accurate differential temperature measurements

[cooltools]

May I connect my RTD's in series to improve differential temperature measurement accuracy. I currently use an SCC RTD01 together with a DAQCARD. My differential temperatures are in the magnitude of 0.5 - 1.0C.

[JDesRosier]

Hello,

What exactly do you mean by �connect in series?� If you're looking to cascade the RTD's, this is not supported by the SCC RTD01.

I do have a couple of recommendations, however, for improving the accuracy of your measurements. First, you can over-sample the incoming signal and average the data. Second, you can upgrade to one of our SCXI devices. The SCXI module will provide higher accuracy than the SCC module, and you will want to use a SCXI-1102 coupled with a SCXI-1531 for current excitation. 

I hope this helps! Please let me know if you need further assistance. Have a great day!

Kind Regards,

Joe Des Rosier
Nation
al Instruments

[tlm123]

Hi:

Thanks for responding.

1. I'm not cascading the RTDs... you can connect RTD's in series to look a resistance that is proportional to a temp. difference as opposed to just an absolute temp. I was curious if you had application notes on this approach

2. Can you point in the direction of "over-sampling" notes -- I'm curious to learn more. Perhaps a sample vi.

3. The SCXI is beyond my budget at this time ... but I"ll keep that in mind. Can you quantify the difference in accuracy between the two systems

thanks again

tom

[JDesRosier]

Tom,

After reading your second post, I realize that you want to couple the RTD's in series. Originally, I thought you wanted to couple the modules in series.

Ok, you can place the RTD's in series, but this will not increase your measurement accuracy. If you decide to experiment with this setup, make sure you provide sufficient current excitation for both RTD's. What will happen is the experimental error you receive at the first thermocouple will be seen by the next RTD in series, so your error will not decrease.

I advise you to try the oversampling idea to increase your accuracy. 

You can use this accuracy calculator  to calculate the accuracy of a given SCXI module and compare this value to the measurement accuracy you're seeing with the SCC module.

I hope this helps! Please let me know if the averaging technique helps to increase your accuracy.

Best of Luck,

Joe Des Rosier
National Instruments

[cooltools]

Thanks.

Here is an example of RTD used to measure differential temp: http://www.sensorsmag.com/articles/0102/rtd/main.shtml
I've seen configurations like this recommended for differential temperatures.

I'll pursue the other leads -- thanks again.

tom