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fast AI and DO using usb-6215

Hi everyone!

I'm trying to use a usb-6215 to aquire a 50 hz signal, and at a certain point on this signal trigger a digital out to kill the signal. As the accuracy is of importance where just a few degrees can differ, timing from AI to DO needs to be in the range of tens of micro seconds. So, my question is thus, is the 6215 too slow for this task? 

I've asked this question in a thread before, where it was implied that it was too slow but just wanted get this confirmed by others before ordering new hardware.

 

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nlx,

 

The AI can sample at a rate of 250 kHz on a single channel which comes out to a sample every 4 usec. However the digital output is sofware timed and so the speed you can output is going to be dependent on your computer, but it's not a realistic expectation to have an output rate higher than 1kHz. If you need to generate a digital sample in the micro-second range you will need a DAQ device with hardware timed DIO.

 

None of the Bus-Powered (621X) USB devices have hardware timed DIO, so you will need to look at an externally powered USB device like the USB-6341. This is the base level USB-DAQ card that would get you everything you have indicated that you need.

Aaron W.
National Instruments
CLA, CTA and CPI
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nlx wrote:

I'm trying to use a usb-6215 to aquire a 50 hz signal, and at a certain point on this signal trigger a digital out to kill the signal. 

 


Do you mean you need to issue a digital output once the signal reaches a certain voltage level?  If so, why not just use an external comparator?

 

 

Best Regards,

John Passiak
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@John_P1 wrote:


nlx wrote:

I'm trying to use a usb-6215 to aquire a 50 hz signal, and at a certain point on this signal trigger a digital out to kill the signal.

 


Do you mean you need to issue a digital output once the signal reaches a certain voltage level?  If so, why not just use an external comparator?

 

 

Best Regards,

John Passiak

 

There will be tests with different voltage levels, which means that the phase angle will change each time the voltage level change.

 

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@nlx wrote:

There will be tests with different voltage levels, which means that the phase angle will change each time the voltage level change.


 

You could use the analog output of the 6215 as one of the comparator inputs to be able to programmatically change the voltage level.

 

 

Even if the AI and DO tasks can be clocked fast enough, if the logic that connects the two resides in software this is going to prevent you from achieving your requirement.  You need to implement the digital output in hardware.  

 

 

Best Regards,

John Passiak
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