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The Myth of Checkweighing
http://www.articlebasement.com/articles/51935/1/The-Myth-of-Checkweighing/Page1.html
George Van Lieu
George Van Lieu is a manager for Belcorp, Inc., an automated packaging equipment supplier located in Cincinnati, Ohio. 
By George Van Lieu
Published on 03/5/2008
 
There has long been a fundamental misunderstanding about the viability of x-ray inspection systems being used also for reliable checkweighing. We all understand the legal and economic reasons for accurate weighing of products. A second reason is somewhat more subtle. Flagrant shipments of underweight products will quickly result in customer complaints and loss of business (and reputation!)
X-Ray VS Checkweighers

There has long been a fundamental misunderstanding about the viability of x-ray inspection systems being used also for reliable checkweighing.

 

We all understand the legal and economic reasons for accurate weighing of products.  A second reason is somewhat more subtle. Flagrant shipments of underweight products will quickly result in customer complaints and loss of business (and reputation !)

 

There are some “MYTHS” surrounding checkweighing systems.

1.       They are very accurate and precise.  -  In a static situation, this is true, but in a high speed production setting, checkweighing is subject to air currents, vibration, spillage on the table, friction issues, and potential for static electricity issues.

2.       X-ray systems don’t meet “weights and measures” standards. Actually, on-line checking systems normally don’t fall under the weights and measures act of most countries.

3.       X-ray systems don’t really weigh product, but checkweighers do. While this is debatable, the final objective is simply to insure the right amount of product is in the container. This is a measurement of quantity or mass.  There is nothing sacred about gravimetric measurement of weight.  How you insure that the fill is correct, is immaterial, as long as it works!

 

X-ray checkweighing is totally non-dependent on any physical movement of a weight table, thereby eliminating most of “myth number 1”. X-ray detection systems also have the ability to segregate weights internal to the package and weigh them independently. (ex: frozen meal trays).

 

In x-ray systems:

1.       The image will remain the same regardless of rotation.

2.       There is no inertial effect, so platen “bounce” is not an issue.

3.       Packages touching each other have no negative effect.

4.       Air currents have no effect

5.       Vibration has no effect.

 

So – in the final analysis – an x-ray detection system should be used whenever it can meet your tolerance needs. This technology is likely to be consistently more accurate in true production situations and it can provide many other monitoring and detection functions simultaneously.