Endress+Hauser Liquisys M CCM223 - Maintenance of Ph Connecting Cables and Junction Boxes (EP Version); Test and Simulation; Chlorine Sensors

Maintenance Liquisys M CCM223/253
98 Endress+Hauser
9.1.5 Maintenance of pH connecting cables and junction boxes (EP
version)
Check the cables and connections for moisture. Moisture is indicated by a sensor slope that
is too small. If nothing more can be displayed or if the display is fixed at pH 7, please check
the following components:
• Sensor head
• Sensor plug
• Junction box, if fitted
• Extension cable
NOTICE
Incorrect measurements caused by moisture in the measuring cable
‣
If there is moisture in the measuring cable, the cable must be replaced!
A shunt in the cable of > 20 MΩ cannot be measured with normal multimeters but is
damaging for the pH measurement. Connect a pH simulator instead of the sensor. The
value that is displayed on the transmitter must match the value set at the simulator. The
value can differ at the second decimal place at the very maximum.
If you do not have a pH simulator, you can test the cable with a commercially available
megohmmeter. Please note the following when performing the test:
• Make sure to disconnect the pH measuring cable from the sensor and device!
• If you are using a junction box, you should check the infeed and outfeed measuring cable
separately.
• Check the cable with 1000 V DC (at least with 500 V DC) testing voltage.
• If the cable is intact, the insulation resistance is > 100 GΩ.
• If the cable is defective (moist), there is flashover.
The cable must be replaced.
You can clean (desalinate) the sensor head and junction box with de-ionized water
and dry them with a hot air dryer.
9.2 Test and simulation
9.2.1 Chlorine sensors
Chlorine sensors work according to the amperometric principle and supply very small
direct currents as the measuring signal.
A chlorine sensor can be simulated by a DC source. Due to the small currents, however, the
simulation is highly sensitive. Use shielded cables and ground the simulator. Typical slope
values are provided in the table below:
Sensor Typical slope value
CCS120 Approx. 115 nA per mg Cl/l
CCS140 Approx. 25 nA per mg Cl/l
CCS141 Approx. 80 nA per mg Cl/l
CCS240 Approx. 100 nA per mg ClO
2
/l
CCS241 Approx. 350 nA per mg ClO
2
/l
963 Approx. 20 μA per mg Cl/l