Sensors of position and motion

Transcription

1 Sensors of position and motion Linear (translational) /angular (rotary) binary (logical output variable) with digital output : incremental (relative) / absolute, optical / magnetic Linear resistive inductance capacitive optical magnetic

2 Sensors of motion with binary output contacting: (switch) microswitch tactile (conductive rubber) Noncontacting: (proximity detector) magnetic optical electromagnetic variable capacitance...

3 Sensors of motion with binary output (proximity switch) Binary : microswitch reed contact Wiegand sensor linear sensor of motion + compator: Hall probe (sensor) magnetoresistor photoelectric switch (PES) capacitive...

4 Reed (relay) contacts Contacts made from magnetically soft material are controlled by permanent magnet switch is open in quiescent state small hysteresis is welcome problem: multiple zones of switching application: revolutions (bike), position (door) Φ F k I 0 F 0 F 0 F 3' 3 4 1' 1 2' x x a) 1' 1 2' b) x 1' 1 2' x c) d)

5 Reed contacts: zones of switching ζ yζ S J ζ 0 Z Z V y V S J ζ 0 Z Z V y y V Z

6 Wiegand sensor Highly asymetric hysteresis loop: great Barkhausen jump (in t1) induces large voltage peak in opposite direction (t2) slow change => low voltage + constant amplitude of induced voltage (unlike classical speeddependent induction coil with magnet) - must be periodically re-magnetized to both polarities B[mT] S 1 J U a) t 2 t b) U[V] c) H [A/cm] t 1 t 2 t Siemens

7 Wiegand sensor Controlled by permanent magnet based on asymmetrical Barkhausen jumps source of energy (generator) waveform of voltage pulse - independent of the rate of change of B Inductive coil (inductive sensor) Controlled by permanent magnet based on Faraday law of induction source of energy (generator) waveform of pulse depends on the rate of change of B!! (i.e. low speed => failure) N S N S

8 Hall switch (solid state switch) One of the most often used position switches does not depend on dφ/dt Hall voltage u = K H BI/d (static response, can measure constant field) technology - often CMOS => cheap production min. 3 output pins various switching characteristics operation in given frequency range of (dynamic type) polarity and hysteresis feasibility of differential mode of operation and smart sensing

9 Hall switch position / speed sensing Placement of permanent magnet Honeywell

10 Hall sensors of velocity and position used for control of the engines with internal combustion Active Speed and Position Sensors for Engine Management Honeywell

11 Intelligent Hall sensor Micronas HAL 800: 3 output leads analogue <> digital mode of operation

12 Magnetoresistors: Ferromagnetic magnetoresistors AMR: Anisotropical magnetoresistance GMR: Giant magnetoseristance (+ semiconductor magnetoresistors = obsolete)

13 potentiometer (not rheostat): Resistive sensors of motion - angular U R R 1 x R 2 single turm multiturn (helical, helipot) - translational (linear) Mechanical gearing can be used to match range cable sensor of motion : up to 40 m - drum, spring nonlinear relation output-position possible (resistance proportional to length of winding i.e. - h(x)... profile potentiometer) h ( x) dx

14 U R R 1 x effect of loading R 2 R z U 2 U 20 R 1 R 2 R z U 2 Must be used with a high Zinp amplifier R v R V U 2 I R 1 + R z R 2 U 2 R R V R V A R v R D R D I a) b)

15 Resistive sensors of position - technology of production metal wirewound! bouncing of wiper (2 wipers), resolution metal layers non - metal (carbon, cermet) conductive plastic (electrolytical, mercury wiper -minimal friction)

16 Resistive sensors of motion - critical items input resistance of measuring circuit limited non linearity dissipated power P = U 2 /R heating, power consumption contact of wiper (influence of impurities and chemical products) noise drift (long term %) dynamic properties (bouncing, friction) reproducibility (< 0.1 %) linearity (1 %.. 20 ppm) noise (for large R) mechanical ruggedness (vibrations) life time (typ cycles)

17 LONG STROKE LINEAR POTENTIOMETERS SPECIFICATIONS Total Resistance: 5000 Ohms ± 20% Linearity: ±1% FS Hysteresis: ±0.001" (0.025 mm) Repeatability: ±0.0005" (0.012 mm) Incremental Sensitivity: " Power Rating: 0.75 watts/stroke inch Temp. Range: -65 to 105 C (-85 to 221 F) Operating Force: 450 grams (1 Lb) maximum Shaft: 0.236" (6 mm) diameter with 1¼4-28 threaded end adapter Life: 100 million operations up to 12" stroke-derated proportionally for longer units (standard rate of travel 2"/sec) Omega