Magnetic sensors are semiconductor devices that can be used in many types of applications such as position, speed or directional motion detection. They are a wide choice of sensors for electronics designers because of their non-contact, wear-free operation, low maintenance, robust design and, as sealed Hall-effect devices, they are immune to vibration, dust and water.
Magnetic sensors are designed to respond to a wide range of positive and negative magnetic fields in a variety of different applications. A type of magnetic sensor whose output signal is a function of the density of the surrounding magnetic field is called a Hall effect sensor.
What is the Hall effect?
The Hall effect is a phenomenon that was discovered by Edwin Hall in 1879. He noticed that when current flows through a conductor and is exposed to an electromagnetic field, the voltage present is perpendicular to the current and the magnetic field. The discovery of this effect allowed us to easily detect magnetic fields.The Hall Effect detector is a semiconductor-based integrated circuit with hall plates that allows us to detect the presence proportional to the magnetic field and its intensity, and to generate a voltage.
Hall-effect sensors are devices that are activated by an external magnetic field. When the magnetic flux density around the sensor exceeds a certain predefined threshold, the sensor detects it and generates an output voltage called Hall voltage.
Hall-effect sensors essentially consist of a thin rectangular piece of p-type semiconductor material, such as gallium arsenide (GaAs), indium antimonide (InSb) or indium arsenide (InAs), through which a direct current flows. When the device is placed in a magnetic field, the magnetic flux lines exert a force on the semiconductor material that deflects charge carriers, electrons and holes across the semiconductor wafer. This movement of the charge carriers is the result of the magnetic force (conductive element) that they experience as they pass through the semiconductor material.
The Hall effect provides information about the type of magnetic pole and the magnitude of the magnetic field. For example, a south pole would cause the device to produce an output voltage, while a north pole would have no effect. Typically, Hall-effect sensors and switches are designed to be in the “OFF” (open circuit) position when there is no magnetic field. They only turn on (closed circuit state) when they are subjected to a magnetic field of sufficient strength and polarity.
Whether they are unipolar or bipolar, Hall sensors are very popular for high-speed sensing applications such as washing machines or speed counters. Analog Hall effect sensors are used in dial position detection. In devices such as coffee machines, level sensors are used to monitor fluid levels. Hall-effect sensors can also be used as speed sensors, especially for speed and direction of rotation.
Hall-effect sensors are available with linear or digital outputs. The output signal for linear (analog) sensors is taken directly from the output of the operational amplifier, the output voltage being directly proportional to the magnetic field passing through the Hall effect sensor. Linear or analog sensors give a DC output voltage that increases with a strong magnetic field and decreases with a weak magnetic field. In Hall effect sensors with linear output, as the magnetic field strength increases, the output voltage is higher.
If we make a comparison Hall effect sensor with Reed technology :
- Both technologies are contactless
- The reed sensor has a zero consumption, unlike the Hall effect sensor which consumes 20mA continuously.
- The Hall effect sensor can give information proportional to the magnetic field unlike the Reed technology which only works in a binary way.
- The packaging of the Hall effect sensor is very small in size.
Littelfuse offers a wide range of overmolded magnets, in shapes and dimensions identical to the sensors, in different materials: ferrites, alnico or rare earth, from the most economical to the most efficient. Littelfuse offers a standard range of current sensors and we also offer you the possibility to modify the packages of existing standard products such as adding connectors, changing the size or length of the wire, or to realize at your request a complete design of your component in order to facilitate its use. Littelfuse is specialized in custom product development, to meet specific customer requirements, in both REED and Hall Effect technologies. We can produce first parts using prototype tools, the production plant has a magnetic simulator to study the feasibility of your project.