question about instruments tolerances

[jumacao]

I am considering a Checkweigher machine to detect missing parts in a assembly. The assemblies have between 3 to 6 different parts. The smaller parts weight around 3 grams.
The assemblies weight variability is up to 0.5 g. What process tolerances should I use? What checkweigher accuracy should I need?

 

[djs]

What is the total wieght of the heavest complete assembly? Min accuracy will then be 0.5g/max weight*100%

 

[IRstuff]

Weighing is usually something you do at the end. Do you really want to potentially start an assembly from scratch at that point? How do you know you're weighing the correct assembly?

In both cases, the issue is not how you measure the weight and determine that there's a missing part; you need to have process controls that prevent that from happening and you need to have in-process checks that assure assembly completeness at various steps along the way.

By way of analogy, do you think it's reasonable to weight an automobile to determine if it's missing its engine or transmission?

TTFN

FAQ731-376

 

[jumacao]

djs , why you use that formula?

The checkweigher if for verification purpose. Others controls are or will be in place. OF all the controls mechanims I want to know the required accuracy.

 

[IRstuff]

Only you can decide what accuracy you need to meet your requirements and minimize false readings.

TTFN

FAQ731-376