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# Shop Balancing Machine Questions - Sensitivity Unit Conversion & Determing Achievable Unbalance2

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## Shop Balancing Machine Questions - Sensitivity Unit Conversion & Determing Achievable Unbalance

(OP)
Hi everyone, I'd appreciate some assistance with the following two questions, I do not have much experience with balancing machines.

I'm attempting to convert a balancing machine sensitivity specification from g-mm/kg to Imperial (USCS) units of oz-in/lb. I've used the following conversion factors but do not seem to obtain a value that is anywhere near the spec provided by a company so I think I must be missing something. (0.0353 oz / 1g)(1 in / 25.4 mm)(1 kg / 2.2 lb) Using those conversion factors for a 0.1 g-mm/kg sensitivity I arrived ~6.3E-5 oz-in/lb vice the company conversion of 0.04 oz-in/lb. I've attached an excerpt from their specs.

[1] Is my approach of just multiplying the conversion factors incorrect? If so, could someone please communicate what I may be missing?

The next item of possible confusion pertains to that sensitivity specification, more specifically its application and relationship to eccentricity, and minimum achievable residual imbalance. These three terms all seem to have the same units and I've read them on different company product specs so I suspect they are similar.
[2] Once the sensitivity is successfully converted, it seems that I could use that value to determine the achievable unbalance (assuming ideal or defined conditions) by simply multiplying by rotor weight with correct units, would that approach be correct?

Thank you so much for any assistance with the above two items.

### RE: Shop Balancing Machine Questions - Sensitivity Unit Conversion & Determing Achievable Unbalance

(OP)
@GregLocock, I'm not sure, it's possible they made a mistake, I just thought it more likely that I did.

In the 2nd question I mentioned rotor weight because we primarily deal with rotor and impeller balancing, but I suppose I should have written rotational part or assembly weight.

### RE: Shop Balancing Machine Questions - Sensitivity Unit Conversion & Determing Achievable Unbalance

I get the same result as OP and Greg.
I used smath as a scratchpad to show the calulation:
https://en.smath.com/cloud/worksheet/MEMTS5qo

=====================================
(2B)+(2B)' ?

### RE: Shop Balancing Machine Questions - Sensitivity Unit Conversion & Determing Achievable Unbalance

#### Quote:

[2] Once the sensitivity is successfully converted, it seems that I could use that value to determine the achievable unbalance (assuming ideal or defined conditions) by simply multiplying by rotor weight with correct units, would that approach be correct?

I agree. Unless there is some other definition given for "sensitivity", I can't think of any meaning for sensitivity other than that it is equivalent to eccentricity e, (with a different choice of units)

Eccentricity e can be converted to unbalance m*r by multiplying by rotating part mass M
(m * r) = e * M

=====================================
(2B)+(2B)' ?

### RE: Shop Balancing Machine Questions - Sensitivity Unit Conversion & Determing Achievable Unbalance

(OP)
@electricpete thank you for taking the time to work through the two questions and provide confirmation. I've bookmarked that smath tool, that is the first time i've seen it, pretty nice.

@GregLocock thank you for the confirmation as well.

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