Thiết bị và hệ thống tự động

Thiết bị và hệ thống tự động

Lecturer Ph.D Truong Dinh Chau, Department of Automatic Control, Faculty of Electrical – Electronics Engineering, HCM. City University of Technology tdchau@hcmut.edu.vn 091. 543-74-40 Industry Automation Outcome 3 Logical Sensors • Sensor wiring; switches, TTL, sourcing, sinking • Proximity detection; contact switches, photo-optics, capacitive, inductive and ultrasonic Topics: • Understand the different types of sensor outputs. • Know the basic sensor types and understand application issues. Objectives: Logical Sensors • Inductive proximity - is a metal object nearby? • Capacitive proximity - is a dielectric object nearby? • Optical presence - is an object breaking a light beam or reflecting light? • Mechanical contact - is an object touching a switch? Sinking/Sourcing - Switches current on or off. Plain Switches - Switches voltage on or off. Solid State Relays - These switch AC outputs. TTL (Transistor Transistor Logic) - Uses 0V and 5V. Sensor output types Switched outputs (e.g. Relays) 24 Vdc Power Supply normally open push-button PLC Input Card 24V DC 00 01 02 03 04 05 06 07 COM + - sensor V+ V- relay output TTL Vi Vo Vi Vo Sourcing (supplies voltage/current) Sensor V+ V- Active physical phenomenon V+ PNP V- sensor output and Detector Line current flows out when switched on Sinking (to the common) Sensor V+ V- Active physical phenomenon V+ NPN V- sensor output and Detector Line current flows in when switched on Wiring power supply sensor V+ V- (common) V+ V- NPN power supply sensor V+ V- (common) V+ V- PNP sinking sourcing A PLC Input Card For a Sinking (NPN) Sensor Internal Card Electronics PLC Data Bus External Electrical NPN sensor power supply +V -V +V NPN -V current flow +V 00 01 Internal Card Electronics PNP sensor power supply +V -V +V PNP -V current flow 00 01 com PLC Input card for Sourcing (PNP) sensors Two wire sensors PLC Input Card two wire sensor power supply +V -V +V -V 00 01 com Note: These sensors require a certain leakage current to power the electronics. PLC Input Card two wire sensor power supply +V -V +V -V 00 01 V+ for Sourcing Sensors for Sinking Sensors NPN (sinking) PNP (sourcing) V+ V-NPN V- V+ PNP black brown white brown blue blue Symbols and Wiring Conventions Contact switches are available as normally open and normally closed. Their housings are reinforced so that they can take repeated mechanical forces. These often have rollers and wear pads for the point of contact. Lightweight contact switches can be purchased for less than a dollar, but heavy duty contact switches will have much higher costs. Examples of applications include motion limit switches and part present detectors. Contact Switches Reed Switches Note: With this device the magnet is moved towards the reed switch. As it gets closer the switch will close. This allows proximity detection without contact, but requires that a separate magnet be attached to a moving part. Photo-optical sensors oscillator +V +V lens lens square wave light LED phototransistor amplifier demodulator detector and switching circuits smaller signal Photo-optic - Opposed mode emitter object detector Photo-optic - retroreflective emitter detector object reflector emitter detector reflector Photo-optic - Diffuse emitter detector object Photo-optic alignment and beam size effect ive beam angle emitter det ector effect ive dete ctor angle effec tive beam alignment is required the smaller beam wi dth is good (but harder to a lign emitter detect or object Capacitive Sensors electric field object electrode electrode oscillator detector load switching +V electrode electrode electrode electrode metal dielectric C A k d ------= where, C = capacitance (Farads) k = dielectric constant A = area of plates d = distance between plates (electrodes) Inductive sensors oscillator and level detector output switching inductive coil metal +V shielded unshielded