Sensores Magnticos Jos Augusto EPUSP 2010 1 The

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Sensores Magnéticos José Augusto EPUSP 2010 1

Sensores Magnéticos José Augusto EPUSP 2010 1

The Types of Magnetic Sensors • • Reed Switches Variable Reluctance Flux-gate Magnetometers Magneto-Inductor

The Types of Magnetic Sensors • • Reed Switches Variable Reluctance Flux-gate Magnetometers Magneto-Inductor Hall solid state devices Anisotropic Magnetoresistive (AMR) New Giant Magnetostrictive (GMR) 2

Magnetic Sensor Technology Field Ranges 3

Magnetic Sensor Technology Field Ranges 3

Hall Effect Magnetic Sensors • Magnetic Sensors based in Hall effect uses Bipolar/FET IC

Hall Effect Magnetic Sensors • Magnetic Sensors based in Hall effect uses Bipolar/FET IC technology in combination with the Hall effect sensor to produce two type detectors: Linear and Threshold. • The Linear sensors detects the motion, position, or change in field strength of an electromagnet, a permanent magnet, or a ferromagnetic material. The output is almost linear in respect to a magnetic field. • The Threshold devices gives digital output capabilities. • When the applied magnetic flux density exceeds a certain limit, the trigger provides fast and clean transition from Off to On. • Hall sensors are reffered as “High Field Sensor” 4

The Hall Effect • The basic Hall element is a small sheet of semiconductor

The Hall Effect • The basic Hall element is a small sheet of semiconductor material, referred as the Hall element, (or active area). • A external constant voltage source forces a constant bias current, to flow in the semiconductor sheet. • The output takes the form of a voltage, measured across the width of the sheet proportional to the magnetic field. E. H. Hall in 1879 5

Linear Hall Effect Sensors • The output voltage of the basic Hall element is

Linear Hall Effect Sensors • The output voltage of the basic Hall element is quite small. The addition of a high-quality dc amplifier and a voltage regulator to the circuit improves the transducer’s output and allows it to operate over a wide range of supply voltages. • The sensor’s frequency response is flat-up on the range 25 k. Hz ~100 k. Hz. Vout= 1 – 25 m. V/G Tr= 3 µS ≈ 116 k. Hz R$ 7, 00 - US$ 20, 00 6

Ratiometric Linear Hall Effect Sensor • These devices has a Bi. CMOS monolithic circuit

Ratiometric Linear Hall Effect Sensor • These devices has a Bi. CMOS monolithic circuit improved temperature-compensating circuitry, small-signal amplifier, filter and a rail-to-rail output. • Sensitivity: 2. 5 m. V/G to 5 m. V/G. • Bandwidth: 30 k. Hz • Ideal for use in the rigorous environments found in automotive and industrial linear sensing systems. • New programmable devices has both the quiescent voltage output and sensitivity adjustable between 2 and 9 m. VG A 1321 R$ 4, 50 7

Digital Hall-Effect Switches • The addition of a Schmitt-trigger threshold detector, with built-in hysteresys

Digital Hall-Effect Switches • The addition of a Schmitt-trigger threshold detector, with built-in hysteresys gives digital output capabilities • An open-collector NPN output transistor added to the circuit gives the switch digital logic compatibility. • Output is clean, fast and typically operates at up to a 100 k. Hz repetition rate. 8

Digital Hall Sensor Operation • In the absence of any magnetic field, most Hall-effect

Digital Hall Sensor Operation • In the absence of any magnetic field, most Hall-effect digital switches are designed to be OFF (open circuit). • When the applied magnetic flux density exceeds a certain limit, the trigger provides a transition from Off to On. • Hall switches have an active area that is closer to one face. To operate the switch, the magnetic flux lines must be perpendicular to this face, and must have the correct polarity. Built-in hysteresis eliminates oscillation by introducing a magnetic dead zone 9

Categories of Digital Hall Effect Sensors • Unipolar- referred to as “switches” require a

Categories of Digital Hall Effect Sensors • Unipolar- referred to as “switches” require a single polarity magnetic field switchpoints (north or south pole) for operation (A). • Latching- require both positive and negative magnetic fields for operation. Are designed for symmetrical operation (B). • Bipolar- have switchpoints that occur in either relatively more positive or more negative ranges. A B 10

Switchpoint for a Bipolar Switch Possible switchpoint ranges for a bipolar switch 11

Switchpoint for a Bipolar Switch Possible switchpoint ranges for a bipolar switch 11

Magnetoresistor • It is possible to measure the increased resistance of special resistors due

Magnetoresistor • It is possible to measure the increased resistance of special resistors due to the deflected electrons. In this case, the sensor is called a Magnetoresistor. Two types are available: • AMR- Anisotropic Magneto Resistive • GMR- Giant Magneto Resistive • Magneto-Resistive sensors (“low-field magnetic sensor”) are usually made of a nickel-iron (Permalloy) thin film deposited on a silicon wafer and patterned as a resistive strip. • The Magnetoresistor AMR Bandwidth 1 -5 MHz Sensivity 2, 5 - 4 m. V/V/Gauss The Giant Magnetoresistance Effect (GMR) has an important application for miniature magnetic sensors in the dataread head for disk drives. Wheatstone Bridge Patterned Array, Philips 12

AMR Sensors Characteristics • AMR sensors are directional and provide only an amplitude response

AMR Sensors Characteristics • AMR sensors are directional and provide only an amplitude response to magnetic fields in their sensitive axis. • By combining two AMR sensors, the part becomes a 2 -axis sensor and when mounted horizontally, is able to detect any horizontal magnetic fields into X and Y directions. HMC 1001 (1 axis) US$ 21, 00 HMC 1002 (2 axis) US$ 25, 00 13

Magnetoresistive Sensor Exemple • Hall effect sensor: measures the magnet field “strength” • Magnetoresistive

Magnetoresistive Sensor Exemple • Hall effect sensor: measures the magnet field “strength” • Magnetoresistive sensor: measures the “angle direction” of magnetic field • The output voltage from the AMR sensor is a function of the sensor sensitivity equation: • VOut+ - VOut- = S * Vb * Bs • For Honeywell HMC 1001 Vout= 2, 5 m. V • S = Sensitivity (nominally 1 m. V/V/gauss)* • Vb = Bridge Supply Voltage in volts (5 V) • Bs = Bridge Applied Magnetic Flux (0. 5 Gauss) 14

Magnetoresistive Sensor Circuit Amplifier • Sometimes the magnetoresistive sensors require follow-on amplification to make

Magnetoresistive Sensor Circuit Amplifier • Sometimes the magnetoresistive sensors require follow-on amplification to make induced field changes easier to detect. • The (diffential) output of the sensors requires a differential amplifier. • For a Amp. Op gain of 200 and Vcc=3 V • Vout ~ 300 m. V 15

Some Vehicle Detection Circuits HMC 1052= R$ 200, 00 Simple Vehicle Detection Circuit Microcontroller-Based

Some Vehicle Detection Circuits HMC 1052= R$ 200, 00 Simple Vehicle Detection Circuit Microcontroller-Based Vehicle Detection Circuit 16

Linear Position Sensing Output P -P Bridge Ohms Sensitivi ty Range 120 m. V

Linear Position Sensing Output P -P Bridge Ohms Sensitivi ty Range 120 m. V 5000 2. 1 m. V/Deg +/- 45 Deg Multiple sensor bridges lined up Combined Bridge Waveforms 17

Compatibility With Microprocessors The analog output voltage of the amplifier is typically fed to

Compatibility With Microprocessors The analog output voltage of the amplifier is typically fed to an Analog-to-Digital Converter (ADC) stage stand-alone or within a microprocessor integrated circuit. A recommendation of 10 -bit ADC circuits or higher is expected. 18

Sensor Solutions for Automotive Applications 19

Sensor Solutions for Automotive Applications 19

FIM 20

FIM 20