how to trigger a trace to capture intermittent problem?

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how to trigger a trace to capture intermittent problem?

Postby hillp » Tue Mar 01, 2005 9:27 pm

I've come to believe that my ADC-40 and ADC-11 are way too slow to capture details of ignition waveforms. One of the posts in a forum suggested running 10 msec per division to capture ignition signals. This is only a tenth of a second total recording on an ADC-212/3, if I understood correctly.

My automotive problem is an intermittent, brief "stumble" that comes and goes at random times. It feels like the engine dies completely, with backfire through the intake sometimes, but it only lasts for a fraction of a second. If I manually stop an ongoing trace right after I feel this stumble, chances are good that I'll have missed it by the time I get my finger to hit the space bar. I have used the ADC-40 to trace fuel pressure and found no drop in pressure during such an episode, at least at the time scales I used.

I've used the triggering function with my ADC-40 and -11 in a completely different application, but at least I know which variable to watch and trigger from. With my current automotive problem, I haven't even narrowed the cause down to ignition or fuel yet. Maybe I can't do this job with the ADC-212/3 I'm considering buying because it doesn't have enough memory? The 212/100 is over 2x the cost. I could swap out a lot of car parts one at a time before I spend that kind of money.

Any suggestions?

Thanks,
Pete.
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Postby Autonerdz » Wed Mar 02, 2005 4:37 pm

The 212/50 would be just as good as the 100 when using both channels, but the 212/3 is very capable also.

You can use trigger to capture an intermittent if you can accurately guess what is failing. You can repeat trigger off of the suspect and if it fails, the scope will stop; hopefully with something useful on the screen.

The other useful technique is to do a 'save on trigger' session. This way, the triggered screens are written to your hard drive automatically for later review. So, if you see something on the screen during a session, and wish you would have gotten that...you already did :D
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intermittent faults

Postby amsterdam cars » Sat Apr 16, 2005 10:30 am

Hallo,I am replying to this post because of the problems intermiitent problems on cars can cause,and the best way to resolve them.What is the "story" with buffering(my ADC212/100 has a 128k buffer I believe.What is the best way of utilising this?If you can buffer a lot of data ,esp when a problem occurs,and you can store this data,or get it onto the screen after problem occurs,trap it and then look at it in leasure later in the shop.That seems the way to go.Is it possible to "buffer"and store this buffer and look at it at a later stage,and if neccessary zoom in on the trace?The problem is I can not find this info in the manual.Are there any(web based) courses?Sorry about all the questions,but here in New Zealand there is a bit of a vacuum when it comes to this sort of training..Also I saw triggering mentioned.How do I set up for a trigger to take effect?

With kind regards,
John Gijsbers for Amsterdam Cars.
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Capturing Intermittents

Postby Autonerdz » Sat Apr 16, 2005 5:13 pm

Hi John,

The dual 128k buffer in your 212/50 allows you to collect up to 128,000 samples on one screen, per channel. Since each channel also has a 50MHz ADC, none of the resources are shared and it samples just as fast on one channel as it does on two. The actual sample rate varies by how much time you have on the screen and the max number of samples you have selected to be captured. You can use the Autonerdz Sample Rate Calculator to see how all this works:

http://www.autonerdz.com/java/SampleRateCalculator.html

With the max number of samples per channel set to 128,000, you can put a lot of time on each screen while maintaining robust sample rates. How fast a sample rate you need will depend on how fast the signal is that you are working with. As long as you have not pushed it too far, you will capture everything during that screen time.

By using the Save On Trigger function, each triggered screen can then be automatically saved to your hard drive. The default is 100 screens but you can make that more. The count starts over each time you stop and start the acquisition. This way you will save everything the scope sees and can review it later, zooming in on each capture as needed to see areas of interest.

The scope is not acquiring data while it is transferring data to the PC, therefore there will be gaps between the captures. How long these gaps will be depends on how much information you are moving. The more samples you collect the slower the screen updates because the larger amount of data takes longer to move. This is not as big of an issue as it seems. When you can put 20 seconds on one screen, the ratio of down time to run time is minimized and your odds are good to catch that intermittent.

I have produced several hours of Flash tutorial movies that cover this and many other PicoScope operation techniques and strategies in detail. These productions are available to all of the Autonerdz support group members. There is a one time fee for this service to join. This may serve your training needs. You can read more about this service here:

http://www.autonerdz.com/picokit.htm

Other training materials are also available. To read what members think of this service:

http://www.autonerdz.com/picousers.htm
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Postby Amsterdam Cars » Sun Apr 17, 2005 3:16 am

Thank you for your reply Autonerds.I will have a look at the websites you suggested,and by the sound of it I will be contacting you.(By the way my scope is a ADC212/100,when I was looking at purchasing a scope I wanted a relatively fast scope because of future developments in the automotive field..This one was on special,but I do not really know he difference between the adc212/50 and adc212/100.Thanks again,
John
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212/50 and 100

Postby Autonerdz » Sun Apr 17, 2005 3:35 am

Oh, right John. You have the 212/100, guess I should have paid better attention. :oops:

The performance of the 212/50 and 212/100 are identical when using both channels. The 100 is only faster when using one channel. Since we use two channels in automotive to observe inputs and the related outputs, they are practically the same. You can enter up to 128,000 and 50MHz in the Autonerdz Sample Rate Calculator for your sample rate calculations. For single channel use put in 100MHz.

You can also select number of samples in the measurements section of PicoScope and they will display at the bottom of the screen.
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