Automated Controls

Question 1

Closed Loop

Answer 1

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

Question 2

Process Variable

Answer 2

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

Question 3

Controller

Answer 3

A device which operates automatically to regulate a controlled variable.

Question 4

Derivative (rate) control action

Answer 4

how fast the error is changing

Question 5

Error Signal

Answer 5

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

Question 6

Integral (reset) control action

Answer 6

how long the error has been present

Question 7

Open loop

Answer 7

a signal path without feedback

Question 8

Process (controlled) variable

Answer 8

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

Question 9

Proportional control action

Answer 9

how big the error is

Question 10

Set-point

Answer 10

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

Question 11

Span

Answer 11

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

Question 12

Transducer

Answer 12

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

Question 13

Dis-continuous Control

Answer 13

uses actuators which are either on or off

ex. baseboard heater, water pump.

Question 14

Continuous Control

Answer 14

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

sensors are analog

Question 15

What does P & ID stand for?

Answer 15

Piping and Instrumentation Drawings

Question 16

What does PID stand for?

Answer 16

Proportional
Integral
Derivative

Question 17

What is a P&ID drawing?

Answer 17

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

Question 18

In a P&ID balloon the first letter =

Answer 18

Process variable

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

Question 19

P&ID next 1,2 or 3 letters =

Answer 19

Instruments

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

Question 20

Proportional control is how ____ the error is?

Answer 20

BIG

Question 21

Integral control is how ____ the error has been present

Answer 21

LONG

Question 22

Derivative control is how _____ the error is changing

Answer 22

FAST

Question 23

Active Transducer

Answer 23

generates output without and external power supply

ex. thermocouple

Question 24

Passive Transducer

Answer 24

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

Question 25

Sensor primary element

Answer 25

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

Question 26

Sensor secondary element

Answer 26

converts the primary element into an electric change | ex. motion to a change in resistance, permeability, etc.

Question 27

Low pressure vacuum/pressure sensor?

Answer 27

Bellow

Question 28

More pressure vacuum/pressure sensor?

Answer 28

Diaphragm

Question 29

Most pressure vacuum/pressure sensor?

Answer 29

Bourdon tube

Question 30

Bonded wire strain gauge characteristics

Answer 30

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

Question 31

Piezoresistive Strain Gauge characteristics

Answer 31

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

Question 32

Thermocouple characteristics

Answer 32

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

Question 33

RTD characteristics

Answer 33

``` most stable most accurate more linear than thermocouple positive temp coefficient expensive current source required ```

Question 34

Thermistor characteristics

Answer 34

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

Question 35

I.C. Sensor characteristics

Answer 35

most linear highest output inexpensive

Question 36

Common output standard control signals

Answer 36

``` 4-20mA 10-50mA 1-5Volts 1-10Volts 3-15 PSI ```

Question 37

Op-Amp open loop Gain =

Answer 37

200,000 w/o feedback

Question 38

Another name for an actuator?

Answer 38

Servomechanism

Question 39

3 types of actuators

Answer 39

hydraulic pneumatic electrical

Question 40

Types of electrical actuators

Answer 40

heaters coolers lights electromechanical

Question 41

types of electromechanical actuators

Answer 41

``` solenoids magnetic clutches stepper motors linear actuators eddy current couplings valves ```

Question 42

Describe a solenoid

Answer 42

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

Question 43

Magnetic Clutch characteristics

Answer 43

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

Question 44

What is an actuator?

Answer 44

a device that converts a signal input into a mechanical motion

Question 45

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

Answer 45

Stepper Motors

Question 46

What is a stepper motor?

Answer 46

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.

Question 47

A stepper motor converts

Answer 47

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

Question 48

Name three stepper motors

Answer 48

Variable reluctance stepper motor Permanent magnet stepper motor Hybrid stepper motor

Question 49

Which is the most widely used stepper motor?

Answer 49

Hybrid

Question 50

what is an encoder?

Answer 50

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

Question 51

What is the most popular encoder?

Answer 51

incremental optical shaft encoder

Question 52

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

Answer 52

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

Question 53

How does a mag meter work to measure liquid flow?

Answer 53

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

Question 54

what is the principle operation of an ultrasonic level sensor?

Answer 54

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

Question 55

RTDs are typically made of?

Answer 55

Platinum and nickel

Question 56

what is the function of a bifilar winding?

Answer 56

eliminate inductance

Question 57

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

Answer 57

Resistance | Temperature

Question 58

Bellows and diaphragms are both used to convert pressure into ?

Answer 58

Motion

Question 59

What is negative feedback?

Answer 59

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

Question 60

What is positive feedback?

Answer 60

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

Question 61

An enclosed thermopile with radiation focused on it is called ?

Answer 61

Radiation pyrometer