The generally maximum magnification of operational amplifier

[Rachel_Anne]

I need to make a thermocouple signal amplification circuit. I use a k-type thermocouple, LM324 operational amplifier, and output voltage required to be between 0 and 5v. I use two operational amplifiers to form a subtractor first to reduce the thermocouple with the minimal output of 4.096mv to 0, and then a non-inverting amplifier is used to amplify 600 times in one go.
Whether there are problems or not when I do that. I am afraid that if the magnification is too large to cause serious distortion of the signal. Whether it needs to be magnified through multiple stages. Perhaps the plan itself has problems, such as the wrong device selection.

[hermit]

Generally this forum is about using Kicad software.

This site is generally more useful for actual project design:
https://www.eevblog.com/

Not saying you won’t get help here but you do sound like you would benefit greatly from a more general site where more topics are covered.

[JohnRob]

The LM324 is not the appropriate choice to deal with thermocouple signals.

1. The input offset is (the voltage that can appear between the +input and -input, should be 0 or at least very small) almost as large as your signal. Won’t be stable.

2. This is not a high gain amplifier. It is more of your garden variety general purpose amplifier.

I would suggest you use a “Type K, AD9485”. It is made for thermocouples and it has cold compensation (google it).

You can get an AD9485 on a board ready to go from a number of vendors on eBay.

And you should post in a more hardware topic board. I just happen to know about thermocouples and hoped I could help.

John

[Naib]

@JohnRob

I would suggest you use a “Type K, AD9485”. It is made for thermocouples and it has cold compensation (google it).

You can get an AD9485 on a board ready to go from a number of vendors on eBay.

Or, if the plan is to sample the data into some uP then considerer the ADS1118, which is essentially a AD9485 frontend with a SigmaDelta + Digital conditioning block exposing a SPI-type interface

[JohnRob]

@Naib

Or, if the plan is to sample the data into some uP then considerer the ADS1118, which is essentially a AD9485 frontend with a SigmaDelta + Digital conditioning block exposing a SPI-type interface

I have been using the MAX31855 board I purchased on ebay. I’ve had good luck with it in a Type K configuration. Also with an SPI interface.

I’ll have to look at the ADS1118 if only because of the dual channel capability.