HEATER CABLE ALARM SYSTEM

• US 3,774,189 A
• Filed: 09/29/1972
• Issued: 11/20/1973
• Est. Priority Date: 09/29/1972
• Status: Expired due to Term

• Current Assignee: General Signal Corporation (SPX Corporation)
• Original Assignee: David O. Brown
• Inventors: Brown, David O.
• Primary Examiner(s): Habecker, Thomas B.
• Application Number:
  US05/293,346
• Time in Patent Office: 417 Days
• Field of Search: 340/253C,253B,256,417 219/510
• US Class Current: 340/655
• CPC Class Codes: G01R 19/145 Indicating the presence of current or voltage

Abstract

In a heater failure alarm system, a current sensor senses the current flow in the heater cable and generates a failure warning signal if there is not current flow when the heater cable is switched on. The current sensing transformer is adapted to be juxtaposed relative to the heater cable and is connected to a self-contained circuit module which closes relay contacts when current flow is not sensed. An alarm switch is mechanically connected to a main power switch for the heater cable and is in series with the relay contacts and an alarm means.

Claims

1. In a failure alarm apparatus for an electrical device, the combination including current sensing means for generating an electrical signal proportional to the current sensed, rectifying means for rectifying said current proportional electrical signal, voltage limiting means for limiting the maximum amplitude of said rectified current proportional signal, capacitor means for integrating said limited, rectified current proportional signal, relay means for operating a set of electrical contacts when energized by said integrated, limited and rectified current proportional signal, and alarm means for producing a warning signal, wherein said alarm means is connected to the electrical contacts of said relay so that a warning signal is produced when a change in current flow is sensed by said current sensing means.

2. In a failure warning apparatus as claimed in claim 1 wherein said voltage limiting means comprises a zener diode in series with a resistor.

3. In a failure warning apparatus as claimed in claim 1 wherein the warning signal is produced when the current flow sensed is below a predetermined level.

4. In an electrical apparatus, the combination including a supply of electrical power, electrical equipment, a first switch interconnecting said electrical equipment and said supply of electrical power, current sensing means for sensing the flow of current to said electrical equipment, a second switch operated by said current sensing means, a third switch mechanically connected to said first switch wherein said second and third switches are connected in series, and alarm means for producing a warning signal, operated by said second and third serially connected switches, wherein when said first switch is interconnecting said electrical equipment and said supply of electrical power and said current sensing means does not sense the flow of current, said second and third switches operate said alarm means to generate a warning signal.

5. An apparatus as claimed in claim 3 wherein said current sensing means comprises a current transformer means for inductively sensing the flow of current in an electrical circuit and producing an electrical signal proportional to the current sensed, rectifying means for rectifying said current proportional electrical signal, voltage limiting means for limiting the maximum amplitude of said rectified current proportional signal, capacitor means for integrating said limited, rectified current proportional signal, and solenoid means for operating said second switch when energized by said integrated, limited and rectified current proportional signal.

6. The apparatus of claim 5 including a thermostat mechanically connected to said first and third switches, wherein said electrical equipment is an electrical heater and said thermostat senses the temperature of the electrical heater and operates the first switch to maintain a relatively constant temperature.

7. In a heater failure alarm for a heater cable energized by alternating current, the combination including a current transformer adapted to be juxtaposed relative to a heater cable for inductively sensing the flow of current in the heater cable and producing an alternating current proportioned electrical signal which is proportional to the current sensed, a diode rectifier for converting said alternating current porportional electrical signal to a direct current signal, zener diode means for limiting the maximum amplitude of said direct current signal, a capacitor for integrating said limited direct current signal, alarm means for producing a warning signal when switched on, a relay for switching said alarm means when energized by said limited direct current signal to prevent said alarm from producing a signal.