10 replies to this topic

[Caddyshack]

Does anyone have any guidance on checkweigher calibration. We are just commisioning a new checkweigher and the machine has built in tolerances that seem to alter depending on some different issues, like pack presentation, weight range.

The company that built the machine have created a rather bespoke machine to suit our pack range and the size of the production line. Also the software was created by "a n other" company and I am struggling to get precise information, I am assured it will all come together and it is a while off being finished yet.

To clarify, I am after the calibration tolerances not the T1 and T2 figures used for average weight systems.

We pack a range of pack weights all as average weight systems from 200g to 2500g

Thanks in advance, Mike

[Amber McCreary]

Caddyshack,

I can understand your frustrations as most of the checkweighers out there do not carry the same manufacturer of the actual machine and software. I am pretty good with the different types of software, but I would need to know which it is before I could assist you in calibration techniques. Please include the names and program version.

A.McCreary

[Caddyshack]

The software is as bespoke as the machine, it is not a nationally recognised software
programme.

I was hoping somebody would give me some + or - weight % or maybe the was an industry guidline etc!

Mike

[Amber McCreary]

I was hoping somebody would give me some + or - weight % or maybe the was an industry guidline etc!

Mike

Well in regards to this, each country has its own weights and measurement acts. You must check the guildlines for your country, usually it invovles package declared weight for each particular product you intend to weigh. Typically you must meet or exceed the declared weight.

Definitions of units of measurements and the provision of the technical equipment relating to weights and measures in the UK are provided by the National Weights and Measures Laboratory, an agency of the Department of Trade and Industry. I would start there.

Hopefully this helps.

[Charles.C]

Dear QAMB,

Well in regards to this, each country has its own weights and measurement acts.

You are quite correct. This was the significance of caddyshacks mentioning the t1,t2 system which is standard within the EC. USA no idea .

@Caddyshack - Clearly the tolerances utilised must be adequate to deliver compliance with the existing regulations. I realise this does not answer the original question but i fear a meaningful operational answer may require knowledge of the specific process, eg typical size of pieces of product etc.

Rgds / Charles.C

[Caddyshack]

Come on guys dig deep into the grey matter!!!!!!!!!


Can anybody help me on the formula for calculation of the "ZOI" (Zone of Indecision) for my checkweigher?.

Is it simply the range the machine displays when a known weight is passed over the machine several times?

I was told once that the ZOI should be 6 x the SD (Standard deviation) although this doesn't stack up on my machine, my local trading standards office could not help either!!

Regards

Caddyshack

[Charles.C]

Dear Caddyshack,

Is this what you want ??

11 Annex F Checkweighers and other automatic instruments
F.1 The place of checkweighers in the average system
F.1.1 The requirements to be met by checkweighers in order to be usable for the checks made by the
packer under the Directive are dependent on the type that is used and their manner of use. There
are no restrictions on the precision of measurement required in the use of checkweighers, but
conditions are laid down for allowances covering tare weight variation of containers and the ‘zone
of indecision’ of the set point.
The ‘zone of indecision’ is the extent, expressed in units of mass, of the zone within which the
machine may take two contrary decisions with respect to the same load. The value of the zone of
indecision is taken as equal to 6xstandard deviation of the accept/reject distribution.
The ‘set point’ is the value, in units of mass, at which the instrument is set to accept/reject product.

http://www.welmec.or...cations/6-5.pdf

Rgds / Charles.C

PS looks like this document is the (original) standard item but my guess is you hv already. It knows yr problem but all my attempts to find the appendix D referred below led to dead links

7. Set points need to be set to ensure that all three packers’ rules are complied with
continuously, and needs to take into account the zone of indecision and variability of the
weight of packaging (tare).

8. Where the zone of indecision (ZoI) is greater than 0.25 TNE then the set point
should be increased by 0.5ZoI – 0.125TNE.

9. Where the tare variability (standard deviation) exceeds 0.1 TNE then a simple
way to address this is to add an allowance of 0.85s on to the set point.

10. For further information on determining the zone of indecision and establishing
appropriate set points see Appendix D of the Packers’ Code.

http://www.nmo.bis.gov.uk/Docs/Legislation/Packaged%20Goods/Packaged%20Goods%20Regulations%202006%20issue%202.pdf

PPS - some very nice maths in first refs !

yu might also find this set of typical specs (inc yr ZOI) for a Sartorius interesting

http://www.sartorius...sheet-SYNUS.pdf

[Caddyshack]

Dear Caddyshack,

Is this what you want ??



http://www.welmec.or...cations/6-5.pdf

Rgds / Charles.C

PS looks like this document is the (original) standard item but my guess is you hv already. It knows yr problem but all my attempts to find the appendix D referred below led to dead links


http://www.nmo.bis.g...20issue%202.pdf

PPS - some very nice maths in first refs !

yu might also find this set of typical specs (inc yr ZOI) for a Sartorius interesting

http://www.sartorius...sheet-SYNUS.pdf

[Caddyshack]

Some very good information there thanks Charles, some of which I had and some new. I will swat and let you know how I get on!!

Cheers Man!!

[GMO]

ZOI generally I believe is taken as 6xSD of a single pack passed over 100 times; there is a more complicated method of calculating it in the packers rules but I'm blown if I understand it! Basically the ZOI is a measure of how accurately the checkweigher will weigh a given pack. A checkweigher is not a static machine and so it will vary and give you a distribution of weights even from one single pack. I can't remember off the top of my head but I know the ZOI has to be less than a fraction of the TNE or you have to make an allowance to your target to account for the inprecision of the instrument.

[Charles.C]

Dear GMO,

Nice to see you posting again.


Hope everything OK post delivery.

Rgds / Charles.C