5.3
Current input
This function group offers two independent application solutions, provided that the current
output of an external measured quantity, e.g. flow meter, is connected to the 4 … 20 mA input
of Liquisys M COM 223 F / 253 F. The following assignments then apply:
5.3.1
Monitoring the flow rate in the main stream
This arrangement is highly practical when the sample stream flowing through the flow assembly
(e.g. COA 250) is totally independent of the flow rate in the main stream. This permits the
signalling of an alarm state in the main stream (flow rate too low or totally stopped) and trigger a
dosing switch-off, even if the measuring water stream is retained due to the installation
configuration.
Flow in
main stream
Current signal
in mA
Current input
signal in %
Lower range limit
current input
Lower setting value
flow meter
4
0
Upper range limit
current input
Upper setting value
flow meter
20
100
Flow in
main stream
Flow alarm
Flow below
switch-off limit Z4
or flow failure
Flow
restored
Alarm relay
Relay contacts
of PID controller
ON
OFF
OFF
OFF
ON
ON
see field Z2
see field Z3
Fig. 5.4
Alarm signalling and dosing
switch-off by the main stream
OM253FE5A.CHP
Liquisys M COM 223 F / 253 F
Instrument configuration
Hauser
25
