kajaaniMCA
i
– Installation, Operating & Service - 11.1 - W4610201 V2.5 EN
11. Troubleshooting & Service
NOTE: Before detaching a sensor or the antenna of a
flow-through model, make sure that the process pipe-
line is empty and unpressurized, and that the work can
proceed safely!
The kajaaniMCAi does not require any regular main-
tenance. This chapter contains instructions for possible
fault situations.
11.A. Troubleshooting
The sensor contains a process measurement channel, an
internal reference channel, and a process temperature
measurement. All of these measurements are moni-
tored by the sensor’s self-diagnostics. When an error or
fault is detected, the self-diagnostics will give an error
message. However, it cannot precisely locate the unit or
module where the fault originated. To locate the origin
of a fault, follow the diagram shown in Fig. 11.1.
11.A.1. Chemicals content
Chemicals dissolved in the process attenuate the micro-
wave signal. A substantial increase in the chemicals
content may attenuate the signal level below the low
limit set for the self-diagnostics. The signal level can be
increased by performing a new start-up (section 6.A) at
the new, higher signal level.
Large variations in the chemicals content may also
cause error in the measurement, even if the signal level
stays within the operating range. In this case, use
chemicals compensation to eliminate the error; see
instructions in section 9.B or 12.C.1 (HART communi-
cator).
11.A.2. Temperature
Water temperature affects the propagation velocity of
microwaves. A substantial drop in process temperature
may attenuate the signal level below the low limit set for
the self-diagnostics. The signal level can be increased
by performing a new start-up (section 6.A) at the new,
higher signal level.
If the signal level stays within the correct operating
range but the measurement shows a temperature effect,
use temperature compensation to eliminate the error;
see instructions in section 8.C or 12.C.2 (HART com-
municator).
11.A.3. Air
Air in the process is a disturbing factor that increases the
consistency reading. To eliminate this, the minimum
process pressure specified for the MCAi is 1.5 bar (21.8
psi). At pressures above this limit the contained air is
dissolved in the water and thus will not disturb the
measurement.
Large air bubbles do not dissolve in water, and thus
it is not possible to give precise pressure specifications
for eliminating them. Large bubbles are generated e.g.
when pulp is dropped into a chest while the level is low,
and especially if pulp is dropped to the intake side of a
pump. The resulting air bubbles have no time to disap-
pear and they will pass into the pipelines. Also strong
agitation while the level in the chest or tank is low may
generate a whirl that sucks air into the stock. Another
source of air in the pulp are possibly leaking joints at the
intake side of a pump.
11.A.4. Leak in microwave antenna
This problem will appear as a slow drift of the measure-
ment signal to one direction, most likely downwards.
The signal level may also decrease slightly. If a leak is
detected, replace the antenna with its antenna cable. To
check an antenna for leaks, open the antenna cable
casing, at the antenna end, and see if it contains water.
Fig. 11.1. Troubleshooting diagram.
Reference
channel fault
See section 11.B.
Check the process conditions
No
Chemicals content/
conductivity?
See section 11.A.1
Process temperature?
See section 11.A.2
No
Air?
See section 11.A.3
No
Antenna leak?
See section 11.A.4
No
Antenna
contamination?
See section 11.A.5
No
Strings or other
material accumulating
on fork-type sensor?
See section 11.A.6
No
Measurement channel
fault in electronics?
See section 11.A.7
No
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