The use of solid-state devices such as magnetic sensors is very popular when necessary to sense position, velocity or directional movement. As they are non-contact and offer wear-free operation, electronics designers prefer to select them for their design. For example, the robust design of sealed Hall Effect devices make them immune to vibration, dust and water, offering a low maintenance solution for the user.
Automotive systems mainly use magnetic sensors for sensing speed, distance and position. For example, the angular position of crankshafts decides the proper firing angle of the spark plugs, air-bag control depends on position of car seats and seat belts and wheel speed detection is necessary for ABS or anti-lock braking system.
Magnetic sensors typically respond to a wide range of magnetic fields and therefore, they are used in a variety of different applications. Hall-effect sensors respond to magnetic field density around them, while generating a proportional electrical output signal. Magnetic fields show two important characteristics, the flux density and the polarity. When activated beyond a preset threshold, the hall-effect sensor develops a voltage linearly proportional to the flux density impinging upon it. However, hall-effect sensors are susceptible to external magnetic fields and/or the presence of metal objects nearby.
Replacing hall-effect sensors with LVDT or Linear Variable Differential Transformers offers superior immunity to noise and interference, while improving the sensitivity tremendously. By using inductive technology, designers avoid the use of magnets, thereby improving immunity to interferences. Now, with LVDT-on-PCB, the inductive sensor IC based on LVDT makes these sensors suitable for use in the automotive and industrial fields.
The device, LVDT-on-PCB, is suitable for several applications related to industrial automation and control systems. Among these are specific applications such as linear displacement measurement. Therefore, such sensors simplify sensing of fluid levels, gear position for transmission actuator positioning and proximity detection of brake lamp switch. Additionally, LVDT-on-PCB sensors are also useful in sensing angular motion such as in rotary controls and measuring pedal positions, rotating shaft positions and robotic arm positions.
As the LVDT senses without making contact, the reliability offered is high. For example, the associated IC LX3301A, from Microsemi, has an embedded 32-bit processing engine running on an internal oscillator of frequency range between 1 and 5 MHz, along with a 12 KB program memory. It offers two sensor input channels with integrated demodulators and two 13-bit ADCs with sample rates up to 2 KHz. The user can save their configuration in the user-programmable non-volatile configuration memory of size 16×16 bits.
The LX3301A processes signals that the inductive sensors generate. As the inductive sensors work on LVDT principles, the IC includes an integrated exciter to drive the PCB-based sensor coils of low inductance. A matched analog channel pair processes the sensor signals as a pair of sine/cosine waves, thereby rejecting the noise sources both internal to and external to the sensor assembly.
You can use the LX3301A for measuring displacement such as linear and/or angular/rotation and proximity in electromechanical systems. The resolution offered is excellent, for example, in applications involving 360-degree rotation, the device can achieve a measurement resolution up to or less than 0.5-degree. You can retain the configuration and calibrations for the sensor system in its internal EEPROM.
