GT4501A Helmholtz Coil Magnetic Field Tester Instruction Manual I. Overview In recent years, in research and industry, integrated Hall sensors are widely used in magnetic field measurement, which has high measurement sensitivity, small volume, and easy movement and positioning in a magnetic field. GT4501A Helmholtz Coil Magnetic Field Tester (hereinafter referred to as Magnetic field tester) uses a constant current source to generate a constant magnetic field, and uses an integrated Hall sensor to measure the magnetic induction of each point on the axis of the current-carrying circular coil and the Helmholtz coil, and study the magnetic field distribution of the Helmholtz coil. The instrument has the advantages of reasonable design, fine production, generous shape and easy operation. It is suitable for use in colleges and universities. Second, the instrument constitutes The Helmholtz coil magnetic field tester consists of two parts. They are the Helmholtz coil magnetic field test frame part (see Figure 1, Figure 2) and the Helmholtz coil magnetic field measuring instrument part (see Figure 3). Figure 1 Helmholtz coil frame section Figure 2 GT4501A Helmholtz coil magnetic field test stand panel Third, the main technical performance 1) Environmental adaptability: Working temperature 10 ~ 35 ° C; relative humidity 25 ~ 80%. Figure 3 GT4501A Helmholtz coil magnetic field measuring instrument panel 2) Helmholtz coil former Two excitation coils: The effective radius of the coil is 110mm, the number of turns of a single coil is 500åŒ, the center distance of the two coils is 110mm, and the maximum load current of temperature rise is not more than 10°C is not less than 0.5A. Measuring magnetic field sensor: Hall element type SS495A Mobile device: axial movable distance 230mm, radial movable distance 75mm, distance resolution 1mm 3) GT4501A Helmholtz magnetic field experiment instrument The GT4501A Helmholtz magnetic field tester consists of an adjustable constant current source and a Gauss meter that measures the magnetic field. Built-in constant current source part: Output current: 0~0.5A, maximum voltage 24V, 3-digit half-meter display, minimum resolution 1mA Built-in magnetic field measurement part (Gauss meter): When working with the Hall sensor in the Helmholtz coil frame, the measuring magnetic field range is 0~2.2mT, and the minimum resolution is 0.001mT. 4) Power supply: 220V±10%, power consumption: 50VA 5) Dimensions: Helmholtz coil frame 340 × 270 × 250mm Magnetic field tester 320 × 300 × 120mm 6) Total mass: 15kg Fourth, the experimental principle 1. Magnetic field of current-carrying circular coil and Helmholtz coil 1) Current-carrying circular coil magnetic field A circular coil with a radius R and a current I, the formula of the magnetic field on the axis is: (1) Where N0 is the number of turns of the circular coil, and X is the distance from a certain point on the axis to the center O. Figure 4 Magnetic field distribution of a single toroidal coil Figure 5 Magnetic field distribution of a Helmholtz coil In this experiment, N0=500åŒ, I=500mA, R=110mm, and the center O is x =0, which can be calculated as the magnetic induction strength of the circular current coil B=1.43mT. 2) Helmholtz coil The so-called Helmholtz coil is two parallel coils that are parallel and coaxial with each other, so that the current I in the same direction is passed through the coil. The theoretical calculation proves that when the coil spacing a is equal to the coil radius R, the two coils are combined on the shaft (two coils) The center of the circle is uniform in the vicinity, as shown in Figure 5. This uniform magnetic field is widely used in engineering applications and scientific experiments. Helmholtz coil magnetic induction =1.43×1.431mT =2.05mT 2. Hall effect method for measuring magnetic field 1) Hall effect method measurement principle When the conductor with the current I is placed in the magnetic field, an additional potential difference EH will be generated in the direction perpendicular to the current I and the magnetic field B. This phenomenon was first discovered by Hall in 1879, so it is called the Hall effect. The difference UH is called the Hall voltage. The Hall effect is essentially the deflection caused by the action of charged particles in the magnetic field by Lorentz forces. When charged particles (electrons or holes) are confined in a solid material, this deflection leads to In the direction of vertical current and magnetic field, positive and negative charges are accumulated on different sides to form an additional transverse electric field. As shown in Fig. 6, the magnetic field B is located in the positive direction of Z, and the semiconductor wafer perpendicular thereto is forwarded along the X direction. The current Is (called the operating current), assuming that the carrier is an electron (N-type semiconductor material), it moves in the negative X direction opposite to the current Is. Due to the action of the Lorentz force f L , the electrons are deflected toward the B side in the negative direction of the y-axis as indicated by the dotted arrow in the figure, and electron accumulation is formed on the B side, while positive charge accumulation is formed on the opposite side A. The moving electrons are also affected by the reverse electric field force f E formed by the two kinds of accumulated heterogeneous charges. As the charge accumulation increases, f E increases, and when the two forces are equal in magnitude (in the opposite direction), f L=- f E, then the electron accumulation reaches dynamic equilibrium. At this time, the electric field established between the end faces of A and B is called the Hall electric field EH, and the corresponding potential difference is called the Hall potential VH. Set the electron to a uniform speed f L=-e Where: e is the amount of electricity, Image 6 At the same time, the force of the electric field acting on the electron is: f E Where: EH is the Hall electric field strength, VH is the Hall potential, and l is the Hall element width When dynamic balance is reached: f L=-f E Let Hall element have a width of I, a thickness of d, and a carrier concentration of n, then the operating current of the Hall element is Available from (2) and (3): (4) That is, the Hall voltage VH (voltage between A and B) is proportional to the product of Is and B, and inversely proportional to the thickness of the Hall element, and the proportional coefficient Called the Hall coefficient, which reflects The strength of the material Hall effect. When the material and thickness of the Hall element are determined, set: Substituting equation (5) into equation (4): In the formula: It can be seen that when I is a constant, there is VH=KHIB =k0B, and by measuring the Hall voltage VH, the unknown magnetic field strength B can be calculated. 2) Integrated Hall sensor Generally, the sensitivity of the Hall element is low, and the Hall voltage value is low when measuring a weak magnetic field. To this end, the Hall element and the amplifying circuit are integrated to increase the output value of the Hall voltage, thus expanding the Hall method magnetic field. The scope of application. The SS495A integrated Hall sensor used in this experiment integrates Hall element, amplifier and thin film resistor residual voltage compensator with small volume. The typical sensitivity is 31.25mV/mT, and the maximum linear measuring magnetic field range is -67~67mT. When the DC 5V is powered, the output of zero magnetic induction is 2.500V. Fifth, the method of use 1. Preparation: Before using the instrument, warm up for 10 minutes. During this time, please familiarize yourself with the composition of the Helmholtz coil test frame and magnetic field measuring instrument, the correct connection method of each terminal, and the instrument. The correct way of operation. 2. Connection between Helmholtz coil former and magnetic field measuring instrument Connect the bias voltage end of the measuring instrument to the bias voltage end of the test stand with the connecting wire of the coaxial plug at both ends. Connect the Hall voltage end of the measuring instrument to the Hall voltage end of the test stand. Fig. 7 Wiring diagram of GT4501A Helmholtz coil magnetic field experiment instrument 3. If only one of the two coils is used to generate the magnetic field, the left or right coil can be selected, and the excitation current of the measuring instrument is connected to both ends of the excitation coil of the test frame by connecting wires with both ends of the insert. The red terminal is connected to the red terminal, and the black terminal is connected to the black terminal. When generating a magnetic field with a Helmholtz coil (double coil), short the black terminal of the excitation coil (left) and the red terminal of the excitation coil (right) with a shorting tab. 4. The center of the Helmholtz coil is provided with a two-dimensional moving device, wherein a long moving device is used to measure the axial magnetic field distribution; a short moving device is used to measure the radial magnetic field distribution, as shown in FIG. Slowly turn the handwheel, and the Hall magnetic sensor box on the moving device moves. By rotating the handwheels of the two moving frames, the Hall magnetic sensor can be moved to the desired position. The position of the magnetic sensor, that is, the magnetic field The position is determined by the corresponding indicator scale. .5, the use of Gauss meter The built-in magnetic field measurement part (Gauss meter), its measurement range is 0 ~ 2.2mT, using a 4-digit digital tube display. Due to the influence of the earth's magnetic field and building construction, when the Helmholtz coil has no current flowing, the display value is not zero. Therefore, when performing the Helmholtz coil magnetic field measurement experiment, the fixed deviation value needs to be corrected. That is, the initial deviation value is deducted in the data processing. Otherwise, the measured value is superimposed on the magnetic field generated by the coil, which causes a large measurement error. For this measuring instrument, there is a design. The zero deviation value automatic correction circuit can memorize this deviation value in the instrument and automatically compensate the fixed deviation value caused by the geomagnetic field. The specific use method is as follows: Connect the measuring instrument to the test stand as shown in Figure 7. Turn on the power, turn the field current potentiometer of the measuring instrument counterclockwise to the end, the ammeter shows zero, the coil does not generate a magnetic field. But this time due to the presence of the earth's magnetic field, As well as the offset voltage of the internal circuit, the display of the millimeter is often not 0. After preheating for 10 to 20 minutes, press the “Zero Adjustment†button on the meter panel until the display on the digital tube changes from 1111 to 3333. Release the button again. This process takes about 2 seconds. At this point, the millimeter header should display 0. If it does not reach zero, repeat the above process. After the zero adjustment is completed, the normal Helmholtz coil magnetic field measurement process can be entered. Sixth, experimental content and data processing 1. Experimental content 1) Measuring the distribution of the magnetic field on the axis of the circular current coil Assume that the excitation coil (left) is selected as the experimental object. The bias voltage on the panel of the meter is connected to the bias voltage of the test rack, and the Hall voltage is connected to the Hall voltage. Connect both ends of the test frame excitation coil (left) to both ends of the excitation current on the measuring instrument. The red terminal is connected to the red terminal and the black terminal is connected to the black terminal. Adjust the excitation current to zero and clear the magnetic induction. Adjust the field current adjustment potentiometer of the magnetic field measuring instrument so that the display value of the meter is 500mA. At this time, the millimeter meter should display a corresponding magnetic induction B value. Taking the center of the circular current coil as the coordinate origin, the value of the magnetic induction B is measured every 10.0 mm, and the excitation current value is kept constant during the measurement. Optional content: In the course of the experiment, the excitation current can be reversed, that is, the connection between the two terminals of the excitation current on the measuring instrument is reversed. Repeat the above process to measure a set of negative magnetic induction B values. The direction of magnetic induction has been reversed. 2) Measure the distribution of the magnetic field on the axis of the Helmholtz coil Wire according to Figure 7, and then zero the magnetic induction when the excitation current is zero. Adjust the field current adjustment potentiometer of the magnetic field measuring instrument so that the display value of the meter is 500mA. At this time, the millimeter meter should display a corresponding magnetic induction B value. Taking the Helmholtz coil center as the coordinate origin, the value of magnetic induction B is measured every 10.0 mm, and the excitation current value is kept constant during the measurement. Optional content: In the course of the experiment, the excitation current can also be reversed, that is, the connection between the two terminals of the excitation current on the measuring instrument is reversed. Repeat the above process to measure a set of negative magnetic induction values ​​B. The direction of the magnetic induction has been reversed. Note: Due to the limitation of the number of displayed bits, when the measured B value reaches or exceeds -2.000mT, the negative mark will flash, indicating that the measured B value is negative. 3) Influence of excitation current magnitude on magnetic field strength At this time, one of the connection methods of the single coil or the Helmholtz coil magnetic field distribution measurement can be selected for wiring, and the magnetic induction intensity is still cleared when the excitation current is zero. Adjust the field current adjustment potentiometer of the magnetic field measuring instrument so that the display value of the meter head is 100mA, and adjust the position of the Hall sensor to the center position of the circular current coil or the center position of the Helmholtz coil. Adjust the excitation current adjustment potentiometer, record the value of the magnetic induction B for every 100mA increase, until the excitation current shows 500mA and record the magnetic induction B value. .2, test data processing 1) Record the measurement data of the magnetic field distribution on the axis of the circular current coil in Table 1. (Note that the origin of the coordinate is set at the center of the circle. The table includes the position of the measuring point, the value of the magnetic induction B (read from the digital millimeter), The experimental curve and the theoretical curve are drawn on the same coordinate paper. Table 1 Axial distance X (mm) B(mT) 2) Record the measurement data of the magnetic field distribution on the Helmholtz coil axis in Table 2 (note that the coordinate origin is set at the midpoint 0 of the two coil center lines), and draw the experimental curve on the grid paper. Table 2 Axial distance X (mm) B(mT) 3) Measure the magnetic field distribution on the Helmholtz coil axis. table 3 Radial distance X (mm) B(mT) 4) Influence of excitation current magnitude on magnetic field strength Table 4 Field current (mA) B(mT) 3. Predicted knowledge related to experiment 1) What is the distribution law of the magnetic field on the axis of a single coil? How is the Helmholtz coil formed? What are the basic conditions? What about its magnetic field distribution characteristics? 2) When measuring the magnetic field with the Hall effect, why is the displayed magnetic field value not zero when the excitation current is zero? 3) Analysis of the cause of the error between the theoretical and experimental values ​​of the circular current magnetic field distribution? Seven, instrument maintenance and maintenance 1. When handling and placing the instrument, avoid strong vibration and impact. 2. When the instrument is not used for a long time, please put on a plastic bag to prevent the humid air from coming into contact with the instrument for a long time. 3. When using the instrument, avoid places with strong magnetic field sources around it. 4. When using it for a long time without using it, please use it before warming up for 30 minutes. Eight, instrument set Product certificate 1 copy Instruction manual 1 copy Power cord 1 Test line 1 group (4) Shorting piece 1 piece Fuse (0.5A) 2 Homecare Bed,Homecare Medical Bed,Nursing Medical Bed,Medical Care Nursing Bed Jiangmen Jia Mei Medical Products Co.,Ltd. , https://www.jiamei-medical.com Its distribution is shown in Figure 4.
, moving in the negative direction of the X in the figure, under the action of the magnetic field B, the Lorentz force is:
B
For the average speed of electron drift, B is the magnetic induction.
I
B=VH/l (2)
(3)
(5)
(6)
It is called the sensitivity of the component. It represents the Hall potential of the Hall element under unit magnetic induction and unit control current. The unit is
, General requirements
The larger the better, the higher the electron concentration (n) of the metal, so its RH or KH is not large, so it is not suitable for the Hall element. In addition, the thinner the element thickness d, the higher the KH, so when it is made, The method of reducing d is often used to increase the sensitivity, but the thinner the d is, the better, because the input and output resistance of the component will increase, which is undesirable for the Hall element.