Greetings every one
I am currently working on a simple RTD Temperature sensing setup , so far i am following this article , i have built the exact same circuit , the only difference is that i am using 3 wire PT100 RTDs insted of the 2 wire PT1000 RTDs used in the article , and now i am stuck with the 3rd wire of the RTDs witch is supposed to reduce the error cused by the RTD wires.
Any advice about how should i modify the circuit in the article to add the 3rd wire to the system ? thank you.
PS : The 3 wires colors are Red, Black , and Blue.
weedpharma:
Look here
http://www.temperature.com.au/Support/RTDSensors/OperationMaintenanceInstructions.aspx
It may help.
Weedpharma
Thank you so much for the link.
So as i understood from the wire setup in the link you shared , i am supposed to connect the red wire to the Vcc and both the black and blue wires to the ground ? am i getting this right ?
The RTD is simply a variable R. It will need to be connected as you would any other variable R. It will need to be part of a voltage divider from 5v, input and ground. You will need to use a suitable R from 5v to the RTC and input, to give a usable analogue read.
Use your multimeter to confirm two of the wires are connected together then you can ignore one of them (unless you require super accuracy).
I will leave it to others to recommend a suitable divider R as the RTD has a low R. Please measure the room temp R of the sensor and let us know what it is.
Weedpharma
Greetings
Thank you weedpharma for you advice , i assumed that i will simple connect the 3rd wire to the ground as the 2 other wires will provide the resistance i need.
For the voltage dividing circuit , i used a 1000 Ohm resistance to account for the RTD resistance at 0 degrees witch is 100 Ohm , then connected the output to a low pass filter as shown in the link i referred.
I will need to wait till i get my hands on a multimeter to make sure that i selected the correct 2 wires , and to complete the calibration explained in the article.
I would love to have any advice from any member who already tried to use the 3 wire RTD.
Thanks once more weedpharma 
!
If you use 1000 ohms from 5v to input and RTD to ground, you will only get a max analogue reading of 100 to 150 rather than 1023 max available.
However if you use the lower reference voltage of 1v, you can get much higher resolution.
I have not used this reference and I would prefer someone more experienced to suggest suitable resistance to use when using the lower reference voltage.
Weedpharma
weedpharma you are the best !
Well , i am sure i am using the full 1023 resolution , because the difference amplifier is used to scale the output to the full range of the Arduino analog input.
You can review the whole circuit and setup in the article , its all well explained and pointed out.
Thank you so much once more for your care and help weedpharma <3
I missed the bit about using the amplifier. In that case you can forget the R from 5v to input.
Weedpharma