TEC controller using analog proportioning controller

Thread Starter

Donahue851

Joined Mar 21, 2018
2
I am trying to build a temperature gradient apparatus for a laboratory experiment using 2 Peltier devices (approximately -15 C to -5 C gradient). High stability is needed. I have two Omega CN745 analog proportioning PID temperature controllers that output 4mA - 20mA DC control signal. I was thinking that I would be able to find an amplifier board that would have the control signal input, DC power input, and a proportioned output signal to power TEC. I am having a hard time of finding such a product and was looking for some advice. Should I be using a time proportional type temperature controller with a relay instead? In this case, I worry about stability as well as cycling the TEC on and off.

I am using a TEC1-12707HT
Imax = 7.4A
Umax = 15.4 V
Qmax= 75W

Any guidance on this project is be appreciated.
 

Thread Starter

Donahue851

Joined Mar 21, 2018
2
Wouldn’t a PWM amplifier basically turn an analog signal into a switching on/off signal? My intention with buying the analog PID temp controller was to be able to have a linear gain, which I think would have better stability than switching on/of system. If I was going to go with a time proportioned on/off signal (PWM), wouldn’t it be easier to use a time proportioned temperature controller with a relay instead? Omega Engineering makes the same temperature controller I have but as a time proportioned (CN742) vs the analog proportioned one I have (CN745).
 

MrChips

Joined Oct 2, 2009
23,080
An analog controller is not very efficient. The power that you do not want to go to the TEC has to be dissipated by the analog controller. Hence the controller runs hot.

A PWM switch is a better solution. A mechanical relay wears out eventually where as an electronic switch will last a lot longer. MOSFETs are either fully ON or fully OFF, much like a relay, but lasts a lot longer.
 

crutschow

Joined Mar 14, 2008
26,769
Wouldn’t a PWM amplifier basically turn an analog signal into a switching on/off signal?
Not if the PWM frequency is much higher than the control loop frequency response.
High frequency PWM driving the TEC will act essentially the same as a linear control if the PWM duty-cycle is linearly proportional to the PWM modulator dc (low frequency) input control voltage.
 
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