6251 AO sample clock

[Dilu]

Hello All,

I am using a M6251 board for analog output. However, I have the problem that the board only allows discrete increments in the frequency of the Analog Output sample clock. The frequency step-size varies, depending on the sample-clock frequency, and reaches around 10kSa/s when the sample clock is running at 1MSa/s. Am I doing something really stupid, or is this a limitation of the board? The digital pulse-train generation does not seem to have this limitation. If this *is* a limitation of the board, is there some way of overcoming it? I have tried to re-route one of the counters into the AO sample clock, but, when I do so, I get an error message saying that resource is already in use.

Any help will be greatly appreciated.

[Marni]

Hello Dilu.

What do you mean when you say frequency? Do you mean frequency of the waveform that you are outputting? Take a look at some of the examples in the Example Finder. They can be found in the Help Menu under Find Examples. Browse Hardware Input and Output>>DAQmx>>Analog Generation>>Voltage. Do you achieve a faster frequency with these examples? Have a great day!

Marni S.

[JaredA]

There are two things that I can think of that could be causing the behavior that you're seeing. The first is that you are using the onboard Frequency Generator to generate the AO Sample Clock. If this is the case, you will notice that the Frequency Generator has limited capabilities in the frequencies it can generate. If this is the case, use the default AO Sample Clock as the clock for your AO application. M Series devices have a dedicated timing engine for AO applicatins, hence, no onboard subsystem (i.e. counters, PFI lines, etc.) will be used up if you use the AO Sample Clock default selection for timing your AO applications.

The second guess that I have is that you are not specifying your AO application correctly in order to get the generated waveform frequency you're expecting. Their are several parameters that you need to set in order to get an expected frequency with AO - rate and samples per channel. Have a look at How Can I Calculate the Output Frequency of my Analog Output. This knowledgebase might currently be written with Traditional NI-DAQ terminology, but it should still help. Also, remember that even though you specify a certain update rate on your analog output, the actual update rate will be slightly different because of limited resolution of the divide down.

Jared Aho