Principles and Applications
This article covers Hall sensors. Modern motor control typically requires closed-loop feedback, so Hall sensors are commonly used measurement devices.
A Hall sensor is based on the Hall effect and detects the presence and strength of a magnetic field. It typically consists of a Hall element, an amplifier, and output circuitry. Hall sensors are used across industry, automotive, electronics, and medical fields to provide reliable magnetic field detection and measurement. Common applications include:
1. Position detection and speed measurement: Hall sensors can detect object position, for example measuring steering angle or vehicle speed. They are also used to measure rotational speed and rotor angle in motor control and vehicle power systems, providing feedback to a processor to monitor motor motion.
2. Proximity switches: Hall sensors can function as proximity switches, detecting when an object approaches or leaves the sensor and triggering appropriate actions to prevent collisions or initiate device behavior.
3. Current measurement: Hall sensors can measure current flowing through a conductor. This is useful in power systems and electronic equipment, and the galvanic isolation provided by Hall sensors helps avoid mutual interference during current sensing. Many microcontrollers sample signals via ADC inputs, which as analog inputs are susceptible to interference; using Hall devices can provide the required isolation.
4. Magnetic field measurement: Hall sensors measure magnetic field strength and direction and are used in geomagnetic sensing, magnetometers, and magnetic resonance imaging. Hall sensors have strong interference immunity and their cost has been decreasing, especially with growing availability of domestically produced chips in the Chinese market, so their use is becoming more widespread.
Classification of Hall Sensors
Two common types of Hall sensors are voltage-output and current-output devices. They differ in operating principle and output signal form.
(1) Voltage-output Hall sensors: These devices output a voltage signal. When the Hall element is exposed to an external magnetic field, a potential difference (Hall voltage) is generated across the element. That voltage is amplified and output as a voltage signal. Voltage-output Hall sensors usually require an external power supply, and the output voltage depends on the magnetic field strength and direction.
Common voltage-type Hall sensors include DRV5015 and DRV5057, which are compact and have high sensitivity.
(2) Current-output Hall sensors: These devices output a current signal. Under an external magnetic field, the Hall element produces a transverse Hall current. By measuring that Hall current, the magnetic field strength and direction can be determined.
Common current-output Hall sensors include ACS714 and ACS725.
When selecting a voltage-type or current-type Hall sensor for a circuit, choose based on design requirements and cost. Voltage-type sensors are suitable for applications requiring high accuracy of magnetic field strength and sensitivity to signal amplitude changes. Current-type sensors are suitable where magnetic field variations are relatively small and signal attenuation is less critical; in some cases, current-type outputs are converted to voltage for MCU ADC sampling.
