Introduction Of Sensing And Actuation

Que. What is Transducer?

• Imagine a translator, but for energy instead of languages.
• That's basically what a transducer is! It's a device that takes energy in one form and converts it into another form.
• In other words transducer convert a signal from one physical form to another physical form. (Physical form: thermal, electric, mechanical, magnetic, chemical and optical.)
• Example:
• Microphone: Convert electrical to sound signal.
• Speaker: Convert sound signal to electrical signal
• Antenna: Convert electromagnetic energy into electricity and vice versa.

Que. What is Sensor?

• The characteristic of any device or material to detect a presence of a particular physical quantity.
• The output of a sensor is signal which is converted to human readable form.
• It performs some functions to input by sensing or feeling some physical changes in the characteristics of a system in response to the physical parameters such as temperature, sound, pressure, light, gas etc.
• Output: Response to physical parameters.

Que. What is static characteristics of a sensor?

Imagine a sensor is like a special dial that translates things we can't directly measure (like temperature) into something which we can understand.

Static characteristics describe how well this dial perform under constant conditions. Different static characteristics are as follows:

• Accuracy:
• It represents the correctness of the output compared to a superior system.
• It is the difference between the standard and the measured value.

• Range:
• It gives the highest and the lowest value of the physical quantity within which the sensor can actually sense.
• Beyond this value there is no sensing and no kind of response.

• Resolution:
• It provides the smallest change in the input that a sensor can capable of sensing.
• Resolution is an important specification towards selection of sensor. Higher the resolution better the precision.

• Error:
• The difference between the standard value and the value measured by the sensor.

• Sensitivity:
• It indicates the ratio of incremental change in the response of the system with respect to incremental change in input parameter.
• It can be found from slope of output characteristic curve of a sensor.

• Linearity:
• The deviation of sensor value of curve from a particular straight line.

• Drift:
• The difference in the measurement of a sensor from a specific reading when kept at that value from a long period of time.

• Repeatability:
• The deviation between measurement in a sequence under same conditions.

Que. What is dynamic characteristic of a sensor? How well a sensor can response to changes in its input?

• Zero order system
• Output shows a response to the input signal with no delay.
• Does not include energy storing element.
• Ex. potentiometer measures linear and rotary displacement.

• First order system
• When the output approaches its final value gradually.
• Consist of an energy storage and dissipation element.

• Second order system
• Complex output response.
• The output response of a sensor oscillates before steady state.

Que. Classification of a sensor.

• Active sensor :
• Independently sense the input.
• Ex. Radar, sounder, laser, altimeter sensor.

• Passive Sensor :
• Cannot independently sense the input.
• Ex. Accelerometer soil moisture, water level and temperature sensor.

• Analog sensor :
• The response or output of the sensor is some continuous function of its input parameter.
• Ex. Temp sensor, LDR, analog pressure sensor, analog hall effect / magnetic sensor.
• A LDR shows continuous variation it its resistance in a function of intensity of light falling on it.

• Digital sensor :
• Response in binary nature
• Design to overcome the disadvantages of analog sensors. Along with the analog sensor it also comprises of extra electronics for bit conversion.
• Example: Passive infrared sensor (PIR) and digital temperature sensor (DS1620).

• Scalar sensor :
• Detect the input parameter only based on its magnitude.
• The response of a sensor is a function of magnitude of the input parameter.
• Not affected by the direction of a input parameter.
• Ex. Temp, gas, strain, color and smoke sensor.

• Vector sensor:
• The response of a sensor is depends on the magnitude of the direction and orientation of the input parameter.
• Ex. Accelerometer, gyroscope, magnetic field and motion detector sensor.

Que. What is Actuator?

• An actuator is the part of the system that deals with the control action required. (Mechanical Action)
• Mechanical or Electromechanical devices.
• A control signal is an input to an actuator and an energy source is required for its operation.
• Available in both micro and macro scales.
• Example: Electric motor, solenoid, hard drive, stepper motor, comb drive, hydraulic cylinder, piezoelectric actuator, and pneumatic actuator.

Que. State the different types of actuator?

• Electric linear actuator
• Powered by electrical signal
• Mechanical device containing linear guides, motors and control mechanism.
• Convert electrical energy into linear displacement.
• Used in automation applications including electrical bell, opening and closing dampers,
• locking doors, and braking machine motions

• Electric rotary actuator
• Powered by electrical signal.
• Convert electrical energy into rotational motion.
• Applications including quarter-turn valves, windows, and robotics.

• Fluid power linear actuator
• Powered by hydraulic fuel, gas or differential air pressure.
• Produces linear displacement.
• Mechanical devices have cylinder and piston mechanisms.
• Primarily used in automation applications including clamping and welding.

• Fluid power rotary actuator
• Powered by hydraulic fuel, gas or differential air pressure and convert it into rotational motion.
• Consisting of gearing, and cylinder and piston mechanisms.
• Primarily applications of this actuator are opening and closing dampers, doors, and clamping.

• Linear chain actuator
• Mechanical devices containing sprockets and section of chain.
• Provides linear motion by the free ends of the specially designed chains.
• Primarily used in motion control application.

• Manual linear actuator
• Provide linear displacement through the translation of manually rotated screws or gears.
• Consists of gearboxes, and hand operated knobs or wheels.
• Primarily used for manipulating tools and workpieces.

• Manual rotary actuator
• Provides rotary output through the translation of manually rotated screws, levers, or gears.
• Consists of hand operated knobs, levers, handwheels, and gearboxes.
•  Primarily used for the operation of valves.