WIKA TC12-M - Handbuch (Seite 33)

GB
10. Maintenance and cleaning / 11. Faults
14083458.01 09/2013 GB/D
WIKA operating instructions models TR12, TC12 (Ex i) 33
10.3 Calibration, Recalibration
It is recommended that the measuring insert is recalibrated at regular intervals (resistance
thermometers: approx. 24 months, thermocouples: approx. 12 months). This period can
reduce, depending on the particular application. The calibration can be carried out by the
manufacturer, as well as on site by qualified technical staff with calibration instruments.
11. Faults
Faults Causes Measures
No signal/line break Mechanical load too high or
overtemperature
Replacement of the sensor or the
measuring insert with a suitable version
Erroneous measured
values
Sensor drift caused by overtemperature Replacement of the sensor or the
measuring insert with a suitable version
Sensor drift caused by chemical attack Use of a suitable thermowell
Erroneous measured
values (too low)
Entry of moisture into cable or
measuring insert
Replacement of the sensor or the
measuring insert with a suitable version
Erroneous measured
values and response
times too long
Wrong mounting geometry, for example
mounting depth too deep or heat
dissipation too high
The temperature-sensitive area of the
sensor must be inside the medium, and
surfaces must be ungrounded
Deposits on the sensor or thermowell Remove deposits
Erroneous
measured values (of
thermocouples)
Parasitic voltages (thermal
voltages, galvanic voltage) or wrong
compensating cable
Use a suitable compensating cable
Indication of the
measured value jumps
Cable break in connecting cable or
loose contact caused by mechanical
overload
Replacement of the sensor or measuring
insert with a suitable design, for example
fitted with strain relief or a thicker conductor
cross-section
Corrosion Composition of the medium not
as expected or modified or wrong
thermowell material selected
Analyse medium and then select a more
suitable material or replace thermowell
regularly
Signal interference Stray currents caused by electric fields
or earth loops
Use of screened connecting cables,
increase in the distance to motors and
power lines
Earth loops Elimination of potentials, use of galvanically
isolated transmitter supply isolators or
transmitters
CAUTION!
If faults cannot be eliminated by means of the measures listed above, the
instrument must be shut down immediately, and it must be ensured that signal
is no longer present, and it must be prevented from being inadvertently put back
into service. In this case, contact the manufacturer.
If a return is needed, follow the instructions given in chapter 12.2 “Return”.