Reducing Sample period of digital input of NI-USB-6009

[indiubhaya]

Hi,

I need to read a digital input line in the NI USB-6009 using NI Signal Express 2013. I have seleted 1 sample (on demand) as the Aquisition mode. I need to set a smaller sample period like 1 ms. But this gives the error sample period too short: "The current sample period is too short.  Please specify a longer sample period.".
I cannot understand the reason for this and a way to slove this.

Any help would be greatly appreciated!!

Thanks!!

[Dennis_Knutson · Accepted solution]

The 6009 does not have a clock that you can set for a sample period. As the spec says, the digital I/O is software timed - the sample on demand you are using now. I am not at all familiar with SignalExpress but I don't think you can come close to a reliable khz sample rate on Windows or any other non-deterministic os.

[SnowMule]

The 6008 *can* sample at 1kHz, but not in on-demand mode.

Configure it to take finite samples, say 1000 of them... and do it at 1kHz.  When you do the read you'll get that second's worth of data.  Fire that task, trigger your event, then look for a transition over a certain level in the data that comes back from the DAQ.

Can't hardware-trigger on the 600x's, so you have to do some analysis in software to find that edge.

[Dennis_Knutson]

SnowMule,

Are you sure about that? I tried to set the acquisition mode to finite samples and I get an error - unsupported value for this property. I've always had to set a DAQ device with software timing to on-demand.

[johnsold]

I agree with Dennis. Only AI on the 6008/6009 is hardware timed.  See quote from the User Guide below.

Perhaps AI and some comparisons in software would work for the OP.

Lynn

[SnowMule]

For analog input, yes.  Digital in, no.  I missed that part.

[kubhayar]

..

[indiubhaya]

Thanks for the replies.

I missed the part of software timed in the spec. 

Now I'm using the position (5V at the highest location and 0 V at all the other locations) as an analog input and use as a reference to the other analog input channels, but with the cost of reduced sample rate.