usb-6009 low resolution(for mV range) problem

[cherkose]

Hi 

I am using NI USB-6009 for a temperature measurement application. My analogue voltage input range is 0-100mV with 0.1667mV/°C. But the resolution of my measured values is  1-2mV. I changed the input range form -5 to5 Volt to 0 to 150 mV but I didn't see any change. Also averaging is not helping me a lot since I want an accuracy of less than 0.1667mV. I am also using differential mode. I read that this devices can not be calibrated.... What are the options to get an accurate result.

Tnx 

[Dennis_Knutson]

Have you looked at the specs?

You options would seem to accept the measurements you are getting or use a board that has much greater accuracy.

[JChec]

Cherkose,

U should be able to set the differential range to -1 to 1 V, I don't think setting your range lower than this will make a difference, your range will probably just coerce to -1 to 1V... 14 bits should give you a 0.122mV resolution on the ADC then.

[Seth_B.]

While 14-bits across the ±1V range will give a code width of 0.122 mV, code width is only one factor in determining the accuracy of a measurement.  Many other factors, such as noise & temperature add to inaccuracy.  As such, it's always best to refer to the absolute accuracy specifications listed in the Detailed Specifications for your device.  For the ±1V range of the USB-6009, the absolute accuracy is ±1.53 mV at 25°C.  As you move away from 25°C, this will get worse.

The USB-6009 is not designed to measure thermocouples, as thermocouples require high accuracy and precision.

Regards,