Electric Heater Controller

I would think that a simple ON/OFF limit switch circuit (simple thermostat) would be sufficient.

Doubtless one of the control chaps will suggest more detailed suggestions.

1.1kw isn't a very big heater...so I'd think that the thermal inertia of the water an the small heater size would make proportional control a bit irrelevant...e.g. You will get loads of hysteresis whatever you do?

I'm happy to be shot down here....

thank you Del the Cat (Guru).

Heater duty is compensating the heat loss of the deaerator body and type of controller is the client request and shall be considerred.

Try looking at this link.

http://iseinc.com/SCR_Power_Controls.htm

I have used a 2.0Mw unit from this company in the past.

It was a water cooled unit operating at 600VAC.

They should be able to help you out with teh controls side of it also.

The two way s you said is one thng.

thermostat is adjustor of controller and scr is excute components of power. you can lack any one of hem.

in fact, thee are lots of such equipments on market for choise. and scr you can just select scr at 10A/500v enough.

the 4-20ma is only a standard remote control signal to contro scr on off to get hte setting temperature.

Dear cnpower

Ouput power of heater shall be changed from 0 to Pmax. by change of 4-20mA control signal from 4mA to 20mA respectively.

Yes, its so called adjust power, but you can get it through voltage.

you can change conduts angle or periodic of scr to achieve it. I can send you a scheme for reference by emial. its not difficult and not too much components.

control signal 4-29ma means 4ma is zero and 20ma is one. they are deffernent concept. not continous. its a encode control.

if not too long and too noise, you neednt use this method and can send a votal or current directly to power amplifier.

The power controller will vary the output from 0 to 100% based on the input signal of 4 - 20 mA.

For that reason the PID temp controller is used.

Process is compared to Setpoint and the controller adjusts its output to the power controller based on the error.

Process below setpoint, ramp up output to add heat.

Process above setpoint, ramp down output to allow process to cool.

4-20ma is a decrete signal not a continous ramp signal. dont make a mistake. its a code sequency. and canb e convert to analog signal by convertor.

pid was include in controller. of casedu feedback control.

this code can be pwm or other type. we ususally use pwm sign. its simple and universal. the convertor is simole it can be control ed directly by amplifier to drive scr k terminal.

Fine. Then a thermostat is not needed, and a 3-term controller is needed instead. Has the client specified the type of control to be adopted: minimum overshoot? Fastest approach to setpoint?

Eurotherm produces units that will do this (usual disclaimers apply). These units have a self-tune function. There is no need to reinvent the proverbial wheel.

Try this site.

It is kind of a small heater, but I think you can find a manufacturer offering an off-the-shelf product for your application. Most SCR electric heat controllers take a 4-20 ma or 2-10V signal. The output is pulse width modulated based on the input signal. I recall one mfg stating that their SCR or Triac would switch when the instantaneous current flow was 0 to minimize line noise.

Indeeco webpage says they have models down to 5 amps.

Abbas,

About this close-loop circuit, try to this site http://www.fastron.com.au/f310-cat.pdf

might this will help.