Can someone elaborate 3-point step control on Auto and Manual mode in general? I have a KS90 controller controlling a servo motor from KROM SCHRODER GT50 to actuate a combustion air valve as part of gas mixing station.

 

Generally 3 point control is to provide basic step control to a device such as open/close a valve as in your example. 3 Term control (PID) is too complex and is impractical as you have only open and close commands without any idea of valve position.

Assuming your valve servo motor can inch your air valve open, depending on process requirements you can open it fully in one go or inch it very slowly, or anything inbetween to suit. Writing software is not difficult - I have written algorithms for penstocks controlling water flow ... inch close to reduce, inch open to increase flow. A similar algorithm can be used for increasing/decreasing the speed of a variable speed motor driving a water pump.

This is Auto - for manual control you would merely inch the valve by hand.

 

I thank you a lot, sir. I have been waiting for a reply for so long as it was urgent at the time.

Your response is very helpful. I do have a few more things I would like you to explain more. What exactly is the "3-point step" it is referring to?

 

These can explain better than I - Siemens of course is overcomplicated as expected.....

http://testcon.info/FB_EN_Dreipunktschrittregler.html

https://cache.industry.siemens.com/dl/files/232/18748232/att_111202/v1/three_step_e.pdf

 

Hi , so this is a three point controlled valve .
so as per ur inputs from the thread , i believe thatwe need to give a supply voltage of 230v and ? what else wires to give to my digital input and output modules?

 

I'm not sure what device we're talking about 7 years after the first post.

In general, there are closed feedback control loops using a motor position signal and open feedback control loops using timing which 'assumes' a given motor actuator time duration/interval, say 2 seconds, will drive the actuator a given distance. The open loop algorithm keeps track of motor position by summing all the positive and negative direction driving time intervals.

Sometimes the open feedback algorithm drives to known position on a cold startup to ensure a known starting position.
Sometimes an open feedback algorithm relies on a 'calibration routine' that supplies the actual timing of the motor as it drives from fully open to fully closed.

Logic drives the DO's to drive the motor open or closed.

If the motor has external limit switches, it helps connect those to DI's so the algorithm to know that it has driven the motor to its limit.

Specifics for a KS90, I don't know.