## mg

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Mark Dalton
TwoWaves
Posts: 86
Joined: Mon Dec 01, 2014 9:35 pm
Location: Melbourne

### mg

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.

STC
Banned
Posts: 790
Joined: Sun Sep 13, 2015 2:10 am

### Re: mg

Mark, have you considered adding that weight and making measurements. Becoming the pioneer ???
Last edited by STC on Wed Aug 30, 2017 7:44 am, edited 1 time in total.

Mark Dalton
TwoWaves
Posts: 86
Joined: Mon Dec 01, 2014 9:35 pm
Location: Melbourne

### Re: mg

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)

Steve Smith
Pico Staff Member
Posts: 658
Joined: Sun Aug 25, 2013 7:22 am

### Re: mg

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

Mark Dalton
TwoWaves
Posts: 86
Joined: Mon Dec 01, 2014 9:35 pm
Location: Melbourne

### Re: mg

Thanks Steve,
Every little bit of knowlege helps.

Steve Smith
Pico Staff Member
Posts: 658
Joined: Sun Aug 25, 2013 7:22 am

### Re: mg

Amen to that Mark.

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

Take care......Steve

Steve Smith
Pico Staff Member
Posts: 658
Joined: Sun Aug 25, 2013 7:22 am

### Re: mg

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.

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

Technician
TwoWaves
Posts: 429
Joined: Thu Apr 24, 2014 8:32 pm

### Re: mg

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.