VEGA VEGAMET 391 4 … 20 mA_HART - Manual (Page 45)

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8 Application examples
VEGAMET 391 • 4 … 20 mA/HART
36032-EN-130701
If the level does not change over a longer period of time, the same
pump would remain switched on. Via the parameter "Changeover
time", a time period can be preset, after which a forced changeover of
the pump is carried out. This function is described under pump control
1/2.
When pump control is activated, pump monitoring can also be
switched on. A return signal to the respective digital input is required
for this. The function is described under pump control 1/2.
If all pumps have the same capacity and are used for the same task
alternately, the running time should always be roughly the same. The
respective operating hours are summed up individually in the signal
conditioning instrument and can be read out in the menu " Diagnose
– Switched-on time ". If a considerable difference between the pumps
is determined, it means the capacity of one of the pumps must have
fallen considerably. This information can be consulted for diagnosis
and service, e.g. to recognize plugged-up filters or worn out bearings.
Since in this case, all pumps are operated alternately in the same
range, the switch on and switch off points should be theoretically
by the same. Due to this, all relays would always switch together. To
reach the respective switchng condition, the requested switching
points must be assigned to a relay, switching points are assigned
to the other relays which are never reached in normal operation, for
example 110 % and -10 %.
Note:
The index of the lastly switched on relay is not saved in case of volt-
age loss, this means that adter switching on the signal conditioning
instrument, always the relay with the lowest index starts.
8.4 Tendency recognition
The function of the tendency recognition is to recognize a defined
change within a certain time period and to transfer this information to
a relay output.
The information for tendency recognition is generated out of the
measured value change per time unit. The output variable is always
the measured value in percent. The function can be configured for
rising and falling tendency. The actual measured value is determined
and summed with a sample rate of a second. After the max. reac-
tion time, the average value is generated out of this sum. The real
measured value change results then of the newly calculated average
value less the previously calculated average value. If this difference
exceeds the defined percentage value, the tendency recognition
responds and the relay deenergises.
Note:
Activation and configuration of tendency recognition requires PACT-
ware with the suitable DTM. The respective parameters cannot be set
via the integrated display and adjustment unit.
Option forced changeo-
ver
Pump monitoring
Diagnosis via running
time
Functional principle
Principle of operation