WO1997034309A1 - Device and method for monitoring a mechanism provided with a sucking coil - Google Patents

Abstract

A device for monitoring a mechanism (10) provided with a sucking coil, comprising means (118, 120) for measuring the power supply magnitude and voltage of the coil, a unit (124, 132) for digitising and recording the power supply magnitude and voltage values, a digital computer (134) for computing at least one descriptor characteristic of the operation of the actuator on the basis of digital data comprising the power supply magnitude and voltage values, and means (138) for displaying the descriptors. The device is useful for monitoring nuclear reactor fuel clusters.

Description

DEVICE AND METHOD FOR CONTROLLING AN EQUIPPED MECHANISM

OF A REEL WITH A DIVING CORE

DESCRIPTION

Technical area

The present invention relates to a device and a method for controlling the proper functioning of a mechanism equipped with an electromechanical actuator with a coil with plunger core. The invention applies to the monitoring of any type of mechanism comprising one or more of such actuators and in particular in industrial installations such as nuclear power plants.

State of the art

Two particular examples illustrate the problems posed for the monitoring of electromagnetic actuators. The first example concerns solenoid valves with a plunger core. These solenoid valves are used in large numbers to control the supply of compressed air to pneumatically operated valve actuators in nuclear power plants. The distribution of these solenoid valves in many different rooms and their location in areas that are difficult to access during normal operation of the plant, makes monitoring them particularly complex and expensive. In addition, to diagnose the proper functioning of an actuator with a coil with plunger core, it is generally necessary to remove and disassemble it.

Another example illustrating the difficulties encountered in monitoring actuators concerns the control mechanisms of the control clusters of a nuclear reactor.

These mechanisms generally include three electromagnetic actuators which set in motion a splined bar by means of a set of grippers and pawls.

As these mechanisms are generally welded directly to the cover of the nuclear reactor, they are not easily removable for visual inspection of their state of mechanical wear.

There are also known monitoring devices and methods based on recording the operating noises of the mechanisms. These methods make it possible to avoid dismantling the mechanisms but do not make it possible to establish an accurate diagnosis of the mechanical state of the latter.

Document (1) FR-A-2 632 443 describes, for example, a system for monitoring the operation of a control rod drive mechanism from an accelerometer mounted in a pressurized envelope.

The object of the present invention is to propose an efficient device and method for controlling and diagnosing a mechanism equipped with an electromechanical actuator, making it possible to avoid the problems usually encountered during such a control and mentioned above.

An object of the present invention is in particular to propose a device and a non-intrusive control method which does not require the disassembly of the actuators and mechanisms.

Yet another object is to propose a control device and method allowing continuous and remote monitoring of a large number of mechanisms with electromagnetic actuators located in different premises of an industrial installation.

An object of the invention is also to propose a device and a method making it possible to control with great precision the mechanical system monitored so as to determine, for example, if the plunger core of the coil remains blocked, if high friction forces interfere the movement of the mechanism, or if the actuator is still operating but is in a degraded state.

Another object of the invention is to propose a device and a method which can be used and implemented on an existing installation without direct access to the mechanisms to be controlled. An object of the invention is finally to propose a device and a method allowing the control of the mechanisms during their operation and which makes it possible to develop information on the mechanical state of the mechanism more precise than that of the existing control devices.

Statement of the invention

To achieve the goals mentioned above, the invention more specifically relates to a device for controlling the behavior in operation of a mechanism equipped with at least one electromechanical actuator with at least one coil with plunger core, characterized in that 'it comprises :

means for measuring a voltage and a supply current to the coil during operation,

a unit for digitizing and recording the supply voltage and current, measured by the measuring means, and

- a digital computer with at least one descriptor characteristic of the operation of the actuator to from digital data of the supply voltage and current, supplied by the digitization and recording unit,

The descriptor is chosen from the following descriptors:

- temporal evolution of the inductance,

- time evolution of the energy supplied by the coil to the plunger core of the coil,

- time evolution of the mechanical power supplied by the coil to the plunger core of the coil,

- energy supplied by the coil to the core as a function of the inductance,

- intensity of latency at the start of movement of the plunger core. For the purposes of the present invention, the term “descriptor” is understood to mean a set of one or more values of a quantity characteristic of the operation of the mechanism or else a set of values of several correlated characteristic quantities. The descriptor can in particular be a curve of temporal evolution of this quantity, a curve of one of the quantities as a function of another, or a characteristic value of the operation.

These descriptors allow, as explained below, to provide a large amount of information on the operation of the mechanism.

The device of the invention may also include means for viewing the calculated descriptor (s). According to a particular embodiment of the device, it may include a microcomputer. The microcomputer includes the unit for digitizing and recording the supply voltage and current, and the digital computer. The microcomputer makes it possible rationally to calculate the descriptors, to record the results of measurement throughout the control of a mechanism, to exploit and analyze the descriptors and finally to display on an appropriate display screen representative curves of the descriptors. The device of the invention makes it possible to control either a single but also a plurality of mechanisms with electromagnetic actuator arranged in different premises of an installation. Indeed, as the descriptors are directly calculated from the supply voltages and currents of the plunging core coils, only an electrical connection is necessary between the supply circuit of the electromagnetic mechanism and the control device.

For this purpose, the measuring means may comprise for each actuator a voltmeter and an ammeter mounted respectively in shunt and in series in a supply circuit of each supply coil, the voltmeter and the ammeter being connected to the microcomputer through an isolation amplifier.

It appears that thanks to the invention, it becomes possible to control the mechanisms arranged in places almost inaccessible to humans.

It also appears that, thanks to the invention, the device can be installed on existing equipment without directly accessing the mechanisms to be controlled. It suffices to have the measuring means on the electrical supply circuit of these mechanisms.

The invention also relates to a method for controlling the operating behavior of a mechanism equipped with an electromechanical actuator with at least one coil with a plunger core. This process can be implemented in particular with the device described above.

In accordance with the invention, to implement the method: a voltage and a supply current of the coil are measured during operation,

- the values of the measured voltage and current are digitized and recorded,

- at least one descriptor of the temporal behavior is calculated from the digitized values of the voltage and the intensity,

- the descriptor is displayed.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows, with reference to the figures of the appended drawings, given purely by way of non-limiting illustration.

Brief description of the figures

FIG. 1 shows an overall view of a control device according to the invention,

- Figure 2 shows a time evolution curve of the intensity of the current passing through a plunger core coil and recorded by the device of the invention, - Figure 3 shows a time evolution curve of the inductance, determined in accordance with the present invention. FIG. 3 also shows by way of comparison, a curve of displacement of the plunging core, - FIG. 4 shows a curve of temporal evolution of the derivative of the inductance of a coil with plunging core,

- Figure 5 shows a time evolution curve of the energy supplied to the plunger core of a coil, determined in accordance with the present invention,

FIG. 6 shows a curve of temporal evolution of a mechanical power supplied to the plunger core,

- Figure 7 shows a curve representing a function of the inductance, the energy supplied to the plunger core of a coil.

The set of curves shown in Figures 2 to 7 is given on an arbitrary scale.

Detailed description of implementations of the invention Figure 1 shows an exemplary embodiment of a control device according to the invention. The reference 10 in FIG. 1 designates a mechanism with an electromagnetic actuator equipped with a coil with a plunger core. The terminals 112, 114 of the coil (not shown) are connected to a supply circuit 116 of the actuator. The control device comprises means for measuring the voltage and the supply current of the coil. Indeed, probes 118, 120 respectively measure a supply voltage across terminals 112, 114 of the coil and a voltage across a resistor 122 connected in series in the supply circuit 116. The resistor 122 is preferably a resistance of low ohmic value and the voltage measured at its terminals is substantially proportional to the current passing through the coil. The probe 120 and the resistor 122 thus constitute a measurement assembly as an ammeter.

The voltages measured at the terminals 112, 114 of the coil and at the terminals of the resistor 122 are applied to an analog / digital converter card 124 of a computer 126, by via a variable gain isolation amplifier 128. The main purpose of the isolation amplifier is to protect the converter card 124, in particular when the measured voltage values are very high relative to the earth.

The analog / digital converter card 124 is, for example, a card with 8 input channels not referenced to ground and allowing a digitization of the signal on 12 or 16 bits, with a sampling frequency greater than or equal to 5 kHz . The sampling frequency is chosen equal to 50 kHz, for example.

The isolation amplifier 128 has a channel-by-channel gain adjustment and in particular makes it possible to achieve gains of a factor less than 1, in order to more easily measure the supply voltage of the actuator coil . A measurement channel of the analog / digital conversion card 124 can also be used to record the signal from a microphone or an accelerometer 130 placed on the body of the mechanism comprising the electromechanical actuator. We can refer to this subject in document (1) for example. The digital data produced by the converter 124, representing the voltage and the supply current of the coil, can be stored in a memory 132 and processed by a calculation unit 134 of the computer 126, to establish the descriptors in accordance with the 'invention.

Curves or values representative of the descriptors can be viewed on a screen 138 connected to the microcomputer 126.

Advantageously, a rejector filter and a low-pass filter are also provided to eliminate the voltage and current components corresponding to noise at frequencies close to 150 Hz and 300 Hz and to noise at frequencies above 2 kHz. The frequencies of 150 Hz and 300 Hz correspond for example to the noise of the three-phase supply of coils and to its second order harmonic.

The low pass filter and rejector filter function can be performed digitally directly by the computing unit 134. To facilitate understanding of the descriptors described in the following text, reference may be made to FIG. 2 which shows the different phases of an actuator. FIG. 2 indicates, as a function of time, the intensity of the current passing through the plunger coil, measured at the terminals of the resistor 122. The intensity and the time are represented in arbitrary scale.

The actuator is energized at an instant indicated by the reference 210 on the curve of FIG. 2. From this instant, the intensity curve presents a jump 212 characteristic of the energization of the coil . It is due to magnetization phenomena of the plunger core.

The intensity then increases steadily up to an intensity threshold indicated by the reference 220 where the slope of the intensity curve changes with respect to the intensity curve normally observed when a power is applied to a coil with plunger core locked in the starting position. The intensity threshold 220, also called latency intensity, is characteristic of the start of the setting in motion of the plunger core.

Thus, according to one aspect of the invention, it is possible to calculate a descriptor called latency intensity, characteristic of the value of the intensity in the coil corresponding to the start of the core movement.

The intensity of latency can be measured or calculated in relation to the curve of the intensity of the current passing through the coil as a function of time. The latency intensity corresponds to the intensity of this current at the moment when the slope of the intensity curve changes compared to the curve normally observed when a coil is energized with its plunger core locked in the position of departure.

The intensity of the latency is directly the image of the magnetic force supplied by the coil to set the plunger core in motion. It is notably a function of static friction at the start of the movement. Thus, it is in particular possible to detect a change in this intensity in the event of a change in the friction forces to which the mechanism is subjected. For a control mechanism for control clusters of a nuclear reactor, the intensity can vary, for example, as a result of friction between the clusters and guide tubes in which they slide.

A rebound in the curve indicated by the reference 230 characterizes the instant when, due to the displacement of the core, the inductance of the coil significantly increases and when part of the electrical energy accumulated in the coil is transformed into kinetic energy.

Finally, a local minimum indicated by the reference 240 characterizes the arrival in abutment of the plunger core. The inductance then becomes constant, the kinetic energy is transformed into heat and the intensity curve follows the curve which corresponds to the load of a coil with substantially constant inductance subjected to the supply voltage. The values of the intensities corresponding to the instants 220, 230 and 240 constitute descriptors making it possible to characterize the operation of the electromagnetic actuator with plunger core. Figure 3 is an illustration of another descriptor. This is the time course of the inductance of a plunger core coil. It is in particular a coil of a cluster control mechanism in a nuclear power plant.

The inductance of the coil indicated on the ordinate is calculated as a function of time, indicated on the abscissa, according to the following formula:

dans laquelle le temps est compté à partir de la mise sous tension de la bobine. Les expressions U(t), i(t) sont respectivement les valeurs au temps t de la tension et du courant d'alimentation de la bobine relevées par les moyens de mesure du dispositif, R est la résistance électrique réelle de la bobine à noyau plongeur.

in which time is counted from the energization of the coil. The expressions U (t), i (t) are respectively the values at time t of the voltage and the supply current of the coil recorded by the measuring means of the device, R is the real electrical resistance of the core coil diver.

To facilitate reading of FIG. 3, reference marks identical to those of FIG. 2, to which 100 have been added, are associated with the respective characteristic instants of the operation of the actuator.

It is noted that at the instant 310 of power-up, the curve 300 of the calculated inductance increases regularly until a change in concavity 320 which characterizes the start of the movement of the plunger core. This first part of the curve is difficult to use because the approximate formula used does not allow the inductance to be correctly calculated in this power-up phase. On the other hand, from the change in concavity 320, we considers that the calculated inductance is a correct representation of the shape of the displacement until the immobilization 340 of the plunger core. The inductance is substantially constant after immobilization of the plunger core.

The movement of the core can be controlled and monitored by considering the inductance curve between instants 320 and 340. Indeed, during the movement of the plunger core, the variation of the inductance of the actuator is substantially proportional to the displacement of the core. This appears experimentally by comparing the curve 300 of the temporal evolution of the induction and the curve 302 which indicates (on an arbitrary scale) the displacement of the plunger nucleus as a function of time.

The amplitude of the movement of the plunger is obtained by considering the difference between the inductances between times 320 and 340.

The curve between these instants also makes it possible to determine the existence of possible mechanical hards and to locate them in the displacement. Thus, thanks to this descriptor, by locating in the movement the place or places where the decelerations occur, it is possible to search which parts of the mechanism are worn, defective, poorly lubricated, etc.

Another method of calculating the latency intensity described above is the temporal localization of the change in concavity of the temporal evolution curve of the inductance. The method for locating this change in concavity implemented by the invention is based on the analysis of the derivative with respect to the time of the inductance L (t) described above.

Figure 4 is an illustration of this latency intensity calculation method. It's about of the time course of the derivative of the inductance of a plunger core coil. It is in particular a coil of a cluster control mechanism in a nuclear power plant.

The derivative of the inductance L '(t) indicated on the ordinate is calculated as a function of time, indicated on the abscissa, according to the following general formula:

dans laquelle le temps est compté à partir de la mise sous tension de la bobine. Les expressions U(t), i(t) sont respectivement les valeurs au temps t de la tension et du courant d'alimentation de la bobine relevées par les moyens de mesure du dispositif, R est la résistance électrique réelle de la bobine à noyau plongeur.

in which time is counted from the energization of the coil. The expressions U (t), i (t) are respectively the values at time t of the voltage and the supply current of the coil recorded by the measuring means of the device, R is the real electrical resistance of the core coil diver.

The instant 420, which corresponds to the start of the movement of the nucleus is determined by locating the minimum of the curve 4 which just precedes the peak 430, the peak which characterizes the movement of the nucleus. This localization can be carried out manually on the curve or automatically by an appropriate calculation algorithm installed in the calculation unit 134 of the computer 126. Knowledge of the instant 420 then makes it possible to determine the intensity measured in the coil at this same instant, from the data measured and stored by the device object of the invention. This intensity thus determined is the latency intensity. FIG. 5 is an illustration of another descriptor usable for all the electromagnetic actuators with a plunger core. This is the time evolution of the energy supplied to the plunger core, descriptor used here in the particular case of a coil of the cluster control mechanism.

dans laquelle le temps est compté à partir de la mise sous tension de la bobine. Cette formule est une approximation de l'énergie mécanique fournie au noyau. Les expressions U(t), i(t) sont respectivement les valeurs au temps t de la tension et du courant d'alimentation de la bobine relevées par les moyens de mesure du dispositif, R est la résistance électrique réelle de la bobine à noyau plongeur, L(t) est la valeur de l'inductance au temps t calculée selon la formule indiquée ci-dessus.The energy is calculated by applying the following formula: E _m (t) = U (t) i (t) dt - Ri ² (t) dt -

in which time is counted from the energization of the coil. This formula is an approximation of the mechanical energy supplied to the nucleus. The expressions U (t), i (t) are respectively the values at time t of the voltage and the supply current of the coil recorded by the measuring means of the device, R is the real electrical resistance of the core coil plunger, L (t) is the value of the inductance at time t calculated according to the formula given above.

In FIG. 5, the energy supplied to the nucleus is indicated on the ordinate, and on an arbitrary scale, and the time is indicated on the abscissa. Identifiers identical to those of FIG. 2, to which 300 have been added, are associated with the respective characteristic instants of the operation of the actuator.

When the actuator is energized at time 510, the calculated energy increases regularly. The plunger core of the coil is stationary. The calculated energy then corresponds to the magnetic losses developed in the actuator.

At instant 520 a slope break appears. This corresponds to the start of the plunger core. The movement of the nucleus implies an increase in work mechanical which results in an increase in the energy supplied to the nucleus.

Between instants 520 and 540, the plunger core is in motion. The calculated energy then corresponds to the work of the magnetic force during the movement of the plunger. The calculated energy value gives information on the mechanical energy which is necessary for the movement of the plunger. An abnormal increase in the energy supplied to the nucleus reflects the presence of additional forces opposing the movement of the nucleus. By relating the energy and the displacement, the displacement being estimated using the descriptor of the inductance, the device of the invention makes it possible to know the variations of energy according to the position of the plunger core during the movement . We can then quantify the magnitude of the forces that hindered the movement and the place where they intervene.

At instant 540, the plunger core comes to a stop and stops. The kinetic energy is transformed into heat, the mechanical energy given to the nucleus then remains constant because there is no more movement. The mechanical energy obtained at the end of the movement 540 is the image of the energy which it was necessary to provide for the movement. If it is too large, high resistance or friction forces have opposed the movement.

FIG. 6 is an illustration of another descriptor usable for all the electromagnetic actuators with a plunger core. This is the time evolution of the mechanical power supplied to the plunger core, descriptor used here in the particular case of a coil of the cluster control mechanism. The power is calculated by applying the following formula:

Pm () = ϋ (t) i (t) - Ri

in which time is counted from the energization of the coil. This formula is an approximation of the instantaneous mechanical power supplied to the core by the coil. The expressions U (t), i (t), R and L (t) are the same as those used above to describe the formula for calculating the energy E _m (t) supplied to the nucleus.

In FIG. 6, the mechanical power supplied to the nucleus is indicated on the ordinate, and on an arbitrary scale, and the time is indicated on the abscissa. Identifiers identical to those of FIG. 2, to which 400 have been added, are associated with the respective characteristic instants of the operation of the actuator.

When the actuator is energized at time 610, the plunger core of the coil remains stationary, it receives no mechanical power. The calculated power takes on a low, non-zero value, which is due to the approximations of the calculation formula, which does not take account of the magnetic losses developed in the actuator.

At instant 620 a rapid increase in the mechanical power transmitted to the nucleus appears. This corresponds to the start of the plunger core.

Between instants 620 and 640, the plunger core is in motion, the calculated power then corresponds to the power transmitted to the core to set it in motion. Between these instants, the power passes through one or more maximums which make it possible to characterize the operation of 1 actuator. The presence of two maximums can be indicative of a hard point in the race of the core. An additional viscous friction will result in a lower maximum value and a higher duration between times 620 and 640. By relating the power and the displacement, the displacement being estimated using the descriptor of the inductance, the device of the invention makes it possible to know the variations in power depending on the position of the plunger core during the movement.

At instant 640, the plunger core comes into abutment and stops. The energy and mechanical power transmitted by electromagnetic effect to the nucleus then cancel each other out. It appears that the descriptors established in accordance with the invention make it possible to provide a precise diagnosis of the operation of the monitored mechanisms and to determine the existence and the causes of an abnormal operation before a breakdown of the mechanisms and without dismantling them.

A diagnosis of the functioning of the mechanisms can also be carried out by comparing the descriptors, or the curves representing the descriptors with descriptors or reference curves recorded from a mechanism in perfect working order.

Unlike the figures described above which relate to descriptors representative of the temporal evolution of a quantity characteristic of the operation of the mechanism, FIG. 7 shows an example of a curve corresponding to the correlated evolution of such characteristic quantities, some depending on the other.

FIG. 7 represents an evolution curve 700 of the energy supplied to the nucleus, as a function of the inductance ^" of the coil. The energy and inductance are descriptors calculated as indicated above. In FIG. 7 the energy is represented on the ordinate and the inductance on the abscissa. The scales are arbitrary.

Analysis of the curve 700 reveals an inflection point 710 around which a change in the slope of the curve is observed.

Such a point of inflection of the curve is ^" indicative of a hard point in the stroke of the plunger or of the mechanical system driven by the plunger.

Indeed, we know that the inductance is substantially linear with the displacement of the core and that the existence of a hard point in the race causes an increase in the energy supplied to the core.

Thus, the descriptor representative of the energy supplied to the core as a function of the inductance of the coil makes it easy to detect the existence of friction or of movement difficulties of the mechanism by locating the points of inflection of the curve.

Claims

1. Device for controlling the operating behavior of a mechanism (10) equipped with at least one electromechanical actuator having at least a core plunger coil, characterized in that it comprises: ^• - means (118, 120) for measuring a voltage and a supply current to the coil during operation, a unit (124, 132) for digitizing and recording values of the supply voltage and current, measured by the measuring means, and - a digital computer (134) of at least one descriptor characteristic of the operation of the actuator from digital data comprising the values of the voltage and of the supply current, supplied by the digitizing unit (124) and recording (132), the descriptor being chosen from the following descriptors: - temporal evolution of the inductance, - time evolution of the energy supplied by the coil to the plunger core of the coil, - time evolution of the mechanical power supplied by the coil to the plunger core of the coil, - energy supplied by the coil to the core as a function of the inductance, - intensity of latency at the start of movement of the plunger core. 2. Device according to claim 1, characterized in that it further comprises means (138) for viewing the descriptor. 3. Device according to claim 1, characterized in that it comprises a microcomputer (126), the microcomputer including the unit (124) of scanning and recording the supply voltage and current, and the digital computer (134). 4. Device according to claim 1, characterized in that the measuring means comprise for each actuator a voltmeter (118) and an ammeter (120, 122) mounted respectively in bypass and in series in a circuit (116) for supplying each supply coil. 5. Method for controlling the behavior in operation of a mechanism equipped with at least one electromechanical actuator with at least one coil with a plunger core, characterized in that: - a voltage and a supply current of the coil are measured during operation, - the values of the measured voltage and current are digitized and recorded, - at least one descriptor of the operation of the actuator is calculated from the digitized values of the voltage and of the current, the descriptor being chosen from the following descriptors: - temporal evolution of the inductance, - time evolution of the energy supplied by the coil to the plunger core of the coil, - time evolution of the mechanical power supplied by the coil to the plunger core of the coil, - energy supplied by the coil to the core as a function of the inductance, - intensity of latency at the start of movement of the plunger core. 6. Method according to claim 5, characterized in that one calculates a descriptor characteristic of the temporal evolution of the inductance of the coil of each actuator according to the following general formula: (U (t) - Rι (t)) dt L (t) = ι (t) where L (t) is the inductance of the coil at time t, U (t) and the voltage measured across the coil at time t, ι (t) is the current of the current flowing through the coil at time t, and where R is the electrical resistance of the coil. 7. Method according to claim 5, characterized in that a descriptor characteristic of the time evolution of the mechanical energy supplied to the plunger core is calculated according to the following general formula: E _m (t) = U (t) ι (t) dt - Rι ² (t) dt -

where E _m (t) is the energy supplied to the coil at time t, U (t) and the voltage measured across the coil at time t, ι (t) is the intensity of the current flowing through the coil at time t, where R is the inherent electrical resistance of the actuator coil, where L (t) is the inductance calculated as claimed in claim 6. 8. Method according to claim 5, characterized in that a descriptor characteristic of the time evolution of the mechanical power supplied to the plunger core by the coil is calculated, according to the following general formula: P _m (t) = U (t) ι (t) - Rι ² (t) - L (t) ι (t) ^ - dt where P _m (t) is the mechanical power supplied to the nucleus at time t, U (t) is the voltage measured across the coil at time t, i (t) is the intensity of the current flowing through the coil at time t, where R is the inherent electrical resistance of the actuator coil, where L (t) is the inductance calculated as following formula: (U (t) - Ri (t)) dt L (t) = i (t) where L (t) is the inductance of the coil at time t, U (t) and the voltage measured across the coil at time t, i (t) is the current of the current flowing through the coil at time t, and where R is the electrical resistance of the coil. 9. Method according to claim 5, characterized in that a descriptor called latency intensity is calculated, characteristic of the value of the intensity in the coil corresponding to the start of the movement of the core, this descriptor being equal to the intensity in the coil at the moment when the derivative curve of the inductance has a minimum, just before a characteristic peak of the displacement of the core, the derivative curve of the inductance being calculated according to the following general formula:

where L '(t) is the derivative of the inductance with respect to time, at time t, U (t) is the voltage measured across the coil at time t, i (t) is the intensity of the current flowing the coil at time t, and where R is the inherent electrical resistance of the actuator coil. 10. Method according to claims 6 and 7, characterized in that the energy supplied to the coil is visualized as a function of the inductance of the coil.