Respected Sir,

I am dealing with controlling of heaters which having various power consumption like 1.7kw, 2.4kw,180w etc. For controlling these heaters, I applied heaters power, its gain and its delay, by means of it i calculate kp, ti and td. And using some nonstandard pid formulae presently i getting control of heaters within +/- 1'c of set value. But when i found delay, and gain of heaters from its graphical response and applied to my system then i can not get the result very frequently. I will do some trial and error method then i get success to control the heaters.

So in this case i need your valuable support for finding out exact pid formulae for above various types of heaters in such a way that with a minimum effort i get the controls of heater within +/- 0.25'c of set value.

I will wait for your reply.

Thanks,

Rajesh Prajapati

 

You do not say what you are heating. If it is fluids, then there is a very good way to compensate for the response lag of the heaters and to maintain very accurate temperature control of the fluids.

The method was described in a paper given at the Texas A&M Instrument Symposium 2000 at College station Texas by Marke Shelley of Fluor and Jon Watson of Solartron where it was used to control the temperature of a flow stream to a process analyser.

In principal, the flow stream is split prior to the heater and some flow heated to above the target value while the balance of the flow is unheated. Downstream of the heater, he flows are recombined in a static mixer and the temperature measured. The temperature signal is used to modulate the flow split. If the temperature starts to increase, more flow is by-passed. This provides a very fast and accurate control response. However, it also requires a second control loop to control the heater to compensate for temperature trends in the fluid. This is the slow response caused by the poor response of heaters and heat exchangers to fast temperature transients.

Of course, if you cannot modulate the heaters to vary the heat input for any single heater, or these are not fluids, then this is of no value to you.

You might also adress your query to heater manufacturers such as ELWA, in Munich Germany. They provide electric heaters for Heavy Fiuel Oil temperature control.