US3638072A

US3638072A - Detecting device for abnormal state in electric circuit

Info

Publication number: US3638072A
Application number: US16854A
Authority: US
Inventors: Kazuo Kobayashi; Yoshihiko Okuda; Sadao Kawamoto
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 1969-03-19
Filing date: 1970-03-05
Publication date: 1972-01-25
Anticipated expiration: 1989-01-25
Also published as: DE2012996A1; FR2035060A1

Abstract

The invention provides a detecting device for abnormal state in electric circuit. The device comprises an input terminal which varies depending on given situation, a high-frequency oscillating circuit, and an amplifier having saturated input and output characteristics. Input signals from said input terminal are mixed with output signals from said high-frequency oscillating circuit, and thus mixed output is applied to the amplifier, an output from which actuates trip coil of an associated cutoff means for the electric circuit.

Description

United States Patent Kobayashi et a1.

DETECTING DEVICEFOR ABNORMAL I STATE IN ELECTRIC CIRCUIT Inventors: Kazuo Kobayashi; Yoshihiko Okuda; Sadao Kawamoto, all of Kadoma-shi,

Japan Assignee: Matsushita Electric Works, Ltd., Osaka,

Japan Filed: Mar. 5, 1970 Appl. No.: 16,854

Foreign Application Priority Data Mar. 19, 1969 Japan ..44/21002 Mar. 24, 1969 Japan.... ...,44/22206 Mar. 26, 1969 Japan ..44/23332 US. Cl .,-..3l7/27 R, 317/18 D, 325/159 Int. Cl. ..H02h 3/28 FieldofSearch ..317/18 D, 27 R;325/159 [451 Jan. 25, 1972 [56] References Cited UNITEDSTATES PATENTS 2,912,570 11/1959 Holzwarth et al ..325/159 X 3,287,636 11/1966 Gagniere .317/18 D 3,525,018 8/1970 Murphy et al ..317/l8 D Primary Examiner- James D. Trammell Attorney-Wolfe, Hubbard, Leydig, Voit & Osann. Ltd.

ABSTRACT The invention provides a detecting device for abnormal state in electric circuit. The device comprises an input terminal which varies depending on given situation, a high-frequency oscillating circuit, and an amplifier having saturated input and output characteristics. Input signals from said input terminal are mixed with output signals from said high-frequency oscillating circuit, and thus mixed output is applied to the amplifier, an output from which actuates trip coil of an associated cutoff means for the electric circuit.

4 Claims, 15 Drawing Figures &

amt-w d PATENTED M25 1972 INVENTORS KAZUO KOBAYASHI YOSHIHIKO Oxum SADAO KAWAMOTO BY W%-,ML \J,% ATTORNEYS slsaaov mmmm I saw 2:- and GS 3206 P3n:/:

TIME

5 $459 zo jcmo A: .ZDUKG @2322 m0 FDnFDO IN verv'roas Kazuo KOBA YAsH/ YOSH/HIKO 0x004 SAD/i0 KAWAMOTO ATTORNEYS PATENIED M25 i972 m st-m4 INVENTORS KAZUO KosAYAsm Yosmmxo OKUDA Sumo KAWAMOTO BY 114%, MM,%,1/ad@w TTORNEYS For conventional devices of general type used in the above cases, there have been those devices which employing the Schmitt circuit, and the relation between input signals and output signals in these circuits is shown in FIGS. 1A and 13.

Referring to the drawings, when the input signal reaches a value A as in FIG. IA, which corresponding to a discriminating level of the Schmitt circuit, the Schmitt circuit is made to operate and circuitry output jumps up to a value B, and then its output signal is transmitted to such an instrument as a relay or the like. such circuit has been used with various instruments, but particular (references intended here should be made to the instability due to employment of the said devices in the alarm devices, protective devices or the'like.

A consideration on how results caused by circuit element troubles in such devices will appear, shall now be made with reference to FIG. 2 in which anexemplary case is shown.

FIG. 2 shows a part of a circuit of the case where a relay-is driven by means of a transistor circuit. In this circuit,'when a short circuitry trouble is caused to occur between the collector and the emitter of transistor Tr, the relay Ry is actuated similarly to the case when the input signal=exceedsa certain limit, irrespective of the presence or absence of the input signal, so that an operation of producing an alarm signal or of cutting off the electric current will be carried out. In the case when, on the other hand, an opening trouble is caused between the collector and emitter, the relay does not, to the contrary, actuate even, when those emergency situations where the alarm signal should be produced or where the power source should be cutoff;

Either one of the above two types of troubles is undesirable, but the former will be a|lowablesincethe result caused by its error operation exists rather at the safety side of the circuit.v

On the other hand, the latter one is not allowable since the result caused by-the error operation is in norisafety side.

The present invention has been-suggestedin order'toprotect human lives and properties from fallinginto more dangerous condition due to any trouble of circuitry elementlby so arranging the device that, as differed from conventionalcases, the device will be settled to be always in a single state whenever any trouble is caused to occur and'that such single state is set to be in the safety side, that is, the sidewhich produces the alarm or cuts off the electric power.

Principle of the present invention shall now be-explained with reference to the accompanying drawings, in particular, FIGS. 3 through 14 thereof, in which:

FIG. 3 shows in block diagram an exemplary device according to the present invention.

FIGS. 4-7 diagrammatically show the input signal, oscillation voltage, mixing circuit output, and output voltage, respectively, the device shown in FIG. 1.

FIG. 8 shows another embodiment of the present invention.

FIGS. 9 and 10 show diagrammatically a high-frequency voltage normally induced at secondary winding of a differential transformer and a voltage consequently produced at secondary winding of an output transformer, respectively, in the embodiment shown in FIG. 8.

FIGS. ll, 12 and 13 show diagrammatically a mixed voltage produced at the secondary winding of the differential transfonner when a leakage exists, a pulse voltage consequently produced at primary winding of the output transformer, and a current passed at this time through a trip coil, respectively, in the embodiment shown in FIG. 8.

FIG. 14 shows a further embodiment of the present invention.

Referring first to FIG. 3, I is an input terminal, and 2 is an oscillating circuit, of which oscillating frequency is set to be sufficiently higher than the maximum harmonics of the input signal. 3 is a circuit for mixing said input signal with oscillation voltage. 4.is an amplifier circuit, which has such a saturation characteristic that, until the input signal reaches a fixed level A as in FIG. 4, it amplifies the signal substantially linearly but .when the signal exceeds the level A the output signal will be kept constant at a level C as in FIG. 7. The ratio of the maximum output voltage of this amplifier circuit with respect to the input voltage is to be sufficiently larger than the amplification factor. 5 is an output terminal.

*The input signalrepresented by x in FIG. 4 is mixed with the oscillation voltage represented by y in FIG. 5 by means of the I mixing circuit 3, so that the output from the mixing circuit 3 will beof a wave 1 as shown in FIG. 6. When such output of the mixing circuit is entered into the amplifier circuit 4, the output of the amplifier circuit will be saturated at a certain value (C in FIG. 7) was not to be larger than that value and, thus, such an output voltage as shown in FIG. 7 will .be obtained. As will be clear from the above, there appears no oscillation-frequency component at the output terminal of the device in the range where the input signal x exceeds a value A. That is, it is possible to detect whether or not the input signal is exceeding the value A, depending on presence or absence of the oscillation-frequency component.

tion voltage value only, so that even when gains of the mixing circuit and amplifier circuit are-increased due to the trouble,

the detecting level A" will not be increased, but if the gains are decreased the detecting level A will be decreased or the oscillation-frequency component obtained at the output terminal 5 will disappearjThus, whenever any part of the device circuitry is involved in any type of the trouble, the oscillation-frequency component produced at the output terminal 5 will be always decreased or will be made to disappear. Thisis the same out- ,put state with that where the input signal exceeds the detecting level A and there exists no oscillation frequency component at the output terminal. Therefore, the device does not fall, depending the condition of the trouble as in the eased the foregoing example, in the same output state with the one where the input signal exceeds the detecting level A or in the same output statewhere the level A is not exceeded. Thus, it

is-made possible to provide the failsafe function to the alarm system or the'like, that is, such system willbe operated into its safety side whenever a trouble is caused to occur, by means of the above-mentioned detecting circuit.

As a further embodiment of the present invention, an example of a leakage-detecting device shall be set forth with reference'to FIG. 8.

In the drawing, 21 through 28 are forming a high-frequency oscillating circuit 2, in which 2l is a transistor, 22 and 23 are resistances, 24 through 26 are condensers, 27 is an oscillation coil, and 28 is a secondary winding for taking out the oscillation voltage after lowering down the same. The oscillation coil 7 27 and secondary winding 28 are coupled through an iron core so as to form a coupling transformer. The sensitivity can be adjusted by varying the combination coefiicient of the secondary coil. 31 is a differential transformer, 11 and 12 are distribution lines respectively inserted through a ring shape iron core of said difierential transformer for the purpose of detecting any abnormal state of the same. 32 is a secondary winding. When a leakage is caused to occur, there will be generated an unbalance current in the two distribution lines 11 and 12, thereby a voltage of 60 Hz. is generated at the secondary coil 32..In this secondary coil 32, the high-frequency oscillation voltage being supplied to a third coil 33 is further simultaneously generated. 41, 42 and 43 are transistors, 44 and 45 are resistances. The

transistors

42 and 43 and resistance 45 are forming an amplifying circuit 4. The transistor 41 and resistance 44 are DC-biasing transistor and resistor for the transistor 42. An output transformer 50 having primary coil 46 and secondary coil 47 is of a small impedance and allows the oscillated high-frequency current to pass therethrough, but does not allow the wave of 60 Hz. The primary coil 46 is formed so as to be of a large DC resistance, so that any current passed therethrough will be restricted and, thus, will be easily saturated. 48 and 49 are diodes for rectifying high-frequency current 51 is a trip coil for operating a eutoff switch 52. 7 is a direct current source. 7

Operations of the above device shall now be explained in the following.

A. In the case no leakage exists:

In this case, there is generated no unbalance current in the distribution lines 11 and 12. Therefore, only such a high-frequency voltage as shown in FIG. 9 will be generated at the secondary winding 32 of the differential transformer 31 by means of the third winding 33 through the coupling transformer in the highfrequency oscillating circuit, and this high-frequency voltage will be amplified by the amplifier section 4 and applied to the primary winding 46 of the output transformer 50. However, due to the fact that this output transformer 50 has the saturation characteristic as described in the foregoing, as well as the sufficient gain provided to the primary winding, the voltage generated at the secondary coil 47 will become the one as shown in FIG. 10. This voltage is then rectified by the

diodes

48 and 49 for rectifying high-frequency current so as to be direct current, which excites the trip coil 51 so that the cutoff switch 52 will be retained in its closed state.

B. In the case when a trouble is caused:

In this case, the high-frequency voltage at the secondary coil 47 of output transformer is decreased as described before, when a trouble is caused in any place of the circuit. Consequently, the exciting current for the trip coil 51 is decreased and the cutoff switch 52 is caused to open.

C. In case a leakage is caused to occur:

In the case when a leakage is caused to occur, the un- 'balance current is produced in the lines l1, l2 and a mixed voltage of the 60-Hz. wave and the high frequency as shown in FIG. 11 is, therefore, generated at the secondary coil 32 of differential transformer 31. The mixed voltage is amplified and, then, there will be generated at the primary winding.46 of output transformer 50 such a voltage as shown in FIG. 12 due to the saturation characteristic of the output transformer. Therefore, lower frequency component of I this generated voltage will be interrupted to pass through the output transformer 50 and the voltage passed therethrough will be rectified by the high-

frequency rectifying diodes

48 and 49, so that the current made to flow through the trip coil 51 will be as shown in FIG. 13. The cutoff switch 52 associated with the coil 51 will be opened at the point I, at which the current is decreased.

Further in the above case, as the wave form of the oscillation voltage is a sine wave, duty cycle of the pulse voltage generated at the secondary winding 47 of output transformer 50 is varied when the 60-I-Iz. wave is mixed, somewhat in contrast to the foregoing principle explanation, and its lower frequency component is interrupted by the output transformer so as to be rectified, so that the effect caused due to the decrease of electric current will be jointly obtained.

While in the foregoing the case of single phase has been referred to, it will be appreciated that in the case of three phase, a further winding added as a primary winding to those windings l1 and 12 will be sufficient.

FIG. I4 shows another embodiment of the structure of the device shown in FIG. 3.

In the drawing, 1 is an input terminal, 3 is a mixing circuit, 4' is an amplifying circuit, 5 is an output terminal, and 6 is a feedback circuit for carrying out phase shifting for the purpose of the oscillation. In this circuit, the oscillation will be performed in a loop of the mixing circuit, amplifying circuit and feedback circuit, and the circuit in this embodiment has exactly the same function as in the case shown in FIG. 3, ex cept that the oscillation circuit therein is not required in the present instance. That is, when a signal of a certain magnitude is applied to the input terminal, the amplifying circuit 4' is saturated and theoscillation is terminated. Thus, there appears no oscillation wave at the output terminal 5. Further in the case when there is caused any trouble in the circuit, there appears likely no oscillation wave at the output terminal 5.

What we claim is:

l. A device for detecting an abnormal state in an electric circuit comprising an input terminal receiving input signals varying in dependence on a given situation, an oscillating section for generating a high-frequency voltage having a frequency substantially higher than the maximum harmonics of said input signals, a mixing section for mixing the input signals from said input terminal with the high-frequency voltage from said oscillating section, and an amplifying section for amplifying outputs from said mixing section, said amplifying section having a saturation characteristic such that it becomes saturated in response to a predetermined magnitude of said input signals so as to remove the high-frequency component from the amplified output signal.

2. A device as set forth in claim 1 which comprising an input terminal, a mixing circuit, an amplifying circuit for amplifying outputs from said mixing circuit, and a feedback circuit for feeding back a part of the outputs from said amplifying circuit.

3. A device as set forth in claim 1 which comprising a differential transformer comprising a ring-shape core, distribution lines passed through the core so as to be primary conductors, and a secondary winding and a third winding respectively wound around the core; a cutoff device inserted at a portion of said distribution lines; a high-frequency oscillating circuit for providing a high-frequency voltage to said third winding; an amplifying section connected to'said secondary winding; and

' an output transformer having a primary winding and asecondary winding, the primary winding of said output transformer receiving an output from said amplifying section so that said cutoff device will be actuated by an output of the secondary winding of the output transformer.

4. A method of detecting-an abnormal state in an' electric circuit, said method comprising the steps of generating an input signal varying in dependence on a given situation, generating a high-frequency voltage having a frequency substantially higher than the maximum harmonics of said input signal, mixing said input signal with said high-frequency voltage and producing a resultant output signal, feeding said output signal to an amplifier adapted to pass said high-frequency voltage when said input signal has a first predetermined magnitude, said amplifier being saturated in response to a second predetermined magnitude of said input signalso as to remove the high-frequency component from the amplified output signal.

Claims

1. A device for detecting an abnormal state in an electric circuit comprising an input terminal receiving input signals varying in dependence on a given situation, an oscillating section for generating a high-frequency voltage having a frequency substantially higher than the maximum harmonics of said input signals, a mixing section for mixing the input signals from said input terminal with the high-frequency voltage from said oscillating section, and an amplifying section for amplifying outputs from said mixing section, said amplifying section having a saturation characteristic such that it becomes saturated in response to a predetermined magnitude of said input signals so as to remove the high-frequency component from the amplified output signal.

3. A device as set forth in claim 1 which comprising a differential transformer comprising a ring-shape core, distribution lines passed through the core so as to be primary conductors, and a secondary winding and a third winding respectIvely wound around the core; a cutoff device inserted at a portion of said distribution lines; a high-frequency oscillating circuit for providing a high-frequency voltage to said third winding; an amplifying section connected to said secondary winding; and an output transformer having a primary winding and a secondary winding, the primary winding of said output transformer receiving an output from said amplifying section so that said cutoff device will be actuated by an output of the secondary winding of the output transformer.

4. A method of detecting an abnormal state in an electric circuit, said method comprising the steps of generating an input signal varying in dependence on a given situation, generating a high-frequency voltage having a frequency substantially higher than the maximum harmonics of said input signal, mixing said input signal with said high-frequency voltage and producing a resultant output signal, feeding said output signal to an amplifier adapted to pass said high-frequency voltage when said input signal has a first predetermined magnitude, said amplifier being saturated in response to a second predetermined magnitude of said input signal so as to remove the high-frequency component from the amplified output signal.