Limit Indicator: Basic Information - wtw TresCon UNO A111 Operating Manual

Operation
Monitoring limiting
values using one or two
relays
5 - 36

5.3.3 Limit indicator: Basic information

With a limit indicator, a relay switches when a specified limiting value is
exceeded or undercut.
Limit indicators can be used in the following way:
 Monitoring a limiting value using a relay:
when a limiting value (upper or lower limiting value) is exceeded or
undercut, a relay switches. The Open or Close relay actions are pos-
sible.
 Monitoring two limiting values using two relays:
If the upper limiting value is exceeded or undercut, a relay switches,
and if the lower limiting value is exceeded or undercut, another relay
switches. The Open or Close relay actions are possible.
Note
If the simple monitoring function (Open, Close) with one or two relays
is not sufficient, use proportional regulation (see section 5.3.1).
Measured
td1
value
Relay 1
UL
2
1
LL
Relay 2
Fig. 5-15 Switching points for relays with the function of a limit indicator
1 Upper limit value (relay 1) exceeded
2 Selected switching delay t1 for relay 1 expired
Relay 1 switches
3 Hysteresis for upper limiting value (relay 1) undercut
4 Selected switching delay td1 for relay 1 expired
Relay 1 switches back
td1
6
4
3
5
td2
TresCon UNO
Hysteresis UL
Hysteresis LL
Time
ba43134e08 05/2017