40 Questions
What are the three main steps in a closed loop industrial control system?
Applying input, controlling the process, and providing feedback
What is the primary function of a sensor in a control system?
To convert the physical quantity into an electrical signal
What is a transducer?
A device that converts one type of energy to another
What type of transducer converts electromagnetic waves into electric current and vice versa?
Antenna
What is the function of a tape head?
To convert changing magnetic fields into electrical form
What type of transducer converts motion into electrical form?
Magnetic cartridge
What type of transducer converts changes in light levels into resistance changes?
Photo-detector or Photo-resistor (LDR)
What is a common categorization of transducers?
By application
What is the primary function of a sensor?
To detect physical phenomena and convert them into measurable electrical signals
What type of sensor is a thermistor?
Active sensor
What is the purpose of a multiplexer (MUX) in a data acquisition system?
To link each sensor individually to a direct analog-to-digital (A/D) converter
What is the role of an excitation circuit in a sensor?
To provide an operational signal to the sensor
What is the main difference between a passive and active sensor?
Passive sensors produce electric signals without external power, while active sensors require an external power source
What is the function of a transducer?
To convert one form of energy into another
What is the purpose of signal conditioning circuitry in a sensor?
To filter out unwanted signals
What is the main function of a sensor?
To receive a signal and transform it into an electrical form
What is the role of a data acquisition system?
To monitor and control physical parameters in various applications
What is the term for the amount that a sensor's output varies when the measured quantity varies?
Sensitivity
What type of sensor is a mercury-in-glass thermometer an example of?
Thermoelectric
What is the term for a device that transforms one type of energy into another?
Transducer
What is an actuator?
A device that takes in energy and moves
What is the main difference between a sensor and a transducer?
A sensor transforms signals, while a transducer transforms energy
What is the purpose of calibrating a sensor?
To ensure the sensor is accurate against recognized standards
Why are smaller sensors often preferred?
Because they have less of an impact on the object being measured
What is the primary difference between contact and non-contact sensors?
Their physical contact with the measured object
What type of sensors detect changes in capacitance?
Capacitive sensors
What is the primary function of an optical proximity sensor?
To detect the presence or absence of an object
What type of transducers convert sound waves into electrical signals?
Microphones
What is the primary application of Hall effect sensors?
Speed measurement
What is the output voltage of a D.C. tachogenerator?
Direct current (DC)
What is the main advantage of non-contact sensors over contact sensors?
Minimizing wear and damage
What is the purpose of a photodetector in an optical proximity sensor?
To detect changes in the reflected or transmitted light
What is the primary function of contact type switches?
To open or close electrical circuits to control the flow of electricity
What is the main difference between A.C. and D.C. tachogenerators?
The type of output signals they produce
What is the function of light transducers?
To convert light energy into electrical signals
What is the purpose of hall effect sensors?
To detect the presence of magnetic fields and convert them into electrical signals
What is the main application of vibration transducers?
Vibration analysis, condition monitoring, and structural health monitoring
What is the function of magnet type switches?
To use the presence or absence of a magnetic field to open or close electrical contacts
What is the purpose of electromagnetic type switches?
To use the principle of electromagnetism to control the switching action
What is the primary function of tachogenerators?
To convert rotational speed into electrical signals
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
Learn about the basics of closed loop industrial control systems, including the role of sensors and transducers in measuring and controlling physical quantities.
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