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Electrical Level 3 and 4 > Automated Controls > Flashcards

Automated Controls Flashcards

1
Q

Closed Loop

A

A signal path which includes a forward path, a feedback path, and a summing point, and forms a closed circuit.

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2
Q

Process Variable

A

The parameter that is desired to be controlled. ex. temperature, flow rate, pressure, liquid level

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3
Q

Controller

A

A device which operates automatically to regulate a controlled variable.

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4
Q

Derivative (rate) control action

A

how fast the error is changing

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5
Q

Error Signal

A

this is the signal derived in a closed loop control system from the difference between the set-point signal and the feed-back signal.

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6
Q

Integral (reset) control action

A

how long the error has been present

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7
Q

Open loop

A

a signal path without feedback

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8
Q

Process (controlled) variable

A

in a control loop, it is the variable which is sensed to originate a feed-back signal.

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9
Q

Proportional control action

A

how big the error is

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10
Q

Set-point

A

an input variable which determines the desired value of the controlled variable

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11
Q

Span

A

the algebraic difference between the upper and lower range values, if the range where -20 to 200, the span would be 220.

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12
Q

Transducer

A

A device or element which converts energy from one type to another

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13
Q

Dis-continuous Control

A

uses actuators which are either on or off

ex. baseboard heater, water pump.

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14
Q

Continuous Control

A

the actuator output is variable and is proportional to the difference between the sensor and the setpoint.

sensors are analog

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15
Q

What does P & ID stand for?

A

Piping and Instrumentation Drawings

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16
Q

What does PID stand for?

A

Proportional
Integral
Derivative

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17
Q

What is a P&ID drawing?

A

process control block diagrams, they are like schematics but include pipes, pumps, tanks, sensors, actuators, controllers etc.

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18
Q

In a P&ID balloon the first letter =

A

Process variable

Ex. T - Temperature, L - Level, F - Flow, P - Pressure

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19
Q

P&ID next 1,2 or 3 letters =

A

Instruments

ex. I - indicator, R - recorder, C - controller, V - valve, A - alarm

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20
Q

Proportional control is how ____ the error is?

A

BIG

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21
Q

Integral control is how ____ the error has been present

A

LONG

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22
Q

Derivative control is how _____ the error is changing

A

FAST

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23
Q

Active Transducer

A

generates output without and external power supply

ex. thermocouple

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24
Q

Passive Transducer

A

do not generate and output, only physically or electrically change, an external supply is required.
ex. RTD

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25
Q

Sensor primary element

A

converts the process variable into a format suitable for measurement
ex. pressure to motion

26
Q

Sensor secondary element

A

converts the primary element into an electric change

ex. motion to a change in resistance, permeability, etc.

27
Q

Low pressure vacuum/pressure sensor?

A

Bellow

28
Q

More pressure vacuum/pressure sensor?

A

Diaphragm

29
Q

Most pressure vacuum/pressure sensor?

A

Bourdon tube

30
Q

Bonded wire strain gauge characteristics

A 
R=Kl/CMA
When stretched R increases
When compressed R decreases
Low "gauge factor"
            Less sensitive
31
Q

Piezoresistive Strain Gauge characteristics

A 
Crystal changes R with force
When stretched R increases
When compressed R decreases
Higher "gauge factor"
         More sensitive
32
Q

Thermocouple characteristics

A 
self powered
simple
rugged
inexpensive 
wide variety
wide temp range 
non-linear
low voltage
least stable
least sensitive
33
Q

RTD characteristics

A 
most stable
most accurate
more linear than thermocouple
positive temp coefficient 
expensive
current source required
34
Q

Thermistor characteristics

A 
high output
fast
two-wire ohms measurement 
non-linear
current source required
negative temperature coefficient
35
Q

I.C. Sensor characteristics

A

most linear
highest output
inexpensive

36
Q

Common output standard control signals

A 
4-20mA
10-50mA
1-5Volts
1-10Volts
3-15 PSI
37
Q

Op-Amp open loop Gain =

A

200,000 w/o feedback

38
Q

Another name for an actuator?

A

Servomechanism

39
Q

3 types of actuators

A

hydraulic
pneumatic
electrical

40
Q

Types of electrical actuators

A

heaters
coolers
lights
electromechanical

41
Q

types of electromechanical actuators

A 
solenoids
magnetic clutches
stepper motors
linear actuators 
eddy current couplings
valves
42
Q

Describe a solenoid

A 
magnetic coil moving a permeable core 
AC or DC available 
Intermittent or Continuous duty 
Single acting spring return
Double acting energized return
43
Q

Magnetic Clutch characteristics

A

Generally fully on or off
friction disks or drums are electrically applied/released
some mag clutches use magnetic particles to engage

44
Q

What is an actuator?

A

a device that converts a signal input into a mechanical motion

45
Q

Accurate positioning control is commonly achieved in applications like robotics and computer disk drives by using unique motors called ?

A

Stepper Motors

46
Q

What is a stepper motor?

A

an increment, brushless DC motor that moves in discrete angular steps in accordance with set sequences of current pulses that are supplied to the motor.

47
Q

A stepper motor converts

A

digital data into an angular position, or pulses into speed of rotation

48
Q

Name three stepper motors

A

Variable reluctance stepper motor
Permanent magnet stepper motor
Hybrid stepper motor

49
Q

Which is the most widely used stepper motor?

A

Hybrid

50
Q

what is an encoder?

A

a device that is fastened to a rotating shaft to produce a series of pulses that indicate shaft position

51
Q

What is the most popular encoder?

A

incremental optical shaft encoder

52
Q

What does the discriminator circuit do when connected to a LVDT?

A

it sends out an output the polarizes the output of the LVDT when the output of the LVDT rises above a predetermined threshold

53
Q

How does a mag meter work to measure liquid flow?

A

liquid with conductive properties passes through a magnetic field induces a voltage proportional to the flow rate

54
Q

what is the principle operation of an ultrasonic level sensor?

A

sound waves are emitted and bounce back from the control variable, the time it takes for this signal to return can be equated to a level

55
Q

RTDs are typically made of?

A

Platinum and nickel

56
Q

what is the function of a bifilar winding?

A

eliminate inductance

57
Q

RTDs and thermistors both indicate a change in ______ for a change in _____

A

Resistance

Temperature

58
Q

Bellows and diaphragms are both used to convert pressure into ?

A

Motion

59
Q

What is negative feedback?

A

compares the set point signal to the process variable (the error)

60
Q

What is positive feedback?

A

adds the process variable and the set point (not good)

61
Q

An enclosed thermopile with radiation focused on it is called ?

A

Radiation pyrometer

Electrical Level 3 and 4 (10 decks)

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