Frequency waveform for 8-wire digital MAF

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AdvTechTS
OneWave
OneWave
Posts: 13
Joined: Wed Jun 18, 2014 12:32 pm

Frequency waveform for 8-wire digital MAF

Post by AdvTechTS »

Hi all, I'm looking for some advice on the waveform I've take from a 2015 Holden Commodore 3.6L V6 SIDI which employs an Hitachi 8-wire MAFM (GM actually call it a multifunction intake air sensor). These new MAFM's output Air Mass, Humidity, Baro and 2 air temp values. With all of that said my capture is simply the MAF Value. I used the digital MAF settings that come preset in the software but had to adjust the channel scale and offset in order to see the signal.

I am used to seeing the interference of the ignition system in the MAF waveform but I have never seen anything like this. I don't believe there is an issue with this signal but I was hoping to get an explanation for the waveform.

***I am referring to the spikes on the frequency trace that are triggering the over-range warning***

Thanks in advance :D
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Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1581
Joined: Sun Aug 25, 2013 7:22 am

Re: Frequency waveform for 8-wire digital MAF

Post by Steve Smith »

Hello and thank you for the post, sorry for such a late reply.
Unfortunately the spikes we see here (Channel A) are a response to the inherent noise present on the
DC signal (Channel B)
Noise detection via Frequency Coupling
Noise detection via Frequency Coupling
If you are using a 4425 or 4225 PicoScope, using the Bandwidth limit feature (Hardware Filter) will remove this noise entirely. Below is a BMW 3 Series N47 without the Bandwidth limiter active:
Without Bandwidth Limit
Without Bandwidth Limit
Below we have the Bandwidth limit feature active
With Bandwidth limit
With Bandwidth limit
Activation of the Bandwidth limit feature can be found here:
https://www.picoauto.com/library/training/filtering

If you are using the 4423 or 4223 PicoScope the Bandwidth limit feature is not available, however all is not lost.

One option that will reduce the captured noise is to amend the Frequency Counting settings found under the Channel Options button.
Amend Frequency Counting settings
Amend Frequency Counting settings
Whilst the noise/spikes are reduced they remain during the WOT test.

Amending the Frequency Counting settings will allow for finer control of the crossing point value (both rising and falling edges) used by the software to calculate the frequency.

This is typically sent to + - 50 mV AC coupled which is fine but if “noise” is present within this “counting” region of the signal, the hardware is will detect and display the noise at the relevant frequency.

Amending the Frequency Counting input coupling setting to DC and shifting the crossing point to +3 V rising edge and 1 V falling edge (which may be more defined than + -50 mV AC) eradicates the noise at idle speed and reduces the noise at WOT

Alternately you can leave the Frequency Counting input coupling to the default AC but amend the crossing point values to a point within the signal where the noise level is reduced.

Below I have opted for + 1 V – 500 mV AC coupled
Amend Frequency Counting AC Coupled
Amend Frequency Counting AC Coupled
Experiment with these input values live whilst capturing the signal will help to fine tune these settings for optimal results.

Alternatively using a Math Channel will allow for filtering of the noise using the low pass filtering feature for the DC coupled signal on Channel B
Freq Math Channel- Low Pass Filtering Active (20 kHz)
Freq Math Channel- Low Pass Filtering Active (20 kHz)
I hope this helps, take care…….Steve

AdvTechTS
OneWave
OneWave
Posts: 13
Joined: Wed Jun 18, 2014 12:32 pm

Re: Frequency waveform for 8-wire digital MAF

Post by AdvTechTS »

Thank you Steve,
I do have the 4423 but it is good to know that all is normal. The interference doesn't bother me now that I know that it is normal. I will try your tweaks next time. Happy New Year :D

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