Role and scope of Sensors

 ROLE AND SCOPE OF SENSORS

We live in a World of Sensors. You can find different types of Sensors in our homes, offices, cars etc. working to make our lives easier by turning on the lights by detecting our presence, adjusting the room temperature, detect smoke or fire, make us delicious coffee, open garage doors as soon as our car is near the door and many other tasks.

Mechatronic systems are composed of mechanical and electrical components, referred as “smart” systems because of the integration of sensors, actuators, and control systems. Essential part of a mechatronics system is the measurement system that senses the variations in the physical parameters, such as temperature, pressure, displacement, and so on, and converts it to an electrical quantity, viz. electric voltage or current. The measurement system consists of mainly two parts: sensor and signal-conditioning circuit. A device that displays, records, or controls the measured variable utilizes the output of the measurement system.

All these and many other automation tasks are possible because of Sensors. Before going in to the details of What is a Sensor, What are the Different Types of Sensors and Applications of these different types of Sensors, we will first take a look at a simple example of an automated system, which is possible because of Sensors (and many other components as well). 

 

 

Real Life Application of sensors in Mechatronic systems

The example we are talking about here is the Autopilot System in aircrafts. Almost all civilian and military aircrafts have the feature of Automatic Flight Control system or sometimes called as Autopilot.

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An Automatic Flight Control System consists of several sensors for various tasks like speed control, height, position, doors, obstacle, fuel, maneuvering and many more. A Computer takes data from all these sensors and processes them by comparing them with pre-designed values.

The computer then provides control signal to different parts like engines, flaps, rudders etc. that help in a smooth flight. The combination of Sensors, Computers and Mechanics makes it possible to run the plane in Autopilot Mode.

All the parameters i.e. the Sensors (which give inputs to the Computers), the Computers (the brains of the system) and the mechanics (the outputs of the system like engines and motors) are equally important in building a successful automated system.



What is a Sensor?

There are numerous definitions as to what a sensor is but I would like to define a Sensor as an input device which provides an output (signal) with respect to a specific physical quantity (input).

The term “input device” in the definition of a Sensor means that it is part of a bigger system which provides input to a main control system (like a Processor or a Microcontroller).

Another unique definition of a Sensor is as follows: It is a device that converts signals from one energy domain to electrical domain. The definition of the Sensor can be understood if we take an example in to consideration.

fig. Different sensors
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The simplest example of a sensor is an LDR or a Light Dependent Resistor. It is a device, whose resistance varies according to intensity of light it is subjected to. When the light falling on an LDR is more, its resistance becomes very less and when the light is less, well, the resistance of the LDR becomes very high.

We can connect this LDR in a voltage divider (along with other resistor) and check the voltage drop across the LDR. This voltage can be calibrated to the amount of light falling on the LDR. Hence, a light sensor.



Classification of Sensors

Now that we have seen what a sensor is, we will proceed further with the classification of Sensors.


Active Sensor: Active Sensors are those which require an external excitation signal or a power signal.

E.g.: LiDAR (Light detection and ranging), photoconductive cell.

 Passive Sensor: Do not require any external power signal and directly generates output response.

E.g.: Radiometers, film photography

 

Based on the means of detection

• Some of the means of detection are Electric, Biological, Chemical, Radioactive etc.

 

Based on the conversion phenomenon  i.e. the input and the output.

 • Some of the conversion phenomena are Photoelectric, Thermoelectric, Electrochemical, Electromagnetic, Thermo-optic, etc.


• Analogue sensors: Produce an analog output.

• Digital Sensors: Work with discrete or digital data.



Different Types of Sensors

The following is a list of different types of sensors that are commonly used in various applications. All these sensors are used for measuring one of the physical properties like Temperature, Resistance, Capacitance, Conduction, Heat Transfer etc.

·        Temperature Sensor

·        Proximity Sensor

·        Accelerometer

·        IR Sensor (Infrared Sensor)

·        Pressure Sensor

·        Light Sensor

·        Ultrasonic Sensor

·        Smoke, Gas and Alcohol Sensor

·        Touch Sensor

·        Color Sensor

·        Humidity Sensor

·        Tilt Sensor

·        Flow and Level Sensor

 



SELECTION OF SENSORS

A number of static, dynamic and other factors must be considered in selecting suitable sensor to measure the desired physical parameter.

 

1. Accuracy required:

It is the difference between measured value and true value. Accuracy of the sensor should be as high as possible.

 

2. Precision:

It is the ability to reproduce repeatedly with a given accuracy. It should be Very high. Error between sensed and actual values should approach zero.

 

3. Sensitivity:

It is the ratio of change in output to a unit change of the input. It should be chosen to allow sufficient output.

4. Operating range:

It is the difference between maximum and minimum value of the sensed parameter. Sensors should have wide operating range and good accuracy over the range.

5. Resolution:

It is the smallest change in the sensor which can differentiate. Sensors should have high resolution.

6. Speed response:

Time taken by the sensor to respond should be minimum. Response time should be very less.

7. Reliability:

Reliability of the sensor should be high. Mean time to failure (MTTF) should be high. It results the increased life.

8. Maintenance 

should also be easy and frequency of maintenance required should be less over the period.

9. Calibration:

Sensors need frequent calibration for many reasons. Hence, it should be easy to calibrate. Drift should be as minimum as possible.

10. Cost:

Cost of the sensor should be low.

11. The nature of output:

 The nature of output required from the sensor whether the digital or analog has to be considered while selecting a sensor.

12. Linearity:

Sensor’s curve should linear. The percentage of deviation from the best-fit linear calibration curve should be less.

13. Environmental conditions:

Sensors should operate over wide environmental conditions such as temperature, corrosion, pressure, shocks etc.

14. Interfacing:

Sensors should be compatible with different instruments for interfacing.

15. Size and weight:

Sensors should have small size and less weight.

 

  

Did You Know?

Sensors are used today almost everywhere. Radar guns bounce microwaves off moving cars. A burglar alarm may use a photosensor to detect when a beam of light has been broken, or may use ultrasonic sound waves that bounce off moving objects. Still other sensors may detect pressure (barometers) or chemicals (Breathalyzers and smoke detectors). Stud finders, used by carpenters to locate wooden studs under a wall, may employ magnets or radar. Wired gloves, which relay information about the position of the fingers, are used in virtual-reality environments. A cheap car alarm may be nothing but a shock sensor, in which a strong vibration will cause two metal surfaces to come together.

 


 

SMART SENSORS

All that we discussed so far was the traditional role and aspects of sensors in mechatronics, now let’s talk about the more advanced and better Smart Sensors


What is a smart sensor and how is it different from a normal sensor?

A sensor is a device that would create an electrical signal which is related to the quantity that is measured by it. So this device would measure the physical quantity and the measurement will be displayed by using an instrument. A smart sensor or an intelligent sensor is a device that has integrated electronics, and they are able to perform certain functions like, logic functions, two-way communications, and are capable to make decisions. These sensors are capable to measure the environmental data more accurately with less noise. Smart sensors are used for monitoring and to do the controlling mechanism in many industrial applications. Mostly a smart sensor has three important parts they are sensing element, signal processing part, and microprocessor. The major difference between smart sensors and a conventional sensor is that the smart sensor is faster than the conventional type and it is accurate too. Smart sensors are smaller in size than a normal sensor and they also consume low power.

 


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What are the major functions of a smart sensor?

§  Information processing

§  Compensation

§  Communication

§  Integration

§  Validation

§  Data fusion



Why smart sensor?

§  Self-calibration

§  Communication

§  Accuracy

§  Computation

§  Multi-sensing

§  Cost-effective

§  Quick response

§  Low power consumption

§  Remote diagnosis


Smart sensors are able to communicate and are capable to do multi-sensing a single sensor can measure pressure, temperature, etc. it is cost-effective and can provide accurate measurement and also it can be integrated into a network of sensors.


What are the features of a smart sensor?

§  Analog to digital converter

§  Microcontroller with advanced features, mostly it would be PIC

§  Sensor identification

§  The information should be calibrated

§  Data logging and real time clock

§  Communication is done by using a serial bus


How to select a smart sensor?

§  It must be selected according to the self-calibration capability

§  Accuracy

§  According to the self-diagnosis ability

§  It must be selected according to the information processing

§  Area coverage

§  Fault tolerance

§  It can also be selected according to the ability to operate in harsh environment

§  Reliability

§  Service life


How do smart sensor work?

Mostly these sensors would measure certain physical quantities like pressure, temperature, humidity, flow, etc. So these sensors would convert the analog input that it receives to a digital with the help of analog to digital converter. This converter would give the converter value to the processor. Smart sensors have memory to store data and programs.

SENSORS + INTEGRATING HARDWARE + Processor = SMART SENSOR


What are the types of smart sensor? 

§  Optical sensor

§  Infrared detector array

§  Accelerometer

§  Integrated multi-sensor

§  Bluetooth based smart sensor


What are the important components of a smart sensor?

§  Sensing/transduction element

§  Amplifier

§  Analog multiplexer

§  Analog to digital converter

§  Digital to analog converter

§  Memory

§  Processor


What are the applications of smart sensor?

§  Industrial applications

§  Automotive

§  Aerospace

§  Defense

§  Industrial

§  Intelligent house

§  Medical

§  Environmental monitoring

§  Flood and water level monitoring system

§  Transport

§  Traffic monitoring and controlling

§  Precision agriculture and animal tracking


These sensors are used in aerospace because a lot of chemical sensing must be done. So the sensing will be done for space vehicles and in aircraft operations. In certain industrial sectors, there would be a harsh environment so humans won’t be able to work properly in these environments so we can use smart sensors for harsh industrial environments. These sensors can also be used as imaging sensors. It is also used as Nano-sensors for certain fields like communication, transportation, medical, etc. Many bio-sensors are smart sensors, biosensors are used in many fields like medical, health care, and environment…


What are the advantages of a smart sensor?

§  System operation will be very quick, due to the decrease of load in the central control system

§  Reduction of cost and maintenance

§  These sensors use the serial bus so the need for connecting wires is reduced and because of this size and cost will reduce too

§  It has high accuracy because of the digital control system

§  The set point and calibration of the sensors can be changed easily from the central control computer

§  These sensors can be integrated into a network of sensors

§  Auto-correction

§  Compact in size

 

 

Smart sensors are truly a technology of the future and are the way moving forward and we have to learn to embrace it.



BY:
Students of Vishwakarma Institute of Technology
Digvijay Gaikwad
Yashraj Desai 
Kunal Deshmukh
Sanket Gaikwad
Umesh Gaikwad






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