electronic systems

Diodes

"check valve" allows one-way current flow

Parallel Circuit Resistance reduction

1/req =(1/R1 +1/R2 +.... +1/Rn)

bits of resolution (8-16 bits) AD/DA converter resolutions

2^bit (ex. 2^8 = 256 #'s of discrete values possible)

rotary electrical Actuators -- DC motors

3 kinds of connections --> series, shunt, combination (what type to choose?) shunt

electrical actuators (rotary)

AC motor, DC motor, stepper motor, servo motor

uses of diodes

AC/DC conversion extraction of signals from radio

General Transducers/Temperature Transducers

Accelerometers Temp: bimetallic strips(Toasters), resistance-temperature-detectors, thermistors, thermocouples

Why are AC ratings often higher for the same switch?

Arcing not sustained when voltage passes through zero

Rotary Electrical Actuators -- AC Motors

Cheaper, expensive for variable speed drives, induction, synchronous

Zener Diode

Designed to "breakdown" at a fixed voltage and conduct backwards precision voltage references

Uses for Capacitors

Energy storage power conditioning/power factor correction filtering & signal conditioning starting capacitors (AC monitors) sensors

common emitter transistor circuit characteristics: active region:

IC alpha IB linear amplification

common emitter transistor circuit characteristics: cutoff region:

IC is near zero

Digital Encoders

Linear and Rotary Position: circular disk w/ digital patterns engraved incremental: only position relative to initial position is known

Rotary Velocity

Magnetic Pickup: cheap, reliable (lose signal at low speeds) D.C. Tachometer/generator: voltage output proportional to shaft speed, no external power needed, good signal

Switches and Relays: Design Challenges 4. Arcing

Max V-breakdown voltage, can occur with inductive loads can be increased by replacing air with vacuum or fluids

Mechanical Relationships

Pulleys: pitch diameters sprockets:teeth gears: teeth

Series Circuit Resistance reduction

Req = R1 +R2 +....+Rn

voltage limits

arcing, current induced failure, heat buildup

stepper motor characteristics

as torque requirement increases, available speed decreases

pneumatic actuators

compress air into linear or rotary motion cylinders, air motors

actuator

converts energy into motion

Potential (Voltage) V

energy per unit charge joules/coulomb = volts (V)

Capacitors

energy storage element (stored electrostatically) materials: ceramic, polyester film, aluminum electrolytic

Solid state relays benefits

fast, cheap, common

Mechanical actuators

gears, pulleys, chains, etc

Linear Electrical Actuators (motor Based)

generally bidirectional, long stroke tradeoffs in speed/force for any given power level can use AC, DC, Linear, stepper motors, etc

digital transducers

great for microcontrolers: already discretize the input, better noise rejection, no A/D required same comments apply to transducers as converters

current limits

heat buildup, wires melting and fires, circuit board failure, battery explosions

transistors for current amplification: needs proper ____ ____

heat sinks ****largest cause of failure

hydraulic actuators

high pressure fluid to linear or rotary motion cylinders, positive displacement motors

Switches and Relays: Design Challenges 2. Startup Loads (Inrush Currents)

incandescent lights 10x, electric motors (capacitors)

Mechatronics

integration of mechanical and electrical systems, often with computers and code optimally controlling the multidisciplinary systems

power = rate of work = energy/time

joules per second = Watts (W)

flow meters

larger problem then pressure accuracy and response time is less axial turbine meters

linear position transducers

limit switches potentiometer LVDT (linear variable differential transformer) magneto restrictive hall effect capacitive laser

electrical actuators

linear -- electromagnetic (solenoid/voice coils), piezoelectric, motor/screw, linear motor rotary -- motor (AC/DC/stepper/servo)

transistors for current amplification: ____ _____ is more difficult to design

linear range

electrical actuators - solenoids

magnetic field produces force on iron plunger (force typically proportional to current) proportionality achieved by adding spring door locks, valve control, factories etc.

optical encoders for velocity

measure pulse frequency to determine velocity

Why transistors over mechanical relays

mechanical relays are too slow wear out at continuous cycling patterns

transistors allow ___________ to 'do something'

microprocessors

Mechanical Actuators

motion converters linear/linear, linear/rotary, cam profiles

stepper motor: permanent magnet

multiple stator poles (tries to align permanent magnet poles with the energize stator poles) small and fast limited to around 500 oz-in of torque

common bipolar junction transistors (2 types)

npn, pnp

Relays/switches: Pole (s)

number of separate circuits controlled by the switch

Relays/switches: Throw

number of separate positions allowed by the switch

solid state relays are designed for ____/____ operation

on/off

gray code

only one bit changes at a time minimizes chances of misreading a pulse

Two common types of stepper motors

permanent magnet variable reluctance

Rotary Position transducers

potentiometers rotary resolvers: inductive angle transducers, nonlinear output, additional circuitry many digital available

solid state relays need _____ ______ for inductive loads

protective diodes

current, i

rate of positive charge flow coulombs per second = Amperes(A)

Inductors

resists changes in current blocks flow of AC, passes DC

Attributes of Rotary Electrical Actuators -- Stepper Motors

resolution: # steps/revolution digital, resistant to noise competitor to DC motor no stability problems no brushes hence no contact surfaces open loop possibilities

Stepper Motor: variable reluctance

rotor carries the magnetic field and tries to find the position of variable reluctance larger torque, up to 2000 oz-in common resolutions: 12, 24, 72, 144, 180, 200 steps/revolution

Basic Transistor switch circuit: when Vin is enough to ______ the non transistor, Vc gets pulled ______ to ground and the load is _______

saturate, close, activated

linear electrical actuators (piezoelectric)

small movements but very fast speakers/buzzers, gas stoves

electrical actuators (linear)

solenoid, voice coils, piezoelectric, motor with screw or rack/pinion

Switches and Relays: Design Challenges 3. Inductive Loads

spark plugs! Electric motors electromagnetic interference/snubber RC circuits/flyback diodes

pressure transducers

strain gage types piezoelectric capacitive devices generally fast compared to system good accuracy

Transistors may be used as _____ or analog amplifiers

switches

Kirchhoff's Voltage Law

the sum of voltages around any closed loop is zero KVL is the conservation of electrical energy-electrical energy can neither be created or destroyed

Potentiometer

three terminal resistor voltage divider sensor (position/old joysticks/radios)

sensors must be a _______

transducer, but a transducer may not be a sensor

PWM (pulse width modulation) keeps _______ _______ more efficient

transistor saturated

Variable Resistor/Rheostat

two terminal resistor

PWM (pulse width modulation) common use

use digital switching to control analog power/systems

Switches and Relays: Design Challenges 1. Corrosion

wetting current- minimum necessary to break oxidation film

Kirchhoff's Current Law

The sum of currents at any node is equal to zero node: point where two or more elements connect KCL is the conservation of charge-charge can neither be created or destroyed charge is flow (conservation of mass)

absolute encoders

absolute position (per revolution) known 3 bit = 8 positions (2^3)