EP1139361B1 - Electrical circuit for the transmitting the status information, particularly for railway material, and system incorporating such a circuit - Google Patents

Abstract

An electrical circuit for transmitting an item of information relating to the state of a parameter or of a piece of equipment, in particular for application in the railway field. The circuit includes a device for regulating the current flowing through the switch, including a switch device for switching over connections and having an inductive energy storage device and a capacitive energy storage device which, under steady conditions, alternate between being a device for storing and a device for restoring a fraction of the energy of the electrical circuit depending on the alternating state of the connections, as defined by the switch device. The invention also provides an electrical system incorporating such a circuit.

Description

The invention relates to an electrical circuit for the routing of all-or-nothing information, particularly for an application in the railway field.

In a train, many all-or-nothing signals indicating the state of a parameter or equipment are routed, for example, to an electronic controller control circuit or to a control and control panel. signaling.

For example, these signals are representative of the state of a circuit breaker or the open or closed position of a car access door.

The signals are intended to be routed with a high degree of security and availability, making the use of computer-based low-energy links unsuitable.

One solution currently used is to connect to the two terminals of a battery a closed loop electrical circuit, which comprises in series at least one switch linked to the state of the body to be monitored, a resistor, and a galvanically isolated connection connected to the receiving device of the information contained in the signal, for example the electronic controller control circuit or the control and signaling board.

The open or closed position of the switch is representative of the state of a parameter or equipment. When the switch is closed, a current, whose intensity is limited by the resistance, circulates in the circuit. When it is open, no current flows. The presence or absence of this current is transformed by the galvanically isolated connection into an all or nothing information communicated to the electronic circuit.

Generally, a train has a plurality of such circuits connected to the terminals of the same accumulator.

As the switches tend to oxidize, a minimum current intensity, of the order of a few tens of milliamperes, must pass through each of these switches to clean them.

This current is consumed at a loss in the resistance.

In addition, the power dissipated in the Joule effect produces heat, which must be removed.

One solution would be to use fans.

However, at present, it is avoided, or even forbidden, to use such fans as a cooling mode of the electronic circuits embedded in the trains for reasons of reliability, a fan with mechanical components likely to get stuck. , to seize and, in general, to cause a breakdown.

The reliability of electrical and electronic components decreases sharply when the ambient temperature increases, we try to produce the least possible heat.

Moreover, the battery generally supplying several circuits, and other equipment, the voltage it delivers varies over time with the level of the load at its terminals.

The intensity of the current in the circuit therefore also varies, in proportion to the state of charge of the accumulator.

Therefore, to obtain the minimum intensity required for the cleaning of the switches, it is necessary to consent to consume a large amount of current and therefore power, during certain periods during the operation of the circuit. The additional heat production that accompanies it increases the problem of the evacuation of this heat.

The amount of heat dissipated increases with the number of switches and information to be transmitted.

DE-A-4,221,916 discloses an electric circuit according to the preamble of claim 1.

The invention aims to reduce the aforementioned drawbacks of the prior art.

The purpose of the invention is therefore to provide the routing of all-or-nothing information with a high degree of reliability and availability, while reducing the power dissipated by the Joule effect.

• une liaison à isolation galvanique entre ledit circuit électrique et une sortie pour l'émission d'une information d'état, et
• un interrupteur dont la position ouverte ou fermée est représentative de l'information d'état et qui détermine le passage d'un courant dans ledit circuit électrique,
  le circuit électrique assurant la transmission de l'information d'état de l'interrupteur vers la sortie, par l'intermédiaire de la liaison à isolation galvanique,

caractérisé en ce qu'il comporte des moyens pour réguler l'intensité du courant dans l'interrupteur, comportant des moyens de commutation des connexions entre les éléments constitutifs du circuit électrique et comportant des moyens d'emmagasinage selfiques en série avec l'interrupteur et des moyens d'emmagasinage capacitifs qui, en régime établi, forment chacun alternativement moyens de stockage et moyens de restitution d'une partie de l'énergie dudit circuit électrique, selon l'état alternatif desdites connexions entre les différents éléments du circuit électrique, déterminé par les moyens de commutation.It therefore relates to an electrical circuit for transmitting the state of a parameter or equipment, intended to be connected to the terminals of a supply battery and comprising:

• a galvanically isolated link between said electrical circuit and an output for transmitting state information, and
• a switch whose open or closed position is representative of the state information and which determines the passage of a current in said electric circuit,
  the electrical circuit for transmitting the status information of the switch to the output, via the galvanically isolated connection,

characterized in that it comprises means for regulating the intensity of the current in the switch, comprising means for switching the connections between the constituent elements of the electrical circuit and comprising inductive storage means in series with the switch and capacitive storage means which, in steady state, each form alternately storage means and means for restoring a portion of the energy of said electric circuit, according to the alternative state of said connections between the various elements of the electric circuit, determined by the switching means.

• la liaison à isolation galvanique est connectée en série avec l'interrupteur ;
• les moyens pour réguler l'intensité du courant dans l'interrupteur comportent en outre des moyens de contrôle d'une grandeur caractéristique de l'état du circuit électrique et de commande alternative des moyens de commutation des connexions entre les éléments constitutifs du circuit électrique en fonction de l'état dudit circuit électrique ;
• les moyens de commutation des connexions entre les éléments constitutifs du circuit électrique connectent alternativement au moins les moyens d'emmagasinage selfiques, l'interrupteur, l'accumulateur et les moyens d'emmagasinage capacitifs en série dans une boucle fermée lors d'une première phase, en régime établi, de restitution par les moyens d'emmagasinage selfiques d'une quantité d'énergie qui est stockée par les moyens d'emmagasinage capacitifs, et les moyens d'emmagasinage selfiques, l'interrupteur et les moyens d'emmagasinage capacitifs en série dans une boucle fermée lors d'une deuxième phase , en régime établi, de restitution par les moyens d'emmagasinage capacitifs d'une quantité d'énergie qui est stockée par les moyens d'emmagasinage selfiques, la polarité des branchements entre les moyens d'emmagasinage selfiques et les moyens d'emmagasinage capacitifs étant inversés entre la première et la deuxième phase ;
• les moyens d'emmagasinage selfiques et les moyens d'emmagasinage capacitifs comportent respectivement une inductance en série avec l'interrupteur et une capacité, le circuit électrique comporte en série avec l'interrupteur et l'inductance, des première et deuxième branches en parallèle, et comporte une résistance en parallèle avec l'interrupteur et l'inductance, et connectée à un point de la deuxième branche, la capacité étant connectée dans la deuxième branche, et les moyens de commutation des connexions comportent des moyens pour diriger alternativement dans les première et deuxième branches le courant passant dans l'interrupteur et l'inductance ;
• la liaison à isolation galvanique est connectée dans la première branche ;
• la liaison à isolation galvanique est connectée en série avec le condensateur dans la deuxième branche ;
• la liaison à isolation galvanique est connectée en série avec la résistance ;
• la période, durant laquelle le courant passant dans l'interrupteur et l'inductance circule successivement dans la première puis dans la deuxième branche, et le rapport cyclique, égal au temps de circulation de ce courant dans la première branche divisé par ladite période, sont respectivement fixe et variable et déterminés par les moyens de contrôle de la grandeur caractéristique de l'état du circuit électrique et de commande périodique des moyens de commutation ;
• les moyens pour diriger alternativement dans les première et deuxième branches le courant passant dans l'interrupteur et l'inductance comportent un interrupteur commandé connecté dans la première branche et une diode connectée dans la deuxième branche entre d'une part, l'une des deux jonctions des première et deuxième branches, et d'autre part, le point de connexion de la résistance sur la deuxième branche, la capacité se trouvant entre d'une part l'autre de ces deux jonctions des première et deuxième branches, et d'autre part, le point de connexion de la résistance sur la deuxième branche ;
• la liaison à isolation galvanique est connectée en série avec la diode ;
• la liaison à isolation galvanique consiste en un opto-coupleur ;
• la liaison à isolation galvanique consiste en un transformateur ;
• le primaire dudit transformateur forme également au moins une partie des moyens d'emmagasinage selfiques ;
• lesdits moyens de contrôle d'une grandeur caractéristique de l'état du circuit électrique et de commande périodique des moyens de commutation forment également la liaison à isolation galvanique et sont, à cet effet, pourvus de ladite sortie pour l'émission de l'information d'une part, et aptes à émettre cette information à partir du traitement de ladite grandeur caractéristique, notamment à partir du rapport cyclique, d'autre part ;
• la valeur de crête, au cours d'une période, du courant passant dans l'interrupteur constitue ladite grandeur caractéristique de l'état du circuit électrique ;
• le potentiel au point de connexion de la résistance sur la deuxième branche constitue ladite grandeur caractéristique de l'état du circuit électrique ;
• la tension aux bornes de la résistance constitue ladite grandeur caractéristique de l'état du circuit électrique ;
• il comporte en outre des moyens pour tester son fonctionnement correct, indépendamment de la position de l'interrupteur d'état ;
• les moyens pour tester le fonctionnement correct de ce circuit électrique comportent :
  • un interrupteur commandé de test et un accumulateur de test connectés dans un premier circuit série qui est à son tour connecté en parallèle avec un deuxième circuit série comportant l'interrupteur d'état et un emplacement destiné au branchement de l'accumulateur d'alimentation, et
  • une unité de test automatique, connectée à la borne de commande de l'interrupteur commandé de test et à la sortie pour l'émission d'une information d'état ;
• les moyens pour tester le fonctionnement correct de ce circuit électrique comportent :
  • un interrupteur commandé de test connecté en parallèle avec l'interrupteur d'état, l'ensemble étant connecté en série avec un emplacement pour le branchement de l'accumulateur d'alimentation destiné à assurer également la fonction d'un accumulateur de test ; et
  • une unité de test automatique, connectée à la borne de commande de l'interrupteur commandé de test et à la sortie pour l'émission d'une information d'état ;
• l'unité de test automatique, également connectée aux moyens de contrôle d'une grandeur caractéristique de l'état du circuit électrique et de commande alternative des moyens de commutation des connexions, est apte à maintenir lesdits moyens de commutation dans au moins une position d'annulation du courant dans ledit circuit électrique ;
• les moyens pour tester le fonctionnement correct de ce circuit électrique comportent au moins une diode de protection connectée en série avec l'interrupteur d'état, pour bloquer un courant en provenance de l'interrupteur commandé de test ;
• les moyens pour tester le fonctionnement correct de ce circuit électrique comportent une autre diode de protection connectée en série avec l'interrupteur commandé de test, pour bloquer un courant en provenance de l'interrupteur d'état.

According to other characteristics of this electric circuit:

• the galvanically isolated connection is connected in series with the switch;
• the means for regulating the intensity of the current in the switch further comprise means for controlling a quantity characteristic of the state of the electric circuit and of the alternative control of the means for switching the connections between the constituent elements of the electrical circuit in function of the state of said electric circuit;
• the means for switching the connections between the constituent elements of the electrical circuit alternately connect at least the inductive storage means, the switch, the accumulator and the capacitive storage means in series in a closed loop during a first phase , in steady state, of restitution by the inductive storage means of an amount of energy which is stored by the capacitive storage means, and the inductive storage means, the switch and the capacitive storage means in series in a closed loop during a second phase, in steady state, of restitution by the capacitive storage means of a quantity of energy which is stored by the inductive storage means, the polarity of the connections between the inductive storage means and the capacitive storage means being reversed between the first and the second phase;
• the inductive storage means and the capacitive storage means respectively comprise an inductance in series with the switch and a capacitance, the electric circuit comprises in series with the switch and the inductor, first and second branches in parallel, and comprises a resistor in parallel with the switch and the inductor, and connected to a point of the second branch, the capacitor being connected in the second branch, and the connection switching means comprise means for alternately directing in the first branch; and second branches the current passing through the switch and the inductor;
• the galvanically isolated connection is connected in the first branch;
• the galvanically isolated connection is connected in series with the capacitor in the second branch;
• the galvanically isolated connection is connected in series with the resistor;
• the period during which the current flowing in the switch and the inductor flows successively in the first and the second branch, and the duty cycle, equal to the circulation time of this current in the first branch divided by said period, are respectively fixed and variable and determined by the control means of the characteristic magnitude of the state of the electric circuit and periodic control of the switching means;
• the means for alternately directing in the first and second branches the current flowing in the switch and the inductor comprise a controlled switch connected in the first branch and a diode connected in the second branch between on the one hand, one of the two junctions of the first and second branches, and secondly, the connection point of the resistance on the second branch, the capacity is finding on the one hand the other of these two junctions of the first and second branches, and on the other hand, the connection point of the resistance on the second branch;
• the galvanically isolated connection is connected in series with the diode;
• the galvanically isolated connection consists of an optocoupler;
• the galvanically isolated connection consists of a transformer;
• the primary of said transformer also forms at least a portion of the inductive storage means;
• said means for controlling a magnitude characteristic of the state of the electrical circuit and periodic control of the switching means also form the galvanically isolated link and are, for this purpose, provided with said output for the transmission of the information on the one hand, and able to transmit this information from the processing of said characteristic quantity, in particular from the duty cycle, on the other hand;
• the peak value, during a period, of the current flowing in the switch constitutes said characteristic quantity of the state of the electric circuit;
• the potential at the connection point of the resistor on the second branch constitutes said characteristic quantity of the state of the electric circuit;
• the voltage across the resistor constitutes said characteristic quantity of the state of the electric circuit;
• it further comprises means for testing its correct operation, regardless of the position of the state switch;
• the means for testing the correct operation of this electrical circuit comprise:
  • a controlled test switch and a test accumulator connected in a first series circuit which is in turn connected in parallel with a second series circuit having the state switch and a location for connecting the supply accumulator, and
  • an automatic test unit, connected to the control terminal of the test controlled switch and to the output for the transmission of status information;
• the means for testing the correct operation of this electrical circuit comprise:
  • a test-controlled switch connected in parallel with the status switch, the assembly being connected in series with a location for connecting the supply battery to also perform the function of a test battery; and
  • an automatic test unit, connected to the control terminal of the test controlled switch and to the output for the transmission of status information;
• the automatic test unit, also connected to the control means of a quantity characteristic of the state of the electrical circuit and of the alternative control of the switching means of the connections, is able to maintain said switching means in at least one position of canceling the current in said electric circuit;
• the means for testing the correct operation of this electrical circuit comprise at least one protection diode connected in series with the state switch, for blocking a current coming from the controlled test switch;
• the means for testing the correct operation of this electrical circuit comprise another protection diode connected in series with the test controlled switch, for blocking a current coming from the state switch.

The invention also relates to an electrical system for transmitting a plurality of status information, characterized in that it comprises an accumulator and a plurality of electrical circuits, as defined above, each intended to transmit a state information and connected in parallel across said accumulator.

According to other characteristics of this electrical system, it is embedded in a railway train, each switch being associated to an organ or equipment of said railway train, to control its state or position.

• la Fig.1 représente un système électrique selon une première variante de réalisation de l'invention pour la transmission d'une pluralité d'informations tout ou rien ;
• la Fig.2 représente un circuit électrique élémentaire du système électrique de la figure 1 pour la transmission d'une information tout ou rien ;
• les graphes des figures 3a, 3b et 3c représentent les valeurs théoriques des courants en fonction du temps, respectivement dans trois branches du circuit de la figure 2 ;
• la Fig.4 représente un circuit élémentaire analogue à celui de la figure 2 selon un exemple de réalisation de la première variante de réalisation de l'invention ;
• la Fig.5 représente un circuit élémentaire analogue à celui de la figure 2 selon une deuxième variante de réalisation de l'invention ;
• la Fig.6 représente un circuit élémentaire analogue à celui de la figure 2 selon une troisième variante de réalisation de l'invention ; et
• la Fig. 7 représente un circuit élémentaire conforme à la première variante de réalisation de l'invention illustrée à la figure 2, ce circuit élémentaire comportant en outre des moyens pour tester automatiquement son fonctionnement correct.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which:

• Fig.1 shows an electrical system according to a first embodiment of the invention for transmitting a plurality of all or nothing information;
• FIG. 2 represents an elementary electrical circuit of the electrical system of FIG. 1 for the transmission of an all or nothing information;
• the graphs of FIGS. 3a, 3b and 3c represent the theoretical values of the currents as a function of time, respectively in three branches of the circuit of FIG. 2;
• 4 represents an elementary circuit similar to that of Figure 2 according to an exemplary embodiment of the first embodiment of the invention;
• FIG. 5 represents an elementary circuit similar to that of FIG. 2 according to a second variant embodiment of the invention;
• Fig.6 shows a similar elementary circuit to that of Figure 2 according to a third embodiment of the invention; and
• FIG. 7 shows an elementary circuit according to the first embodiment of the invention illustrated in Figure 2, this elementary circuit further comprising means for automatically testing its correct operation.

A first embodiment of an electrical system 1 according to the invention is illustrated in FIG.

The electrical system 1 is able to transmit a plurality of all or nothing information to an electronic control circuit 2 of the controllers.

The electrical system 1 comprises a plurality of elementary electrical circuits CE (i), here n in number, connected in parallel to the terminals of a supply accumulator 3. As will be explained below, each elementary circuit CE (i ) is able to transmit information all or nothing representative of the state of an organ or equipment to be controlled, including a railway vehicle equipment.

A connection S (1) ... S (i) ... S (n) retrieves at the output of each elementary circuit CE (i), the all or nothing information by means of a connection which will be described below. to transmit it to one of the input ports P (1) ... P (i) ... P (n) of the electronic circuit 2.

The electronic circuit 2 also includes output ports 4 for example for the control of PLCs (not shown).

In the main application referred to, the supply accumulator 3, the electrical system 1 and the electronic circuit 2 are intended to be embedded in a train. It goes without saying that the electronic control circuit 2 of PLCs can be replaced by a control and signaling board or by any device capable of receiving and processing an all or nothing information.

Generally, the supply accumulator 3 is the only source of DC voltage for the entire train. Also, the various on-board equipment that requires a DC power supply are powered by this single battery 3. The voltage it delivers is therefore likely to vary over time, depending on the load at its terminals, between 0.6 times and 1.4 times its nominal voltage.

Accumulators 3 generally currently used in trains, have nominal voltages of 24 volts, 36 volts, 48 volts, 96 volts and 110 volts.

For the sake of clarity, an elementary electrical circuit CE (i) entering the construction of the electrical system 1 has been isolated in FIG. 2. This elementary circuit CE (i) comprises a loop B fed by the accumulator 3 and which comprises , arranged in series, a state switch 5, an inductor 6, a galvanically isolated connection 7 which can for example be achieved by means of an optocoupler, and two branches 8 and 9 in parallel.

For the sake of convenience, the following convention is adopted in the rest of the description: the flow direction of a current in the loop B from the + terminal to the - terminal of the battery 3 defines a positive orientation of this loop B.

The branch 8 comprises, arranged in series, a transistor 10 and a regulating device 11 controlling said transistor 10. The polarization of the transistor 10 is such that a current flowing between the two main electrodes, other than that of the control, of the transistor is positive according to the conventional orientation of the B loop adopted previously.

The regulating device 11 comprises means for measuring the intensity of the current flowing through the branch 8, as well as a clock (not shown).

The second branch 9 comprises a diode 12 and a capacitor 13 in series.

A resistor 14 is disposed between a point P of the branch 9 located between the diode 12 and the capacitor 13, and the + terminal of the accumulator 3.

The diode 12 is polarized so as to prevent the discharge of the capacitor 13 other than by the resistor 14.

The organ or the equipment whose state is to be controlled actuates the closing and opening of the state switch 5.

When the switch 5 is open, no current flows in the loop B through the galvanic connection 7, which, when it consists of an opto-coupler, delivers no output current on the connection S (i) or output for issuing state information.

The control frequency of the transistor 10 is set, for example around 240 kHz, by the clock of the regulator 11. During a period T defined as the inverse of this control frequency of the transistor 10, which period is, in the example described fixed, but which can be made variable in other embodiments, the transistor 10 is consecutively turned on then blocked. The duty cycle α, equal to the time during which the transistor 10 is passing divided by the period T, is variable. It is determined by the regulating device 11 by comparing the peak value of the current traversing the branch 8 during a period T to a set value of the order of 25 mA stored in the regulating device 11, in order to regulate the current in the loop B.

When the switch 5 is open, the current in the branch 8 is zero, and therefore less than the set value of the regulator 11. The duty cycle α is then equal to 1 and the transistor 10 is moving in a manner keep on going.

It will also be noted that, in this position of the switch 5, the potential V _p at the point P is equal to the voltage E at the terminals of the accumulator 3.

et croît exponentiellement en fonction du temps t dans le cas général et sensiblement linéairement lorsque la période de commande est très inférieure à la constante de temps de l'inductance 6 de valeur L/r.When the switch 5 is actuated from its open position to its closed position, then starts a transient phase. Since the transistor 10 is on, the inductance 6 of value L and of its own resistance r is subjected to the voltage E delivered by the accumulator 3. The intensity i ₆ of the current in the inductor 6 is determined by the relation: $$\mathrm{E}\mathrm{=}\mathrm{The}\frac{{\mathrm{di}}_{\mathrm{6}}}{\mathrm{dt}}\mathrm{+}{\mathrm{<figure-callout\; id="6"\; label="ri"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">ri</figure-callout>}}_{\mathrm{6}}$$

and exponentially increases as a function of time t in the general case and substantially linearly when the control period is much lower than the time constant of inductance 6 of value L / r.

After one or more periods T, the current i ₆ has reached a value such that the duty cycle α begins to move away from its initial value equal to 1 and the transistor 10 is blocked.

The inductor 6 is demagnetized by a current i ₁₂ passing through the diode 12, towards the point P. This current i ₁₂ divides into P in two currents i ₁₃ and i ₁₄ which respectively traverse the capacitor 13 and the resistor 14. The current i ₁₄ is initially relatively low, since most of the current i ₁₂ from the diode 12 is applied to the capacitor 13. The current i ₁₃ increases the charge of the capacitor 13 and the potential V _p at the point P increases above of its initial value E.

At the end of the period T, the transistor 10 is switched on again and if the switch 5 is still closed, the cycle just described repeats several times in an almost identical manner, except that the potential V _p at point P now increases.

est égale à la valeur moyenne du courant i₁₂ à travers la diode 12.At each new cycle, the potential V _p gradually increases to tend towards a stabilization value after the transient phase which has just been described. The stabilization value of V _p is reached when the average of the intensity of the current i ₁₄ , determined by the voltage across the resistor 14 and the value R of this resistor 14 according to the relation ${\mathrm{i}}_{14}=\frac{V_p-E}{R},$

is equal to the average value of the current i ₁₂ through the diode 12.

From now on, the elementary circuit CE (i) has entered a substantially stabilized regime. The value of the potential V _p at the point P is then substantially constant.

FIGS. 3a, 3b and 3c illustrate the operation of the elementary circuit CE (i) once it has entered this substantially stabilized regime where the current flowing in the inductor is not interrupted.

More precisely, curve 3a shows the variation of current i ₆ in function of time in the inductor 6, and curves 3b and 3c show the contribution of this current i ₆ in the intensities of the respectively current i ₁₀ flowing through the transistor 10 and the current i ₁₂ passing in the diode 12.

ou encore, par la relation ${\mathrm{i}}_{\mathrm{6}}\mathrm{=}\frac{\mathit{E}}{\mathit{L}}\mathrm{t}\mathrm{+}{\mathrm{i}}_{\mathrm{6}\mathrm{m}}\mathrm{,}$

dans lesquelles t est le temps et i_6m est la valeur minimale du courant i₆ à l'instant où le transistor 10 devient passant.When the transistor 10 is at the beginning of the period T for a duration αT, the potential E of the accumulator 3 is applied to the inductor 6. The current i ₆ which is established in the switch 5, the inductor 6 the galvanically isolated connection 7 and the transistor 10 are determined, in a first approximation, if the control period is much shorter than the time constant of inductance 6, by the relation:
$\mathrm{E}\mathrm{=}\mathrm{The}\frac{{\mathit{di}}_{\mathrm{6}}}{\mathit{dt}},$

or again, by the relation ${\mathrm{i}}_{}$${\mathrm{}}_{\mathrm{6}}\mathrm{=}\frac{\mathit{E}}{\mathit{The}}\mathrm{t}\mathrm{+}{\mathrm{<figure-callout\; id="6"\; label="i"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">i</figure-callout>}}_{\mathrm{6}\mathrm{m}}\mathrm{,}$

where t is the time and i _6m is the minimum value of the current i ₆ at the moment the transistor 10 becomes on.

à partir d'une intensité minimale i_6m jusqu'à une intensité i_6M maximale.The intensity of the current i ₆ increases approximately linearly over time t with a slope $\frac{\mathit{E}}{\mathit{The}},$

from a minimum intensity i _6m to a maximum intensity i _6M .

• ${\mathrm{i}}_{\mathrm{6}}\mathrm{=}\frac{\mathit{E}-V_p}{\mathit{L}}\mathrm{t}\mathrm{+}{\mathrm{<figure-callout\; id="6"\; label="i"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">i</figure-callout>}}_{\mathrm{6}\mathrm{M}}\mathrm{,}$
  
  et décroît linéairement de la valeur maximale i_6M jusqu'à la valeur minimale i_6m.

After a duration αT, the transistor 10 is blocked until the end of the period T. The voltage across the inductance 6 is equal to EV _p , the potential V _P at the point P being substantially constant and greater than E The intensity of the current i ₆ which passes through the inductor 6 is in first approximation determined by the relation:

• ${\mathrm{i}}_{\mathrm{6}}\mathrm{=}\frac{\mathit{E}-V_p}{\mathit{The}}\mathrm{t}\mathrm{+}{\mathrm{<figure-callout\; id="6"\; label="i"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">i</figure-callout>}}_{\mathrm{6}\mathrm{M}}\mathrm{,}$
  
  and decreases linearly from the maximum value i _6M to the minimum value i _6m .

This current i ₆ through the inductor 6 flows partly into the closed loop comprising the inductor 6, the diode 12, the capacitor 13, the accumulator 3 and the switch 5. The other part of this current i ₆ flows in the resistor 14 and goes through the closed loop comprising the inductor 6, the diode 12, the resistor 14 and the switch 5.

The part of the current i ₆ which passes into the capacitor 13 when the transistor 10 is off and the inductor 6 discharges, maintains the charge of this capacitor 13 and the potential V _P at the point P.

Indeed, the capacitor 13 also discharges during the time αT, while the diode 12 is blocked, by an amount that must be equal on average to its recharge by the diode 12 during the time (1-α) T , in steady state.

When it discharges, the capacitor 13 returns a portion of its energy to the circuit by supplying at least the switch 5, the inductor 6, the galvanically isolated connection 7 and the transistor 10, and possibly also supplying the accumulator 3.

From an energy point of view, at the beginning of the period T, during αT, the capacitor 13 discharges, and a part of its energy is transferred to the inductor 6 which is magnetized, which generates the current i ₆ in the 5, the inductance 6, the galvanically isolated connection and the transistor 10. At the end of the period T, during (1-α) T, the inductance demagnetizes and a part of its energy is transferred to the capacitor 13 which is charge, which generates the current i ₆ in the switch 5, the inductor 6 and the connection with galvanic isolation 7.

The current i ₆ is therefore partly the consequence of a transfer of energy from the capacitor 13 to the inductor 6, then from the inductance 6 to the capacitor 13. It should be noted that between these two phases of transfer of energy, the polarity of the connections between the inductor 6 and the capacitor 13 are reversed. The accumulator 13 maintains the energy level of the circuit by compensating for the losses, in particular in the resistor 14. The accumulator 3 also has the function of supplying the initial energy to the circuit during the transient start phase commented previously.

The regulation device 11 determines the duty cycle α so as to regulate the intensity of the current i ₆ which passes through the inductor 6. When the transistor 10 is on, the current i ₆ increases. Conversely, this current i ₆ decreases when the transistor 10 is off. The cyclic ratio α thus determines the durations of the growth and decay phases of the current i ₆ during a period T. By increasing one of said durations relative to the other, the regulating device 11 can vary the intensity of the current i ₆ between the beginning and the end of the period T.

In steady state, the current i ₆ in the inductor 6 as shown in Figure 3a, without being quite continuous, evolves only over a reduced range between i _6m and i _6M . Its average value is adjusted so as to obtain the passage of the minimum current required to clean the switch 5.

However, the current flowing through the inductor 6 also flows in the galvanically isolated connection 7.

Thus, when the switch 5 is closed, a current is established in the galvanically isolated connection 7, which produces in response an output signal on the connection S (i).

The position of the galvanically isolated connection 7 in series with the switch 5 is advantageous since the signal that it generates at the output is a substantially faithful image of the current flowing through this switch 5.

It will be noted that the higher the capacitance C of the capacitor 13, the more the potential V _P is stable.

Indeed, the voltage variation across the capacitor 13 due to a given variation of its load, is inversely proportional to its capacitance C.

However, the duration of the transient conditions at the opening and closing of the switch 5 during which the capacitor 13 respectively charges and discharges and that we want the shortest possible, evolve with the capacitor C of this capacitor 13 and in the same sense as it. Also, the determination of C lies in a compromise.

The current coming from the capacitor 13 or outgoing current and which passes through the resistor 14 is the one which ensures the discharge of the capacitor 13. Now, in steady state, the average current leaving the capacitor 13 is equal to the current i ₆ coming from the inductance 6 that goes into it. The latter is fixed by the regulating device 11.

Consequently, the current coming from the capacitor 13 and passing through the resistor 14 is also determined by the regulating device 11. The potential difference V _P -E across the resistor 14 is set to a value proportional to the voltage. intensity of this current and inversely proportional to the value R of this resistor 14. Also, the value R of the resistor 14 makes it possible to determine the potential difference V _P -E, the value of the current i ₆ being fixed elsewhere.

The operation of the invention which has just been described reduces the energy dissipated by the Joule effect in two ways.

First, the accumulator 3 maintains the energy level in the circuit, and only the power it releases for this purpose is consumed by Joule effect. The current i ₆ in the switch 5 is not limited only by a resistor which necessarily dissipates energy by Joule effect as in the cited prior art, but also by the alternative transfer of a quantity of energy which causes a growth then a decrease of this current i ₆ and allows its regulation.

Secondly, the intensity of the current i ₆ injected into the circuit is regulated by its maximum value i _6M which is independent of the voltage E delivered by the accumulator 3. Contrary to what is obtained in the prior art, a variation of the voltage E delivered by the accumulator 3 does not introduce a variation of the current consumed by the resistor 14.

In FIG. 4, the galvanically isolated connection consists of a magnetic coupling produced by a transformer 7 ', with an air gap in the case where the DC component of the current flowing through the primary is large, the primary winding of which also forms, at least in part, that of the inductor 6. The secondary is, for its part, connected to the connection S (i).

The operation of the elementary circuit CE (i) remains unchanged. The variation of the current i ₆ in the inductance 6 between i _6m and i _6M , when the switch 5 is closed, produces a voltage output and / or a current across the secondary of the transformer 7 'which constitute the output signal after recovery by an unrepresented rectifier.

In the variant embodiment shown in FIG. 5, the galvanically isolated connection 7 has been moved from a position in series with the inductor 6 to a position in series with the transistor 10, on the branch 8. The operation of the elementary circuit CE (i) remains the same, the output signal recovered on the connection S (i) being intermittent as the current i ₁₀ which passes through the transistor 10. Means for smoothing or averaging this output signal can be provided on the output circuit associated with the output connection S (i).

In the variant embodiment of FIG. 6, the regulation device 11 has been replaced by a regulation device 11 'which comprises means for measuring the voltage V _P across the capacitor 13.

The regulation device 11 'determines the duty cycle α and controls the transistor 10 so as to regulate the voltage V _P across the capacitor 13 around a set value.

Indeed, when the duty cycle α increases, the average intensity of the current i ₆ in the inductor 6 increases as has been seen previously, as well as the share of this current i ₆ flowing in the capacitor 13 and the charge. This has the effect of increasing the potential V _P at point P.

Indeed, in steady state, the average current coming out of the capacitor 13 must be equal to the average current from the inductor 6 which enters. However, this current coming out of the capacitor 13 and discharging it is also established in the resistor 14 and is determined by the potential difference V _P -E across this resistor 14.

In the opposite direction, a decrease in the duty cycle α makes it possible to reduce the value of the potential V _P to the point P, which represents a decrease in the average intensity of the current i ₆ flowing in the inductor 6. The operation of the circuit elementary EC (i) remains unchanged elsewhere.

An advantageous control variant uses a measurement of the voltage V _p -E across the resistor 14 to regulate the current in the resistor 14 by the relation (V _p -E) / R and thus the power dissipated (V _p -E ) ² / R, while maintaining a current in the switch 5 slightly decreasing as a function of the voltage of the accumulator 3.

The invention is not limited to the embodiments that have just been described. In particular, the galvanically isolated connection may be arranged on any one of the branches of the elementary circuit CE (i), for example in series with the diode 12, the capacitor 13 or with the resistor 14.

Similarly, the transistor 10 can be replaced by any type of controlled switch.

Also, the output information can be generated by the regulating device 11 or 11 ', which then fulfills the function of the galvanically isolated connection 7 or 7', on the basis of the value of the duty cycle α, which is equal to to 1 when the switch 5 is open and deviates from 1 when it is closed.

Moreover, a failure for example following the failure of a component can occur, in an elementary circuit CE (i) according to the invention, without being detected or at least not before a time that can be longer or shorter. such a possibility affecting the reliability sought.

Since the state switch determines the passage of the current in this elementary circuit CE (i), it may be envisaged, in a first step, to use it to perform a test of operation in which the actual reception of the all-or-nothing signal is checked. However, this state switch is not always accessible and / or easily operable. For example, it can be placed in a place on the train away from the place where the reception is tested.

Also, the elementary circuit CE (i) illustrated in FIG. 7 comprises means 15 able to test its correct operation, whatever the position of the state switch.

This elementary circuit CE (i) has a basic structure identical to that of the first embodiment of the invention illustrated in Figure 2 and previously commented, and has the same elements. However, the state switch and the galvanically isolated link are here formed respectively of a voltage inverter 5 'and an optocoupler 7 ", this particular choice being only intended to illustrate certain characteristics.

The means 15 for testing the correct operation of the elementary circuit CE (i) comprise a protection diode 16 arranged between the voltage inverter 5 'and the inductor 6, and polarized so as to allow the passage of a positive current according to the conventional orientation of the B loop adopted previously. Connected in parallel with the series circuit comprising the protection diode 16, the voltage inverter 5 'and the supply accumulator 3, another series circuit comprises another protection diode 17, a test switch formed of a transistor 18, and a test accumulator 19, all of which belong to the means 15. The protection diode 17 and the test accumulator 19 are polarized so that the latter is able to supply the elementary circuit CE (i ), with the exception of the voltage inverter 5 ', producing a current of direction identical to that provided by the supply accumulator 3, in place of the latter.

With respect to this current emitted by the positive terminal of the test battery 19, the protective diode 17 is advantageously disposed downstream of the transistor 18, itself disposed downstream of this test battery 19.

The means 15 for testing the correct operation of the electric circuit CE (i) also comprise an automatic test unit 20, connected to the transistor 18 and advantageously to the regulating device 11, and receiving the status information transmitted by the opto- 7 "coupler thanks to a connection on connection S (i).

Advantageously, the protection diode 16 is located on one side or the other of the assembly comprising the voltage inverter 5 'and the supply accumulator 3 in series. Thus, optional charges C (1)... C (j)... C (m) but represented to illustrate certain operating characteristics, formed for example of relays, actuators, circuit breaker closing coils and / or or of indicator lamps, and whose state, like that of the opto-coupler 7 ", is intended to be connected to the open or closed position of the voltage inverter 5 ', are each arranged in parallel with the series circuit comprising the voltage inverter 5 'and the supply accumulator 3, with the exception of the protective diode 16.

Out of the test, the operation of this electric circuit CE (i) remains identical to that previously described, the current through the voltage inverter 5 'and the inductance 6 also passing through the protective diode 16.

The automatic test unit 20 is capable of conducting an automated test verifying that the electrical circuit CE (i) is functioning correctly, said test being triggered for example by each new start of the train.

It should be noted that the voltage inverter 5 ', whose operation can be made tedious because of the large number of such switches, can be indifferently in an open or closed position.

During a first step of the test, the automatic test unit 20 commands the transistor 18 to close, thus ensuring that the portion of the electrical circuit CE (i) located downstream of the protection diode 16 is energized. This unit 20 then verifies the transmission, in the connection S (i), of information representative of the passage of a current in the opto-coupler 7 ", which must occur when this part of the circuit CE (i), located downstream of the protection diode 16, operates correctly.

Since the galvanically isolated connection here is formed of an opto-coupler 7 ", it should also be verified that the phototransistor of this opto-coupler, passing when it receives the luminous information due to the passage of a current in the associated light-emitting diode returns to its off state, corresponding to an open switch, in the absence of this current, but, as previously mentioned, the voltage inverter 5 'can be in any state. Also, in a second step of the test, the automatic test unit 20 maintains, via the regulating device 11, the transistor 10 in the off state The current flowing through the opto-coupler 7 "s' gradually cancels out due to the energy stored in the inductor 6, during a transient period which can be estimated at 5 times the time constant of this inductance (5xL / r). Indeed, since the voltage at the terminals of the test battery 19 is here chosen to be equal to or less than that at the terminals of the accumulator 3, the current that could flow through the resistor 14 of the one towards the other of these two accumulators due to the potential difference across their terminals is blocked by the protective diode 17. After waiting for the transient period to elapse, the automatic test unit 20 verifies that the signal it receives the connection S (i) effectively corresponds to a blocked state of the phototransistor of the opto-coupler 7 ".

During this test considered in its entirety, only the protective diode 16 is not tested, and will advantageously be oversized accordingly.

When the voltage at the terminals of the supply accumulator 3 is greater than that at the terminals of the test accumulator 19, the protective diode 17 prevents a current from being established between these two accumulators, if the inverter Voltage 5 'is closed at the moment when the automatic test unit 20 keeps the transistor 18 in the on state.

Advantageously disposed downstream of the transistor 18 with respect to a current emitted by the positive terminal of the test battery 19, this protection diode 17 further protects the transistor 18 destructive effects of a too high negative voltage at its terminals.

For its part, the protection diode 16 isolates the accumulators 3 and 19 and avoids a current from one to the other, when the test voltage is greater than the supply voltage, a situation that can be encountered when the second step of the aforementioned test is not provided, for example because the galvanically isolated connection is not an optocoupler.

This protection diode 16 also prevents a short-circuit current emitted by the test battery 19 from being set up when the voltage inverter 5 'is in the open position, that is to say when it disconnects. the elementary circuit CE (i) of the supply accumulator 3 and imposes a zero voltage across this electric circuit CE (i), while, parallel, the transistor 18 is passing. Of course, this situation that is to be avoided does not exist when a simple switch is disposed in place of this voltage inverter 5 '.

The protection diode 16 also avoids being powered by the test battery 19, when the transistor 18 is conducting, the charges C (1) ... C (j) ... C (m), of which it is appropriate remember that the state is intended to be linked to that of the voltage inverter 5 '.

Alternatively, the supply accumulator 3, while keeping its arrangement inside the electrical circuit CE (i), can also be connected so as to replace the test accumulator 19. In such an arrangement, the The supply accumulator successively fulfills two distinct functions over time, thus making it possible to economize on a specific test accumulator. The transistor 18 is then connected directly in parallel with the voltage inverter 5 '. The protection diode 17 becomes superfluous. As for the protective diode 16, only the presence of the charges C (1) ... C (j) ... C (m) or the use of a voltage inverter 5 'instead of a simple switch make it necessary.

It goes without saying that any type of switch can replace the voltage inverter 5 ', it has been chosen only to illustrate the particular role performed by the protective diode 16 in the case where it is used.

The opto-coupler 7 "having been chosen for similar reasons, it too can be replaced by any other component capable of making a connection with galvanic isolation, some of them, such as for example the previously mentioned transformer, do not require a second test phase, since they can not generate alone, that is to say in the absence of any current passing through them, an output signal on the connection S (i) corresponding to such a current In this case, the connection connecting the automatic test unit 20 to the regulating device 11 is no longer necessary.

For its part, transistor 18 may be replaced by any component fulfilling the function of controlled switch.

The means 15 for testing the correct operation of the electric circuit CE (i) are intended to be adapted to any variant embodiment of the invention, for example to all those which have previously been described, although these means have been presented in FIG. a particular combination with only one of them.

The invention is not limited to a railway application, but relates to the transmission, in any field, of all-or-nothing information.

Among the advantages of the invention, it will be noted that the reduction of the total power dissipated by the Joule effect in a circuit according to the invention makes it possible to reduce the size of the resistances, the most bulky components, at temperature and at air speed. identical cooling.

This reduction in size makes it possible to reduce the size of a reading channel, and thus to make room for a larger number of reading circuits on an identical electronic card surface, despite a larger number of components.

Means 15 for automatically testing the operation of the electrical circuit CE (i) have the particular advantage of being in the form of a simple circuit, using few components and, therefore, inexpensive.

In addition, these means 15 allow to implement a test whose coverage rate is close to 100%, only the protective diode 16 is not verified.

Oversizing this protection diode 16 significantly reduces the risk of seeing it cause a failure.

Claims (26)

1. Electric circuit (CE(i)) for transmission of the state of a parameter or equipment, intended to be connected to the terminals of a supply storage battery (3) and comprising:

   - a galvanic isolation stage (7; 7') between said electric circuit (CE(i)) and an output (S(i)) for outputting a state datum, and

   - a state-representing circuit breaker (5; 5'), the open or closed position of which is representative of the state datum and which determines the passage, in non-test operation, of current through said electric circuit (CE(i)),

   the electric circuit (CE(i)) carrying out the transmission of the state datum from the state-representing circuit breaker (5; 5') to the output (S(i)) by way of the galvanic isolation stage (7; 7'),
   characterised in that it comprises means for regulating the intensity of the current in the state-representing circuit breaker (5; 5'), comprising means for switching over (10, 12) the connections between the elements making up the electric circuit (CE(i)) and comprising inductive storage means (6) in series with the state-representing circuit breaker (5; 5') and capacitative storage means (13) which, in the steady state, each alternatively form means for storing and means for returning part of the energy of said electric circuit (CE(i)), depending on the particular alternative state of said connections between the various elements of the electric circuit (CE(i)), determined by the switching-over means.
2. Electric circuit (CE(i)) according to claim 1, characterised in that the galvanic isolation stage (7, 7') is connected in series with the state-representing circuit breaker (5; 5').
3. Electric circuit (CE(i)) according to claim 1 or 2, characterised in that the means for regulating the intensity of the current in the state-representing circuit breaker (5; 5') additionally comprise means (11; 11') for checking a quantity characteristic of the state of the electric circuit (CE(i)) and for alternation control of the means for switching over (10, 12) the connections between the elements making up the electric circuit (CE(i)) as a function of the state of said electric circuit.
4. Electric circuit (CE(i)) according to any one of the preceding claims,
   characterised in that the means for switching over (10, 12) the connections between the elements making up the electric circuit (CE(i)) connect alternatively at least:

   - the inductive storage means (6), the state-representing circuit breaker (5; 5'), the storage battery (3) and the capacitative storage means (13) in series in a closed loop during a first phase - in the steady state - of returning, by the inductive storage means (6), a quantity of energy, which is stored by the capacitative storage means (13), and

   - the inductive storage means (6), the state-representing circuit breaker (5; 5') and the capacitative storage means (13) in series in a closed loop during a second phase - in the steady state - of returning, by the capacitative storage means (13), a quantity of energy, which is stored by the inductive storage means (6), the polarity of the connections between the inductive storage means (6) and the capacitative storage means (13) being reversed between the first and the second phase.
5. Electric circuit (CE(i)) according to any one of the preceding claims, characterised in that the inductive storage means and the capacitative storage means comprise, respectively, an inductance (6) in series with the state-representing circuit breaker (5; 5') and a capacitance (13); in that the electric circuit (CE(i)) comprises, in series with the state-representing circuit breaker (5; 5') and the inductance (6), first and second branches (8, 9) in parallel and comprises a resistance (14) in parallel with the state-representing circuit breaker (5; 5') and the inductance (6) and connected to a point (P) in the second branch (9), the capacitance (13) being connected in the second branch (9); and in that the means for switching over the connections comprise means (10, 12) for alternately directing into the first and second branches (8, 9) the current passing through the state-representing circuit breaker (5; 5') and the inductance (6).
6. Electric circuit (CE(i)) according to claim 5, characterised in that the galvanic isolation stage (7; 7') is connected in the first branch (8).
7. Electric circuit (CE(i)) according to claim 5, characterised in that the galvanic isolation stage (7; 7') is connected in series with the capacitor (13) in the second branch (9).
8. Electric circuit (CE(i)) according to claim 5, characterised in that the galvanic isolation stage (7; 7') is connected in series with the resistance (14).
9. Electric circuit (CE(i)) according to any one of claims 5 to 8, characterised in that the period (T) during which the current passing through the state-representing circuit breaker (5; 5') and the inductance (6) flows successively in the first (8) and then in the second branch (9), and the cycle ratio (α), equal to the time of flow of that current in the first branch (8) divided by said period (T) are, respectively, fixed and variable and determined by the means (11; 11') for checking the quantity characteristic of the state of the electric circuit (CE(i)) and for periodic control of the switching-over means (10, 12).
10. Electric circuit (CE(i)) according to any one of claims 5 to 9, characterised in that the means (10) for alternately directing into the first and second branches (8, 9) the current passing through the state-representing circuit breaker (5; 5') and the inductance (6) comprise a controlled circuit breaker (10) connected in the first branch (8) and a diode (12) connected in the second branch (9) between, on the one hand, one of the two junctions of the first and second branches (8, 9) and, on the other hand, the point (P) of connection of the resistance (14) on the second branch (9), the capacitance (13) being located between, on the one hand, the other of those two junctions of the first and second branches (8, 9) and, on the other hand, the point (P) of connection of the resistance (14) on the second branch (9).
11. Electric circuit (CE(i)) according to claim 10, characterised in that the galvanic isolation stage (7; 7') is connected in series with the diode (12).
12. Electric circuit (CE(i)) according to any one of the preceding claims,
    characterised in that the galvanic isolation stage (7) consists of an optocoupler.
13. Electric circuit (CE(i)) according to any one of the preceding claims,
    characterised in that the galvanic isolation stage consists of a transformer (7').
14. Electric circuit according to any one of claims 1 to 6, characterised in that the galvanic isolation stage (7; 7') consists of a transformer (7') which is connected in series with the state-representing circuit breaker (5; 5') and the primary of which also forms at least part of the inductive storage means.
15. Electric circuit (CE(i)) according to any one of claims 3 to 14, characterised in that said means (11; 11') for checking a quantity characteristic of the state of the electric circuit (CE(i)) and for periodic control of the switching-over means (10, 12) also form the galvanic isolation stage (7; 7') and to that end, on the one hand, are provided with said output S(i) for outputting the datum and, on the other hand, are arranged to output that datum based on the processing of said characteristic quantity, especially based on the cycle ratio (α).
16. Electric circuit (CE(i)) according to any one of claims 3 to 15, characterised in that the peak value, in the course of a period (T), of the current passing through the state-representing circuit breaker (5; 5') constitutes said quantity characteristic of the state of the electric circuit (CE(i)).
17. Electric circuit (CE(i)) according to any one of claims 5 to 15, characterised in that the potential (Vp) at the point (P) of connection of the resistance (14) on the second branch (9) constitutes said quantity characteristic of the state of the electric circuit (CE(i)).
18. Electric circuit (CE(i)) according to any one of claims 5 to 15, characterised in that the voltage (E-Vp) at the terminals of the resistance (14) constitutes said quantity characteristic of the state of the electric circuit (CE(i)).
19. Electric circuit (CE(i)) according to any one of the preceding claims, characterised in that it additionally comprises means (15) for testing its correct operation, independently of the position of the state-representing circuit breaker (5; 5').
20. Electric circuit (CE(i)) according to claim 19, characterised in that the means (15) for testing the correct operation of that electric circuit (CE(i)) comprise:

    - a controlled test circuit breaker (18) and a test storage battery (19) connected in a first series circuit which is in turn connected in parallel with a second series circuit comprising the state-representing circuit breaker (5; 5') and a location intended for the connection of the supply storage battery (3), and

    - an automatic test unit (20) connected to the control terminal of the controlled test circuit braker (18) and to the output (S(i)) for outputting a state datum.
21. Electric circuit (CE(i)) according to claim 19, characterised in that the means (15) for testing the correct operation of that electric circuit (CE(i)) comprise:

    - a controlled test circuit breaker (18) connected in parallel with the state-representing circuit breaker (5; 5'), that arrangement being connected in series with a location for the connection of the supply storage battery (3), which is also intended to carry out the function of a test storage battery; and

    - an automatic test unit (20) connected to the control terminal of the controlled test circuit breaker (18) and to the output (S(i)) for outputting a state datum.
22. Electric circuit (CE(i)) according to claim 20 or 21, characterised in that the automatic test unit (20), also connected to the means (11; 11') for checking a quantity characteristic of the state of the electric circuit (CE(i)) and for alternation control of the means for switching over (10, 12) the connections, is capable of maintaining said switching-over means (10, 12) in at least one position of zero current in said electric circuit (CE(i)).
23. Electric circuit (CE(i)) according to any one of claims 20 to 22, characterised in that the means (15) for testing the correct operation of that electric circuit (CE(i)) comprise at least one protection diode (16) connected in series with the state-representing circuit breaker (5; 5') for blocking a current coming from the controlled test circuit breaker (18).
24. Electric circuit (CE(i)) according to any one of claims 20 to 23, characterised in that the means (15) for testing the correct operation of that electric circuit (CE(i)) comprise another protection diode (17) connected in series with the controlled test circuit breaker (18) for blocking a current coming from the state-representing circuit breaker (5; 5').
25. Electric system (1) intended for transmission of a plurality of state data, characterised in that it comprises a supply storage battery (3) and a plurality of electric circuits (CE(i)) according to any one of claims 1 to 24 each of which is intended for transmission of a state datum and which are connected in parallel to the terminals of said storage battery (3).
26. Electric system (1) according to claim 25, characterised in that it is provided on a railway train, each state-representing circuit breaker (5; 5') being associated with a device or equipment of said railway train for monitoring the state or position thereof.

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