Ask questions relating specifically to the PicoDiagnostics NVH equipment and software here.
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Steve Smith
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by Steve Smith » Wed Mar 30, 2016 10:10 pm
I can remember a forum post some time ago about a request for a “real-time” feature within the NVH software with regards to measuring harshness such as knocks, creaks and squeaks.
Such noises/harshness (whilst annoying) are present for a very short period of time with insufficient energy to be transferred and displayed in the Frequency Display (FFT) of the NVH user interface.
Well, the great news from Pico (thanks to the software team) is that we can now introduce the “Time Domain” feature of NVH in the latest Automotive Beta release 6.12.1.1691
So why the “Time Domain” feature?
Well, how often are we presented with squeaks, creaks, rattles and knocks etc.?
For those who have used the NVH software, you may have noticed the effect on the signal history chart when monitoring vibration/noise when the vehicle hits a pot-hole?
The event (pot-hole strike) is captured in the signal history as this displays the input of the attached mic or accelerometer live (relative to time).
Such events are not transferred for view in the Frequency display as we require a minimum of 2.5 seconds of continual disturbance in order to process the event.
Until now, symptoms such of these would be reserved for “listening devices”, enabling the technician to listen to the intensity of noises delivered to a headset from microphones placed about the offending area of the vehicle. The results however are subjective and open to misinterpretation
Example of Time Domain in action:
Using contact microphones whilst looking for a suspension knock over uneven road surfaces at low speed, 4 x contact mics were attached to 4 possible offending suspension components in order to locate the source of the knocking sound.
The image below demonstrates a typical set-up using Multiple Sensor Mode where our contact mics have been selected, connected to the TA149 interface units and located at point about the suspension recorded in the notes section.
I cannot stress at this point how important it is to get the set-up correct and indicate how and where you have placed your mic’s. If this information is not correct your diagnosis will be off course. (Notice my mistake for channel D as I have not selected “microphone”)
The vehicle was then driven at low speed over uneven ground to produce the knock whilst the “Time Domain” display is selected. The green markers in the signal history denote when the knock occurred and you can listen to the knock via headphones connected to your PC.
To listen to each knock individually (each mic in turn) right click on the Time Domain display and select “channel in view” Here you can select the channels you wish to view, measure and listen to via headphones.
Removing “channels from view” allows the technician to analyse the input from each mic individually. Based upon the peak amplitudes captured, we can locate the source of the knocking noise and replace the relevant component. In the case below the NSF lower suspension arm produced the highest amplitude (during the knock) which was later confirmed as lower wishbone ball joint.
Over and above the Time Domain feature we have additional features available under the “Options” tab of the NVH software.
1. Load Audi Files will allow for .wav files to be loaded into the NVH software for analysis. Typical scenarios would be sounds/video recorded by customers via Smart phones. Here we obtain the customers recording, extract and convert the audio file to a .wav audio file (using third party software) and then import into the NVH software for analysis
2. Function Generator will allow for the playback of audio at specific frequencies. This feature will allow technicians to listen to audio played back at specific frequencies and match the audio to sounds present on a vehicle. This could be a transmission whine measured using the NVH mic at 1200 Hz. How do we know what 1200 Hz sounds like? Using the function generator we can playback audio at 1200 Hz and confirm the playback matches the pitch of the transmission whine. Our peak amplitude measured using with the mic at 1200 Hz is therefore relevant to the whining transmission as the measured frequency pitch matches the audio playback
We can manipulate this feature to playback audio into the vehicle In Car Entertainment system (ICE) via the PC headphone socket, streamed from the PC via Bluetooth or FM Modulator if the vehicle is without Aux and Bluetooth. So why would this be useful?
Customers who complain of interior rattles will often have difficulty in describing the sound or pin pointing the location. If we playback variable low frequencies into the ICE using the Function Generator and increase the volume we can generate rattles inside the cabin that can be confirmed by the customer and assist the technician with location. In this scenario the technician identifies the rattle with the customer present and area of the cabin at fault.
Onward and upward with NVH and there is so much more to come.
Take care………Steve
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volrem
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by volrem » Thu Mar 31, 2016 4:30 pm
Nice features and another reason to finally get NVH kit.
One annoying thing though.
When right clicking to select channels in view and then selecting channel I can only select one.
It would be great if menu wouldn't go away each time I click on channel. I would like it to be visible until I click elswhere so that I can turn off all three for example.
To keep only one visible I have to run three times sequence: right click -> Channels in view -> A / B / C / D
If the menu would stay visible even after selecting channel then it would be quicker and more user friendly.
Small but important thing I think. In PicoScope software visible channel selection works as it should.
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Steve Smith
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by Steve Smith » Thu Mar 31, 2016 7:35 pm
Thank you Volrem for the feedback and well spotted.
I have reported this issue and it will be resolved rest assured.
Take care........Steve
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eric989
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by eric989 » Thu Apr 21, 2016 9:11 am
The TA149 interface have 3 output to Scope. Which output should be connected to scope when using multiple sensors mode selected microphone? I thougt any output should be ok, and the signal from the 3 output would be same. Right?
Thank you, Steve.
Eric Chen
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Steve Smith
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by Steve Smith » Tue May 17, 2016 4:04 pm
Hello Eric, sorry for the late reply and thank you for the post.
You are correct when using the Pico NVH microphone with the 3 output interface TA149/TA259, the output to the scope will be the same regardless of which output you use.
When using a 3 axis accelerometer, this requires a little more consideration.
Your initial run/road test will be with the accelerometer attached to the driver’s seat bolt in the correct orientation to define the axis with the highest vibration level. (For example T1 Y axis 30 mg)
You will have discovered it was the Y axis when using Display mode “Single”
You can then use Channel D with another 3 output interface and mount an accelerometer on each corner of the vehicle in order to determine the highest amplitude of vibration.
Given you know the Y axis is the offending vibration, use the Y output of the 3 output interface to connect to channel D of the scope but be sure to mount the accelerometer vertically at each corner of the vehicle (as you have with the accelerometer mounted on the seat bolt)
If you are not interested in discovering the axis of vibration and only concerned about the combined amplitude (Display mode “Vector Sum”) then you can mount the accelerometer on each corner of the vehicle in any orientation and choose any output on the 3 output interface to connect to channel D as all axis of the offending vibration are vector summed.
I hope this helps, take care........Steve
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Mark Dalton
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by Mark Dalton » Fri May 20, 2016 4:13 am
Hi Steve,
Are you using any particular brand of contact Mic. or are you just using the accelerometer, if it's not the accelerometer, how are they being connected up to the interface Box.
Thanks.
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Steve Smith
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by Steve Smith » Wed May 25, 2016 10:21 pm
Hi Mark, thank you for the post.
The development contact mics were Piezo based mics requiring no power and so could connect straight to the scope via the BNC terminals
Be careful though Mark a the difference between mics of the same specification was "varied" to say the least and could lead you astray.
It is certainly worth experimenting with if you have access to such mics.
Multiple Pico accelerometers however make for far more robust test results
Take care........Steve
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Mark Dalton
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by Mark Dalton » Thu May 26, 2016 5:11 am
This is sort of why I was asking. I've experimented with Piezo Transducer Mic's from a chassis ear kit we had and also bought some Transducers myself and made my own Mic's and I found it was difficult to get consistent results. I did a little bit of research as to whether giving each Mic. it's own Amplifier and filter Circuitry would help , but it ended up becoming a bit time consuming trying to build prototype circuitry. So when I seen your comments about clip on Microphones I got all excited, thinking you may have found a supplier that gave good consistent results.
Can the Accelerometers be bought separately??
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Steve Smith
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by Steve Smith » Sat Jun 04, 2016 1:23 pm
Hello Mark, sorry for the late reply.
This is where we are right now with the development of clip on mics. (It will happen)
Consistency is everything and they must reveal the relevant amplitude at the correct time or the results are useless
At present you can purchase a 3 axis accelerometer either via the Pico Auto site, or the Pico Tech site (Test @ Measurement)
https://www.picoauto.com/products/nvh-a ... it-in-foam
https://www.picotech.com/accessories/ac ... elerometer
Both contain the 3 output interface but one with foam storage and an extra BNC cable.
Could I ask Mark, would you like to purchase a 3 axis accelerometer without the 3 output interface?
Accessories for our kits are always under review and any feedback here is most helpful
Take care........Steve
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Mark Dalton
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by Mark Dalton » Tue Jun 14, 2016 11:33 am
For the time being, neither I guess. I would hang on for the clip on mics. What I'm hoping the clip on mics will allow me to do is...get a quantitative measurement of squeaks, creaks and knocks , so i can triangulate to pin point the source of a noise. I'm not sure I'll be able to do that with the current accelerometers and interfaces, can I?
