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Hi ALL,

I am a new user of LabVIEW.
I have been assigned to acquire a signal from a sensor at a car.
However, all these signals must be filtered.

But I am not sure, what type of filter most powerful. Besides, as I
know, different type of signal needs differenct type of filter.

Anybody can help me to solve my problems.

Your kind cooperation is highly appreciated.

Regards,

M. Firdaus,
France
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Message 1 of 7
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There are two sorts of filters:

Normal filters working on an aquired signal as an array and PointByPoint filters working on one value. The first one you can use for offline analysis and the second one for in time filtering.

 

Which typ of filter is best depends on the signal how it should look without any distortion. Maybe a lowpass or bandpass filter is a good starting point. To eleminate any noise resulting from the revolution of the motor a bandstop filter is a good choise.

Waldemar

Using 7.1.1, 8.5.1, 8.6.1, 2009 on XP and RT
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Message 2 of 7
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Fird wrote:
> Hi ALL,
> I am a new user of LabVIEW.
> I have been assigned to acquire a signal from a sensor at a car.
> However, all these signals must be filtered.
>
> But I am not sure, what type of filter most powerful. Besides, as I
> know, different type of signal needs difference type of filter.
> Anybody can help me to solve my problems.
> Your kind cooperation is highly appreciated.
> Regards,
> M. Firdaus,
> France

1) assuming the signal is analog, connect an analog or high frequency digital oscilloscope or signal analyzer and get an idea of the amplitude and frequency content of the signal and any noise that might be on that channel.

2) once you have that information, you can select an appropriate filter. Note that you may require an anti-aliasing "analog" filter, prior to sampling to avoid any noise aliasing issues.

3) If the noise is tied to engine speed, (for example the ignition system), then you may need a tracking filter that varies its notch frequency with the speed of the engine. But if your only interested in slow or DC measurements a low pass filter or averaging might suffice.

60Hz noise isn't typically a problem in car.
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PointOnePa schrieb: 

60Hz noise isn't typically a problem in car.

This is true but you have a ripple on the 12 Volt Power line resulting from the electric generator which can or can not be visible in the signal.

Message Edited by waldemar.hersacher on 01-28-2009 03:56 PM
Waldemar

Using 7.1.1, 8.5.1, 8.6.1, 2009 on XP and RT
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In addition to generator (alternator) noise, add: fuel injectors, ABS solenoids, ignition spark, powertrain solenoids. Can be a nasty environment.

 

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
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Message 5 of 7
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Just as a side note, you might want to come up with a better post title next time, such as "Signal filtering" or similar.

 

Since this is a LabVIEW forum, all threads here are related to LabVIEW, so your title is 100% redundant and has zero information content. Imagine the mess if every single post were titled "LabVIEW". 😮

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An often forgotten point is that the filter approach varies depending on whether the energy you are trying to remove is in-band or out-of-band. In-band energy (meaning any components with a frequency up to 1/2 the sample rate) can be removed by filtering in software. Out-of-band energy has to be done in hardware because the purpose if this filtering (sometimes called anti-alias filtering) is to remove any frequency components greater than 1/2 the sample rate so they don't corrupt the output of the A/D converter.

 

Having said all that: Spark plugs are amazing things - harmonically speaking... Look at them as small very-very-wideband transmitters. Their fundamental frequency is obviously a function of engine speed, but the harmonics go much much higher.

 

Mike...


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