Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1997-09-03
2000-04-11
Lefkowitz, Edward
Communications: electrical
Condition responsive indicating system
Specific condition
318671, 318768, 318780, G08B 2100
Patent
active
060492848
ABSTRACT:
A method and apparatus for monitoring a three-phase electric motor which has been disconnected from the electrical mains and is running down, one phase of the voltage generated by the motor being checked respectively in each of two channels for zero crossings and, if a zero crossing occurs, a signal being produced which, after DC-decoupling, is used to control the operation of a safety device. The safety devices are mutually interlocked and control signals therefor are produced only when the period between zero-crossings detected in both channels indicates that the motor output shaft has ceased rotation.
REFERENCES:
patent: 5151642 (1992-09-01), Lombardi et al.
patent: 5300870 (1994-04-01), Smith
patent: 5488281 (1996-01-01), Unsworth et al.
patent: 5767639 (1998-06-01), Sakaguchi et al.
K. A. Schmersal GmbH & Co.
Lefkowitz Edward
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