Error in Sampling Rate NI9234

[Nickolayf]

1) Software Platform

- API Software and Version:

LabVIEW Signal Express 2011

Version 5.0.0

- Toolkits and Versions:  

- Operating System:

Windows 7 Enterprise 64bit SP1


2) Hardware Interface

I guess that  the hardware is not the problem but if so...


- Hardware Used in System?

1. cDAQ-9171

2. NI9234

- Driver Software and Version?

For both:

Version 2.8.0f0

Driver date: 19.7.2011

3) Reproducing the Problem

- Latest version of the software and driver you were able to reproduce the problem?

- Is the problem reproducible in several machines?   If no, what are the differences between the machines?

Yes.

2 different PCs and One Dell laptop.

Totally different hardware setups. Labview SE installation from the same discs.

cDAQ and NI 9234 were used in all configurations along with our acceleration sensors (KB12VD).

- List the steps to reproduce the problem?
Running SE 2011 - starting empty project

Adding "Acquire Signal" step -> DAQmx Acquire -> Analog Input -> Acceleration

Choosing the right channel

In the configuration window tab:

Device tab : Coupling mode -> AC

Settings tab: Setting the right units, sensitivity and scale for our measurements.

Iex Source : Internal

Iex Value : 2mA

dbReferance: 1

Timing settings:

Acquisition mode -> Continuous samples

Samples to read -> 10k

Rate (HZ) -> 1k

Recording the data

4)  Your questions:

In all samples I've acquired from different station, my sample rate was ~1653Hz instead of 1kHz as supposed.

I'm exporting the data to Excel and in the beginning of the data it states the "Delta_X" = 0.000605 and it realy is when I check the samples.

Attaching one of the Excel export files made in configuration stated above.

What I'm doing wrong and how to fix it?

If I've forgot to mention something important in configuration, please tell me and I'll check it and add.

Thanks ahead,

Nickolay

[Dennis_Knutson]

Did you look at the manual and read the section on the supported sample rates?

[Nickolayf]

We actualy havent recieved one, so thanks for pointing out.

There is a section in manual speaking about "Data Range rate (fs) using internal master timebase" and in "minimum" option there is "1.652 kS/s"

So I presume that's my minimal sampling rate, right?

[Luke_B]

Yes, the minimum sample rate that the 9234 can run at using its normal internal timebase is 1.652 kS/s. If you set the value to anything less than that, the driver will round it up to the next valid value.

If you'd like to see the data at 1kS/s, you might try using the Subset and Resample step to resample the data to your desired sampling rate.

I hope this helps,

Regards,

Luke B.

[Nickolayf]

Thank you very much.)

It helps.