PT100 temperature sensor

Hi everybody ! :slight_smile:

I know this is not the first time you see this subject, but I would like to read your concerns about my project. Thx for your time !

I need a sensor to get the temperature of the water in a pipe. The only cheap sensor I found that answers my needs is a PT100 :

http://fr.rs-online.com/web/p/capteurs-de-temperature-a-resistance-platine/6084492/

To get the data, I think I’m gonna use an Arduino Duemilanove, I have not decided yet. But what is sure is that I will have a 5V output on by board, analog inputs, and a ADC in the board (maybe 10 bits, surely more).

Now I want to get the values returned from the sensor. I use a voltage divider to get the voltage in relation to the impedance of my sensor, with a 10k resistor to avoid heating up the sensor (and get wrong values hehe 8) )

But with this divider, the voltage in output is so low I think it’s impossible to read the right values (a few mV !). So I found out two ways to get rid of this problem :

  1. Have a better ADC

  2. Amplify the signal, the solution i chosed. I would like to use a non-inverting amplifier with an Operational amplifier, do you think it could work ? I can’t test my work I’ve no components yet… Here is attached a schematic of my work. Do you have any better simple schematic to amplify the signal ?

PT100.png

slash-07:
. The only cheap sensor I found that answers my needs is a PT100 :

http://fr.rs-online.com/web/p/capteurs-de-temperature-a-resistance-platine/6084492/

That sensor costs about ten times what most other people are paying, and I suggest you look a bit harder.
The only reasons for using a PT100 are that you need very accurate readings more frequently than about five per second. A DS18B20 is probably all you really need, costs just just a few dollars, and is a lot easier to use.

Nick_Pyner: That sensor costs about ten times what most other people are paying, and I suggest you look a bit harder. The only reasons for using a PT100 are that you need very accurate readings more frequently than about five per second. A DS18B20 is probably all you really need, costs just just a few dollars, and is a lot easier to use.

You are right this sensor is expensive compared to the DS18B20 (I know I'm using DS18B20 for others parts of my project hehe :grin: . I could use a DS18B20 sensor and fix it to the pipe, with heat grease between the sensor and the surface. But I'd rather buy sensor built to do this job, and there are not many on the market ! Moreover, this sensor has to work 24/7 during months, maybe years ! A Hand made sensor is not optimal, I prefer pay more and have a better mean time between failure :stuck_out_tongue: .

Ive choosen these values for resistors : R1 = 10k, R2 = 100 ohms, R3 = 7k

slash-07: I could use a DS18B20 sensor and fix it to the pipe, with heat grease between the sensor and the surface......................A Hand made sensor is not optimal

You are definitely not looking hard enough........

http://www.ebay.com.au/itm/DS18B20-Temperature-Temp-Sensor-Thermal-Probe-Thermometer-Waterproof-For-Arduino-/400805445386?pt=AU_B_I_Electrical_Test_Equipment&hash=item5d51ddbf0a

http://www.ebay.com.au/itm/3m-Digital-Thermal-Tank-Sensor-Horizontal-DS18B20-PIC-Arduino-AVR-AU-Stock-/181596699960?pt=AU_B_I_Electrical_Test_Equipment&hash=item2a4801bd38

Nick_Pyner: You are definitely not looking hard enough........

http://www.ebay.com.au/itm/DS18B20-Temperature-Temp-Sensor-Thermal-Probe-Thermometer-Waterproof-For-Arduino-/400805445386?pt=AU_B_I_Electrical_Test_Equipment&hash=item5d51ddbf0a

http://www.ebay.com.au/itm/3m-Digital-Thermal-Tank-Sensor-Horizontal-DS18B20-PIC-Arduino-AVR-AU-Stock-/181596699960?pt=AU_B_I_Electrical_Test_Equipment&hash=item2a4801bd38

Those sensors are made to be put IN the water. I can't do that, my sensor must be put on the pipe

The first one works on a pipe just fine. It can also go in a thermowell.

Picture shows OUT in a thermowell and IN simply under an insulated sleeve