Patent Description:
Solenoid valves are often used as control devices in industrial pneumatic systems, wherein control of direction of a flow of air enabling the solenoid to open and close is achieved by changing a position of a slider (connected to the solenoid linor or without the linor) by means of an electromagnetic field generated in the solenoid coil. Malfunction of even a single solenoid valve may result in a malfunction of the entire system, If the system contains many solenoid valves, this may result in a time-consuming and labour-intensive search for the location of the fault. Therefore, there have been designed devices for monitoring operation of solenoid valves to facilitate identification of malfunctioning solenoid valves.

One of known methods of monitoring a correct operation of a solenoid valve is to measure changes in inductance of the coil of the solenoid valve. Such solution is described in a European patent <CIT>, wherein a simple electronic analogue circuit is used that compares voltage values at the coil current measurement resistor during the momentary current drop at the moment of the correct operation of the solenoid valve. A comparator signal is used to power a light diode, an acoustic signal or a control unit, so that a potential problem can be quickly identified. However, the solution of <CIT> does not allow assessment of changes of operation of the solenoid valve, such as a depth of the slider or a rate at which the slider moves. Furthermore, such device requires calibration (i.e. adjustment of its electronic components) in order to match a sensitivity of the device to characteristics of the monitored solenoid valve. Moreover, the solution of <CIT> does not protect against short circuits in the coil. Furthermore, the system of <CIT> indicates correct switching of the solenoid valve when it detects a drop in the current flowing through the coil. However, this drop can be caused not only by the switching of the solenoid valve, but also by a momentary drop in the supply voltage, a burning of the coil shortly after switching, or some disturbance. Therefore, the system of <CIT> is susceptible to various types of instability.

There are also known some digital solutions that utilize a microprocessor chip, for example a TIDA-<NUM> circuit by Texas Instruments. A reference solution for use of TIDA-<NUM> in a system for monitoring a solenoid valve coil, as described at www. com/lit/pdf/tiduco6, may fulfil many industrial needs, but is not universal. A single device based on this reference solution cannot be used for coils of different types. Therefore, if one were to use the reference solution for coils of different types, it would be necessary to develop a series of devices adapted to specific operating ranges of various solenoid valves.

There is a need to provide a method and a device for monitoring operation of solenoid valves that would allow monitoring correct operation of the solenoid valve on an ongoing basis and indicate abnormalities in its operation without interfering with the structure of the solenoid valve. The solution shall be a universal one, intended to monitor a wide variety of solenoid valves, without the need to adapt parameters of the monitoring device to different types of solenoid valve. Preferably, the device should be compact enough to be inserted into a plug of the solenoid valve power cable.

In one aspect, the invention relates to a device for monitoring operation of a solenoid valve, the device comprising: a circuit for supplying power to a coil of a solenoid valve, comprising terminals connected in series with a power source, the terminals configured to be connected to the coil, a power supply switching transistor and a measurement resistor; and a microprocessor-based measurement system configured to monitor supply current consumed by the coil while the coil is switched on, by measuring voltage at the measurement resistor, and to control the power supply switching transistor. The microprocessor-based measurement system comprises an analogue-to-digital converter comprising a consumed current measurement channel connected to the measurement resistor and a consumed current amplified measurement channel connected to the consumed current measurement channel via an adjustable amplifier. The microprocessor-based measurement system is configured to: switch off the power supply switching transistor when a voltage having a value higher than a threshold value is detected on the consumed current measurement channel; and control the gain of the adjustable amplifier so that the signal at the input of the consumed current amplified measurement channel is lower than the measurement range of this channel.

The analogue-to-digital converter may further comprise a supply voltage measurement channel connected to a resistive voltage divider connected between the supply voltage and the ground, and the microprocessor-based measurement system is configured to monitor the range of the supply voltage and the voltage fluctuation when the power supply is being switched on.

The consumed current measurement channel can be connected to the measurement resistor via a low-pass filter.

The microprocessor-based measurement system may further comprise an input/output interface configured to receive a parameter determining the gain value of the adjustable amplifier.

The microprocessor-based measurement system can be further configured to control the gain of the adjustable amplifier so that the signal at the input of the consumed current amplified measurement channel is higher than the threshold minimum value.

The microprocessor-based measurement system can be further configured to control the gain of the adjustable amplifier so that the signal at the input of the consumed current amplified measurement channel is lower than the threshold maximum value.

The microprocessor-based measurement system can be further configured to control the gain of the adjustable amplifier so that the signal at the input of the consumed current amplified measurement channel after stabilisation of the coil current is close to the threshold maximum value.

The device may have its components arranged on a PCB enclosed by a plug configured to connect a power supply to the solenoid valve.

In another aspect, the invention relates to a method for monitoring operation of a solenoid valve, comprising the steps of: connecting a device as described herein to a coil of the solenoid valve; switching on power supply to the power supply switching transistor; awaiting for a signal at the input of the consumed current amplified measurement channel to exceed the minimum value threshold; examining the slope (α) of the characteristics of the consumed current amplified measurement channel and storing the value of the signal of the consumed current amplified measurement channel when the slope (α) reaches the horizontal, and determining, based on the stored value, the values of the minimum slope (αMIN), the limit value of the increment (ΔIL) and the stabilisation value; continuing examination of the slope (α) when the slope (α) falls to a value below the minimum slope, until the direction of the slope (α) changes from descending to ascending and from this point onwards, checking the signal value increment of the consumed current amplified measurement channel and when it exceeds the increment limit value, awaiting for the current value to stabilise such that the difference between the maximum and minimum values during the specified stabilisation time is smaller than the stabilisation value; reporting that the solenoid valve is switched on correctly if the current value stabilises within the specified final stabilisation time and the current stabilisation does not occur later than the permissible total switch-on time since exceeding the minimum value threshold; and reporting that the solenoid valve failed if the current value does not stabilise before the specified switch-on time since exceeding the minimum value threshold.

The method and device according to the invention allow monitoring operation of solenoid valves, by tracking the values of current of the solenoid valve coil based on monitoring changes in coil inductance over time. By using digital solutions and taking the time parameter into account, the solution according to the invention provides broader diagnostic capabilities than the prior art solutions. In particular, it allows detection of abnormal switching characteristics of the solenoid valve, which can be an early indication of a need to replace the solenoid valve, even before the solenoid valve actually fails. A monitoring device according to the present invention can indicate correct switching of the solenoid valve (or lack of correct switching). It also allows, when the coil is short circuited, protecting the power supply source and elements of the path for measuring and controlling the switching of the coil, by cutting off the supply of power to the faulty coil. Moreover, the monitoring device allows to indicate that the supply voltage provided to the coil is too low or too high (via a LED or an IO-Link interface). Furthermore, the solution according to the present invention not only indicates the correct switching of the solenoid valve, but also measures electrical and timing parameters that can be read by the host system and used to assess changes in the operation or wear and tear of the solenoid valve or to schedule maintenance of the solenoid valve.

The device according to the invention fits into standard solenoid valve power plugs, therefore it can be used to monitor solenoid valves of various manufacturers without having to adjust the device parameters to the specificity of a given solenoid valve. At the same time, due to the use of an adjustable gain subsystem in a path for measuring a current-time waveform, it was possible to achieve versatility in terms of cooperation with a wide current spectrum of solenoid valves without having to adapt the structure of the device to different coil operating currents.

The solution according to the invention allows to use the same physical shunt in a form of a measuring resistor in the coil current measurement path for a very diverse range of operating currents of solenoid valve coils available on the market, having values in the order of tens of mA to a few A, and allows use of a shunt (resistor) with a low resistance, which as a result reduces the amount of heat released at the shunt.

The reference solution for the TIDA-<NUM> circuit described in the background section, without the modification to the coil current measurement path as provided by the present invention, would require splitting of the physical layer into dedicated electronic packages for specific operating ranges of solenoid valves, because (due to the measurement range and resolution of the ADC converter) it is not possible to assess correctness of coil current waveform for a specific shunt resistance for such diverse operating current ranges of solenoid valve coils. In the absence of an adjustable amplifier, the shunt resistance and the amplifier gain are optimally selected for a group of coils with a specific rated power range, and the use of such a device for a coil significantly different in its rated power from the adopted assumptions causes that the range of the voltage signal reflecting the coil current either exceeds the measuring range of the ADC converter, or changes only in a small measuring range of the ADC converter, which in both cases will result in the inability to correctly assess the coil current shape by the processor algorithm. This, in turn, excludes the versatility of the solution in a commercial sense - one electronic module in the plug for all solenoid valves.

These and other features, aspects and advantages of the invention will become better understood with reference to the following drawings, descriptions and claims.

Various embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein:.

<FIG> shows an example embodiment of a functional diagram of device according to the invention. Preferably, the components of the device are installed within a solenoid valve power plug.

The device comprises a connection interface to connect it to a coil <NUM> of a solenoid valve. The connection interface comprises a first terminal 100A connected to a supply voltage <NUM>+ and configured to be connected to a first terminal of the coil <NUM> of the solenoid valve, and a second terminal 100B configured to be connected to a second terminal of the coil <NUM> of the solenoid valve.

The device comprises a power supply switching transistor <NUM> connected between the second terminal 100B and a measurement resistor <NUM> connected to a ground (GND) potential of the system. The power supply switching transistor <NUM> is preferably a MOSFET type transistor. The power supply switching transistor <NUM> provides current to the coil in order to switch the solenoid valve on and off.

The voltage at the measurement resistor <NUM> at point 100C reflects the power supply current consumed by the coil when it is switched on. This voltage is monitored by a microprocessor-based measurement system <NUM> that also controls the transistor <NUM> that switches on the coil power supply via a power supply control output OUT.

A protection resistor <NUM> protects the power supply switching transistor <NUM> from accidentally switching on during an initial phase of operation, after power has been applied to the system, when the microprocessor-based measurement system <NUM> is just starting up and the power supply control output OUT is not yet controlled by the microprocessor-based measurement system <NUM> and set as unpolarised. During this period, the protection resistor <NUM> connects the gate of the power supply switching transistor <NUM> to the GND potential, which prevents the power supply switching transistor <NUM> from switching on. When the microprocessor-based measurement system <NUM> starts and configures the power supply control output OUT, the resistance of the protection resistor <NUM> is irrelevant in controlling the power supply switching transistor <NUM>.

The microprocessor-based measurement system <NUM> comprises an analogue-to-digital converter <NUM>. The converter <NUM> may have a form of a single multi-channel converter, of an assembly of multiple single-channel converters, or of a combination thereof. The analogue-to-digital converter <NUM> has three channels: CH1, CH2, CH3. The first channel CH1 is configured to measure the voltage at a voltage divider composed of series-connected resistors <NUM>, <NUM> and connected between the supply voltage <NUM>+ of the coil and the GND potential. The signal from the analogue-to-digital converter <NUM> from the first channel CH1 (also referred to as the supply voltage measurement channel) is used to assess the quality of the supply voltage, i.e. whether the supply voltage is within a permissible range, whether there are fluctuations when the solenoid valve power supply is being switched on (that could affect the switching current characteristics and incorrect detection of switching on the solenoid valve). The second channel CH2 (also referred to as the consumed current measurement channel) is used to measure the voltage at the measurement resistor <NUM> after filtering through a low-pass filter <NUM>. The signal from the low-pass filter <NUM> is also supplied to an adjustable amplifier <NUM>, the output of which is connected to the third channel CH3 of the analogue-to-digital converter <NUM>.

The voltage at the measurement resistor <NUM> at point 100C is proportional to the instantaneous current of the coil. This signal may, in addition to the voltage proportional to the coil current, also contain noise (interference) from the power supply path or from the environment wherein the system operates. The low-pass filter <NUM> eliminates these noises by passing only the lower-frequency useful signal that is supplied to the second channel CH2 of the analogue-to-digital converter <NUM> and to the input of the adjustable amplifier <NUM>. For example, the low-pass filter may have a cut-off frequency of <NUM>. The signal from the adjustable amplifier <NUM> is supplied to the third channel CH3 of the analogue-to-digital converter <NUM>. The measurement resistor <NUM> has a fixed known value, hence the voltage on the second channel CH2 of the analogue-to-digital converter <NUM> is proportional to the coil current, with a constant ratio. The signal supplied to the second channel CH2 is used to detect a short circuit in the coil <NUM> of the solenoid valve and to calculate a new gain for the adjustable amplifier <NUM>. An occurrence (on the second channel CH2) of a voltage greater than the adopted threshold value considered as the short-circuit threshold, causes the power supply switching transistor <NUM> to be switched off immediately, by setting the power supply control output OUT to a low state L. The signal at the input of the third channel CH3 of the analogue-to-digital converter <NUM> is the signal amplified by the adjustable amplifier <NUM>, supplied from the low-pass filter <NUM> - the same as the signal supplied to the input of the second channel CH2. The adjustable amplifier <NUM> allows the low-value signal from the low-pass filter <NUM> to be adapted to the measurement range of the analogue-to-digital converter <NUM> in order to monitor the current waveform of the coil <NUM> with a resolution as high as possible. As a result, the device can be connected to coils <NUM> having various powers, which will cause flow of currents of various values. The gain in the adjustable amplifier <NUM> may be adjusted linearly or stepwise, depending on the functionality of the adjustable amplifier <NUM> used, and the adjustment is performed by the gain signal output GAIN of the microprocessor-based measurement system <NUM>, that may be an analogue output (such as a signal from a digital-to-analogue converter), one or more binary outputs allowing stepwise changes in gain, or a digital interface allowing the microprocessor-based measurement system <NUM> to set the gain in the adjustable amplifier <NUM>. The signal connected to the input of the second channel CH2 of the analogue-to-digital converter <NUM> is also used (in addition to short-circuit detection) to roughly determine the coil current when, for the actual gain of the adjustable amplifier <NUM>, the signal supplied to the input of the third channel CH3 of the analogue-to-digital converter <NUM> exceeds its measurement range (this situation may occur, for example, after the coil <NUM> has been replaced by a coil of a higher power) and the measurements for the second channel CH2 are used to calculate the new gain setting of the adjustable amplifier <NUM>. The optimum gain of the adjustable amplifier <NUM> should be such that the signal at the input of the third channel CH3 of the analogue-to-digital converter <NUM> (after the current of the coil <NUM> has stabilised) is approximately <NUM>% of the measurement range of the third channel CH3 of the analogue-to-digital converter <NUM>. The remaining <NUM>% (i.e. the interval from <NUM>-<NUM>%) of the measurement range of the analogue-to-digital converter <NUM> is the measurement margin for a possible increase in the coil current, resulting from changes in supply voltage or from changes in coil or ambient temperature. The adjustable amplifier <NUM> has at least as many possible gain levels that, for the intended range of currents of the coils <NUM>, the signal at the input of the third channel CH3 of the analogue-to-digital converter <NUM>, after stabilisation, has a value in the range from an adopted threshold minimum value LIMIT-MIN to a threshold maximum value LIMIT-MAX, for example equal to about <NUM>% of the measurement range of the analogue-to-digital converter <NUM>. The minimum value LIMIT-MIN should be greater than the limit of the possibility of correct switching detection, for example <NUM>% of the measurement range of the analogue-to-digital converter <NUM>. It is preferable to use such adjustable amplifier <NUM> that will allow the gain to be set so that, irrespective of the coil connected to the system, the signal at the input CH3 of the analogue-to-digital converter <NUM>, after stabilisation of the current of the coil <NUM>, is as close as possible to <NUM>% of the measurement range of the analogue-to-digital converter <NUM>.

The of <NUM>% for the range for LIMIT-MIN and <NUM>% for the range for LIMIT-MAX are to be regarded, as preferable, wherein other embodiments are also possible within the scope of this invention, wherein the LIMIT-MIN value is equal to <NUM>% or <NUM>% and the LIMIT-MAX value is equal to <NUM>% or <NUM>%.

If the signal at the input of the third channel CH3 of the analogue-to-digital converter <NUM> exceeds <NUM>% after stabilisation, the microprocessor-based measurement system <NUM> reduces the gain of the adjustable amplifier <NUM> using the gain signal output GAIN. If the signal at the input CH3 of the analogue-to-digital converter <NUM> is below the LIMIT-MIN value after stabilisation, the microprocessor-based measurement system <NUM> increases the gain of the adjustable amplifier <NUM> using the gain signal output GAIN.

The microprocessor-based measurement system <NUM> further comprises an input/output interface <NUM> connected to an input/output controller <NUM>. Via the input/output interface <NUM>, the user can manually configure the parameters (e.g. gain) for the coil of the solenoid valve with which the device will cooperate - this is particularly useful as the device performs a gain adjustment when first powered up with a new coil, which involves switching on the solenoid valve twice in a short time. Such action may not be advisable for the machine in which the solenoid valve operates. Furthermore, the user can set some specific parameters, such as the thresholds, for which the algorithm checks the successive conditions for switching on the solenoid valve.

<FIG> shows an example of signal waveforms in a situation when a coil having a much higher power (higher current) is connected to the system as compared to the coil that was connected during the previous switch-on cycle. The microprocessor-based measurement system <NUM>, having received a command, via the IO-Link interface, to switch on the solenoid valve, sets the power supply control output OUT to a high state H, which causes the power supply switching transistor <NUM> to switch on and a current to flow through the coil, wherein said current causes a voltage drop at the measurement resistor <NUM> (voltage at point 100C) proportional to the coil current. The voltage at point 100C, after filtering out interferences in the low-pass filter <NUM>, is supplied to the input of the second channel CH2 of the analogue-to-digital converter <NUM>, and to the input of the adjustable amplifier <NUM>, while the signal from the amplifier is supplied to the input of the third channel CH3 of the analogue-to-digital converter <NUM>. Because of a high gain set in the adjustable amplifier <NUM>, the signal at the input of the third channel CH3 at a certain moment exceeds the measurement range of the analogue-to-digital converter <NUM> and of the microprocessor-based measurement system <NUM>. If such situation is detected, the device monitors the signal from the input of the second channel CH2 and waits for it to stabilise. When the signal of the second channel CH2 stabilises, the microprocessor-based measurement system <NUM> measures it and, based on the measurement, calculates and sets the gain of the adjustable amplifier <NUM>, stores the gain setting in non-volatile memory and switches off the coil power supply by setting the power supply control output OUT to a low state L. When the signal at the input of the third channel CH3 falls to about <NUM> V, the microprocessor-based measurement system <NUM> switches the power supply to the coil <NUM> again by setting the power control output OUT to a high state H which switches on the power supply switching transistor <NUM> and makes the current flow through the coil and through the measurement resistor <NUM> at which the voltage drop is proportional to the current, this voltage is supplied to the low-pass filter <NUM> and then to the input of the second channel CH2 of the analogue-to-digital converter <NUM> and to the input of the adjustable amplifier <NUM> which now has a new lower gain value set. The amplified signal from the amplifier is supplied to the input of the third channel CH3 of the ADC converter <NUM>.

<FIG> shows a signal waveform in a situation when a coil having a much lower power (lower current) is connected to the system as compared to the coil that was connected during the previous switch-on. The microprocessor-based measurement system <NUM>, having received a command, via the IO-Link interface, to switch on the solenoid valve, sets the power supply control output OUT to a high state H, which causes the power supply switching transistor <NUM> to switch on and a current to flow through the coil, said current causing a voltage drop at the measurement resistor <NUM> (voltage at point 100C) proportional to the current. This voltage, after filtering out interferences in the low-pass filter <NUM>, is supplied to the input of the second channel CH2 of the analogue-to-digital converter <NUM>, and to the input of the adjustable amplifier <NUM>, and then the signal from the amplifier is supplied to the input of the third channel CH3 of the analogue-to-digital converter <NUM>. Because the gain at the amplifier <NUM> is set low, the signal at the input of the third channel CH3, once stabilised, is below the lower limit LIMIT-MIN, which indicates the need to increase the gain on the amplifier <NUM>. The microprocessor-based measurement system <NUM> measures it and uses the measured value to calculate the new gain value, then sets the new gain of the adjustable amplifier <NUM>, and stores the gain setting in a non-volatile memory and switches off the coil power supply by setting the power control output OUT to a low state L. When the signal at the input of the third channel CH3 falls to about <NUM> V, the microprocessor-based measurement system <NUM> switches the power supply to the coil again by setting the power control output OUT to a high state H, which switches on the power supply switching transistor <NUM> and makes the current flow through the coil and through the measurement resistor <NUM> at which the voltage drop is proportional to the current. This voltage is supplied to the low-pass filter <NUM> and then to the input of the second channel CH2 of the analogue-to-digital converter <NUM> and to the input of the adjustable amplifier <NUM> which now has a new higher gain value set. The amplified signal from the amplifier is supplied to the input of the third channel CH3 of the analogue-to-digital converter <NUM>.

At the first start (for a brand-new device), the average value of the amplifier gain is set at the output of the gain signal GAIN and the power supply of the coil <NUM> is switched on. The static current of the coil measured in the second channel CH2 and the third channel CH3 by the analogue-to-digital converter <NUM> in a steady state after switching on is used to determine an optimal gain for the adjustable amplifier <NUM>, and a value of this gain is stored in the non-volatile memory of the microprocessor-based measurement system <NUM>. The gain, set autonomously in this way, allows the coil <NUM> current characteristics to be measured optimally over time, with successive starts (switching on the coil). If, during successive switch-ons, the static current of the coil is in the upper part of the measurement range (for example, above the value LIMIT-MAX equal to <NUM>% value of the measurement range) or in the lower part of the measurement range (for example, below the value LIMIT-MIN equal to <NUM>% value of the measurement range) of the analogue-to-digital converter <NUM> in the third channel CH3, the microcontroller corrects such a state by changing the value of the gain signal GAIN of the adjustable amplifier <NUM>, and the result of the correction, i.e. its new value of the gain signal GAIN, is stored in the non-volatile memory.

Such a mechanism allows coils to be replaced with the same type or a different type (coils with a different current consumption in a steady state, compatible with the mechanics and power plug of the solenoid valve coil) without the need for cumbersome maintenance involving entering new settings into the microcontroller memory for proper operation, although such functionality is provided 'externally' by the interface of the IO-link module integrated in the electronics package. Furthermore, coil replacement does not require physical changes to the electronics package nested in the coil power plug due to the fact that it does not require the need for different shunts in the coil current measurement system.

An example of a coil power plug structure is shown in <FIG>. The components of the system shown in <FIG> are mounted on a PCB <NUM> which is placed in a housing <NUM>, <NUM>.

<FIG> illustrates operation of an algorithm for assessment of a coil current. After switching on the power supply switching transistor <NUM> in step <NUM> (power supply signal OUT set to high state H), the algorithm waits until the signal at the input of the third channel CH3 of the analogue-to-digital converter <NUM> exceeds the minimum value threshold IMIN, beyond which, in step <NUM>, the slope of the current curve characteristics is examined. When the slope of the curve, represented by an angle α, is horizontal (i.e. the angle α equal to <NUM> or <NUM> degrees), the value I<NUM> of the signal at the input of the third channel CH3 is stored. Based on the value I<NUM>, the parameters considered in the following part of the algorithm (αMIN, ΔIL, IS) are calculated. Next, the algorithm examines whether the slope α will be smaller than the minimum slope αMIN and, when this is the case, proceeds to step <NUM>. In step <NUM>, the examination of the slope of the characteristics continues until the direction of the characteristics changes from a descending to an ascending one. From this point onwards, the increment of the signal value at the input of the third channel CH3 is checked. When it exceeds the increment limit ΔIL, the algorithm proceeds to step <NUM>. In step <NUM>, the algorithm waits for the current to stabilise, i.e. it checks whether the difference between the maximum and minimum current values, at the time of stabilisation TS from the last measurements was lower than the stabilisation value IS. When the current stabilisation is detected, the algorithm proceeds to step <NUM>, which indicates that the solenoid valve is correctly switched on. If the correct switch-on of the solenoid valve is not detected within the specified switch-on time Tz, for example <NUM>, i.e. if the time counted from step <NUM> to step <NUM> exceeds the exemplary <NUM> or step <NUM> is not reached, the system reports a failure of the solenoid valve.

Examples of values of parameters IMIN, αMIN, ΔIL, IS, TS and a method of calculating them based on value I<NUM> are given below. I<NUM> is specified as a percentage of the measurement range of the ADC converter. The calculated parameters (%) refer to the measurement range of the ADC converter: <MAT> <MAT> <MAT> <MAT> <MAT>.

Claim 1:
A device for monitoring operation of a solenoid valve, the device comprising:
- a circuit for supplying power to a coil (<NUM>) of a solenoid valve, comprising terminals (100A, 100B) connected in series with a power source, the terminals (100A, 100B) configured to be connected to the coil (<NUM>), a power supply switching transistor (<NUM>) and a measurement resistor (<NUM>);
- a microprocessor-based measurement (<NUM>) system configured to monitor supply current consumed by the coil (<NUM>) while the coil (<NUM>) is switched on, by measuring voltage at the measurement resistor (<NUM>), and to control the power supply switching transistor (<NUM>);
characterised in that:
- the microprocessor-based measurement system (<NUM>):
- comprises an analogue-to-digital converter (<NUM>) comprising a consumed current measurement channel (CH2) connected to the measurement resistor (<NUM>) and a consumed current amplified measurement channel (CH3) connected to the consumed current measurement channel (CH2) via an adjustable amplifier (<NUM>);
- and is configured to:
- switch off the power supply switching transistor (<NUM>) when a voltage having a value higher than a threshold value is detected on the consumed current measurement channel (CH2);
- control the gain (GAIN) of the adjustable amplifier (<NUM>) so that the signal at the input of the consumed current amplified measurement channel (CH3) is lower than the measurement range of this channel (CH3).