Industrial Control Systems: Sensors and Transducers

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Questions and Answers

What is the main advantage of using micro-sensors over macroscopic methods?

Higher cost

Larger size

Far higher speed and sensitivity (correct)

Slower response time

What is the function of sensor 5 in the data acquisition system?

To monitor the internal workings of the system (correct)

To detect the object without physical contact

To measure the object's temperature

To convert the signal into digital format

What is the purpose of a multiplexer (MUX) in a data acquisition system?

To generate an excitation signal for active sensors

To amplify the signal from the sensor

To link each sensor individually to an A/D converter (correct)

To display the output of the system

What is the main difference between active and passive sensors?

Active sensors require an external power source Signup and view all the answers

What is the function of an actuator in a data acquisition system?

To act on the object being measured Signup and view all the answers

What is the purpose of signal conditioners in a data acquisition system?

To couple sensors to conventional electronic circuits Signup and view all the answers

What is the main function of sensors in modern technology?

To monitor and control physical parameters Signup and view all the answers

What is the main difference between sensors and transducers?

Sensors detect physical phenomena, while transducers convert energy Signup and view all the answers

What do transducers convert physical quantities into?

Electrical signals Signup and view all the answers

What is the main difference between contact and non-contact sensors?

The requirement of physical contact with the measured object Signup and view all the answers

What type of sensors use infrared or visible light sources and photodetectors?

Optical proximity sensors Signup and view all the answers

What type of sensors detect physical contact or position changes?

Contact type switches Signup and view all the answers

What type of transducers convert sound waves into electrical signals?

Sound transducers Signup and view all the answers

What type of sensors detect magnetic fields and convert them into voltage or current signals?

Hall effect sensors Signup and view all the answers

What type of devices convert rotational speed into electrical signals?

Tachogenerators Signup and view all the answers

What is the main application of tachogenerators?

Speed measurement and control Signup and view all the answers

What is the primary purpose of sensors in a closed loop industrial control system?

To measure changes in the controlled physical quantity Signup and view all the answers

What is the term used to describe a device that converts one type of energy to another?

Transducer Signup and view all the answers

What is an example of an electromagnetic transducer?

All of the above Signup and view all the answers

What does a photo-detector or photo-resistor (LDR) convert?

Changes in light levels into resistance changes Signup and view all the answers

What is the purpose of the feedback stage in a closed loop industrial control system?

To measure the output and apply it back to the input stage Signup and view all the answers

What is the term used to describe a device that converts electrical signals into visual form?

Cathode ray tube (CRT) Signup and view all the answers

What is the function of a tape head?

Converts changing magnetic fields into electrical form Signup and view all the answers

What is an example of a transducer that converts motion into electrical form?

Magnetic cartridge Signup and view all the answers

What is the primary function of switches in electronic circuits?

To control the flow of electricity Signup and view all the answers

Which type of switch operates by physically making or breaking contact between conducting elements?

Contact Type Switches Signup and view all the answers

What is the primary function of transducers in electronic systems?

To convert one form of energy into another Signup and view all the answers

Which type of transducer converts sound waves into electrical signals or vice versa?

Sound Transducers Signup and view all the answers

What is the primary function of tachogenerators in electronic systems?

To convert rotational speed into electrical signals Signup and view all the answers

What is the primary difference between A.C. and D.C. tachogenerators?

Output signal type (A.C. or D.C.) Signup and view all the answers

Which type of switch uses the presence or absence of a magnetic field to open or close electrical contacts?

Magnet Type Switches Signup and view all the answers

What is the primary application of vibration transducers?

Vibration analysis Signup and view all the answers

What is the primary function of a sensor?

To detect a parameter and report it in another form Signup and view all the answers

What is an actuator?

A device that takes in energy and moves Signup and view all the answers

What is the term for the amount that a sensor's output varies when the measured quantity varies?

Sensitivity Signup and view all the answers

What is the purpose of calibrating a sensor?

To ensure its accuracy against recognized standards Signup and view all the answers

What is the difference between a sensor and a transducer?

A sensor receives a signal and transforms it into an electrical signal, while a transducer transforms one type of energy into another Signup and view all the answers

What is an example of an electrochemical sensor?

Hydrogen sensor Signup and view all the answers

What is the effect of using smaller sensors?

They reduce the impact on the object being measured Signup and view all the answers

What is an example of an electromechanical sensor?

Galvanometer Signup and view all the answers

Study Notes

Introduction to Industrial Control Systems

A closed-loop industrial control system consists of three steps: applying the input (reference value), controlling the process, and feedback (negative feedback) that measures the output and applies it back to the input stage.
Sensors are special devices that sense changes in the controlled physical quantity.
Transducers are devices that convert one type of energy into another.

Types of Transducers

Electromagnetic transducers:
- Convert electromagnetic waves into electric current and vice versa (e.g., antenna, cathode ray tube (CRT))
- Convert electrical signals into visual form (e.g., CRT)
- Convert electrical power into visible light (e.g., fluorescent lamp, light bulb)
Electrochemical transducers:
- pH probes
- Electro-galvanic fuel cell
- Hydrogen sensor
Electromechanical transducers:
- Electro-active polymers
- Galvanometer
- Micro-electromechanical systems (MEMS)
- Rotary motor, linear motor
- Vibration powered generator
Electrostatic transducers:
- Electrometer
Photoelectric transducers:
- Laser diode, light-emitting diode (convert electrical power into forms of light)
- Photoresistor, phototransistor, photomultiplier tube (convert changing light levels into electrical form)
Thermoelectric transducers:
- RTD (Resistance Temperature Detector)
- Photodiode
- Thermocouple
- Peltier cooler
- Thermistor (includes PTC resistor and NTC resistor)
Electroacoustic transducers:
- Loudspeaker, earphone (convert electrical signals into sound)
- Microphone (convert sound into an electrical signal)

Sensors

A sensor is a device that uses one type of energy to detect a parameter and report it in another (often an electrical or digital signal).
Sensors can be classified as:
- Contact sensors: require physical contact with the measured object (e.g., switches, pressure sensors, temperature sensors)
- Non-contact sensors: operate without physical contact with the measured object (e.g., optical sensors, capacitive sensors, inductive sensors)
Sensors have various applications, including:
- Automation
- Robotics
- Object detection
- Position sensing
- Industrial machinery
- Assembly lines
- Conveyor systems
- Automotive applications
- Consumer electronics

Sensor Characteristics

Sensitivity: measures the amount of change in the sensor's output when the measured quantity changes
Sensors can affect the object being measured (e.g., thermometer cooling the liquid, liquid heating the thermometer)

Data Acquisition and Control Systems

A block schematic of a data acquisition and control device consists of:
- Sensors
- Multiplexer (MUX)
- Analog-to-digital (A/D) converter
- Computer
- Actuator
- Control signals
The system can include various components and peripheral devices, such as amplifiers, sample-and-hold circuits, filters, and data recorders.

Transducers and Sensors

Sensors detect physical phenomena and convert them into measurable electrical signals.
Transducers convert physical quantities into electrical signals.
Transducers can be classified as:
- Contact type: require physical contact with the measured object
- Non-contact type: operate without physical contact with the measured object

Optical Proximity Sensors

Basic principle: detect the presence or absence of an object by emitting light and detecting changes in the reflected or transmitted light
Construction: consist of a light emitter (LED or laser diode) and a photodetector (photodiode or phototransistor) housed in a compact package
Applications: widely used in automation, robotics, object detection, and position sensing applications

Other Types of Sensors and Transducers

Switches:
- Contact type switches (e.g., push buttons, limit switches)
- Magnet type switches (e.g., reed switches)
- Electromagnetic type switches (e.g., relays)
Sound transducers: convert sound waves into electrical signals or vice versa
Light transducers: convert light energy into electrical signals
Pressure transducers: measure pressure and convert it into an electrical signal
Vibration transducers: convert mechanical vibrations into electrical signals
Hall effect sensors: detect magnetic fields and convert them into electrical signals
A.C./D.C. tachogenerators: convert rotational speed into electrical signals

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Description

Learn about the three steps in a closed loop industrial control system, including the role of sensors and transducers in measuring and controlling physical quantities.