NI-6221 maximum sample rate digital channel

[PeterFoerster]

Hello everyone,

a colleague of mine told me the other day that the sample rate of the NI-6221 is 250kS/s, but only for the analog channels. I want to acquire a digital signal at the rate of at least 11kS/s. Is this possible? What's the maximum sample rate of the digital channel.

I also read something about event detection i.e. detecting a rising edge. Does this work with the NI-6221? How exact can I measure the time between several events, using that method?

Any help is greatly appreciated

[PeterFoerster]

Another Question, regarding the 6221:

are the grounds of the Digital Output channels linked internally?

I need to supply 5 Volts to make it detectable on the digital input while maintaining a galvanic isolation. On the other side of my Optocoupler another Digital Output is linked to the common ground, so if they are connected internally I would loose the galvanic isolation. Can I do this using a digital output? Or do I have to supply another galvanically isolated 5V supply.

[jtagg · Accepted solution]

Hi jak,

it is true that the 250 kS/s is given for the analog inputs. The digital inputs have no hardware clock to speak of. Either you do the clocking in software (won't work for 11kHz) or you do what is called correlated DIO, which essentially means you generate a clock with counters or you use the one from AI or AO.

Here is some information on the subject:

http://sine.ni.com/devzone/cda/epd/p/id/1566

The specs state that the DIO can manage up to 1MHz in this way.

Here is an example on change detection:

http://zone.ni.com/devzone/cda/epd/p/id/317

Note that this would only work on the PCI-6221, not USB-6221. Since you didn't specify which bus, I added the difference.

The grounds of the DIO channels are linked internally.

Regards,

Joseph Tagg