Hardware Trigger on E series Card

[cool]

I m using the NI-DAQ-16E-4 PCMCIA card.I am planning to use 8 channels.My input frequncy is 1KHz so I will sample around 10KHz on each channel so my aggregate sample rate will be 80KHz.Now I want to start the data acquisition sequence on some external trigger(e.g trigger signal of the function generator).I will apply this external trigger on PFI0/TRIG1 pin.I saw the DAQ card's manual on page 4-22 figure 4.10 shows the postriggered acquisition.Now in this timing diagram I have a question like wat if my TRIG1 signal is repeated again before my scan sequence is completed??Will it ignore this additional TRIG1 signal or will it be confused??

Another thing is if i keep the same sample/scan rate and i increase the number of samples,will tha
t effect the timing of the trigger signal(i.e I will have to apply the trigger signal little late)??

Similarly wat kind of change I have to make if I increase the sample rate and scan rate?

Thanks

[RIO-Todd]

Good question. The DAQCard won't be confused if the trigger signal occurs again before the scan sequence is completed. Since you have configured the acquisition with a start trigger, the hardware will look for the first instance of the trigger and start when that occurs. Once that first trigger is seen the hardware will not look at the trigger line again.

Increasing the number of samples to read won't affect the timing of the trigger signal. The number of samples just tells the software how many samples to read from the software buffer at a time, and will have no affect on the hardware triggering. The hardware trigger functionality will not change when changing this parameter.

To increase the sampling rate of the device, you will just need to increase the s
ample rate input of your progam. Increasing the sample rate of the hardware will also not affect the hardware triggering.

I hope this helps.

Regards,

Todd D.
NI Applications Engineer

[cool]

HI Todd

Thanks this will certainly help.If you can answer to couple of more questions that will be great.

I m using the NI-DAQ-16E-4 PCMCIA card.I am little confused about the scan rate and sample rate.I was going through the shipped program ScanSingleBufAsync.c and in this example 2 channels are scanned.Sample rate is set to 10,000 S/s(i.e. dSampRate=10,000).Is this rate same for both the channels or is this rate the aggregate sampling rate??I am using 8 channels and wanted to sample each channel at 10Khz,so in this dSampRate should I put 10,000 or 80,000(10,000 * 8=aggregate sample rate)??


Similarly wat should be my scan rate for my application?I want to take 100 samples on each channel so I think the "ulCount" parameter should be set to 800.Simi
larly the size of the arrays piBuffer & pdVoltBuffer would be 800.

Has this number to do anything with the scan rate?
Please clarify.

Thanks

[RIO-Todd]

The sampling rate will be the aggregate rate. If you are wanting all of the channels to read at 10 kHz, then you will want to set the scan rate at 10 kHz and increase the sampling rate so that scanning through all 8 channels will complete before the next scan starts (I would go with 100000 just to make sure that scanning through 8 channels completes). The NI-DAQ Function Reference Manual (linked below) has explains the scan rate and sampling rate in more detail which might provide additional help (look at the help for the SCAN_Start function).

NI-DAQ Function Reference Manual for PC Compatibles
http://digital.ni.com/manuals.nsf/webAdvsearch/1630A0B68738B269862567C1007A2912?OpenDocument&vid=niwc&node=132100_US

The count won't have affect the
sampling rate. Changing this parameter will only change how much data you collect from the DAQ device. The sampling rate won't be affected by this.

I hope this helps.

Regards,

Todd D.