WO2010029241A1

WO2010029241A1 - Temperature measurement in a heat welding system

Info

Publication number: WO2010029241A1
Application number: PCT/FR2009/051608
Authority: WO
Inventors: Jacques Lecourt; Jean Pierre Sozanski; Jean Marc Gourlet; Jacques Baron
Original assignee: Etablissements Bernhardt Et Cie
Priority date: 2008-09-09
Filing date: 2009-08-20
Publication date: 2010-03-18
Also published as: FR2935632A1

Abstract

The invention relates to a method for measuring the temperature (T) of a heating element used in a heat welding system (200) during a welding cycle, wherein said method comprises: a preliminary calibration step that consists of measuring the initial temperature (T0) in absolute value of said heating element; a step of applying a voltage in order to modify the temperature of said heating element; at least one step of measuring an electric variable G(ΔT) based on the temperature variation (ΔT) of said heating element; and a step of determining the temperature T (ΔT, T0) of the heating element from the measured value of the variable G(ΔT) and the initial temperature (T0).

Description

MEASURING TEMPERATURE IN A HEATING WELDING SYSTEM

BACKGROUND OF THE INVENTION The invention is in the field of thermoplastic welding or "heat sealing", used in particular in the packaging industry.

In the context of the invention, the materials to be welded relate to plastics which melt, or at least soften under the effect of heat.

These materials can also be rigid parts or monolayer (polyethylene, polypropylene, etc.) or multilayer films, which have the same properties as plastics when subjected to high temperatures. In known manner, thermoplastic welding techniques mainly comprise a three-phase welding cycle: (1) a temperature rise phase up to a determined welding temperature which makes it possible to obtain the softening of the two materials, which is (2) simultaneously followed by an assembly phase at this temperature by exerting a certain pressure on the two materials by the bars of the welding system; then (3) a cooling phase which makes it possible to obtain the solidification of the two assembled materials.

More generally, two welding techniques are distinguished: constant-power heat-sealing and constant-temperature heat-sealing.

Constant-power heat-sealing, the principle of which is based on the "all or nothing" principle, essentially consists in energizing a resistor to create a heat pulse for a certain period of time. This powering up of the electrode makes it possible to obtain the fusion and the assembly of the two materials.

In contrast, constant-temperature heat-sealing ensures the softening of both materials, as its name suggests, by maintaining a constant temperature resistance. The principle of its operation is based on the measurement of the temperature of the electrode: The power is delivered according to the measured temperature.

Then, whatever the welding technique used (at constant power or at constant temperature), a clamping pressure of the bars on the two materials is exerted for a given time at a given temperature to assemble the two materials.

The solidification of the materials thus assembled is obtained by cooling means, such as the weight of the bar or a water or air cooling system, which are well known to those skilled in the art. In an industrial environment such as packaging, the constant power welding is required for reasons of technical simplicity: the use of a simple electromechanical relay is sufficient for the implementation of this technique.

However, although a minimum of technical equipment suffices for constant power welding, this technique consumes energy throughout the soldering period.

Constant temperature welding therefore has the advantage of reducing consumption in kilowatts by consuming energy only during the welding phases. However, in this context, it is crucial at all times to be able to control and regulate the temperature of the electrode which is applied to the materials to be welded during a welding cycle, both in the temperature rise phase and in the cooling phase.

Since the welding temperature is often close to a temperature of more than 150 ^° C., a temperature probe can not be in direct contact with the electrode or the materials to be welded.

This control of the temperature measurement by a probe directly or near the materials to be welded is very difficult to implement. This measurement is all the more difficult as the electrode of the welding system which allows the variation of temperature is often isolated from the bar of the welding system.

This electrode can also be protected from the material to be welded by a Teflon® type non-stick protective layer, which often relies on an additional lining of the glass fiber type or heat-resistant film at high temperature. Furthermore, the response times of the probe are too slow for industrial processes: the duration of the rise in temperature is of the order of 0.5 to 3 seconds while the duration of the cooling is substantially equal to 1.5 times the rise time, which is not satisfactory for a good control of the weld.

Finally, after a certain time, there is a strong dissipation of the temperature at the bar and the materials to be welded.

Thus, when a voltage is passed for 1 to 2 seconds in a resistor to vary the temperature of 30 to 150 ⁰ C, the temperature probe can not accurately inform the temperature level of the resistance, and therefore the soldering material; the probe being able to indicate only the temperature of the support or of the bar, and not that of the electrode or the material to be welded.

In any case, it is necessary to be able to estimate the welding temperature by other more precise techniques.

Document WO 97/18504 describes, for a welding process adapted to the packaging industry, a method and an analog type of control system (integrator circuit) of a heating element from a voltage measured at terminals of the electrode. More specifically, the document describes a DC welding process in which, between each pulse of the supply current, it is possible to pass a measurement current to obtain the voltage across the electrode.

Then, a regulator will compare the measured voltage with a regulation setpoint corresponding to a reference voltage which is a function of a target temperature variation. The regulator will thus be able to modulate the pulses of the supply current to reach and maintain this target temperature variation.

The method and the system according to this document allow only the estimation of a relative temperature, that is to say the estimate of a variation of temperature.

In addition, the adjustment of the regulation setpoint depends closely on certain physical parameters specific to the resistance of the electrode (length, thickness, type, etc.). The setting of the regulation setpoint must therefore be adapted to each electrode change since the new electrode presents new characteristics (dimensional dispersion of the electrode, etc.), which involves manipulations between each electrode change.

It is also possible to mention DE 38 02 995 which discloses a welding method adapted for controlling the temperature of a heating wire.

More particularly, in the welding method according to the present document DE 38 02 995, the temperature T of the heating wire is determined by measuring during the welding the resistance R of the wire according to the formula:

R = R _k (l + αT) where Rk is the resistance of the heating element at room temperature, and α is the temperature coefficient of the resistance.

Summary and object of the invention

The object of the invention attempts to overcome the aforementioned drawbacks.

For this purpose, the subject of the invention relates to a method for measuring the temperature T of a heating element; such a measuring method that can be used in a heating welding system during a welding cycle.

The measuring method according to the present invention comprises a step of energizing in order to vary the temperature of said heating element, and at least one step of measuring an electrical quantity G (ΔT), a function of the temperature variation ΔT of said heating element.

Said measurement method further comprises, prior to the power-up step, a calibration step of measuring the initial temperature TO in absolute value of said heating element.

Following the step of measuring the electrical quantity G (ΔT), the method comprises a step of determining the temperature T (ΔT,

TO) in absolute value of the heating element from the measured value of the magnitude G (ΔT) and the initial temperature TO.

Associate with the law of variation of the temperature, the calibration of the Electrode temperature before starting the weld allows continuous tracking of the absolute value of electrode temperature during a weld cycle.

In addition, the measurement of the electrical quantity depends here only on the nature of the heating element, and does not add any thermal element between the heating element and a temperature sensor of the thermocouple type. The delay time between the actual value and the measured value is therefore almost zero.

In a preferred embodiment, energizing the electrode to increase the temperature of the electrode is by applying an alternating current across the heater.

Advantageously, the step of measuring the electrical quantity comprises switching off the alternating current for a determined period of time t. This time must be short enough to be able to determine the temperature almost continuously, and long enough to pass through a continuous current.

Generally, this time period has a duration of 10 to 100ms.

Then, the measuring step comprises establishing a direct current Ic across the terminals of the heating element during this period of time t; then, a measurement step, strictly speaking, of the electrical quantity G (ΔT) during said lapse of time t.

The implementation of this measurement method, said alternating method, advantageously allows the implementation of the measuring method according to the invention, in the context of a welding using an alternating current for energizing the electrode.

According to an alternative embodiment, the measured electrical quantity G (ΔT) is the voltage V at the terminals of the heating element. In this case, the step of determining the temperature T (ΔT, TO) of the heating element takes place according to the following formula:

T = (V -V0) / (V0 * a) + T0 where a is the coefficient of ohmic variation per degree Celsius, and VO is the initial voltage across the heating element at the initial temperature TO during calibration.

According to another variant embodiment, the measured electrical quantity G (ΔT) is the resistance R of the heating element. In this case, the step of determining the temperature T (ΔT, TO) of the heating element takes place according to the following formula:

where a is the coefficient of ohmic variation per degree Celsius, and RO is the initial resistance of the heating element to the initial temperature TO during calibration.

Advantageously, the heating element is an electrode.

The measurement method furthermore comprises the display of values such as the measured value of the measured electrical value G (ΔT) or the value of the determined temperature T (ΔT, TO), and the storage of the temperature history. T determined.

The establishment of temperature history is important, especially in some areas of industry such as the pharmaceutical field that requires traceability of all events in a production chain.

Furthermore, the method includes a step of alerting to trigger a maintenance operation according to the history of the determined temperatures T.

Correlatively, the invention relates to a method for controlling the temperature T of a welding system comprising a heating element during a welding cycle.

According to the embodiment implemented, this control method comprises each of the steps of the measuring method described above; it further comprises an additional step of regulating said temperature T of the heating element as a function of at least one regulation setpoint. For this purpose, the control method may comprise a prior step of entering at least one regulation setpoint, unless this regulation setpoint is already predetermined.

Advantageously, this regulation setpoint corresponds to a soldering temperature Ts, which is a function of the nature of the material to be welded.

The control method may also include a step of storing the parameters, for example the time and the welding pressure of each welding cycle. The invention also relates to a device for measuring the temperature T of a heating element used in a welding system by heating during a welding cycle.

This device according to the invention comprises: a heating module for varying the temperature of the heating element; a measurement module comprising means for measuring the initial temperature TO as an absolute value of the heating element, and measuring means suitable for measuring an electrical quantity G (ΔT), which is a function of the variation in the temperature of the the heating element, when the electrode is crossed by a continuous current Ic; and an integrated circuit adapted to determine the temperature T (ΔT, TO) in absolute value of the heating element from a measured electrical quantity G (ΔT) and an initial temperature TO measured during the calibration.

Preferably, the measuring means according to the invention comprise means for generating a direct current Ic adapted to pass through the electrode a continuous current Ic for a certain period of time t, which is preferably between 10 and 100ms. These measuring means further comprise means for measuring an electrical magnitude G (ΔT) of the electrode when said electrode is traversed by a continuous current Ic during said lapse of time t.

Advantageously, the integrated circuit is an integrated circuit of the type microcontroller comprising a processor, a RAM type RAM, and a ROM type ROM storing a computer program.

This integrated circuit may include storage means, for example a Flash type memory, for storing the history of the temperature measurements T of each soldering cycle; these means may optionally store parameters related to the time and the pressure of each welding cycle.

The processor may also be adapted to trigger a maintenance operation based on the history and / or predetermined parameters.

In an advantageous embodiment, the device comprises a man / machine interface comprising display means and input means. Correlatively, the object of the invention relates to a device for regulating the temperature T of a heating element used in a welding system by heating during a welding cycle.

According to the embodiment implemented, the device each comprises means of the measuring device described above. The computer program of the regulating device is further adapted to regulate the temperature T (ΔT, TO) determined according to at least one regulation setpoint during the welding cycle.

The invention relates to a welding system which comprises either a measuring device or a control device as described above.

The invention finally relates to a method of welding two thermoplastic elements by this welding system. The method comprises an optional preheating phase; a heating phase up to a predetermined welding temperature; a welding phase at said welding temperature for a predetermined welding time, said welding phase comprising a under pressure of the two elements to be welded in order to assemble the two thermoplastic elements; a cooling phase during a predetermined cooling time in order to obtain the solidification of the two assembled thermoplastic elements. Of course, each welding cycle is a function of predetermined parameters (time and pressure) which can be variable from one cycle to another.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will emerge from the following description, with reference to the appended figures which illustrate an embodiment of this embodiment devoid of any limiting character and in which:

- Figure 1 shows a welding system according to the invention;

- Figure 2 shows a control device according to the invention, in a particular embodiment;

FIG. 3 represents, in flowchart form, the main steps of the regulation method according to a particular embodiment of the invention; and

- Figure 4 shows a graph corresponding to the use of the welding system during a plurality of welding cycles in a particular embodiment of the invention.

Detailed description of an embodiment

A welding system and method according to a particular embodiment of the invention will now be described with reference to Figures 1 to 4.

In FIG. 1, is schematically represented a welding system 200 that allows the welding of two thermoplastic elements

(not shown in the figure) by an EC heating element supported by a bar B.

Preferentially and in the following of our example, this heating element EC is an electrode.

In the embodiment described here, the EC electrode is isolated from the B bar (not shown in the figure); the electrode is also covered with a non-stick Teflon® type layer (not shown in the figure).

The welding system 200 comprises a regulating device

100 according to the invention comprising a heating module MC and a measurement module ME both connected to the terminals of the electrode EC, and an integrated circuit 10 adapted for implementing the control method according to the invention .

FIG. 2 describes in more detail a particular embodiment of the regulation device 100. In the embodiment described here, the regulation device 100 comprises an integrated circuit 10 which is able to determine the temperature T of the electrode, and which is further able to regulate this temperature T according to a predetermined regulation regulation CR.

The integrated circuit 10 is preferably a microcontroller comprising a processor 11, a random-access memory 12 of the RAM type, a ROM-type read-only memory 13 storing a computer program PG adapted for implementing the regulation method in accordance with FIG. This computer program PG allows both the determination and the regulation of the temperature. The invention is described here in the particular context of regulating the temperature of a welding system. However, it will be understood from this description that the object of the invention lies mainly in the determination of the temperature in absolute value of the heating element. Indeed, the regulation of the temperature is a particular mode of implementation of the determination of the temperature in which one adds a regulation step according to the determined temperature.

This regulation as a function of the determined temperature is obtained automatically by the use of an integrated circuit, and in particular of a computer program PG which allows the execution of specific instructions for the implementation of said control method.

The integrated circuit also comprises storage means 14, such as a FLASH memory, capable of storing the history of the determined temperatures; these means 14, in the embodiment described here, also store the parameters (time and welding pressure) associated for each welding cycle.

The device 100 further comprises a heating module MC which is able to increase the temperature of the electrode EC; and a measurement module ME comprising measuring means 20 for the calibration temperature capable of providing a temperature in absolute value, typically a probe or a thermocouple, as well as measuring means 40.

These measuring means 40 comprise a generator GE of direct current Ic, and measuring means MG of an electrical value G (ΔT) which is a function of the temperature variation ΔT.

Finally, the device 100 comprises a man / machine interface 50 comprising MP input means as well as display means MA.

Since the temperature T of an electrode can not be obtained directly by a probe in a welding process according to the state of the art, the object of the present invention is to determine the absolute temperature of this electrode and to regulate this temperature. T according to at least one predetermined regulation setpoint.

The principle of the invention resides in the fact that the resistance value of an electrode or the voltage across this electrode varies proportionally with the temperature through an electrode. analog / digital comparator.

By knowing the initial temperature of the electrode, it is then possible to follow the evolution of the absolute temperature of the electrode and to set limits and thresholds in order to regulate this temperature during welding.

The control method according to the invention will be better understood in the following with reference to Figures 3 and 4.

To answer the regulation problem posed above, the operator first enters one or more regulation instructions CR via input means MP. It should be noted that, according to the invention, the regulation setpoint (s) may, beforehand, be stored in the storage means (14).

This regulation set point CR here corresponds to a soldering temperature Ts (equal to the order 150 ⁰ C) to be attained in order to obtain the softening of the two thermoplastic elements to be welded.

It may be entered other regulation instructions or parameters, such as the welding time ts (1 to 5 seconds), the envelope time of a welding cycle, the presentation time tp of two new elements to be welded, the sampling time tx between each temperature determination (10ms to 60ms), or else the cooling temperature Tr (70 ^° C.), which are characteristic of the materials of the elements to be welded; these regulation instructions and / or parameters that can be specific to each welding cycle. The operator will then be able to measure (ElO, phase A, point 1) in absolute value, by means of standard measuring means, the "cold" temperature TO of the electrode EC.

It should be noted that this calibration step is performed only once before the chain start welding operations. This calibration temperature corresponds to the initial temperature of the electrode. Depending on the ambient environment, it varies generally, between 10 ° and 30 ^° C. However, in certain cases that may be described as difficult, this temperature may be negative (or greater than 40 ^° C.).

Determining directly the temperature T1 of the EC electrode in absolute value during a welding cycle by means of a prior calibration step is characteristic of the invention.

Once the calibration has been performed, the circuit 10 controls the energizing E20 of the electrode EC by the heating module MC by applying an alternating current CA to the electrode EC in order to increase the temperature of the electrode EC, according to the state of the art.

This increase in temperature comprises a preheating phase B (slow passage of 10 ⁰ C to 30 ⁰ C, points 1 to 2) to condition the electrode EC, and a heating phase C (points 2 to 3) fast corresponding to the start of a welding cycle (start of the envelope time te).

At the end of the sampling time tx, the circuit 10 will proceed to the measurement (E30) of an electrical quantity G (ΔT) which is a function of the variation of the temperature ΔT of the electrode EC (see FIG. R)

To do this, the alternating current CA is cut for a relatively short period of time, which is preferably between 10 and 100 ms, and during which a continuous current Ic (100 mA for example) is passed through the electrode EC thanks to the GE generator. During this period of time, the means MG measure the desired physical magnitude G (ΔT).

According to the preferred embodiments, the means MG measure the voltage V across the terminals (or the resistor R) of the electrode EC.

The processor 11 of the circuit 10 determines (E40) the temperature Tl in absolute value of the electrode by applying the law of the variation of the temperature as a function of the value of the voltage V (or of the resistance R) measured. As a function of the result of this temperature T1, the circuit will regulate (E50) the temperature of the electrode EC as a function of the set point CR regulation entered beforehand.

If the temperature T1 is lower than the temperature of the control set point CR (soldering temperature Ts), then the circuit 10 will restart the steps E20 to E50 until a temperature equal to the soldering temperature Ts is reached.

If the temperature T1 is equal to (or greater than) the temperature of the set point CR, the circuit 10 will maintain (phase D, points 3 to 4) the temperature of the electrode during a predetermined welding time ts to allow the assembly two thermoplastic elements. This continuous determination of the temperature in absolute value during each soldering cycle thus allows the implementation of a predictive method for quasi-sensitively regulating said welding temperature throughout each of the welding cycles. Thus, the present invention allows the saving of material by optimizing and industrializing each of the welding cycles.

Likewise, this automated regulation makes it possible to achieve particularly advantageous energy savings.

It is also observed that the implementation of such a welding process makes it possible to reduce the costs relating to the maintenance of the welding stations.

This regulation which takes into account the temperature in absolute value makes it possible to use electrodes covered with teflon®, and thus makes it possible to avoid the use of non-sticking pad protections. In a particular embodiment, the circuit 10 is adapted to make reliable the quality of the weld, especially in the first welding cycles. This embodiment is advantageous for optimizing the industrial welding process, especially in winter when the cold prevails in the welding workshops. To do this, it is important to note that the quality of a weld depends not only on compliance with the regulation instructions with a automation of the regulation thanks to a knowledge of the temperature of the electrode continuously, but also of the initial conditions of the welding. The knowledge of the initial temperature TO of the electrode makes it possible to deduce the initial conditions of the support bar as close as possible to the electrode.

Depending on the measured initial temperature TO, the cycle, especially in its preheating phase and / or heating may require more or less energy.

If the temperature TO is less than a predetermined threshold, for example less than 0 ⁰ C, the integrated circuit 10 can provide two possible options to make reliable the quality of the weld: either by increasing the time of preheating or welding, or by increasing the welding temperature level.

Conversely, if the temperature TO is greater than another predetermined threshold (equal to 40 ^° C., for example), the energy input is decreased by a shorter or less hot weld.

In general, the circuit 10 is adapted to secure and make reliable the weld at each soldering cycle as a function of the measured temperature TO or determined temperatures T1. This is made possible by a suitable programming circuit 10 which is able to modulate at any time the parameters relating to time, the welding temperature or pressure.

It should be noted that the circuit 10 is also adapted to control the pressurization of the bar B on two elements to obtain the assembly of these elements; the pressurization can obviously be obtained with the cooperation of a second bar B 'of the welding system 200.

Once the soldering time ts has elapsed, the electrode (phase E) is cooled down to a cooling temperature Tr, preferably equal to 70 ^° C., corresponding to point 5 in FIG. 4. The cooling E is obtained either by the mass of the bar or by cooling means MR type circuit of water or air, well known to those skilled in the art.

In order to time and optimize the welds in an industrialized process of series welding, the phases C, D and E of the welding cycle have a total duration equal to an envelope time te.

However, after a certain number of welding cycles, it can be seen in FIG. 4 that the cooling temperature takes longer to reach, in particular because of the heat dissipation between the bar and the electrode ( see Cycle 1, Cycle 2 and Cycle 3).

The integrated circuit 10 is thus configured so that the presentation (phase F) of the two next elements to be welded in the welding process is triggered at the end of the envelope time and once the cooling temperature Tr is reached. The configuration of the processor 11 described in the particular embodiment described above must not be limiting in nature.

Thus, the determination and control of the temperature of the electrode by the integrated circuit 10 according to the invention allows a great deal of control of industrial heat sealing processes, allowing the control of a pulse welding process.

Indeed, as explained above, the knowledge at each instant of the temperature of the resistance in absolute value allows a good control of the heating temperature and the cooling temperature, and the use of an integrated circuit specially programmed to this effect makes it possible to automatically regulate the welding, and this with a minimum of response time.

It should be observed that this detailed description relates to a particular embodiment of the control method, but in no case this description is of any nature limiting to the subject of the invention; on the contrary, its purpose is to remove any imprecision or misinterpretation of the following claims.

Claims

1. Method for measuring the temperature (T) of a heating element (EC), for example of the electrode type, used in particular in a heating system

Soldering by heating during a soldering cycle, said method comprising a power-up step (E20) for varying the temperature of said heating element (EC), and at least one measuring step (E30) of an electric magnitude G (ΔT), a function of the temperature variation (ΔT) of said heating element (EC), characterized in that it further comprises:

prior to the energizing step (E20), a calibration step (ElO) of measuring the initial temperature (TO) in absolute value of said heating element (EC);

after the measuring step (E30), a step of determining (E40) the temperature T (ΔT, TO) in absolute value of the heating element (EC) from the measured value of the quantity G ( ΔT) and the initial temperature (TO).

Measuring method according to claim 1, the energizing (E20) 0 consisting of the application of an alternating current (AC) to the terminals of the heating element (EC), said measuring method being characterized in that that the measuring step (E30) comprises:

a step of breaking the alternating current (AC) for a predetermined period of time (t), preferably between 10 and 1005 ms;

a step of establishing a direct current (Ic) through the terminals of the heating element (EC) during said lapse of time (t); and

a step of measuring said electrical quantity G (ΔT) during said period of time (t).

3. Measuring method according to any one of claims 1 or 2, characterized in that the step of determining (E40) the temperature T (ΔT, TO) of the heating element (EC) operates according to the following formula:

T0 where a is the coefficient of ohmic variation per degree Celsius, and GO is the initial value of the electrical magnitude G (ΔT) measured at the initial temperature (TO) during calibration.

4. Measuring method according to any one of claims 1 to 3, characterized in that the measured electrical magnitude G (ΔT) is the voltage (V) at the terminals of the heating element (EC) or the resistance (R). of the heating element (EC).

5. A method for regulating the temperature (T) of a welding system comprising a heating element (EC), for example an electrode, during a welding cycle, characterized in that it comprises the steps of the measuring method according to any one of claims 1 to 4, and in that it comprises an additional step of regulating (E50) said temperature (T) of the heating element (EC) as a function of at least one regulation setpoint (CR).

6. Control method according to claim 5, characterized in that the regulation setpoint (CR) corresponds to a welding temperature (Ts), which is optionally a function of the material to be welded.

7. A device (100) for measuring the temperature (T) of a heating element (EC), for example of the electrode type, used in a welding system (200) by heating during a welding cycle, said measuring device (100) being characterized in that it comprises: - a heating module (MC) for varying the temperature of the heating element (EC);

a measuring module (ME) comprising measuring means (20) for the initial temperature (TO) in absolute value of the heating element (EC), and measuring means (40) suitable for measuring an electrical quantity G (ΔT), a function of the variation of the temperature of the heating element, when said electrode is traversed by a direct current (Ic);

an integrated circuit (10) adapted to determine the temperature T (ΔT, TO) in absolute value of the heating element (EC) from said electrical quantity G (ΔT) and the initial temperature (TO) measured during the a calibration step (ElO).

8. Measuring device (100) according to claim 7, characterized in that the measuring means (40) comprise on the one hand generation means (GE) of a direct current (Ic) adapted to pass through the electrode a direct current (Ic) for a predetermined period of time (t), preferably between 10 to 100 ms, and secondly measuring means (MG) of an electric magnitude G (ΔT) of the electrode when said electrode is traversed by said continuous current (Ic) during said short period of time (t).

9. Welding system (200) characterized in that it comprises a measuring device (100) according to any one of claims 7 or 8.

Device for regulating (100) the temperature (T) of a heating element (EC), for example an electrode, used in a welding system (200) by heating during a welding cycle, characterized in that it comprises a measuring device according to claim 7, and in that the integrated circuit (10) is adapted to regulate the temperature T (ΔT, TO) determined according to at least one regulation setpoint (CR) during the welding cycle.

11. soldering system (200) characterized in that it comprises a control device (100) according to claim 10.

12. A method of welding two thermoplastic elements by a welding system (200) according to claim 11, characterized in that it comprises: an optional preheating phase (B);

a heating phase (C) up to a predetermined welding temperature (Ts);

- A welding phase (D) at said welding temperature (Ts) for a predetermined welding time, said welding phase comprising a pressurization of the two elements to be welded in order to assemble the two thermoplastic elements;

- A cooling phase (E) during a predetermined cooling time in order to obtain solidification of the two assembled thermoplastic elements.

Welding method according to Claim 12, characterized in that the duration of the preheating phase (B) and / or the duration of the welding phase (C) and / or the welding temperature (Ts) is / are function (s) of the calibration temperature (TO); this said calibration temperature (TO) being measured during the calibration step (ElO) according to the measuring method according to any one of claims 1 to 4.