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How to read temperatures using PT1000 with ADCPi ?

2798 Views - Created 05/10/2015

14/08/2015

Posted by:
Blindfreddy

Last edited: 05/10/2015

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I'd like to read temperatures using PT1000 sensors - seeing that the ADCPi already has an inbuilt voltage divider for each channel, is it possible to connect the PT1000 directly to 5V and one of the inputs ? I should think so, the PT1000 has 1000Ohm resistance at 0°C and varies from 900Ohm at -25°C to around 2000Ohm at 250°C, so probably need to crank up the gain to get decent range, but just wanted to check that I understand it correctly. Many thanks for your response.

14/08/2015

Posted by:
andrew

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United Kingdom

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The ADCPi should work with the PT1000 sensors.  The sensor would be in series with the 10K resistor on the voltage divider so at 0°C it would be 11K and at 250°C it would be 12K.  As the sensor would be in series with the input resistor the voltage would decrease as the temperature increases.

For this sensor the Delta-Sigma Pi may be a better option as it does not include a voltage divider so you can create your own with lower value resistors which will give you a bigger voltage swing and therefore better accuracy.  The Delta-Sigma Pi has a maximum voltage of 2.048V so can use the 5V rail to power the sensor as long as you pick a suitable divider resistor to bring the maximum voltage down below 2.048V.  We have a voltage divider calculator which will help you with picking a suitable resistor.  Using the Delta-Sigma Pi will also have the advantage that you can put the sensor on the ground side of the voltage divider which will mean the voltage will increase with the temperature making measurements simpler. 

AB Electronics UK Tech Support

14/08/2015

Posted by:
Blindfreddy

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Many thanks for the prompt response.  What makes the ADCPi attractive is that there is no soldering required.  Also, the bigger the resistance the lower the current and hence self-heating of t he PT1000.   I already have a working PT1000 circuit using an MCP3208 in place and had to solder a simple circuit with voltage dividers for each channel - but soldering it's still a pain, so the ADCPi is very attractive in that respect.  My software can handle both VCC and ground side by way of configuration, so no problem there either. And I only need accuracy to 0.5C. I'll order one soon !

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