Hach pHD sc Analog Differential pH/ORP Sensors Manuel D'utilisation page 17

Pre-requisite: Prepare a mild soap solution with a non-abrasive
dishwashing detergent that does not contain lanolin. Lanolin leaves a
film on the electrode surface that can degrade the sensor performance.
Examine the sensor periodically for debris and deposits. Clean the
sensor when there is a buildup of deposits or when performance has
degraded.
1. Use a clean, soft cloth to remove loose debris from the end of the
sensor. Rinse the sensor with clean, warm water.
2. Soak the sensor for 2 to 3 minutes in the soap solution.
3. Use a soft bristle brush to scrub the entire measuring end of the
sensor.
4. If debris remains, soak the measuring end of the sensor in a dilute
acid solution such as < 5% HCl for a maximum of 5 minutes.
5. Rinse the sensor with water and then return to the soap solution for
2 to 3 minutes.
6. Rinse the sensor with clean water.
Note: Sensors with antimony electrodes for HF applications may require
additional cleaning. Contact technical support.
Always calibrate the sensor after maintenance procedures are done.
5.3 Replace the salt bridge
Differential sensors have a removable salt bridge
sensor has been cleaned but fails calibration, replace the salt bridge and
the standard cell solution. Refer to the instructions included with the salt
bridge.
Figure 6 Salt bridge
1 Salt bridge
Always calibrate the sensor after maintenance procedures.
Section 6 Troubleshooting
6.1 Intermittent data
During calibration, data is not sent to the datalog. Thus, the datalog can
have areas where the data is intermittent.
6.2 Test the pH sensor
Pre-requisites: Two pH buffers and a multimeter.
If a calibration fails, first complete the maintenance procedures in
Maintenance
(Figure 6). If the
1. Put the sensor in a pH 7 buffer solution and wait for the temperature
2. Disconnect the red, green, yellow and black sensor wires from the
3. Measure the resistance between the yellow and black wires to verify
4. Measure the DC mV with the multimeter (+) lead connected to the
on page 16.
of the sensor and buffer to reach room temperature.
module.
the operation of the temperature element. The resistance should be
between 250 and 350 ohms at approximately 25 ºC.
If the temperature element is good, reconnect the yellow and black
wires to the module.
red wire and the (–) lead connected to the green wire. The reading
should be between –50 and + 50 mV.
2 Differential sensor
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