PCI-6033E Resolution Question

[arj]

I'm trying to read approx 57mV with a PCI-6033E and an SCB-100 signal conditioning box.  I use the test panel in DAQ MX and set the range from 0-.2V and differential as the input type. The readback is all over the place from 30mV up to 80mV. Is this card capable of giving me better resolution than this? thanks

[Wilfried_71]

If you have a look in the product manual, you can see that the card is able to select the 0-2V range (so your choice is good) and A/D converter have a accuracy of 16 bit, so 65536 points on the selected range. So you have a accuracy voltage of 2 / 65536 = 0.030 mV !!

[arj]

The range is set from 0-200mV not 0-2V so the resolution should be like 3mV

[Wilfried_71]

Yes, it works too. Have a look to the NI 6030E/6031E/6032E/6033E Family Specifications that you can find on the web site of NI to see what is the available gains.

[AnalogKid2DigitalMan]

arj- I think you slipped in the units

0.2/65536 ~ 0.000003 = 3uV (microvolts).

You may be picking up external noise if your signal is still drifting or not what you expect it to be.

[arj]

Thanks, I'll look into the possible noise issue.

[Mark_E]

Hi arj,

There’s a difference between accuracy and resolution. Resolution is the voltage range divided by 2 to the bits of resolution, whereas accuracy is the specification you use to determine the overall uncertainty of your measurement. Absolute accuracy specifications apply only to a successfully calibrated device and within a specific temperature range. The considerations for accuracy are better described by this Developer Zone document: Accuracy.

So, some questions that may help guide you to a successful reading include:

1.       1. When did you last calibrate (internally or externally) your card?

2.       2. What is the environment like where you have your measurement system?

3.       3. What is your input signal? There may be other noise considerations to consider depending on what it’s like. (See Accuracy.)

4.       4. Do you get a stable measurement when measuring something very stable, such as a battery?

The Differences Between Accuracy and Bit Resolution

The links I’ve included in the body of the message are very helpful resources, but feel free to repost if you have further questions.

Message Edited by Mark E on 01-04-2008 01:33 PM