Faults - WIKA TC90 Mode D'emploi

8. Faults

8. Faults
Faults
Cracks or deformations
GB
No signal/ line break
Erroneous measured values
(too low)
Erroneous measured values
and response times too long
Erroneous measured values
(of thermocouples)
Measurement signal -
"comes and goes"
Corrosion
Signal interference
Leakage of process media
from the mounting plane
■
process to high-pressure
thermocouple
on the junction of the high-
■
pressure thermocouple with
the temperature sensor or
on the temperature sensor
CAUTION!
If faults cannot be eliminated by means of the measures listed above, shut
down the instrument immediately, and ensure that pressure and/or signal are no
longer present, and secure the instrument from being put back into operation
inadvertently. In this case, contact the manufacturer.
If a return is needed, follow the instructions given in chapter 9.2 "Return".
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Causes
Mechanical loads too high
Mechanical load too high or
overtemperature
Entry of moisture into cable or
measuring insert
Wrong mounting geometry, for
example mounting depth too
deep or heat dissipation too
high
Deposits on the sensor
Parasitic voltages (thermal
voltages, galvanic voltage) or
wrong equalisation line
Cable break in connecting
cable or loose contact caused
by mechanical overload
Composition of the medium
not as expected or modified
or wrong thermowell material
selected
Stray currents caused by
electric fields or earth loops
Earth circuits
Faults during mounting
Defects, e.g. by operating of
the high-pressure thermocou-
ple in the case of resonance
Measures
Safe operation of the plant can no
longer be guaranteed
If necessary, replace probe or
measuring insert with a suitable
design
Replace probe or measuring insert
with a suitable design
The temperature-sensitive area
of the sensor must be inside the
medium, and surfaces must be
ungrounded
Remove deposits
Use suitable compensating cable
Replace probe or measuring insert
with a suitable design, for example
equipped with a strain relief or a
thicker conductor cross-section
Analyse medium and then select a
more-suitable material
Use shielded connecting cables,
and increase the separation from
motors and power cables
Eliminate potential differences by
using galvanically isolated transmit-
ter supply isolators or transmitters
Check tightening torques, check
whether the high-pressure thermo-
couple is mounted properly
Safe operation of the plant can no
longer be guaranteed
WIKA operating instructions model TC90