Choosing Sample Rate and Using Memory

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Choosing Sample Rate and Using Memory

Postby hexibot43 » Tue Jul 17, 2012 3:41 pm

Hello All,
I keep reading all the posts here, and was recently reading about recording Waveforms and deriving MAF using math channel. They talked about making sure you were giving enough resolution to the waveform to ensure the math would come out right. I'm currently using the 4423 Automotive scope and still learning the ins and outs of the software.
I'm looking for suggestions as to how best to set up scope sample rate. Would you always be trying to maximize the sample rate? The whole screens things is confusing me. I'm not use to having to think like this. I'm use to putting the best image I can get up on the screen period. I see there is a give and take between sample rate and how many screens you will end up with in the sample. From what I understand you can't just continually sample to memory in the PC, or dump to hard drive. I get this. So what I guess I'm asking is, does anyone have a rule of thumb as to how best to set the scope with sample rate in mind? Are there pitfalls I should be looking out for?

Thanks,

Marcello
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Re: Choosing Sample Rate and Using Memory

Postby Autonerdz » Tue Jul 17, 2012 4:20 pm

Marcello,

That's an excellent question. We even have an entire movie dedicated to 4000 scope power management for our Picogroup members. But here it is in a nutshell....

Watch your properties as a speedometer. If you are looking at secondary ignition, keep sample rate about 1 MS/s (1us sample intervals). Much lower than this will miss some KV spikes. Most other components like crank and cam can have a lower sample rate if desired. Of course, this is dependent on RPM.

Not much reason to go over that 1MS/s threshold unless you are looking at bus communications.
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Re: Choosing Sample Rate and Using Memory

Postby hexibot43 » Wed Jul 18, 2012 4:05 pm

Thanx AutoNerdz,

I'm still waiting for my Matco dealer to tell me how he got the scope. Perhaps he did buy it through you...

Anyways, Thanks for the reply. You are reminding me of a project I once did where I was looking at address control lines of an Eprom. I wanted to swap one Eprom for another on the fly. I was looking at control lines of a 27c256 with my old LS2000. The scope wasn't up to it. I finally just attempted it based on what I knew the logic should be instead of what I was looking at. It worked. But the scope patter I had gotten was telling me something completely different. I bought a Tektronix 2232 which is a 100 MHZ bandwidth scope if I remember right. Low and Behold I had a pattern that made complete sense when I looked at the same circuit. If I had had this scope before I started this project I would have been done much sooner. And I wouldn't have been questioning myself so much. And this is why I'm so hung up on sample rate and bandwidth. I'm going to have to look at that same Eprom again with my PicoScope and see how it does.

I guess so far in automotive I haven't yet run across bandwidth being a problem. Usually the biggest problem is me the operator doing something stupid.
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Re: Choosing Sample Rate and Using Memory

Postby Autonerdz » Wed Jul 18, 2012 4:27 pm

Perhaps he did buy it through you...


We do work with the tool dealers quite often but I don't have enough info here to tell if that was the case with you. I would think your Matco guy would have given us your details as the end user and we would have plugged you all in. That's how it is supposed to work.

Feel free to email me. We wouldn't want you to miss out on all the resources you are entitled to.

http://www.autonerdz.com/cgi/yabb2/YaBB ... 1336513824
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