Pid Implementation

[lchamarthi 2]

Hello, I am new to the PID & I would like to take suggestion in the implementation 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 (Scaling ) 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 Edited 17 Mar 2006 by lchamarthi

[Snerkel 0]

Generally I use my own custom PID designed to suit the process as the built-in PID systems are often lacking in some way. However I can see a few problems with your control, the main one it seems way too simplistic. You need to consider the process time, the consiquence of someone opening the door, opening the gas valve 10% is unlikely to increase the temperature by 10% etc

[Stupidav 1]

Hopefully you are working with a SLC50X to use the SCL. The SCL works Great for "Scaleing", to get a proportional output driven from your input. This is nothing like a PID! PID output is driven primarily by the Error between you Setpoint and your Process Value. For Tempature control you probably are going to want to use a PID, especially if you want to keep the fluctuation to a minimum.