Process Unit 73 LF - Knick

Process Unit 73 LF
Controller Output
The method for determining the controller output
(manipulated variable) is the same for the digital
and the analog controller. However, the output of
the manipulated variable at the limit contacts or at
output 2 differs as follows:
Digital Controller
The controller output (manipulated variable) is output
via the two limit contacts 1 and 2.
Limit contact 1
operates in the controller output range of
0 to +100 %
Controlled variable < setpoint
Limit contact 2
operates in the controller output range of
0 to –100 %
Controlled variable > setpoint
The contacts can control valves of feeding pumps,
for example. Contact ON time or switching frequency,
resp., vary according to the controller output.
The currently valid controller output can be read
out on the secondary display (see page 2–1).
As delivered, the relay contacts are suitable for
low signal currents (down to approx. 1 mA).
If currents above approx. 100 mA are switched,
the gold plating is destroyed during the switching
process. After that, the contacts will not reliably
switch low currents.
Analog Controller
The manipulated variable is output proportionally
as an analog current via output 2.
Controller type A (3-way mixing valve)
operates in the controller output range
–100 to +100 %
Controller type B (straightway valve)
operates in the controller output range
0 to +100 %
Controlled variable < setpoint
Controller type C (straightway valve)
operates in the controller output range
0 to –100 %
Controlled variable > setpoint
9–34 Capabilities