advantages of integral cycle heat control

[sjjm]

hello
Can somebody pliz tel me the advantages of using the method of integral cycle method of heat control over any other methods that can b used.
YO help is greatly appreciated!!!!!

thanx

 

[VVV]

I hope I understand the question correctly. I know the method is called time-proportional temperature control, but I think it is the same thing.

Essentially, in one approach you can have a phase-controlled SCR or triac, that adjusts the voltage (and hence the power) of the heating element. The problem is the relatively high EMI because the triac or SCR turns on rapidly, somewhere in the middle of the AC cycle.

But you can also turn on the triac at the zero-crossing of the AC cycle and keep it on for several cycles. When it needs to turn off, the triac will turn off again at the zero-crossing and will stay off for several cycles.
Thus, the AVERAGE power delivered to the heating element can be adjusted by the number of full cycles it is on, versus the number of full cycles it is off.
This is time-proportional control. Since it always turns on the heater for complete cycles, I think it is the same as the one you mention.

The advantage is lower EMI and lower current waveform distortion, thus lower harmonic content (because the current will closely follow the line voltage when the triac is on and will be zero when off, instead of being a chopped sinewave). That means a higher power factor.

 

[Siniša]

Integral method has advantage that brings error to 0 value, while just proportional control will stabilize with error value depending on the gain of the system. If you try to reduce this error by increasing gain you will get unstable system prone to oscillation, and if you try to offset it, offest value would have to be input level dependant.
-Therefore if you require system where you set certain value ahead and expect system to conform to that command than you need integration part in your control loop.
-If you look at resulting value of the system while adjusting it and leaving it at that value (e.g. setting oven temperature while looking at thermometer) than you are doing compensation of system error manually and you don't need integral part of the control loop, simple PD controller would suffice.