design of temperature regulator

Discussion in 'Homework Help' started by assuc, Dec 14, 2013.

Mar 23, 2012
77
1
Greetings,
Could anyone help me explaining the following circuit

Actually i have been assigned to build a circuit with pi controller to maintain the temperature set point of 40C of an incubator. the above is proposed to be used as the first stage before pi controller.
Explanation with mathematical relations would do great.

Last edited by a moderator: Dec 15, 2013

Mar 23, 2012
77
1
I have made the following pi controller design but in this the relay does not switches when temp goes above 40

What could be the problem?? Please figure it out asap.
REFERENCEhttp://www.ecircuitcenter.com/Circui...pid/op_pid.htm

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Last edited: Dec 25, 2013
3. Brownout Well-Known Member

Jan 10, 2012
2,374
999
Your schematic is too small to see.

Mar 23, 2012
77
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Now it can be viewed

Jul 18, 2013
13,160
3,630
Must be getting smaller?
Max.

Apr 5, 2008
17,127
3,001
Hello,

How are the opamps powered?
It can NOT be a single supply, as some of the inputs of the opamps are grounded.

Bertus

7. Brownout Well-Known Member

Jan 10, 2012
2,374
999
You don't need all those amplification stages. And what is the purpose of the U2 stage? You need one stage configured as a wheatstone bridge ( as the first stage in your textbook is configured ) and a transistor switch. Maybe one stage of amplification on the front end, but probably not.

Mar 23, 2012
77
1
All opamps are poered via a single 12volt variable power supply and all the grounds of opamps are common

Mar 23, 2012
77
1
Basically its a PI controller to control the temperature(as in this case 40 C) of the incubator box. U2 is the integrator whose output is summed up with the proportional controller output

10. Brownout Well-Known Member

Jan 10, 2012
2,374
999
PI controllers don't work with relays. That's you first of many issues.

Mar 23, 2012
77
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so what would you propose to control the ac incandescent bulb which is working on 220v 50Hz

12. Brownout Well-Known Member

Jan 10, 2012
2,374
999
I answered that in post #7.

There are many schematics that implement this simple control method. Quickly searching "opamp wheatstone bridge" and "temperature controller" should produce a torrent of information.

Apr 5, 2008
17,127
3,001
Hello,

As I told you before: the inputs of the opamps can NOT be put to ground on a single supply.
The opamps can NOT have any input voltages below the ground value.

You will need to compare the output of the LM35 with a reference voltage.
At 40 °C the output voltage of the LM35 will be 0.4 Volts.

Adding a hysteresis will prevent the relays from scattering.
On this page of the eBook you will find some info on this:

Bertus

Last edited: Dec 26, 2013

Mar 23, 2012
77
1
if that was the only case i wouldn't have posted here, its difficult for me to choose out of tons of schematics so this was the only source to seek infromation!