Composite multifunctional electromagnetic induction experimental instrument

Abstract

The invention discloses a composite multifunctional electromagnetic induction experimental instrument, which belongs to the technical field of electromagnetic induction and comprises a magnetic field generation part, a magnetic field detection part and a control part, the self-made induction coil part comprises induction coil groups with different turns and a telescopic arm; the data acquisition part comprises intelligent mobile phone phyphox software, a digital voltmeter, a DIS voltage sensing module and a homemade diode voltage comparator, a group of Helmholtz coils are homemade, and a voltmeter sensor in the intelligent mobile phone phyphox software is utilized, so that the research on the magnetic field distribution rule of the Helmholtz coils is realized; a Helmholtz coil is used for building a magnetic field, and a self-made induction coil group, a digital voltmeter or an oscilloscope and the like are combined to realize research on an electromagnetic induction phenomenon: a self-made diode voltage comparator is used for quantitatively describing a magnetic field distribution rule in the Helmholtz coil.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic induction, in particular to a composite multifunctional electromagnetic induction experiment instrument. Background Art

[0002] With the development of science and technology, the high precision and strong sensitivity of the internal sensors of smartphones have gradually made them used in experimental design and teaching, and have become a powerful assistant for physical experimental teaching. Faraday's law of electromagnetic induction is a key and difficult point in the teaching of electromagnetics in middle school physics. It is closely related to electric fields, magnetic fields and constant currents, and is an important basis for learning alternating current, electromagnetic oscillations and electromagnetic waves. However, in the experimental design of the law of electromagnetic induction, most of them are limited to demonstration phenomena but ignore quantitative research. Some experiments focus on quantitative research but ignore demonstration phenomena. For example, Oersted's "electricity-induced magnetism" experiment and Faraday's "magnetism-induced electricity" experiment are relatively simple in design and lack quantitative exploration experiments. In college physics teaching, the principle of magnetic field superposition is studied in depth, but experimental designs that use experimental methods to verify the principle of magnetic field superposition are relatively rare.

[0003] In the current educational environment, there are some limitations in the teaching and experimental demonstration of electromagnetic induction, especially in terms of intuitiveness and immediate feedback. Students often find it difficult to intuitively observe and understand the electromagnetic induction phenomenon and the changes in the magnitude of the induced electromotive force, mainly because the induced electromotive force is small. Summary of the invention

[0004] The purpose of the present invention is to provide a composite multifunctional electromagnetic induction experiment instrument, and a multifunctional electromagnetic experiment instrument with a Helmholtz coil is designed and developed. The experimental device can be used to carry out multiple electromagnetic experimental projects such as quantitative research on electromagnetic induction phenomena and magnetic field characteristics generated by Helmholtz coils, which is of great significance to make up for the lack of electromagnetic induction quantitative exploration experiments in current middle school physics textbooks, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a composite multifunctional electromagnetic induction experiment instrument, comprising:

[0006] A magnetic field generating part, wherein the magnetic field generating part comprises a power supply, a Helmholtz coil and a strong magnet;

[0007] A self-made induction coil part, wherein the induction coil part comprises an induction coil group with different numbers of turns and a telescopic arm;

[0008] The data acquisition part includes a smartphone phyphox software, a digital voltmeter, a DIS voltage sensor module, and a homemade diode voltage comparator.

[0009] Preferably, the magnetic field generating part further includes a function signal generator, the Helmholtz coil is handmade by enameled wire with a diameter of 0.7-0.9 mm, and the specifications of the Helmholtz coil are an outer diameter of 21-23 cm, an inner diameter of 19-21 cm, and 340-360 turns.

[0010] Preferably, the induction coil group includes a circular induction coil and a rectangular induction coil, which are used to explore the induced electromotive force and the motional electromotive force respectively.

[0011] Preferably, the circular induction coil is a single-layer coil wound by self-winding an enameled wire with a diameter of 0.3-0.5 mm, and the specifications of the circular induction coil are a radius of 4.6-4.8 cm and 190-210 turns.

[0012] Preferably, the rectangular induction coil is made of 0.4 mm enameled wire, and its size is 10 cm*19-21 cm, but the number of turns is 100 turns, 200 turns, and 300 turns.

[0013] Preferably, the rectangular induction coil is mounted on a telescopic arm, the telescopic arm has a telescopic length of 10-20 cm and an adjustable speed range of 0-9 m / s.

[0014] Preferably, the data acquisition part includes an induced electromotive force acquisition part and a magnetic field acquisition part, the induced electromotive force acquisition part includes a four-and-a-half-digit high-precision digital voltmeter, a self-designed diode voltage comparator and a DIS voltage sensor module, and the magnetic field acquisition part collects data through a magnetometer sensor in the phyphox software of a smartphone.

[0015] Preferably, the data acquisition part also includes a display, and the display is connected to a computer host.

[0016] Preferably, the Helmholtz coil comprises two groups of coils parallel to each other, and the two groups of parallel coils are connected and coaxial.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention uses a group of Helmholtz coils and a voltmeter sensor in the smartphone phyphox software to study the magnetic field distribution law of the Helmholtz coils; uses the Helmholtz coils to "build a magnetic field" and combines a self-made induction coil group, a digital voltmeter or an oscilloscope to study the electromagnetic induction phenomenon: uses a self-made diode voltage comparator to quantitatively describe the magnetic field distribution law in the Helmholtz coil, and uses a DIS voltage sensor module and a self-made diode voltage comparator for fitting correction.

[0019] 2. The present invention can complete multiple experimental projects on the overall frame of the instrument by replacing components, reflecting the versatility of the test instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of the induction coil and the magnetic field generating part in this embodiment;

[0021] Figure 2 Schematic diagram of the structure of the data acquisition part in this embodiment;

[0022] Figure 3 is a magnetic field distribution diagram of a single current-carrying coil on its central axis in this embodiment;

[0023] Figure 4 is a magnetic field distribution diagram of the Helmholtz coil on its axis in this embodiment;

[0024] Figure 5 : is the magnetic field distribution diagram on the axis of the Helmholtz coil in this embodiment;

[0025] Figure 6 is a relationship diagram between the induced electromotive force and the rate of change of the magnetic field in this embodiment;

[0026] Figure 7 It is a schematic diagram of a bipolar voltage indicator based on a voltage comparator;

[0027] Figure 8 This is a diagram to introduce the functions of the operational amplifier LM741;

[0028] Fig. 9 This is a diagram to introduce the functions of the operational amplifier LM741;

[0029] Fig.10 This is the schematic diagram of the LM339 voltage comparator;

[0030] Fig.11 This is the pin diagram of the LM339 voltage comparator;

[0031] Fig.12 This is the appearance and pin arrangement diagram of LM339N;

[0032] Fig.13 Pinout for LM339N;

[0033] Fig.14 This is a schematic diagram of the overheat detection protection circuit;

[0034] Fig.15 A hysteresis comparator circuit and a hysteresis comparator transfer characteristic;

[0035] Fig.16 Improved circuit for hysteresis comparator;

[0036] Fig.17 It is a power grid overvoltage detection circuit in the induction cooker circuit;

[0037] Fig.18 The LM339 window comparator circuit and the instrument can be expanded and extended;

[0038] Fig.19 The audio square wave oscillator is composed of LM339.

[0039] Numbers in the figure: 1, magnetic field generating part; 101, power supply; 102, Helmholtz coil; 2, induction coil part; 201, induction coil group; 202, telescopic arm; 3, data acquisition part; 301, diode voltage comparator; 302, display; 303, computer host. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figure 1-2 As shown, a composite multifunctional electromagnetic induction experiment instrument comprises:

[0042] A magnetic field generating part 1, the magnetic field generating part 1 comprises a power source 101, a Helmholtz coil 102 and a strong magnet;

[0043] A self-made induction coil part 2, the self-made induction coil part 2 comprises an induction coil group 201 with different numbers of turns and a telescopic arm 202;

[0044] Data acquisition part 3, data acquisition part 3 includes smart phone phyphox software, digital voltmeter, DIS voltage sensor module, and self-made diode voltage comparator 301.

[0045] This experimental design mainly consists of the magnetic field generation part 1, the self-made induction coil part 2 and the data acquisition part 3. In the experimental device, a set of Helmholtz coils 102 were made by ourselves, and the voltmeter sensor in the smartphone phyphox software was used to study the magnetic field distribution law of the Helmholtz coils 102; the Helmholtz coils 102 were used to "build a magnetic field" and combined with the self-made induction coils, digital voltmeters or oscilloscopes, etc., to study the electromagnetic induction phenomenon: the self-made diode voltage comparator 301 was used to quantitatively describe the magnetic field distribution law in the Helmholtz coils 102, and the DIS voltage sensor module and the self-made diode voltage comparator 301 were used for fitting correction.

[0046] The magnetic field generating part 1 also includes a function signal generator. The Helmholtz coil 102 is handmade by using enameled wire with a diameter of 0.7-0.9 mm. The specifications of the Helmholtz coil 102 are an outer diameter of 21-23 cm, an inner diameter of 19-21 cm, and 340-360 turns.

[0047] The induction coil group 201 includes a circular induction coil and a rectangular induction coil, which are used to explore the induced electromotive force and the motional electromotive force respectively.

[0048] The circular induction coil is a single-layer coil wound by self-winding an enameled wire with a diameter of 0.3-0.5 mm. The specification of the circular induction coil is a radius of 4.6-4.8 cm and a number of turns of 190-210 turns.

[0049] The rectangular induction coil is made of 0.4mm enameled wire, and its size is 10cm*19-21cm. However, the number of turns is 100 turns, 200 turns, and 300 turns. Variable research is carried out through rectangular induction coils with different numbers of turns.

[0050] The rectangular induction coil is mounted on the telescopic arm 202. The telescopic arm 202 has a telescopic length of 10-20 cm and an adjustable speed range of 0-9 m / s to adjust the height of the rectangular induction coil.

[0051] The data acquisition part 3 includes an induced electromotive force acquisition part and a magnetic field acquisition part. The induced electromotive force acquisition part includes a four-and-a-half-digit high-precision digital voltmeter, a self-designed diode voltage comparator 301, and a DIS voltage sensor module. The magnetic field acquisition part collects data through the magnetometer sensor in the phyphox software of the smartphone.

[0052] The data acquisition part 3 also includes a display 302 , and the display 302 is connected to a computer host 303 .

[0053] The Helmholtz coil 102 includes two groups of coils parallel to each other, and the two groups of parallel coils are connected and coaxial.

[0054] The following will be further described in conjunction with specific embodiments:

[0055] 1. Product structure, principle and production:

[0056] 1.1 Design principle:

[0057] This experimental design is mainly composed of the magnetic field generating part 1 (power supply 101, Helmholtz coil 102, strong magnet, etc.), the homemade induction coil part 2 (including induction coil groups 201 with different turns, telescopic arm 202, etc.) and the data acquisition part 3 (including smartphone phyphox software, digital voltmeter, DIS voltage sensor module, homemade diode voltage comparator 301, etc.). In the experimental device, a group of Helmholtz coils 102 were made by themselves, and the voltmeter sensor in the smartphone phyphox software was used to study the magnetic field distribution law of the Helmholtz coil 102; the Helmholtz coil 102 was used to "build a magnetic field", combined with the homemade induction coil group 201, digital voltmeter or oscilloscope, etc., to realize the study of electromagnetic induction phenomenon: the homemade diode voltage comparator 301 was used to quantitatively describe the magnetic field distribution law in the Helmholtz coil 102, and the DIS voltage sensor module and the homemade diode voltage comparator 301 were used for fitting correction. In this experimental design, "building a magnetic field" is an important link. The theoretical basis of "building a magnetic field" is:

[0058] According to the Biot-Savart law, the magnetic induction intensity at any point on the straight line (axis) perpendicular to the plane of the current-carrying coil where the center of the current-carrying coil is located is:

[0059]

[0060] Where μ0 is the vacuum permeability, is the average radius from the current-carrying coil to the center of the circle, x is the distance from the center of the circle to the point, N is the number of turns of the current-carrying coil, and I is the intensity of the current passing through the current-carrying coil. Therefore, the magnetic induction intensity B0 at the center of the circle is:

[0061]

[0062] In the Helmholtz coil 102 used to simulate a uniform magnetic field, two coils are placed parallel to each other and connected to form two coaxial circular coils. Currents of the same direction and magnitude are passed through the two coils, and the distance d between the two identical coils is exactly the same as the radius R of the two coaxial circular coils. The two coils combined in this way are called the Helmholtz coil 102. The characteristic of the Helmholtz coil 102 is that it can generate a wider uniform magnetic field area near the midpoint of the common axis of the two coils.

[0063] Assume that a certain point on the central axis of the Helmholtz coil 102 is at a distance Z from the center point O of the axis of the two coils constituting the Helmholtz coil 102. Then, the magnetic induction intensity at any position on the axis of the Helmholtz coil 102 is:

[0064]

[0065] The magnetic flux density B at the center point O on the axis of the Helmholtz coil 102 is O for:

[0066]

[0067] The magnetic field distribution of a single current-carrying coil on its central axis and the magnetic field distribution of the Helmholtz coil 102 on its axis are as follows: Figure 3 , Figure 4 As shown (the X-axis represents the distance from the center point O, and the Y-axis represents the magnetic field strength at that location)

[0068] Thus, two coils of the same size were made to form the Helmholtz coil 102, which served as the magnetic field generating part 1 of the device, and "built" the magnetic field required for the investigation.

[0069] 1.2 Structural design and production of experimental instrument

[0070] The actual picture of this device is as follows Figure 1 and Figure 2 As shown, it mainly includes a magnetic field generating part 1, an induction coil group 201 and a data acquisition part 3, and the design of each part is as follows:

[0071] (1) Magnetic field generating part 1: This part mainly includes Helmholtz coil 102, DC power supply 101, power function signal generator and other devices. Among them, Helmholtz coil 102 is handmade with enameled wire (enameled wire diameter is 0.7-0.9mm). The outer diameter of the homemade Helmholtz coil 102 is 21-23cm, the inner diameter is 19-21cm, and the number of turns is 340-360 turns.

[0072] (2) Induction coil part 2: It includes two specifications: a circular induction coil for exploring induced electromotive force and a rectangular induction coil for exploring motional electromotive force.

[0073] Investigate the circular induction coil that generates induced electromotive force: The circular induction coil is a self-wound single-layer coil. The diameter of the enameled wire used is 0.4mm. The radius of the circular induction coil is 4.6-4.8cm, and the number of turns is 200.

[0074] Rectangular induction coil for exploring motional electromotive force: This part consists of a rectangular induction coil and a telescopic arm 202. The diameter of the enameled wire used is 0.4mm, and the size of the rectangular induction coil is 10cm*19-21cm, but the number of turns is 100 turns, 200 turns, and 300 turns. The telescopic arm 202 can be extended to a length of 10-20cm, and the speed range is adjustable from 0-9m / s.

[0075] (3) Data acquisition part 3: including the induced electromotive force acquisition part and the magnetic field acquisition part.

[0076] Induced electromotive force collection part: Since the induced electromotive force is small, a four-and-a-half-digit high-precision digital voltmeter can be used to collect the induced electromotive force. At the same time, the independently designed diode voltage comparator 301 circuit is used to explore the induced electromotive force and is equipped with a DIS voltage sensor module for data correction. The size of the induced electromotive force can also be intuitively compared through the brightness of the light-emitting diode to obtain the size of the electromotive force under different experimental conditions.

[0077] Magnetic field collection part: Use the magnetometer sensor in the phyphox software on the smartphone to collect data, and the collected data can be displayed in real time through the computer at the same time.

[0078] (4) Homemade voltage comparator:

[0079] Working principle: The electromagnetic induction peak voltage display circuit based on voltage comparator is shown in the figure. In the figure, the signal source V2 is equivalent to the part of the conductor (electromagnetic induction power supply) that generates the induced voltage by electromagnetic induction. The voltage comparator LM339 constitutes eight voltage comparators. The voltage output by the electromagnetic induction power supply passes through the voltage follower composed of the operational amplifier LM741, and its output signal is sent to the in-phase end of the comparator U1A~U1D, and also to the inverting end of the comparator U2A~U2D. The voltage settings of the reference ends of the eight voltage comparators and the light-emitting diodes driven by them are shown in the table below.

[0080]

[0081] The power supply VCC is connected to the positive pole of the light-emitting diode LED1 through a 1k resistor. When the peak value of the output voltage of the electromagnetic induction power supply is less than 0.4V, the light-emitting diode LED1 lights up, indicating that no electromagnetic induction occurs and that the power supply VCC is normal; when the peak value of the output voltage of the electromagnetic induction power supply is greater than 0.4V and less than 0.8V, the light-emitting diodes LED1, LED2, and LED9 light up; when the peak value of the output voltage of the electromagnetic induction power supply is greater than 0.8V and less than 0.1.2V, the light-emitting diodes LED 1, LED2, LED9, LED3, and LED 8 light up; when the peak value of the output voltage of the electromagnetic induction power supply is greater than 1.2V and less than 1.6V, the light-emitting diodes LED 1, LED2, LED9, LED3, LED8, LED4, and LED7 light up; when the peak value of the output voltage of the electromagnetic induction power supply is greater than 1.6V, all the light-emitting diodes light up. This circuit can display the voltage peak generated by electromagnetic induction.

[0082] Design and production of a multifunctional electromagnetic induction experimental instrument

[0083] In the current educational environment, there are some limitations in the teaching and experimental demonstration of electromagnetic induction, especially in terms of intuitiveness and immediate feedback. Students often find it difficult to intuitively observe and understand the electromagnetic induction phenomenon and the changes in the magnitude of the induced electromotive force. The main reason is that the induced electromotive force is small. [5] To solve this problem, this multifunctional electromagnetic induction experiment instrument uses four-and-a-half-digit high-precision digital data to collect induced electromotive force, and uses a self-designed bipolar voltage indicator to explore the induced electromotive force and is equipped with a DIS voltage sensor module for data correction. Its advantage is that the size of the electromotive force under different experimental conditions can be intuitively compared through the brightness of the light-emitting diode.

[0084] 1.1 Bipolar voltage indicator circuit design

[0085] The feasibility of the design concept is verified by Multisim simulation software, such as Figure 7 , Figure 7 The signal source V2 is used to debug and calibrate the voltage indicator. The voltage comparator LM339 forms eight voltage comparators. The voltage output by the test power supply V2 passes through the voltage follower formed by the operational amplifier LM741, and its output signal is sent to the comparator U 1A -U 1D The non-inverting terminal is also fed to the comparator U 2A -U 2D The voltage settings of the inverting terminal, the reference terminal of the eight voltage comparators and the light-emitting diodes they drive are shown in the table below.

[0086] Meter voltage setting parameters

[0087]

[0088]

[0089] Voltage Setting Parameters

[0090]

[0091] 1.2 Introduction to Bipolar Voltage Indicator Circuit Components

[0092] (1) Operational amplifier LM741 function introduction Figure 8 :

[0093] The functions of each pin of the LM741 integrated operational amplifier are as follows:

[0094] Pin 2 - Inverting input

[0095] Pin 3 - Non-inverting input

[0096] Pin 7 - Power supply voltage positive terminal

[0097] Pin 4 - Negative terminal of power supply voltage

[0098] Pin 6 - Output

[0099] Pin 1, 5 - Zero adjustment terminal

[0100] The integrated operational amplifier is a direct-coupled multi-stage amplifier circuit with high amplification factor, high input impedance, and low output impedance. It has two input terminals and one output terminal and can amplify DC and AC signals. After an external deep negative feedback circuit is connected, the output voltage V o With input voltage V i The operational relationship depends only on the external feedback network and the external impedance of the input terminal, and has nothing to do with the operational amplifier itself. The unity gain bandwidth of this operational amplifier is 1MHz.

[0101] Application examples: Fig. 9 As shown, an inverting proportional operational amplifier circuit is formed.

[0102] The operational relationship between output and input

[0103]

[0104] (1) If R F =R1, then it is an inverter, that is, V0 = -V i

[0105] (2) Functional introduction of operational amplifier LM339

[0106] Voltage comparator (hereinafter referred to as comparator) Figure 4 As shown: It is a commonly used integrated circuit. It can be used in alarm circuits, automatic control circuits, measurement technology, V / F conversion circuits, A / D conversion circuits, high-speed sampling circuits, power supply voltage monitoring circuits, oscillators and voltage-controlled oscillator circuits, zero-crossing detection circuits, etc. Simply put, the voltage comparator compares the size of two analog voltages (there are also two digital voltage comparisons, which are not introduced here) and determines which voltage is higher.

[0107] Fig.10 (a) is a comparator, which has two input terminals: the non-inverting input terminal ("+" terminal) and the inverting input terminal ("-" terminal), and an output terminal V out (Output level signal). In addition, there is a power supply V + and ground (this is a single-supply comparator), the non-inverting input voltage V A , inverting input V B . V A and V B changes, such as Fig.10 (b). At time 0 to t1, V A ≥VB ; At t1~t2, V B ≥V A ; At t2~t, V A ≥V B In this case, V out The output is as follows Fig.10 As shown in (c), when V A ≥V B When V out Output high level (saturated output); V B ≥V A When V out Output low level. According to the output level, we can know which voltage is larger.

[0108] If V A Input to the inverting terminal, V B Input to the non-inverting terminal, V A and V B The voltage change is still as Fig.10 (b) shows, then V out Output like Fig.10 (d) is shown. Fig.10 (c) Compared with the output level, the output level is reversed. The output level change is related to V A 、V B The input terminal is related to .

[0109] If the input voltage V A With a fixed voltage V B In comparison, Fig.11 (a). This V B It is called reference voltage, base voltage or threshold voltage. If this reference voltage is 0V (ground level), Fig.11 As shown in (b), it is generally used for zero-crossing detection.

[0110] (3)LM339 voltage comparator

[0111] The LM339 integrated circuit has four independent voltage comparators installed inside. The characteristics of the voltage comparator are:

[0112] ①The offset voltage is small, the typical value is 2mV;

[0113] ②The power supply voltage range is wide, the single power supply voltage is 236V, and the dual power supply voltage is ±1V±18V;

[0114] ③ The internal resistance limit of the comparison signal source is relatively wide;

[0115] ④The common mode range is very large, from 0 to (V cc 1.5V)V o ;

[0116] ⑤ The differential input voltage range is large, large enough to be equal to the power supply voltage;

[0117] ⑥The output terminal potential can be selected flexibly and conveniently.

[0118] The LM339 integrated block adopts C14 package. The appearance and pin arrangement of LM339N are as follows: Fig.12 Because LM339 is flexible and widely used, major IC manufacturers and companies in the world are competing to launch their own quad comparators, such as IR2339, ANI339, SF339, etc. Their parameters are basically the same and can be used interchangeably. LM339 is similar to an operational amplifier with non-adjustable gain. Each comparator has two input terminals and one output terminal. One of the two input terminals is called the in-phase input terminal, represented by "+", and the other is called the inverting input terminal, represented by "". When used to compare two voltages, a fixed voltage is added to any input terminal as a reference voltage (also called a threshold level, which can be selected at any point in the LM339 input common mode range), and a signal voltage to be compared is added to the other terminal. When the voltage at the "+" terminal is higher than that at the "" terminal, the output tube is cut off, which is equivalent to an open circuit at the output terminal. When the voltage at the "" terminal is higher than that at the "+" terminal, the output tube is saturated, which is equivalent to a low potential at the output terminal. If the voltage difference between the two input terminals is greater than 10mV, it can ensure that the output can be reliably converted from one state to another. Therefore, it is ideal to use LM339 in occasions such as weak signal detection. The output of LM339 is equivalent to a transistor without collector resistor. When in use, a resistor (called pull-up resistor, 315K) is usually connected from the output to the positive power supply. Selecting pull-up resistors with different resistance values ​​will affect the value of the high potential of the output. Because when the output transistor is cut off, its collector voltage basically depends on the value of the pull-up resistor and the load. In addition, the output of each comparator can be connected together. The pin functions of LM339 are as follows: Fig.13 Shown on the left

[0119] (4) Single limit comparator circuit such as Fig.13 Shown on the right.

[0120] (5) Fig.14 This is an overheat detection protection circuit in a certain instrument. It is powered by a single power supply, and a fixed reference voltage is added to the inverting input of 1 / 4LM339, and its value depends on R1 and R2.

[0121]

[0122] The voltage at the in-phase end is equal to the voltage drop of thermistor R1. When the temperature inside the machine is below the set value, the voltage at the "+" end is greater than the voltage at the "+" end, and V0 is a high potential. When the temperature rises above the set value, the voltage at the "-" end is greater than the "+" end, the comparator is reversed, and V0 outputs zero potential, causing the protection circuit to operate. Adjusting the value of R1 can change the threshold voltage, that is, the size of the set temperature value.

[0123] (6) Hysteresis comparator

[0124] Fig.15 (a) shows a hysteresis comparator. The familiar "Schmitt" circuit is a comparator with hysteresis. Fig.15 (b) is the transfer characteristic of the hysteresis comparator. It is not difficult to see that once the output state is converted, as long as the interference near the jump voltage value does not exceed the value of ΔV, the output voltage value will be stable. But this is accompanied by a reduction in resolution. Because for the hysteresis comparator, it cannot distinguish between two input voltage values ​​with a difference less than ΔV. The hysteresis comparator with positive feedback can speed up the response speed of the comparator, which is one of its advantages. In addition, since the positive feedback added to the hysteresis comparator is very strong, much stronger than the parasitic coupling in the circuit, the hysteresis comparator can also avoid self-oscillation caused by parasitic coupling in the circuit. If a jump point needs to be fixed at a certain reference voltage value, a nonlinear element, such as a crystal diode, can be connected to the positive feedback circuit. The unidirectional conductivity of the diode can be used to achieve the above requirements. The improved circuit of the hysteresis comparator is as follows Fig.16 shown.

[0125] Fig.17 This is the overvoltage detection circuit of the power grid in a certain induction cooker circuit. When the power grid voltage is normal, the V4≤2.8V of 1 / 4LM339, V5=2.8V output is open, the overvoltage protection circuit does not work, and the emitter follower BG1 as positive feedback is turned on. When the power grid voltage is greater than 242V, V4≤2.8V, the comparator flips, the output is 0V, BG1 is cut off, and the voltage of V5 is completely determined by the voltage divider value of R1 and R2, which is 2.7V, making V4 greater than V5, which makes the state after flipping extremely stable, avoiding the instability caused by the small fluctuation of the power grid voltage near the overvoltage point. Due to the creation of a certain hysteresis, after the overvoltage protection, the power grid voltage must drop to 2425=237V, V4≤V5, and the induction cooker will start working again.

[0126] (7) Dual limit comparator (window comparator)

[0127] The circuit consists of two LM339s forming a window comparator. Fig.18 (a). When the compared signal voltage U in When between the threshold voltages (U R1≤U in ≤U R2 ), the output is high potential (U O =U OH ). When U in When it is not within the threshold potential range, (U in ≥U R2 or U in ≤U R1 ) output is low potential (U O =U OL ), window voltage ΔU=U R2 -U R1 It can be used to determine whether the input signal potential is between the specified threshold potentials, such as Fig.18 (b).

[0128] (8)LM339 oscillator

[0129] like Fig.19 , the oscillator composed of LM339 has a circuit of audio square wave oscillator composed of 1 / 4 LM339. Changing C1 can change the frequency of the output square wave. In this circuit, when C1=0.1μF, f=53Hz; when C1=0.01μF, f=530Hz; when C1=0.001μF, f=5300Hz. LM339 can also form a high-voltage digital logic gate circuit and can directly interface with TTL and CMOS circuits.

[0130] 1.3 Bipolar Voltage Indicator Circuit Finished Product and Evaluation

[0131] (1) Equipment: soldering iron, circuit board, voltage comparator, wire, light-emitting diode:

[0132] (2) Product optimization: ① Simplified the user interface to make it more intuitive and easier to understand, reducing the difficulty of operation.

[0133] ② Enhanced data visualization function, through improved LED indication and digital display, making the changes of induced electromotive force more obvious.

[0134] ③The size and structural design of the experimental instrument were adjusted to adapt to different classroom environments and laboratory bench layouts.

[0135] ④ The durability and stability of the experimental instrument were tested, and corresponding structural reinforcement and material upgrades were carried out based on the test results. Through these iterations, the performance and user experience of the experimental instrument were improved to ensure that the final product can meet the needs of education and experiments.

[0136] The above experimental device is mainly used to complete the following experimental projects:

[0137] (1) A direct current power source is used to supply power to the Helmholtz coil 102 so as to generate a magnetic field. A magnetometer in the phyphox program of a smartphone is used to measure and study the distribution law and characteristics of the magnetic field generated by the Helmholtz coil 102.

[0138] (2) Induced electromotive force Research:

[0139] Method 1: Place the induction coil group 201 at the axis of the Helmholtz coil 102, use the power function signal generator as the power source, and pass a triangular wave power supply into the Helmholtz coil 102, so that it generates a uniformly changing magnetic field under the action of a uniformly changing current. The uniformly changing magnetic field is measured by the magnetometer of the smartphone phyphox software and displays a changing image, and its slope is The induction coil group 201 will generate an induced electromotive force under the action of a uniformly changing magnetic field. However, the generated induced electromotive force is small, and a digital voltmeter is used to display and record data. By comparing the theoretical calculated value with the measured value of the actual induced electromotive force, the induced electromotive force in the law of electromagnetic induction is studied.

[0140] Method 2: Use a coil with variable turns, a strong magnet, and a homemade circuit to measure the size of the induced electromotive force. The size of the induced electromotive force is obtained by the reading of the homemade light-emitting diode voltage comparator 301, and the DIS voltage sensing module is connected to the instrument, and then the data is imported into the computer to statistically analyze the sample data and convert it into a line graph. The corresponding peak-to-peak value is obtained by selecting the display coordinate data to verify the experimental data of the homemade light-emitting diode voltage comparator 301, so as to achieve the purpose of the exploration experiment. The experimental instrument can change the number of coil turns to determine the size of the induced electromotive force; change the number of magnets to determine the size of the induced electromotive force; change the speed of the magnet to change the time required for the change of magnetic flux on the size of the induced electromotive force.

[0141] (3) Research on motional electromotive force E=NBLV: A DC regulated current is passed through the Helmholtz coil 102 to generate a uniform magnetic field. The rectangular induction coil is fixed on the telescopic arm 202, and the telescopic arm 202 is used to drive the rectangular induction coil to move back and forth, so that it cuts the magnetic flux lines in the magnetic field, thereby generating a motional electromotive force. By changing the motion speed v, the magnetic field strength B, and the number of turns N of the rectangular induction coil, the motional electromotive force is studied by controlling the variables.

[0142] (4) In the above study of induced electromotive force and motional electromotive force, by controlling variables, such as changing the rate of change of magnetic field, the number of turns of the induction coil group 201, the speed of the telescopic arm 202, etc., the influencing factors of the magnitude of the induced electromotive force in the law of electromagnetic induction are studied.

[0143] 2. Application of the multifunctional electromagnetic experiment instrument of Helmholtz coil 102 in teaching

[0144] 2.1 Study on the distribution law of the magnetic field generated by the Helmholtz coil 102

[0145] Connect the power supply 101 to the Helmholtz coil 102 and adjust it to a DC 1A input. Place the mobile phone on the axis of the Helmholtz coil 102, measure the magnetic field magnitudes at 33 positions from -16cm to 16cm at intervals of 1cm, and export the data.

[0146] 2.2 Experimental study of induced electromotive force

[0147] Method 1:

[0148] (1) The self-made induction coil group 201 is placed in the groove of the experimental instrument and connected to a digital voltmeter; the signal sent by the function signal generator is connected to the Helmholtz coil 102, and a triangular waveform current is passed through the function signal generator, so that a uniformly changing magnetic field is generated inside the Helmholtz coil 102.

[0149] (2) Open the phyphox software on the mobile phone and connect it to the computer. Place the mobile phone in the self-made induction coil group 201. Observe that the Bt image on the phyphox computer experimental interface shows a triangular wave change pattern. Measure the Bt image of 3 to 5 triangular wave cycles. The slope of each half cycle is (Magnetic field change rate) is constant, so we can choose a section of the magnetic field in the upper half of the Bt image to find the slope By selecting the data option on this image, you can directly read the data change rate between the two selected points by selecting any two points Keep the triangular wave frequency of the function signal generator unchanged, and change the amplitude of the input triangular wave to change the slope. Take 6 different amplitudes for multiple measurements and record the data.

[0150] Method 2:

[0151] (1) Connect the telescopic arm 202 controller directly to a 220V power supply, fix the magnet at the lower end of the telescopic arm 202, and connect the two ends of the induction coil group 201 to a self-made light-emitting diode voltage comparator 301; then connect the two ends of the DIS voltage sensor to the computer host 303 and the two ends of the induction coil group 201 respectively.

[0152] (2) Open the DISLAB general software, select the voltage sensor module, call up the curve display, set the "sampling frequency" to 100 Hz, and click the "data acquisition" button on the DISLAB interface when starting the telescopic arm 202 to start the experiment.

[0153] (3) After the collected image has stabilized for a period of time, click the Pause button, turn off the power of the robotic arm, right-click the peak point of the obtained curve, check "Show data points in the graph" and "Show coordinate values ​​with mouse", move the mouse to the sample point to be measured, and the Y value of the coordinate corresponding to the sample point is the peak value of the induced electromotive force at that location.

[0154] The data obtained by measuring the induced electromotive force of low gear and high gear respectively.

[0155] 2.3 Experimental study of motional electromotive force

[0156] (1) A DC power source 101 is connected to the Helmholtz coil 102 to generate a uniform magnetic field in the middle of the Helmholtz coil 102; the controller of the telescopic arm 202 is directly connected to the 220V power supply, a rectangular induction coil is fixed at the lower end of the telescopic arm 202, and both ends of the induction coil group 201 are connected to a digital voltmeter;

[0157] (2) Keeping the number of coil turns and the speed of the telescopic arm 202 constant, different currents are passed through the power supply 101 to make the Helmholtz coil 102 generate magnetic fields of different strengths, and explore the relationship between the electromotive force E generated by the induction coil group 201 and the magnetic field size B;

[0158] (3) Keeping the current supplied by the power source 101 unchanged and the speed of the telescopic arm 202 unchanged, the number of coil turns is changed (to 100 turns, 200 turns, and 300 turns respectively); explore the relationship between the electromotive force E generated by the induction coil group 201 and the number of coil turns N;

[0159] (4) Keeping the current supplied by the power source 101 unchanged and the number of coil turns unchanged, changing the extension speed of the telescopic arm 202, and exploring the relationship between the electromotive force E generated by the induction coil group 201 and the speed V of the magnetic flux lines cut by the coil;

[0160] (5) After the experiment, the recorded data was processed and analyzed using MATLAB.

[0161] 2.4 Experimental results of the multifunctional electromagnetic experiment instrument based on phyphox software and Helmholtz coil 102

[0162] 2.4.1 Study and Analysis of the Magnetic Field Distribution Law of the Helmholtz Coil 102

[0163] (1) Before the experiment, the geomagnetic intensity in the direction of the device’s axis was measured to be 40.15 B / uT, which was used to correct the experimental results.

[0164] (2) When a current of 1 A is passed through the Helmholtz coil 102, the magnitude of the magnetic field is measured by the phyphox software on a mobile phone to obtain accurate experimental data.

[0165] (3) MATLAB is used to process the data of the Helmholtz magnetic field distribution law, and the magnetic field distribution around the Helmholtz coil 102 is studied using the magnetometer in the phyphox software, as shown in FIG. Figure 5 shown.

[0166] Through a large number of experiments, it is found that when the mobile phone is located near the middle axis of the two coils, the center point of the axis is taken as the origin, and the magnetometer shows that the difference in the magnitude of the magnetic field near the origin is not large. This shows that the self-made Helmholtz coil 102 of the device has a relatively large range of uniform magnetic field near the axis of the two coil centers, which is consistent with the distribution of the magnetic field generated around the Helmholtz coil 102 in theory, and the experimental design is scientific and effective.

[0167] 2.4.2 Experimental examples of induced electromotive force

[0168] (1) The radius of the induction coil group 201 is 0.047 m, and the number of turns N is 200 turns;

[0169] (2) When a power triangle wave current is passed into the Helmholtz coil 102, the rate of change of magnetic flux in the coil is measured by the mobile phone phyphox software At the same time, the actual induced electromotive force is recorded by a digital voltmeter.

[0170] (3) When the area of ​​the induction coil group 201 is constant, the induced electromotive force The slope can be automatically generated by selecting data in the Bt diagram of the magnetic field measured by 5phyphox software Therefore, the theoretical value of the induced electromotive force can be calculated and accurate experimental data can be obtained.

[0171] (4) Data processing of the induced electromotive force experiment was performed using MATLAB, and the relationship between the induced electromotive force and the rate of change of the magnetic field was obtained as shown in the figure below: Figure 6 shown.

[0172] Experiments show that through the law of electromagnetic induction The calculated theoretical value (shown by the dotted line in the figure) is basically consistent with the actual measured value (shown by the solid line in the figure) at both ends of the induction coil group 201, and the error is within 2%. According to the experimental data and the linear fitting analysis of Matlab, the induced electromotive force generated in the closed circuit coil is proportional to the rate of change of the magnetic field (magnetic flux).

[0173] 2.4.3 Experimental examples of exploring motional electromotive force

[0174] (1) The size of the rectangular induction coil is 10cm*19-21cm. When cutting back and forth, the lower 10cm edge of the rectangular coil effectively cuts the magnetic flux lines.

[0175] (2) A DC power source is supplied to the Helmholtz coil 102, and the telescopic arm 202 is started to make the lower end of the coil move in the magnetic field to cut the magnetic flux lines, and the actual induced electromotive force is recorded by a digital voltmeter.

[0176] (3) Keeping the number of turns N of the rectangular induction coil unchanged and the speed of the telescopic arm 202 unchanged, currents of 0.3A, 0.6A, 0.9A, 1.2A, and 1.5A are respectively passed through the Helmholtz coil 102 to change the magnitude of the magnetic field B (B1<B2<B3<B4<B5), and the relationship between the motional electromotive force and the magnitude of the magnetic field is explored to obtain corresponding conclusions.

[0177] (4) A current of 1A is passed through the Helmholtz coil 102 to keep the magnetic field size B constant and the movement speed of the telescopic arm 202 constant. Rectangular induction coils with 100 turns, 200 turns, and 300 turns are used to cut the magnetic flux lines, respectively, to explore the relationship between the motional electromotive force and the number of turns of the induction coil group 201, and to obtain the corresponding experimental conclusions.

[0178] (5) A current of 1A is passed through the Helmholtz coil 102 to keep the magnetic field B constant. A rectangular induction coil with 200 turns is used to cut the magnetic flux lines, and the speed of the telescopic arm 202 is gradually increased (V1<V2<V3<V4<V5). The relationship between the motional electromotive force and the speed at which the coil cuts the magnetic flux lines is explored, and the corresponding experimental conclusions are obtained.

[0179] 2.4.4 Conclusion

[0180] The design of the device involves the comprehensive application of modern technologies and basic physical principles such as electromagnetism, superposition of magnetic fields, phyphox software, and electromagnetic induction phenomenon. The magnetic field generated by the device is controllable, and the strength of the magnetic field can be changed by changing the current input into the Helmholtz coil 102. In the case of the Helmholtz coil 102, a thicker enameled wire is used to increase the current that the coil can carry, and at the same time, the adjustable range of the magnetic field is increased. This article mainly conducts experimental exploration from three experimental projects, but the experimental projects that can be carried out are not limited to these three projects. Take the above operation as an example:

[0181] The magnetometer in the smartphone phyphox software was used to study the magnetic field distribution around the Helmholtz coil 102. The experimental results show that when the mobile phone is near the middle axis of the two coils, the magnetometer measurement shows that the magnitude of the magnetic field is the same, indicating that the Helmholtz coil 102 made by the device has a relatively uniform magnetic field in a large range near the central axis, which is consistent with the theoretical magnetic field distribution around the Helmholtz coil 102. In the process of exploring the magnetic field using the phyphox software, the magnetometer sensor has good performance, high accuracy and easy operation.

[0182] After the triangular wave power supply is passed through the Helmholtz coil 102, the magnetic field near the central axis can be uniformly changed. A circular induction coil is placed in the middle of the axis, and the two ends of the coil are connected to a digital voltmeter or an oscilloscope to measure the generated induced electromotive force. It can be observed that as the triangular wave current changes, the magnetic field in the Helmholtz coil 102 changes, thereby generating an induced electromotive force, thereby realizing the study of the induced electromotive force.

[0183] After a DC power supply is passed through the self-made Helmholtz coil 102, a steady magnetic field can be generated near the central axis. A rectangular induction coil is fixed on the telescopic arm 202 and the coil is connected to a digital voltmeter or an oscilloscope. Under the drive of the telescopic arm 202, one side of the rectangular induction coil cuts the magnetic flux line to generate an induced current, thereby analyzing and studying the motional electromotive force.

[0184] The design of this experimental instrument involves a wide range of knowledge, is highly comprehensive, and has rich functions, realizing "one device for multiple uses". The equipment has good experimental results and small errors, is easy to make and obtain materials, has good repeatability, is easy to make and promote, and is conducive to making up for the lack of quantitative exploration in electromagnetic induction experiments.

[0185] The design of this experimental instrument involves a wide range of knowledge, is highly comprehensive, and has rich functions, realizing "one device for multiple uses". The equipment has good experimental results and small errors, is easy to make and obtain materials, has good repeatability, is easy to make and promote, and is conducive to making up for the lack of quantitative exploration in electromagnetic induction experiments.

[0186] The main functions of teaching aids are:

[0187] (1) Demonstration of physical phenomena. Physical teaching aids can be used to demonstrate the physical phenomenon of electromagnetic induction, allowing students to better understand the laws and principles of electromagnetic induction.

[0188] (2) Cultivate practical and innovative abilities. By integrating the DIS modern voltage sensor module with the self-made light-emitting diode voltage comparator 301, the electromagnetic induction experiment is explored to train students' physical thinking. In the process of operation, students' hands-on problem-solving ability is cultivated. The instrument also supports students to carry out a series of scientific innovations based on their original foundation.

[0189] (3) It is conducive to the introduction of modern educational technology into the classroom. By integrating modern educational technology with traditional physics teaching, the analysis of induced electromotive force from qualitative to quantitative has been realized, which has promoted the popularization of modern educational technology in border areas.

[0190] Application of teaching aids:

[0191] (1) Assisting scientific research. This physics teaching aid can assist middle school teachers in scientific research, help teachers conduct deeper research on the law of electromagnetic induction, and play a role in feeding back scientific research to teaching.

[0192] (2) Scientific demonstrations and popular science activities. Physics teaching aids can be used in scientific demonstrations and popular science activities to show the public physical principles and phenomena. For example, by showing the multifunctional electromagnetic induction quantitative exploration instrument in this experiment, the audience can be attracted to increase their understanding and knowledge of physical science.

[0193] (3) Scientific competitions and games. Physics teaching aids can be used in scientific competitions and games to help students conduct experiments and solve physical problems. For example, in a physics competition, students can use a multifunctional electromagnetic induction quantitative exploration instrument to conduct experimental verification and data analysis, demonstrating their physical experimental skills and scientific thinking ability.

[0194] The distribution of induced electromotive force can be obtained from the experimental data graph, but it is still not an ideal sinusoidal distribution. The initial guess is that it may be because the metal reciprocating rod is magnetized by the induced current in the coil when entering the coil, so that the metal magnet that excites the induced electromotive force is no longer excited by a strong magnet, but by the induced electromotive force excited by the exciting magnet composed of a strong magnet and a magnetized metal rod. Therefore, the obtained experimental data sample fitting curve is not a standard triangular curve. Moreover, due to the mechanical characteristics of the reciprocating metal rod, it can be seen that the symmetry axis of the obtained sample curve moves downward at the same frequency at high-end. The preliminary analysis is that the rate of descent of the metal rod is faster than the rate of ascent, so the peak of the positive half-axis is higher than the peak of the negative half-axis. The unevenness of the data obtained at high-end is not smooth. We believe that this is because the reciprocating motion of the metal rod is accelerated at high-end, but the hardware conditions of the instrument for measurement and recording are limited, so we will try to optimize the hardware system in the future to conduct more accurate data testing. In the future, we plan to use Fourier transform to divide the sample data into different waves to distinguish the causes of the waves and noise waves required for our experiment one by one, and then make further improvements to the subsequent teaching aids structure and materials based on the causes.

[0195] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite multifunctional electromagnetic induction experiment instrument, characterized in that: include: A magnetic field generating part (1), the magnetic field generating part (1) comprising a power source (101), a Helmholtz coil (102) and a strong magnet; A self-made induction coil part (2), wherein the induction coil part (2) comprises an induction coil group (201) with different numbers of turns and a telescopic arm (202); A data acquisition part (3), wherein the data acquisition part (3) includes a smartphone phyphox software, a digital voltmeter, a DIS voltage sensor module, and a self-made diode voltage comparator (301); The self-made diode voltage comparator (301) is composed of eight LM339 voltage comparators, and the voltage generated by electromagnetic induction is sent to the non-inverting terminal and the inverting terminal of the comparator through the voltage formed by the operational amplifier LM741. The self-made diode voltage comparator (301) is provided with a plurality of reference voltage levels, and each level of reference voltage is connected to a light-emitting diode. When the output voltage of the electromagnetic induction power supply exceeds the corresponding reference voltage, the corresponding light-emitting diode lights up. The principle diagram thereof is shown in FIG7.

2. A composite multifunctional electromagnetic induction experiment instrument according to claim 1, characterized in that: The magnetic field generating part (1) also includes a function signal generator. The Helmholtz coil (102) is passed through an enameled wire with a diameter of 0.7-0.9 mm. The Helmholtz coil (102) has an outer diameter of 21-23 cm, an inner diameter of 19-21 cm, and 340-360 turns.

3. A composite multifunctional electromagnetic induction experiment instrument according to claim 1, characterized in that: The induction coil group (201) comprises a circular induction coil and a rectangular induction coil, which are used to explore the induced electromotive force and the motional electromotive force respectively.

4. A composite multifunctional electromagnetic induction experiment instrument according to claim 3, characterized in that: The circular induction coil is a single-layer coil wound by self-winding an enameled wire with a diameter of 0.3-0.5 mm. The specifications of the circular induction coil are a radius of 4.6-4.8 cm and a number of turns of 190-210.

5. The composite multifunctional electromagnetic induction experiment instrument according to claim 3, characterized in that: The rectangular induction coil is made of 0.4mm enameled wire, and its size is 10cm*19-21cm, but the number of turns is 100 turns, 200 turns, and 300 turns.

6. The composite multifunctional electromagnetic induction experiment instrument according to claim 3, characterized in that: The rectangular induction coil is mounted on a telescopic arm (202); the telescopic arm (202) has a telescopic length of 10-20 cm and an adjustable speed range of 0-9 m / s.

7. The composite multifunctional electromagnetic induction experiment instrument according to claim 1, characterized in that: The data acquisition part (3) comprises an induced electromotive force acquisition part and a magnetic field acquisition part. The induced electromotive force acquisition part comprises a four-and-a-half-digit high-precision digital voltmeter and a self-designed diode voltage comparator (301) and a DIS voltage sensor module. The magnetic field acquisition part acquires data through a magnetometer sensor in the phyphox software of a smartphone.

8. The composite multifunctional electromagnetic induction tester according to claim 1, characterized in that: The data acquisition part (3) also includes a display (302), and the display (302) is connected to a computer host (303).

9. The composite multifunctional electromagnetic induction experiment instrument according to claim 1, characterized in that: The Helmholtz coil (102) comprises two groups of coils parallel to each other, and the two groups of parallel coils are connected and coaxial.

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