Model: LC5296 Dual Channel Temperature Controller
Doc. Ref. no.:- m61C/om/101
Issue no. 01D/ENGG-114
User’s Manual
Page 23 of 30
7
. CONTROL FUNCTION
7.1 ON/OFF Control
ON/OFF Controller is the simplest form of temperature control device. The output
from the device is either on or off, with no middle state. An on-off controller will
switch the output only when the temperature crosses the set point. For heating
control, the output is on when the temperature is below the set point, and off above
set point.
Since the temperature crosses the set point to change the output stage, the process
temperature will be cycling continually, going from below set point to above, and
back below. In cases where this cycling occurs rapidly, and to prevent contactors
and valves from getting damaged, an on-
off differential, or “hysteresis,” is added to
the controller operations. On-
Off hysteresis prevents the output from “chattering” or
making fast, continual switches if the cycling above and below the set point occurs
very rapidly.
Figure 8.1: Typical Relay operation
High type (H-ON):
For High type of set value, once process value reaches up to set point + Hysteresis
value, relay will be ON after few seconds (as per relay delay) and it will be ON until
process value goes down to Set point.
Low type (L-ON):
For Low type of set value, once process value reaches down to set point
–
Hysteresis value relay will be ON after nearly few seconds (as per relay delay) and it
will be ON until process value goes up toward Set point.
