Reading Analog Sinyal From RTD(PT100)...

omeraygor said:

I want to use MSP430 including Delta-Sigma ADC. Which one can i use?

Alls MSP with an SD16 module :)
The product selector available on the TI MSP430 home page allows you filtering the MSP family for MSPs with SD16/SD16A module.

For 4-wire PTC usage, you usually want to put an impedance transducer between the PTC and the MSP, but the PT100 has a low enough impedance so that the comparably low input impedance of the SD16 doesn't count.

However, getting a voltage high enough to give a significant signal on the SD16 (even with an input amplification of 32, as some SD16 offer), will require a relatively large current through the PT100, which in turn will influence the sensor readings. (several 100µA  give several µW internal heating, without amplification, this will enlarge to some mW!)

So I suggest using an external OpAmp that amplifies teh PT100 voltage by a suitable factor (e.g. 100). It will be more precise than the internal amplification of the SD16 too and give a better SNR.

Hi Micheal.

Nİce to meet you again.

I looked into some ICs that include Sigma - Delta ADC and suitable to measure RTD. These is AD7714 and AD7730.

These have opamp and Sigma - Delta ADC block.

What about your opinion?

In the circuit above, teh OpAmps are used as a (not 100% but nearly) constant current source (the current changes with the resistance of RTD, but with a factor of 200 less). So the voltage over the RTD changes linear with the temperature. Ref- is Vin and Ref+ is Vin +2V. Power over the RTD is 1µW

However, the voltage over the RTD is only 10mV, which is really not much.  So I would still suggest an external  amplification by a factor 100.