Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Patent
1982-09-23
1985-04-23
Tokar, Michael J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
324117R, 324129, G01R 1900
Patent
active
045132461
ABSTRACT:
A clamp-on ammeter for measuring current flows in a conductor is described. The ammeter is of a type comprising a magnetic core which can be located about a conductor and an indicator which responds to the magnetic flux consequently generated in the magnetic core to produce a signal indicative of the magnitude of the conductor current. Means are provided for restoring the magnetic core to a predetermined magnetic state for each measurement. The resetting means include a coil wound about the core and a coil energizing circuit which can be activated to produce in the core a residual magnetic flux substantially identical to that produced in the core when unmagnetized by a DC conductor current of predetermined magnitude, which represents the maximum value of any DC current which can be measured by the ammeter. The ammeter includes another coil and energizing circuitry which then produce in the core an offsetting magnetic flux equal in magnitude but opposite in direction to the residual magnetic flux, thereby eliminating any offset which would otherwise be generated by the indicator in response to the residual magnetic flux. To adapt the ammeter for AC measurements, another coil is wound on the core and is electrically shorted when the magnetic flux cutting the windings of the coil changes direction from that of the residual magnetic flux. The shorting of the coil tends to reduce the magnitude of the magnetic flux in the core to substantially zero. By emplying an indicator responsive to a time average magnitude of the core magnetic flux a signal indicative of the magnitude of an alternating current carried by a conductor is produced.
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O'Shea Kevin D.
Tokar Michael J.
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