Alternative Technologies For Assuring Product Mass, Fill, Or Weight With X-Ray Technology

By J. Craig Lewis

Although X-ray inspection systems, designed to detect contaminants, have long included the capability to also measure the mass or weight of the inspected products, many users have mistakenly assumed that dedicated gravimetric “Checkweighers” are either necessary or superior for performing this function in the production line. This whitepaper will examine some of the misconceptions which may influence the cost and effectiveness of choosing between these alternative technologies for assuring correct and consistent product mass, fill, or weight.

The old adage “use the right tool for the job” certainly applies to choosing a technology for assuring consistent and correct product mass or weight. But, in order to choose “the right tool”, we must first define the objectives, constraints, and environment in which that tool will be used. For example, a micrometer is certainly more accurate than a yardstick. But that does not make the micrometer a better choice for every application. If a fabric store used a micrometer to measure out cloth to every customer, the result would be very slow service and a lot of unnecessary labor expense to achieve a level of accuracy that provides no benefit to either the vendor or the customer.

Therefore, we must examine the requirements and objectives of installing product weighing equipment in the production line. In order to do so, we must first discuss the scientific concepts of accuracy, precision, and reliability, which are actually very different and independent parameters. Any measurement system can be accurate but not precise, precise but not accurate, or accurate and precise but not reliable under a wide variety of operating conditions. It is unfortunate that confusion over the definitions of these terms is often perpetuated by lax and ambiguous usage in the literature produced by many checkweigher vendors. To clarify, we will present the correct scientific definitions.