Remote sensor and method for detecting the on/off status of an automatically controlled appliance

• US 5,506,573 A
• Filed: 06/21/1994
• Issued: 04/09/1996
• Est. Priority Date: 05/13/1993
• Status: Expired due to Term

• Current Assignee: Server Technology Incorporated (Legrand SA)
• Original Assignee: Server Technology Incorporated (Legrand SA)
• Inventors: Cleveland, Andrew J., Ewing, Carrell W.
• Primary Examiner(s): Swarthout, Brent A.
• Assistant Examiner(s): LIEU, JULIE BICHNGOC
• Application Number:
  US08/263,035
• Time in Patent Office: 658 Days
• Field of Search: 340/644, 340/654, 340/635, 340/652, 340/657, 340/658, 324/415
• US Class Current: 340/644
• CPC Class Codes: G01R 31/3275 Fault detection or status indication
• CPC Class Codes: H01H 9/167 Circuits for remote indication

Abstract

A method for sensing the on/off status condition of a power switch in an appliance includes applying a series of alternating current (AC) voltage pulses to an appliance with an on/off switch that are synchronized to a source of AC power, sensing the presence of any series of AC current pulses that result if said appliance switch is closed, analyzing any AC current pulses detected in the step of sensing to determine if they resulted from the application of the AC voltage in the step of applying, and outputting an on/off status indication for the appliance switch.

Claims

1. A method for externally sensing the on/off status condition of a load power switch in an appliance from an AC-Only power source connection of the appliance, comprising the steps of:

applying a positive voltage pulse and a negative voltage pulse each delayed from a zero crossing of an AC power source to an external power connection for said AC Dower source of an appliance having an internal load power switch with on and off conditions;

sensing the presence of any current flowing through said external power connection to said appliance;

analyzing said any current flowing for its relationship to said positive and negative pulses; and

outputting an "on" status indication for said internal load power switch when said any current is determined to be related to said positive and negative pulses, and outputting an "off" status indication otherwise.

2. An appliance power switch status detection device, comprising:

a set of AC power supply terminals providing for the only connection of AC input power to an external AC power connection of an appliance with an internal load power switch that is not directly accessible through said external AC power connection because of an internal connection of an internal appliance load;

synchronized pulse generation means connected to the AC power supply terminals for applying a positive voltage pulse and a negative voltage pulse each delayed from a zero-crossing of an AC power source to AC power supply terminals;

a diode and resistor combination connected in series between the AC power supply terminals and the synchronized pulse generation means for converting a current flowing through said internal power switch, said internal appliance load and said external AC power connection into a voltage; and

a microprocessor connected to both the synchronized pulse generation means and the the diode and resistor combination and an opto-isolator for analyzing said current flowing for its relationship to said positive and negative pulses, and for outputting an "on" status indication for said internal load power switch when said current flowing is determined to be related to said positive and negative pulses, and outputting an "off" status indication otherwise.

3. The device of claim 2, wherein:

the AC power supply terminals comprise hot, neutral and ground connections for powering said appliance;

the synchronized pulse generation means includes a clock generator with an output that coincides with each zero-crossing of said AC power source;

the resistor and diode combination comprises back-to-back connected diodes in parallel and connected to provide a limited voltage input to said opto-isolator; and

the microprocessor is connected to control the timing of the synchronized pulse generation means according to a delay from a connection to said zero-crossing output.

4. An appliance power switch status detection device (10), comprising:

AC power input terminals (24, 26,

     28) providing for connection to a source of AC utility power;

a power supply and clock generator (12) connected to the AC power input terminals and providing for a zero-crossing clock that signals the zero-crossing event of said AC utility power, a DC power supply and a reduced-voltage AC power supply;

a microprocessor (20) connected to receive said zero-crossing clock and an appliance current sense signal and connected to output a control signal delayed from each occurrence of said zero-crossing clock;

a solid-state relay (18) connected to control an appliance signal voltage from said reduced-voltage AC power supply in response to a connection to said microprocessor control signal output providing for a positive voltage pulse and a negative voltage pulse;

AC power output terminals (36, 38,

     40) providing for a through connection of AC power from the AC power input terminals to a connected appliance (22) having a load (Z_L) in series with a on/off switch (23) and an automatic remote control switch (42); and

a current sensor (14) connected in series with one of said AC power output terminals and said positive and negative voltage pulses provided by the solid-state relay and providing for the measurement of current through said on/off switch (23) and having an output connected to provide said appliance current sense signal to the microprocessor;

wherein the he microprocessor analyzes and stores its determination of whether said on/off switch (23) is closed, and wherein such determination is useful to control said automatic remote control switch (42).

5. The device (10) of claim 4, wherein:

the microprocessor (20) is connected to control said automatic remote control switch (42) and provides for a connection to a modem for communicating said determination of the on/off status of said on/off switch (23) to remote locations.