Figure 100 Controlled Restart After Power Loss - Honeywell HC900 Reference Manual

Function Blocks
SPP Function Block
Example 5 - Controlled Restart after Power Loss
SCENARIO A
To prevent stress to the work in a furnace on
power up after a power loss, you may use the
Restart feature of the SP programmer. This
feature will use the PV (connected to PV1) as
the initial starting point for the Setpoint and
will use a configurable ramp rate for the
profile. When the temperature gets to the
original Setpoint prior to power down, the
program will continue. You may gate this
Restart input to the programmer to only apply
after a certain time off and/or a certain
segment if desired using Compare function
blocks.
This example uses the System Monitor
block to provide a restart pulse to the
programmer Restart input after power
restore. This will initiate the restart
procedure.
power loss
Initial PV
value on
power
restore
SCENARIO B
A System Monitor block output
(RESTART) is on for the first scan cycle
after a power loss plus TIME_OFF
output indicates the time the power has
been off. A Compare block can be used
to evaluate the time off and cause an
output to initiate the restart if greater
than a set amount.
Time Off is in seconds.
352
program
continues
restore ramp
rate
If Time OFF is greater than SET_TOFF, execute restart
NOTE: Execution sequence relative to SPP block

Figure 100 Controlled restart after power loss

HC900 Hybrid Control Designer Function Block Reference Guide Revision 11
2/07