moneyfreddie
Member
can any one tell me how to keep my pid from going back to the last value recorded in auto mode, when i switch form manuel to auto.
pid
- Thread starter moneyfreddie
- Start date
Steve Bailey
Lifetime Supporting Member + Moderator
Not without more information. Nobody here is looking at your system. Nor are we mind readers. Based on what you've told us, the best answer you can expect is, "Configure your controller so it doesn't do that". Try searching your documentation for "bumpless transfer".
Peter Nachtwey
Member
A general case
Set the SP to the PV so there is no error and load the integrator control signal with the current control signal.
If you must leave the SP alone then the integrator must be modified as follows:
IntgratorControl=LastControl-Kp(Sp-PV)
I am assuming the IntegratorControl is in control output units. Otherwise you need to adjust the accumulated error.
IntgratorControl=Kp*Δt/τi*Σerrors
So
(Kp*Δt/τi)*Σerrors=LastControl-Kp(Sp-PV)
or
Σerrors=(LastControl-Kp(Sp-PV))*τi/Kp*Δt
Easy
Set the SP to the PV so there is no error and load the integrator control signal with the current control signal.
If you must leave the SP alone then the integrator must be modified as follows:
IntgratorControl=LastControl-Kp(Sp-PV)
I am assuming the IntegratorControl is in control output units. Otherwise you need to adjust the accumulated error.
IntgratorControl=Kp*Δt/τi*Σerrors
So
(Kp*Δt/τi)*Σerrors=LastControl-Kp(Sp-PV)
or
Σerrors=(LastControl-Kp(Sp-PV))*τi/Kp*Δt
Easy
Ron Beaufort
Lifetime Supporting Member
can you post your program file? ... (note that you'll have to ZIP it first) ...
at this point, we don't even know what brand of PLC you're using (or if you've even using a PLC at all) ... it's impossible to give you detailed answers without more information ...
we'll be glad to try to help - but you've got to give us a lot more to work with than you've posted so far ...
and welcome to the forum ...
at this point, we don't even know what brand of PLC you're using (or if you've even using a PLC at all) ... it's impossible to give you detailed answers without more information ...
we'll be glad to try to help - but you've got to give us a lot more to work with than you've posted so far ...
and welcome to the forum ...
Paul B
Member
Of course you want bumpless both ways - Auto to Manual and then Manual to Auto. It depends upon the controller...
With a GE or Siemens PLC my program turns on the Manual bit of the PID loop. When manual is on the manual setpoint is moved into the PID loop. When manual is switched off the PID loop takes off from there - naturally bumpless. Then when in Auto (not manual), the program moves the pid output to the Manual setpoint, making it bumpless the other way.
With a GE or Siemens PLC my program turns on the Manual bit of the PID loop. When manual is on the manual setpoint is moved into the PID loop. When manual is switched off the PID loop takes off from there - naturally bumpless. Then when in Auto (not manual), the program moves the pid output to the Manual setpoint, making it bumpless the other way.
moneyfreddie
Member
OP
thanks for replying,it is a slc 5/04 and making it bumpless is what i was told to do but how.i have looked up pid control bumpless transfer and still do not understand.
Last edited:
Ron Beaufort
Lifetime Supporting Member
once again ...
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