PXIe-4309 flexible resolution read in program uncorrectly

[YuWang822]

Hi all,

I'm using PXIe-4309. I read the spec and it says that PXIe-4309 has a flexible resolution which depends on the sample rate, but I didn't find a document explaining the relationship between them. So I tried to read the ADC resolution in example vi by adding a property node, as shown below.

I tried some devices with inflexible resolution like ni-9215, PXIe-4499. The result is the same as the spec.  

But with PXIe-4309, I tried the sample rate 2~2M S/s, the result was always 31 while the measure resolution on spec is 18~28 bits.

Can anyone explain the reason or provide me a document of how PXIe-4309 resolution change per sample rate?

Thanks in advance.

[VA.KI]

Hello YuWang822,

There is no open document.

The resolution flexibility lays on methodology, using appropriate signal conditioning, in face of block terminals like: TB-4309 and properties like: Chopping and Auto Zero that module has.

In short, ADC resolution of the NI PXIe-4309 is 18 bit and can operate up to 2 MS/s/ch.

• By using a single channel per ADC you remove the potential for ghosting or capacitive discharge during muxing to affect measurements.
• In order to obtain the best resolution, the PXIe-4309 will average as many converts per channel as possible over the course of a sample period. A slower sampling rate results in more converts per channel, yielding a higher resolution per sample.
• Two noise canceling techniques, Autozero and Chop, which can be used to reduce noise and remove offset voltages.

The main idea is the following: there are two concepts/ideas/types of resolution. There is 'resolution' which is based on the number of bits used to represent the input signal. This is generally limited by the bitness of the ADC or averaging can increase the relative number of bits used for the measurement.