Example 5 - Controlled Restart After Power Loss - Honeywell UMC800 Reference Manual

2.60 SPP Function Block,

2.60.5 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
Restrart 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
3/99
continued
program
continues
restore ramp
rate
Figure 2-67 Controlled Restart after Power Loss
Function Block Reference Guide
If Time OFF is greater than SET_TOFF, execute restart
NOTE: Execution sequence relative to SPP block
Function Blocks
189