Analog frontend circuit for 4-wire RTD

Thanks Raymond,

As shown in the block diagram, I'm planning to use MCU's internal ADC in our application. I'm looking for lower-cost (< 2.5 US$) solution for analog front-end circuits (excluding ADC/MCU).

Can you suggest 4-wire PT100 design components for PT100 temperature sensing from -10degC to 140degC

Hi Sadashiva,

I am using American RTD temperature R figure with α = 0.00392. Due to low cost design approach, we are unable to use ADS1247/8 or similar IC.  

Enclosed is a low cost Pt100 RTD measurement solution. As you can see, Vout has very narrow range, which means that your ADC has to be high in resolution, and you have to maximize the ADC to utilize its conversion range. 

If this approach is not satisfactory, you may consider to adapt 3-wire RTD measurement system (which it can maximize the RTD's output range). But it will require two precision current sources (e.g. REF200). I did not find you 1mA precision current source in the configuration. A cost of precision current source will exceed your current design budget. We may have to design a current source with discrete components in order to meet your requirements. 

BTW, what is available supply voltage rails in the RTD design. 

Please let me know if this is what you have in mind. 

Best,

Raymond 

Raymond,

+24V, +5V, +3.3V available in my design. 4-wire measurement needed.

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I got below link on 4-wires PT100.

Can you suggest alternate low-cost parts (LM4140,LMP2011)? Please refer Figure. 1

 We’re looking for PT100 sensing of -10degC to 140degC

 A precision interface for a Resistance Temperature Detector (RTD) (ti.com)

Hi Sadashiva,

This approach is the same as what I proposed in the previous reply. The red boxed section is an instrumentation amplifier (IA), which is the same as INA317. In fact, INA317 will outperform the discrete IA configuration with LMP2011 or other op amps due to INA317's internal precision resistor matching,  and it only cost less than a dollar, see the captured image below. 

The blue circled part is 1mA constant current source. I did not suggest one because there are many options. If you want to proceed with the design, I can send you a simulation later. 

Best,

Raymond

Thanks Raymond for Prompt response,

Can you suggest alternate part to A1 & VREF ?

Please share simulation file with VREF, A1 & INA317 once it is ready

Thanks, This helps..!