K type thermocouple Amplifier needed

[baileychic]

Hi,

Can somebody show a K-Type Themocouple amplifier circuit with cold junction compensation using general purpose OpAmp ?

I tried to design one using MCP6002 but it is not working. My temperature range is 0 to 450 degree C.

I will be reading the output of the amplifier using Arduino Uno.

 

[asimov_18]

Use single chip solution like MAX31855

 

[baileychic]

I need cheaper solution.

 

[FvM]

I tried to design one using MCP6002 but it is not working.

Won't blame MCP6002 for the failure, although you might choose an OP with lower offset and offset drift. Why not show your design?

 

[DNA Robotics]

I don.t know if you can interface to it.
High Temperature Thermostat -30 to 999Deg. Sale: $9.95
https://www.mpja.com/High-Temperature-Thermostat-30-to-999Deg/productinfo/34687+MP

 

[baileychic]

This is the circuit I designed and it is working fine now.

 

[FvM]

Yes, basically O.K. As said, you would want to use a precision OP for the input stage. "Cold junction compensation" is a dummy yet, it should inject a temperature dependent voltage with 40 µV/K slope input related, respectively 10 mV/K after the preamp. Or use any available digital thermometer and perform the compensation in the digital domain.

 

[baileychic]

@FvM

Please mention some cheaper priced precision OpAmps.

 

[KlausST]

HI,

Go to an Opamp manufacturer, they usally have interactive selection guides...or a distributor's web site.

Klaus

 

[FvM]

A "zero-drift" (chopper stabilized) OP like MCP6V31 may serve the purpose.

 

[KlausST]

Hi,

The circuit of post#6 doesn't include an cold junction compensation.
Thus the output accuracy is wrong by the cold junction temperature.
And the output is as precise as the cold junction temperature.

All in all not a very precise measurement method.
Thus your Opamp doesn't need better specification than the method.

This means: you don' need an Opamp with better than 25°C or about 1mV
And the drift doesn't need to be better than 40 uV/K.

You can safe money by omitting the second Opamp, because it is useless in your circuit.

Klaus

 

[baileychic]

Klaus can you provide a better circuit with MCP6002 with cold junction compensation ?

 

[KlausST]

Hi,

I used a LinearTechnology device with analog output and a Maxim device with digital output. Both fairly accurate, but not cheap.

A special high precision Opamp usually isn't as cheap as a general purpose Opamp.

Circuits, discussions, application notes....are easy to find.

Klaus