MECHENG 201 Part 2: Electronics, Sensors and Actuators

Get Started. It's Free
or sign up with your email address
MECHENG 201 Part 2: Electronics, Sensors and Actuators by Mind Map: MECHENG 201  Part 2: Electronics, Sensors and Actuators

1. Electronics: Diodes

1.1. Introduction

1.1.1. Active

1.1.2. Passive

1.1.3. Electro-mechanic

1.2. Diodes

1.2.1. a two-terminal electronic component that conducts primarily in one direction Role: allow current to pass in forward direction, block current in reverse direction Analogous example: Check Valve First Diode: Thermionic Diode Edison Effect: when hot, the cathode releases electrons into the vacuum Types: Diode LED Photodiode Zener Diode Schottky Diode Transient-voltage-suppression Diode (TVS) Tunnel Diode Varicap Ideal Diode: Forward Biased Reverse Biased NO Break down region Real Diode: Forward Biased Reverse Biased Breakdown Other Functions: Unidirectional behaviour = Rectification: - convert AC to DC - detect AM radio signals - voltage drop is a function of temperature = use as a temperature sensor or voltage reference Avalanche Diode: protect circuits from high voltage Varactor Diode: tune radio and TV receivers Tunnel, Gunn and IMPATT Diode: - generate radio frequency oscillations - create microwave and switching circuits Diode + Inductors: current stopped = 0 --> stored energy creates reverse voltage spike (flyback) that can damage switch Diode-Resistor Logic (DRL): OR Gate AND Gate

1.3. Integrated Circuit

1.3.1. a set of electronic circuits on one small chip (semiconductor material e.g silicon

2. Sensors

2.1. never used by themselves!

2.2. = element that produces a signal relating to the quantity being measured

2.3. Transducer:

2.3.1. = device that converts energy from one form to another

2.4. Absolute & Incremental Sensors

2.4.1. Absolute: detect a unique position - not power dependent

2.4.2. Incremental: measure a relative position - depends on a prior position or last power on/off

2.5. Analog & Digital Sensors

2.5.1. Analogue: continuous output signal or voltage proportional to quantity being measured e.g voltage measured by potentiometer is proportional to the angle it is measuring Example: Thermocouple Measurement: 1. Linear 2. Polynomial 3. Exponential y = measurement x = sensor output signal

2.5.2. Digital: discrete digital output signal or voltage - step response binary output signal Signal conditioning Example: Light Sensor

2.6. Selecting a Sensor:

2.6.1. 1. Nature of measurement required nominal value of variable range of values accuracy required required speed of measurement reliability required

2.6.2. 2. Nature of output required from sensor

2.6.3. 3. Factors of the sensor range accuracy linearity speed of response reliability life power supply requirements cost size

3. Sensors: Examples

3.1. Strain Gauge Pressure Sensor

3.1.1. change in R/R = G.E E = strain G = proportionality factor

3.2. Pressure Sensor

3.2.1. pressure measurements of gases or liquids produces proportional output voltage

3.2.2. can indirectly measure volume or alititude

3.3. Barometric Sensors

3.3.1. detect atmospheric pressure

3.3.2. Tactile Sensors

3.4. Potentiometer

3.4.1. example of an encoder

3.4.2. absolute analog sensor that measures angular position after a few revolutions, it will reset to zero it works like a variable resistor turning the shaft changes the resistance

3.5. Radar Sensor

3.5.1. "Radio detection and ranging" emits very small wavelength radio frequency signals detect - moving objects (planes) - shape of land

3.5.2. radio waves

3.6. Sonar

3.6.1. "Sound navigation and ranging" generates ultrasonic waves and the receiver captures waves that bounce back from the target timer calculates how long it takes for signal to return using speed of sound in the air long range poor resolution

3.6.2. sound waves

3.7. Infrared Sensor

3.7.1. accurate, medium range, non contact position measurement

3.7.2. small maximum range better resolution compared to Sonar sensor

3.8. Optical Position Sensor

3.8.1. measure position of a target infrared emitting diode + NPN infrared silicon phototransistor used in assembly lines, machine automation, edge detection

4. Sensors: Types

4.1. Types:

4.1.1. Displacement, Position & Proximity Sensors (either contact or non-contact) Displacement Sensors focus on measuring how much the object has moved Position Sensors focus on the position of the object to a reference point Proximity Sensors are position sensors that sense whether the object has moved within a critical distance = give ON/OFF outputs

4.1.2. Velocity & Motion monitor linear and angular velocity and detect motion e.g security systems cash machine screens

4.1.3. Force Sensors focus on measuring forces applied on them e.g spring balance - displacement is a measure of force

4.1.4. Fluid Pressure & Level Fluid Pressure monitors fluid pressure Fluid Level Directly Indirectly Pressure Sensing Technologies Force Collector Types Other Types

4.1.5. Environmental Sensors Temperature Sensors changes commonly used are - expansion/contraction of solids/liquids/gases - change in resistance of conductors Light Sensors measure intensity of light Humidity Sensors Wind Sensors

5. Sensors: Characteristics

5.1. Characteristics

5.1.1. Performance 1. Range the limits between which the input can vary 2. Span maximum value - minimum value input 3. Error Error = measured value - true value 4. Accuracy extent to which the value might be wrong 5. Sensitivity how much output there is per unit input = output/input 6. Hysteresis Error same point being measured, different outputs, due to continuously increasing or decreasing change 7. Repeatability ability to give the same output for repeated applications of the same input value Repeatability = (max - min values given)/full range x 100% 8. Stability and Drift Stability Drift Zero Drift 9. Dead Band Dead Band or Dead Space Dead Time 10. Resolution the smallest change in the input value that will produce an observable change in output 11. Output Impedance electrical output is interfaced with an electronic circuit = there will be output impedance having a sensor that reads the output impedance can modify the behavior of the system

5.1.2. Static VS Dynamic Static Characteristics values given when steady-state conditions occur Dynamic Characteristics behavior of the sensor between the time that the input value changes and the time that the value given by the sensor settles down to steady-state. Response Time Time Constant Rise Time Settling Time

6. Actuators

6.1. part of the machine that moves or controls something

6.1.1. Types: 1. Mechanical conversion of rotary motion to linear motion 2. Electric 3. Electro-mechanic like mechanical actuators but control knob/handle is replaced with electric motor rotary motion converted to linear displacement 4. Piezoelectric very short range of motion very high voltages = tiny expansions 5. Hydraulic converts hydraulic pressure + flow into torque + angular displacement (rotation) 6. Pneumatic air 7. Thermal material in actuator changes from solid <--> liquid narrow temperature range = precise control 8. Magnetic

6.1.2. Types of Motion: Linear Rotary/Circular

6.1.3. Performance Metrics: Force Speed Operating conditions Durability

6.1.4. Electric Motors DC Motors continuous movement, speed of rotation easily controlled AC Motors outside Stator/inside Rotor/ Permanent Magnets or electrical windings Stepper Motors electromechanical Solenoids coil of electrical wire with an armature electromagnet and plunger inside coil

6.1.5. Smart Motors: in a Single Servo Model: DC Motor Reduction Gearhead Encoder + Controller + Driver Communications

7. Electronics: Microcontrollers and Microprocessors

7.1. Microcontrollers and Microprocessors

7.1.1. Microprocessor heart of a computer CPU complete computation engine General/personal purpose use Example: Raspberry Pi

7.1.2. Microcontroller MCU small computer on one IC one or more CPUs Embedded applications Example: Arduino Selecting a Microcontroller:

7.1.3. Microprocessor Systems 1. Central Processing Unit (CPU) or Microprocessor Roles: Parts: 2. Memory stores binary data Size: depends on number of wires in the address bus 3. Input and Output Interfaces transfer of data between the microprocessor and the external world 4. Buses Data Bus Address Bus Control Bus

7.1.4. Microcontroller VS Microprocessor System Microprocessor systems have an external peripheral Microcontrollers have RAM, ROM, EEPROM embedded internally Microcontrollers = all on ONE CHIP Microprocessor Systems = many chips Microcontrollers = cheaper Microprocessor Systems = expensive Microcontrollers = lower processing speed (8 to 50MHz) Microprocessor Systems = high processing speed (>1GHz) Microcontrollers = simpler tasks Microprocessor Systems = more complex tasks

7.1.5. Computer Structure: 1. Input devices 2. Processor 3. Main memory 4. Output devices 5. Backing storage Classification: Structure Type Size

8. Electronics: Filters

8.1. Filters

8.1.1. Signal Processing a device or process that removes some unwanted components or features from a signal

8.1.2. Electronics a circuit designed to pass inputs in a certain frequency range while blocking other inputs

8.1.3. Classes: Linear or Nonlinear Time invariant or Time variant Causal or Not causal Active or Passive Active Passive Analog or Digital Discrete time (sampled) or Continuous Time Infinite Impulse Response (IIR) or Finite Impulse Response (FIR)

8.1.4. Types: Low-Pass Filter "High-cut" High-Pass Filter "Low-cut" Band-Pass Filter based on a frequency range Band-Stop Filter "Band-reject"

9. Electronics: 555 Timer

9.1. Timer 555

9.1.1. an integrated circuit used in a variety of timer, pulse generation, and oscillator applications Structure: a SR Flip-flop 2 comparators (OPAMPS) transistor Q1 = switch Modes of Operation: 1. Monostable 2. Astable 3. Bistable Pulse Width Modulation (PWM) modulation = changing allow the control of power supplied to electrical devices

10. Electronics: OPAMPS

10.1. OPAMP

10.1.1. a high-gain electronic voltage amplifier with a differential input and a single-ended output Used in: 1. Signal conditioning 2. Filtering 3. Perform math operations Symbols: V+ V- Vout Vs+ Vs- Structure: 20 BJT transistors 11 resistors 1 capacitor Types: Comparator Inverting amplifier Non-inverting amplifier Differential amplifier Summing amplifier Differentiator Integrator Instrumentation amplifer Ideal OPAMP: Open-loop gain (AOL) = infinite zero gain for common mode signal (only has gain when there is a voltage difference) infinite input impedence zero output impedence infinite bandwith Real OPAMP: Bandwidth Considerations Non Linear Limitations Slew Rate DC Imperfections Summing Point Constraint Negative Feedback Loop

11. Electronics: Transistors

11.1. Transistor

11.1.1. a semiconductor device used to amplify or switch electronic signals and electronic power made from semiconductor material (silicone) through DOPING Triode Doping Advantages 1. no cathode heater 2. very small size and weight 3. lots of transistors can be made on one IC 4. low operating Voltage 5. physically robust 6. no maintenance Limitations 1. silicon can age and fail 2. high power/frequency operation better suited for vacuum tubes where e- can move better 3. sensitive to radiation and cosmic rays Types: FETS Field-effect Transistors BJTS Bipolar junction Transistors Categories: Semiconductor Material Structure Electrical Polarity Maximum power rating Maximum operating frequency Application Physical Packaging Amplification Factor Operation Modes: 1. Saturation 2. Cut off 3. Active 4. Reverse Active Transistor as Switches making use of cutoff and saturation states Advantages of TRANSISTORS Advantages of RELAY SWITCHES (a substitute)

12. Sensors: Encoders

12.1. capture position or orientation

12.1.1. Rotary Encoder electro-mechanical device converts angular position/motion to analog/digital signal

12.1.2. Linear Encoder paired with a scale which the encoder reads from converts encoded position to analog/digital signal

12.2. Absolute

12.2.1. unambiguous position (doesn't depend on previous position) robust to interruptions

12.3. Incremental

12.3.1. cyclical, ambiguous (counting of cycles)

13. Switches

13.1. Microswitch

13.2. Push Button

13.3. Optical Switch

13.3.1. photo-micro sensor non-contact triggering triggers when object comes between components