Xylem WQ770-B TURBIDITY METER - Manual (Page 9)

Global Water
800-876-1172
• globalw.com
- 9 -
Preparation:
a. Set up a test stand with a rod and clamp to hold the sensor. Beakers
will be placed underneath the clamp so the sensor can be inserted into
the liquid.
b. The sensor must have the stainless steel section of the body in contact
with the test solution. Install the sensor so that the end of the sensor
is at least 3 inches from the bottom. If the sensor is too close to the
bottom, infrared light may be reflected from the glass and effect the
measurements.
c. The lenses must be gently cleaned with a cotton swab and isopropyl
alcohol before each calibration step.
d. Fill a large beaker with distilled water. This will be used to rinse
solution from the sensor in between steps.
e. Fill three more beakers with 0.0 NTU Standard, 50 NTU Standard and
1000 NTU Standard. These beakers must be at least 500 ml in size or
the end of the sensor will be too close to the bottom for accurate
calibration. This generally requires solution volumes of at least 500ml.
f. The calibration process should not be done in bright light if possible.
While not generally required, the extra step of covering the outside of
the beakers with a non-transparent material may help to prevent stray
light from the outside affecting the readings.
Note: The sensor is factory calibrated and will provide output currents
of 20mA at the maximum turbidity values; however, some small drift in
this output current can occur over time. These adjustments are done
internally, access to these settings are not available to the user. The
sensors should never be disassembled. The following process
describes how to re-calibrate the meter and sensor to compensate for
any drift.