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Verification of checkweighers


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classic

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Posted 14 April 2015 - 03:11 PM

Hi

We are currently verifying our checkweighers at 30 minute intervals using test packs. The test packs are the same size as product and are periodically replaced. The test packs are made up of a pack without the product contents but with a 'filler' to the weight that is required.

This is in addition to start up checks where a calibrated weight is used.

The checkweighers reject at T1 and we have never had an issue with underweights

We feel that what we are doing is somewhat over the top but as the original staff who set the system up some years ago are no longer with the company there is no one to confirm why it was decided to verify at 30 min intervals

Can anyone advise what the practice is for verifying the checkweighers on their sites and whether or not you use test packs.

Thanks



Charles.C

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Posted 14 April 2015 - 04:23 PM

Hi Classic,

 

I would suggest you try a little searching for checkweighers.

 

There are 2 possible aspects -

 

(1) whether the procedure must conform to the details of the UK weights and measures regulations. There were extremely detailed discussions here over this general topic about 4-5 years ago. I can recall that the requirements were complex and the relevant documents were all uploaded here.

 

(2) If the query is independent of (1) and  confined to generically verifying a checkweigher, a table of typical calibration intervals (possibly vs weight range involved) as recommended by a manufacturer was also uploaded here a few years back. I recall it followed the usual practice of initially starting at an elevated frequency whch was then gradually decreased if satisfactory check results were obtained.

 

Offhand, assuming the calibration is stable, it sounds over the top to me also. But perhaps depending on the value of the Goods. :smile:


Kind Regards,

 

Charles.C


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Charles.C

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Posted 14 April 2015 - 05:21 PM

addendum to previous -

 

The post i was thinking of is probably -

 

http://www.ifsqn.com...ion/#entry36561

 

welmec document is, i think, including checkweigher requirements as related to weights and measures regs.

 

Later sartorius  link is a basic checkweigher calibration schedule from memory. Sadly the link is long-gone, will post back if in my archives.

(added - found but not relevant)

 

Assuming aspect (2) in previous post, some support for a daily check here -

 

Attached File  UKAS,LAB14, Calibration weighing machines.pdf   108.37KB   195 downloads

(eg sections 3.12, 6)

 

A brief overview here -

 

http://www.scsukltd.com/weightlaw

------------------------------------------------------------------------------

This is a recognized method (amongst several) for revising calibration intervals -

Method 1: Automatic adjustment or “staircase” (calendar-time)

Each  time  an  instrument  is  calibrated  on  a  routine  basis,  the  subsequent  interval  is  extended  if  it  is found to be within e.g. 80 % of the maximum permissible error that is required for measurement, or reduced  if  it  is  found  to  be  outside  this  maximum  permissible  error.  This  “staircase”  response  may produce a rapid adjustment of intervals and is easily carried out without clerical effort. When records are  maintained  and  used,  possible  trouble  with  a  group  of  instruments  indicating  the  need  for  a technical modification, or preventive maintenance, will be known.

 

 

Attached File  COP Calibration Industrial weighing systems.pdf   1.28MB   139 downloads

Attached File  Guidelines determination Calibration Intervals.pdf   66.95KB   131 downloads

 


Kind Regards,

 

Charles.C


shea quay

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Posted 14 April 2015 - 11:32 PM

Hey Classic, 

 

Yes, weight verification is a pain, especially in the UK. It is good news that your customer complaints on this issue are low. By the sounds of it, your company are doing a good job on this front. 

If you are looking for an addition to your system, throw in a monthly or weekly test whereby you take 40 consecutive packs and weight them. It's just a statistical analysis, but it backs up both what you're lads on the floor are saying in addition to your customer's (lack of) feedback. Are all random packs within T1? If so, happy days. The regularity will depend on your throughput, so I'll leave that up to you! 

Last point, you said you check at start up and every 30 minutes thereafter. Like metal detection, don't forget the finish. If your production lads carry out a test at 23:00 and finish at 23:20, who is to say your systems have been in control for the last 20 minutes?

So go on - tell us the gorey details of the ridiculous non-conformance!






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