LF 170
Operation
103
ba54104e09
11/2010
Example:
Monitoring of limit
values with one or two
relays
Fig. 4-2
Switching points of relays working as limit indicators
The selected limit value (UL/LL) is exceeded/undercut.
The hysteresis HS that was set for the limit value is exceeded/
undercut. The switching delay td for the limit value is started.
If the limit value including the hysteresis is still exceeded/
undercut and the switching delay for the limit value has expired
the relay switches.
Time
Measured value
UL
LL
Hysteresis HS1
Hysteresis HS1
Relay 1
td2
td2
td1
td1
Hysteresis HS2
Hysteresis HS2
Relay 2
Relay 2
Time
Relay state
Relay 1
on
on
off
off
