Questions about NI9234: how to change different sampling rates.

[rico1985]

Hi,

I am using NI 9234 with NI 9172 and Labview Signal Express 3.0. I have a question abou how to change the sampling rate. When I was doing my test, the sampling rate was fixed in Signal Express, which is 25600Hz, the half of the maximum master timebase. When I used different values for the sampling rate, like 500Hz, 10000Hz or 20000Hz, the samping rate didn't change. I think that's the problem of internal and external master timebase. I am wondering how to change it from internal to external master timebase. Then I can use any samping rate using NI 9234. 

Thanks,

[Margaret F.]

Hi Ningyu,

Thank you for posting to the NI Forums!! Before we dive into this futher, I want to clarify some things. Where exactly are you changing the sampling rate and are you also changing the samples to read?

Also, what do you mean by the sampling rate did not change? Do you mean that the number did not change when you entered a new one, or you think that perhaps the waveform does not reflect your change? Thanks for the info! We'll go from here!

[rico1985]

Hi Margaret,

Thank you for your reply. I am changing both the sampling rate and the samples to read at the same time in the generate-signal step and the aquire-signal step, but Signal Express was always using its own sampling rate, 25600 Hz in all of the saved data. The number changed when I entered a new one. When I connected another DAQ board to the computer, I didn't have this problem. Therefore, I feel confused about how the NI 9234 works. Thank you.

Ningyu 

[Margaret F.]

Hello again Ningyu,

The 9234 is an analog input module, so I'm wondering if you have other modules in your chassis that you are using for the generate signal step that you referenced in your last post. The reason behind your sampling rate problem could be the result of the limitations of other modules in your chassis. Please tell me what other DAQ hardware you are using. Thanks!

[rico1985]

Hi Margaret,

The analog input module is NI 9234 and the chassis is NI 9172. Do you mean the problem is the result of the limitations of NI 9172?

Thanks,

[Margaret F.]

Hello,

Since the only module in the chassis is the 9234, let's try using the test panels in Measurement and Automation Explorer (MAX) to see if we can adjust the sampling rate there. You can access the test panels by opening MAX (Start>>Programs>>National Instruments>>Measurement and Automation Explorer.) Under Devices and Interfaces, you will see the 9234. Right click on the module and select "Test Panels." Try adjusting the sampling rate there and let me know the result. Thanks!

[KyleBryson]

Hi Ningyu,

I'll let Margaret help you through the software issues, but I just wanted to make sure that you were aware of the info that is available on the sampling rate of your 9234.  Check out the "Understanding NI 9234 Data Rates" section of the manual for info on what sampling rates the hardware can run at; there are some specific divisors from the maximum 51.2 kS/s rate available, and there is a minimum.  With only one (or more) NI 9234 modules in your cDAQ-9172 chassis, though, you should be able to access any of those valid rates through any of our software interfaces.  The test panel is a great place to start and make sure everything is working the way that you expect.

Regards,
Kyle

[Andy_N.]

Hi NI technician,

I am using the same hardware (9172 chassis+9234 module) and LV Signal Express 2009 for my test but I failed to get different sampling rates by changing directly the rate in the Test Panel (MAX) as you instructed. Please see attached the snapshot of the tab where I changed the rate. The current sampling rate is fixed at 1766S/s and I guess it was from the 9234 module's internal timebase (13.1072Mhz) and the integer n=29 (so far I don't know to change n though it was said to be able to accept any integer value from 1 to 31). I have also read from another thread that we can use one of 9172 chassis timebases (80Mhz, 20Mhz &100kHz) as external timebase for 9234 and we can config it using LV Signal Express. However, the Reference clock setting tab is locked to the internal type only (see attached another snapshot) and I could not get it accepted any external timebase. Please advise me how to solve the problems.

Regards,

Andy N.

[KatieC]

Andy, 

I am a little unclear of what is going on after looking at your pictures. In your picture titled "Test panel" the sample rate is set to 25600, and I do not see the 1766 number at all. Could you please clarify? Once I understand the question, I would be more than happy to help!

Katie