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8-channel thermocouple acquisition with myRIO

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8-channel thermocouple acquisition with myRIO

Hi, I've tried to find any example on the internet with thermocouple reading for myRIO - with no luck. The thing is I need a temperature logger for eight thermocouples as quick as possible. I've got myRIO which has 8 analog inputs, but there will be problem with the cold junction compensation, right? Should I use the MAX6675 interface (or equivalent), or there is chance to interface "bare" thermocouples with myRIO analog frontend? Than You in advance for reply. Best Regards Mike
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Accepted by topic author mgrzelczak
‎03-20-2017 06:15 AM

Re: 8-channel thermocouple acquisition with myRIO

Dear Mike,

 

if we are speaking about regular thermocouples, just compare their characteristics with the specifications of myRIO analog inputs, and you will see, that it is not sufficient to be able to read temperature using thermocouples with sufficient precision (also accuracy). Not to mention the cold junction compensation as you wrote.

 

You can use the mentioned MAX6675, but be aware, that it uses SPI - most probably you can wire together the SCK and SO pins together, but you need separate DO for each CS of each MAX6675 (and most probably you will need to program the FPGA on myRIO).

 

Think about you needs, and maybe it would be also possible to use something simple - as MAX6666 that is a temperature sensor with PWM output (each sensor needs just power and one DO line on myRIO). To measuring PWM on FPGA is much easier then to detect some protocol. There are also other active sensors that output frequency, or analog in range sufficient for myRIO AI's, or so... So if you don't need to measure high temperatures, consider different sensors, that you could use directly with myRIO, or consider different HW (e.g. NI-9213 in a one slot USB cDAQ chassis like 9171).

 

B/R

Jozef Lipták
NI AE-CZ/SK
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Re: 8-channel thermocouple acquisition with myRIO

Dear Jozef, Thank You very much for fast response. I've just bought the MAX6675 modules and they may do. This solution is fair enough for temperatures up to 700 - above it introduces greater error. Actually the program works and I am happy with that ; ) Regards Mike
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Re: 8-channel thermocouple acquisition with myRIO

Welcome. If the last post can be considered as some answer, you can mark it as a solution. Thanks and good luck with your projects Smiley Wink

 

B/R

Jozef Lipták
NI AE-CZ/SK
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