Connecting a PT100 2-wire thin film sensor to PIC16F877A

[ah_loon]

Hi,

I am required to connect a PT100 2-wire thin film sensor to a PIC16F877A.
I am connecting the sensor to RA0 of the PIC. But it seems like my PIC is not getting any readings. Do I need to connect any other components? Please help me.

 

[ericgibbs]

Hi,

I am required to connect a PT100 2-wire thin film sensor to a PIC16F877A.
I am connecting the sensor to RA0 of the PIC. But it seems like my PIC is not getting any readings. Do I need to connect any other components? Please help me.

hi,
The PT100 is a resistive sensor, it will not generate a voltage for the analog input.

You need to make a half or full bridge with the PT100 as one of the elements.

The output from the bridge will require amplifying with a OPA.

Do you follow OK.?

 

[ah_loon]

Hi eric,
Yup, after reading through i understand that. do you have a sample circuit that i can follow to understand better?

 

[ah_loon]

hi,
The PT100 is a resistive sensor, it will not generate a voltage for the analog input.

You need to make a half or full bridge with the PT100 as one of the elements.

The output from the bridge will require amplifying with a OPA.

Do you follow OK.?

Hi Eric,
Thanks for the advise. after reading through, i understand that we need to use a opamp. do you have a sample circuit that i can follow to understand better?

 

[ericgibbs]

Hi Eric,
Thanks for the advise. after reading through, i understand that we need to use a opamp. do you have a sample circuit that i can follow to understand better?

hi,
Look at this option.
You did not state the temperature range so used -200C thru +200C

new image.

 

[ah_loon]

hi,
Look at this option.
You did not state the temperature range so used -200C thru +200C

new image.

Hi Eric,
Thanks alot. sorry i forget to indicate that the range is from -100 to 100 degrees.
Where do i connect the other end of pt100 and R3?

 

[ericgibbs]

Hi Eric,
Thanks alot. sorry i forget to indicate that the range is from -100 to 100 degrees.
Where do i connect the other end of pt100 and R3?

hi,
The 'triangle' symbol is 0V,,, R3 and the end of the PT100.

EDIT:
this plot is for -100C thru +100C.
If the Span is not sufficient I would recommend a 2nd OPA, the gain of the first OPA is ~214 already.

 

[ah_loon]

hi,
The 'triangle' symbol is 0V,,, R3 and the end of the PT100.

EDIT:
this plot is for -100C thru +100C.
If the Span is not sufficient I would recommend a 2nd OPA, the gain of the first OPA is ~214 already.

Hi Eric,
Thanks alot. i shall try it out.