Chapter 9 Limits; Understanding Limits, Set Points And Return Points - Honeywell SC1000 Owner's Manual

Chapter 9
Limits

9.1 Understanding Limits, Set Points and Return Points

Limits are signal levels at which some action (such as a light to come on or go out,
or a switch to close) is desired to take place. The point at which this action takes
place is the SET POINT. The RETURN POINT is the point at which the action that
took place at the SET POINT returns to its original state.
If the SET POINT and RETURN POINT are identical and the signal level is
changing slowly near these points, "chatter" may result and the limit rapidly ener-
gizes and de-energizes. To keep this from happening, we can specify the SET
POINT at which the action would occur as well as the RETURN POINT where we
want the action to cease. If the amount of "dead band" between these two values
is more than the expected noise, the desired action will take place only once. The
SET POINT and the RETURN POINT should always be separated to insure that
small amounts of noise on the signal will not become a problem.
A good general rule for SET POINT and RETURN POINT values is that they
should be separated by at least one percent of the full-scale value.
SC Series Instruction Manual page 53