Hach GS1440 User Manual page 22

Note: The function of the O-rings that are seen when the sensor cap is removed is to hold the sensor cap and not
to keep water out.
A replacement O-ring, O-ring grease and replacement instructions are included in the installation
spare parts kit. Refer to
Section 6 Troubleshooting
Problem
The measurements
are almost zero all of
the time, but a grab
sample measurement
shows there are
significant sulfide
concentrations.
The sensor
measurements are not
correct.
The sensor
measurements are not
correct after
calibration.
22 English
Parts and accessories
Possible cause
• There is a blockage at
the inlet of the sensor.
• The pH of the water is
higher than 8.
The sensor is not
calibrated.
The sensor was not
calibrated correctly.
on page 23 for ordering information.
Make sure that the measuring end of the sensor is not
covered with unwanted material.
Rinse the sensor and gently wipe the sensor with a wet
cloth. Make sure to not apply force around the inlets of the
sensing elements.
If the pH of the water is higher than 8, the dissolved sulfide
-
is mostly on the HS form, which is not measured by the
sensor. Use the sensor in a low-volume sidestream reactor,
where the wastewater is acidified to make sure that all of
the dissolved sulfide is on the H
Use the calibration gas to identify the accuracy of the
sensor.
1. Take the sensor and calibration gas, calibration cap
and flow regulator outside.
2. Clean the measuring end of the sensor. Refer to
Examine and clean the sensor
3. Put the calibration cap near the measuring end of the
sensor.
4. Turn the calibration cap 180 degrees relative to the
calibration orientation.
5. Fully open the flow regulator.
6. Wait 2 minutes.
7. If the measured value is not within 5% of the value on
the calibration gas bottle, calibrate the sensor. Refer to
Calibration on page 16
Do not use liquid samples for verification.
Make sure to follow all of the instructions supplied with the
calibration cap and flow regulator. If the problem continues,
contact technical support.
For the best accuracy, calibrate the sensor at a
temperature equivalent to the temperature of subsequent
measurements.
Solution
S form.
2
on page 20.