Continuous acqusition of data through mutliple triggering

[lfw]

Hi all,

I realised that a trigger rate of 100kHz is not sufficient for my application, I need at least a few hundred Hz. I was wondering if I can change my analog triggering wave (more than 100khz) into a TTL signal externally and input the TTL into the digitizer. Will this actually enable me to achieve a higher trigger rate or am I still bounded by the re-arm time?

Sorry if it does not makes sense.

Regards,

lfw

[Jeff_B.]

lfw,

The same trigger rearm time applies, regardless of the trigger source.

Is your trigger always periodic?  If so, could you trigger once and use the deep onboard memory of the 5922 to store the entire waveform, then fetch back only the portions you are interested in?

[kentang]

Hello All,

I am a newbie for using labivew and national instrument stuffs..
I've got similar trouble for this continous data acquisition.

I'm using PCI-5124.
My signal trigger is periodic (actually not using actual trigger, but the data comes at every certain amount of time i.e. with freq 100 Hz).
I have problems getting, for example, 10 consecutive signals (10 records).
I kept loosing some data.
My sample rate is 10 MS/s.
And the record length for each record is 100000.

Attached are the VI file and a word file that shows that I lost some data.

Can one of the experts help me, please?

thanks,
andy

[Sean_C.]

Hi Andy,

From your word document, it looks like your trigger occurs immediately after each acquired record.  What might be happening is that your trigger condition for the next record sometimes occurs within the previous record's acquisition, so the digitizer misses that trigger.  You can test this by reducing your record size.  Try using 90,000 instead of 100,000.  Do you still miss triggers?

If this is the case, then your best solution would be to reduce your record size to ensure that you are not still acquiring data when the triggers occur.  Or simply acquire all the data in one waveform (as in the second graph) and split it into 10 waveforms in software.

I hope this helps.  Let me know if you have any further questions.

Regards,
Sean Close
Product Support Engineer:  High-Speed Digitizers

[kentang]

Hello Sean,

Thanks for the quick response.

It's been quite long just to figure out this matter. :s

I'm wondering what the real definition for trigger is. I didn't use the 'real' triggers as the curve will come every 10 ms by setting a frequency of 100 Hz. Can this 100 Hz frequency be called as trigger as well?.... just wondering if we are in the same way of thinking 🙂

In general, if we set the number of record of 10, will the program read the data after each trigger occurs,  even we don't have 'real' triggers (only a signal which has a certain frequency)? For example, when we have a sine wave signal with frequency of 100 Hz, and want to read the first 5000 points of data with sample rate of 10 MS/s, then the program will read exactly 5000 points every 10 ms after the first reading. (without any missing triggers).

Hope you are not confused with my 'story', as I'm not really good in explaining technically.

regards,

andy

[Sean_C.]

Hi kentang,

"I'm wondering what the real definition for trigger is. I didn't use the 'real' triggers as the curve will come every 10 ms by setting a frequency of 100 Hz. Can this 100 Hz frequency be called as trigger as well?.... just wondering if we are in the same way of thinking" I was assuming that you were triggering off of the same signal that you were acquiring.  In this case, triggering everytime the signal crossed the x axis with a rising edge.  Is this not the case?  If not, then what was your trigger signal?

[kentang]

Hi Sean,

I made a modulated and carrier sine wave with a waveform generator.

The pictures in the word file are the 100 Hz carrier sine wave, with a modulated sine wave of 10 Hz frequency.

So I think there was no 'real trigger' used?

please correct me if I'm wrong, or if i don't use the same term with what people usually do.

regards,

andy

[Sean_C.]

According to your VI, you are triggering off of channel 0.  The default is a rising edge trigger with a trigger level of 0 V.  So it does appear that you are triggering off of your input signal.

What exactly are you trying to accomplish here?  What are you having problems with? 

[kentang]

Hi Sean,

Now I get it with what you meant with triggering off my input signal that I was acquiring.
Sorry for the confusement.

Then the problem is the same with the first reply I did for this tread:

Hello All,

I am a newbie for using labivew and national instrument stuffs..
I've got similar trouble for this continous data acquisition.

I'm using PCI-5124.
My signal trigger is periodic (actually not using actual trigger, but the data comes at every certain amount of time i.e. with freq 100 Hz).
I have problems getting, for example, 10 consecutive signals (10 records).
I kept loosing some data.
My sample rate is 10 MS/s.
And the record length for each record is 100000.

Attached are the VI file and a word file that shows that I lost some data.

Can one of the experts help me, please?

Currently is friday night at my place.
I'll try to do your suggestion on monday morning.

Just really want to have some discussion to 'enlight my vision'.

If I only take 1000 points instead of 100000 or 90000, do you think this will not miss any trigger at all? Or will it be some missed ones? Is there any proven case for his high speed digitizer?

Thanks
andy

[Sean_C.]

Hi kentang,

If you only take 1000 samples per record and you acquiring data at 10 MS/s then each record will span 100 us.  If your triggers occur every 10 ms, then you should not miss any.  I believe you were missing triggers before because you were still acquiring data from a previous trigger when a new trigger occurred.  You could test this be reducing your record size.

Let me know your results.

Regards,
Sean Close