Hi,
I am studying PLC's in the UK and I am trying to find infomation on PID bump less transfer. Can anyone explain how bump less transfer works
please?

Andy
[email protected]

 

Andy,

Here is a novel and easy way to get smarter: do a Google search on this term - "PID Control Bumpless Transfer", and read most of the links. If in doubt after this, go to this website and buy any of the books on Process Control:
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Bumpless transfer allows the process to be changed from auto to manual without upsetting the process. The way to do it in a plc. When in auto, load the pid output register value into a spare register will call register x. The pid is running fine and no problems. When switched to manual mode load register x into the pid output register. This allows the auto/manual modes to start their control from the same output value.

good luck,
cvw mont

 

When transferring from Auto to Manual the Output does not change. Basically make sure the manual is equal to the PV while in AUTO. when You switch to Manual it will already be in the same place.

Brian

 

Bumpless transfer allows the controller to be switched between manual and automatic modes and back again without the control output suddenly 'bumping' to a different value.

Bumpless transfer is often implemented by making the setpoint track the PV when in manual mode. On changing back to auto, the SP and PV will initially be the same (i.e. error=0) so the output will also stay the same. The disadvantage is that the operator has to re-adjust the setpoint back to where it was - if he can remember where it was! Not that I've ever fallen for that one!

There are other ways of doing it. For example, when in manual mode, any change to the control output is added/substracted from the integral term. When the controller is put back into auto, it starts off with the integrator maintaining the current control output rather than jumping back to the previous value.

Hope this helps
Regards
John Green
Contek Systems Ltd,
Process Control Consultancy
Aberdeen, UK

http://www.contek-systems.co.uk

 

Bumpless transfer is either a manual or automatic transfer procedure used when switching a PID controller from auto to manual or vice versa. Its aim is to keep the controllers output the same when switching auto/manual, that is if the controller is at 50% output in auto it should retain that 50% output as you switch it to manual. If you switch from manual to auto the same should apply. Most modern PID controllers have bumpless transfer built in, including PLC and DCS PID controllers.

The term bumpless transfer refers to the process being controlled, meaning that the process is not disturbed when switching the PID controller from Auto to manual or from manual to auto.

 

PID controls whether PLC or loop controllers can be configured for bumpless transfer. When the controller is in MANUAL mode, the output control is adjusted manually, and the controller setpoint tracks (is set equal to) the process variable. When the control is switched to AUTOMATIC, the setpoint and process variable are equal to each other so there is no sudden "bump" in output.

 

Lets take Cascade control. You are having primary and secondary controller. Assume primary controller is in Manual and secondary is in Manual mode. Noe change the secondary control to Auto. Change the Set Value of the Secondary controller. Same time the Primary controller has to track the Sv of secondary with respect to the scale of Primary output. Say your secondary controller SV range is 0 to 45 m3/hr. IF your SV is changed to 22.2m3/hr then Primary controller output should shown as of 50%. When you change Secondary controller mode to Cascade there will not be any bump between those two controller. This concept is inline with yokogawa system.

 

Thank you.
A good concise answer

>Bumpless transfer is either a manual or automatic transfer procedure used when
> switching a PID controller from auto to manual or vice versa. Its aim is to keep

---- snip ----

 

All the above is right for more common cases when switching between two or more controllers are using for the same process as well.