PT100 Temperature not getting correct output

[saiamar]

I am using RTD 2 wire PT100. it is a +ve temperature coefficient (PTC) type that means when temperature increases the resistance also increases. I am checked temperature sensor at normal room temperature. It is showing 110 Ohms in the multimeter. when the temperature is applied to the sensor. the resistance also keeps on increasing. but in the program, I am not getting proper output. I connected the circuit like a pulldown with a 15 Ohm resistor. if you have a proper code please send me. I want to read the ADC signals and after that, I have to convert to the voltage, resistance, and temperature by using formulla.

[pert]

I moved your topic to an appropriate forum category @saiamar.

In the future, please take some time to pick the forum category that best suits the subject of your topic. There is an "About the _____ category" topic at the top of each category that explains its purpose.

This is an important part of responsible forum usage, as explained in the "How to get the best out of this forum" guide. The guide contains a lot of other useful information. Please read it.

Thanks in advance for your cooperation.

[TomGeorge]

Hi, @saiamar
Welcome to the forum.

How to get the best out of this forum

See also FAQ - Arduino Forum for general rules on forum behaviour and etiquette. Hello, Welcome to the Arduino Forum. This guide explains how to get the best out of this forum. Please read and follow the instructions below. Being new here you might think this is having rules for the sake of rules, but that is not the case. If you don’t follow the guidelines all that happens is there is a long exchange of posts while we try to get you to tell us what we need in order to help you, which is fru…

What controller are you using?

Have you Googled;

arduino pt100

Tom..

[jim-p]

@saiamar

I connected the circuit like a pulldown with a 15 Ohm resistor.

Can you show a quick picture / hand drawn sketch of how you have it connected?

[johnerrington]

@saiamar

I connected the circuit like a pulldown with a 15 Ohm resistor

Its better to describe ypur circuit with a schematic. We need to know the supply and arduino connections. Also please show us the code you are using.

How to make a schematic you can post.

When you submit a question on the forum you will usually need to add a schematic (circuit diagram). The tutorial that follows will explain some ways to create a useful image; however lets start by explaining how to add the image to your post. Its easy. Having created the image all you need to do is : Save the image somewhere convenient - maybe your desktop Start your post, and place the cursor (insertion point) where you want the image to be shown; [upload image to forum] 3: click th…

@saiamar

if you have a proper code please send me

To start use the example to read a value from the adc.

@saiamar

in the program, I am not getting proper output.

you will need to show us your code.

[Wawa]

A PT100 sensor doesn't have enough resistance variation to be properly read with an Arduino A/D. You need a specialised chip, like the MAX31865, between sensor and Arduino.
Leo..

[JohnRob]

Assuming you are using a 5V source, with a 15 ohm series resistor you are putting too much current into the PT100 sensor. You will have to look at your sensor spec for the recommended max current.

Also you should calculate the PT100 resistance change for 1 °C and calculate the input voltage to your ADC. I recall it is a little less than 1/2 ohm per °C

Now assume you have a 100 ohm series resistor, calculate the voltage at 0 °C and 1 °C. Compare this to the ability of your ADC to read small voltage changes.

I know what I've said is not a "out of the box" solution but with a little investigation you will get the information you need and at the same time learn what matters when making a measurement of this type.

[Wawa]

@JohnRob

Also you should calculate the PT100 resistance change for 1 °C and calculate the input voltage to your ADC.

About one A/D step per degree C at room temp with a 110 ohm pull up resistor and a 10-bit A/D.
Worse if the fixed resistor has a higher or lower value than that.
A DS18B20 has a 15x higher resolution.
Leo..

[johnerrington]

We dont know the application (or much else).
Generally the 31865 looks a good way to get useful readings.

MAX31865.pdf