So up until this point we have looked at vibration only
What about complaints of noise cabin whine or whistle
These are all higher frequencies
We have got a case study here which we can replicate
That turns out to be a cooling fan issue
The story goes that there is minor accident damage at the front end of the vehicle
Body repair is perfectly fine but at certain moments
There is quite an intense vibration passing through into the cabin
So if there is a compliant of noise we should include the microphone
We can still use the accelerometer but let us add the microphone
And place that in the cabin
Ideally next to the drivers ear if it is them who is complaining of the noise
Or maybe rear view mirror as that will give us an
Overview of all the noises present in the cabin during a road test
So let us have a look at the animation
Here we are adding the microphone to channel D
There we have the issue which was a damaged cooling fan
And here we explain the noise in bar graph view
You can see there we have the intense vibration
That comes on when the cooling fan comes on at top speed
And we are displaying there the bar graph view
On the right hand side you will see the top five unknown vibrations
That is unknown because it is not linked to engine or road speed
It is an electric cooling fan
What I have picked up there from the bar graph
Is that it is an unknown frequency
It is no related to something we are able to synchronise
To known data from the vehicle set up
That is exactly right Frank and the view we have chosen there
On the right hand side the bar graph view is showing
The top five unknown vibrations
We have highlighted vibration 1
39 Hz it is
Peak vibration detected by the accelerometer in the vertical axis
But also detected by the microphone inside the cabin
So we are certainly tuned into the customers complaint
Let us go and replicate this on our van
What we have done here with the van is simulated exactly what you saw in the animation
We have introduced a deliberate imbalance to the cooling fan
We have also introduced the microphone into the cabin
So not only will we measure the vibration but we will measure the sound
Which remember is one and the same thing
The microphone and the accelerometer both detect the vibration
The sound generated
And display them differently but at the same frequency
So we can use either or in this scenario
Certainly this would be your choice of measurement for chasing
A transmission whine for example or brake squeal
Anything above 200Hz
So really this technique is for nondescript noises
That can not be identified to a particular component
So connection wise we have gone for 3 axis plus single channel
So still use one accelerometer measuring all three axis
But the additional channel now channel D
Is the microphone connected to the rear view mirror
So in a road test example the microphone will detect all noises
But there is a specific noise we are chasing here which is
The noise generated from the imbalance in the cooling fan
For the set up we do also recommend moving the position of the microphone
Once you are homing in on the noise to perhaps increase the amplitude of the results
The opportunities are endless really because
Certainly always keep a microphone in the cabin as a reference
Because that is what the customer can hear
Perhaps keep one in the cabin and one in the engine bay
And also keep the accelerometer as well so you have
Three points of reference really
Think of bearing noise if you have got the luxury of four
Microphones four accelerometers
One road test one measurement with a reference inside the cabin
Would you also recommend multiple microphones in the same way
You recommend multiple accelerometers
I would most certainly yes
The advantage of the accelerometers is we loose a lot of the ambient noise
However the microphone gives a true representation of what the customer can hear
So always include a microphone in these kinds of measurements
As your customer reference
An indication of what the customer can hear
The set up here for the cooling fan noise vibration
We have gone for a static RPM
Remember we are not road testing we are not looking for a
Vibration relative to engine or road speed
We have gone for a 3 axis plus single channel measurement
3 axis is our accelerometer mounted to the drivers seat
And the microphone is up at the rear view mirror
That is giving us the customers audio reference if you like
What the customer can hear
If we go to record and analyse
We will restart the recording because we have previous data here
There is a warning there to let you know that
If you do restart the recording everything that you have here is now lost
We will start the recording here
We use the autoscale feature
And we will let the scan tool software run the cooling fan
OK if we can stop the cooling fan there
We will pause the software
And we can then drag our highlighter here
Pull that onto the offending area which was this area here
Use the right click autoscale feature
And we can see that both the accelerometer and the microphone have
Picked up the frequency the offending vibration noise
The customer can hear
We can just use the channel in view and concentrate on the audio
So channel in view enables us to take away
Channels A B and C which is our accelerometer
And we are left then with this offending frequency
The highest peak in the spectrum
This is approximately 36 Hz this is our offending frequency
Steve how come we have got this 38 Hz
How can we then relate that to a specific component
That is a great question
We know that that is the peak that we have captured during the vibration
During the noise
We know that frequency and speed are directly related
Hz times 60 is RPM
But we could actually use the speed of the cooling fan
If we have got one disturbance from this cooling fan
Remember in the animation there is a blade missing
On this cooling fan we have added weight
One disturbance per revolution
Let us use an optical pick up on the fan
Which theoretically should give us a frequency of 36 to 38 Hz
Just using an independent hand held optical interface using PicoScope
So how have we created the imbalance in the cooling fan
Simulating what you saw in the animation which was a missing blade
We have placed a bolt through this blade here
For one revolution of the fan that will create one disturbance
How can we determine the speed frequency of this fan
Remember speed and frequency are one and the same
We attach some silver tape here
And point the optical pick up at the cooling fan
So every time the optical tape passes the optical pick up
It generates one pulse per revolution
That will give us the frequency of the fan
We then use PicoScope to not only count those pulses
But display the frequency of those pulses
Which should come out about 36 Hz
Because we captured our peak amplitude vibration
At 36 Hz in NVH
So using the optical pick up to determine the frequency
Of the cooling fan
We will connect that into channel A of PicoScope
Run the cooling fan at top speed
There is only one speed setting for this one
And see what PicoScope displays in terms of frequency
As you will see there I have placed
A marker signal ruler at 36 Hz
PicoScope is frequency coupled
Theoretically if we have got our maths right
When we run the cooling fan we will see that
Top speed or peak vibration occurs at 36 Hz
Can you run that please
OK can you switch the cooling fan off now
If we pause the software at that point
We can see how the frequency climbed as the speed of the fan increased
And topped out at approximately 36 Hz
If we do the maths on that
36 x 60 giving the cooling fan 2160 RPM
So another way Frank of qualifying the frequency speed of a component
It may be worth mentioning also that the channel input command
Had been set not for AC DC But to frequency
To obtain this information
Frequency coupling with PicoScope is available in current 4000
And previous 4000 generations of PicoScope
I think the really interesting thing I have picked up
From this bar graph is that we can clearly see on the right hand side
That this frequency of around 35 Hz
Sits quite nicely between E1 and E2
So we know it is not the engine
The way I am thinking at the moment is
If we increase the frequency of the engine
There could be a situation where we get resonance
Where we get two forces out of balance which add together
But looking at it in this way
We are able to separate this issue and see very clearly
This is a non engine related component
Causing this problem
So we have concentrated on the frequency view
This is exactly the same data but in bar graph view
Where we have used the software to highlight
The know vibrations on the left
And the top five unknown on the right
In this scenario we had 39 Hz
Remember cooling fan frequency will be dependant
On battery voltage as well
So if we are going to run the cooling fan for simulation
Battery voltage is key for RPM
So that concludes the introduction of microphone in this presentation
Join us in the final presentation where we look at
A number of real life case studies
Where we have used a combination of the accelerometer and the microphone
To determine the cause of customer complaints of vibration and noise