JUMO dTRANS pH 02, Operating Manual, Page: 118 / 136

18 Appendix
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Impedance monitoring
Impedance monitoring of glass pH combination electrodes places high
demands on the transmitter electronics. The measurement required for this
purpose takes place at the same time the main measured value is recorded. To
minimize the electrode load, a response time of up to one minute is possible.
With an asymmetrical connection of glass and reference electrode, the overall
impedance can be monitored.
Monitoring of the reference electrode is not recommended, since the mea-
sured value is difficult to interpret.
The impedance measurement depends on the cable material, the line length
and the components used. JUMO special lines for pH measurements are lim-
ited in length to 10 m.
If ISFET sensors or impedance converters are used, impedance monitoring is
not possible.
Wash timer
The wash timer can be used to implement automated sensor cleaning. To do
this, the function is assigned to a switching output.
The cycle time (cleaning interval) can be adjusted in the range from 0.0 to
240.0 hours.
A cycle time of "0.0" means the wash timer is deactivated.
The wash time (cleaning duration) is adjustable from 1 to 1800 seconds.
During the wash time the controller goes into the HOLD state, which is
maintained for 10 seconds after completion of the wash time. A sensor
calibration within the cycle time restarts the wash timer.
Parameter block switching
Some processes (different process steps) benefit from having two complete
parameter blocks available.
Defining of the parameter blocks see chapter 13.5 "Parameter sets", page 93.
Activation of the predefined parameter blocks occurs over the binary input.
If impedance monitoring responds, the controller switches to the "HOLD"
state and the measured value is set to "invalid". The analog outputs and limit
switches respond according to their configuration in case of error.
This note applies as of software version 268.02.04.