor to the logger.
d. An approximate check of the WQ-FDO sensor performance can be
done using this method. Place a clean glass of fresh water with the
surface exposed to the open air for at least 24 hours. Maintaining a
fairly constant temperature will improve the accuracy of this test. The
percentage of oxygen in air is 20.1% and in 100% saturated water the
partial pressure of the oxygen in water will be the same as in the air.
Multiple the atmospheric pressure in your area by 20.1% to find out the