Setting the sampling rate in SignalExpress

[jkorth]

I am using a cDAQ-9172 with a strain gauge module and a thermocouple module and using SignalExpress.  I want to acquire data at a pretty low frequency rate (2Hz), but I am unable to use 1 sample on demand in the acquisition setup.  I get the following error.

Error -201087 occurred at DAQ Assistant

Possible Reason(s):

Measurements: Task contains physical channels on one or more devices that require you to specify the Sample Clock Rate.

Specify a Sample Clock Rate.

Device: cDAQ1

I am unable to setup a sample clock rate as it is 'blacked' out by the software in the 1 sample on demand mode.

When I try to use continuous or 'N' sample mode, the cDaq is sampling at a rate of around 1600 Hz, even though I am putting in a value of 1Hz on the seti[ screen.  The large amount of data will prevent me from downloading the data to Excel for further reporting.  I obviouisly don't need to sample my TC module at that rate either.   

Is there anything I can 'easily' do to decrease the sampling rate down to a low level?  Everything I have tried doesn't seem to work and I don't really want to go away from SignalExpress.

Jay 

[Chris_K_]

Hi Jay

I am assuming that you are using the NI-9237.  This strain module has only a specific set of sampling rates.  If you specify a rate that is not supported it will corers the rate to the next higher sampling rate.  Also since you are using the cDAQ chassis, there is only sample clock so it must choose the highest sampling rate.  So it is not possible to sample at a lower rate.  Please see the following link.

If you have access to LabVIEW then I would suggest taking your readings at the fast rate and then average the samples before you write them to your file.  The following link has some more information on this. 

If you are limited to Signal Express, this task is tricky.  If you select a N-Sample acquisition, set the samples to read to greater than two, and set the post acquisition delay  under the execution control tab to 1000, you acquisition will acquire the two samples at the very fast rate, but it will wait 1000mS between each acquisition.  This will slow the overall sample rate.

Chris_K