PID Loop Operation
Maintenance
and Troubleshooting
8–58
PID Loop Operation
Now that we have described the general ramp/soak generator operation, we list its
specific features:
S Each loop has its own ramp/soak generator (use is optional).
S You may specify up to eight ramp/soak steps (16 segments).
S The ramp soak generator can run anytime the PLC is in Run mode. Its
operation is independent of the loop mode (Manual or Auto).
S Ramp/soak real-time controls include Start, Hold, Resume, and Jog.
S Ramp/soak monitoring includes Profile Complete, Soak Deviation (SP
minus PV), and current ramp/soak step number.
The following figure shows a SP profile consisting of ramp/soak segment pairs. The
segments are individually numbered as steps from 1 to 16. The slope of each of the
ramp may be either increasing or decreasing. The ramp/soak generator
automatically knows whether to increase or decrease the SP based on the relative
values of a ramp’s end points. These values come from the ramp/soak table.
SP
Ramp
Soak
Step
1
2
Ramp
Soak
3
4
Ramp
Soak
5
6
Ramp
Soak
13
14
Ramp
Soak
15
16
The parameters which define the
ramp/soak profile for a loop are in a
ramp/soak table. Each loop may have its
own ramp/soak table, but it is optional.
Recall the Loop Parameter table consists
a 32-word block of memory for each loop,
and together they occupy one contiguous
memory area. However, the ramp/soak
table for a loop is individually located,
because it is optional for each loop. An
address pointer in location V+34 in the
loop table specifies the starting location of
the ramp/soak table.
In the example to the right, the loop
parameter tables for Loop #1 and #2
occupy contiguous 32-word blocks as
shown. Each has a pointer to its
ramp/soak table, independently located
elsewhere in user V-memory. Of course,
you may locate all the tables in one group,
as long as they do not overlap.
V–Memory Space
User Data
LOOP #1
V2000
32 words
LOOP #2
32 words
V2037
Ramp/Soak #1
32 words
V3000
V2034 =
3000 octal
Ramp/Soak #2
32 words
V3600
V2074 =
3600 octal
V2040
V2077
Ramp/Soak Table
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