Bell Telephone Laboratories - Relay Contact Inspection
July 1955 Radio & Television News

July 1955 Radio & TV News

[Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio & Television News, published 1919-1959. All copyrights hereby acknowledged.

Back in the day, Bell Telephone Labs' name was synonymous with cutting edge technology and brainiac scientists and engineers, similar to IBM (International Business Machines), Boeing, Chevrolet, Westinghouse, and Hewlett Packard, amongst others. Bell Labs often ran full-page promotions in electronics magazines like this one in a 1955 issue of Radio & Television News that spotlighted a method they developed for inspecting relay contacts without having to remove it from the circuit. Prior to solid state switches, electromechanical relays did the circuit routing for the millions of calls crossing the United States (prior to that, ladies sitting in front of switchboards used cables and plugs to route calls manually). Those relays opened and closed thousands of times each day, so they were subject to a lot of wear and tear. Bell Telephone invested a lot of time and money into designing high quality relays that would stand up to the usage. They also developed this method for inspecting the health of relays to assist in improving the design.

Bell Telephone Laboratories Ad

He's "fingerprinting" a relay contact.

Bell Laboratories microchemists have perfected an ingenious new technique for "fingerprinting" relay contacts, the tiny switches on which a dial telephone system critically depends.

Using a portable test set, a chemist makes a plastic print of a contact. On-the-spot examination of the print with a microscope and chemical reagents quickly reveals the effects, if any, of arcing, friction, dust or corrosive vapor. While the chemist studies the print, urgently needed contacts continue in service. Findings point the way to improve relay performance.

This is another example of how Bell Telephone Laboratories research helps to keep your telephone system the world's best.

Above, Bell Laboratories microchemist applies plastic disc in heated clamp to relay contact. Imprint reveals contours of surface and picks up contaminants, if any. Part of portable test set is shown on table. Contacts, shown in small sketches, are of precious metal fused to base metal.

Preparing disc for microscopic examination. On-the-spot examination may reveal acid, alkali, sulfur, soot or other polluting agents peculiar to an area.

A microscopic look at disc often provides lead to nature of trouble. Unlike actual contact, print can be examined with transmitted light and high magnification.

Here the plastic disc has picked up microscopic lint that insulates contact, stops current. (Picture enlarged 200 times.) Traces of contaminants are identified in microgram quantities. Inert plastic resists test chemicals that would damage contact.

Bell Telephone Laboratories

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Posted July 15, 2020