Using a multimeter to test Hall effect devices

Using a multimeter to test Hall effect devices

1. The principle of Hall device

The Hall effect is a magnetoelectric effect. When current passes through a metal foil, if a magnetic field is applied perpendicular to the current, a lateral potential difference will appear on both sides of the metal foil. The Hall effect in semiconductors is more obvious than in metal foils, and ferromagnetic metals will show a very strong Hall effect below the Curie temperature, as shown in Figure 1.

The basic relationship of the Hall voltage UH is: UH=(RH/d)IB;

Where RH is the Hall coefficient;

I - the current passing through;

B - the magnetic induction intensity perpendicular to I;

d - the thickness of the Hall element.

RH/d is called the sensitivity of the Hall element, and its unit is mV/(mA・T).

Hall elements made of semiconductor materials have the advantages of being sensitive to magnetic fields, simple and reliable in structure, low cost, small in size, wide in frequency response, large in output voltage variation and long in service life. They are mainly used in the following areas: measuring magnetic fields, measuring semiconductor characteristics, magnetohydrodynamic power generation, electromagnetic nondestructive testing, Hall sensors, etc.

2. Detection of Hall Elements

The Hall element is generally a four-terminal device. Its basic usage is shown in Figure 2.

The "×" in the figure indicates that the direction of the magnetic field points to the paper surface, E is a DC power supply, R is used to adjust the size of the control current, RL is the load resistor, the two ends of the current I are the input ends, and its internal resistance is the input resistance. I is generally tens to hundreds of milliamperes. The two ends connected to EH are the output ends, and its internal resistance is the output resistance. The domestic Hall elements mainly include HZ, HT, HS series, etc. The main parameters are shown in the attached table

1. Detection method

The input resistance and output resistance of the Hall element can be measured using a multimeter. The measurement circuit is shown in Figure 3.

When measuring the HZ series, the multimeter's Rx10 block should be used, which is more suitable for testing current. For the HT and HS series, the multimeter's Rx1 block should be used. The measured results should be consistent with the corresponding manual. If the resistance is zero or infinite, it means that the component is broken.

2. Estimating sensitivity

Take two multimeters and connect the circuit according to Figure 4.

Set meter I to Rx10 or Rx1 (depending on the control current), provide control current I to the Hall element, and then set meter II to DC 2.5V to measure the Hall electromotive force EH. Move the N pole of a bar magnet vertically close to the surface of the Hall element until the pointer of the meter is observed to deflect. Under the same test conditions, the greater the deflection angle of the pointer of meter II, the higher the sensitivity of the Hall element. It should be noted that when estimating the sensitivity, the input and output leads of the Hall element must not be connected in reverse to increase the Hall electromotive force. Two Hall elements can also be used in series.

3. Detection of Hall Effect Sensor

Sensor

1. Hall sensor

The device made by integrating the Hall element and the measurement circuit using integrated circuit technology is called an integrated Hall sensor. The Hall sensor has the advantages of small size, high sensitivity, large output amplitude, small temperature drift, and low requirement for power supply stability. Hall sensors are widely used in motor speed detection, intelligent electric speed measurement, CNC machine tools and electronic switching circuits. Hall sensors can be divided into two categories: linear and switch types. Their internal circuits are shown in Figure 5.

The Hall sensor is a three-terminal device, with Ucc as the positive power supply terminal, GND as the ground terminal, and Uo as the output terminal. Pin definition (with the side with the model mark facing you): (left) positive power supply; (middle) ground; (right) signal output. The internal components mainly include Hall element (also known as Hall electromotive force generator), operational amplifier, Schmitt trigger, open collector transistor VT and voltage regulator. The voltage regulator provides a rated power supply voltage of 3.4V to the Hall element, operational amplifier and Schmitt trigger. The Hall element can generate a Hall electromotive force that is linearly related to the external magnetic field. It is first amplified by the amplifier, then shaped by the Schmitt trigger, and finally the switching signal voltage is output by VT to obtain a waveform with steep edges to improve the device's anti-interference ability and prevent false operation.

2. Detection of switch type Hall sensor

The test method of switch type Hall sensor is as follows:

First, find a 2k ohm resistor R, connect it between pins ① and ③ as shown in Figure 6, and connect the positive pole of the 12V DC power supply to pin ① of the switch type Hall sensor, and the negative pole to pin ②. Set the multimeter to the DC 50V range, connect the red test lead to pin ③, and the black test lead to pin ②, and observe the changes in the pointer of the multimeter. When the N pole of the magnet approaches the test point of the sensor, the pointer of the multimeter deflects from the high level to the low level; when the N pole of the magnet is away from the test point of the sensor, the pointer of the multimeter deflects from the low level to the high level. If the pointer of the multimeter does not deflect when the N pole of the magnet approaches or moves away from the test point of the sensor. This means that the sensor is damaged and should be replaced in time. In addition, it should be noted that the side of the Hall device with the model mark is the sensitive side, which should face the corresponding magnetic pole of the permanent magnet, that is, the N-type device faces the N pole, and the S-type device faces the S pole. Otherwise, the sensitivity of the device will be greatly reduced, or even stop working.

3. Detection of linear Hall sensor

The test method of linear Hall sensor is as follows: First, connect the resistor RL between pins ② and ③ in Figure 6, and connect the positive pole of the 12V DC power supply to pin ① of the linear Hall sensor, and the negative pole to pin ② of the linear sensor. Set the multimeter to the DC 50V range, connect the red probe of the multimeter to pin ③, and the black probe to pin ②, and observe the change of the pointer of the multimeter. When the N pole of the magnet gradually approaches the test point of the sensor, the voltage measured by the multimeter should change linearly, otherwise, it means that the Hall sensor is damaged and should be replaced in time.