Maintenance Liquisys M CPM223/253
90 Endress+Hauser
Reduced reference system
The inner metal lead of the reference system (Ag/AgCl) of a combination electrode or a
separate reference electrode is usually light-brown and matt. A silver-colored reference sys-
tem is reduced and therefore defective. The cause is a current flowing through the reference
element. Possible causes:
• Incorrect operating mode selected for the measuring device (PM pin connected but
unsymmetrical operating mode selected ("no PM"). See the function description on
"Selecting the type of connection".
• Shunt in measuring cable (e.g. due to humidity) between reference line and grounded
screen or PM line.
• Measuring instrument defective (shunt in reference input or entire input amplifier
downstream of PE).
8.1.3 Maintaining digital sensors
Proceed as follows to maintain the digital sensors with Memosens functionality:
1. If an error occurs or the sensor has to be replaced according to the maintenance
schedule, take a new or precalibrated sensor from the lab.
In the lab, a sensor is calibrated under optimum external conditions to ensure a higher
quality of measurement.
2. Remove the contaminated sensor and insert the new sensor.
3. A calibration is necessary if you are using a sensor which was not pre-calibrated.
4. The sensor data are automatically taken by the transmitter. No release code is required.
5. Measurement is continued.
6. Take the used sensor back to the lab. Here you can possibly make the sensor ready for
use again without the measuring point having to suffer downtime.
– Clean the sensor. For this purpose, use the cleaning agent indicated for the sensor.
– Inspect the sensor for cracks or other damage.
– Regenerate the sensor if it is not damaged. Store it for 24 hours in a 3M KCl solution.
– Recalibrate the sensor for the next use.
8.1.4 Liquid KCl supply
• The KCl must be free of bubbles. In the case of an unpressurized version, check whether
the cotton thread is present in the hose.
• In the case of counterpressure, check whether the pressure in the KCl tank is min. 0.8 bar
(11.6 psi) above the medium pressure.
• The KCl consumption should be low but noticeable. Approx. 1 to 10 ml/day is typical.
• The opening for sensors with a KCl top-up opening at the glass shaft must be clear.
8.1.5 Assembly
Please refer to the corresponding assembly Operating Instructions for information on
maintaining and trouble-shooting the assembly. Here you can find a description for
assembling and disassembling, sensor replacement, seal replacement, as well as
information on stability and spare parts and accessories.
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