US 3611364 A
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United States Patent 10/1952 Foote et a1 3,147,464 9/1964 Spielman 340/415 3,292,036 12/1966 Colton et a1 340/324 X 3,401,399 9/1968 Tegholm 340/324 X ABSTRACT: A fault-finding apparatus that acts to determine which of several of series connected contacts has opened first is composed of a plurality of electronic switches, e.g. thyristor-s, each connected in series with an indicator such as a neon glow bulb. The thyristors are connected in parallel across a power supply which is in turn connected across the electric power circuit being monitored. The gate of each thyristor is coupled by means of a quick disconnect fastener to one of the contacts being monitored which when closed connects the gate to its cathode. When a contact opens, the change in potential of one gate causes its thyristor to fire thereby energizing the glow bulb connected to that thyristor.
APPARATUS FOR DETERMINING THE SEQUENCE OF CIRCUIT DISCONTINUITIES IN "A SEALING CIRCUIT FOR A POWER OUTPUT DEVICE A relay-sealing circuit can be defined as an electrical circuit composed of a number of contacts in series with a power output device, e.g. a relay. All of the contacts in this series have to be closed in order for the output device to be energized. Circuits of this kind are used widely in operating machinery,
boilers and the like, in which event a drive motor or control motor is energized by the relay. When a failure of one set of contacts causes a shutdown, it is difficult to correct because it is impossible to know which of the several contacts opened first.
Although test equipment has been previously proposed for finding which particular component of the circuit has failed as illustrated by U.S. Pat. No. 3,147,464, no provision is made for detecting discontinuities in a plurality of series connected contacts. Moreover, because the contacts have different response time constants, a fast acting switch might be indicated as having opened ahead of a slow acting one although it failed after the other switch. Thus, the use of auxiliary contacts for monitoring purposes is unsatisfactory.
In view of these and other defects in the prior art, it is one object of the present invention to provide an improved faultfinding circuit of the type described for detecting which of a plurality of series connected contacts opened first.
Another object is to provide an improved circuit of the type described which requires no auxiliary relay contacts.
A further object of the invention is the provision of an improved fault-finding circuit of the type described which is characterized by having a sufficiently rapid response time to correctly designate which of the series of contacts opened first even when other contacts are opened as the result of the same failure.
A further object of the invention is the provision of an improved fault-finding circuit which can be quickly connected to a variety of different kinds of equipment.
A further object is the provision of an improved fault-finder which can be used on either AC or DC circuits.
Another object is to provide a fault-finding apparatus which is relatively simple in construction, durable and can be manufactured inexpensively.
These and other more specific objects will be apparent in view of the following specification and drawings wherein:
FIG. I is a'circuit diagram of the invention, and
FIG. 2 is a perspective view of the invention.
The invention will now be briefly described.
The present invention consists of a plurality of electronic switches, e.g. thyristors, each connected to a thyristor indicator such as a pilot light such that closing of the switch will energize the associated visual indicator. Any other wellknown three-element electronic switch such as an S.C.R. or a gas-filled thyratron can be used. One side of the switch is connected to one side of the circuit being monitored to maintain one side of each switch at a first potential and the other side of the switch is held at a different potential. The switches are each suitably supplied with power. Each of the switches includes a switch-triggering means, i.e. agate and each gate is coupled preferably by means of a quick disconnect fastener to a different one of the contacts that are to be monitored. When all of the contacts are closed, the gateiis held at a potential that will prevent the thyristor from becoming conducting. When one contact opens, at least one thyristor will fire by virtue of its gate having been changed sufiiciently in potential to cause the thyristor to conduct. In a preferred form of the invention firing is accomplished by disconnecting the gate from its cathode and connected to its anode through the power output device.
To the accomplishment of the foregoing and related ends, the invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forthin detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.
In FIG. I, relay 10, represents a relay for a device such as an electric motor used for running equipment or a boiler or a variety of other kinds of equipment connected across AC power lines 14 and 16 of which line 14 is the neutral normally grounded terminal and the line 16 is hot. A conductor 18 connects the relay 10 through a plurality of series connected contacts 20 through 23.
The fault-finding circuit which is indicated generally by the numeral 24 is composed of conductors 26 and 28 connected across the monitored electric power circuit by means of suitable releasable fasteners or connectors such as alligator clips 30 and 32. A diode 34 and resistor 35 connected in series in the line 26 a filter capacitor 36 serves as a rectifier and power supply for the fault-finder. A normally closed reset button 37 is connected in series with the power supply to reactivate the circuit after it has been operated.
Connected in parallel across the lines 26 and 28 are a plurality of switches consisting of thyristors 38 each having an anode, a cathode 39 and a gate 41 which is connected through a resistor 40 and capacitor 42 to one of lead lines 56, 58, 60 and 62 that are in turn connected to our side of the respective contacts 20-23 with suitable fasteners such as alligator clips 56a, 58a, 60a and 62a. Neon glow bulbs 64 are connected in series with each of the thyristors 38.
The resistor 40 is used to limit the gate current for thyristor protection, resistor 43 is used to stabilize the thyristor so that it will not fire due to any transients in its anode circuit and resistor 65 is used to ensure the thyristor enough current to latch, and hold itself on.
The apparatus is placed in a housing 66 (H6. 2). Each of the leads 56 through 62 is positioned on the housing 66 in alignment with the particular bulb 64 to which it is connected electrically.
Although the values employed can be varied considerably within the scope of the invention, suitable components are designated in the table below.
The operation of the circuit will now be described. It will be assumed first that all of the contacts 20 through 23 are closed and that the relay 10 is energized. Under these circumstances, the gates of the thyristors 38 will ball be connected through the leads 56-62 to their common cathodes 39. If, for example, the contact 20 opens, the gate of the first thyristor on the left is disconnected from the cathode and is connected to the anode through relay 10 thus causing the thyristor to conduct. This, of course, energizes the associated lamp 64. Since'the thyristors are fed from a DC supply, the conducting thyristor 38 will remain in that state until the power is removed by opening the reset switch 37. The opening of any of the other three contacts after the opening of contact 20 will have no effect on the other thyristors since their gates will have no connection to a voltage high enough to trigger them. On the other hand, if contact 21 had opened first, the two lamps 64 at the left would remain energized until reset. This would indicate that the contact just to the left of the terminal 580 was the first to open. Accordingly, in the circuit illustrated, theenergized lamp furthest to the right signifies which of the contacts 20 through 23 opened first. Each thyristor 38 in order to hold itself on must have a minimum current across its anode. and cathode. The resistor 65 provides this current from supply lines 14 and 16.
lt is apparent that many modifications and variations of this invention as hereinbefore set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only and the invention is limited only by the terms of the appended claims. A
1. A fault-finding circuit for determining which of several series connected contactthat are wired to a potential source opens first in a sealing circuit for a power output device, said circuit comprising: a plurality of switches, visual indicator means, means connecting each switch to one visual indicator such that closing of the switch will energize its associated indicator, means initially maintaining one side of each switch at a first potential, means initially maintaining the other side of each switch at a second potential, each of the switches includes a switch-triggering means, a conductor connecting each triggering means to one side of one of the contacts that are to be monitored, the contacts when closed maintaining the triggering means at a potential that will prevent its associated switch from conducting and the opening of one of the contacts changing the potential of at least one triggering means sufficiently to cause its switch to become conducting thereby energizing its associated indicator whereby when one of said contacts opens, the potential of those triggering means between the open contact and the potential source will be changed to make their asociated switches conduct and the opening of said contact preventing the potential source from energizing the triggering means of any of the switches remote from said potential source from the switch that is conducting.
2. A fault-finding apparatus for detennining the opening sequence of a plurality of contacts connected to a power supply means in a sealing circuit for a power output device, said apparatus comprising a plurality of switches, each switch containing a cathode, an anode and a gate, an indicator connected in series with each switch, said power supply means being connected to each of the switches to initially maintain each anode at a first potential and cathode at a second potential, said indicators connected to each switch such that each indicator will be energized only when its associated switch is in the on" condition, leads for connecting each anode and cathode of the switches across the monitored electric power circuit, leads for connecting each gate to one side of each of the contacts being monitored, the opening of one of the contacts will cause the gate of the associated switch to be connected through the power output device to the cathode thus causing the switch to become conducting and after a contact opens only those switches having their gates connected to the anode through the power output device thereof will be turned on" and those which remain connected to the cathode remain in an off" condition whereby when one of said contacts opens, the potential of those gates between the open contact and the potential source will be changed to make their associated switches conduct and the opening of said contact preventing the potential source from energizing the gates of any of the switches remote from said potential source from the switch that the switch that is conducting.
3. The apparatus of claim 1 wherein each switch comprises a silicon controlled rectifier.
4. The apparatus of claim 1 wherein a power supply is connected across the main power line being monitored and the switches are connected in parallel across the power supply.
5. The apparatus of claim 1 wherein the means connecting the gate of each of the thyristors to the circuit being monitored comprises a releasable connector.
6. The apparatus of claim 1 wherein each of the switches comprises a thyristor having a cathode, an anode and a gate and each of the contacts is connected to the gate through a capacitor for blocking DC currents.
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