Process Unit 73 LF - Knick

Process Unit 73 LF
Power Output
The Process Unit 73 LF provides a floating, shortcircuit-proof
power output (as standard).
With this power output, you can, for example, supply
sensors or switching contacts with 24 Vdc,
30 mA (see Fig. 9–9, page 9–26).
How to use the power output together with the current
input to form a ”2-wire transmitter supply” is
described as follows:
Current Input
The Process Unit 73 LF provides a current input
(as standard). The current input processes standard
signals of 0 to 20 mA or 4 to 20 mA.
The input current can be read out on the secondary
display (see page 2–1).
In addition, the input current can be monitored by
alarm limits (see page 9–27). Warning and failure
limits can be set in the menu ”Alarm Settings”.
The alarm limits are entered as percentage of input
current range.
With
0 % corresponding to 0 or 4 mA,
100 % corresponding to 20 mA.
With current input setting ”Input 0...100%
4...20mA”, you can enter negative percentage values.
–25 % correspond to 0 mA.
The currently active alarm messages can be read
out in the Diagnostics menu ”Message List” (see
page 3–2).
Typical Application
The application example in Fig. 9–9, page 9–26
shows the connection of a 2-wire flow transmitter.
During a bypass measurement, for example, the
flow transmitter can be used to monitor if the flow
of the process medium is sufficient.
The flow transmitter is supplied from the power
output.
The current from the flow transmitter is measured
via the current input. The flow transmitter signal
can be monitored by setting four alarm limits for
the current input.
9–42 Capabilities