Abstract: A contact wear detector includes an electrical contact 100 having a base layer 110 composed of a first material and a contacting layer 120 composed of a second material, to electrically contact an opposing contact in the circuit. The base layer is capable of having portions exposed through worn areas 125 of the contacting layer. The first material of the base layer is configured to form an arc 210 between the portions of the base layer exposed through the worn areas and the opposing contact when the contacts separate. The arc thus formed emits light 212 having a characteristic optical spectrum of the first material. An optical detector 220 is proximate to the electrical contacts, to detect the characteristic optical spectrum of the light emitted by the arc between the portions of the base layer exposed through the worn areas and the opposing contact.

Abstract: A contact wear detector includes an electrical contact 100 having a base layer 110 composed of a first material and a contacting layer 120 composed of a second material, to electrically contact an opposing contact in the circuit. The base layer is capable of having portions exposed through worn areas 125 of the contacting layer. The first material of the base layer is configured to form an arc 210 between the portions of the base layer exposed through the worn areas and the opposing contact when the contacts separate. The arc thus formed emits light 212 having a characteristic optical spectrum of the first material. An optical detector 220 is proximate to the electrical contacts, to detect the characteristic optical spectrum of the light emitted by the arc between the portions of the base layer exposed through the worn areas and the opposing contact.

Abstract: A selective call controller, such as a paging terminal, and a method therefor is provided for receiving calls comprising first and second types of signal, such as numeric/alphanumeric or modem/DTMF. A determination is made of the type of signal being received, and a destination address and message signal is selected accordingly.

Abstract: A selective call system is provided in which string searching or text matching operations are performed on data from data generating devices such as condition sensors in a security system. When a predetermined string is identified, an address of a selective call receiver such as a pager is generated and that receiver is called. The invention is applicable to other applications where data is generated which includes predetermined character strings.

Abstract: A two-way communications system for use with a host computer includes a control unit, a base station and multiple radio/data terminal units. The control unit interfaces directly with the computer but uses a radio link to the portable units. Voice and data signals can be transmitted and data between units is decoded, sorted, stored, encoded, and sent to its destination in accordance with predetermined protocol in queue discipline. An extensive self-diagnostic system is included. An active redundancy arrangement switches between two control units/base stations on a regular schedule if both units are up, and instantaneously if the "on" unit goes down.