MAF Signal

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Re: MAF Signal

Postby Valhalla » Sat Jun 15, 2013 11:45 pm

s4c wrote:Please have a look at the attached post. If you could work it out it would be great. Also, if you could show me the workings for future ref that would also be great.


Simon,
As everyone points out correctly, your sample rate is way too low - you should be sampling at no more than 25us for looking at these sorts of frequencies (20Hz to 2000Hz). The method Robski was using is the only option open to you, i.e use the cursors to measure the period. To get a direct frequency measure, you will need to add a measurement on channel B, set it to "Freq" and set it to measure the range between the cursors. That will give you some idea of the frequencies that you are seeing, if you span a couple of cycles with your cursors.

There is enough data to see that you have an airflow oscillation when the TPS is opened, and it doesn't seem to attenuate towards the end of the TPS = 5v part of the trace. So you need to measure again, maybe add a channel for engine speed (one coil primary input would give you a rough speed indication for 720degs CA) at a better rate. I think that you have a valve sticking problem, but without an engine speed, you have got nothing to divide the airflow by, and that is assuming you can scale frequency to airflow.... You might just be seeing a signal drop-out on the MAF meter, but with your present sampling, who can say?
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Re: MAF Signal

Postby Autonerdz » Sun Jun 16, 2013 1:48 am

Valhalla wrote:The method Robski was using is the only option open to you, i.e use the cursors to measure the period.


Would it not be better to graph the frequency like this? This can be done with any PicoScope capture. You don't have to have a 4000 series.

freqgraph.gif


I think this is what Alan was referring to. Just trying to help out, Alan.... :shock:

In this example, freq(B-2) Range 0 to 1000 Hz.

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Re: MAF Signal

Postby Robski » Sun Jun 16, 2013 7:17 am

Valhalla wrote:
The method Robski was using is the only option open to you, i.e use the cursors to measure the period.

I had a quick look that way & with a measurement at the bottom of the screen, I looked for a formula to do the same as Tom has but didn't go too deep.....
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Re: MAF Signal

Postby Valhalla » Sun Jun 16, 2013 11:03 pm

Autonerdz wrote:Would it not be better to graph the frequency like this? This can be done with any PicoScope capture. You don't have to have a 4000 series.

In this example, freq(B-2) Range 0 to 1000 Hz.

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It's much better graphing the frequency like that! I had a go, as well, but omitted to make the math function "freq(B-2)" and therefore failed to get any read-out. Because, of course, the maths needs a zero-crossing over the 0v line to work... :roll:

Thanks Tom, I'll go back and have another go. :) Is it a dynamic frequency display that is peculiar to the 4000series, or is this an anomaly in the Automotive presets help screen (that needs editing)?
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Re: MAF Signal

Postby Autonerdz » Sun Jun 16, 2013 11:57 pm

Valhalla wrote:Is it a dynamic frequency display that is peculiar to the 4000series


Yes. But the freq math function is available on any saved capture.

anomaly in the Automotive presets help screen (that needs editing)?


The automotive menu is full of 'anomalies'. Many of the setups and hook up logistics shown are actually incorrect. We do not recommend any of the automotive presets actually be used in the field. Some good stuff in there though in the way of examples and things to read. Unfortunately some of it is incorrect.

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Last edited by Autonerdz on Mon Jun 17, 2013 2:32 pm, edited 1 time in total.
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Re: MAF Signal

Postby Fat Freddy » Mon Jun 17, 2013 1:40 am

I think this is what Alan was referring to.


Yes, I thought the same.

I was just hoping we would see a better capture first.
My thoughts was the sample rate was too low. Therefore applying the maths there may give an incorrect result. - It's not the Pico way.


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Re: MAF Signal

Postby Robski » Mon Jun 17, 2013 9:58 am

Tom

just an FYI, the statement you quoted for me wasn't actually me saying that !
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Re: MAF Signal

Postby Autonerdz » Mon Jun 17, 2013 1:43 pm

Sorry Robski. I just highlighted and hit quote. I don't know how that happened.

There...I fixed it.
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Re: MAF Signal

Postby Robski » Mon Jun 17, 2013 7:27 pm

Autonerdz wrote:Sorry Robski. I just highlighted and hit quote. I don't know how that happened.

There...I fixed it.

No worries Tom........no drama :wink:
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Re: MAF Signal

Postby s4c » Wed Jun 19, 2013 8:53 am

Hi

Many thanks, that was the type of thing I was trying to achive.

I will have to up the samples and have another try.

I am greatfull for your help

Simon
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