mg

Ask questions relating specifically to the PicoDiagnostics NVH equipment and software here.

mg

Postby Mark Dalton » Tue Aug 29, 2017 7:23 am

I have just been thinking (Probably the cause of the smell of burning rubber in the office). So, the amplitude for vibrations are measured in mg. Am I correct in assuming that this is milli-g? So then is that 0.0098 m/s2?
Is there an easy way to visualise what, eg 40 mg is. I'm so used to thinking about balance in terms of wheel balancing and gram weights.
Say if I deliberately stuck a 10 gram weight on a tailshaft, would it be possible to calculate what effect this would have in terms of mg?
Not sure I'm even asking the correct questions here, just trying to get my head around this.
User avatar
Mark Dalton
TwoWaves
TwoWaves
 
Posts: 81
Joined: Mon Dec 01, 2014 11:35 pm
Location: Melbourne

Re: mg

Postby STC » Wed Aug 30, 2017 12:11 am

Mark, have you considered adding that weight and making measurements. Becoming the pioneer ???
Last edited by STC on Wed Aug 30, 2017 9:44 am, edited 1 time in total.
User avatar
STC
Banned
 
Posts: 790
Joined: Sun Sep 13, 2015 4:10 am

Re: mg

Postby Mark Dalton » Wed Aug 30, 2017 9:44 am

I haven't bothered trying the thing with the weight. My assumption would be that the formula/methodology for the conversion is well over my head to be able to reverse engineer.
I've also had someone suggest that the Amplitude is in Gal (Galileo - 1 cm/s2)
User avatar
Mark Dalton
TwoWaves
TwoWaves
 
Posts: 81
Joined: Mon Dec 01, 2014 11:35 pm
Location: Melbourne

Re: mg

Postby Steve Smith » Fri Sep 01, 2017 11:30 am

Hello and thank you for the posts, sorry again for a late reply.

This has rolled around my head for a while as there must be a correlation between mg and the amount of imbalance weight applied.

This is the exact process the Propshaft Balancing software uses to determine the amount and position of weight to be applied to a shaft in order to reduce the vibration level (measured in mg)

Just going back to your posts Mark, 1 mg = 0.0098 m/s2 and the Gal unit is used to measure the amplitude of vibration. Both these statements are correct (1 Gal = 0.01 m/s2)

Using the NVH software we choose the mg unit to denote the amplitude level but you can alter this by selecting Option > Advanced Options > Accelerometer Units where you can switch between mg, m/s2 and dBg

Coming back to the original question re the correlation between mg and weight:

The Prop-shaft Balancing software initially measures the level of vibration in mg (Initial Run)
We are then asked to apply weight a 3 strategic point about the circumference of the shaft (Test Runs)
Here we introduce a deliberate 3 point imbalance allowing the software to calculate the relative position and mass of our correcting weight in order to reduce the vibration level.
We then confirm the reduced vibration during the Verification Run where we aim for less than 20.0 g.cm

What I am getting at here is we are using mg (vibration level) as one of the essential units in the formula to determine the weight (grams) to minimise vibration
Within this formula we also require the Propshaft Speed and Circumference as both these fundamentals will have a dramatic effect on vibration.

I will dig a little deeper here Mark and look at the formula to see how mg and weight correlate.

Whilst I was looking into the above Wikipedia has a great description of Rotating Unbalance which helps to visualize why we experience vibration.

Rotating unbalance is the uneven distribution of mass around an axis of rotation. A rotating mass, or rotor, is said to be out of balance when its center of mass (inertia axis) is out of alignment with the center of rotation (geometric axis). Unbalance causes a moment which gives the rotor a wobbling movement characteristic of vibration of rotating structures.

I hope this helps, take care.......Steve
Steve Smith
Pico Staff Member
Pico Staff Member
 
Posts: 481
Joined: Sun Aug 25, 2013 9:22 am

Re: mg

Postby Mark Dalton » Mon Sep 04, 2017 7:58 am

Thanks Steve,
Every little bit of knowlege helps.
User avatar
Mark Dalton
TwoWaves
TwoWaves
 
Posts: 81
Joined: Mon Dec 01, 2014 11:35 pm
Location: Melbourne

Re: mg

Postby Steve Smith » Mon Sep 04, 2017 8:26 am

Amen to that Mark.

Everyday we grasp a bit more, the trick is logging and recalling it when required.

I will add more ASAP

Take care......Steve
Steve Smith
Pico Staff Member
Pico Staff Member
 
Posts: 481
Joined: Sun Aug 25, 2013 9:22 am

Re: mg

Postby Steve Smith » Fri Sep 08, 2017 11:15 am

Still looking into the mg to gram correlation issue but for now this came to light thanks to Alan here at Pico

If you want to dip your toe into NVH make this video the one to watch.

https://www.youtube.com/watch?v=RWhyI6EcUgM

This is a Toyota Service Training video from yester-year but the content is both awesome and relevant today.

In particular take a look at 21 to 24 minutes how wheel and tyre run out issues are tackled statically and 28 to 32 minutes looking at propshaft balancing.

There is a formula contained within the propshaft balancing sequence that goes a long way to correlating vibration levels to weight applied (mg to gram correlation)

Take care.......Steve
Steve Smith
Pico Staff Member
Pico Staff Member
 
Posts: 481
Joined: Sun Aug 25, 2013 9:22 am

Re: mg

Postby Technician » Sat Sep 09, 2017 11:20 am

I was very impressed Steve with the Utube video Toyota have completed. About 20 years ago I was at University completing a BENG degree, yes a life time ago now, but still got the files of work I completed. Harmonic motion, vibration, noise etc was apart of our studies back in the day. The NVH kit (not got one) for what I have seen looks an impressive kit, I wonder of the people having these kits do you supply or have training material like Toyota provided with your kit, or are buyers left to their own devices once bought?

Thanks

Tech.
Technician
TwoWaves
TwoWaves
 
Posts: 262
Joined: Thu Apr 24, 2014 10:32 pm


Return to PicoDiagnostics NVH

Who is online

Users browsing this forum: No registered users and 0 guests