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By volodesigns
#139379
I've got an application where I need to read two temperatures and one pressure (~ 10 times per second). The temperature is being read with a thermocouple (type K) (output .4 - 15 millivolts) and the pressure with a transducer (input 5V - output .5 to 4.5V) - not sure of the best way to connect these to the Arduino UNO - Looking at the MAX6675 for thermocouple but not sure about the pressure transducer or how to do the second thermocouple. Any suggestions on best way to go here ?

Thanks,
Tim
By Mee_n_Mac
#139490
The thermocouple will require a dedicated amp to bring the voltage up to something reasonable to digitize with an Arduino. You can use 2 of these or use the MAX6675s. With the latter, what's the issue ? Just use 2 lines for chip selects for each and let them share the clock and data line. It looks like the pressure sensor can just be divided down* and fed into an analog pin and digitized.

http://www.analog.com/en/mems-sensors/a ... oduct.html

*I think the UNO is a 3.3V part ? If so use a voltage divider to reduce what would be 5V out to ~3V into the UNO. If not just input the pressure signal into an analog pin, no divider needed.
By Philba
#139501
This is an easy project and you shouldn't have any problems (famous last words...). What temperature range(s) are you measuring? If it's below 200F or so, there are far easier and cheaper ways to do it. Not that thermocouples are particularly hard, they just need interface/conditioning chips that cost more than the ATMega chip and need some sort circuit board where as other temperature sensors can be fed directly into the analog pins.

The uno is 5V device so no translation of the pressure voltage needed.
By volodesigns
#139502
Philba wrote:This is an easy project and you shouldn't have any problems (famous last words...). What temperature range(s) are you measuring? If it's below 200F or so, there are far easier and cheaper ways to do it. Not that thermocouples are particularly hard, they just need interface/conditioning chips that cost more than the ATMega chip and need some sort circuit board where as other temperature sensors can be fed directly into the analog pins.

The uno is 5V device so no translation of the pressure voltage needed.
Thanks Philba,
I need to measure from around 50F to 600F - what would you recommend for the thermocouple interface ? The ATMega chip ? and I take it, I can plug the pressure transducer directly into the Arduino - is that correct ? Can you recommend a example project that may be out there ?
Tim
By volodesigns
#139503
Mee_n_Mac wrote:The thermocouple will require a dedicated amp to bring the voltage up to something reasonable to digitize with an Arduino. You can use 2 of these or use the MAX6675s. With the latter, what's the issue ? Just use 2 lines for chip selects for each and let them share the clock and data line. It looks like the pressure sensor can just be divided down* and fed into an analog pin and digitized.

http://www.analog.com/en/mems-sensors/a ... oduct.html

*I think the UNO is a 3.3V part ? If so use a voltage divider to reduce what would be 5V out to ~3V into the UNO. If not just input the pressure signal into an analog pin, no divider needed.
Thank Mee_n_Mac,
I'll check that site out.
Tim
By Philba
#139524
yup, that's definitely a job Mr Thermocouple. An arduino is fine for doing ADC and other stuff. The AD or Max conditioning chips will work fine though they are all surface mount, afaik. There's an older chip the AD595 that comes in a dip package but it's like $15 from even a disti. If you are comfortable dealing with SMDs, go for it - a relative bargain. Maybe it's time to learn , if you aren't.

Basically, all you will be doing is reading analog inputs so any arduino will be fine if 10 bits of resolution works ok for you. There are plenty of sketches doing ADC. As for thermocouple conditioning. which ever chip you choose will have lots of application information in the datasheet. Pay attention to the junction information (temperature and specific metals involved) as it can affect your accuracy if you don't. But don't worry, it's all spelled out and I think the newer chips take care of a lot of the details. Wiring it up is pretty simple, the inputs connect to the thermocouple and the outputs go to the analog inputs of the arduino. From there it's just readAnalog. Sounds like a fun project.
By volodesigns
#139532
Philba wrote:yup, that's definitely a job Mr Thermocouple. An arduino is fine for doing ADC and other stuff. The AD or Max conditioning chips will work fine though they are all surface mount, afaik. There's an older chip the AD595 that comes in a dip package but it's like $15 from even a disti. If you are comfortable dealing with SMDs, go for it - a relative bargain. Maybe it's time to learn , if you aren't.

Basically, all you will be doing is reading analog inputs so any arduino will be fine if 10 bits of resolution works ok for you. There are plenty of sketches doing ADC. As for thermocouple conditioning. which ever chip you choose will have lots of application information in the datasheet. Pay attention to the junction information (temperature and specific metals involved) as it can affect your accuracy if you don't. But don't worry, it's all spelled out and I think the newer chips take care of a lot of the details. Wiring it up is pretty simple, the inputs connect to the thermocouple and the outputs go to the analog inputs of the arduino. From there it's just readAnalog. Sounds like a fun project.
Thanks Philba - sounds good -yes, it is a fun project - got this heat engine that I need to optimize by understanding the hot temp, the cold temp and the pressure.

Tim