Design of a thermocouple temperature measurement circuit

[steve1]

Hi,

I am trying to design a temperature measurement system using thermocouple that can measure process temperature between 50 to 150 degree centigrade.

The required output range is 0V - 10V. Non- linearity of less than 1% is desired and a resolution of 0.5%.
The ambient temperature range is 0 to 25 degree centigrade.

Pls I will like to know the required signal conditioning and the appropriate circuitry.

Looking forward contributions here.

Regards

 

[erikl]

Is it really worth to design such a system if you can buy it for less than 50 bucks , incl. NiCr-Ni (K-) sensor and display?

 

[steve1]

Is it really worth to design such a system if you can buy it for less than 50 bucks , incl. NiCr-Ni (K-) sensor and display?

Hi,

Thanks for the contribution, but I'm to design it as part of a project I'm doing. I'll welcome any hint you can give

 

[BradtheRad]

An op amp is suitable as an amplifier in this case. Sounds as though you want to detect a fraction of a volt and multiply it by 100 or so.

Some situations call for an instrumentation amplifier which a hobbyist might build from three op amps. Or else it's available in one package.

There's the question whether your thermocouple can deliver linear performance across your temperature range. If not then you may need to tailor a feedback circuit to achieve linear response.

Try a search at this board on 'thermocouple'.

 

[steve1]

An op amp is suitable as an amplifier in this case. Sounds as though you want to detect a fraction of a volt and multiply it by 100 or so.

Some situations call for an instrumentation amplifier which a hobbyist might build from three op amps. Or else it's available in one package.

There's the question whether your thermocouple can deliver linear performance across your temperature range. If not then you may need to tailor a feedback circuit to achieve linear response.

Try a search at this board on 'thermocouple'.

The thermocouple i want to use is linear between the temperature range i want to measure.(50 - 150 degree celsius)

My main challenge is how to design the cold junction compensation and add an offset voltage adjustment on the instrument amplifier such that the output voltage is 0v at 50 degree celsius and 10v at 150 degree.

Expecting your inputs.

Regards.

 

[BradtheRad]

You can adjust the op amp to give zero output for small input, by putting a potentiometer across the zero offset pins of an op amp.

There's these recent discussions on how to amplify a thermocouple output:

https://www.edaboard.com/threads/211197/

https://www.edaboard.com/threads/208996/

 

[pr978]

You can adjust the op amp to give zero output for small input, by putting a potentiometer across the zero offset pins of an op amp.

There's these recent discussions on how to amplify a thermocouple output:

https://www.edaboard.com/threads/211197/

https://www.edaboard.com/threads/208996/

Hi, Did you manage to design it? I am doing same project now and stuck with same question how to get 0V output at temperature where thermocouple gives some out put. I thought of using offset but that is not ideal as it will give negative reading for temperature measurement below my set temp.

 

[BradtheRad]

Hi, Did you manage to design it? I am doing same project now and stuck with same question how to get 0V output at temperature where thermocouple gives some out put. I thought of using offset but that is not ideal as it will give negative reading for temperature measurement below my set temp.

1.

If you adjust the amplifier to give 0V output when the thermocouple is just beginning to give some output...

then it makes me wonder if a thermocouple can produce negative voltage?


2.

A helpful strategy is to draw a graph of input V versus your desired output V.

3.

If you don't want negative output, then give the op amp a single polarity supply. Use a model of op amp that can work on a single supply, meaning that it can produce output all the way down to 0 V.

 

[pr978]

Hi I have done it using op non inverting amplifier with use of ref voltage. It worked on paper need to try practically. Any one had any experience of it, please share. Much appreciated.

1.

If you adjust the amplifier to give 0V output when the thermocouple is just beginning to give some output...

then it makes me wonder if a thermocouple can produce negative voltage?


2.

A helpful strategy is to draw a graph of input V versus your desired output V.

3.

If you don't want negative output, then give the op amp a single polarity supply. Use a model of op amp that can work on a single supply, meaning that it can produce output all the way down to 0 V.