kajaaniMCA
i
– Installation, Operating & Service - 11.2 - W4610201 V2.5 EN
11.A.5. Antenna contamination
Contamination problems will appear as an upwards
drift of the measurement. If the antenna gets cleaned
from time to time, for example when the wood species
changes, the drift may disappear. The antennas are
made of glazed ceramic, and contamination may be
caused by some substance adhering to the glass surface.
11.A.6. String or other material attached to the fork-
type sensor
This kind of problems appear either as a drift in the
measurement (most likely upwards), or as a rapid level
change, depending on whether the material accumu-
lates gradually on the sensor or gets suddenly stuck to
it. If such problems are expected or observed, install a
deflector plate to divert this kind of materials past the
sensor. The deflector plate is available as option.
11.A.7. Measurement channel fault in electronics
Fault in the measurement channel may appear as a very
low signal level, unstable measurement signal, mea-
surement drift, or a sudden level change. Especially a
sudden level change most probably indicates an elec-
tronics fault. The other effects may also be caused by
process conditions, leaks in the antennas, contamina-
tion, and the accumulation of strings or other material
on a fork-type sensor.
The signal level of the measurement channel can be
checked by using a simulation cable (see section 10.C).
If the test shows that the measurement channel (elec-
tronics) is faulty, replace the unit and perform a new
start-up as instructed in section 6.A or in chapter 12.
(HART communicator).
11.A.8. Current signal fault
If the MCAi reading and the current signal value do not
match, the current signal (in electronics) is faulty.
Before replacing the electronics, make sure that the
current signal cables are correctly connected – a wrong
connection may cause the problem!
Note that the MCA
i
current signals use their own power
supply. Do not connect an external power supply to the
current signals!
11.B. Error Messages of Selfdiagnostics
When the sensor’s self-diagnostics detects a fault, the
current signal is set to the selected fault status (0, 4, 20
mA, or freeze) and gives an alarm through the alarm
relay. In addition, an error message will appear on the
Status line in the bottom of the Communicator-i Main
Menu and in the Device status menu of the HART
communicator, and the fault will appear in the error
history. The following error messages are possible:
Reference channel fault
This fault is always caused by the Electronics Unit. It
may appear either as a low reference signal level or
unstable signal, detected by the self-diagnostics:
• Reference signal level low
The reference signal level is below the low limit set to
self-diagnostics. Replace the Electronics Unit and per-
form a new start-up as instructed in section 6.A or in
chapter 12. (HART communicator).
• Unstable reference signal
Rapid fluctuations in the reference signal. The elec-
tronics Unit is faulty. Replace the Electronics Unit and
perform a new start-up as instructed in section 6.A or in
chapter 12. (HART communicator).
Measurement signal level low
The measurement signal level is below the low limit set
to self-diagnostics. Possible causes:
• fault in Electronics Unit,
• significant increase in the chemicals content (con-
ductivity) of the process,
• significant drop in process temperature,
• damaged microwave antenna.
Measurement signal level high
The measurement signal level is over the high limit set
to self-diagnostics. This phenomenon is caused either
by a substantial decrease in the chemicals content
(conductivity) of the process or an increase in temper-
ature, not by any device fault. This error message may
also come up if the process pipeline is empty.
Measurement signal unstable
Rapid fluctuations (duration less than 1 second) in the
measurement signal. Possible causes: large air pockets
in the stock.
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