Hardy HI 1756-nDF - Manual (Page 25)

21
●
●
●
●
●
Chapter 4
Ref# Relay Mode Description of Relay Operation
1 Sequential Relay
Operation Relay RA is set to the CLOSED state, and relay RB
set to the OPEN state at the beginning of the fill
cycle. When the absolute net weight value is greater
than or equal to the set point SPA relay RA is OPEN
and relay RB is CLOSED, when the absolute net
weight value is greater than or equal to set point SPB
both relays are OPEN.
Automatic refill not allowed.
SPA = target weight TA – preact PA
SPB = target weight TB – preact PB
2 Parallel Relay
Operation [Default Mode of Operation for each weigh scale]
Relay RA and relay RB are both set to the CLOSED
state at the beginning of the fill cycle. When the
absolute net weight value is greater or equal to set
point SPA relay RA is OPEN or when the absolute
net weight value is greater or equal to set point SPB
relay RB is OPEN.
Automatic refill not allowed.
SPA = target weight TA – preact PA
SPB = target weight TB – preact PB
2 Speed (Fast/Slow) Mode Considerations
The 1756-nDF can be purchased with two relays per weigh scale channel. The
architecture can be configured so both relays start at the same time (simultaneous feed)
and have different target weights so the “fast” feed is closed before the “slow” feed; or
the two relays can start sequentially (sequential feed) with the “fast” relay (relay A) being
closed when it reaches its target weight and the ‘slow” relay (relay B) opening as soon as
the “fast” relay is closed. Automatic refill not allowed.
In both situations the “fast” relay will never see a stable weight on the scale before the
“slow” relay allows additional material onto the scale. Therefore the “fast” relay will be
treated as a coarse adjustment and will be set to provide a maximum percentage of the
final target weight value, and the auto-preact algorithm will run only on the slow relay to
provide the accurate final dispense cycle to reach the desired target weight.
When setting up the process for the first time the “fast” relay should be run on its own
with the “slow” relay initially disabled; the target weight for the “fast” relay will be set
by running several test dispense cycles. Once the “fast” relay target is set, the slow relay
will be enabled and tests repeated to verify that the vessel does not overfill. If this occurs,
one of two actions can occur:
1. If the auto-preact is at zero or below the “fast adjust” percentage of the target
weight then the fast relay target has been programmed too high. If the “fast
adjust” value is not 0.0% then the target weight set for the “fast” relay will be
reduced by the percentage programmed into the “fast adjust” parameter and the
auto-preact reduced by the same percentage or reset to zero if the residual value
in the auto-preact output is below the “fast adjust” percentage times the target
weight value. This repeats until the unit hits the desired target weight.
2. If the “fast adjust” bit is set 0.0%, then the control system is expected to monitor
the error between the final weight and the desired target weight and should
reduce the fast relays target value. Any change in the fast relay target value
resets the auto-preact value to zero.