how to connect thermocouple with a micro controller

RE: how to connect thermocouple with a micro controller

dougw — Tue, 18 Mar 2014 19:58:06 GMT

Hi Alex,

Thermocouples produce pretty low voltages - for example a K type might generate just over 6 millivolts at 150 degrees C. This means you need an amplifier with a gain of about 700 to get good resolution from your A/D converter. They only generate a signal that is proportional to the difference in temperature between the 2 ends of the wire, so you need to know the temperature at the amplifier end in order to calculate the temperature at the sensor end.

Another issue is they are not quite linear, so if you need the best precision you need to correct for the non-linearity. As other have mentioned thermistors might be a bit easier to use. Another alternative is a semiconductor temperature sensor like an LM35. They can measure up to 150 degrees C and have a high level output that does not need amplification. They typically output 10 millivolts per degree so 150 degrees would cause the output to be 1.5 volts. They are pretty simple to hook up - 3 wires - ground, 5 volt power and the signal wire goes to an A/D pin.

Doug

RE: how to connect thermocouple with a micro controller

gihu — Tue, 18 Mar 2014 17:27:29 GMT

Hi Alex,

If you need to use an thermocoupler, check this:

Thermocouple Amplifier MAX31855 breakout board (MAX6675 upgrade) [v2.0] ID: 269 - $14.95 : Adafruit Industries, Unique &…

Then you can read the temperature just over SPI.

You also can use thermistors or platinium resitance (PT100, PT1000...), take into account that that it will be easier if you use a platinium resistances because it is linear whereas thermistor are non-linear. So with a PT1000 you will need a formula like "y = mx + n", to translate between voltage measured to temperature, while with a thermistor I think you will need to create a table into your code or an extra circuitry to make linear the analog signal.

Hope it helps,

Miguel

RE: how to connect thermocouple with a micro controller

michaelkellett — Tue, 18 Mar 2014 08:43:00 GMT

You need to read up on thermocouples - try Google and Analog Devices web site for some basic information.

To use a thermocouple you need an amplifier and a cold junction. It's much easier to use either a thermistor or a platinum resistance sensor.

If you must use a thermocouple and can't make any sense of the AD's app notes then ask again.

This thermistor might do:

EPCOS - B57863S103F040 - SENSOR, MINIATURE, NTC, 10K

Image is for illustrative purposes only.
Please refer to product description

Manufacturer:: EPCOS
Order Code:: 1299930
Manufacturer Part No:: B57863S103F040

: Technical Data Sheet (258.01KB) EN; MK