Counter configuration DAQPad6015 (BNC)

[tnk_csiro]

Hi

Under DAQmx I'm using ctr0 on a DAQPad6015 to read in multiple samples from an external pulse source (position sensor) having variable pulse rate. I would like to acquire multiple samples in equal time steps (e.g 10000 samples at 1ms intervals). In this mode I need to supply an external clock source for the counter. I thought maybe I could use ctr1 as the 'external' source by setting it running in continuous pulse output mode before initiating the read from ctr0. I physically wire ctr1 output to the digital input port selected on the ctr0 configuration. I find in practice I can't run this output counter at more than ~40Hz[12ms on/12ms off] before I receive an error message suggesting the input is being overwritten before ctr0 data set can be written to output. As yet I haven't tried a true external source to clock ctr0 reads. Why can't I sample at a much higher rate without the data overrun occurring - using the aforementioned approach? Will I have more success using an independent clock source?

Regards,
Trevor

[Laura F.]

Hi Trevor,

Using the second counter as the external clock is fine.  The problem lies in the fact that the DAQPad-6015 probably cannot transfer data any faster than the rate you are using without overwriting previous data.  The counters on this device have a small FIFO for transferring data, so it will fill up quickly.  If it is important that you have a faster rate and a USB device, you might consider NI CompactDAQ.

Regards,

Laura

[tnk_csiro]

Hello Laura,

Many thanks for your reply. I suspected this was a hardware limitation, but it is sometimes difficult to interpret product spec. sheets with respect to a particular requirement - such as this.

The DAQPad box belongs to a colleague who asked for some assistance and may be disappointed with the outcome (such is life) - I'll pass on your advice re CompactDAQ.

Cheers,

Trevor.