NI 9201 Noisy Measurements

[Pacsoft]

Hi,

We are currently using a NI9201 cDAQ module for analog acquisition. We found out that the voltage levels read are too noisy. We thought it would be a ground loop, so used a battery instead but the noise is still there. The same happens even when we connect an analog input directly to the COMM pin: we expected to read zero volts but got little noise instead.

When we measure signals with our PCI boards there is no noise. In all cases we use a RSE configuration for both cDAQ and PCI based measurements.

Has the same happened to any one of you ?

Regards

[hoffiz]

Hi,

There are going to be some differences between the PCI boards and cDAQ boards. Since the cDAQ is a low cost solution its performance is not going to be exactly the same to, for example, an M series. The first we need to figure out if your noise is between specifications or not, you can find this information in the 9201 Manual page 16, also if you can post a picture of your result it will help us a lot troubleshoot your issue, specially the battery test result.

As you can read here: Input Configuration Modes for USB-9201 the 9201 only supports RSE:, remember that RSE is not recommended for grounded signal sources because of possible ground loops, although with the battery you should be reading the correct 1.25 volts since is a floating source, I would like to know the results if you decrease the sampling rate on you battery test.

Please take a look at this DevZone article Field Wiring and Noise Considerations for Analog Signals and check what type of source you are trying to read, you might need to upgrade to a NI 9205, 32 single-ended or 16 differential analog inputs.

I hope it helps