Fault Sense Relay
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-06
Ernst, LM: AUTHOR [+3]
AbstractThis article describes a circuit for providing positive protective action when a hazardous voltage condition comes to exist on a hot roll fuser of an electrophotographic machine.
Fault Sense Relay
This article describes a circuit for providing positive protective action when a hazardous voltage condition comes to exist on a hot roll fuser of an electrophotographic machine.
Hot roll fusers contain temperature sensing devices for controlling the time period that energy is supplied to heating devices. This enables the provision of proper temperature condition on the fuser. Many such temperature sensing devices obtain information through conductive brushes placed against the roll surface. In order to detect the continuity of the brush circuit, a current sense device is provided that will shut down the machine if the temperature sense circuit is broken.
The present improvement is a voltage sense circuit in addition to the current sense circuit to detect the presence of hazardous voltage on the hot roll. The circuit calls for connecting one of the brushes to ground through a voltage sense relay coil such that the presence of a hazardous voltage will operate the relay and shut down the machine. Positive protection can be provided by placing a fuse in the relay circuit.
The figure shows a hot roll 10, brushes 11, a current sense device 12, voltage sense coil 13 and fuser power relay 14. If a high voltage condition is present, coil 13 will operate contact 15 placing voltage source 17 across fuse 16, blowing the fuse and thereby creating a physical break in the circuit of main power relay 14.