K type thermocouple sensor without MAX6675

Other Hardware Sensors
1

Hello,

I am exploring the MAX6675 thermocouple reader and i like that it can convert the millivolt signal that the T-couple outputs into a readable temperature.

I can order one of course, but I would really like to know if there was a way that my Arduino UNO can read the difference in millivolts by directly connecting the two metals into analog inputs.

First, is this possible that the arduino can directly read changes in volts this way?

Second, would there then be a way to insert a library to the arduino that converts the millivolt reading to actual temperature in celcius?

Third: is the code to perform this already on the web somewhere?

Thanks in advance!

2

I would like to describe what im trying to do as well: i am trying to get a real time reading of a small heat fin that is attached to a thermoelectric plate. I want temperature readings of both hot and cold sides which both sides have heat fins.

and I would like to add this to my questions,

I explored the LM35 temperature sensor. I understand that this sensor is probably best for reading ambient air temperature.

Can i actually just use this on the heat fin? for example, using thermal paste, to attach it to the fin, solder extension wires to the power, gnd, and the input pin?

once again, Thanks in advance!

3

Yes to the first two questions in the OP, with extremely poor accuracy and resolution. Consult the K-type thermocouple table to see the problem.

4

Yes, I am aware of the K-type thermo couple tables. I think my question about if it can be done was more of a, "how do i insert a conversion table into my code?" but i can look at other threads here in the forums.

Now, i noticed that a MAX6675 takes up 3 digital pins. Is it possible to get the readings of two different thermocouples simultaneously? The next beggin question is also , i would need two MAX6675 modules to take 2 temperature readings on the same arduino UNO board.

correct?

Thanks

5

Hi,
What range of temperatures?

The easiest to use is the DS18B20. You can connect several to a single Arduino pin.

See THIS for Information.

See THIS for how-to connect multiple sensors.

You can epoxy the TO92 sensors to a metal fin etc. The waterproof versions can also be epoxied on; I use these on metal pipes.

6

I think my question about if it can be done was more of a, "how do i insert a conversion table into my code?"

Clearly, you do not understand the problem.

You can measure voltages to about +/- 1 mV using the ADC and the 1.1 V internal reference.

This corresponds to about +/- 30 degrees Celsius error in temperature measurements, using a naked K type thermocouple, neglecting the additional reference junction problem.

So, your proposed connection method might be able to tell the difference between room temperature water and boiling water. No one would do such a silly thing, so you won't find code on the web. Use a thermistor instead.

7

jremington,

Thanks for the input. I did not know the severity of the error caused by a naked K type setup.

Would a thermistor setup, with some basic coding of conditions, be easy to set up with a relay? i need the temperature feedback to arduino so it can send signals to a relay to open and close under certain conditions.

Thanks

8

terryking228,

The TO92 sensors would work with the DS18B20 interface? and you can attach more than one DS18B20 to the interface? did i get that right?

And what is the advantage of using the DS18B20 over the K type thermocouple with the MAX6675?

THanks,

9

Would a thermistor setup, with some basic coding of conditions, be easy to set up with a relay?

Of course. Google "arduino thermistor" for thousands of how-to articles.