PT1000 shield

Sprigo · February 10, 2015, 4:14pm

So you Vin value should be around 1.711V. What voltage are you getting?

Sps84 · February 10, 2015, 4:23pm

I use extender module vIn pin 3.3

Sprigo · February 10, 2015, 4:30pm

What voltage are you reading on the analogue input pin at this line?

Sps84 · February 10, 2015, 4:36pm

Voltage 1.5516129032258064V
Voltage 1.5548387096774194V
Voltage 1.5483870967741935V
Voltage 1.5548387096774194V
Voltage 1.5580645161290323V
Voltage 1.5612903225806452V
Voltage 1.5516129032258064V
Voltage 1.5612903225806452V
Voltage 1.5516129032258064V
Voltage 1.5677419354838709V
Voltage 1.5580645161290323V
Voltage 1.5580645161290323V
Voltage 1.5483870967741935V
Voltage 1.5516129032258064V
Voltage 1.5548387096774194V
Voltage 1.564516129032258V
Voltage 1.5580645161290323V

Sprigo · February 10, 2015, 4:46pm

Assuming that the PT1000 is currently at 20.0 deg C and Vin is 3.30V this would mean that R1 is around 1216 ohms.

Looking back through your posts It doesn’t look like you are using a precision resistor for R1 so I suspect that the maths and methology is ok but you are seeing errors inherent in the setup due to tolerance and stray resistances.

What sort of accuracy are you looking to achieve and over what range of temperatures?

Sps84 · February 10, 2015, 5:02pm

It’s for a boiler pellet, but I bought this

Sprigo · February 10, 2015, 5:13pm

Take a look at this codeshare. https://www.ghielectronics.com/community/codeshare/entry/961

I don’t have a Max31865 to be able to test it with but it looks like you should be able to get this working.

Sps84 · February 10, 2015, 5:25pm

thanks for all Sprigo

Dave_McLaughlin · February 10, 2015, 10:18pm

Another option is to use a PT100 or PT1000 with an XTR105 to generate a 4-20mA output. The XTR105 datasheet has all the schematic and data to do this. You need to use precision (0.1% resistors) with it.

The beauty of this is that it can drive long cables so you can locate your CPU well away from the boiler and the input to the ADC is a simple 100R 0.1% resistor to ground.

I use this in a sensor to measure temperature in a water well with a pump. It can drive up to 3000ft of cable (with the right supply voltage of course)

You can buy off the shelf RTD 4-20mA modules that would be around the same price as your MAX board from eBay. I used the XTR105 as I need it small to fit inside a pressure housing.