EP1916877A1 - Method and device for adjusting the electrical power supply of a magnetron, and installation for treatment of thermoplastic containers applying same - Google Patents

Abstract

A regulation of the power supply of a magnetron (M) as a function of an instant microwave power setpoint consists in: predetermining and storing (20) the value (η) of the electrical efficiency of the magnetron; sensing (19) a desired average microwave power value and converting it to a low frequency reference instantaneous power signal that is sampled at a high frequency; measuring (8, 9) and sampling the instantaneous values of the anode current and the high magnetron supply voltage; calculating (10) the difference, at a sampling instant (n), between the instantaneous reference microwave power and the product intensity x high voltage x efficiency; determining a value of the instantaneous microwave power at the consecutive sampling time (n + 1) corrected according to a predetermined regulation law valid at said instant (n + 1); and converting it into a corrected instantaneous microwave power analog signal to power the magnetron.

Description

The present invention relates to improvements made in the field of regulation as a function of an instant microwave power setpoint, the power supply of a magnetron belonging to UHF electromagnetic wave generating means.

The improvements proposed by the invention must find a preferred application, although not exclusive, in the field of the deposition of a coating, such as a barrier coating, on one side of at least one container of thermoplastic material to using a low-pressure plasma by excitation of a precursor gas by electromagnetic waves included in the UHF band in a vacuum cavity of cylindrical shape adapted to receive said container, said UHF electromagnetic waves being emitted by a generator of UHF wave comprising a magnetron having an anode and power supply means connected to said anode for supplying it with current under a high voltage.

It is in this context that the invention will be more particularly described, it being understood that the regulation of the magnetron power supply proposed by the invention can be implemented in other areas.

The document FR 2,776,540 exposes such a process of formation of a barrier layer and in particular the documents FR 2 783 667 , FR 2 792 854 , FR 2,847,912 present various examples of devices for performing such a deposit.

It is known to one skilled in the art that, in cold plasma processes, such as, for example, the one known in the art under the designation PECVD (Plasma Enhanced Chemical Vapor Deposition), the precision of the level of the instantaneous microwaves energy emitted and the waveform of the power emitted during the treatment cycle is one of the main factors making it possible to obtain a substantially constant quality of the deposition of the coating, in other words allowing over time to obtain containers of substantially identical quality. A fortiori, in the case of industrial installations with a large production capacity comprising a multiplicity of deposition devices, it is important to control the precision of the level of the instantaneous microwaves energy supplied in all the cavities of all the devices of the installation so as to minimize the disparity of performance between the devices of the same machine, or even between various machines, and thus the quality disparities between the containers that have been treated respectively in a plurality of devices.

There are certainly known various equipment that are available to precisely adjust this level of microwave energy (circulators, devices for measuring actual microwave power emitted, keys or "stubs" agree, ...). However, these equipment are expensive and therefore difficult to envisage in an industrial installation for which the search for a minimum cost price is a permanent concern; moreover they are bulky and therefore difficult to implement in an industrial machine, especially rotary type, which is otherwise very crowded and in which there is little space available; finally the effective and efficient implementation of these materials requires adjustments and precise calibrations that can only be provided by qualified personnel, who are not always present in industrial production facilities in large series for which the simplicity of implementation and operation of the technical means is a constant concern.

It is therefore necessary, in order to meet the requirement of reducing the dispersion of the characteristics of the coating deposited on containers in a high speed industrial process, to find a specific and economical solution for precisely controlling the operation of the magnetron.

It will be recalled that the magnetron, which is the heart of any system using microwaves, transforms a high input voltage (several kilovolts) into a given ultra-high frequency electromagnetic wave (microwave). The high voltage is delivered by a high voltage generator which is suitable for transforming a low supply voltage (in particular the voltage of a conventional power supply network, for example 400 volts three-phase) into a high voltage modulated as a function of the desired microwave energy at the output of the magnetron. The magnetron manufacturers provide, for each magnetron reference, the basic curves for defining the characteristics of the high voltage generator. Thus, for each magnetron reference, in particular the curve of variation of the anode current as a function of the microwave power emitted, the curve of variation of the electrical efficiency as a function of the micro power can be arranged. emitted waves, and the variation curve of the high voltage to be applied to the magnetron as a function of the microwave power emitted.

The electrical efficiency of the magnetron is substantially stable for a given microwave power emitted and it varies slightly as a function of the microwave power emitted (in a typical example of a magnetron, the variation of the electrical efficiency is of the order of 2, 8% for an emitted microwave power ranging from 350 to 900 W).

However, all these characteristics of the magnetron are valid only when the magnetron is coupled on a so-called adapted load, that is to say on a load such that it does not reflect towards the magnetron a fraction of the micro energy it receives from it.

• au démarrage du processus, le plasma n'est pas encore établi ; la charge couplée au magnétron est mal adaptée et l'énergie qu'elle réfléchit est importante ;
• puis, le plasma s'établit au sein de la cavité ; la charge couplée au magnétron est mieux adaptée et l'énergie qu'elle réfléchit est moindre.

However, in the case of devices more specifically targeted by the invention, which are intended for depositing a coating on a container of thermoplastic material using a low-pressure plasma by excitation of a precursor gas with UHF electromagnetic waves in a vacuum cavity of cylindrical shape receiving said container, not only the load coupled to the magnetron is not suitable, but also it is not constant in time and its variations are very fast (from the order of magnitude of a few milliseconds). These load variations are inherent to the conditions of formation of the plasma in the cavity for a given average microwave power emission (operating condition of the device displayed by the operator as operating instruction):

• at the start of the process, the plasma is not yet established; the charge coupled to the magnetron is poorly adapted and the energy it reflects is important;
• then, the plasma is established within the cavity; the charge coupled to the magnetron is better adapted and the energy it reflects is less.

It should be emphasized here that the average power setpoint does not vary between these two phases of operation. The variations of the voltage and the current applied to the magnetron are solely related to the behavior of the magnetron to a reflected energy which varies.

In an attempt to maintain the microwave power effectively emitted by the magnetron at the reference value, it is known to implement anodic current regulation: an anodic current / microwave power proportionality coefficient is predefined (this characteristic may be part of the data provided by the magnetron manufacturer); in operation, the value of the anode current is measured continuously and a proportional correction is applied to the anode current as a function of the load variations of the high voltage generator so as to keep the microwave power emitted by the magnetron as constant as possible relative to the setpoint power.

The regulation speed of the generator is chosen relatively slow (response time greater than 100 milliseconds), whereas the transition from the highly unsuitable load condition to the better adapted load condition is very short and can correspond approximately to a period of high voltage (for example of the order of 10 to 20 ms). As a result, mainly in the start-up phase, the imbalance mentioned above can extend over several pulses of the high voltage, with an imbalance of the power delivered by the high voltage generator for a substantially similar emitted microwave power.

In order to fix the ideas better, FIG. 1 of the appended drawings shows a graph characterizing the operation of a typical example of a magnetron and showing, as a function of time (in abscissae, expressed in seconds), the evolution ( solid line curve) of the high voltage across the magnetron (on the ordinate on the right scale, expressed in volts) and the evolution (dashed curve) concomitant of the anode current regulated under the aforementioned conditions (on the ordinate on the left scale, expressed in milliamperes).

It can be seen that, for the group of the first two cycles (on the left of the graph), the high voltage has a minimum value of -3.6 kV; the percentage of energy reflected by the poorly adapted charge (the plasma is not yet established) is high. For the group of subsequent cycles, the high voltage takes a value of -4 kV; the plasma is established and the charge is better adapted with a percentage of reflected energy which is less.

• impulsion PA : le courant anodique a une valeur de 360 mA ; le fabricant du magnétron donnant un coefficient de proportionnalité de 3 W micro-ondes/ mA, la puissance micro-ondes instantanée délivrée par le magnétron est 360 x 3, soit 1080 W ;
• impulsion PB : le courant anodique a une valeur de 305 mA ; la puissance micro-ondes instantanée délivrée par le magnétron est 305 x 3, soit 915 W.

The anode current regulation applied to the generator is not very fast, with a response time of the order of 40 ms. The peak instantaneous power of the PA pulses (belonging to the group of the first cycles) and PB (belonging to the group of the following cycles) is the following:

• pulse PA: the anode current has a value of 360 mA; the manufacturer of the magnetron giving a coefficient of proportionality of 3 W microwave / mA, the instantaneous microwave power delivered by the magnetron is 360 x 3, ie 1080 W;
• PB pulse: the anode current has a value of 305 mA; the instantaneous microwave power delivered by the magnetron is 305 x 3, or 915 W.

For the two pulses PA and PB designated in FIG. 1 as being the closest together during the change of operating mode, it can be considered that, in view of the relatively slow regulation of the generator, the internal operating parameters of the generator have not been modified. The deviation of the microwave power delivered by the magnetron, attributable to the variation in the adaptation of the magnetron-coupled load of which the mean microwave power emitted remains substantially similar in both cases, is about 15% and so is very important.

As a result, the operating conditions of the current devices, equipped with high-voltage generators with anodic current regulation for maintaining the microwave power emitted by the magnetron at a set value, are not optimal because the high voltage generator undergoes large and rapid variations in power.

The object of the invention is to propose improved means (method and device) which better meet the requirements of the practice, and which in particular make it possible to improve and optimize at lower cost the accuracy of the instantaneous microwave power emitted by the magnetron with respect to the instantaneous reference power in the context where a rapidly variable level of microwave energy is reflected towards the magnetron.

• déterminer au préalable et tenir en mémoire au moins une valeur du rendement électrique du magnétron ;
• on saisit une valeur de puissance micro-ondes moyenne de consigne ;
• on convertit cette valeur de puissance micro-ondes moyenne de consigne, pour constituer un signal de puissance instantanée de consigne à basse fréquence ;
• on échantillonne ce signal de puissance instantanée de consigne avec une fréquence élevée d'échantillonnage ;
• on mesure et on échantillonne les valeurs instantanées de courant anodique et de haute tension d'alimentation du magnétron ;
• on calcule le produit de la valeur instantanée du courant anodique à un instant d'échantillonnage par la valeur instantanée de la haute tension à cet instant d'échantillonnage et par la valeur préalablement déterminée du rendement électrique du magnétron pour obtenir la valeur de la puissance micro-ondes instantanée mesurée à cet instant d'échantillonnage;
• on compare cette valeur de puissance micro-ondes instantanée mesurée avec la valeur de puissance instantanée de consigne échantillonnée à un instant correspondant et on en déduit une valeur d'écart à cet instant d'échantillonnage;
• on détermine une valeur de puissance micro-ondes instantanée à l'instant d'échantillonnage immédiatement consécutif corrigée en fonction d'une loi de régulation prédéterminée valable audit instant d'échantillonnage immédiatement consécutif, de ladite valeur d'écart calculée à l'instant d'échantillonnage et de la valeur de la puissance instantanée de consigne échantillonnée audit instant d'échantillonnage immédiatement consécutif ; et
• on effectue une conversion puissance-grandeur électrique de commande pour obtenir un signal analogique de puissance micro-ondes instantanée corrigée propre à commander l'alimentation du magnétron.

For these purposes, according to a first of its aspects, the invention proposes a regulation method for regulating, as a function of a microwave power set point. instant, the power supply of a magnetron belonging to UHF electromagnetic wave generating means, which method according to the invention is characterized in that it comprises the steps of:

• to determine in advance and store in memory at least one value of the electrical efficiency of the magnetron;
• a mean microwave power value of setpoint is entered;
• this average microwave power value of reference is converted to form a low-frequency reference instantaneous power signal;
• this instantaneous reference power signal is sampled with a high sampling frequency;
• the instantaneous values of anode current and high magnetron supply voltage are sampled and sampled;
• the product of the instantaneous value of the anode current at a sampling instant is calculated by the instantaneous value of the high voltage at this sampling instant and by the previously determined value of the electrical efficiency of the magnetron to obtain the value of the micro power. instantaneous waves measured at this sampling time;
• this instantaneous measured microwave power value is compared with the instantaneous reference power value sampled at a corresponding instant and a deviation value is deduced at this sampling instant;
• an instantaneous microwave power value is determined at the immediately following sampling time corrected according to a predetermined regulation law valid at said sampling instant immediately following, said calculated difference value at the sampling instant and the value of the sampled instantaneous reference power at said immediately consecutive sampling instant; and
• a control electrical power-to-magnitude conversion is performed to obtain a corrected instantaneous microwave power analog signal suitable for controlling the power supply of the magnetron.

Thanks to the implementation of the arrangements according to the invention, it is possible to significantly reduce the difference in the instantaneous power of the high voltage generator for emitted microwave power remaining substantially similar.

• impulsion PA : pour un courant anodique de 360 mA, une haute tension de -3550 V et un rendement électrique moyen du magnétron (caractéristique prédéterminée fournie par le fabricant du magnétron ou relevée au préalable) de 73,7%, la puissance micro-ondes instantanée émise du magnétron est de 942 W;
• impulsion PB : pour un courant anodique de 305 mA, une haute tension de -4050 V et un rendement électrique moyen du magnétron de 73,7 %, la puissance micro-ondes instantanée émise du magnétron est de 910 W.

If we take again the numerical example quoted above relating to the pulses PA and PB, the results obtained by implementation of the process according to the invention are the following ones:

• pulse PA: for an anode current of 360 mA, a high voltage of -3550 V and an average electrical efficiency of the magnetron (predetermined characteristic provided by the manufacturer of the magnetron or raised beforehand) of 73.7%, the microwave power instant emitted from the magnetron is 942 W;
• PB pulse: for an anode current of 305 mA, a high voltage of -4050 V and a mean electrical efficiency of the magnetron of 73.7%, the instantaneous microwave power emitted from the magnetron is 910 W.

Thus, the difference in the instantaneous microwave power emitted by the magnetron between the two pulses PA and PB is only 3.4% for a near average transmitted microwave power. Setting The implementation of a regulation according to the invention makes it possible, in a simple manner and with an inexpensive implementation, to divide by four the disparity in operating power of the high voltage generator with respect to the simple regulation of the anode current implemented. until then.

In addition and very interestingly, the arrangements according to the invention are very advantageous because of the high speed of response thus obtained.

The arrangements according to the invention can give rise to various control variants.

In a particular embodiment of the method of the invention, a power-frequency conversion is performed to control resonant converter power supply means.

• le taux d'onde stationnaire étant relativement faible et inférieur à une valeur de seuil donnée, le rendement électrique du magnétron est supposé constant et la valeur mesurée par une détermination préalable et tenue en mémoire est la valeur du rendement électrique moyen du magnétron ;
• le taux d'onde stationnaire étant relativement élevé et supérieur à un seuil prédéterminé, on établit au préalable et on mémorise une correspondance entre les couples de valeurs mesurées du courant anodique instantané et de la tension instantanée appliqués au magnétron et les valeurs correspondantes du rendement électrique du magnétron, et, en fonctionnement, la puissance instantanée est déterminée à partir des valeurs mesurées du courant anodique instantané et de la tension instantanée appliquée au magnétron et à partir de la valeur du rendement électrique du magnétron tenue en mémoire en correspondance avec le couple des valeurs instantanées mesurées du courant anodique et de la tension.

Since the electrical efficiency of the magnetron varies considerably as a function of the standing wave ratio, it will be possible, for the determination of the instantaneous power delivered to the magnetron, to resort to one or the other of the following solutions depending on the conditions Operating :

• the stationary wave ratio being relatively low and less than a given threshold value, the electrical efficiency of the magnetron is assumed to be constant and the value measured by a preliminary determination and kept in memory is the value of the average electrical efficiency of the magnetron;
• the stationary wave ratio being relatively high and greater than a predetermined threshold, a correspondence between the measured value pairs of the instantaneous anode current and the instantaneous voltage applied to the magnetron and the corresponding values of the electrical efficiency of the magnetron, and, in operation, the instantaneous power is determined from the measured values of the instantaneous anode current and the instantaneous voltage applied to the magnetron and from the value of the electrical efficiency of the magnetron held in memory in correspondence with the pair of measured instantaneous values of the anode current and the voltage.

The process which has just been described can find an application that is particularly advantageous when the magnetron emits UHF electromagnetic waves into a vacuum cavity of substantially cylindrical shape adapted to receive at least one container of thermoplastic material on one side of which a coating of a barrier material is deposited using a low-pressure plasma by excitation of a precursor gas by said UHF electromagnetic waves.

• des moyens de mémorisation pour tenir en mémoire au moins une valeur préalablement déterminée du rendement électrique du magnétron, et
• un microcontrôleur comportant :
  • des moyens de saisie d'une valeur de puissance micro-ondes moyenne de consigne ;
  • une unité de conversion propre à convertir cette valeur de puissance micro-ondes moyenne de consigne en un signal de puissance instantanée de consigne à basse fréquence ;
  • une unité d'échantillonnage propre à échantillonner ce signal de puissance instantanée de consigne avec une fréquence élevée d'échantillonnage ;
  • des moyens de mesure et une unité d'échantillonnage propres à capter et à échantillonner les valeurs instantanées de courant anodique et de haute tension d'alimentation du magnétron ;
  • des moyens agencés pour calculer le produit de la valeur instantanée du courant anodique à un instant d'échantillonnage par la valeur instantanée de la haute tension à cet instant d'échantillonnage et par la valeur préalablement déterminée du rendement électrique du magnétron pour déterminer la valeur de la puissance micro-ondes instantanée mesurée à cet instant d'échantillonnage ;
  • d'un comparateur agencé pour comparer cette valeur de puissance micro-ondes instantanée mesurée avec la valeur de puissance instantanée de consigne échantillonnée à un instant correspondant et délivrer une valeur d'écart à cet instant d'échantillonnage ;
  • des moyens de détermination d'une valeur de puissance micro-ondes instantanée à l'instant d'échantillonnage immédiatement consécutif corrigée en fonction d'une loi de régulation prédéterminée valable audit instant d'échantillonnage immédiatement consécutif, de ladite valeur d'écart calculée à l'instant d'échantillonnage et de la valeur de puissance instantanée de consigne échantillonnée à l'instant d'échantillonnage immédiatement consécutif ; et
  • des moyens convertisseurs puissance-grandeur électrique de commande propres à effectuer une conversion entre la puissance et la grandeur électrique de commande de la valeur de puissance micro-ondes instantanée corrigée pour obtenir un signal analogique de puissance micro-ondes instantanée corrigée propre à la commande de l'alimentation du magnétron.

According to a second of its aspects, the invention proposes a regulation device for regulating, as a function of an instant microwave power setpoint, the power supply of a magnetron of a UHF electromagnetic wave generator, which The device, being suitable for carrying out the process described above and being arranged in accordance with the invention, is characterized in that the regulation means comprise:

• storage means for storing in memory at least one predetermined value of the electrical efficiency of the magnetron, and
• a microcontroller comprising:
  • means for entering a desired average microwave power value;
  • a conversion unit suitable for converting said set mean microwave power value into a low frequency reference instantaneous power signal;
  • a sampling unit capable of sampling this instantaneous reference power signal with a high sampling frequency;
  • measuring means and a sampling unit adapted to capture and sample the instantaneous values of anode current and high voltage supply of the magnetron;
  • means arranged to calculate the product of the instantaneous value of the anode current at a sampling instant by the instantaneous value of the high voltage at this sampling instant and by the previously determined value of the electrical efficiency of the magnetron to determine the value of the instantaneous microwave power measured at this time of sampling;
  • a comparator arranged to compare this measured instantaneous microwave power value with the sampled instantaneous power value sampled at a corresponding instant and output a deviation value at that sampling instant;
  • means for determining an instantaneous microwave power value at the immediately following sampling time corrected according to a predetermined regulation law valid at said immediately consecutive sampling instant, said deviation value calculated at the sampling instant and the instantaneous reference power value sampled at the immediately following sampling instant; and
  • electrical power-magnitude control converter means capable of converting between the power and the electrical control quantity of the corrected instantaneous microwave power value to obtain a corrected instantaneous microwave power analogue signal specific to the control of the power supply of the magnetron.

Such a device can be arranged to implement various control variants.

In a practical embodiment, the power supply means are of the resonance converter type whose resonant frequency is the electrical control quantity and the electric power-magnitude control converter means are power-frequency converter means.

In a simple embodiment that can be implemented when the standing wave ratio is relatively low and below a predetermined threshold (for example typically less than about 2), the electrical efficiency of the magnetron is a predetermined constant value held in memory. .

On the other hand, when the standing wave ratio is relatively high and greater than a predetermined threshold (for example typically greater than about 2), the device comprises storage means capable of holding in memory a correspondence between a plurality of pairs of values. the magnitude of the anode current of the magnetron and the voltage across the magnetron and the same plurality of respective values of the electrical efficiency of the magnetron.

In a preferred embodiment, the electrical power supply means of the magnetron anode comprise a switched-mode power supply. resonance incorporating a bridge of power switches controlled in pairs respectively by two control units and a resonance filter mounted in a diagonal of said jumper bridge and said power-frequency converter means have two phase-opposite outputs which are connected respectively to said two control units.

The control device which has just been exposed can be implemented in a particularly advantageous manner in an installation for depositing a coating on one side of at least one container of thermoplastic material using a low pressure plasma by exciting a precursor gas by UHF electromagnetic waves in a cylindrical vacuum cavity receiving said container, said apparatus comprising a UHF wave generator and a UHF waveguide for connecting said generator to a sidewall window of the cavity, said UHF wave generator comprising a magnetron having an anode, power supply means connected to said anode for supplying said anode with current under a high supply voltage and a regulating device for regulating, in function of an instant microwave power set point, the magnetron power supply; in particular, it may be a carousel type rotating installation equipped with a multiplicity of processing stations each provided with a magnetron with its regulated power supply in accordance with the invention.

• la figure 1 est un graphique caractérisant le fonctionnement d'un exemple typique de magnétron et montrant, en fonction du temps (en abscisses, exprimé en secondes), l'évolution (courbe en trait plein) de la haute tension aux bornes du magnétron (en ordonnées sur l'échelle de droite, exprimée en volts) et l'évolution (courbe en tirets) concomitante du courant anodique régulé dans les conditions précitées (en ordonnées sur l'échelle de gauche, exprimé en milliampères) ;
• la figure 2 est un schéma synoptique simplifié d'un mode de réalisation préféré d'un dispositif d'alimentation en haute tension d'un magnétron mettant en oeuvre les moyens conformes à l'invention ;
• la figure 3 est un schéma synoptique d'un exemple de réalisation d'un microcontrôleur mis en oeuvre dans le dispositif de la figure 2 ; et
• la figure 4 est un graphique résumant le mode de fonctionnement du dispositif des figures 2 et 3.

The invention will be better understood on reading the detailed description of certain preferred embodiments given as purely illustrative examples. In this description, reference is made to the accompanying drawings in which:

• FIG. 1 is a graph characterizing the operation of a typical example of a magnetron and showing, as a function of time (in abscissae, expressed in seconds), the evolution (solid line curve) of the high voltage across the magnetron ( on the ordinate on the scale on the right, expressed in volts) and the evolution (concave curve) concomitant of the anodic current regulated under the aforementioned conditions (in ordinates on the scale on the left, expressed in milliamperes);
• FIG. 2 is a simplified block diagram of a preferred embodiment of a high voltage power supply device of a magnetron implementing the means according to the invention;
• FIG. 3 is a block diagram of an exemplary embodiment of a microcontroller implemented in the device of FIG. 2; and
• FIG. 4 is a graph summarizing the operating mode of the device of FIGS. 2 and 3.

Reference is now made first to FIG. 2, on which is shown a simplified block diagram of a preferred embodiment according to the invention of a high voltage power supply device of a magnetron designated M to from a power source which, in practice, may be a general AC power supply network, typically a three-phase network under 400 V, designated S.

The device is, in general, an AC-type power supply. For this purpose, the device comprises, at the input, a stage 1 for rectifying and filtering the alternating voltage, which delivers a rectified and smoothed voltage which is applied static power supply means 2, which may have any suitable constitution, in order to generate an alternating voltage.

In practice, it may be preferable to use resonant-type generator power supply means 2 which comprises, as illustrated, a set of four switches Q1 to Q4 (typically fast switching transistors) mounted in bridge and two control units 3 and 4 for controlling each a pair of switches respectively Q1, Q3 and Q2, Q4. A resonance filter 5 is mounted in the diagonal of the bridge between Q1, Q3 on one side and Q2, Q4 on the other side.

This resonant filter 5, located in the current branch of the converter, is constituted by a combination of inductances and capacitors whose values are chosen so as to obtain an optimum resonant frequency with an appropriate overvoltage coefficient (or quality). . The operation of this feed is known to those skilled in the art and will be briefly recalled below.

The resonance filter modulates the amplitude of the input signal. The value of this amplitude variation is a function of the characteristics of the elements composing the filter and the frequency of the signal. It also modifies the phase difference existing between the voltage and the current. The amplitude is maximum when the signal frequency corresponds to the resonant frequency of the filter. It is attenuated according to the difference between the resonance frequency and the actual signal frequency.

At the output of the resonance filter, the alternating voltage is collected in an amplifier unit 6. very high frequency which is then amplified in amplitude in said amplifier unit 6. After recovery and smoothing in an output unit 7, located downstream of the amplifying unit 6, the UHF power signal is applied to the magnetron anode M.

The control loop may comprise, at the output of the output unit 7, intensity measuring means 8 and voltage measuring means 9, constituted by sensors, known per se, which respectively detect the intensity instantaneous anodic current Ib and the instantaneous value Ebm of the high voltage which are delivered on the anode of the magnetron M.

With regard to the measurements of the anode current and the voltage delivered to the magnetron, it should be emphasized that these measurements can be made as close as possible to the magnetron, as has just been described, so as to measure the exact power supply values. magnetron. But it is also possible that these measurements are made at other points of the circuit, distant from the magnetron; a proportional relationship is then established by prior measurements between the measured value at the far point and the actual value measured on the magnetron, and in operation the measured value is exploited at a remote point corrected by the predetermined proportionality relation. .

The means 8, 9 for measuring the intensity and the high voltage are connected to two respective inputs of a microcontroller 10, for example of the DSP (Digital Signal Processor) type, of which two out of phase outputs are respectively connected to the control inputs of control units 3 and 4 of switches Q1 to Q4. The microcontroller 10 processes the values of anode current Ib and high voltage Ebm and manages the power regulation by acting on the control units 3, 4 which drive the power switches Q1 to Q4 in high frequency, in particular by implementing a pulse width modulation technique.

Microcontroller 10 is also applied, by a device 19 of human-machine interface, information Pmoy of set power (average microwave power) given by the operator and from which is established the instantaneous power microwaves desired for the operation of the device.

Finally, storage means 20, connected to the microcontroller 10, store in memory at least one value of the electrical efficiency n of the magnetron M which has been predetermined.

• Puissance instantanée mesurée = Ib x Ebm x rendement électrique du magnétron
• puis calcule la différence entre la puissance instantanée micro-ondes de consigne et la puissance instantanée mesurée.

The microcontroller 10 calculates the instantaneous power measured from the measurements of the instantaneous values of the anode current Ib and the high voltage Ebm:

• Measured instantaneous power = Ib x Ebm x electrical efficiency of the magnetron
• then calculates the difference between the instantaneous reference microwave power and the measured instantaneous power.

• de la consigne de puissance micro-ondes instantanée,
• de la différence calculée (et éventuellement en tenant compte de la différence déterminée lors d'au moins une mesure précédente), et
• d'une loi de régulation prédéterminée préalablement établie et/ou sélectionnée pour l'obtention de la régulation souhaitée (cette loi de régulation pouvant être de tout type approprié, par exemple du type PID) et entrée dans le microcontrôleur,

le microcontrôleur 10 émet un signal de contrôle des unités 3, 4 de commande des interrupteurs Q1 à Q4.Then, from

• the instant microwave power setpoint,
• the calculated difference (and possibly taking into account the difference determined in at least one previous measurement), and
• a predetermined regulation law previously established and / or selected to obtain the desired regulation (this regulation law can be of any suitable type, for example of the PID type) and input into the microcontroller,

the microcontroller 10 emits a control signal from the control units 3, 4 of the switches Q1 to Q4.

• impulsion PA : pour un courant anodique de 360 mA, une haute tension de -3550 V et un rendement électrique moyen du magnétron (caractéristique prédéterminée fournie par le fabricant du magnétron ou relevée au préalable) de 73,7%, la puissance micro-ondes instantanée du magnétron est de 942 W ;
• impulsion PB : pour un courant anodique de 305 mA, une haute tension de -4050 V et un rendement électrique moyen du magnétron de 73,7%, la puissance micro-ondes instantanée du magnétron est de 910 W.

If we take again the numerical example quoted above relating to the pulses PA and PB, the results obtained by implementation of the provisions of the invention are the following ones:

• pulse PA: for an anode current of 360 mA, a high voltage of -3550 V and an average electrical efficiency of the magnetron (predetermined characteristic provided by the manufacturer of the magnetron or raised beforehand) of 73.7%, the microwave power instant magnetron is 942 W;
• PB pulse: for an anode current of 305 mA, a high voltage of -4050 V and a mean electrical efficiency of the magnetron of 73.7%, the instantaneous microwave power of the magnetron is 910 W.

The difference in magnetron power between the two pulses PA and PB is only 3.4% for a near average transmitted microwave power. The magnetron thus operates in conditions of regularity much better than in the current devices.

FIG. 3 illustrates an advantageous concrete example of embodiment of the microcontroller 10.

The average power Pmoy setpoint that is entered by the operator by means of the device 19 man-machine interface is processed by a conversion unit 11 which converts it into a nominal instantaneous power signal having a low frequency that can be typically of the order of 100 Hz. The instantaneous reference power signal is then digitized in a sampling unit 12. The sampling frequency can typically be of the order of 20 kHz, which leads to about 200 measurement points on a period T of the instantaneous reference power signal.

The sampling unit 12 is provided with two outputs delivering the sampling values at two consecutive sampling points n and n + 1 respectively.

The output receiving the value Pinst_c at the sampling point n is connected to an input (for example the + input) of a comparator 13, such as an algebraic comparator. The other input (input -) of the algebraic comparator 13 receives the signal of a control loop which is constituted as follows.

The measured instantaneous high-voltage signals Ebm_m and measured instantaneous anode current Ib_m are respectively detected by the two aforementioned measurement means 9 and 8 at the terminals of the magnetron M, and are then sent to a sampling unit 16 for these two signals. The corresponding sampled data respectively Ebm and Ib are applied to first means 17 multipliers providing instantaneous electrical power measured Pect_m = Ebm x Ib, in other words the electrical power actually delivered to the magnetron.

This quantity is in turn applied to an input of second multiplier means 18, of which another input receives the output information of the magnetron M. The output signal of the second multiplier means 18 represents the measured instantaneous microwave power Pinst_m, otherwise says the power effectively transformed into microwave power by the magnetron. From the instantaneous microwave power measured Pinst_m, the average microwave power is calculated using means 21 integrators. measured that is presented to the operator (human-machine interface device 19) to allow a visual comparison with the average microwave power setpoint.

It is this instantaneous microwave power signal measured Pinst_m which is applied to the other input (here the negative input) of the aforementioned comparator 13.

The output of the comparator 13, on which appears the value of the difference ε between the instantaneous microwaves of reference and measured, is connected to an input of an instantaneous power correction unit 14, with limitation to limit values. predetermined, which has a main input connected to the other output of the sampling unit 12 which delivers the value Pinst_c to the point n + 1. The correction unit 14 algebraically corrects the value Pinst_c at the point n + 1 with the value of the difference ε calculated at the sampling instant at the point n, as a function of the value of the instantaneous reference power sampled at said instant immediately following sampling, at the point n + 1, and the predetermined regulation law valid at said sampling time at the point n + 1.

The output of the correction unit 14 is connected to a control electric power / quantity conversion unit 15 (the control electrical quantity is the frequency in the example considered of a resonance converter generator) which is suitable for processing an approximately linear variation portion, defined between limit values of frequency F_max and F_min, of the power curve as a function of the frequency centered on a value Fr: Po = f (Fr, F_min, F_max). Finally, the control power / electrical quantity conversion unit 15 delivers a signal of frequency as a function of time, limited to F_min and F_max values.

Finally, it is this output signal of the electrical power / control quantity conversion unit 15 which is sent to the power supply means 2, amplifier unit 6, output unit 7, previously described, which is connected to the magnetron M.

• on détermine au préalable et on tient en mémoire dans les moyens 20 de mémorisation au moins une valeur η du rendement électrique du magnétron M,
• on saisit en 19 une valeur de puissance micro-ondes moyenne de consigne Pmoy ;
• on convertit en 11 cette valeur de puissance micro-ondes moyenne de consigne, pour constituer un signal de puissance instantanée de consigne à basse fréquence;
• on échantillonne dans l'unité 12 d'échantillonnage ce signal de puissance instantanée de consigne avec une fréquence élevée d'échantillonnage ;
• on mesure grâce aux moyens 8, 9 de mesure et on échantillonne grâce aux moyens 16 d'échantillonnage les valeurs instantanées de courant anodique et de haute tension d'alimentation du magnétron,
• on calcule grâce aux moyens 17, 18 le produit de la valeur instantanée du courant anodique à un instant d'échantillonnage n par la valeur instantanée de la haute tension à cet instant d'échantillonnage n et par la valeur préalablement déterminée du rendement électrique du magnétron pour obtenir la valeur de la puissance micro-ondes instantanée mesurée à cet instant d'échantillonnage n;
• on compare dans le comparateur 13 cette valeur de puissance micro-ondes instantanée mesurée avec la valeur de puissance instantanée de consigne échantillonnée à un instant n correspondant et on en déduit une valeur d'écart ε à cet instant d'échantillonnage n ;
• on détermine une valeur de puissance micro-ondes instantanée à l'instant d'échantillonnage immédiatement consécutif n+1 corrigée en fonction de la loi de régulation prédéterminée valable audit instant d'échantillonnage immédiatement consécutif n+1, de ladite valeur d'écart calculée à l'instant d'échantillonnage n et de la valeur de la puissance instantanée de consigne échantillonnée audit instant d'échantillonnage immédiatement consécutif n+1 ; et
• on effectue par les moyens 15 une conversion puissance-grandeur électrique de commande pour obtenir un signal analogique de puissance micro-ondes instantanée corrigée propre à commander l'alimentation du magnétron.

In summary, the control method for regulating, as a function of an instantaneous microwave power setpoint, the power supply of the magnetron M comprises the following steps:

• the at least one value η of the electrical efficiency of the magnetron M is previously determined and stored in the storage means 20,
• a value of average microwave power Pmoy is entered at 19;
• this setpoint mean microwave power value is converted to 11 in order to constitute a low frequency reference instantaneous power signal;
• sampling is sampled in the sampling unit 12 this instantaneous reference power signal with a high sampling frequency;
• the measuring means 8, 9 measure and sample, using the sampling means 16, the instantaneous values of the anode current and the high magnetron supply voltage,
• the product of the instantaneous value of the anode current at a sampling instant n is calculated by means of the instantaneous value of the high voltage at this sampling instant n and by the previously determined value of the electrical efficiency of the magnetron by means 17, 18 to get the value of the instantaneous microwave power measured at this sampling instant n;
• the measured instantaneous microwave power value is compared in the comparator 13 with the sampled instantaneous power value sampled at a corresponding instant n and a difference value ε is deduced at this sampling instant n;
• an instantaneous microwave power value is determined at the immediately following sampling time n + 1 corrected according to the predetermined regulation law valid at said immediately consecutive sampling time n + 1, of said calculated difference value at the sampling time n and the value of the sampled instantaneous reference power at said immediately consecutive sampling time n + 1; and
• by the means 15 is carried out an electrical power-magnitude control conversion to obtain a corrected instantaneous microwave power analog signal suitable for controlling the power supply of the magnetron.

• des moyens 20 de mémorisation pour tenir en mémoire au moins une valeur préalablement déterminée du rendement électrique η du magnétron M, et
• un microcontrôleur 10 comportant :
  • des moyens 19 de saisie d'une valeur de puissance micro-ondes moyenne de consigne Pmoy ;
  • une unité 11 de conversion propre à convertir cette valeur de puissance micro-ondes moyenne de consigne en un signal de puissance instantanée de consigne à basse fréquence ;
  • une unité 12 d'échantillonnage propre à échantillonner ce signal de puissance instantanée de consigne avec une fréquence élevée d'échantillonnage ;
  • des moyens 8, 9 de mesure et une unité 16 d'échantillonnage propres à capter et à échantillonner les valeurs instantanées de courant anodique et de haute tension d'alimentation du magnétron ;
  • des moyens 17, 18 agencés pour calculer le produit de la valeur instantanée du courant anodique à un instant d'échantillonnage n par la valeur instantanée de la haute tension à cet instant d'échantillonnage n et par la valeur préalablement déterminée du rendement électrique du magnétron pour déterminer la valeur de la puissance micro-ondes instantanée mesurée à cet instant d'échantillonnage n ;
  • d'un comparateur 13 agencé pour comparer cette valeur de puissance micro-ondes instantanée mesurée avec la valeur de puissance instantanée de consigne échantillonnée à un instant n correspondant et délivrer une valeur d'écart ε à cet instant d'échantillonnage n;
  • des moyens de détermination d'une valeur de puissance micro-ondes instantanée à l'instant d'échantillonnage immédiatement consécutif n+1 corrigée en fonction de la loi de régulation prédéterminée valable audit instant d'échantillonnage immédiatement consécutif n+1, de ladite valeur d'écart calculée à l'instant d'échantillonnage n et de la valeur de puissance instantanée de consigne échantillonnée à l'instant d'échantillonnage immédiatement consécutif n+1 ; et
  • des moyens 15 convertisseurs puissance-grandeur électrique de commande propres à effectuer une conversion entre la puissance et la grandeur électrique de commande de la valeur de puissance micro-ondes instantanée corrigée pour obtenir un signal analogique de puissance micro-ondes instantanée corrigée propre à la commande de l'alimentation du magnétron.

The above method can be implemented thanks to the regulation device for regulating, as a function of an instantaneous microwave power setpoint, the power supply of the magnetron M, a device in which the regulation means comprise:

• storage means 20 for storing in memory at least one previously determined value of the electrical efficiency η of the magnetron M, and
• a microcontroller 10 comprising:
  • means 19 for entering an average microwave power value Pmoy setpoint;
  • a conversion unit 11 suitable for converting said set mean microwave power value into a low frequency reference instantaneous power signal;
  • a sampling unit 12 capable of sampling this instantaneous reference power signal with a high sampling frequency;
  • measurement means 8, 9 and a sampling unit 16 adapted to capture and sample the instantaneous values of anode current and magnetron high supply voltage;
  • means 17, 18 arranged to calculate the product of the instantaneous value of the anode current at a sampling instant n by the instantaneous value of the high voltage at this sampling instant n and by the previously determined value of the electrical efficiency of the magnetron to determine the instantaneous microwave power value measured at this sampling instant n;
  • a comparator 13 arranged to compare this measured instantaneous microwave power value with the sampled instantaneous power value sampled at a corresponding instant n and to output a difference value ε at this sampling instant n;
  • means for determining an instantaneous microwave power value at the immediately consecutive sampling time n + 1 corrected according to the predetermined regulation law valid at said immediately consecutive sampling time n + 1, of said value deviation calculated at the sampling instant n and the instantaneous reference power value sampled at the immediately consecutive sampling time n + 1; and
  • electric power-magnitude control converter means capable of converting between the power and the electrical control quantity of the corrected instantaneous microwave power value to obtain a corrected instantaneous microwave power analogue signal specific to the control of the magnetron power supply.

Thus, the magnetron M is supplied with a power regulated according to the power setpoint given by the user.

In the case where a generator of a different type is used than a generator with a resonance converter and in which it is another electrical quantity that the frequency is controlled (for example the intensity or the phase ) to carry out the control, a power-to-control electrical power conversion is performed. The power delivered to the magnetron is thus regulated according to a power instruction given by the user.

1. (a) Pmoya (en pratique il s'agit de la valeur de consigne affichée pour la conduite du processus) s'exprime en fonction de la puissance instantanée de consigne en (b), P_b(t), de la façon suivante : $$\mathrm{Pmoya}\mathrm{=}\frac{\mathrm{1}}{T}{\displaystyle {\mathrm{\int }}_{\mathrm{0}}^T}{\mathrm{P}}_{\mathrm{b}}\left(\mathrm{t}\right)\mathrm{.}\mathrm{d}\mathrm{t}$$
   
   tandis que la puissance micro-ondes moyenne mesurée en (g), Pmoyg s'exprime en fonction de la puissance micro-ondes instantanée régulée en (f), P_f(t), de la façon suivante : $$\mathrm{Pmoyg}\mathrm{=}\frac{\mathrm{1}}{T}{\displaystyle {\mathrm{\int }}_{\mathrm{0}}^T}{\mathrm{P}}_{\mathrm{f}}\left(\mathrm{t}\right)\mathrm{.}\mathrm{d}\mathrm{t}$$
   

In FIG. 4, and with reference to FIG. 3, are represented two graphs which summarize the operation of the device arranged according to the invention: on the graph A (instantaneous power as abscissa as a function of time on the ordinates) the instantaneous power of the setpoint shown in (b) (output signal of the conversion unit 11 in FIG. 3) and the regulated instantaneous microwave power measured in (f); in the graph B (average power as abscissa versus time on the ordinate), the average microwave power setpoint shown in (a) (input signal of the conversion unit 11 in FIG. 3) and the power measured average microwave shown in (g). Mathematically, the average microwave power setpoint in

1. (a) Pmoya (in practice this is the set value displayed for the process control) is expressed as a function of the instantaneous reference power in (b), P _b (t), as follows: $$\mathrm{Pmoya}\mathrm{=}\frac{\mathrm{1}}{T}{\displaystyle {\mathrm{\int }}_{\mathrm{0}}^T}{\mathrm{P}}_{\mathrm{b}}\left(\mathrm{t}\right)\mathrm{.}\mathrm{d}\mathrm{t}$$
   
   while the average microwave power measured in (g), Pmoyg is expressed as a function of the instantaneous microwaves power regulated in (f), P _f (t), as follows: $$\mathrm{Pmoyg}\mathrm{=}\frac{\mathrm{1}}{T}{\displaystyle {\mathrm{\int }}_{\mathrm{0}}^T}{\mathrm{P}}_{\mathrm{f}}\left(\mathrm{t}\right)\mathrm{.}\mathrm{d}\mathrm{t}$$
   

It is perfectly visible that the difference between the two curves of reference power and effective power is very small.

In order for the implementation of the process according to the invention to lead to as precise a regulation as possible, it is necessary that the used value of the electrical efficiency of the magnetron be as accurate as possible. This value can vary considerably depending on the operating conditions of the magnetron.

When the stationary wave ratio (TOS) is relatively low (typically less than about 2), there is almost no energy reflected by the charge and almost all of the microwave energy is absorbed. by the charge. In this case, the electrical efficiency of the magnetron can be considered as substantially constant, and its value is determined by prior measurements. It is this value that is exploited and entering the second means 18 multipliers aforementioned.

• d'abord mesure du courant anodique instantané et de la tension instantanée appliquée au magnétron, et détermination (par exemple recherche dans la table ou mise en oeuvre de l'équation de modélisation) par le microcontrôleur de la valeur du rendement électrique du magnétron qui correspond au couple des valeurs mesurées,
• puis détermination de la puissance instantanée à partir du couple des valeurs mesurées et de la valeur correspondante déterminée pour le rendement électrique du magnétron.

On the other hand, if the TOS is relatively high (typically greater than about 2), the microwave energy reflected by the load towards the power supply means 2 is relatively high and the electrical efficiency of the magnetron decreases appreciably. More precisely, the electrical efficiency of the magnetron is related to two quantities that are characteristic of the operating conditions, namely the level of microwave energy required and the TOS. The search for as precise a regulation as possible then requires to use, for the optimal implementation of the method of the invention, a value of the electrical efficiency of the magnetron which is not more constant, but adapted to the instantaneous operating conditions. . Under these conditions, by preliminary tests, an approximate value of the average electrical efficiency of the magnetron is determined for torques of values of instantaneous supply voltage of the magnetron and of intensity of the anode current consumed by the magnetron (or of instantaneous power consumed by the magnetron). It is then possible to establish a table of efficiency values or a modeling equation that is stored in the microcontroller 10. In operation, during regulation, the microcontroller calculates in two stages the instantaneous power emitted:

• firstly, measuring the instantaneous anode current and the instantaneous voltage applied to the magnetron, and determining (for example searching the table or implementing the modeling equation) by the microcontroller the value of the electrical efficiency of the magnetron; magnetron corresponding to the pair of measured values,
• then determining the instantaneous power from the pair of measured values and the corresponding value determined for the electrical efficiency of the magnetron.

The advantage of the proposed solution lies in its very great simplicity and its great economy of implementation which does not use any sensor or additional calculation means; since the microcontroller is already required for the operation of the installation in which the magnetron is included with its regulated power supply and the measurements of the instantaneous anode current and the instantaneous voltage applied to the magnetron being necessary elsewhere, the only specific requirement lies in the predetermination of a table or a modeling equation giving the various values of the electrical efficiency of the magnetron as a function of the instantaneous current-current value couples, which, given the performance of current electronic equipment, does not constitute a penalizing constraint .

The arrangements according to the invention can find a very interesting application in an installation for depositing a coating on one side of at least one container of thermoplastic material using a low-pressure plasma by excitation of a precursor gas. by UHF electromagnetic waves in a cylindrical vacuum cavity receiving said container, said installation comprising a UHF wave generator and a UHF waveguide for connecting said generator to a window of the cavity side wall, said generator of UHF waves comprising a magnetron M having an anode, power supply means 2 connected to said anode for supplying it with current under a high supply voltage and a regulating device for regulating, according to a microwave power set point In practice, it may advantageously be a rotating carousel-type installation equipped with a multiplicity of container treatment stations, each of which includes a magnetron with its regulated power supply.

Claims (11)

A regulation method for regulating, according to an instant microwave power setpoint, the power supply of a magnetron (M) belonging to UHF electromagnetic wave generating means,
characterized in that it comprises the steps of: - Beforehand determine and store (at 20) at least one value (η) of the electrical efficiency of the magnetron (M); - We enter (in 19) a value of average microwave power setpoint (Pmoy); this average microwave power value is converted (to 11) to form a low frequency reference instantaneous power signal; this instantaneous reference power signal is sampled (at 12) with a high sampling frequency; measuring (at 8, 9) and sampling (at 16) the instantaneous values of anode current and high supply voltage of the magnetron; the product of the instantaneous value of the anode current at a sampling instant (n) is calculated by the instantaneous value of the high voltage at this sampling instant (n) and by the value previously determined. the electrical efficiency (η) of the magnetron to obtain the value of the instantaneous microwave power measured at this sampling instant (n); this measured instantaneous microwave power value is compared (at 13) with the instantaneous reference power value sampled at a time (n) corresponding and we deduce a difference value (ε) at this sampling time (n); an instantaneous microwave power value is determined at the immediately following sampling time (n + 1) corrected according to a predetermined regulation law valid at said immediately following sampling time (n + 1), said calculated deviation value at the sampling instant (n) and the value of the sampled instantaneous reference power at said immediately consecutive sampling time (n + 1); and - Performing (in 15) a power-to-control electrical magnitude conversion to obtain a corrected instantaneous microwave power analog signal adapted to control the power supply of the magnetron. Method according to Claim 1, characterized in that a power-to-frequency conversion is carried out to control resonant converter power supply means (2). Method according to Claim 1 or 2, characterized in that , since the standing wave ratio is relatively low and less than a given threshold value, the electrical efficiency of the magnetron is assumed to be constant and the value measured by prior determination and maintained memory (at 20) is the value of the average electrical efficiency of the magnetron. Method according to Claim 1 or 2, characterized in that , since the standing wave ratio is relatively high and greater than a predetermined threshold, a correspondence between the measured value pairs of the instantaneous anode current and the instantaneous voltage applied to magnetron and the corresponding values of the electrical efficiency of the magnetron and that in operation the instantaneous power is determined from the measured values of the instantaneous anode current and the instantaneous voltage applied to the magnetron and from the value of the electrical efficiency of the magnetron held in memory (at 20) in correspondence with the measured instantaneous value couple of the anode current and the voltage. Process according to any one of Claims 1 to 4, characterized in that the magnetron (M) emits UHF electromagnetic waves in a substantially cylindrical vacuum cavity capable of accommodating at least one container of thermoplastic material on one face of which a coating of a barrier material is deposited using a low pressure plasma by excitation of a precursor gas by said UHF electromagnetic waves. Control device for regulating, according to an instantaneous microwave power setpoint, the power supply of a magnetron (M) of a UHF electromagnetic wave generator, for carrying out the method according to any one of the preceding claims,
characterized in that the regulating means comprises: storage means (20) for storing at least one previously determined value of the electrical efficiency (η) of the magnetron (M), and a microcontroller (10) comprising: means (19) for entering a desired average microwave power value (Pmoy); a conversion unit (11) capable of converting said set mean microwave power value into a low frequency reference instantaneous power signal; a sampling unit (12) capable of sampling this instantaneous reference power signal with a high sampling frequency; measuring means (8, 9) and a sampling unit (16) capable of sensing and sampling the instantaneous values of the anode current and the high magnetron supply voltage; means (17, 18) arranged to calculate the product of the instantaneous value of the anode current at a sampling instant (n) by the instantaneous value of the high voltage at this sampling instant (n) and by the value previously determined the electrical efficiency (η) of the magnetron to determine the value of the instantaneous microwave power measured at this sampling instant (n); a comparator (13) arranged to compare this measured instantaneous microwave power value with the instantaneous reference power value sampled at a corresponding instant (n) and to output a difference value (ε) at this instant of sampling (n); means for determining an instantaneous microwave power value at the immediately consecutive sampling time (n + 1) corrected according to a predetermined regulation law valid at said immediately consecutive sampling instant (n + 1), said deviation value calculated at the sampling instant (n) and the power value instantaneous setpoint sampled at the immediately following sampling time (n + 1); and means (15) electrical power-magnitude control converter capable of converting the power and the electrical control quantity of the corrected instantaneous microwave power value to obtain a corrected instantaneous microwave power analog signal; to the control of the power supply of the magnetron. Device according to Claim 6, characterized in that the power supply means (2) are of the resonance converter type whose resonant frequency is the control electrical quantity and the electric power-magnitude control converter means are means power-frequency converters. Device according to Claim 6 or 7, characterized in that , since the standing wave ratio is relatively low and less than a given threshold value and the electrical efficiency of the magnetron is assumed to be constant, the storage means (20) are suitable for keep in memory a previously determined value of the average electrical efficiency of the magnetron. Device according to Claim 6 or 7, characterized in that the standing wave ratio is relatively high and higher than a predetermined threshold and a plurality of values of the electrical efficiency of the magnetron being determined in correspondence with an identical plurality of pairs of values. respective measured instantaneous current and instantaneous voltage applied to the magnetron, the storage means (20) are adapted to hold in memory said plurality of values of the electrical efficiency of the magnetron in correspondence with said identical plurality of respective measured value pairs of the instantaneous anode current and the instantaneous voltage applied to the magnetron. Device according to any one of claims 6 to 9, characterized in that the means (2) for power supply of the magnetron anode (M) comprise a resonance switching power supply incorporating a switch bridge (Q1 -Q4) controlled by pairs respectively by two control units (3, 4) and a resonance filter (5) mounted in a diagonal of said switch bridge and in that the said means (15) power-frequency converters have two anti-phase outputs which are respectively connected to said two control units (3, 4). Installation for depositing a coating on one side of at least one container of thermoplastic material using a low-pressure plasma by excitation of a precursor gas by UHF electromagnetic waves in a vacuum cavity of cylindrical shape receiving said container, said apparatus comprising a UHF wave generator and a UHF waveguide for connecting said generator to a window of the cavity side wall, said UHF wave generator comprising a magnetron (M) having an anode, power supply means (2) connected to said anode for supplying power to said anode under a high supply voltage and a regulating device for regulating, according to an instantaneous microwave power setpoint, the power supply electric magnetron (M), characterized in that the regulating device is arranged according to any one of claims 6 to 10.

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