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Process Controls > Common Types of Sensors and Transducers > Flashcards

Common Types of Sensors and Transducers Flashcards

1
Q

What is a transducer?

A

Device the converts energy from one form to another

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2
Q

What is the difference between an analogue sensor and a digital sensor?

A

Analogue sensor’s output varies continuously and smoothly over its sensing range. Digital sensor’s output is in definite steps.

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3
Q

What are some common categories of sensors?

A
  • Sensors of motion
  • Sensors of force
  • Sensors of fluids
  • Sensors of light
  • Sensors of temperature
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4
Q

What are four basic principles used to sense linear motion?

A
  • Resistance change
  • Inductance change
  • Capacitance change
  • Transformer coupling change
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5
Q

What device is commonly used to express rotary motion as an electrical signal?

A

Tachogenerators

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6
Q

What resistance parameters are changed when a strain gauge is subjected to a compression force?

A

Decrease in length and increase in cross-sectional area

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7
Q

What are three types of fluid pressure sensors?

A
  • Bourdon tube
  • Bellows
  • Diaphragm
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8
Q

How does a piezoelectric crystal work as a sensor?

A

Can separate charges (create voltage) according to the amount of mechanical pressure applied. It is used to sense mechanical pressure changes.

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9
Q

On what principle does a magnetic flow meter work?

A

Principle of generation (electromagnetism)

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10
Q

What are the differences between an RTD and a thermistor?

A

RTD - made of metal wires or film and has a POSITIVE temperature coefficient of resistance

Thermistor - made of semiconductor material and has a NEGATIVE coefficient of resistance

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11
Q

What are three basic principles used in light sensors?

A
  • Photoemission
  • Photoconduction
  • Photovoltaic
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12
Q

What is the function of a transmitter?

A

Accept sensor information and provide standard types of output signals for transmission over long distances

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13
Q

Controllers usually work with ________ and _______ forms of energy

A

electrical, pneumatic

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14
Q

Why does a linear motion potentiometer require periodic maintenance?

A

Slider of the potentiometer wipes mechanically on the resistance element, causing it to wear out over time

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15
Q

Why does a linear motion variable inductor last longer than a linear potentiometer?

A

Does not have contact wear

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16
Q

What are some unique features and characteristics of a linear variable differential transformer (LVDT)?

A
  • can be made very small
  • very sensitive to motion
  • can be used with other circuit components to provide polarity sensitive DC voltage
  • has two identical secondary windings and a single primary winding
17
Q

How does a linear motion variable capacitor work?

A

Distance between fixed plate and movable plate varies according to linear position. As plate is moved closer to the fixed plate, its capacitance increases; when it is moved further away, its capacitance decreases.

18
Q

How can you get a single voltage signal from a LVDT?

A

Connecting the two secondary windings in series opposition (differential) connection

19
Q

What do fluid sensors supply information on?

A
  • Fluid pressure
  • Fluid flow
  • Liquid level
20
Q

What are some characteristics of a bourdon tube?

A
  • slightly flattened tube of flexible steel arranged in a semicircle
  • one end of tube is closed, other is open and fixed
  • inexpensive, quite accurate, rugged, and reliable
21
Q

How does a bourdon tube work?

A

As pressure in tube increases at the open end, the closed end tends to straighten. As pressure is reduced, the closed end moves back to its original position

22
Q

What are some characteristics of a bellows?

A
  • more sensitive than bourdon tubes

- used for low pressure applications

23
Q

_____________ and ___________ are used to sense rates of fluid flow

A

orifice plates, manometers

24
Q

What is a radiation pyrometer often used for?

A

Sensing very high temperatures of metals being melted in a furnace

25
Q

What is the principle of photoemission?

A

Electrons are liberated from the material when light energy falls on it

26
Q

What is the principle of photoconduction?

A

The resistance of the material is reduced with light

27
Q

What is the principle of photovoltaic?

A

Voltage is generated in a cell due to light falling on it

28
Q

A phototube works on what principle?

A

photoemission, where a cathode is coated with a light-sensitive substance that releases electrons when light shines on it

29
Q

A light-dependant resistor (LDR) works on what principle?

A

Photoconduction

30
Q

What are some characteristics of a photovoltaic cell?

A

Consists of a P-N junction with a large light-collecting surface area that generates emf according to the amount of light

31
Q

What is usually an electrical output signal standard

A

4mA to 20mA direct current signal range, or 10mA to 50mA direct current signal range

Process Controls (4 decks)

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