Temperature datalogger plot a real time graph on a PC Help with MuxThermocouples

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1

Hi I am building a temperature datalogger that will plot a real time graph on a PC.

The basic spec is:-

  • 13 Channel data logger with K-Type Thermocouples
  • Measure Temperature range 4c to 120c at a resolution 0.01c
  • Sample rate 4 readings of all channels per second
  • Arduino – Sends all 13 Temperatures over USB Serial communication to Laptop running a Visual Basic Application plotting real time temperature graph, saves and loads results.
  • The thermocouples are placed across a thermal block to validate temperature across the block and measure temperature non-uniformity.

So far, I have the programmed an application with Visual Basic that plots the data and saves the plot and can load a saved temperature trace.

I have used the Maxim DS18B20 temperature sensors instead of thermocouples basically because I could buy some so cheap it was worth it to prototype a sketch on the Arduino that would read temperatures and send them over serial communication via the Arduino usb port and to create the visual basic application to validate the temperatures and plot them.

Now I have this side working I need to take the plunge into using thermocouples and understand the need for cold junction compensation, for the resolution I think I’m right to say I need a 20/24 bit ADC.

I also will need to multiplex the thermocouples.

I am struggling to find any boards that will fit the spec does anybody know of any suitable boards or solutions, even if I build the circuit myself?

Any help, advice, nudge in the right direction gratefully appreciated…….

2

Something like this has been asked before.

Try Googling something like "thermocouple 0.01C site:arduino.cc"
Leo..

3

Wawa:
Something like this has been asked before.

Try Googling something like "thermocouple 0.01C site:arduino.cc"
Leo..

Had a google and have been trying myself to find a solution but still struggling to find something suitable...

Would anyone know:-

Would the Mux II board from Mayhew Labs work for multiplexing Thermocouples?

4

https://www.amazon.com/Arduino-Thermocouple-Multiplexer-Shield-MAX31855K/dp/B00I0HEWJUhow about

5

So you did't see in those posts that you Googled that what you're asking is almost impossible.
AFAIK a MAX31855 has a resolution of 0.25C. You're asking for a 25x increase in resolution.
Leo..

6

I'm not sure about the speed part but the Iowa Scaled Engineering LTC 2499 shield will do most of what you want.
http://www.iascaled.com/store/ARD-LTC2499

7

0.01C accuracy with a thermocouple? Nope, that's not going to happen:

I doubt the resolution of 0.01 is useful/meaningful for a device with a basic accuracy of
about 1 degree. The DS18B20's might be better. Although if you're looking for detecting
small changes it might be reasonable to want a massive amount more resolution than
accuracy.

[ pet peeve: c is the speed of light, C is short for centigrade/Celcius. ]