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Electrical - Level 4 > Automated Controls > Flashcards

Automated Controls Flashcards

1
Q

Where are automated controls most common?

A

commercial and industrial applications

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2
Q

List examples of an automated control system

A
  • Cruise Control
  • HVAC
  • Food Production
  • PF correction
  • Autopilot for ships and aircrafts
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3
Q

List benefits of automated controls

A
  • Consistent
  • Reduced labour (initial labour is usually much higher)
  • Improved safety
  • Lower operating cost
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4
Q

What are the two categories for AC?

A

Open Loop and Closed Loop

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5
Q

Open loop characteristics and examples of applications?

A
  • Requires an operator
  • not self correcting
  • no feedback
  • Bathroom heat lamp
  • Heat and a/c for most cars
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6
Q

Closed loop characteristics and examples?

A
  • no operator required
  • self correcting
  • has feedback
  • Bathroom baseboard heat
  • climate control in some cars
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7
Q

advantages and disadvantages of open loop?

A

Advantages:

  • Low initial cost
  • easy to install
  • simple to troubleshoot

Disadvantages:

  • ongoing labour
  • error
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8
Q

Closed loop advantages and disadvantages?

A

Advantages:

  • self correcting
  • reduced ongoing labour costs
  • reduced error
  • higher performance

Disadvantages:

  • High initial cost
  • expensive to install
  • more complex to troubleshoot
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9
Q

What is the error signal?

A

the difference between the set point and sensor signals

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10
Q

Examples of process variables?

A
  • temperature
  • level
  • pressure
  • speed
  • light
  • flow
  • weight
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11
Q

What are the two modes of control for each category?

A
  1. Discontinuous

2. Continuous

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12
Q

What do discontinuous controls use and what are the characteristics? How is the process variable corrected?

A
  • Use actuators which are either on or off

- corrected by varying the time intervals in which the actuator is on or off

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13
Q

In discontinuous control, the process variable error can be substantial if the ___________ is too wide

A

Dead Band

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14
Q

In continuous control, the actuator output is ________________________________________?

A

variable and proportional to the difference between the set point and the sensor.

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15
Q

Are the sensors in continuous control analog or digital? Why?

A

Analog, because their output can vary continuously

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16
Q

What is the process variable error dependant on?

A
  • RESOLUTION of the sensors
  • PERFORMANCE of the actuators
  • COMPLIANCE of the process variable
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17
Q

what does the “PID” stand for in PID control?

A
  • Proportional
  • Integral
  • Derivative
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18
Q

What are P & ID Drawings, what do they include and which block diagram is it?

A
  • Piping and Instrumentation Drawings
  • Pipes, pumps, tanks, sensors, actuators, controllers, etc…
  • Process control block diagrams
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19
Q

What does the first and then remaining letters stand for in a P & ID balloon

A

First letter = Process Variable

Next letters = instrument

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20
Q

List the methods and what they mean in PID Control

A 
Proportional = "How BIG is the error?"
Integral = "How Long has the error been present?"
Derivative = "How FAST is the error changing?"
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21
Q

What are sensors also known as?

A

Transducers

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22
Q

What does a transducer do?

A

Converts one form of energy to another

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23
Q

What do active transducers do? list an example

A
  • Generate output without an external supply

- a thermo couple which generates a small voltage when heated up

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24
Q

What do passive transducers do? list an example

A
  • Do not generate an output
  • only physically or electrically change
  • a resistive thermal device changes resistance with temperature
25
Q

What are the two elements within sensors?

A

Primary and secondary

26
Q

What does the primary element do in a sensor

A

convert the process variable into a format suitable for measurement

27
Q

what does the secondary element of a sensor do?

A

convert the primary element into an electric change

28
Q

What are the 3 pressure/vacuum sensors and their properties?

A

Bellows = LOW pressure
Diaphragms = MORE pressure
Bourdon Tubes = MOST pressure

29
Q

What are strain gauges?

A

Sensors of FORCE

30
Q

Characteristics of a bonded wire strain gauge?

A

R=Kl/CMA

  • when stretched R increases
  • when compressed R decreases
  • Low gauge factor (less sensitive)
31
Q

Characteristics of Piezoresistive strain gauges?

A
  • Crystal changes R with force
  • When stretched R increases
  • When compressed R decreases
  • High gauge factor (more sensistive)
32
Q

List examples of Flow sensors

A
  • Flow Switches
  • Manometer (atmospheric Pressure gauge)
  • Turbine Flow Meter
  • Magnetic Flow Meter
33
Q

list examples of level sensors

A
  • Floats
  • Switches
  • Conduction
  • Ultrasonic
34
Q

As a temperature sensor, bimetallic strips are used in what systems?

A

Discontinuous

35
Q

What is a thermocouple and its characteristics?

A
  • Temperature sensor
  • generates a small voltage
  • continuous or discontinuous
  • active sensor
36
Q

What are several thermocouples connected in series called?

A

Thermopile

37
Q

An enclosed thermopile with radiation focused on it is called?

A

A radiation pyrometer

38
Q

Resistive thermal device characteristics?

A
  • positive temperature coefficient

- considered linear

39
Q

Thermistor characteristics?

A
  • negative temperature coefficient

- non linear

40
Q

Integrated circuit temperature sensor characteristics? standard output control signals?

A

-Uses either a RTD or Thermistor and corrects any non linearity
-requires a power supply
4-20mA, 10-50mA, 1-5 Volts, 1-10 Volts, 3-15 PSI

41
Q

Give 5 examples of sensors

A
  • Thermostat
  • Thermocouple
  • Float
  • Limit switch
  • Photocell
42
Q

What is the first step in troubleshooting?

A

Verify the Problem

43
Q

what does a phototube (photo-emissive cell) have within it?

A

a photosensitive cathode that emits electrons when exposed to light

44
Q

in a photo tube (photo-emissive cell), what happens when a potential is placed across it?

A

the electrons emitted by the the cathode will be attracted to the anode and a micro current will flow

45
Q

Characteristics of a Light Dependant Resistor (LDR) ?

A
  • Resistance changes with light intensity
  • usually made with cadmium sulphide
  • Light releases free electrons
46
Q

What is the comparison of resistance between the light and dark in a LDR?

A
  • 100M ohms in darkness

- less than 100 ohms in sunlight

47
Q

What is a Photovoltaic Cell (solar cell) and what does it do?

A
  • PN Junction with a LARGE light sensitive area

- converts light energy to electrical energy with no external power supply

48
Q

What can a single solar cell produce?

A

about .5 volts and 4 amps

49
Q

how are the output voltage and current increased in Photovoltaic Cells (solar cells) ?

A
  • Output voltage is increased by adding cells in series

- Output current is increased by adding cells in parallel

50
Q

How does a Photo Diode work?

A
  • Reverse leakage current increases with temperature

- if light is directed on PN Junction, current will be proportional to the amount of light

51
Q

How are Phototransistors made and what are they sensitive to?

A
  • Made like a conventional BJT with a lens to focus light on ther base-collector junction
  • sensitive to heat/light
52
Q

How are Light Activated SCR’s made, how do they work and what is the max wattage they can control?

A
  • Similar to a conventional SCR but has a lens to focus light on the GATE
  • Light will trigger SCR on
  • 500W max
53
Q

How do LEDS create energy?

A

Light energy (photons) striking a PN Junction

54
Q

How are photons produced in a LED?

A

When electron/hole pairs recombine

55
Q

What is a LEDs approx PIV?

A

about 6 Volts

56
Q

What do LEDS require?

A

current limiting resistor

57
Q

What is the max amps on an LED?

A

about 10 to 50 mA

58
Q

What do Opto-Couplers do? What do they eliminate? What are they used for?

A
  • isolate systems electrically
  • eliminates propagation of EMI and RF noise
  • Used for solid state relays

Electrical - Level 4 (8 decks)

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