Troubleshooting: Industrial Metal Detectors
Metal detectors are precise measurement devices. When working with metal detection in the food and pharmaceutical industries, there are many common issues that we see. Food metal detectors are often found in harsh plant conditions. Many other pieces of equipment come together to form the processing line, and often, metal detectors are inserted into the line in multiple different locations. At different places in the line, some issues are more present than others. For all metal detectors, when these issues are encountered, changes need to be made to allow the metal detector to function properly.
Belt Contamination
One of the easiest, and most commonly missed, issues for industrial metal detectors in food and pharmaceutical applications is conveyor belt contamination. No matter if you have a Safeline metal detector, a Ceia metal detector, a Fortress metal detector, a Loma metal detector, an Anritsu metal detector, or any other brand, none can function properly when you have contamination in your belt. If you do not address this issue you will either continue to see false rejects, or you will have to operate your metal detector in a lower sensitivity setting to allow the contaminated belt to pass through without rejecting, which will hurt your overall metal sensitivity performance.
To check if you have belt contamination, a simple technique can be used:
1. Watch the signal indicator on your industrial metal detector.
2. Pay attention to the spike for about 60 seconds. Does it appear to spike at about the same frequency each rotation of the belt?
3. Get a marker, and mark the belt on the edge near the area where it spikes.
4. If the metal detector signal spikes each time that portion of the belt goes through the aperture, then you likely have some belt contamination in that portion of the belt.
5. If it is a modular belt, replace that portion. If it is a flat belt, you will need a new belt.
Electrical Noise
Electrical Noise can be one of the most difficult issues that a manufacturing plant can face when working with different types of inspection equipment. Depending on the level of sensitivity and accuracy that is being attempted, any electrical noise will impact results. Electrical noise can be found in power supply lines, variable frequency drives, and existing surrounding equipment. Filtering techniques, isolation, and other methods can be used to attack electrical noise issues.
Vibration
Vibration has long been considered a source of interference for the electromagnetic fields generated by the coils in food metal detectors. In some cases, with specific types of metal detectors, vibration can be filtered out to allow for reliable and repeatable sensitivities and performance. Many manufacturers utilize heavy filling of their heads to combat vibration, but some have developed algorithms and special fills to achieve superior results.
Product Effect
Conductivity and magnetic properties from the product being inspected cause problems for all types of metal detection systems. It is important to make sure you are using the best technology available for your specific product, to minimize the product effect as much as possible, so you can obtain the maximum sensitivities. Adjusting sensitivity and phase will only take you so far, and may not always be repeatable and reliable.
Temperature Change
As temperature changes in a manufacturing facility, the product signal also changes. Dealing with this in places where it can not be avoided is tricky. There are specific ways to deal with the change in signal that the detector sees. Most methods involve giving up some sensitivity for consistent inspection levels, but the reduction of re-work usually justifies these approaches.