3 replies to this topic

[Benty666]

Hi All,

 

At the risk of this being a ridiculous question but what exactly is standard deviation?

 

We've been using a recording software for our checkweighers now for a few years and we've just noticed that the standard deviation is only recording when it wants to. So this morning it was recording fine but then part way through the shift it just reverts to zero and I've no idea why. I've spoken to SNB (they do our commissions and calibrations for our CW and MD) and they are awaiting a response from the manufacturer, Penko.

 

Screenshot of the software attached.

 

Thank you

[Tony-C]

Hi Benty666,

 

In statistics, the standard deviation is a measure of the amount of variation of a random variable expected about its mean. A low standard deviation indicates that the values tend to be close to the mean of the set, while a high standard deviation indicates that the values are spread out over a wider range.

 

Although SD is important, your software should be ensuring that you comply with legislation and in particular minimum weight or average and TNE ‘tolerable negative error’ requirements. See relevant legislation below.

 

How packaged goods are regulated: https://www.gov.uk/g...res-regulations

 

Three Packers Rules

These set out 3 rules that packers and importers must comply with:

The contents of the packages must not be less on average than the nominal quantity

The proportion of packages which are short of the stated quantity by more than a defined amount (the ‘tolerable negative error’) should be less than a specified level

No package should be short by twice the tolerable negative error

They provide protection for consumers on short measure.

 

Weights and measures: the law: https://www.gov.uk/w.../packaged-goods

 

Minimum system

You can pack your products so that they contain at least the quantity displayed on the label. The packages can contain more than the label says, but not less.

 

Average system

You can pack your products to an average measurement that is on the label. You must check your packages to make sure a random sample is packed to meet all these rules - known as the ‘three packers’ rules’:

The contents of the packages must not be less, on average, than the weight on the label

Only a small number can fall below a certain margin of error, known as the ‘tolerable negative error’ (TNE)

No package can be underweight by more than twice the TNE

 

Image: Pack Weight Legislation UK with TNEs

 

 Pack Weight Legislation UK.png   751.09KB   0 downloads

 

Kind regards,

 

Tony

 

 

[Benty666]

Hi Tony,

 

Sorry for the late reply. I'm clued up on the TNE, three packers etc. but for some reason the SD evades me, it's only since we picked up it's not recording correctly I've really looked into it but Google hasn't been as helpful as I thought it would. SNB have suggested upgrading our firmware for both the checkweighers and recording software to see if that fixes the issue.

[Tony-C]

Hi Benty666,

 

The SD is an indication of the level and control and accuracy of your weights/filling machine. It sometimes needs looking at if there is a large SD, which means a wide spread of product weights which can cause more product rejections.

 

Kind regards,

 

Tony