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7
POSSIBLE PROBLEMS WHEN COMMISSIONING
7.1
No flow rate indication
Check that the cables for remote electronic units have been correctly connected. Inverted
coil cables or electrode cables will have the same effect as inverting flow direction.
Check that the electrodes are perpendicular to the flow direction. If the sensor is mounted
with the electrodes aligned with the flow direction the output signal will be very poor and
the flow rate reading could be zero.
Check that the electrodes are clean and free from grease. If the electrodes are dirty with
grease or other insulating substance there will be no output signal. In this case the
electronics units usually indicate "empty pipe". See the point 8, to proceed to clean them.
Check that the pipe is completely full. (That the electrodes are fully covered with liquid).
7.2
The reading is not stable
Check that there are no obstacles or bends near the sensor, especially upstream from it,
that can produce important turbulences (see table of page 4).
Check that there are no air bubbles or solids that interrupt the conduction path between
the electrodes producing instability in the signal level
The electronic converters have a configurable filter. In most cases a stable reading can be
obtained by means of the filter configuration. The filters have two characteristics that
govern their operation:
7.2.1
Integration time
It is the time during which the average value is calculated. In the supposition that the
instrument takes 10 readings per second, if an integration time of 5 seconds is selected
the flow rate reading will be the average of the last 50 readings. If an integration time of
10 seconds is selected the flow rate reading will be the average of the last 100 readings.
Logically, when there are fluctuations in the flow rate, the greater the integration time is,
the more stable the readings will be.
7.2.2
Filter reset
Whilst the oscillations are within the window defined by the selected % in the filter reset
configuration, the filter will average the readings over the established integration time.
When there are readings outside this window the averaging of the readings will start again
and the flow rate reading can give the instantaneous reading. In these cases the filter
reset window must be increased to obtain a more stable reading.
The only inconvenience in leaving the window at very high levels is that the response to a
sharp change in flow rate will be slower.
7.3
Empty pipe
Even when it has been checked that the pipe is full, if there is empty pipe indication, this
may be caused by electrical currents that flow in the liquid inside the pipe. This problem is
more common when the pipe is made of plastic or other insulating material. To eliminate
this problem the metallic housings should be disconnected from the mains earth. The
electronic converters have the possibility to disconnect the empty pipe detection.
10
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