PT100 Voltages

[Suraj143]

Hello I'm going to read the PT100 from a PIC A/D.

I have the resistance table attached.I need the voltage levels of 0'C & 300'C.It has only resistance values.

Thanks.

 

[Reloadron]

I have the resistance table attached.I need the voltage levels of 0'C & 300'C.It has only resistance values.

I do believe you may want to give this a read and gain an understanding of how a PRT works.

The voltage out will be a function of the current flowing through the resistance. At for example 0 Degrees C the resistance is 100 Ohms and I have a fixed current of 1 mA the output will be 1 mV drop across the PRT. If the current is 10 mA I would get 10 mV. This looks good till I get into trouble with self heating effect, I suggest you study up on that a little too.

Generally you could place your PRT 100 in a bridge circuit and then signal condition and amplify the output and then feed your PIC. Also don't forget to figure in the A/D bits of the PIC so you can understand your resolution.

<EDIT>

What is self heating?Pt100 are constructed of very fine wires or very thin coatings. The very small cross-sectional areas in the sensing elements will tend to heat when electrical current is applied.

Most of the Pt100 are specified to be operated with a current of 1 milliamp or less.

The test for self-heating as detailed by the European Standard IEC60751:2008 involves placing the sensor in a controlled temperature bath of water at a temperature between 0°C and 30°C with a liquid flow > 0.2 m/s and/or in flowing air with a velocity of (3±0.3) m/s. The sensor' s resistance is measured with the minimum current and then measured with current increased in steps.A typical range for self-heating in an industrial Pt100 is 30 to 60mW/°C.

</EDIT>

Also you may want to give this a read.

Ron

 

[Boncuk]

The PT100 is used for building management purposes in Germany with great success.

(e.g. temperature control of air movement systems or fire warnings)

However, running a fixed voltage across it the self-heating effect might reduce it's accuracy a lot at low temperatures.

It is normally used in a voltage divider, reducing self heating with increasing temperature due to increasing resistance.

Using a PT100 without a precision resistor in a voltage divider circuit is good for nothing!

Boncuk