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Corrupted Magnetic Tracking System

Corrupted Magnetic Tracking System
Magnetic traveler cards were being used to track information. Suddenly one section was unable to read the data. What was the cause?
Mysteries of Science


An electronics factory was testing several tracking system for in-process materials and products. Instead of using a standard bar code systems, this company wanted the ability to add new information as the product moved through production.

A magnetic "traveler" system was being used. The credit card-like label accompanied the bin of parts. This was used to record the number of parts and other useful information.

The card could be inserted into each station reader as the parts were being processed. Before the parts moved onto the next step, the operator could type in new information that would be transferred to the card.

The cards had unique numbers printed on the face, and the magnetic strip held the product information.

Suddenly one of the in-process test sections was unable to read the data from the cards. The cards became completely or only partially unreadable. What was corrupting the cards at this section?

Here's the rest of the story

It was theorized that heat, moisture, radiation, or chemicals, could all cause problems, but the investigators could not find any of these factors in the proximity.

However, observation of the area supervisor noted that he had a habit of picking up a card and wiping it on his shirt before reading a number.

The supervisor was confronted and the problem explained. He picked up a card rubbed it across his pocket and placed it in the card reader. "No data" showed on the screen.

Then he reached into his pocket and pulled out a floppy disk. The supervisor was in the habit of carrying his floppy disk of test data in his shirt pocket. A floppy disk is made of strong magnetic material. Whipping the magnetic card across his pocket destroyed data on the strip.


I am also highly doubtful the floppy disk could do this damage. The floppy is recorded with a low level modulated AC signal (FM or MFM) that is stored on a thin oxide layer. From a distance greater than the read head, I suggest the sum of the stored data magnetic fields would tend to cancel anyway.

If the floppy had a large external field, it would probably make the floppy read head's job even more difficult due to head saturation issues. The magnetized screw driver or a magnetic pick up tool makes far more sense.

I am very curious that this has been independently verified.
John Wright, CDI, USA
We (us guys at work) don't believe a floppy disk has an external magnetic field strong enough to compromise mag-stripe data. If that was the case, you could use floppy disks as refrigerator magnets, and mag-stripe cards would probably erase each other while stacked in a wallet. It is more likely that the operator (who was wiping the cards on his shirt pocket) had a screwdriver with a magnetized tip in his pocket. The real test would be to take the suspected cause (floppy disk) and apply it to the mag-stripe card to see if it actually caused the problem.
Carl B. Van Wormer, Cipher Systems, Inc.

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