Watlow Series 1500 - Manual (Page 24)

C.
In your sample program’s Wait Step, you used “Wait for time” because you
aren’t connected to a variable oven yet. A more common use of the Wait Step
could be as follows:
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In Step #2, you have allowed exactly four minutes to reach 400°,
90%RH. Depending upon your system, this may either be impossible
to do, or you may reach the desired conditions much earlier than that.
This could result in bad apple pies.
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lf you reprogrammed Step # 2 as a Wait Step, you could measure how
long it takes to achieve the desired conditions, and then react
immediately. Much better apple pies.
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But, there is a choice to make here: The Wait Step does not follow the
linear ramping path to reach the new conditions as a Set Point Step
does. A Wait Step uses the previous step’s Set Point. To optimize
control (reduce the overshoot and undershoot) a Wait Step uses the
“PID Parameters” to satisfy the wait condition. In other words, select
the step type which best matches your needs. (The PID parameters
are discussed in the Technical Reference Section that follows).
4. Jump Loop Step (JL)
A. In the sample program, you used this capability to jump from Step #6 back to
Step #4 two times. Your “Jump Count” (JC) was set to “2.” Any value from
1 to 255 can be used in loops of this type.
B. If you program “0” into “JC,” the JUMP will occur infinitely. This action could
set up a never-ending loop if the jump is backwards. Or you can set up a
one-time “unconditional jump” if the jump is forward. If you use a forward
jump, the 0 choice makes no difference. The jump will be performed once.
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But why would you ever want to simply jump forward and skip over some
steps, you ask?
Suppose your overall program has various functional sections, not all of
which you want to do every time. By ending each section with a Jump
Step, you can easily alter the program to perform various sections in
diierent sequences.
During programming work, you may want to develop and test a program in
sections. You can develop the separate sections with unprogrammed
Blank Steps between them, then unite the separate sections laterwith
Jump Steps.
C. As you learned earlier, jumping or looping into Steps from “different
directions” can sometimes cause unexpected results due to different
starting conditions as you enter a new step. Watch for such possibilities.
5. Recycle
With the Recycle option active, you might expect to see continuous activity as the
process repeats the program sequence. This sample program will, in fact,
immediately start Step #1 after it completes Step # 8 .
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WATLOW Series 1500 User's Manual Sample Program, Chapter 2