VEGA VEGAMET 391 4 … 20 mA_HART - Manual (Page 46)

46
8 Application examples
VEGAMET 391 • 4 … 20 mA/HART
36032-EN-130701
•
Measured value change higher: Measured value change per
time unit, at which the tendency recognition should respond
•
Max. reaction time: Time after which a new measured value
generation is carried out and the measured value change is
recalculated
•
Hysteresis: is automatically always 10 % of the value of "Meas-
ured value change larger than"
•
Reaction in case of failure: In case of a failure, the relay goes
into the defined condition
Note:
After switching on or a failure, always two complete cycles must be
executed until a measured value difference can be calculated and a
tendency can be outputted.
The level in a basin should be monitored on rising tendency. If the rise
is higher than 25 % per minute, an additional emptying pumpt should
be switched on. The max. reaction time should be one minute. In case
of a probable failure, the pump should be switched off.
Select in the DTM navigation section the menu items "Meas. loop -
Outputs - Relay".
•
E.g. set for relay 1 the mode "Rising tendency"
•
Select under "Reaction in case of failure" the option "Switching
condition off"
•
Enter the following values into the parameter fields:
– Measured value more than 25 %/min.
– Max. reaction time 1 min.
The function of the tendency recognition is shown in detail in the fol-
lowing diagram. The previously described example is used as a basis.
t
t
m
t
m
t
m
t
m
120 180 240
ON
OFF
60
[sec]
1 2 3 4
5
... ...
...
...
100
75
50
25
0
%
...
Fig. 18: Example for tendency recognition
1 Old average value = 25 %, new average value = 25 %
Difference < 25 % -> Relay ON
2 Old average value = 25 %, new average value = 37.5 %
Difference < 25 % -> Relay ON
3 Old average value = 37.5 %, new average value = 62.5 %
Difference = 25 % -> Relay OFF
4 Old average value = 62.5 %, new average value = 75 %
Difference < 25 % -> Relay ON
5 tm -> max. reaction time
Parameter
Example
Setup