Hello,
I am new to the PID & I would like to take suggestion in the implementation

My temperature range: 0----250 So Set Value will be in this range given from HMI.
Module resolution is from 0----0FA0 ( which is equivalent to 0----10v)

Generally I planned to implement like this without using PID instruction

If Suppose SV=250
PV=100
difference=SV-PV=+150

This Maximum difference will be 250
for 250 Centigrade-------0FA0 (10V output)
So 150.. -------= (150 *10)/250 =6V (interms of volts)
Gas valve will open proportionately 0--10v.
Can I use SCL instruction for this manipulation?

The above calucation will be going on as long as difference carries positive sign.
If it is Negative sign, immediately we will stop/close (0 Volts output) the Gas valve & will continue till reaches Zero.

It is the general idea but i don't know what kind of problems i will face with this?
Also I would like to know what are the advantages of PID over above?
I really looking for the earliest possible reply

Thanks in Advance
Lakshmi

 

This seems to be a simple proportional control. Which is not too good for continuous process control. This algorithm cannot match PV and SV because the output is proportional to the Error and Error has to exist for any output generated to open the valve.

If you use PID controller (generally PI controller) the I component keeps an accumulated history of errors and gives output even when there is no difference between PV and SV, thus making it possible to match PV and SV. The P components only takes action when there is difference between PV and SV but when the process becomes stable and PV matches SV, then the I component maintains the output to the valve even when error is zero. This is not possible with pure proportional control. like the one you stated above.

 

I have the sufficient Hot airflow (we generate) through a valve/damper onto a material. Obviously Temp depends on the amount of air that we allowed from the valve/damper.
There is no subtance for heat production.
Just my job is to control only the percentage opening of Valve depends on the error.
This valve is Analog output.
I hope u understood the application.

Now can anybody suggests constant values for p=?, I=? D=? for the above application.

Change of these values By trial& error doen't giving me a good response.