hi guys:
I have a question about different wires pt100. Is there any difference between 2, 3, 4 wire pt100? If so, what are the differences. How to wire them. Can they be replaced by other type of pt100?
I've used them with MAX31865,
connected in 2 wire more.
datasheet shows how to wire up for 2,3,4 wire modes.
As to why a particular mode:
A 2-wire connection (see the Typical Application Circuits)
can give acceptable results when the RTD is located
close to the MAX31865. Note that, for a PT100, series
resistance of 0.4I causes an error of approximately 1NC.
Therefore, as the cable length increases, the error due to
cable resistance can become excessive.
The 4-wire connection eliminates errors due to cable
resistance by using separate force and sense leads.
A 3-wire connection is a compromise approach that
uses one less conductor than the 4-wire approach. To
compensate for the voltage drop across the return wire,
the voltage between FORCE+ and RTDIN+ is subtracted
from (RTDIN+ - RTDIN-). This is accomplished using
the FORCE2 sampling input. If the cable resistances
are well-matched, the error due to cable resistance is
cancelled. Select 3-wire operation by setting the 3-wire
bit in the Configuration register to 1.
Thank you CrossRoad. I have a 3 wire pt100. Is there any other way to connect it to MAX31865?
I am only aware of what is in the datasheet.
You could look at this also
I have a ADS1115 which I bought from adafruit. Is there any way I can connect 3 wire pt100 to this ADC?
I suppose - wire it up like the app note.
To: CrossRod
I saw this chip. It's MAX31865. Do you know where I can get the library for this chip. This chip is design for RTD-to-Digital convertor and the data sheet it's also provide the connection of PT-100. Do you have any idea about writing or finding the library?
When I was doing a 15-chip board, see attached, I got this code from MAXIM for the MAX31865.
I integrated it with my code for a 15-chip loop.
I tried using TXB0108s for level shifting. Didn't exactly work. MAX31865s didn't have enough drive for their SDO to go back thru the chip, and the TXB0108 didn't have enough drive for SCK to come out clean. Had to rework the board to resolve those.
max31865Hani.ino (9.97 KB)
