Leak Detection Device And Associated Electrical Power Supply

Abstract

A leak detection device includes a space intended to receive a part to be tested, at least two electrodes disposed on either side of the reception space, a direct-current electrical power supply supplying at least one of the electrodes with an output voltage, and a current detector configured to measure the current generated by the voltage difference between the electrodes. The electrical power supply is a power supply including a transformer having a midpoint primary, a transistor connected to said midpoint of the transformer, switches whose succession of openings and closures has at least one duty cycle and enables the transmission of energy through the transformer, and at least one regulation circuit regulating the value of the duty cycle and the voltage supplying the base of the transistor.

Claims

1. A leak detection device, said device comprising: a space intended to receive a part to be tested; at least two electrodes disposed on either side of said space; a direct-current electrical power supply supplying at least one of said electrodes with an output voltage; and a current detector configured to measure current generated by a voltage difference between said electrodes, wherein said electrical power supply is a power supply comprising: a transformer having a primary with a midpoint; a transistor connected to said midpoint of said transformer; switches whose succession of openings and closures has a duty cycle and enables a transmission of energy through the transformer; and at least one regulation circuit regulating a value of the duty cycle and a voltage supplying a base of said transistor.

2. The leak detection device according to claim 1, wherein the at least one regulation circuit of said electrical power supply comprises: a first regulation circuit that regulates a power supply of the base of said transistor; and a second regulation circuit that regulates the duty cycle.

3. The leak detection device according to claim 2, wherein said second circuit regulates the value of the duty cycle according to a reference voltage, the output voltage, and a modulation signal having a frequency.

4. The leak detection device according to claim 1, wherein a first regulation circuit of the at least one regulation circuit regulates a voltage delivered by the transistor to the primary of the transformer according to a reference voltage.

5. The leak detection device according to claim 2, wherein a frequency of opening and closure of the switches is constant.

6. The leak detection device according to claim 2, wherein a frequency of opening and closure of the switches has a value setting the first regulation circuit and the second regulation circuit in an underdamped mode.

7. The leak detection device according to claim 6, wherein the second regulation circuit comprises: a shaping circuit for shaping values of a reference voltage and of the output voltage; and a control circuit for controlling the opening and closure of the switches.

8. The leak detection device according to claim 7, wherein said transformer is a step-up voltage transformer.

9. The leak detection device according to claim 1, wherein the electrical power supply comprises a rectifying and filtering circuit configured to rectify an alternating-current signal derived from a secondary of the transformer before said signal is applied to at least one of the electrodes.

10. The leak detection device according to claim 9, wherein the electrical power supply further comprises a compensation circuit configured to compensate a value of a voltage actually delivered at an output by the transformer when an impedance of said part to be tested varies, at least one input of said compensation circuit being placed at an output of said rectifying and filtering circuit.

11. A direct-current electrical power supply for a leak detection device, the leak detection device comprising: a space intended to receive a part to be tested; at least two electrodes disposed on either side of said space; and a current detector configured to measure current generated by a voltage difference between said electrodes, wherein the direct-current electrical power supply supplies at least one of said electrodes with an output voltage.

12. The direct-current electrical power supply according to claim 11, comprising: a transformer having a primary with a midpoint; a transistor connected to the midpoint of the primary of said transformer; switches whose succession of openings and closures has a duty cycle and enables transmission of energy through the transformer; and at least one regulation circuit regulating a value of the duty cycle and a voltage supplying a base of said transistor.

13. The direct-current electrical power supply according to claim 12, comprising a resistor disposed between the transistor and the midpoint of the primary of the transformer.

14. The direct-current electrical power supply according to claim 13, comprising, at a secondary of the transformer, a rectifying and filtering circuit configured to rectify and filter an alternating-current signal at a secondary of the transformer, before said signal supplies an injection electrode of the at least two electrodes.

15. The direct-current electrical power supply according to claim 11, comprising a short-circuit resistor to limit current at an injection electrode of the at least two electrodes.

16. The device according to claim 2, wherein the first regulation circuit regulates a voltage delivered by the transistor to the primary of the transformer according to a reference voltage.

17. The device according to claim 3, wherein a frequency of opening and closure of the switches is constant.

18. The device according to claim 4, wherein a frequency of opening and closure of the switches is constant.

19. The device according to claim 3, wherein a frequency of opening and closure of the switches has a value setting the first regulation circuit and the second regulation circuit in an underdamped mode.

20. The device according to claim 5, wherein the frequency of opening and closure of the switches has a value setting the first regulation circuit and the second regulation circuit in an underdamped mode.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0025] The invention will be better understood, and other aims, details, features and advantages thereof will appear more clearly through the following description of particular embodiments of the invention, given only for illustration and without limitation, with reference to the appended drawings.

[0026] FIG. 1 is a simplified schematic representation of a leak detection device according to an embodiment of the invention.

[0027] FIG. 2 is a simplified schematic representation of the electrodes of the device of FIG. 1 during testing of a part.

[0028] FIG. 3 is a simplified schematic representation of an electrical power supply of the device of FIG. 1.

[0029] FIG. 3A is a detailed schematic view of a rectifying and filtering circuit according to an embodiment of the invention.

[0030] FIG. 4 is a detailed view of the second regulation circuit of the power supply of FIG. 3.

[0031] FIG. 5 is a detailed view of the first regulation circuit of the power supply of FIG. 3.

[0032] FIG. 6 is a schematic and detailed view of a variant embodiment of the circuit of FIG. 1.

[0033] FIG. 7 is a simplified equivalent circuit of the transformer of the power supply of FIG. 3.

[0034] FIG. 8 represents examples of signals specific to the regulation circuit of FIG. 3.

[0035] FIG. 9 represents the signals received by the switches of the power supply of FIG. 3 and the output signal at the secondary of the transformer.

DETAILED DESCRIPTION

[0036] FIG. 1 is a simplified schematic representation of a leak detection device 1 according to an embodiment of the invention. The leak detection device 1 includes a space 3 intended to receive the part to be tested 5, two electrodes 7 and 9, a direct-current electrical power supply 11 supplying at least one of said electrodes 7, the electrode supplied by said power supply 11 being called the injection electrode, and a current measuring device 13, such as a transimpedance op-amp type ammeter, configured to measure the current flowing through the part to be tested 5 when the latter is exposed to a voltage difference.

[0037] More particularly, said electrical power supply 11, represented in particular in FIG. 3 includes a transformer 101 having a midpoint primary, a transistor T connected to the midpoint of the primary of said transformer 101, switches M1 and M2 whose succession of openings and closures has at least a duty cycle α and enables the transmission of energy through the transformer 101, and at least one regulation circuit 105 and 103 regulating the value of the duty cycle α and the voltage supplying the base of said transistor T.

[0038] It should be noted that, as illustrated in FIG. 3, the power supply 11 may also comprise a resistor R.sub.P disposed between the transistor T and the midpoint of the primary of the transformer 101. This may have the effect of limiting the intensity of the electric current at the primary.

[0039] It should also be noted that, as illustrated in the detailed embodiment, the power supply 11 may comprise, at the secondary of the transformer 101, a rectifying and filtering circuit 107 configured to rectify and filter the alternating-current signal at the secondary of the transformer 101, before this signal supplies the injection electrode 7. Said power supply 11 may also comprise a resistor R.sub.S (illustrated in particular in FIG. 7), called a short-circuit resistor, to limit the current at the injection electrode.

[0040] The rectifying and filtering circuit 107, illustrated more particularly in FIG. 3A, herein comprises two diodes D.sub.1 and D.sub.2, as well as two capacitors C.sub.1 and C.sub.2 disposed so as to form a Schenkel type voltage doubler. This mounting type allows both rectifying and filtering the alternating voltage present at the secondary of the transformer T.

[0041] Said power supply 11 may also comprise a voltage divider bridge arranged at the output of the rectifying and filtering circuit 107. This mounting type allows for example obtaining an image of the test voltage V.sub.S, this image voltage being referenced V′.sub.S hereinafter and illustrated for example in FIGS. 3A and 4.

[0042] More particularly, the divider bridge comprises two resistors R.sub.1 and R.sub.2. The voltage at the terminals of the resistor R.sub.2 is the image voltage V′.sub.S. This image voltage V′.sub.S is related to the load voltage V.sub.S according to the following formula:

[00001]$V_S^{\prime }=\frac{R_2}{R_1+R_2}{V}_S=k{V}_S,$

with k therefore being a factor depending on the resistors R.sub.1 and R.sub.2.

[0043] More particularly, said at least one regulation circuit 105 and 103 has at the input a reference voltage or reference voltage V.sub.ref, the value of the reference voltage V.sub.ref being proportional to the test voltage value V.sub.S that should be obtained at the output, the image voltage V′.sub.S, which is an image of the output voltage V.sub.S, this image voltage V′.sub.S being obtained for example by means of a divider bridge, and a modulation signal S.sub.M that determines the variation of the duty cycle α. Thus, said power supply 11 comprises a first regulation circuit 105 that regulates the supply of the base of said transistor T and a second regulation circuit 103 that regulates the value of the duty cycle α. In particular, the regulation of the duty cycle α is carried out according to the values of the reference voltage V.sub.ref, of the load voltage V.sub.S (indirectly via the image voltage V′.sub.S of the voltage V.sub.S) and of the modulation signal S.sub.M.

[0044] The first regulation circuit 105, illustrated more particularly in FIG. 5, comprises an operational amplifier AO.sub.5 associated with two resistors R.sub.4 and R.sub.5 mounted as a non-inverting amplifier receiving the reference voltage V.sub.ref at the input (for example the values of the resistors R.sub.4 and R.sub.5 are equal).

[0045] The first regulation circuit 105 is configured to regulate the injection voltage V.sub.S at the injection electrode 7. Regulation by the first circuit 105 is predominant when not loaded, i.e., said circuit 105 via the transistor T is predominant in setting the value of the injection voltage when not loaded.

[0046] Thus, the transistor T is supplied at the collector with a direct voltage V.sub.alim and is connected at its base to the output of the first regulation circuit 105. According to the voltage V.sub.AO5 derived from said first circuit 105, this arrangement allows the voltage at the primary of the transformer 101 to vary.

[0047] The emitter of the transistor delivers a voltage value that lies between the value of k V.sub.ref and zero (where k is equal to 1+R.sub.5/R.sub.4), this value being regulated according to the reference voltage V.sub.ref.

[0048] The regulation circuit 105 according to the variation of the reference voltage V.sub.ref allows regulating the voltage on the midpoint of the primary and consequently obtaining the desired voltage at the secondary, and therefore the output voltage V.sub.S too.

[0049] More particularly, the regulation of the voltage delivered by the transistor T thus allows servo-controlling the test voltage to the reference voltage requested by the operator, whereas the second regulation circuit 103 comes into action to compensate for the test voltage and maintain the test voltage in case of a load variation (i.e., a variation in the insulation resistance of the tested part). Each of the regulation circuits 105 and 103 functions as a servo that allows for a much finer regulation over a wide range of values of the test voltage V.sub.S.

[0050] The second regulation circuit 103, illustrated more particularly in FIG. 4, includes a shaping circuit 103a comprising an operational amplifier AO.sub.3, mounted as a comparator-integrator, associated with a capacitor C.sub.3 and a resistor R.sub.3. The second regulation circuit also includes a control circuit 103b, which has as input the output of the operational amplifier AO.sub.3, as well as the modulation signal S.sub.m of the voltage V.sub.osc and of the frequency f.sub.osc. The control circuit 103b is configured to generate a Pulse Width Modulation (PWM) signal with a duty cycle α, which controls opening and closure of the switches M1 and M2.

[0051] Thus, the operational amplifier AO.sub.3 receives at the input the image voltage V′.sub.S and the reference voltage V.sub.ref and delivers at the output a resulting voltage V.sub.AO3 in the form ∫(V.sub.ref−V.sub.S′)dt.

[0052] In turn, said control circuit 103b (seen more particularly in FIG. 4) includes an operational amplifier AO.sub.4 mounted as a comparator, whose inputs receive the modulating signal S.sub.M with the frequency f.sub.osc and the output signal V.sub.AO3 of the operational amplifier AO.sub.3, and two logic gates P.sub.1 and P.sub.2, phase-shifted by π with respect to each other, so that the closure and opening of said switches M1 and M2 are carried out in phase opposition.

[0053] More particularly, the operational amplifier AO.sub.4 thus compares the output voltage V.sub.AO3 of the shaping circuit 103a with the voltage V.sub.osc of the modulating signal S.sub.M (for example of the ramp or sawtooth type). The frequency f.sub.osc of the modulator is a fixed value corresponding substantially to the resonance frequency of the electrical power supply 11 (i.e., of the inductance of the primary as well as the capacitances present at the secondary brought back to the primary).

[0054] It should be noted that in a variant partially represented in FIG. 6, the image voltage V′.sub.S is not derived solely and directly from a voltage divider bridge as explained before. More particularly, as illustrated in this FIG. 6, in addition to the resistors R.sub.1 and R.sub.2 of the divider bridge, there is a shunt resistor R.sub.SH disposed between the rectifying and filtering circuit 107 and the resistor R.sub.2. Thus, the power supply 11 comprises a load variation compensation circuit 109, having as inputs the terminals of the shunt resistor R.sub.SH, as well as the output voltage V.sub.S′ of the divider bridge formed by the resistors R.sub.1 and R.sub.2. Thus, when the impedance of the tested object varies, for example decreases, the efficiency of the transformer decreases, said compensation circuit 109 then allows compensating for the value of the voltage actually delivered at the output by the transformer. Thus, it is possible to increase the measurement dynamics while keeping the same current measurement accuracy.

[0055] Thus, said compensation circuit 109 includes a first operational amplifier AO.sub.6 whose inputs are connected to the terminals of the shunt resistor R.sub.SH to which a predetermined gain G is applied. There is therefore a voltage at the output of the op-amp AO.sub.6 that is related to the value of the current flowing in the secondary of the transformer 101. Said compensation circuit 109 also includes a second operational amplifier AO.sub.7 that adds the values of the voltages derived from the divider bridge and the op-amp AO.sub.6.

[0056] Hence, at the output of the circuit 109, an image of the voltage denoted V″.sub.S is obtained compensated for the voltage drops of the secondary, said image of the voltage V″.sub.S is then used the input value of the second regulation circuit 103.

[0057] Moreover, the selection of the frequency f.sub.osc of closure and opening of the switches M.sub.1 and M.sub.2 in phase opposition allows reconstituting a sinusoidal signal at the secondary of the transformer 101. In particular, this allows maximising the transfer of energy through the transformer 101 by limiting the generation of noises on the current delivered by the secondary of the transformer 101.

[0058] Indeed, a power supply portion of FIG. 3 can be modelled in the form of a simplified equivalent circuit. This simplified equivalent circuit is illustrated more particularly in FIG. 7. Thus, seen from the primary, the circuit can be considered as an RLC circuit including a voltage source E, resistors R.sub.S, R.sub.B, R.sub.P corresponding respectively to the internal resistance (and to the short-circuit resistance) of the generator, to the resistance of the winding of the primary, and to the resistance connected to the midpoint of the transformer 101, an inductance L.sub.MAG corresponding to the magnetising inductance of the primary, and a capacitance CP corresponding to the capacitance present at the terminals of the set of the two primaries. It should be noted that the resistance of the transistor allows obtaining the equivalent of a variable voltage regulator.

[0059] In the present case, the resistance of the primary winding can be neglected in comparison with the value of the other resistances.

[0060] Thus, the natural pulsation ω.sub.0 of such an RLC circuit is as follows:

[00002]${\omega }_0=\frac{1}{\sqrt{L_{MAG}{C}_P}}$

[0061] In the same manner, one can determine a reduced damping coefficient m as follows:

[00003]$m=\frac{R_s+R_P}{2}\sqrt{\frac{C_P}{L_{MAG}}}$

[0062] Thus, in pseudo-periodic mode, it is possible to define a pseudo-pulsation cop such that:

ω.sub.P=ω.sub.0√{square root over (1−m.sup.2)}

[0063] However, when the frequency of the modulator f.sub.osc is equal (or substantially equal) to the frequency of the equivalent circuit, more particularly in sustained subcritical mode, m is well below 1 and ω≈ω.sub.0.

[0064] The voltage U.sub.M delivered by the transformer is then in the form U.sub.M≈αE, where α is the duty cycle of the first regulation circuit 103, and λ is a coefficient depending on the transfer function of the PWM control circuit.

[0065] Thus, as illustrated in FIG. 8, the shaping circuit 103a integrates the difference between the image voltage V′.sub.S and the reference voltage V.sub.ref, and therefore outputs a direct voltage V.sub.AO3. Thus, this voltage V.sub.AO3 is compared with the modulating voltage V.sub.osc, and allows generation of a square signal S.sub.PWM. The duty cycle α of said square signal is modified according to the variation of the load current. More particularly, if the reference voltage V.sub.ref increases, then the voltage V.sub.AO3 decreases, and the duty cycle α of the resulting square signal S.sub.PWM increases. Indeed, when the value of the resistance (or of the load) of the tested part decreases, then the duty cycle α increases to preserve the test voltage.

[0066] Hence, the square signal S.sub.PWM is the output signal of the control circuit 103b that controls opening and closure of the switches M.sub.1 and M.sub.2. The square signal S.sub.PWM has a constant frequency f.sub.osc. Hence, the opening and closure of the switches M1 and M2 supplies alternately, with a phase shift of π, each of the portions of the primary of the transformer 101.

[0067] As represented in FIG. 9, each of the closures and openings of said switches M.sub.1 and M.sub.2 thus allows reconstituting the fundamental of a square signal, i.e., by definition, the signal S.sub.sec generated by a parallel resonance oscillator is operating in a forced underdamped mode. Thus, the modification of the duty cycle α allows acting on the amount of transferred energy and therefore on the value of the voltage of the alternating signal S.sub.sec at the secondary of the transformer 101.