Illegal block size and data stream blocked

[ACEllis]

I'm trying to sample a signal that is about 20 kHz and my max sampling rate is 50kHz.  I set up dasylab to sample at 50kHz and a block size of 4,960.  I want to use an FFT module so I made sure my block size is a power of 2. I also need to have the block size divisible by 31 because I'm using a measurement computing USB interface to the computer (USB-1608FS). When I try to start the dasylab worksheet, I get errors saying that the block size is illegal (the FFT module name is in the title bar of the error window). I also will get an error saying that worksheet cannot execute at the Y/t module. When I have the signal generator sending a signal of about 20kHz, I will also get an error saying the data stream is blocked by one of the following modules with Dev1-Al (which is what the input module of the USB interface is named) in the title bar of that error window.  I click ok and the error message goes away and the worksheet seems to operate normally after that.

I'm also curious if I'm using the experiment setup correctly. There are three options to change sampling rate and block size (Dev-1, Dasylab, PC Clock), do I need them all to be the same? 

Thanks for any help or info!

Amanda

[CJ_Butler__DASYLab_Pro]

You may get a better answer if you try the forum at www.measurementcomputing.com; they have a DASYLab section, too.

For your device, you need to configure the sample rate for the device using either the Experiment->Experiment Setup->MCCDAQ or the Experiment->Timebase dialogs. Depending on the number of installed devices, you will have one or more tabs for the MCC devices.

You do need a block size that is a multiple of 31, either 4092 or 4991 should work well. Then, use the Data Window module to convert the block size to 4096 (or more or less, as long as it's a power of two.)

Hope this helps,

[ACEllis]

Thanks for the quick response! I posted to the MCC forum and they gave me similar advice. I did as you both suggested and it works great now. Thanks so much!

Amanda