JP4055946B2 - Electromagnetic induction heating cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic induction heating cooker that uses an inverter circuit to supply a high-frequency current to an induction heating coil to heat a cooking pan by electromagnetic induction, and is particularly mounted on a top plate on the upper surface of the induction heating coil. The present invention relates to a technique for determining the presence or absence of a pan.
[0002]
[Prior art]
FIG. 8 is an electrical connection diagram of a conventional electromagnetic induction heating cooker. In FIG. 8, 1 is a commercial power source, 2 is a rectifier circuit that rectifies the commercial power source 1, 10 is a smoothing circuit 3 that smoothes the output of the rectifier circuit 2 into a direct current, an induction heating coil 4, a resonant capacitor 4, and a bipolar transistor. And an inverter circuit having a switching element 6 having an antiparallel diode, 7 is an oscillation control unit for controlling on / off of the switching element 6, and 8 is a load for determining whether a load magnetically coupled to the induction heating coil 4 is appropriate or inappropriate. A detection device 9 is a switch for turning on and off the output signal of the load detection device 8 to the oscillation control unit 7.
[0003]
Normally, the user keeps the switch 9 closed. When the load is appropriate, no signal is output from the load detection device, the oscillation control unit 7 drives the switching element 6, and the switching element 6 is inductively heated. The coil 4 is energized to overheat the load. The load detection device 8 outputs a signal when the load is inappropriate such as a knife or fork placed incorrectly, and the oscillation control unit 7 stops oscillation to the switching element 6 and is not heated when the load is inappropriate.
[0004]
Next, a case where a load that is determined to be inappropriate by the load detection device 8, for example, a load having a small shape, is to be heated will be described. The user opens the switch 9. The load detection device 8 determines that the load is inappropriate and outputs a signal. However, since the switch 9 is open, the signal is not input to the oscillation control unit 7, the oscillation control unit 7 oscillates to the switching element 6, and the switching element 6 energizes the induction heating coil 4 to apply an inappropriate load. Heat. However, if the user forgets to close the switch 9 and keeps it open, the unsuitable load will be heated. (See Patent Document 1)
[0005]
The electromagnetic induction heating cooker of Prior Art 2 increases the output frequency of the inverter when the current exceeds the set value of the current setter, and the phase difference detection circuit that detects the phase difference between the output voltage and current of the inverter circuit. The current holding circuit that holds the current below the set value, the phase difference detection value and the phase difference set value of the phase difference setter are compared, and when the detected value is larger than the set value, the load container is a non-magnetic material Alternatively, a load determination circuit is provided that determines that there is no load and determines that the load container is a magnetic material when the detected value is equal to or less than a set value. However, when the output frequency of the inverter circuit increases, the accuracy of the phase difference detection value deteriorates.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-10947
[Problems to be solved by the invention]
In a conventional electromagnetic induction heating cooker, the placement of a pan or the like is electrically detected on the top plate, and when it is determined that there is no pan, a measure is taken to stop the output of the inverter for the purpose of preventing waste of power. It was. However, when cooking is performed with the power set value set to the minimum, there is a problem in the discrimination accuracy of the pot detection circuit shown below, and there is a problem that the output of the inverter circuit is stopped and cooking cannot be performed. Moreover, there existed a problem which discriminate | determined a small pan from having no pan by the difference in the magnitude | size of the diameter of a pan.
[0008]
[Means for Solving the Problems]
The invention of claim 1 includes resonant capacitors C2 and C3, an induction heating coil HL that forms a series resonance with the resonant capacitors C2 and C3, a rectifier circuit DR1 that rectifies a commercial AC power source and converts it into a DC voltage, An inverter circuit that supplies a high frequency current to the induction heating coil HL using the DC voltage of the rectifier circuit DR1 as an input, a power calculation circuit SA that calculates the input power of the inverter circuit and outputs a power calculation signal Sa, and a predetermined value. A power setting circuit PC that outputs the power setting signal Pc, a differential amplifier circuit CO that differentially amplifies the power calculation signal Sa and the power setting signal Pc, and the inverter circuit according to the differential amplification signal ΔI And detecting the phase difference between the output voltage Cv2 and the output current Ct2 of the inverter circuit. The phase difference detection circuit PD that outputs the difference detection signal Pd, and the pan is determined that the pan is not placed when the value of the phase difference detection signal Pd is larger than the value of the predetermined phase difference determination signal Pr. A pan detection circuit that outputs a non-detection signal Cp to stop the drive of the inverter drive circuit SD and stop the supply of the high-frequency current. The pan placed on the induction heating coil HL has an electromagnetic induction effect. When the output frequency of the inverter circuit is higher than a predetermined value of the frequency discrimination signal Fr, the operation of the pan detection circuit is stopped and the output frequency of the frequency discrimination signal Fr is An electromagnetic induction heating cooker comprising a frequency-compatible pan detection control circuit that operates the pan detection circuit when the value is lower than a value.
[0009]
The invention of claim 2 stops the operation of the pan detection circuit when the output current of the inverter circuit is smaller than a predetermined value of the current determination signal Er, and the output current is larger than the value of the current determination signal Er. 2. The electromagnetic induction heating cooker according to claim 1, wherein the current corresponding pan detection control circuit for operating the pan detection circuit is replaced with the frequency corresponding pan detection control circuit.
[0010]
The invention of claim 3 stops the operation of the pan detection circuit when the power setting signal Pc is smaller than a predetermined value of the power discrimination signal Pf, and the power setting signal Pc is greater than the value of the power discrimination signal Pf. 2. The electromagnetic induction heating cooker according to claim 1, wherein a power corresponding pot detection control circuit for operating the pot detection circuit when the size is large is replaced with the frequency corresponding pot detection control circuit.
[0011]
According to a fourth aspect of the present invention, when the pan no detection signal Cp of the pan detection circuit is input to the inverter drive circuit SD, the panless state is displayed by the indicator LED. The electromagnetic induction heating cooker of Claim 2 or Claim 3.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an electrical connection diagram of an electromagnetic induction heating cooker according to the present invention.
[0013]
In FIG. 1, the rectifier circuit DR1 rectifies the output of the commercial AC power source and converts it into a DC voltage, and the smoothing capacitor C1 smoothes the voltage converted into DC.
[0014]
The input current detection circuit ID detects an input current value and outputs an input current detection signal Id, and the input voltage detection circuit IV detects an input voltage value and outputs an input voltage detection signal Iv.
[0015]
The switching element TR1 and the switching element TR2 are switching elements that form a half-bridge type inverter circuit, and for example, MOSFETs or IGBTs are used. The induction heating coil HL forms a series resonance with the resonance capacitor C2 and the resonance capacitor C3. The pan PB is placed on the induction heating coil HL and heated by electromagnetic induction.
[0016]
The inverter drive circuit SD performs PFM control for modulating the pulse frequency with a constant pulse width ratio according to the value of the control processing signal Sc from the control arithmetic circuit SC, and alternately switches the switching element TR1 and the switching element TR2. The switching element drive signal Sd1 and the switching element drive signal Sd2 are output.
[0017]
The power calculation circuit SA inputs the input current detection signal Id and the input voltage detection signal Iv and calculates the input power of the inverter. The power setting circuit PC sets a predetermined power setting signal Pc.
[0018]
The differential amplifier circuit CO differentially amplifies the power setting signal Pc and the power calculation signal Sa, and outputs the value of the differential amplification signal ΔI. The control arithmetic circuit SC starts operation when a heating start signal Ts is input from the heating switch TS, performs an operation according to the value of the differential amplification signal ΔI, and when the value of the differential amplification signal ΔI is large. The value of the control processing signal Sc is decreased, and conversely, when the value of the differential amplification signal ΔI is small, the value of the control processing signal Sc is increased. Further, a predetermined phase difference setting value and a predetermined frequency setting value input by the operation panel OA are calculated, converted into a phase difference determination signal Pr and a frequency determination signal Fr, and output.
[0019]
When the value of the control processing calculation signal Sc input from the control calculation circuit SC is small, the inverter drive circuit SD increases the frequency of the PFM control to increase the impedance value of the resonance tank including the induction heating coil HL and the resonance capacitors C2 and C3. To increase the current flowing through the induction heating coil HL. On the contrary, when the value of the control calculation signal Sc is large, the current flowing through the induction heating coil HL is increased by lowering the frequency of the PFM control and decreasing the impedance value of the resonance tank to increase the current flowing through the induction heating coil HL. Perform current control. Further, when the output signal from the AND circuit AND becomes High level, the operation of the inverter drive circuit SD is stopped.
[0020]
The pan detection circuit is formed of a phase difference detection circuit PD and a comparison circuit CP. The comparison circuit CP compares the phase difference detection signal Pd with the phase difference determination signal Pr, and the phase difference detection signal Pd When it is larger than the phase difference determination signal Pr, it is determined that there is no pan and a pan non-detection signal Cp is output.
[0021]
The phase difference detection circuit PD is formed by the pulsing circuit PK and the phase difference / voltage conversion circuit PE shown in FIG. 2, and the pulsing circuit PK is a positive time of the output current detection signal Ct2 shown in FIG. The width is converted into a pulse signal Pk shown in FIG. The output voltage detection circuit CV2 performs half-wave rectification on the AC output voltage of an inverter circuit (not shown) and outputs an output voltage detection signal Cv2 shown in FIG. The phase difference / voltage conversion circuit PE detects the phase difference θ between the pulse signal Pk and the output voltage detection signal Cv2, converts this phase difference θ into a voltage, and outputs it as a phase difference detection signal Pd. When the value of the phase difference θ is large, the output voltage becomes high. Conversely, when the value of the phase difference θ is small, the output voltage becomes small.
[0022]
The frequency corresponding pan detection control circuit is formed by the frequency / voltage conversion circuit FV, the second comparison circuit CP2, and the AND circuit AND, and the frequency / voltage conversion circuit FV converts the frequency of the output voltage detection signal Cv2 into a voltage, When this frequency is high, the output voltage increases. Conversely, when the frequency is low, the output voltage decreases. The second comparison circuit CP2 compares the frequency / voltage conversion signal Fv with the frequency discrimination signal Fr, and when the frequency / voltage conversion signal Fv is larger than the frequency discrimination signal Fr, the pan detection control signal Cp2 is set to Low. Output as level. The AND circuit AND operates the inverter drive circuit SD regardless of the pan non-detection signal Cp when the pan detection control signal Cp2 becomes Low level.
[0023]
FIG. 3 is a waveform diagram for explaining the operation of the present invention. 3A shows the output voltage detection signal Cv2, and FIG. 3B shows the output current detection signal Ct2 when the pan PB is placed or not. 3 (C) shows the pulse signal Pk when the pan PB is not placed, FIG. 3 (D) shows the pulse signal Pk when the pan PB is placed, and FIG. E) shows the phase difference detection signal Pd when the pan PB is placed or not, and FIG. 3E shows when the pan PB is placed or placed. The frequency / voltage conversion signal Fv when not present is shown.
[0024]
Next, the operation for determining whether or not there is a pan on the top plate will be described with reference to the waveform diagram shown in FIG.
[0025]
First, when the power is set to a predetermined value that is normally used for the value of the power setting signal Pc and heating is performed without a pan, the pan detection circuit uses the phase difference / voltage conversion circuit PE to perform the operation shown in FIG. ) Of the output voltage detection signal Cv2 of FIG. 3 and the pulse signal Pk of FIG. 3C are detected. At this time, the value of the phase difference θ increases, and the phase difference θ is converted into a voltage and output as a phase difference detection signal Pd shown in FIG. The comparison circuit CP compares the phase difference detection signal Pd with the phase difference determination signal Pr, the phase difference detection signal Pd becomes larger than the phase difference determination signal Pr, and determines that there is no pan and no pan detection signal. Cp is set to High level and output to the AND circuit AND. In addition, by changing the value of the phase difference determination signal Pr from the operation panel, it is possible to determine that a conventional small pan is determined to have no pan as having a pan.
[0026]
The frequency / voltage conversion circuit FV of the frequency corresponding pan detection control circuit converts the frequency of the output voltage detection signal Cv2 into a voltage and outputs a frequency / voltage conversion signal Fv shown in FIG. At this time, the power setting signal Pc is set to the power to be normally used, and when heating without a pan, a current flows through the induction heating coil HL, and the frequency of the output voltage detection signal Cv2 becomes lower. The value of the voltage conversion signal Fv becomes small. The second comparison circuit CP2 compares the frequency / voltage conversion signal Fv with the frequency discrimination signal Fr, the frequency / voltage conversion signal Fv becomes smaller than the frequency discrimination signal Fr, and the pan detection control signal is set to High level. Output to the AND circuit AND. The AND circuit AND stops the operation of the inverter drive circuit SD by setting the output signal to a high level because the pan detection control signal Cp2 and the pan non-detection signal Cp are at a high level.
[0027]
When the value of the power setting signal Pc is set to the power to be used normally and heating is performed with a pan, the pan detection circuit detects the output voltage detection signal Cv2 of FIG. The phase difference θ shown in FIG. 3D with respect to the 3 (D) pulse signal Pk is detected. At this time, the value of the phase difference θ is smaller than that in the no pan state, and the phase difference detection signal Pd is smaller. The comparison circuit CP compares the phase difference detection signal Pd with the phase difference determination signal Pr, determines that the phase difference detection signal Pd is smaller than the phase difference determination signal Pr, and has a pan, and sets the pan no detection signal Cp to Low. The level is output to the AND circuit AND. In the AND circuit AND, when the panless detection signal Cp becomes low level, the output signal becomes low level, and the inverter drive circuit SD is operated. Further, the value of the phase difference θ varies depending on the size of the diameter of the pan PB, and the value of the phase difference θ increases when the diameter is small. From the above, depending on the value of the phase difference determination signal Pr, a pot having a small diameter may be determined as a no pan state. Further, in the present invention, the phase difference determination signal Pr is set to an optimum value by the operation panel OA, so that the pan having a small diameter can be determined as having a pan.
[0028]
When cooking is performed by setting the value of the power setting signal Pc to the minimum power consumption, the frequency of the output voltage and output current of the inverter circuit becomes very high. At this time, the value of the phase difference θ by the phase difference / voltage conversion circuit PE causes an error in the detection of the phase difference because the frequency of the output voltage and output current becomes very high. There is a problem with sex.
[0029]
When the value of the power setting signal Pc is set to the minimum operating power, the frequency corresponding pan detection control circuit increases the frequency of the output voltage detection signal Cv2 and increases the value of the frequency / voltage conversion signal Fv. The second comparison circuit CP2 compares the frequency / voltage conversion signal Fv with the frequency discrimination signal, the frequency / voltage conversion signal Fv becomes larger than the frequency discrimination signal, and the pan detection control signal is set to Low level. Output to AND. When the pan detection control signal Cp2 becomes low level, the AND circuit AND makes the output signal low level regardless of the pan non-detection signal Cp, and operates the inverter drive circuit SD. As described above, cooking is not stopped by the pan detection circuit even when cooking is performed with the power setting signal Pc set to the minimum power consumption. At this time, even if small items such as knives and forks are placed, it is the minimum power and cannot be heated.
[0030]
[Example 2]
FIG. 4 is an electrical connection diagram of the electromagnetic induction heating cooker according to the second embodiment. In the figure, the same reference numerals as those in the electrical connection diagram of the electromagnetic induction heating cooker of the present invention shown in FIG.
[0031]
The current corresponding pan detection control circuit is formed by a current holding circuit EP, a third comparison circuit CP3, and an AND circuit AND.
[0032]
The current holding circuit EP shown in FIG. 5 performs a peak hold operation constituted by the double-wave rectifier circuit WD, the amplifier circuit OP, the diode DR2, the capacitor C4, and the resistor R1. Both-wave rectifier circuit WD rectifies both-wave output current detection signal Ct2. The current holding circuit EP holds the highest signal value of the input signal at both ends of the capacitor C4, and discharges the charge of the capacitor C4 by a return resistor R1 for a predetermined time.
[0033]
FIG. 6 is a waveform diagram for explaining the operation of the second embodiment. 6A shows the output voltage detection signal Cv2, and FIG. 6B shows the output current detection signal Ct2 when the pan PB is placed or not. 6 (C) shows the pulse signal Pk when the pan PB is not placed, FIG. 6 (D) shows the pulse signal Pk when the pan PB is placed, and FIG. E) shows the phase difference detection signal Pd when the pan PB is placed or not, and FIG. 6E shows when the pan PB is placed or placed. The current holding signal Ep when not present is shown.
[0034]
First, when the value of the power setting signal Pc is set to the power to be used normally and heating is performed without the pan, the pan detection circuit uses the phase difference / voltage conversion circuit PE to display the phase difference shown in FIG. θ is detected. At this time, the value of the phase difference θ increases, and the phase difference θ is converted into a voltage and output as a phase difference detection signal Pd shown in FIG. The comparison circuit CP compares the phase difference detection signal Pd with the phase difference determination signal Pr, determines that the phase difference detection signal Pd is greater than the phase difference determination signal Pr and that there is no pan, and uses the pan no detection signal Cp. High level is output to the AND circuit AND.
[0035]
The current holding circuit EP of the current corresponding pan detection control circuit holds the peak current of the output current detection signal Ct2, and outputs a current holding signal Ep shown in FIG. At this time, when the electric power setting signal Pc is set to the electric power normally used and heating is performed without the pan, current flows through the induction heating coil HL and the current holding signal Ep is determined as shown in FIG. 6 (F). The third comparison circuit CP3 sets the pan detection control signal Cp3 to the High level and outputs it to the AND circuit AND. The AND circuit AND stops the operation of the inverter drive circuit SD because the pan detection control signal Cp3 and the pan non-detection signal Cp are at a high level because the output signal is at a high level.
[0036]
When the value of the power setting signal Pc is set to the power that is normally used and heating is performed with the pan present, the value of the phase difference θ is small. The comparison circuit CP compares the phase difference detection signal Pd with the phase difference determination signal Pr, determines that the phase difference detection signal Pd is smaller than the phase difference determination signal Pr, and that there is a pan, and sets the pan no detection signal Cp to the low level. And output to the AND circuit AND. When the panless detection signal Cp becomes the Low level, the AND circuit AND sets the output to the Low level regardless of the pan detection control signal Cp3 and operates the inverter drive circuit SD.
[0037]
In the current corresponding pan detection control circuit, when the value of the power setting signal Pc is set to the minimum operating power, the current flowing through the induction heating coil HL becomes small and the current holding signal Ep is a current discrimination signal as shown in FIG. The third comparison circuit CP becomes lower than Fr and sets the pan detection control signal Cp3 to the Low level and outputs it to the AND circuit AND. When the pan detection control signal Cp3 becomes low level, the AND circuit AND sets the output signal to low level and operates the inverter drive circuit SD regardless of the pan non-detection signal Cp.
[0038]
[Example 3]
FIG. 7 is an electrical connection diagram of the electromagnetic induction heating cooker according to the third embodiment. In the figure, the same reference numerals as those in the electrical connection diagram of the electromagnetic induction heating cooker of the present invention shown in FIG.
[0039]
The power corresponding pan detection control circuit is formed by the fourth comparison circuit CP4 and the AND circuit AND.
[0040]
The fourth comparison circuit CP4 compares the power setting signal Pc with the power discrimination signal Pf and outputs a pan detection control signal Cp4.
[0041]
When the value of the power setting signal Pc is set to the power that is normally used in the power corresponding pan detection control circuit, the power setting signal Pc becomes larger than the power determination signal Pf, and the fourth comparison circuit CP4 of the power corresponding pan detection control circuit The pan detection control signal is set to High level and output to the AND circuit AND. Therefore, the AND circuit AND sets the output signal to the high level and stops the inverter drive circuit SD when the panless detection signal Cp becomes the high level.
[0042]
When the value of the power setting signal Pc is set to the minimum power consumption, the power setting signal Pc becomes smaller than the power discrimination signal Pf, and the fourth comparison circuit CP4 of the power corresponding pan detection control circuit sets the pan detection control signal Cp4 to the low level. And output to the AND circuit AND. When the pan detection control signal Cp becomes low level, the AND circuit AND causes the output signal to go low regardless of the pan non-detection signal Cp and operates the inverter drive circuit SD.
[0043]
When the output signal of the AND circuit AND becomes High level and the inverter drive circuit SD is stopped, the indicator LED is turned on to display the no pan state.
【The invention's effect】
In the electromagnetic induction heating cooker of the present invention, cooking can be continued without stopping the inverter circuit, which automatically stops the operation of the pan detection circuit when cooking is performed with a small power set value. Moreover, the problem of discriminating a small pan from the absence of a pan due to the difference in the diameter of the pan can be solved.
[Brief description of the drawings]
FIG. 1 is an electrical connection diagram of an electromagnetic induction heating cooker according to the present invention.
FIG. 2 is a detailed connection diagram of the phase difference detection circuit shown in FIG.
FIG. 3 is a waveform diagram illustrating the operation of the present invention.
FIG. 4 is an electrical connection diagram of the electromagnetic induction heating cooker according to the second embodiment.
FIG. 5 is a detailed connection diagram of the current holding circuit shown in FIG. 4;
FIG. 6 is a waveform diagram for explaining the operation of the second embodiment.
7 is an electrical connection diagram of the electromagnetic induction heating cooker of Example 3. FIG.
FIG. 8 is an electrical connection diagram of a conventional electromagnetic induction heating cooker.
[Explanation of symbols]
AND AND circuit CO differential amplifier circuit CP comparison circuit C1 smoothing capacitor C2 resonance capacitor C3 resonance capacitor C4 capacitor CP2 second comparison circuit CP3 third comparison circuit CP4 fourth comparison circuit CT2 output current detection circuit CV2 output voltage detection circuit DR1 Rectifier circuit DR2 Diode EP Current holding circuit FV Frequency / voltage conversion circuit HL Induction heating coil ID Input current detection circuit IV Input voltage detection circuit LED Display OA Operation panel OP Amplification circuit PB Pan PC Power setting circuit PD Phase difference detection circuit PE Phase difference / voltage conversion circuit PK Pulsing circuit PL Top plate R1 Resistor SA Power operation circuit SC Control operation circuit SD Inverter drive circuit TS Heating switch TR1 Switching element TR2 Switching element WD Both-wave rectification circuit Cp Panless detection signal Cp2 Pan detection control signal Ct2 Output current detection signal Cv2 Output voltage detection signal Ep Current holding signal Er Current discrimination signal Fv Frequency / voltage conversion signal Fr Frequency discrimination signal Id Input current detection signal Iv Input voltage detection signal ΔI Differential amplification signal Ld Display signal Oa operation signal Pc power setting signal Pd phase difference detection signal Pf power discrimination signal Pk pulse signal Pr phase difference discrimination signal Sa power calculation signal Sc control calculation signal Ts heating start signal Sd1 switching element drive signal Sd2 switching element drive signal Wd both-wave rectification signal

Claims (2)

A resonant capacitor; an induction heating coil that forms a series resonance with the resonant capacitor; a rectifier circuit that rectifies a commercial AC power supply to convert it into a DC voltage; and a high-frequency current in the induction heating coil using the DC voltage of the rectifier circuit as an input An inverter circuit that supplies power, a power calculation circuit that calculates input power of the inverter circuit and outputs a power calculation signal, a power setting circuit that outputs a power setting signal, the power calculation signal and the power setting signal A differential amplifier circuit for differential amplification, an inverter drive circuit for controlling the output frequency of the inverter circuit according to the differential amplification signal, and a phase difference between the output voltage and the output current of the inverter circuit A phase difference detection circuit that outputs a phase difference detection signal, and a pan is placed when the value of the phase difference detection signal is greater than a predetermined phase difference determination value. A pan detection circuit that discriminates that there is no pan and outputs a no pan detection signal to stop the drive of the inverter drive circuit and stop the supply of the high frequency current, and the pan placed on the induction heating coil is electromagnetic In an electromagnetic induction heating cooker that heats by induction, the output frequency of the inverter circuit is detected, and the operation of the pan detection circuit is stopped when the detection accuracy of the phase difference is higher than a predetermined frequency discrimination value that decreases. An electromagnetic induction heating cooker comprising a frequency corresponding pan detection control circuit that operates the pan detection circuit when the output frequency is lower than the frequency discrimination value.   When the peak value of the output current of the inverter circuit is detected and the detection accuracy of the phase difference is smaller than a predetermined current discrimination value, the operation of the pan detection circuit is stopped, and the peak value is the current discrimination value 2. The electromagnetic induction heating cooker according to claim 1, wherein the current corresponding pot detection control circuit for operating the pot detection circuit when the value is larger is replaced with the frequency corresponding pot detection control circuit.

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