ECET 211 Electric Machines & Controls Lecture 4-2 Motor Control Devices: Part 3. Sensors, Part 4. Actuators Text Book: Electric Motors and Control Systems, by Frank D. Petruzella, published by McGraw Hill, 2015. Paul I-Hai Lin, Professor of Electrical and Computer Engineering Technology P.E. States of Indiana & California Dept. of Computer, Electrical and Information Technology Purdue University Fort Wayne Campus Prof. Paul Lin 1 Lecture 4 Motor Control Devices Chapter 4. Motor Control Devices Part 1. Manually Operated Switches Part 2. Mechanically Operated Switches Part 3. Sensors Part 4. Actuators Prof. Paul Lin 2 1
Sensors Part 3 Sensors Devices that are used to detect, and often to measure, the magnitude of real world parameters such as distance, position velocity, acceleration, temperature, sound, force, light, etc Operated by converting mechanical, magnetic, thermal, optical, and chemical variations into electrical voltage and currents. Sensors are categorized by what they measure Proximity Sensors, Photoelectric Sensors Hall Effect Sensors, Ultrasonic Sensors Temperature Sensors, Velocity and Position Sensors Flow Measurement, Magnetic Flowmeters Play an important role in modern manufacturing process control Prof. Paul Lin 3 Part 3 Sensors Figure 4-33 Typical sensor Applications Light sensor Pressure sensor Bard code sensor (reader) Prof. Paul Lin 4 2
Proximity Sensors Part 3 Sensors: Proximity Sensors Detect the presence of an object without physical contact (non-contact) Object types: metal, glass, plastics, most liquids Sensor measurement methods or operating principles depends on the type of matter being detected: Inductive type: for ferrous metals (containing iron), nonferrous metals (copper, aluminum, brass) Capacitive type: for sensing metal objects nonmetallic materials (paper, glass, liquids, cloth, etc) Figure 4-34 Proximity sensor and symbols Prof. Paul Lin 5 Part 3 Sensors: Proximity Sensors Inductive Proximity Sensors Detect the presence of a metal object using the principles of AC inductance, where a fluctuating AC current induces an electromotive force (emf) in a sensing target Figure 4-35 shows a block diagram of the Inductive proximity sensors Figure 4-35 Inductive Proximity sensor Prof. Paul Lin 6 3
Part 3 Sensors: Proximity Sensors Inductive Proximity Sensors Operating point the point at which the proximity sensor recognize an incoming target Release point the point at which the proximity sensor recognizes an outgoing target Hysteresis Specifies as a percentage of the nominal sensing range Needed to keep proximity sensors from chattering when subject to Shock and Vibration, Slow-moving targets, or Minor disturbances such as electrical noise and temperature drift. Figure 4-36 Proximity sensor sensing range Prof. Paul Lin 7 Part 3 Sensors: Proximity Sensors Inductive Proximity Sensors Sensor operating voltage levels: 24 V DC or 120 V AC Figure 4-37 Typical two-wire and three wire sensor connections 3-wire DC proximity sensor: Figure 4-37a has the positive and negative DC line leads, and NO or NC contact 2-wire AC proximity sensor: Figure 4-37b, the load is connected in series with L1 and L2 power source Load type: starter, magnetic contactors, relays, solenoids Should not be used to directly operate a motor Figure 4-37 Typical two-wire and three-wire sensor connections Prof. Paul Lin 8 4
Proximity Sensors Capacitive Proximity Sensors Detect the presence of a metal object using the principles of capacitance (C = ε A/d); where C is the capacitance, ε is the dielectric constant, A is the metal electrode area, and d is the distance between the two electrodes Figure 4-38 Capacitive proximity sensor Prof. Paul Lin 9 Proximity Sensors Capacitive Proximity Sensors Figure 4-39 Capacitive proximity sensor liquid detection An application example for detecting empty container Cardboard container: lower dielectric constant, ε C Liquid: higher dielectric constant, ε Liquid Empty containers are automatically diverted via the push rod Prof. Paul Lin 10 5
Photoelectric Sensors Photoelectric Sensors An optical control device that operates by detecting a visible or non-visible beam of light and responding to a change in the receiving light intensity. Two components: a transmitter (light source) and a receiver (sensor), may or may not be housed in the same unit Figure 4-40 Photoelectric sensor Scan techniques to detect object Through-Beam Scanning Retro-reflective Scanning Diffuse scanning Fiber-optics Prof. Paul Lin 11 Through-Beam Scanning Photoelectric Sensors Direct scan, placed the transmitter and receiver in direct line with each other Detect: Light being blocked - Yes/No Long range sensing: up to 300 feet More reliable method in area of heavy dust, mist, and other types of airborne contaminants Figure 4-41 Through-beam scan An example: Garage door opener Prof. Paul Lin 12 6
Photoelectric Sensors Retro-reflective Scan Sensor (Figure 4-42) The transmitter and receiver are housed in the same enclosure Used for medium-range applications May not be able to detect shiny targets Because it cannot differentiate the Light reflective back from the reflector vs. Light reflective back from the target Polarized Retro-reflective Scan Sensor (Figure 4-43): Over come this problem Prof. Paul Lin 13 Photoelectric Sensors Diffuse Scan Sensor The transmitter and receiver are housed in the same enclosure. A light reflector is not needed. Receiver picks up some of the diffused (scattered) light. Maximum sensing length: 40 inch Figure 4-44 Diffuse scan sensor: inspect the presence of the polarity mark on a capacitor (or any other mark inspection) Prof. Paul Lin 14 7
Fiber Optics Sensor Use a flexible fiber-optic cable that channel light from emitter to receiver Can be used with Through-beam, Retro-reflective scan, or diffuse scan sensors: Figure 4-45 Fiber optic sensors Immune from all forms of electrical interference Can be safely used in the most hazardous sensing environment such as: Refinery for producing gases Grain bins Mining Pharmaceutical manufacturing Chemical processing Prof. Paul Lin 15 Part 3 Sensors Hall Effect Sensors Detect the proximity and strength of magnetic field when a current carry conductor is placed into a magnetic field, a voltage will be generated perpendicular to both the current and the field Figure 4-46 Hall effect Sensor Analog-Type Hall Effector Sensor (Figure 4-47) Current transformer used in the clamp meter for measurement current Prof. Paul Lin 16 8
Part 3 Sensors Hall Effect Sensors Digital-Type Hall Effector Sensor Figure 4-48 Monitoring speed using a Hall effect sensor Prof. Paul Lin 17 Part 3 Sensors Ultrasonic Sensors Ultrasonic Sensor (operating theory) Operates by sending high frequency sound waves toward the targets and measuring the time its takes for the pulses to bounce back Figure 4-49 Ultrasonic sensor with 4 to 20 ma output 1) Detecting the level of chocolate 2) Detecting transparent bottles 3) Liquid level detection Prof. Paul Lin 18 9
Part 3 Sensors Ultrasonic Sensors Figure 4-50 Ultrasonic wind sensor Wind turbine system application for determining wind speed and direction Four sensors, one at each major compass point (N-S, E-W) Operating Theory N S, E W: fire ultrasonic sound pulses to opposing sensors In still air: all pulses time of flight are equal Wind blow: it increases the time of flight for pulses traveling against it System calculates the wind speed and direction Prof. Paul Lin 19 Part 3 Sensors Temperature Sensors Types of sensors Thermocouple: High temperature measurement; output DC mv Type B (870 C to 1700 C / 1000 F to 3100 F) Type E (-200 C to 900 C / -330 F to 1600 F) Type J (0 C to 760 C / 32 F to 1400 F) Type K (-200 C to 1260 C / -330 F to 2300 F) Types R, S, T, C, P Resistance Temperature Detector (RTD): Positive temperature coefficient (PTC) R: Temp increase => R increase Thermistor: negative temperature coefficient (NTC) R IC sensor Prof. Paul Lin 20 10
Part 3 Sensors Temperature Sensors Types of sensors Thermistor: Negative temperature coefficient (NTC) R Temperature range: -100 C to 500 C IC sensor RTD, Thermistor, Thermocouple Comparison Chart, http://digital.ni.com/public.nsf/allkb/c50fa55b3b2f85d986257 2D00083350E Criteria Thermocouple RTD Thermistor Temp Range -267 C to 2316 C -240 C to 649 C -100 C to 500 C Accuracy Good Best Good Linearity Better Best Good Sensitivity Good Better Best Cost Best Good Better Prof. Paul Lin 21 Part 3 Sensors Temperature Sensors Figure 4-51 Thermocouple heat sensor Hot junction (measurement junction) Cold junction (reference junction) Type K (-200 C to 1260 C / -330 F to 2300 F Hot junction at 300 C => 12.2 mv Prof. Paul Lin 22 11
Part 3 Sensors Temperature Sensors Figure 4-52 Thermocouple tip styles Figure 4-53 Typical thermowell installation Prof. Paul Lin 23 Part 3 Sensors Temperature Sensors Resistance Temperature Detector (RTD): Positive temperature coefficient (PTC) R Temp increase => R increase Temperature Ranges: -50 C to 500 C for thin film RTD, -200 C to 850 C for wire-wound RTD, http://www.omega.com/temperature/pdf/rtd_gen_specs_ref.pdf Figure 4-54 Resistance temperature detector Prof. Paul Lin 24 12
Part 3 Sensors Temperature Sensors Thermistors Thermally sensitive resistor NTC (Negative Temp Coefficient): Temp increase, R decrease Figure 4-55 Thermistors IC Temperature Sensor Figure 4-56 Integrated circuit temperature sensor Prof. Paul Lin 25 Part 3 Sensors Velocity & Position Sensors Tachometer Figure 4-57 Tachometer generator Magnetic Pickup Sensor (Figure 4-58) Encoder (Figure 4-9 Optical encoder) Figure 4-59 Figure 4-58 Prof. Paul Lin 26 13
Part 3 Sensors Flow Measurement Turbine Flowmeters Like windmills utilizes their angular velocity (rotational speed) to indicate flow velocity Figure 4-60 Target Flowmeters Measure the drag force on the inserted target flat disk, and convert it to the flow velocity Figure 4-61 Prof. Paul Lin 27 Part 3 Sensors Flow Measurement Magnetic Flowmeters Electromagnetic flowmeters or induction flowmeters Obtained the flow velocity by measuring the changes of induced voltage of the conductive fluid passing across a controlled magnetic field Figure 4-62 Magnetic flowmeter Prof. Paul Lin 28 14
Part 4 Actuators Relays Solenoids Solenoid Valves Stepper Motors Servo Motors Prof. Paul Lin 29 Part 4 Actuators Actuator A device that converts electrical signal to mechanical movement. Actuator Types Relays Solenoids Solenoid Valves Stepper Motors Servo Motors Prof. Paul Lin 30 15
Figure 4-63 Electromagnetic relay Part 4 Actuators Figure 4-64 Relay motor control circuit Prof. Paul Lin 31 Part 4 Actuators Figure 4-65 Double-break contacts Relay contacts use two pairs of contacts that open circuit in two places, creating two air gaps Dissipate heat more rapidly => Longer life Enabling the contact to handle higher voltages Benefits: Greater DC load breaking capability and better isolation of contact Prof. Paul Lin 32 16
Part 4 Actuators Dry contact A dry contact refers to one that has both terminals available and in which neither contact is initially connected to a voltage source Figure 4-66 shows a magnetic starter with an extra dry contact Prof. Paul Lin 33 Solenoid A electromechanical solenoid is a device that uses electrical energy to cause mechanical control action A solenoid consists of A coil Frame Part 4 Actuators Plunger (or armature) Types: AC or DC solenoid Categories: Linear, Rotary Action: energized vs deenergized Figure 4-67 Solenoid construction and operation Prof. Paul Lin 34 17
Solenoid A electromechanical solenoid is a device that uses electrical energy to cause mechanical control action A solenoid consists of a coil, frame, plunger (or armature), Figure 4-67 Solenoid construction and operation Types: AC or DC solenoid Categories: Linear, Rotary; Figure 4-68 Actions: energized vs deenergized Part 4 Actuators Prof. Paul Lin 35 Solenoid Valve A combination of a solenoid coil operator and value It controls the flow of liquids, gases, steam, and other media. Figure 4-69 Solenoid value construction and principle of operation Part 4 Actuators Prof. Paul Lin 36 18
Figure 4-70 Solenoid valve operated tank filling and empty operation Tank filling operation: Solenoid A Fill tank sensor Control relay (1CR) Tank emptying : Solenoid B Empty tank sensor Control relay (2CR) Part 4 Actuators Prof. Paul Lin 37 Part 4 Actuators Stepper Motors A brushless DC motor with the rotor carries a set of permanent magnets, and the stator has a set of coils. Figure 4-72 Stepper Motor operation The shaft of a stepper motor rotate in discrete increments when electrical command pulsed are applied to it in proper sequence. An example: a stepper that 1.8 degree per pulse step, would take 200 pulses to make a 360 degree rotation Stepper system are used most often in open-loop control system Figure 4-71 Stepper motor/drive Prof. Paul Lin 38 unit 19
Part 4 Actuators Servo Motors All servo motors operate in closeloop mode with speed or position feedback. Stepper system are used most often in open-loop control system Figure 4-73 Open- and closed-loop motor control system Prof. Paul Lin 39 Part 4 Actuators Figure 4-74 Closed-loop servo system Major component Controller Servo amplifier Servo motor Load Feedback devices (position, speed) Prof. Paul Lin 40 20
Part 4 Actuators Figure 4-75 Brushless DC motor with integrated drive Major component Reference, Run/Stop, FWD/REV Controller Driver Brushless DC motors (BLDCs), with three-phase stator (A-B-C) Prof. Paul Lin 41 Summary & Conclusion Questions? Contact Prof. Lin through: Email: lin@ipfw.edu LINE Group discussion forum Prof. Paul Lin 42 21