Using the NVH time domain feature that is going to enable us
To locate the source of those intermittent knocking noises
The one off events that happen instantaneously
They generate a lot of noise a real nuisance
A real true complaint from customers
How can we use time domain NVH to locate the source of
Intermittent knocking creaking squeaking noises
I am quite comfortable with amplitude and frequency
I understand that concept and I am very interested in this because
Throughout my career we have had any number of noises
Exactly as you have described as a one off event
That is almost impossible to nail
What exactly is the difference with time domain
Where is the offending noise coming from
That is really how we want to use the software to our advantage
NVH time domain you can see here that we have four accelerometers
Connected to one PicoScope
We have chosen the vertical axis from each accelerometer
And channel A here is recording the highest amplitude
What we cannot do with NVH time domain
Is measure time
Because that amplitude can trip us over
Depending how we have located the accelerometer and the
Mass which the accelerometer is attached to
But if we were to use PicoScope time domain
Then we can measure time
We can zoom in and find out which accelerometer was the first responder
The first responder will be the closest to the source off the knocking noise
And we will demonstrate this a little bit later on
So from my understanding of what you have just said is
In time domain what we are looking for
Is the first event which responds with the noise
The first accelerometer that responds to the event
And we are looking at that
With the scope in an infinitely variable time base
I think we will run the demonstration in NVH
So you can see time domain function with NVH
It will detect the knocking noise
We will see amplitude and be able to determine
One or two accelerometers that are the closest to the noise
But we can confirm this categorically using PicoScope
To measure the first responding accelerometer
The accelerometer that responded first would be closest to the source of the noise
So time domain how do we apply the accelerometers
It is exactly the same as we would if we were chasing a vibration
You can see here that we have accelerometers at four key points of the suspension
So we know we have a complaint from the drivers rear suspension
An intermittent knocking noise
We have accelerometers at track control arm
Tie rods
Bottom wishbone
Track control arm
One of those will respond first to the knocking noise
We could possibly see one accelerometer display a greater amplitude
But that may be after the event
What is important what is key here is that we capture the
Accelerometer which responds first to the knocking noise
Let us look how we would apply theses accelerometers on a vehicle
To capture an intermittent knocking noise
The challenge we are facing here with this vehicle
Arises from a customer complaint of an intermittent knock
We have established that it is from the nearside rear of the vehicle
And as is common with most vehicles now
We have light weight suspension components
Multi link set up is identifying precisely which component
Is responsible for this knock or noise
So Steve
Suspension knock on the left hand rear of this vehicle
We are going to take advantage of the NVH advanced kit
Because we have four accelerometers that we can
Position about the suspension
You could use the standard kit with two accelerometers
But more measurements would be required
Before we have the advantage of pin pointing and triangulating
The source of the knocking noise
So accelerometer at the moment one mounted to the
Track control arm at the suspension hub
One at the lower suspension arm at the hub assembly
Track control arm at the sub frame
So the opposite end of the track control arm
And then one at the trailing arm as well at the hub assembly
So know we will be able to manoeuvre the suspension however
It is necessary to generate that knock
And look in the time domain of PicoScope
To try and determine which accelerometer
Is responding with the greatest amplitude
Something you said to me while setting this up
Was the fact that you deliberately align all the accelerometers
In a similar physical direction
As you can see we have accelerometers and we have rotated
The magnet on the accelerometer because we can put this vertically
Or rotate it 90 degrees
That gives us the option or angle to measure
The vertical axis as that is our chosen axis of each accelerometer
In other words we will compare each accelerometer mounted
In the same orientation on the same axis
This is comparing apples with apples
So to make life easier here
We have colour coded each one of the accelerometers
Just with a coloured sticker
So if we follow these cables through
Each accelerometer is connected to an interface
Through the interface into PicoScope
We have chosen to measure the Y axis
From each accelerometer so we are comparing
The Y axis from each accelerometer in the same orientation
The set up for the time domain differs now from a road test
Because remember this vehicle is on the ramp
We do not need to obtain engine speed or road speed
It is a static test so here we will put a
Static RPM value in there
We will say that we want to measure with multiple sensors
So it is multiple sensor mode with four accelerometers
We will say that each accelerometer is mounted in the engine compartment
Consider that as being outside of the vehicle not inside the vehicle
It is important in each of these sections to write down
Exactly where your accelerometer is because we need to refer to
These locations later when we are looking at the
Response from each accelerometer
So we go to record and analyse because there is
No need to enter information like tyre size
Click on the record and analyse button
And there we will see each channel
Live in what we call a time domain
So any noise any knock any input to accelerometer
Will be met with a response we can measure in the time domain
So a tip here Frank is to test each accelerometer before we move on
So just tap each accelerometer and check for a response
Perfect we can see there if we pause the software
And highlight one of those areas
There is a response from each accelerometer
You will see how the amplitude differs
Depending on which accelerometer we are striking
You mentioned Frank about response from each of these
Yes it was interesting that the transfer path
Can both absorb energy and amplify energy
And as we said that the amplitude alone
Is not the definitive measurement
It is difficult to ensure you connect every accelerometer
To a surface of the same mass same dimension
At this stage we are looking at response
That will certainly pinpoint and lead us to an area of concern
So now we have confirmed an input or response from each accelerometer
We will restart the software
And we will generate this knock for real
So Frank if you could have a look there and see
The movement and identify the knocking noise
I can see movement and that is often the case
But I am very aware that if I go and observe the screen
There is a specific response from the red accelerometer
So lets pull that back and drag it over
There is the movement that is the knock we were generating
And clearly red is responding there is a greater amplitude
From the red accelerometer so that leads us
Certainly closer to the hub than further away
Based on the red accelerometer location
So we can use a couple of features in the software
We can hide a few channels
The best way to do that is to right click on the software
And let us take away channel A
We can also take away channel D
There is very little response from that accelerometer
We can clearly see there then that B
Based on amplitude alone is closest to the source
But how could we measure that more accurately
Ideally we are looking for the first responder
As that will be the closest to the source of the noise
For that we would use PicoScope because there
We can measure time and we can zoom in
So our voltage settings for the accelerometer
We have gone for 100 mV
AC coupled
We set the time frame to 200 ms divisions
And we have gone for 1 million samples
That gives us the perfect setting to capture the
Response from each accelerometer and once we have captured the response
We have the additional feature of zooming and
Measuring the time looking for the first responding accelerometer
Because the accelerometer that responds first
Is the closest to the source of the noise
A complete tip here is to make sure you identify
The positions as we did with NVH
So using the channel labels using the notes feature
Identify where each accelerometer is mounted
Because it could be that you have generated the noise
You are analysing away from the vehicle
It is important that we identify accelerometer positions
I understand the set up for the scope which I thank you for Steve
I guess that for your input command you are choosing
A x1 standard lead set up
And that you have not gone into the component menu
So I guess there is no accelerometer within this
Specific help menu within Pico software is that correct
There is not but you can create one
You could create a custom probe so that rather than measuring voltage
You would have a mg measurement
But for the purpose of this test we are just looking remember
For the first responding accelerometer
So the voltage output from the accelerometer
Is fine there is enough information right there
And I guess depending on the amount of energy we are measuring
Would also affect the amplitude for the setting of the
The scaling of the probe input
Absolutely the point to remember is keep everything the same
So it is AC coupled for each one
Same voltage measurement so we are on the same range
All comparisons are than equal
Let us generate this knock for real
Then we will use the features of PicoScope to zoom in
And determine which was the first responding accelerometer
Have you captured that Frank
Yes I captured that
It is interesting as well that how you put effort into the suspension
Does effect the results so maybe do multiple tests
Just to clarify the results
So zooming in on the test result
We can see certainly that the amplitude from the
Red accelerometer is greater
But more importantly that the red accelerometer
Was the first to deviate from zero the first responder
So here we are relying on time to give us the indication
Rather than amplitude
The very interesting thing for me here watching
You do that test was although I could physically see
Movement in the suspension I could not see which joint it was coming from
Whereas with NVH you can very clearly
Other uses for time domain
Clicks creaks
Panels and fretting noises they all spring to mind
Think of sub frames where different sections of frame come together
At one point multiple weld points
Multiple panel joints where a hinge panel is reinforced
A tailgate hinge a door hinge reinforcement there
Any slight movement will generate click or creek
Or even knock in worse case scenario
The base of the A post again there are so many panels come together
The floor meets the sill meets the A post meets the bulkhead
Any movement there as the car hits a pot hole
Or flexes in cornering
How could you possibly pinpoint something like that
What tools have we got other than NVH
I can certainly recount on at least a couple of occasions
When we had some very high end vehicles in the workshop
With exactly that phenomenon it is a sudden noise
It is an aggressive noise it is a loud noise
And the potential cost has been prohibitive
And we actually did turn the work down
If I understand this right I am getting a feel for this now
What we are actually doing with time domain
Is turning sound into vision
Absolutely
So we can then understand where that noise is coming from
Yes we can view the amplitude of the noise
Remember we can also play this noise back
Because we can listen to accelerometers as easily as we can microphones
That concludes time domain
In the next video we will look at the application of microphones
Investigating complaints of noise