Hardy HI 2151/30WC Single-Scale Controller - Manual (Page 103)

Chapter 7 - Operation
7-5
For example: if a set point value was 1000 pounds and the dead band
was set to -5 pounds, the relay would close at a 1000 pounds but not
open until the weight dropped to 995 pounds. This would be used if a
set point is a high trip limit. A positive dead band would be used for a
low trip limit. Examples are shown for Low and High Trip Limits.
(See Fig. 7-3) Using a set point of 1,000 pounds and a dead band of -
800 pounds will cause the level to remain between 200 and 1,000
pounds.
Three General Rules
for Setpoints 1. Set points activate at the set point plus the preact.
2. Set points deactivate at the set point plus the deadband.
3. The deadband should be numerically larger than the preact to pre-
vent relay chatter.
FIG. 7-3 LOW AND HIGH PREACT TRIP LIMITS
Preact Limits (See
Fig. 7-3) • The preact value is the number of units below (negative value) or
above (positive value) the set point value at which the relay will
trip.
• It is used as an "in-flight" compensation value when filling a vessel.
If set to zero, there will be no compensation.
Entering Set Points
About the Set Point
Menu • Used to enter the set point, dead band, and preact values for the two
standard internal relays.
• Used to enter the associated values for the six optional, external
relays when installed.
NOTE: To scroll forward or backward through the Set Point Menus, press the Up or Down
arrow
↑↓
buttons.
SET POINT
(-) PREACT
SETPOINT
AFTER TRIP
PROCESS
RELAY TRIPS
RELAY RESETS
(-) PREACT
SETPOINT
AFTER TRIP
SET POINT
RELAY RESETS
RELAY TRIPS
LOW TRIP LIMIT
HIGH TRIP LIMIT
NEGATIVE
DEADBAND
POSITIVE
DEADBAND
TIME
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TIME
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