Figure 3: AuditCheck (Thermo Fisher Scientific) block diagrams. The diagram on the left is a side view of the metal detector,
displaying where the product and AuditCheck device passes through the electromagnetic field. The diagram on the right shows
how the magnetic (X) and conductive (R) signals are calibrated with AuditCheck and how warning and alarm limits are set.
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Quality control.
One key consideration is how the detection system is audited. Typically, manufacturers audit detection systems every 1 to
2 hours during production to check for detection sensitivity (see Table I). Most of these audits involve simple pass/fail
checks. An additional automatic early-warning system has been developed (Thermo Scientific AuditCheck) that can be set to
periodically (i.e., based on user-defined preferences) pass a metal piece through the detector's fields to measure the two
primary signals previously defined (X and R) (see Figure 3). These signals are calibrated during set-up, and any changes from
the expected values can generate warnings or alarms to the user. An early warning allows the user to take immediate action
such as cleaning the detector of foreign material or adjusting the detection threshold. As a result, production volume and
time can be maximized. In addition, the automation of the audit can help to reduce labor resources.
Operation and deployment
After selecting and implementing a new or upgraded metal-detection system, a short on-line trial test is advised to further
determine how the system is performing during production. In addition to the criteria outlined in Table II, one should consider
the following:
1. Did the system reliably detect the metal sizes and types in question
2. Were there false rejects and, if so, why? Can they be avoided or minimized?
3. Did the system jam?
4. Can the system be adjusted easily to the production process with no loss of material?
5. Was set-up easy and how much operator intervention is needed to run the system?
6. How is the system audited and documented?
7. Can the system be cleaned easily? Can it be disassembled and reassembled quickly?
8. Did the system produce any errors? If so, how did it react?
Conclusion
Foreign-metal-object detection systems can help to prevent product contamination. Selecting a system requires a trial-and-error
approach that takes into consideration the system's sensitivity, ease of use, and audit ability. Once implemented on a production
scale, a metal-detection system can help to maximize product volume and quality.
Bob Ries is a lead product manager at Thermo Fisher Scientific, tel. 763.783.2500, bob.ries@thermofisher.com
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