NI Daq Memory

[PnRaja89]

Hi all I am using NI DAQ 9188 and I have integrated the module NI 9205 to it.

In NI 9205 data sheet it is written that it has 250 k S/s ( http://www.ni.com/datasheet/pdf/en/ds-190 )

In NI 9188 data sheet it is written that it has 127 samples / slot ( http://www.ni.com/pdf/manuals/370086a.pdf )

 1)  So what is the difference between these two samples ?

 2) where will be the data memory . i.e where will be the samples get stored through which we read it from the LabView Software

Thank you

-Naga

[ShamWOW!!]

Hello Naga,

The 9205 250kS/s is the sample rate of the device. When a voltage is flowing into the device, it can read 250,000 samples every second that voltage flows into it.

The 9188 127 samples/slot is the FIFO (First In First Out) is the size of the memory buffer. This means that when recording data, a maximum of 127 samples can be stored on the device before they need to be read by the LabVIEW program.

To put these together. If you decide to use the max sample rate (250 kS/s) of your 9205 on the 9188, you need to make sure your LabVIEW VI reads at least 127 samples from the memory every 0.0005 seconds. Since a large number of computers will no be able to keep up with that, using a slower sample rate will increase the odds of not overflowing the memory buffer.

Best,

Shamik C

Applications Engineer 

National Instruments 

http://www.ni.com/support 

[Mcdan · Accepted solution]

Some clarification:

During acquisition, DAQmx will atomatically transfer data from your device (in this case 9205/9188) into memory on your computer.  As long as there is room in this buffer, daqmx will transfer data.  When you call DAQmx Read, it will return data from this buffer on your computer.  The size of this buffer can be set or queried via the DAQmx Buffer Property Node->Input.BufSize property.  You will need to configure your LabVIEW application to read from this buffer before it fills up.  I make this distinction because it means that you don't strictly need a loop which reads 127 samples every 0.0005 seconds.  You can read much less frequently if you read larger chunks of data.  You just need to ensure that you're pulling data out of the buffer as fast as hardware is producing data (for the 9205, this maxes out at 250 kS/s).

I hope that helps,

Dan