Endress+Hauser Liquisys M CUM223, Руководство по эксплуатации

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Liquisys M CUM223/253 Commissioning
Hauser 37
6.4.3 Current input
To use the "Current input" function group, you need a relay board with current input which is
not part of the basic version. With this 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 %
Flowmeter start of measuring
range
4 0
Flowmeter end of measuring range 20 100
a0008923
Fig. 20: 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 Z4 or flow failure
Flow alarm
F
Z2
Z3
0
1
Flow restoration
Delay for controller switch-off, see field Z2
Delay for controller switch-on, see field Z3
Off
On
A
E
D F
C
B
1
0
0
0
1
1
Z2 Z3