Data Acquisition - RTD Sensor

[Shreyans]

I need to perform data acquisition for my RTD (PT 100) temperature sensor. My sensor is first attached to Broderson PXT 10 temperature converter and then to national instruments BNC 2090 - NI DAQ board.  

PXT 10 gives 0-10V DC as output, which is then supplied to BNC 2090.

As BNC 2090 reads only voltage, the DAQ gives certain voltage readings. I want to know how can I convert the obtained voltage reading through DAQ into corresponding temperature.

Currently I am using Callendar Van Dussen equation for the conversion. As I am taking a very low exciation current, the conversion gives me resistance values in thousand ohm, and hence I do not get the correct temperature value.  I have attached an image for reference.

Can somebody please help?

Thank you.

[johnsold]

The PXT-10 temperature converter probably does some or all of the conversion to temperature. Read the manual to learn how the 0-10 V scales to temperature.

Lynn

[Shreyans]

Lynn,

Thank you for the reply.

Unfortunately PXT 10 manual does not mention about the scaling technique. It just mentions about how the connections has to be done, and what are the output signal parameters.

I have attached the PXT 10 data sheet.

Thank you.

Shreyans

[johnsold · Accepted solution]

Shreyans,

Although the data sheet is not explicit, the implication is that the output (0-5 V) is linear over the selected temperature range. So 0 volts would represent - 50 C and +5 V would represent either 300 C or 100 C depending on the range. All you will need is linear (m*x+b) scaling to get the temperatures.

You should probably run some simple calibration check tests to verify that it works that way.

Lynn

[Shreyans]

Lynn,

Thank you for the suggestion. Actually I was doing the same calibration test. I tried the temperature measuremnet device to know the temperature measured by the RTD sensor and corresponded that to the output voltage. As the sensor is linear, I got a good graph from it. 

I was wondering if I can get the exact excitation current and the gain value so that I can use a defined algorith to get the temperature readings. But, i think this technique should be okay as per my requirement.

Thanks a lot.

Shreyans

[johnsold]

If you want to measure the current, substitute a precision 1000 ohm or 100 ohm resistor for the temperature sensor and measure the voltage. Calculate the curretn from Ohm's Law.

Lynn