Detection system and metal continuous casting system

Abstract

The utility model relates to a detection system and a metal continuous casting system. The detection system monitors and / or controls liquid metal during a metal manufacturing process. The system includes an electromagnetic sensor with an excitation coil and a receiver, an AC current unit for energizing the excitation coil, a synchronization circuit, and a controller. The synchronization circuit includes an input terminal that receives an AC phase voltage from the three-phase power supply and outputs a pulse sequence having a pulse sequence frequency fP, fP = M * fAC, M is an integer and M > = 1, fAC is a frequency of an AC cycle associated with the AC phase voltage. The controller is configured to control the electromagnetic sensor in a batch mode including successive batch cycles, each batch cycle including a first time window to energize the excitation coil and acquire the response signal and a second time window to de-energize the excitation coil. The controller is configured to receive a sequence of pulses and start a first time window by selecting a pulse from the sequence of pulses for each batch cycle and triggering activation of the AC current unit with the selected pulse.

Description

Technical Field

[0001] The present disclosure relates to a detection system for monitoring and / or controlling liquid metal during a metal manufacturing process. More specifically, the present disclosure relates to a detection system including an electromagnetic sensor. Background Art

[0002] During a metal manufacturing process (e.g., continuous casting), electromagnetic sensors are typically used to detect certain parameters, such as the level of molten steel in a continuous caster mold or the flow rate of liquid steel flowing through the continuous caster mold.

[0003] Generally, an electromagnetic sensor for liquid metal detection includes an excitation coil for generating a magnetic field that interacts with the liquid metal being processed (e.g., liquid steel in a mold during continuous casting). An AC current source is used to power the excitation coil and generate a varying magnetic field. The magnetic field from the excitation coil induces eddy currents in the molten metal, which in turn changes the magnetic field. In fact, it is well known that eddy currents generate a secondary magnetic field that is opposite to the primary magnetic field that causes the eddy currents. The electromagnetic sensor includes a receiver for receiving one or more response signals, which typically includes at least one receiver coil, and these response signals reveal the magnetic field changes caused by the eddy currents in the liquid metal.

[0004] In the steel industry, electromagnetic sensors are used, for example, to determine the level of liquid metal (e.g., liquid steel) in a mold during continuous casting. In fact, the level of liquid metal is a critical parameter that needs to be carefully monitored and controlled to ensure the correct dimensions and quality of the final product.

[0005] Electromagnetic sensors are sensitive to detecting changes in the level of liquid metal in a continuous caster mold. In fact, when the metal level in the mold rises or falls, the magnetic field sensed by the receiver coil changes. Generally, before operating the electromagnetic sensor, calibration is performed to establish the relationship between the detected magnetic field changes and the level of liquid metal in the mold.

[0006] An example of an electromagnetic sensor is described in patent US8714234B2, where the sensor is located on the periphery of a continuous caster mold for measuring the level of molten metal during continuous casting. In this example, the electromagnetic sensor is at least partially surrounded by a water-cooled metal housing to be well isolated from the molten metal in the mold. In these embodiments, the AC current source for powering the excitation coil operates in the range between 400 Hz and 1500 Hz.

[0007] While electromagnetic sensors have proven to be valuable detectors for metal manufacturing processes, particularly due to their accuracy and non-intrusiveness, significant challenges remain. One issue with electromagnetic sensors is their susceptibility to external electromagnetic interference, such as electromagnetic interference (EMI). This EMI can originate from a variety of sources, including electrical equipment, motors, and power supplies located in the sensor's environment.

[0008] Due to these electromagnetic interferences, the accuracy of electromagnetic sensors will be reduced.

[0009] Thus, there is room for improvement in detection systems for monitoring and / or controlling liquid metal during metal manufacturing processes. Utility Model Content

[0010] An object of the present disclosure is to provide a detection system for monitoring and / or controlling liquid metal during a metal manufacturing process, wherein the effects of electromagnetic interference are reduced compared to known prior art detection systems, thereby improving detection accuracy.

[0011] The present invention is based at least in part on the inventors' observation that electromagnetic interference that disrupts a response signal detected by an electromagnetic sensor is primarily repetitive. In other words, electromagnetic interference can be interpreted as a signal with a repetitive pattern.

[0012] In fact, measurements performed using an electromagnetic sensor of the type described in, for example, US Pat. No. 8,714,234 B2 revealed the presence of an electromagnetic interference having a pattern that repeats at 300 Hz. The repetitive interference pattern also revealed the presence of harmonics at frequencies of 600, 1200 and 1500 Hz. This interference is believed to originate from the electrical equipment used during the casting process, for example, a DC drive for an EM crystallizer stirrer. In fact, such a DC drive for an EM crystallizer stirrer comprises a Graetz bridge for converting three-phase 50 Hz AC input power into DC output power. This DC power is not continuous, but appears at a fundamental frequency of 300 Hz, corresponding to six DC pulses generated per 50 Hz AC cycle. Therefore, an electromagnetic sensor that is geometrically close to the EM crystallizer stirrer will be affected by the 300 Hz electromagnetic interference pattern (which includes higher harmonics).

[0013] For example, if a typical frequency in the range of 1200 Hz to 1500 Hz is used to power the excitation coil of an electromagnetic sensor, especially the higher harmonics of 1200 Hz and 1500 Hz in the interference pattern will be detrimental to detecting small magnetic field changes with high accuracy.

[0014] refer to Figure 1, schematically shows detection problems encountered by an electromagnetic sensor for monitoring and / or controlling liquid metal during a metal manufacturing process. The electromagnetic sensor operates in a batch mode, in which the excitation coil is repeatedly energized and de-energized at a batch frequency f B Thus, the response signal of the sensor appears only during the energization period of the excitation coil. In Figure 1 the top panel, an example of an undisturbed response signal S U appearing when the excitation coil is excited is shown. In the middle panel, the observed electromagnetic interference EM DIS is shown as having a repeating interference pattern repeating at 300 Hz. As described above, this electromagnetic interference EM DIS is caused by an external device (such as an ES stirrer driver powered by a three-phase power supply), so the interference EM DIS persists even when the excitation coil is cut off. Throughout this disclosure, the interference pattern repeating at 300 Hz is also referred to as an interference signal DIS. As Figure 1 schematically shown, there are six interference patterns DIS in each AC cycle period P AC of the three-phase power supply powering the EM stirrer driver, that is, there are two interference patterns DIS for each pair of phase voltages V1-V2, V2-V3, and V3-V1 of the three-phase power supply. In the bottom panel, an undisturbed repeating signal S U and the sum of the electromagnetic interference EM DIS are shown, corresponding to the total signal present when the excitation coil is repeatedly turned on and off. As Figure 1 shown in the bottom panel of, when data acquisition is performed in batch mode, the total signal S U +EM DIS detected during these three subsequent acquisition time windows AW of each batch cycle is different between different batch cycles. This is because the batch period P B defining the delay time between the starts of two acquisition time windows AW is not necessarily a multiple of the interference period P DIS . Therefore, the start of the acquisition time window is out of phase with the interference signal DIS. These differences in interference between different batch cycles cannot be corrected, thus reducing the accuracy of the electromagnetic sensor.

[0015] To solve this problem, the inventors provide a novel detection system configured to fully consider the repetition and phase of the interference signal.

[0016] The appended independent claims define the invention. The dependent claims define advantageous embodiments.

[0017] The detection system according to the present disclosure is characterized in that it includes a synchronization circuit, the synchronization circuit including input terminals for receiving one or more AC phase voltages from a three-phase power supply, and wherein the synchronization circuit is configured to output a pulse sequence having a pulse sequence frequency f P of, where f P = M × f AC , and wherein M is an integer and M ≥ 1, and wherein f AC is the frequency of the AC cycle associated with the one or more AC phase voltages.

[0018] The detection system according to the present disclosure is further characterized in that it includes a controller configured to control an electromagnetic sensor in a batch mode including consecutive batch cycles, and wherein each batch processing cycle includes a first time window for energizing an excitation coil and acquiring one or more response signals and one or more second time windows for de-energizing the excitation coil. The controller is further configured to receive the pulse sequence from the synchronization circuit and start the first time window by selecting one pulse from the pulse sequence for each batch cycle and triggering the start of the AC current unit with the selected pulse.

[0019] Advantageously, by providing a synchronization circuit configured to output a pulse sequence having a pulse sequence frequency equal to or a multiple of the AC cycle frequency of, for example, the three-phase power supply used by the drive of an EM crystallizer stirrer, the energization of the excitation coil can be triggered by a selected pulse from the pulse sequence, i.e., the energization of the excitation coil will occur at the moment defined by the pulse in the pulse sequence. In this way, the time interval between the starts of consecutive first time windows is determined by the time interval between the selected pulses that trigger the energization of the excitation coil. In other words, the time interval between the starts of the first time windows is not determined, for example, by the internal clock of the microprocessor of the data acquisition system as is the case in conventional data acquisition systems.

[0020] By using a pulse selected from the pulse sequence to start the energization of the excitation coil, the start of the first time window will always occur at the same phase of the repetitive interference pattern. In fact, the pulses in the pulse sequence specify a given phase of the interference pattern. Since for each batch, the first time window always starts from the same phase of the interference pattern, the interference pattern always interferes with the useful non-interfered signal in the same way, i.e., it is a constant alteration that is invariant between different batches. This allows for better compensation or correction of the detected signal. In this way, the detection system according to the present disclosure can detect magnetic field changes caused by eddy current variations more accurately compared to a detection system that does not have the synchronization circuit and controller claimed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These aspects and further aspects of the present disclosure will be explained in more detail by way of example and with reference to the accompanying drawings, in which:

[0022] Figure 1 Schematically shows the problems observed in electromagnetic sensors.

[0023] Figure 2 Schematically shows an example of a detection system according to the present disclosure,

[0024] Figure 3 Schematically shows an example of a detection system according to the present disclosure, which is located in an exemplary metal manufacturing plant having a continuous casting mold and an EM mold stirrer,

[0025] Figure 4 Schematically shows the principle of batch mode acquisition performed using an embodiment of the detection system according to the present disclosure,

[0026] Figure 5 Schematically shows the building blocks of a controller for controlling an electromagnetic sensor according to the present disclosure,

[0027] Figures 6 to 8 Schematically shows the principle of batch mode acquisition performed using an alternative embodiment of the detection system according to the present disclosure,

[0028] Figure 9 Schematically shows an exemplary embodiment of a synchronization circuit for outputting a pulse sequence from an AC phase voltage,

[0029] Figure 10 Shows the relationship with Figure 9 The variation of various voltage signals related to the shown synchronization circuit over time.

[0030] These drawings are neither drawn to scale nor in proportion. Generally, the same components are denoted by the same reference numerals in the drawings. Detailed Description

[0031] Detection System

[0032] According to the present disclosure, a detection system 1 for monitoring and / or controlling liquid metal during a metal manufacturing process is provided. Refer to Figure 2, schematically shows an example of an embodiment of a detection system 1 according to the present disclosure to illustrate the main building blocks. The main building blocks of the detection system 1 are an electromagnetic sensor 10 having an excitation coil 11 and a receiver, an AC current unit 15 for energizing the excitation coil 11, a synchronization circuit 20 configured to output a pulse sequence, and a controller 30 for controlling the AC current unit and acquiring one or more response signals from the receiver. Various embodiments of these building blocks of the detection system according to the present disclosure will be discussed in detail below.

[0033] To better illustrate the working principle of the detection system 1, Figure 3 shows a part of a metal continuous casting system, wherein the casting system includes a continuous casting machine mold 100 for receiving liquid metal 300, an EM mold stirrer 200 coupled to the mold 100, an EM stirrer driver 220 for driving the EM mold stirrer, and a three-phase power supply 250 for powering the driver 220. The three-phase power supply 250 has phase voltages V1, V2, and V3, for example, as Figure 3 schematically shown. In this example, the electromagnetic sensor 10 of the detection system is positioned around the exemplary mold 100. One or more response signals of the receiver of the electromagnetic sensor allow the determination of the liquid level of the liquid metal 300 in the continuous casting machine mold 100. In fact, since the distance between the electromagnetic sensor and the liquid metal changes depending on the liquid level of the liquid metal in the mold, the eddy currents generated in the liquid metal also change with the liquid level of the metal in the mold.

[0034] In an embodiment, the EM stirrer driver 220 is a DC driver. In other embodiments, the EM stirrer driver 220 is an AC driver.

[0035] The present disclosure is not limited to a specific type of electromagnetic sensor. The common feature of the electromagnetic sensors 10 according to the present disclosure is that they include an excitation coil 11 for generating a magnetic field that interacts with the liquid metal being processed and a receiver 12 configured to receive one or more response signals that reveal changes in the magnetic field caused by eddy currents induced in the liquid metal. As discussed above, the eddy currents generate an opposing magnetic field, thereby changing the magnetic field.

[0036] In an embodiment, the receiver 12 includes a receiving coil 12a, wherein a change in the magnetic field observed by the receiving coil causes a change in the voltage induced in the receiving coil 12a. Therefore, the response signal is typically interpreted as a voltage signal.

[0037] The excitation coil 11 is powered by an AC current unit 15 configured to supply an AC current. In an embodiment, an alternating current having a frequency range between 400 and 1600 Hz is provided. In an embodiment, the AC current is, for example, 4 A. The AC current unit 15 includes interfaces for receiving a start trigger signal and a stop trigger signal for respectively starting and stopping energizing the excitation coil. This enables the controller 30 to operate the electromagnetic sensor 10 in a batch mode as will be discussed in more detail below. The overall advantage of using the batch processing operation mode is that it helps avoid overheating of the excitation coil of the electromagnetic sensor.

[0038] In an embodiment, an electromagnetic sensor is used, wherein the frequency of the AC current powering the excitation coil is much higher and is in the range of, for example, 5 kHz to 50 kHz.

[0039] An example of an electromagnetic sensor for measuring the level of liquid metal in a continuous casting machine mold during continuous casting is described in patent US8714234B2, and such an electromagnetic sensor is also schematically shown in Figure 2 In this embodiment, the receiver 12 includes a first receiving coil 12a and a second receiving coil 12b superimposed on the first receiving coil. The first receiving coil and the second receiving coil respectively receive a first response signal R1 and a second response signal R2. In Figure 3 the configuration shown, the first receiving coil and the second receiving coil may also be referred to as a lower receiving coil and an upper receiving coil, respectively. The lower receiving coil is positioned closer to the metal surface in the mold compared to the upper receiving coil. In this way, due to the difference in the positions of the first receiving coil and the second receiving coil relative to the metal in the mold, the induced voltages in the upper coil and the lower coil are different, and this difference allows, for example, determination of the level of liquid metal in the mold.

[0040] In embodiments where the receiver 12 includes a first receiving coil 12a and a second receiving coil 12b, the first receiving coil 12a and the second receiving coil 12b are electrically coupled within the receiver 12 to form a single response signal R indicative of the magnetic field difference observed by the two receiving coils. In these embodiments, the single response signal R is then received by the controller 30.

[0041] In other embodiments where the receiver 12 includes a first receiving coil 12a and a second receiving coil 12b, the corresponding first response signal R1 and second response signal R2 are both received and processed by the controller 30 to reveal the magnetic field changes caused by eddy currents in the liquid metal.

[0042] In an embodiment, the receiver 12 does not include a receiver coil, but instead includes, for example, a circuit configured to detect the voltage of the excitation coil 11. In these embodiments, this voltage of the excitation coil forms the response signal R. In fact, as discussed above, eddy currents generate a secondary magnetic field that changes the main magnetic field, and thus the voltage of the excitation coil will also be changed by the eddy currents.

[0043] In an embodiment, the electromagnetic sensor 10 includes a plurality of receivers, where each receiver includes at least one receiving coil. These plurality of receiving coils are located, for example, at different positions relative to the continuous casting machine mold.

[0044] Figure 3 The embodiment of the electromagnetic sensor schematically shown in is a so-called ledge sensor, i.e., a sensor located on the outer boundary of the continuous casting machine mold, typically near the mold edge. In other embodiments, the electromagnetic sensor is a so-called hanging sensor, where the sensor is located above the liquid metal. Generally speaking, the hanging sensor has an excitation coil that can operate at a higher frequency of 5 kHz and above.

[0045] As Figure 2 schematically shown, the detection system according to the present disclosure further includes a synchronization circuit 20, the synchronization circuit including input terminals for receiving one or more AC phase voltages V1, V2 from, for example, a three-phase power supply having an AC cycle frequency of 50 Hz or 60 Hz. The synchronization circuit 20 is configured to output a pulse sequence CLK having a pulse sequence frequency f P where f P = M × f AC , and where M is an integer and M ≥ 1, and where f AC is the frequency of the AC cycle associated with the one or more phase voltages received from the three-phase power supply.

[0046] In an embodiment, the pulse sequence CLK is a series of rectangular pulses or square pulses. As will be discussed in more detail below, the pulse sequence is used to control the timing of energizing the excitation coil 11 and starting to acquire the response data obtained using the electromagnetic sensor.

[0047] Since the frequency of the pulse sequence is equal to or a multiple of the frequency of the AC cycle associated with one or more AC phase voltages V1, V2, V3, one or more pulses are output per AC cycle, and each pulse output per AC cycle defines a phase of the AC cycle. Preferably, more than one pulse is output per AC cycle. If two pulses are output per AC cycle, for example, a 50 Hz AC cycle outputs a 100 Hz pulse sequence or a 60 Hz AC cycle outputs a 120 Hz pulse sequence, the phases of these two pulses are separated by 180°. The rising edges of the first pulse and the second pulse can, for example, specify phases of 60° and 240° relative to the first AC voltage V1 of the three-phase power supply, respectively. Alternatively, the falling edges of the first pulse and the second pulse can, for example, define phases of 180° and 0°, respectively.

[0048] The frequency of the pulse sequence should be interpreted as a fixed frequency. Since the pulse sequence has a fixed frequency equal to or a multiple of the AC cycle frequency, the phase of the AC cycle specified by the pulses output per AC cycle is the same as the phase specified by the pulses output during subsequent AC cycles.

[0049] In an embodiment, the pulse sequence CLK includes pulses specifying phases of 0° and / or 180° of the AC cycle relative to the received phase voltages V1, V2, V3, for example. In other embodiments, the pulses in the pulse sequence specify phases different from 0° and different from 180°. In other words, as further outlined below, the exact value of the phase specified by the pulse sequence is not important. What is important is that the pulse frequency is equal to or a multiple of the AC cycle frequency so that the pulses observed within subsequent AC cycles can specify the same phase as the AC cycle.

[0050] Since, for example Figure 1 the electromagnetic interference EM shown in the middle panel DIS is related to the AC cycle frequency (which is related to the phase voltage), more precisely, the interference signal DIS is a signal that repeats at a frequency equal to 6 times the AC cycle frequency. Therefore, the phase specified by the pulses in the pulse sequence also specifies the starting point or phase of the interference signal.

[0051] The detection system 1 according to the present disclosure includes a controller 30 configured to control the electromagnetic sensor 10 in a batch mode including consecutive batch cycles. Each batch cycle includes a first time window AW in which the excitation coil 11 is energized and one or more response signals R, R1, R2 are acquired, and one or more second time windows DW in which the excitation coil 11 is de-energized.

[0052] The first time window AW can also be referred to as the acquisition time window because, as the name implies, data acquisition is performed when the electromagnetic sensor is turned on (i.e., when the excitation coil is energized). In the specification, the two terms, the first time window and the acquisition time window, will be used interchangeably. The second time window DW can also be referred to as the delay time window.

[0053] Energizing the excitation coil 11 should be understood as sending an AC current flowing through the excitation coil to generate a changing magnetic field. De-energizing the excitation coil should be understood as stopping the sending of the AC current flowing through the excitation coil so that the excitation coil no longer generates a magnetic field.

[0054] Reference Figure 3 to the reference numeral 50 in B illustrates schematically the operation in the batch mode of the batch frequency f B Three batch cycles are shown in this example, and the period P of each batch cycle

[0055] During the first time window AW when the excitation coil is energized, the response signal from the electromagnetic sensor and the interference signal are acquired.

[0056] In an embodiment, during the second time window DW, data acquisition stops. Generally, the second time window DW is used for data processing and / or reading out data.

[0057] In an embodiment, in each batch cycle, multiple delay time windows DW for de-energizing the excitation coil can be used for different purposes. For example, the first delay time window DW can be used for data processing of the acquired data, the second delay time window DW can be used for acquiring the interference signal, and the third delay time window can be used for processing the interference signal.

[0058] The controller 30 according to the present disclosure is further configured to start the first time window AW by performing the following steps for each batch cycle: select a pulse from the pulse sequence CLK and use the selected pulse to trigger the start of the AC current unit 15. As a result of triggering the start of the AC current unit 15, the excitation coil will be energized.

[0059] Therefore, for each batch cycle, one pulse in the pulse sequence will be selected to trigger the start of the AC current unit. By performing the batch processing operation in this way, the first time window AW is always triggered by a pulse in the pulse sequence, and for each batch cycle, the acquisition time window AW starts in phase with the interference signal. In other words, the start of the first time window is not determined by, for example, the internal clock of the controller (as is usually the case in a conventional data acquisition system), but is triggered by a pulse sequence output by a dedicated synchronization circuit.

[0060] Advantageously, by triggering the AC current unit using the pulses in the pulse sequence for each acquisition time window, the interference signal or partial interference signal observed during the acquisition time window is the same for each subsequent acquisition time window, which helps to correct the acquired signal for repetitive interference signals. This is important especially when the excitation coil operates in the frequency range of 400 to 1500 kHz, i.e., in the frequency range where harmonics of the interference signal appear, and thus it becomes very difficult to filter out the interference signal. However, an electromagnetic sensor having an excitation coil operating in a higher frequency range (e.g., above 5 kHz as described above) can also utilize the control techniques herein to reduce the harmful effects of EM interference.

[0061] In an embodiment, the controller 30 is configured to trigger a start signal for starting to acquire one or more response signals R, R1, R2, and this triggering of the start signal for starting the acquisition is synchronized with the triggering of the AC current unit 15 to start energizing the excitation coil 11.

[0062] However, in an embodiment, there may be a fixed delay between the triggering of the start signal for starting to acquire one or more response signals and the effective start of the acquisition. For example, this enables the electromagnetic sensor to stabilize before the effective start of the acquisition. But since this delay is constant, for each batch cycle, the effective start of the acquisition always starts from the same phase of the interference signal.

[0063] In an embodiment, the duration of the first time window AW is specified by a predefined time period, and the controller 30 includes an internal clock for controlling when the predefined time period has elapsed.

[0064] In an embodiment, the controller 30 is further configured to stop the first time window AW by performing the following steps for each batch cycle: monitoring the passage of time since the start of the first time window AW, and if the predefined time period has elapsed, triggering the stop of the AC current unit 15 to stop energizing the excitation coil.

[0065] In an embodiment, the predefined time period can be a configurable value. This value can be a parameter stored in the memory of the controller.

[0066] The predefined time period defining the duration of the first time window is typically specified to be equal to K × 1 / f C , where K is an integer and K ≥ 1, preferably K ≥ 2, more preferably K ≥ 3, and where f C corresponds to the AC excitation frequency for energizing the excitation coil 11. In other words, the predefined value is specified to cover the number of AC cycles for powering the excitation coil.

[0067] In an embodiment, the controller 30 is configured to trigger a stop signal for stopping the acquisition of one or more response signals. This triggering of the stop signal for stopping the acquisition is synchronized with the triggering of the stop of the AC unit. In this way, unnecessary background signals will not be continuously acquired after the excitation coil is de-energized.

[0068] As discussed above, each batch cycle selects one pulse of the pulse sequence to trigger the start of the AC current unit. Which pulses are selected from the pulse sequence to trigger the energization of the excitation coil depends on the batch frequency f B . In fact, if, for example, the pulse frequency in the pulse sequence is higher than the batch frequency, then multiple pulses will occur within one batch cycle. Therefore, for each batch cycle, some pulses of the pulse sequence need to be skipped because each batch cycle only requires one pulse to start the acquisition time window for acquiring one or more response signals. What the batch frequency actually is depends on the detailed implementation of the detection system, such as the speed of the CPU of the controller, which determines how much time should be reserved between two first time windows. Various embodiments regarding how to select pulses will be discussed below when discussing the detailed embodiments of the controller.

[0069] Further discuss the detailed embodiments of two important components (i.e., the controller and the synchronization circuit) of the electromagnetic detection system according to the present disclosure.

[0070] Embodiment of a controller operating at a fixed batch frequency

[0071] Two main types of embodiment categories of the controller according to the present disclosure can be distinguished. The difference between these two categories is related to the way of selecting pulses from the pulse sequence to use the pulses to trigger the energization of the excitation coil.

[0072] The first type of controller is configured to control the electromagnetic sensor 10 in batch mode, where the batch cycle repeats at a fixed batch frequency. The fixed batch frequency means that the batch frequency remains constant during the operation of the detection system.

[0073] In these embodiments of the first type, the step of the controller selecting one pulse from the pulse sequence CLK for each batch cycle includes the following sub-steps: detecting the pulse that first arrives since the start of the new batch cycle and selecting the first-arriving pulse to trigger the start of the AC current unit. The first-arriving pulse should be interpreted as the pulse that arrives first in time since the start of the new batch processing cycle.

[0074] In some embodiments of the first type, the control of the fixed batch frequency is independent of the frequency of the pulse sequence CLK. In an embodiment, the controller includes, for example, a microcontroller that controls the batch frequency with a fixed predetermined value, independent of the control of the pulse sequence frequency controlled by the synchronization circuit.

[0075] In embodiments of the first type, the batch frequency is controlled, for example, by the internal clock of the controller. In an embodiment, the batch frequency can be a configurable value. For example, the batch frequency can be set to 33.0 Hz, 50.0 Hz, 66.66 Hz, or any other selected value. What frequency to use will depend largely on the time required to process data between two consecutive acquisition time windows and thus will depend largely on the type of microprocessor used for data acquisition.

[0076] Reference Figure 4 , further discussion is made of the operation of the batch mode according to an embodiment of the controller 30 of the first type. In Figure 4 the example shown, a batch cycle is executed at a batch frequency f B corresponding to 66.66 Hz for a batch period P B of 15 ms. The top panel shows the undisturbed signal S U that appears each time the excitation coil is energized. The panel below the undisturbed signal shows the electromagnetic interference EM DIS that is always present as discussed above. However, the electromagnetic interference DIS exhibits a repeating pattern, called the interference signal DIS, which in this example repeats at 300 Hz. As previously mentioned, this corresponds to the interference expected to be generated by a DC drive of an EM stirrer powered, for example, by a 50 Hz three-phase power supply. If the power supply is a 60 Hz power supply, then the interference signal will repeat at a frequency of 360 Hz. In the panel below the electromagnetic interference EM DIS , the signal from the receiver of the electromagnetic sensor acquired using the controller 30 is shown. The acquired signal S U +DIS is the sum of the undisturbed signal S U and at least a portion of the interference signal DIS. Note that the period AW of the acquisition time window is generally not equal to the period P DIS of the interference signal, and thus only a portion of the interference signal DIS is typically acquired during the acquisition time window AW. When the reference indication S U +DIS is used in the figure to indicate the signal acquired during the acquisition time window AW, it should be interpreted as the sum of the undisturbed signal S U and the corresponding portion of the interference signal DIS observed in the time window AW.

[0077] Figure 4 The bottom panel of P shows the pulse sequence CLK, which in this example has a pulse frequency f U of 100 Hz. The acquired signal S U +DIS is acquired during the first time window AW of each batch cycle. As mentioned above, the first time window AW is the time window during which the excitation coil is energized and data acquisition of the response signal is performed. AsFigure 4 As shown, the start of the acquisition time window AW is triggered by a selected pulse in the pulse sequence. In this example, the trigger is based on the rising edge of a pulse in the pulse sequence.

[0078] The use of a first type of controller to select the pulse in the pulse sequence for triggering the start of the first time window AW is further discussed. Refer to Figure 4 , for the first batch processing cycle shown, the first time window starts, for example, at time zero and stops after a certain number of excitation cycles of the excitation coil (after four excitation cycles in this example). In this example, the excitation frequency of the excitation coil is 1350 Hz, resulting in a time period of 2.96 ms for the first time window AW. After the first time window AW is a second time window DW-P, during which the data acquired during the first time window AW is processed. This processing time window DW-P is a fixed time period defined by the processing time required to process the data. In this example, the time window DW-P for processing the acquired signal is set to approximately 6 ms. To end the 15 ms batch cycle P B , a delay time window DW-D of approximately 6 ms is also required. Note that according to the first type of controller 30, the batch cycle has a fixed period P B , and in this example, although a new cycle of the repetitive interference pattern DIS starts at the 10 ms mark, given the 15 ms fixed batch cycle, a new acquisition time window AW cannot start. When the first batch cycle ends, the second batch cycle starts, and the controller 30 continues to monitor the pulse sequence CLK and selects the first pulse received since the start of the second batch. In this example, a time period (5 ms in this example) has elapsed before the first pulse arrives, so the second batch cycle starts with a delay time window DW-D of 5 ms. After the rising edge of the first pulse received since the start of the second batch cycle, the first time window AW for data acquisition starts again, lasting for a time period of 2.96 ms. Thereafter, the response signal acquired during the first time window AW of the second batch cycle is processed during the time window DW-P of the second batch cycle, which also requires approximately 6 ms. To end the second batch cycle exactly at 15 ms, a delay time window DW-D of approximately 1 ms is also required. After the second batch cycle is completed, the third batch cycle starts. In this example, the third batch cycle starts immediately with the first time window AW for acquiring response data because there is a pulse in the pulse sequence that arrives exactly at the moment the third batch starts (i.e., at 30 ms).

[0079] As Figure 4As shown, as a result of the steps performed when the controller starts the first time window AW (i.e., starts energizing the excitation coil and starts data acquisition), each of these three time windows AW for data acquisition starts in phase with the interference signal DIS, i.e., the interference signal, a part of which exists during the acquisition time window AW, is the same for each batch cycle.

[0080] As a result of the pulse selection mechanism discussed above, for an embodiment of the first type of controller 30, the predefined batch frequency f B must be selected to be lower than the frequency f of the pulse sequence P . What batch frequency to use in relation to the pulse frequency will be determined according to the duration required for performing, for example, the second time window of data processing.

[0081] For the first type of controller operating at a fixed predefined batch frequency and applying the pulse selection mechanism discussed above, another result is that the time interval between the starts of two consecutive first time windows is not necessarily constant, but is defined by the time interval between the selected pulses in the pulse sequence. For example, as Figure 4 schematically shown, the time interval between the starts of the first and second acquisition time windows AW is 20 ms, and the time interval between the starts of the second and third acquisition time windows AW is 10 ms. For data reading / output and data processing, the exact position of the first window within the batch cycle is not important because there is sufficient time within the batch cycle to perform data processing. What is important is that for each batch cycle, the start of the first time window AW is triggered by a pulse in the pulse sequence such that each first time window starts from the same phase of the interference signal.

[0082] Referring to Figure 5 , an exemplary embodiment of the controller 30 is schematically shown. In this example, the controller 30 includes: a signal conditioning unit 34 for initially shaping one or more response signals; an analog-to-digital converter ADC 36; a microcontroller 38; and a trigger control unit 39 configured to receive pulses from the pulse sequence and control the selection of the pulses in the pulse sequence for triggering the excitation coil. The optional signal conditioning unit 34 is used to shape the response signals ready to be received by the ADC. Generally, the signal conditioning unit includes a signal amplifier.

[0083] Figure 5 The shown embodiment of the controller 30 is configured to receive one response signal R from the receiver 12, where, as discussed above, the signal R reveals the change in the magnetic field caused by the eddy currents in the liquid metal.

[0084] In other embodiments, also discussed above, the receiver 12 outputs two response signals R1 and R2, and the combination of these two signals reveals the change in the magnetic field caused by the eddy current. For these embodiments, the controller is configured to receive these two response signals R1 and R2. This is Figure 5 schematically illustrated in, where the dashed arrow indicates an embodiment having a second input that receives, in addition to the first response signal R1, a second response signal R2.

[0085] In embodiments where the controller receives two response signals R1 and R2, the controller includes, for example, two ADCs, and the acquisition of both signals R1 and R2 is performed during a first time window AW, as discussed above.

[0086] In Figure 5 the embodiment shown, the trigger control unit 39 generates a first trigger signal S-C from a pulse selected from the pulse sequence and sends the first trigger signal S-C to the AC current unit 15 to start energizing the excitation coil.

[0087] When a predefined time has elapsed since the start of the first time window AW (i.e., since the start of triggering the AC current unit to energize the excitation coil), the microcontroller 38 generates a second trigger signal STP-C and sends the second trigger signal STP-C to the AC current unit 15 to stop energizing the excitation coil.

[0088] As Figure 5 further shown, sampling of data is started by sending a trigger signal S-A to the ADC 36, and the acquisition of the response data starts synchronously with the energization of the excitation coil. When a predefined time for data acquisition has passed, the microcontroller sends a trigger signal STP-A to the ADC 36 to stop sampling the data.

[0089] The microcontroller 38 can be, for example, a DSP (Digital Signal Processor), which is a specialized form of microcontroller. The architecture and configuration of a DSP are typically optimized for real-time digital signal processing. Generally, a DSP contains on-board volatile and non-volatile memory and provides a range of peripheral interfaces.

[0090] In Figure 5In the illustrated embodiment, the controller 30 belongs to the first type as discussed above, and the microcontroller 38 controls the batch frequency. In this example, when one batch cycle ends and a new batch cycle begins, the microcontroller 38 sends a trigger request signal TR to the trigger control unit 39, thereby requesting to select the first pulse in the pulse sequence after this request. The trigger control unit 39 receiving the pulse sequence CLK then selects the pulse that is first received in the pulse sequence after receiving the request signal TR. This first received pulse is selected as the pulse for energizing the excitation coil.

[0091] Generally, each pulse in the pulse sequence CLK includes a rising edge and a falling edge. In the embodiment, the trigger control unit 39 includes an edge detection circuit for detecting the rising edge or the falling edge of the selected pulse.

[0092] For example, in Figure 5 the illustrated embodiment, or based on the detected rising edge of the selected pulse or the detected falling edge of the selected pulse, the trigger control unit will generate two start signals. The first start signal S-C is used to trigger the excitation coil 11 to be energized using the AC current unit, while the second start signal S-A is used to start collecting one or more response signals by triggering the ADC 36. In the embodiment, a fixed delay line can be used to delay the start signal S-A relative to the start signal S-C, for example.

[0093] Embodiment of a controller operating at a batch frequency determined by the pulse sequence frequency

[0094] The second type of controller does not use a predefined batch frequency controlled by the internal clock of the controller like the first type of controller.

[0095] For the second type of embodiment, the controller 30 is configured to repeat batch cycles at a batch frequency f P determined by the frequency f B of the pulse sequence CLK, where f B = f P / N, where N is an integer and N ≥ 1. The step of selecting one pulse from the pulse sequence CLK that the controller performs for each batch cycle is carried out by selecting one pulse in the pulse sequence every N pulses.

[0096] Therefore, for the second type of embodiment, the batch period 1 / f B is defined as the time difference between N pulses, and the batch mode operates at a batch frequency f B = f P / N, where f P is the pulse frequency of the pulse sequence CLK.

[0097] The value of the number N will depend on the processing speed of the controller (e.g., the time required to process the data collected during the batch cycle) and the pulse frequency of the pulse sequence. In a preferred embodiment, N ≥ 2. This is preferred when operating at a pulse sequence frequency of 100 Hz or higher.

[0098] Reference Figure 6 、 Figure 7 and Figure 8 ,further discuss the operation of the second type of controller according to the present disclosure. In the top panel, continuous electromagnetic interference EM DIS is shown to have a repetitive interference signal DIS that repeats at 300 Hz. The middle panel shows the pulse sequence CLK, and the bottom panel shows the undisturbed response signal S U summed with the interference signal DIS collected within the acquisition time window AW. Figure 6 、 Figure 7 and Figure 8 The difference between these three embodiments shown is the clock frequencies of 100 Hz, 150 Hz, and 300 Hz respectively used for the pulse sequence. As discussed above, in these embodiments of the second type of controller, the batch cycle P B is proportional to the period of the pulse sequence. Figure 6 and Figure 7 show embodiments in which the batch frequency is equal to the frequency of the pulse sequence, while the batch cycle P Figure 8 in the embodiment shown in B is twice the pulse sequence period P P .

[0099] As discussed above, as a result of the steps performed as the first time window AW for data acquisition when the second type of controller starts, Figures 6 to 8 each time window AW for data acquisition shown in

[0100] starts in phase with the interference signal DIS. Figure 5 An embodiment of the controller 30 according to the second type is similar to the controller of the first type shown in, for example,

[0101] However, in the embodiments of the second type, when the batch cycle ends, the microcontroller 38 does not send a trigger request TR to the trigger control unit 39. Instead, the trigger control unit 39 includes circuitry that is configured to select one pulse from the pulse sequence every N pulses. After receiving every N pulses, the trigger control unit 39 is further configured to output a first trigger signal S-C to start the AC current unit and output a second trigger signal S-A to start the ADC 36 to begin sampling the response data.

[0102] In some embodiments, as described above, each batch cycle can have multiple delay time windows DW during which the excitation coil is de-energized, and these multiple delay times can be used for different purposes. For example, dedicated background delay time windows can be used to acquire interference signals.

[0103] In these embodiments, for each batch cycle, the controller is configured to select a second pulse from the pulse sequence and use this second pulse to trigger a start signal to start acquiring interference signals during the dedicated background delay time window.

[0104] The duration of the dedicated background delay time window can be specified by a predefined time period and is preferably set to be equal to the time period of the first time window AW, or alternatively set to be equal to the time period P of the interference signal. DIS The controller is further configured to trigger a stop signal to stop acquiring interference signals if the predefined time period has elapsed.

[0105] After acquiring the interference signals, a further delay time window DW-P is provided to process the acquired interference signals.

[0106] For the first type of controller discussed above, the controller will select the second pulse by selecting the first received pulse after the end of data processing during the delay time window DW-P, which is used to process the signals acquired during the acquisition time window AW. In these embodiments where interference signals are additionally acquired, compared to the embodiments where interference signals are not measured, the batch period P B is selected to be longer. Those skilled in the art will define the batch frequency by considering the various delay time windows required for acquiring and processing both response signals and interference signals.

[0107] For the second type of controller discussed above, the controller is configured to select a second pulse for starting to acquire interference signals by selecting one pulse from X pulses received after the pulse used to start the AC current unit has been selected. Wherein, X is an integer greater than or equal to one and X < N, where N is the integer that defines the batch frequency as f B = f P / N.

[0108] Those skilled in the art will define the values of X and N such that the batch period is long enough to include the various time windows for acquiring and processing response signals and interference signals.

[0109] Advantageously, by acquiring the interference signals, the interference signals can be subtracted from the response signals measured during the first time window AW.

[0110] Synchronization circuit embodiments

[0111] Those skilled in the art can envision various embodiments of a synchronization circuit that generates a pulse sequence based on an AC phase voltage input. Such a synchronization circuit 20 includes a voltage transformer 22 for step - down transforming the AC phase voltage to a lower AC voltage, and a rectifier circuit 24 coupled to the voltage transformer 22. And wherein, the rectifier circuit is configured to rectify the AC current and generate an analog voltage pulse synchronized with the AC cycle of the three - phase power supply. The synchronization circuit 20 further includes an output circuit 25, which is configured to generate a string of digital pulses synchronously with the analog voltage pulses generated by the rectifier circuit 24. This string of digital pulses forms a pulse sequence CLK.

[0112] In Figure 9 the illustrated embodiment, the synchronization circuit is configured to receive two phase voltages V1 and V2 at its input terminals. The synchronization circuit includes a voltage transformer 22 having a set of three transformer coils T1, T2, and T3 coupled in a so - called delta configuration. The secondary winding of each transformer coil forms three closed - loop circuits with corresponding resistors R1, R2, and R3. The rectifier circuit 24 shown in this example is a so - called three - phase bridge rectifier circuit for rectifying the current flowing through these three closed - loop circuits. To rectify the current, the rectifier circuit 24 includes an arrangement of six diodes D1 to D6, as Figure 9 shown. The rectified current forms a closed - loop circuit through resistor R4, capacitor C1, and resistor R5, so that the output voltage can be detected. The output voltage then passes through a voltage follower 26 acting as an isolation buffer, and finally the output voltage is converted into a square pulse by a comparator circuit 28. In Figure 9 the illustrated exemplary synchronization circuit 20, the values of resistors R1, R2, R3, R4, R5 are 50Ω, 50Ω, 50Ω, 10kΩ, 500kΩ respectively, and the value of capacitor C1 is 100nF.

[0113] Referring to Figure 10 shows the variations of various voltage signals over time related to the embodiment of the synchronization circuit shown in Figure 9 . The voltage V1 shown in the top panel is the first phase voltage received at the input terminals of the synchronization circuit, and I - 1 is the corresponding current flowing into the first voltage line. Figure 10 The second phase voltage V2 is not shown in AC , but the second phase voltage is a voltage that is phase - shifted 120° relative to the first phase voltage V1. The AC voltage V1 is received in an AC cycle with a period of P Figure 10 The voltage V - GB shown is the analog voltage associated with the rectifier circuit and corresponds to Figure 9 the voltage observed across transistor R4 shown in Figure 9The analog voltage signal measured at the output of the voltage follower 26 shown. And finally, the bottom panel shows the resulting clock signal CLK output by Figure 9 the comparator 28 shown.

[0114] Therefore, for Figure 9 the embodiment where the input terminal shown has two phase voltages, the frequency of the pulse sequence output by the synchronization circuit is twice the AC cycle frequency of the three-phase power supply. For example, for a power supply with an AC cycle of 50 Hz or 60 Hz at the input terminal, a 100 Hz pulse sequence or a 120 Hz pulse sequence will be generated. In Figure 9 the embodiment shown, these two pulses output per AC cycle specify one phase of the AC cycle. This is shown in Figure 9 where the rising edges of these two pulses specify the 160° and 240° phases relative to the phase voltage V1. And alternatively, the falling edges of these two pulses specify the 180° and 0° phases relative to the phase voltage V1 respectively. These falling edges or rising edges can be used to accurately define the trigger signal for starting the AC current circuit to energize the excitation coil.

[0115] In other embodiments, the pulse sequence can be generated based on the combination of a single-phase line and the ground wire. The ground wire can be, for example, the ground wire of a three-phase power supply with a ground wire.

[0116] In the embodiment where the synchronization circuit receives only one phase voltage and the ground voltage as inputs, the rectification circuit of the synchronization circuit can be configured to rectify only the positive voltage, for example, such that the frequency of the output pulse sequence is equal to the AC cycle frequency of the phase voltage, such as a 50 Hz or 60 Hz pulse sequence.

[0117] In a further embodiment, the input terminals are configured to receive the three phase lines of a three-phase power supply, and the synchronization circuit is configured to output a pulse sequence based on the three phase voltages V1, V2, and V3. In this way, the frequency of the output pulse sequence is six times the AC cycle frequency. For example, if the AC cycle frequency is 50 Hz, a 300 Hz pulse sequence CLK can be output, as shown in Figure 8 shown.

[0118] In the embodiment, the synchronization circuit includes a voltage transformer 22 having a set of three transformer coils T1, T2, and T3 coupled in a so-called star configuration. In these embodiments, the input terminals of the synchronization circuit are configured to receive the neutral voltage or the ground voltage in addition to receiving one or more phase voltages. In this star configuration, the three transformer coils T1, T2, and T3 of the voltage transformer 22 are connected to a common point through one of their respective ends, and this common point is connected to the neutral voltage or the ground voltage received at the input terminals of the synchronization circuit.

[0119] In an embodiment, the synchronization circuit 20 includes a phase shifter configured to shift the phase of a pulse sequence relative to the phase of an AC cycle of one or more phase voltages (i.e., relative to the AC cycle of a three-phase power supply supplying one or more phase voltages).

[0120] As discussed above, the pulses in the pulse sequence not only specify the phase of the AC cycle of one or more phase voltages, but also the phase of the interference signal DIS. By using a phase shifter, the phase of the pulse sequence can be selected such that the rising edge of the pulses in the pulse sequence occurs at the most appropriate moment to start the first time window AW, i.e., to start energizing the excitation coil 11 and start acquisition. More precisely, the phase of the pulse sequence can be selected to minimize the distortion of the undisturbed signal S U caused by the interference signal DIS. A person skilled in the art will select the required phase shift to minimize the influence of the interference signal on the undisturbed signal, for example by performing measurements with various phase shifts. Thus, by using a phase shifter, the rising edge of the pulses in the pulse sequence does not necessarily fall at, for example, the 0° phase of the interference signal DIS, as Figure 4 and Figures 6 to 8 schematically shown for the pulses, but the rising edge of the pulses can fall at any phase selected by the phase shifter. Adding such an optional phase shift circuit is advantageous, especially when the frequency of the excitation coil 11 is close to the frequency of one of the higher harmonics of the interference signal.

[0121] Thus, for embodiments where the synchronization circuit includes a phase shifter, not only does the acquisition time window AW start at the same phase of the repetitive interference pattern for each batch cycle (which is the case for all embodiments of the present disclosure), but additionally, by appropriately selecting the phase shift with the phase shifter, the distortion of the undisturbed signal caused by the interference signal is also minimized.

[0122] An embodiment of the synchronization circuit including a phase shifter is similar to the synchronization circuit shown in Figure 9 , except that the pulse sequence (which can be referred to as the first pulse sequence) output by the circuit shown in Figure 9 is received by the phase shifter, which outputs a second pulse sequence whose phase is offset relative to the first pulse sequence. Then, the second pulse sequence is received by the controller 30. Phase shift circuits or delay line circuits for generating phase shifts are known in the art. A phase shifter is a circuit that includes, for example, an operational amplifier configured to generate a phase shift.

[0123] Based on the teachings given above, a person skilled in the art can develop alternative embodiments of the synchronization circuit for outputting a pulse sequence based on one or more AC phase voltages received at its input.

[0124] Further, those skilled in the art will design a synchronization circuit to output a pulse sequence having a preferred pulse sequence frequency f P of the pulse sequence. To optimize the detection system, the frequency f of the pulse sequence can be specified relative to the frequency of the interference pattern P . For example, for a 50 Hz or 60 Hz three-phase power supply powering an EM stirrer driver, the interference patterns are patterns that repeat at frequencies of 300 Hz and 360 Hz respectively. For example, the frequency of the pulse sequence can be selected such that each pulse in the pulse sequence defines the same phase of the interference pattern. This helps in selecting the pulses for triggering the energization of the excitation coil. Thus, preferably, M is an integer equal to any one of: 1, 2, 3, or 6. By selecting the number M in this way, each pulse of the pulse sequence can define the same phase of the interference pattern DIS.

[0125] In a more preferred embodiment, M = 2. For example, this corresponds to the embodiment discussed above with reference to Figure 9 . In this way, the pulses in the pulse sequence not only define the same phase of the interference pattern, but the pulses also only relate to the interference pattern associated with one pair of AC phase voltages (e.g., V1 - V2) out of the three possible combinations of voltage pairs of the three-phase power supply. Since there may be slight differences between the interference patterns associated with each of these three pairs of phase voltages V1 - V2, V2 - V3, V3 - V1, selecting M = 2 is the optimum value.

[0126] The present disclosure has been described in terms of specific embodiments, which are illustrative of the present disclosure and should not be construed as restrictive. Those skilled in the art should understand that the present disclosure is not limited to what has been specifically shown and / or described, and alternative or modified embodiments can be developed in light of the overall teachings of the present disclosure. The described drawings are merely illustrative and not restrictive.

[0127] The use of the verb “comprise” and its corresponding variations does not exclude the presence of other elements in addition to the stated elements. The use of the articles “a”, “an” or “the” before an element does not exclude the presence of a plurality of such elements.

[0128] Also, the terms first, second, etc. in the description and claims are used to distinguish similar elements and not necessarily to describe an order in time, space, rank, or in any other way.

[0129] References to "an embodiment" or "embodiments" throughout the specification mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present disclosure. Thus, the phrases "in an embodiment" or "in embodiments" that appear throughout the specification do not necessarily all refer to the same embodiment, but may. Additionally, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner, which will be apparent to those of ordinary skill in the art from the present disclosure.

[0130] Reference numeral

[0131] 1 Detector 10 Electromagnetic sensor 11 Excitation coil 12 Receiver 12a First receiving coil 12b Second receiving coil 15 AC current unit 20 Synchronization circuit 21 Input terminal 22 Voltage transformer 24 Rectifier circuit 25 Output circuit 26 Voltage follower 28 Comparator circuit 30 Controller 34 Signal conditioning unit 36 ADC 38 Microcontroller 39 Trigger control unit 50 Batch data sequence 100 Continuous casting mold 200 EM stirrer 220 EM stirrer driver 250 Three-phase power supply 300 Liquid metal

Claims

1. A detection system (1) for monitoring and / or controlling liquid metal during a metal manufacturing process, the detection system comprising: · An electromagnetic sensor (10) having an excitation coil (11) configured to generate a magnetic field that interacts with the liquid metal being processed, and having a receiver (12) configured to detect one or more response signals (R, R1, R2), the response signals revealing magnetic field changes caused by eddy currents induced in the liquid metal. · An AC current unit (15) for energizing the excitation coil (11), and wherein the AC current unit is configured to receive a start trigger signal and a stop trigger signal for respectively starting and stopping energizing the excitation coil. Characterized in that the detection system further comprises: · A synchronization circuit (20), the synchronization circuit including input terminals (21) for receiving one or more AC phase voltages (V1, V2, V3) from a three-phase power supply, and wherein the synchronization circuit (20) is configured to output a pulse sequence CLK having a pulse sequence frequency f P where f P = M × f AC and wherein M is an integer and M ≥ 1, and wherein f AC is the frequency of the AC cycle associated with the one or more AC phase voltages · A controller (30) configured to control the electromagnetic sensor (10) in a batch mode including consecutive batch cycles, and wherein each batch cycle includes a first time window (AW) for energizing the excitation coil (11) and acquiring the one or more response signals (R, R1, R2), and one or more second time windows (DW, DW-P, DW-D) for de-energizing the excitation coil (11). And wherein the controller (30) is further configured to receive the pulse sequence CLK, and start the first time window (AW) by selecting one pulse from the pulse sequence CLK for each batch cycle and triggering the start of the AC current unit (15) with the selected pulse.

2. The detection system according to claim 1, wherein, The controller (30) is configured to trigger a start signal for starting the acquisition of the one or more response signals (R, R1, R2), and wherein the triggering of the start signal for starting the acquisition is synchronized with the triggering of the start of the AC current unit (15).

3. The detection system according to any one of claims 1-2, wherein, The duration of the first time window (AW) is specified by a predefined time period, and wherein the controller (30) includes an internal clock for controlling when the predefined time period has elapsed.

4. The detection system according to claim 3, wherein, The controller (30) is configured to stop the first time window (AW) by monitoring the passage of time since the start of the first time window (AW) for each batch cycle, and if the predefined time period has elapsed, trigger the stop of the AC current unit (15).

5. The detection system according to claim 4, wherein, The controller (30) is configured to trigger a stop signal for stopping the acquisition of the one or more response signals, and wherein the triggering of the stop signal for stopping the acquisition of the one or more response signals is synchronized with the triggering of the stop of the AC current unit.

6. The detection system according to claim 3, wherein, The predefined time period is designated to be equal to K×1 / f C , where K is an integer and K≥1, and where f C corresponds to the AC excitation frequency for energizing the excitation coil (11).

7. The detection system according to claim 6, wherein, K≥2。 8. The detection system according to claim 7, wherein, K≥3。 9. The detection system according to claim 6, wherein, Each pulse in the pulse sequence CLK includes a rising edge and a falling edge, and wherein the controller (30) includes a trigger control unit (39) configured to detect the rising edge or the falling edge of a pulse in the pulse sequence CLK.

10. The detection system according to claim 1, wherein, The synchronization circuit (20) includes: a voltage transformer (22) for step - down converting the received one or more AC phase voltages to a lower AC voltage; a rectification circuit (24) coupled to the voltage transformer (22) and configured to rectify the AC current and generate analog voltage pulses; and an output circuit (25) configured to generate a string of digital pulses synchronously with the analog voltage pulses generated by the rectification circuit (24), and wherein the string of digital pulses forms the pulse sequence CLK.

11. The detection system according to claim 10, wherein, The voltage transformer includes a set of three transformer coils coupled in a delta configuration or a star configuration.

12. The detection system according to claim 1, wherein, The controller (30) is configured to repeat the batch cycle at a fixed batch frequency, and wherein selecting one pulse from the pulse sequence CLK for each batch cycle includes: detecting the first - arriving pulse since the start of the new batch cycle and selecting the first - arriving pulse to trigger the start of the AC current unit.

13. The detection system according to claim 12, wherein, The fixed batch frequency is lower than the frequency of the pulse sequence CLK.

14. The detection system according to claim 13, wherein, The fixed batch frequency is in the range between 20 Hz and 150 Hz.

15. The detection system according to claim 14, wherein, The fixed batch frequency is in the range between 25 Hz and 100 Hz.

16. The detection system according to claim 1, wherein, The controller (30) is configured to generate a pulse sequence CLK at a frequency f P Determine the batch frequency f B Repeat the batch cycle, where f B =f P / N, wherein N is an integer and N≧1, and wherein the selecting a pulse from the pulse sequence CLK for each batch cycle is performed by selecting one pulse from the pulse sequence CLK for every N pulses.

17. The detection system according to claim 16, wherein, N≥2。 18. The detection system according to claim 1, wherein, The integer M is selected from any one of the following: 1, 2, 3, or 6.

19. The detection system according to claim 18, wherein, M＝2。 20. The detection system according to claim 1, wherein, The input terminals of the synchronization circuit are configured to receive two AC phase voltages from the three - phase power supply, and wherein the synchronization circuit is configured to generate the pulse sequence CLK based on the two AC phase voltages.

21. A metal continuous casting system, characterized in that, The metal continuous casting system includes: · a continuous casting machine mold (100) for receiving liquid metal (300), · an EM mold stirrer (200) coupled to the continuous casting machine mold (100), a driver (220) for driving the EM mold stirrer, and a three - phase power supply (250) for powering the driver (220), · a detection system according to any one of the preceding claims 1 - 20, wherein one or more phase voltage lines of the three - phase power supply (250) are connected to the input terminals (21) of the synchronization circuit (20).

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