Summary

Extremely large quantities of materials are handled at rapid speed in the food industry. Often, at the raw food stage unwanted rocks, bones, pits and sometimes metal pieces are left in the food items. During processing, metal pieces from machines and other objects can be introduced in the products. In recent years, the food industry as well as the consumer has become very sensitive to the problem of foreign objects in the final product. The regulatory agencies have also come out with definitive maximum size of foreign objects in a final food product.

Most often, the metal detectors are used in the industry to detect the metal foreign objects. The metal detectors are relatively inexpensive, easy to operate and mostly indestructible. In many food products, they perform fairly well to meet the regulatory requirements. The metal detectors are limited to detecting only metal objects in the food products. As indicated, often nonmetal objects like bones, rocks and plastics are of equal concern to the industry.

Omega has developed a high speed and highly sensitive x-ray system to detect any type of foreign objects in the product. The heart of our system is a very sensitive x-ray detector array and high speed data collection hardware and quantitative analysis technique. The entire system consists of a high speed conveyor belt, a 100 kV x-ray generating system, a 80 channel solid state detector array and 100 kHz 12 BIT PC based analog-to-digital conversion (ADC) system, a 80486 based laptop PC computer system and Omega's custom analysis software. The system is capable of detecting as small as 0.1 mm diameter steel wires through most cereal, chips and lunch packages at > 100 feet per minute conveyor speed. The system can detect 0.5 mm diameter steel ball through most lunch packages at similar conveyor speed. The bones of 0.5 mm cross sections can be detected within the lunch packages at similar speed. Small size Wish bones can also be detected without problem within boneless chicken packages. 

System Description

Detector System: The heart of the system is a 80 channel linear array of solid state x-ray detectors. The design of this detector array is similar to the solid state detector systems used in most medical CT scanners. The entire 80 channel detector array is fabricated on a single Printed Circuit Board to reduce the system cost and achieve high reliability. Each x-ray detector channel consists of a 3 mm x 3 mm single crystal CdWO₄ scintillator, a similar size PIN silicon photo diode, an extremely low noise amplifier, an active integrator, and a sample-and-hold (S/H) circuit. The output of 8 x-ray detector channels is routed to one 8:1 multiplexer circuit. There are a total of 10 such 8:1 multiplexers located on the 80 channel detector board to handle 80 individual x-ray detector channels. The output of these 10 multiplexers are further multiplexed using additional multipl
exers to a single channel differential analog output. After a high speed buffer amplifier, this output differential signal from the entire detector system is sent to the ADC board located at the computer system.

The 80 channel detector Printed Circuit Board also contains logic circuits to control and drive the integrators, S/H circuits and provide convert timing signals for the ADC. Figure 1, shows the block diagram of the total system and figure 2 shows the picture of the 80 channel detector system.