Configuring optimally for secondary ignition...

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Configuring optimally for secondary ignition...

Postby markzb » Thu May 01, 2003 9:01 am

Hello

I would be grateful if I could ask any kind folks here how to go about configuring a ADC 212-100 scope for viewing secondary ignition waveforms.

I am just a beginer here, so I do hope that you will bear with me.

I am capable of setting up the trigger and timebase etc, so I can definitely get a well shaped wave on the screen.

My concern though is how "faithful" this wave is to what is happening in reality.

A little knowledge is a dangerous thing they say! Intuitively, I am trying to get the faithfulness that analog scope users talk about. I do not mind that what I see is actually a historical event.
My fear is that due to oversampling and averaging etc, the waveform that I see on the screen is perhaps a composite and thus anomalies and events or perhaps more importantly, none events become "filled in" by the softwares setup.


I believed in the picoscope approach after much consideration a couple of years ago. I think mine was software version 3.04 if I recall. I sure am glad that I chose the picoscope approach, and am thankful - proud even and so grateful that you guys continually update the software.


But...I have never used it much..and the reason is that on secondary patterns.....the firing line just bounces up and down, and from day one....I have never been certain that my unit has worked right. I live in Malaysia, and am alone here..so I cant exactly compare it with a friends for example. Maybe to clarify a bit better.....

If for example i look at an injector waveform...and set a timebase to get a single firing to fill the screen....I get to see the "kickback" of say 70 to 80 volts everytime.

...but if I leave every setting intact but only expand the time base and can see say 4 firings.....then I only see this kickback happening once every 3 or 5 firings.




So to clarify...not knowing how to setup the parameters such as:
Max displays per second, samples per scope trace, readings per sample,
ets oversample and update speed and perhaps others in the win.ini file.....
and wether the units is perfectly fine....has left me feeling that I just cant trust what I see.

I thus appeal to anyone here...to take the time to share with me the setup parameters I mentioned above to optimise the faithfulness of the secondary ignition waveforms.

Many thanks

Mark
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Secondary Ignition

Postby Carl Grotti » Sat May 03, 2003 8:05 pm

Hi Mark,

Welcome aboard.

It is normal to see fluctuations in the firing line to a certain extent. I'm assuming yours is deviating from the norm. I don't focus a great deal on the firing line unless the deviation is consistantly higher or lower than the others. My focus is usually on the burn voltage and duration. That is my window into the combustion chamber most often.

I use the 212/3 that comes with the automotive kit. I have my requested sampling rate turned up to the maximum of 32,000 samples per second and it works out nicely.

What sampling rate is yours set at?

Carl
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optimising setup

Postby markzb » Sun May 04, 2003 12:20 pm

Hi Carl!

Thanks for your reply. Much appreciated. I must apologize that my choice of the term firing line was done without sufficient thought on my part.

I was refering to the peak KV voltage at commencement of firing, and how it keeps changing extremely from firing to firing. For the moment, let us not get into ignition analysis of the waveform we obtain.

The main issue that I would be so grateful have answered here perhaps by you, AND MATHEW ( pretty please!!!) and autonerdz and others is.....



How do we configure the Picoscope so that we know we are seeing the best possible representation of each displayed firing event?



Thanks to Picoscope, many of us can now go into ignition diagnosis. The 12 bit resolution afforded to us is what made me get it in the first place.....the 8 bit vertical resolution looked so piddly. Thanks to the web, we can collectively share and transfer our diagnostic discoveries to each other.

For amateurs like myself, it is hard enough understanding the combustion chamber dynamics, interpretation of waveforms and so on. But I wish to persevere and master it.

Now....I have the situation were I am not sure that my scope is configured optimally, and thus I do not know with certainty that the waveform I see is "correct".

I want to get over this stumbling block first. When I have the faith that "the markings on my ruler are in place", then i shall begin to go measure and diagnose.

Youve started the ball rolling wonderfully.....now...that 32K you refer to...
is that max samples per scope trace?

I have an ADC 212-100...cos that is what was reccomended to me back then!

So.....Lets start with Max samples Per Scope Trace. What should it be set to? I believe the default in my current software is 2500. Now....in the help section, there is no mention of this feature.

Should we always just run this settings value to the to the maximum allowable? Or is there a time and place that you dont? Also...is it correct to say that what this setting does is determine the horizontal resolution of each trace we see on the screen?

Hope we can go thru each of the setup parameters and their effects for the benefit of others and myself.

I think that the correct setting, and the understanding of the effect of these parameters on the way they affect the display are of paramount importance!

The other important thing I hope someone can explain to me is...

Max readings per sample (we can select between 1 to 16)

Does this mean that for every trace we see....the trace is the "average" of a certain number of traces before hand?

Let me explain it different...lets say I choose a value of 5. Does this mean that the picoscope software puts 5 traces in memory, superimposes them on each other, and then displays the average of the traces on the 6th and every 6th trace?

Many thanks to everyone for reading this.

I am a slow learner and hope I do not offended anyone here by requesting we go thru this slowly. What may come as extremely basic to many of you visitors and require so little explanation to make you understand...well..I need some compassion!

Ok....we have 2 things to discuss now.

Max samples per scope trace
Max readings per sample

Could someone elaborate on what these parameters should be set to for ignition diagnosis, and how they affect the display.

Thank you so much

mark
markzb
 

Set-up

Postby Carl Grotti » Sun May 04, 2003 5:22 pm

Mark,

We are both referring to the same thing when speaking of the firing line and peak KV. :wink:

I'm understanding your issue better now that you've stated your Max Samples Per Scope Trace is set to the default value of 2500. You are missing a great amount of detail. :shock: I agree that the default value is very low. Especially when you can crank yours up to 100,000. :D I however max out at 32,000 which isn't bad. There aren't many scopes out there that have that kind of usable sample rate. And to think you have a 128k buffer. Now I'm jealous. :(

I would start by turning up your SAMPLES PER SCOPE TRACE. How high? Dunno for sure on your unit. Turn that puppy up to 50k and see what happens. Turn it up to 100k and see what happens. The worst that can happen is you may get a fair amount of underhood noise. As I said, you are missing a great amount of detail at 2500. Also, make sure you are using block mode.

Regards,

Carl
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Postby Guest » Sun May 04, 2003 6:59 pm

Hi Mark,

Carl's answer is excellent. The time base and number of samples per trace has a direct effect on sample rate. To get a rough idea of sample rate take the number of scope samples tou have selected and divide by the screen total time in milliseconds. The result is the requested sample rate in KHZ. I use the 212/3 also so can select up to 32K samples per trace. You can probably select up to 128K.


Now, a secondary firing line may be only 10us in duration. You need at least 5 samples during that time to reliably capture that event. Therefore, you should sample at 500khz.

To figure the number of samples in a given time, multiply the sample rate by the time (500,000 x .00001 = 5)

Do the numbers and you will see why you will not see the full firing line reliably at lower settings.

The actual sample rate will be less than the calculation above because the available sample rates the scope works with are powers of 2 of the max speed (in your case 100 million samples per second).

As far as maximum readings per sample, you must be using an earlier version of the software. That selection isn't available in my version. I remember that though. It is an averaging function. You will not want to use that unless you want to reduce noise. It will smooth the detail which is not desirable whwn viewing most automotive signals.

Hope this helps. :shock:
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Postby Autonerdz » Sun May 04, 2003 7:02 pm

That above reply was mine. I didn't realize I had been automatically logged out before I pressed the submit button. :shock:
Tom Roberts
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I understand better now!!

Postby markz » Mon May 05, 2003 9:09 am

Hi Guys...

For starters..I went and looked at the handbook that I got with the scope...and I again have made a boo boo...I guess I have what you
guys have....a 212/3 picoscope. No need for any jealousy now eh! :P
Were brothers!

I thought I had a 212-100 for the reason that I recalled it being a 100Khz scope...and also that when I got it...they kinda named things differently then and had a different product range.

WHATS BEEN LEARNT

No.1
Ok.. so instead of 2500 samples per scope trace.....I should be setting it to 32000 samples per scope trace. That explains where all the missing events went!

No.2
For those of you who can set the "Max readings per sample" in an older version of picoscope software between 1 and 16, choose 1 for automotive work.


Thanks so much guys!!!!!

Now to kinda get to the tail end of questions.....


WHAT REMAINS!


What is this ETS feature..I believe you can set it between a value of 2 and 5, and also there is a slow and fast mode.

Could someone explain if and how these can affect our ignition waveforms? What should we be setting them to.

Also...there is another setting in the win.ini file... I think it is "No of times to update display" or something like that ( i am not at my pico pc!).
I think it is set at 10 on my pc.

Could someone please explain what this does to our ignition waveforms, and what we should set it to.....I dont quite know what this does either!

Thanks so much guys!!!

Regards

Mark

P.S. Im so glad there is a "R" after the "G", Carl....elsewise..I wouldnt quite trust you with a "scope" in your hands!!!
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Re: I understand better now!!

Postby Autonerdz » Mon May 05, 2003 7:49 pm

markz wrote:WHATS BEEN LEARNT

No.1
Ok.. so instead of 2500 samples per scope trace.....I should be setting it to 32000 samples per scope trace. That explains where all the missing events went!


Yes, when you want the higher sample rate and more resolution. This will slow the screen update rate though so, if you do not need the resolution turning it down will speed things up. When capturing something as fast as a secondary firing line your 212/3 will begin to break down at 10ms/div.

Let's do the math for the 212/3:

32,000 samples / 100ms = 320khz requested sample rate

The scope then chooses 187.5khz since 320khz is between ranges.

187,500 samples x .00001 firing line duration = 1.9 samples maxed out.

This will show most of the high peaks. Longer time basses will not. You can overcome this by using the mix/max and current selection which will leave shadows of the minimum and maximum values for each trace while showing the current trace as it is updated. Just a few passes and you will reliably see the high spike shadows on the screen. You may have to update your software to get that feature but it's free :D

markz wrote:No. 2
For those of you who can set the "Max readings per sample" in an older version of picoscope software between 1 and 16, choose 1 for automotive work.


Yes.

markz wrote:WHAT REMAINS!

What is this ETS feature..I believe you can set it between a value of 2 and 5, and also there is a slow and fast mode.

Could someone explain if and how these can affect our ignition waveforms? What should we be setting them to.


Don't use this feature on an automotive application. This is for very fast repetative signals. The scope takes a few passes then constructs the waveform from the data. We don't deal with steady repetative signals so this would only serve to distort the picture.

markz wrote:Also...there is another setting in the win.ini file... I think it is "No of times to update display" or something like that ( i am not at my pico pc!). I think it is set at 10 on my pc.


Screen Update Rate? Maximum is 30 screens per second. I leave mine maxed at 30. It will be considerably slower than this dependent on the time base and the number of samples. It can make the PC pretty busy so if yours seems to lock up and get unresponsive to the controls, turn it down a little.

Hope this helps :shock:
Tom Roberts
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Postby matthew » Wed May 07, 2003 8:39 am

Hi Tom / Carl,

Thanks for looking at this, I hope you don't mind me putting a few quote marks in your post above to make it more readable (I'm sure other automotive users will find these answers very useful).

Just one small point ... the ETS mode is, as you correctly say, for fast repetitive waveforms, but this only works on the ADC-212/50 and ADC-212/100.

Thanks again :D ,
Matt Everett

Pico Software Engineer
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Display Preferences

Postby Carl Grotti » Thu May 08, 2003 12:42 am

Hi Mark,

You don't need to go into the win. ini file to change your updates per second. i.e, UPDATES PER SECOND=30. I prefer to stay away from editing that file due the chance of an accident by one slip of a keystroke.

Your MAX DISPLAYS PER SECOND is found in Display Preferences within PicoScope. Go to File | Setup | Display and enter 30. As Tom stated, "decrease it if the computer gets to busy and the controls aren't responding".

Good luck and let us know how you like the greater detail and performance,

Carl
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