The company where I worked used a variety of tapes for many purposes in wire and cable manufacturing. One of the uses involves wraps for mechanical and electrical purposes, as well as laminated-metal tapes commonly used for shielding. One day, we received a visit by a supplier of such tapes.
The young salesman who showed up that day was very excited about a new tape his employer was producing for cable shielding. Rather than the conventional laminated construction, this new type of tape featured an electrodeposited aluminum coating. The advantages he touted included lower cost and lighter weight.
I asked about coating thickness. According to the product information, it was very thin. I was surprised by how thin it was. I then asked, "With a clear backing, how will an operator know which side is conductive?" As a note, laminated tapes use a tinted laminating adhesive, often blue, so you can easily distinguish the back from the front. This is an important matter, since the conductive side of a tape shield must be in contact with the drain wire.
Since I couldn’t tell much of a difference by looking at it, I noted that we should easily be able to determine the answer by using an ohmmeter or other continuity-testing device. We trotted off to the lab to do a quick test. To our mutual surprise, there was no discernible conductivity on either side of the tape. The electrodeposited coating was so thin that virtually none of the metal atoms were “holding hands.” The new tape had been manufactured and launched, apparently, without anyone recognizing this problem.
This entry was submitted by Peter M. Blackford and edited by Rob Spiegel.
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