PT100 RTD interface

Hello.

I'm reading this note:

ww1.microchip.com/downloads/en/AppNotes/00687c.pdf (page 4, figure 5)

and I've got some questions:

If I use a 5V Vref.... will i get 0-5v measure? will Irref be 1mA again?

How can I get aprox 0 volts at -50ºC and aprox Vref at 350ºC? How can i tune the circuit to use all the ADC's range?

Thank you very much

PD: Page 5, paragraph 1 -- R10 and R11 set a gain of 7.47 V/V. -- I think that is a mistake. 20.0k / 3.09k = 6.47 I'm not sure because i don't now anything about opamps

PD2: I think that the solutions of my questions is near the filter and gain stage. Changing gain and adding offset, but I don't now how.

Thanks again.

If I use a 5V Vref… will i get 0-5v measure? will Irref be 1mA again?

Yes it looks like it to me.

I think that is a mistake. 20.0k / 3.09k = 6.47

Yes I get 6.47 as well.

I’m not sure because i don’t now anything about opamps

Well you know enough to spot the gain of the inverting amplifier was wrong. :wink:
Note that Fig 5 is not a full schematic, you will need a split power supply as well as some decoupling and a decent layout. That is don’t expect it to work well on solder less bread board.

Well you know enough to spot the gain of the inverting amplifier was wrong.

Am I right? ::)

Note that Fig 5 is not a full schematic, you will need a split power supply as well as some decoupling and a decent layout. That is don't expect it to work well on solder less bread board.

split power supply: I think you mean " a good Vref and GND". Can I use a 5v precision voltage reference for this circuit and for Arduino Aref?

Am I right?

Well i agree with you on the gain of that amp, so if you are wrong we are wrong together.

I think you mean " a good Vref and GND".

No a split power supply is one that has both positive and negative rails as well as a ground. This will have to be something above the Vref you want to use. Typically an op amp will have a +/- 12V supply.

MCP609 has +vcc and gnd only. Am I wrong?