Some opinions on Arduino-PT100-TLK31-RS458 project


There's a project that i have to make and i would like to know your opinion on some problems that exist.
One part of the project (I will not bother you with the rest since there's no need) is that I need to take a value from the PT100 temprature sensor (RTD 3 wires) and send it to Arduino. However the PT100 is already conected to a TLK 31. This is a microcontroller with Display that shows the temprature value from the PT100.
I want to take this PT100 value to Arduino without bothering the PT100 - TLK 31 connection.
I also noticed (in the datasheet) that 3 pins of the TLK 31 is dedicated for RS485 connection.

So, Ι come to the substance:
How can I get the PT100 value to Arduino? Do I have to use RS485 pins from TLK 31 maybe with a RS485 module for Arduino to send the data from TLK31 to Arduino?
Can I just connect some wires simple on the PT100 to take the value?
I saw that RTDs sensors (like PT100) may need a kind of circuit before the Arduino input pin (bridge, op-amps). But if I use this kind of circuit on the connection of PT100 with TLK 31 won't I go bad the TLK 31's measurement?

I'm in the very start of the project so every opinion, idea, suggestion would be more than useful.
Whoever has some knowledge on this topic, it would be very nice to share it.
Thanks for reading my topic, I'm looking forward to see your opinions.
Good afternoon

You can try to connect your own circuitry to the Pt100, but this will require some electronic skills. You can find out easily if it works, when the TLK31 output does not change with your circuit attached/detached.

The RS-485 pins most probably can be connected directly to Arduino Rx/Tx pins, with the third pin indicating the current direction of transmission (send/receive), what's only required for RS-485 line drivers. You have to identify the Tx pin and the baudrate, and if characters are received, decode the temperature.

PT100 can be read directly by an arduino with some associated electronics.

Google on kelvin connection , both 3 and 4 wire.

A pt100 has a basic resistance of 100 ohms at 0 deg c.

It is possible to use the arduino a to d converter to read this.

However it needs some appropriate electronics according to application.

The reason for the kelvin connection (3 wire ) is to remove the effect of temperature resistance changes of the connecting wires.

PT resistance thermometers are capable of very precise measurement provided the associated circuitry is correct.

There are also some I2C or SPI PTC sensors available whith phenomenal accuracy available which can be read with the arduino with ease.

Directly attaching another circuit to the PT100 will not work.

The PT100 will already have a circuit connected from the TLK31 that is feeding current through the PT100.
Any loading will cause the reading to be inaccurate.

The manual for the TLK31 is attached.

Tom… :slight_smile:

MTLK31ENG2.pdf (1.19 MB)

Thanks for the answers. It seems that the solution is the serial connection between the TLK 31 and the Arduino (probably through the RS485 pins of TLK31). Although I read the manual of the TLK31, I don't know how to do this. TLK31's has got 3 pins (RS485). Do I have to buy the RS485 module for Arduino? And then just the 3 wires? And what about the code? Do I have to code only the Arduino to "ask" from the TLK31 for the data?
(sorry for my English). thank you again, I'm looking forward for your answers