Commissioning Liquisys M CPM223/253
44 Endress+Hauser
6.6.3 Current input
With the "Current input" function group, you can monitor process parameters and use these
for feedforward control. For this purpose, you must connect the current output of an external
measured variable (e.g. flowmeter) to the 4 to 20 mA input of the transmitter. The following
assignment applies:
Monitoring of flow in main stream
This arrangement is particularly practical if the sample flow through a flow assembly in an
open outlet is completely independent of the flow in the main stream.
This permits signalling of an alarm condition in the main stream (flow too low or has
completely stopped) and triggers dosing switch-off even if the medium flow is retained due
to the method of installation.
Flow in main stream Current signal in mA Current input signal in
%
Current input lower
range limit
Flowmeter lower setting
value
40
Current input upper
range limit
Flowmeter upper setting
value
20 100
C07-CPM2x3xx-05-06-00-xx-001.eps
Fig. 32: Alarm signalling and dosing switch-off by the main stream
A
B
C
D
E
Flow in main stream
Relay contacts of PID controller
Alarm relay
Flow below switch-off limit Z 4 or flow failure
Flow alarm
F
Z2
Z3
0
1
Flow restoration
Delay for controller switch-off, see field Z2
Delay for controller switch-up, see field Z3
Off
On
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