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Sensors are devices that are used to measure physical variables like temperature, pH, velocity, rotational rate, flow rate, pressure and many others.
Â Today, most sensors do not indicate a reading on an analog scale (like a thermometer), but, rather, they produce a voltage or a digital signal that is indicative of the physical variable they measure.Â
Those signals are often imported into computer programs, stored in files, plotted on computers and analyzed to death.
Â Â Â Â Â Â Â Sensors come in many kinds and shapes to measure all kinds of physical variables.
Â However, many sensors have some sort of voltage output.Â There are a number of implications to that.Â
Here are some:
If a sensor has a voltage output, thenÂ it is a voltage sourceÂ that is controlled by the physical variable it measures.
If the sensor is a voltage source, you need to remember that no physical voltage sources areÂ ideal, and non-ideal voltage sources are usually best described with aÂ Thevinin Equivalent CircuitÂ that contains the voltage source and an internal resistance.
If a source has an internal resistance, there is a possibility of loading the source.Â If a significant load is attached to the source, the terminal voltage will drop.Â At that point, the terminal voltage is not what you expect it to be (from calibrations, spec sheets, etc.)
A sensors is a device that produces a measurable response to a change in a physical condition, such as temperature or thermal conductivities or a change in a chemical concentration .
Sensors are particularly useful for making in-situ measurments such as in industrial process control or medical applications.
A sensors is a usually packaged as a complete unit, discrete light detectors and ion detectors.
Examples of some sensors:
A thermocouple converts temperature to an output voltage which can be read by aÂ voltmeter . For accuracy, most sensors areÂ calibrated Â against known standards
A sensors is also used in the daily life.It is used in the TV remote, and is slso used in the the antenna.
It is also used in the speakers,also used in the bathroom and many computer appliances.
TYPES OF SENSORS
In the today life , the fast growing world ,the human species have been dependent on the sensors in every aspects of the life.
So every things in today world we used consist of sensors .
Giving an example of the common sensors , the human body is a sensors .
If someone hits us we immediately hit that person back in a fractions
of second .
SO SOME OF THE DIFFERENT TYPES OF SENSORS
1. BIOLOGICAL SENSORS
2. CHEMICAL SENSORS
3. PHYSICAL PROPERTY SENSORS
4. NUCLEAR RADIATIONS ON SENSORS
A biosensor is an analytical device comprising two elements
in spatial proximity:
1.1 A biological recognition element able to interact
Specifically with a target
1.2 A transducer able to convert the recognition event into a
Immunosensors are biosensors in which the recognition element is composed of antibodies. Antibodies are powerful recognition tools because of theiraffinity and specificity of recognition for the target (antigens), and because oftheir diversity, potentially allowing the monitoring of any compound.
2.NUCLEAR RADIATIONS SENSORS Fundamental mechanisms and interactions that allow detection and measurement of nuclear/ionizing radiation (e.g., free carrier generation in materials, optical scintillation, optically active defect creation in detectors, etc.
Sensor Devices:Â A device that can detect and measure a specific type/energy of nuclear or ionizing radiation. The sensor will rely on one or more sensing mechanisms and produce a signal that indicates the nuclear/ionizing radiation value.
3. CHEMICAL SENSORS
A chemical sensor is a device that transforms chemical information, ranging from the concentration of a
specific sample component to total composition analysis, into an analytically useful signal.
The chemical information, mentioned above, may originate from a chemical reaction of the analyte or from a
physical property of the system investigated
Chemical sensors contain two basic functional units: a receptor part and a transducer part. Some sensors
may include a separator which is, for example, a membrane.
1.1 In the receptor part of a sensor the chemical information is transformed into a form of energy which
may be measured by the transducer.
1.2 The transducer part is a device capable of transforming the energy carrying the chemical information
about the sample into a useful analytical signal. The transducer as such does not show selectivity
A common examples of chemical sensors is the robotic fish which is now used for some kind of investigating.
Some types of chemical sensors are:
1. OPTICAL DEVICES
2. ELECTRO CHEMICAL DEVICES
3. MAGNEETIC DEVICES
4. MASS SENSITIVE DEVICES
The sensors have some characteristic properties.
5. HYSTERESIS 1.1 ACCURACY
Accuracy is defined as, "The ability of a measurement to match the actual value of the quantity being measured".
If in reality it is 34.0 F outside and a temperature sensor reads 34.0 F, then than sensor is accurate.
Precision is defined as, " The ability of a measurement to be consistently reproduced" and " The number of significant digits to which a value has been reliably measured".
If on several tests the temperature sensor matches the actual temperature while the actual temperature is held constant, then the temperature sensor is precise.
By the second definition, the number 3.1415 is more precise than the number 3.14
There is a slight bit of difference between the term accuracy and precision.
The accuracy means being correct and true in every detail, precision means being more exact and to the point in reference to a certain standard or method.
For example, you can be accurate with your answer but you can be precise with the method of calculation.
The can be explain with the help of some more examples like:
The term accuracy refers more to the correctness of data, precision can also refer to greater detail in description of an object or concept. For example, accuracy can be kept in mind while collecting people's opinion on the social system of marriage but precision will be required in detailing each case study and interpreting it.
If we deal in term of the sensors we can understand it by an example of a sensors with good accuracy and good precision.
Suppose a lab refrigerator holds a constant temperature of 38.0 F. A temperature sensor is tested 10 times in the refrigerator.
The temperatures from the test yield the temperatures of: 38.0, 38.0, 37.8, 38.1, 38.0, 37.9, 38.0, 38.2, 38.0, 37.9.
This distribution does show a tendency toward a particular value (high precision) and is very near the actual temperature each time (high accuracy).
Difference between theÂ actual valueÂ of aÂ quantityÂ and theÂ valueÂ obtained by aÂ measurement.
Repeating the measurement willÂ reduce theÂ random errorÂ (caused by theÂ accuracyÂ limit of the measuringÂ instrument) but not theÂ systemic errorÂ (caused by incorrectÂ calibrationÂ of the measuring instrument).
Random errors in experimental measurements are caused by unknown and unpredictable changes in the experiment. These changes may occur in the measuring instruments or in the environmental conditions.
Examples of causes of random errors are:
electronic noise in the circuit of an electrical instrument,
irregular changes in the heat loss rate from a solar collector due to changes in the wind.
Random errors often have a Gaussian normal distribution . In such cases statistical methods may be used to analyze the data.
The meanÂ mÂ of a number of measurements of the same quantity is the best estimate of that quantity, and the standard deviationÂ sÂ of the measurements shows the accuracy of the estimate. The standard error of the estimateÂ mÂ isÂ s/sqrt(n), whereÂ nÂ is the number of measurements.
TheÂ precisionÂ of a measurement is how close a number of measurements of the same quantity agree with each other.
The precision is limited by the random errors. It may usually be determined by repeating the measurements.
Systematic errors in experimental observations usually come from the measuring instruments. They may occur because:
there is something wrong with the instrument or its data handling system, or
because the instrument is wrongly used by the experimenter.
Two types of systematic error can occur with instruments having a linear response:
OffsetÂ orÂ zero setting errorÂ in which the instrument does not read zero when the quantity to be measured is zero.
MultiplierÂ orÂ scale factor errorÂ in which the instrument consistently reads changes in the quantity to be measured greater or less than the actual changes.
Examples of systematic errors caused by the wrong use of instruments are:
errors in measurements of temperature due to poor thermal contact between the thermometer and the substance whose temperature is to be found,
errors in measurements of solar radiation because trees or buildings shade the radiometer.
TheÂ accuracyÂ of a measurement is how close the measurement is to the true value of the quantity being measured.
The accuracy of measurements is often reduced by systematic errors, which are difficult to detect even for experience research workers.
Ideal sensors will have a large and constant sensitivity.
Sensitivity-related errors ;saturation and
The difference between two output values that correspond to the same output depending on the trajectory followed by the sensors (i.e, magnetization in ferromagnetic materials)
RRELATION BETWEEN ACCURACY AND PRECISION
Accuracy is the capacity of a measuring instrument to give
RESULTS close to the TRUE VALUE of the measured quantity
Accuracy is related to the bias of a set of measurements
(IN)Accuracy is measured by the absolute and relative errors
= RESULT-TRUE VALUE
= ABSOLUTE ERROR
The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring.
Often in aÂ digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved.
The resolution is related to theÂ precisionÂ with which the measurement is made.
For example, aÂ scanning tunneling probeÂ (a fine tip near a surface collects an electron tunnelling current) can resolveÂ atomsÂ andÂ molecules.
APPLICATIONS OF SENSORS
There are a wide range of applications of the sensors in the daily life.
1 IN HEAD PHONES
Ultrasonic sensors depend highly upon sound waves or radio sounds in order to interpret the echoes and evaluate certain attributes of their targets. They are often referred to as transceivers especially when they function both in the sending and receiving of sound waves similar to the roles of the sonar or the radar. They work as high frequency waves of sound are generated and evaluated. The sensor calculates the interval by which the signal is received thereby interpreting its distance from the object.
There are many uses for ultrasonic sensors aside from the interpretation of the distance of the target to another object. One is for the measurement of wind direction or speed relying upon the anemometer technology. Air and water speed as well as tank fullness may also be measured. Multiple detectors are also utilized in the process.
Ultrasonography, burglar alarms and humidifiers depend much upon these sensors too.Â
A-Wear headphones provide the wearer with a second set of sensory 'ears' which detect movement, much like the proximity sensors found on the back of cars, which are used to aid parking. The use of headphones means that the wearer's hearing is effectively disabled as a warning system. In this application the sensors warn the wearer of any fast oncoming objects, like cars. The shape of the headphones is also integral to the design. Based on that of an auditorium, it is designed to enhance the quality of the sound.
2 FOR MILITARY AND NAVY SECURITY
Detecting the stealthy submarine starts with maintaining a tool kit of different sensors. Each sensor has specificÂ applicationsÂ that counters different submarine operations.
Many of these sensors complement and corroborate each other to enhance ASW effectiveness. Air ASW sensors are divided into two basic types; acoustic and non-acoustic. In some foreign services, these acoustic and non-acoustic sensors are commonly referred to as wet- and dry-end sensors,
Non-acoustic sensors augment the detection capability provided by acoustic sensors. These sensors use radar to detect exposed periscopes and hull surfaces, electro-magnetic systems to intercept the radar emissions from submarines, infra-red receivers to detect the heat signatures of surfaced submarines, or Magnetic Anomaly Detectors (MAD) to sense small changes in the Earth's magnetic field caused by the passage of a submarine. This sophisticatedÂ technologyÂ is further enhanced by vigilant lookouts who are carefully scanning the turbulent ocean surface for submarine periscopes and wakes.
Radar sensors have been used since World War II for the detection of surfaced or snorkelling submarines. Back then, submarines relied upon their batteries for submerged operations. Eventually their batteries would become drained to the point where they were forced to return to the surface and operate their diesel engines to re-charge the battery. While surfaced, the submarine was extremely vulnerable to detection by both radar and visual sensors. The addition of a snorkel enabled the submarine to operate its battery-charging diesel engines while minimizing its exposure to radar and visual sensors. Additionally, the background clutter of the surrounding ocean waves limited radar and visual detection. Also, the development of submarine-based electro-magnetic sensors provided the submarine commander with suffficient warning to dive if approaching radar emissions were detected.
Eventually, nuclear submarines where developed which eliminated the need to periodically recharge the batteries. Despite this significant advance, not all nations were able to build nuclear submarines due to financial and technological reasons. Those nations which remain committed to diesel power have pursued technology which limits the number of times the submarine has to recharge its batteries. However, many submarine commanders must still use their periscopes to provide final visual classification of targets prior to attack. Because of this requirement for target verification, radar systems are still used to detect submarine periscopes.
Today's airborne radar systems must be lightweight yet sufficiently capable for ASW operations, long-range detection and surveillance of surface vessels, airborne navigation, and weather avoidance. For that purpose, many Air ASW radar systems use different radar frequencies, scanning speeds, transmission characteristics, pulse lengths, and signal processing methods that reduce background sea clutter and enhance radar returns from exposed pericopes and submarine hulls. The hostile submarine using electro-magnetic sensors, however, can still detect ASW aircraft radar emissions at a much greater distance than the aircraft can detect the submarine by radar. Nevertheless, the threat of radar detection is sufficient to keep the submarine submerged. Radar systems now used aboard U.S. Navy ASW aircraft include the AN/APS-115 (P-3C), AN/APS-124 (SH-60B), and AN/APS-137Â
3 Magnetic Anomaly Detection (MAD) Sensors
MAD sensors are used to detect the natural and manmade differences in the Earth's magnetic fields. Some of these differences are caused by the Earth's geological structures and sunspot activity. Other changes can be caused by the passing of large ferrous objects, such as ships, submarines or even aircraft through the Earth's magnetic field. MAD sensor operation is similar in principle to the metal detector used by a treasure hunter or the devices used by utility companies to find underground pipes.
For ASW purposes, the ASW aircraft must almost be essentially overhead or very near the submarine's position to detect the change or anomaly. The detection range is normally related to the distance between the aircraft sensor ("MAD head") and the submarine. Naturally, the size of the submarine and its hull material composition normally determines the strength of the anomaly. Additionally, the direction travelled by both the aircraft and the submarine relative to the Earth's magnetic field is also a factor. Nevertheless, the close proximity required for magnetic anomaly detection makes the MAD system an excellent sensor for pinpointing a submarine's position prior to an air-launched torpedo attack.
In order to detect an anomaly, the MAD head of the aircraft tries to align itself with the noise produced by the Earth's magnetic field. Through this alignment, the noise appears as a near-constant background noise value which enables the operator to recognize any contrasting submarine magnetic anomalies from the background noise. However, any rapid changes in aircraft direction or the operation of certain electronic equipment and electric motors can produce so much aircraft electro-magnetic noise that makes the detection of the submarine's magnetic signature virtually impossible. Special electronic circuitry is enabled to compensate and null out this aircraft magnetic noise. Additionally, the MAD head is placed the farthest distance away from all the interfering sources. That is why the P-3C Orion aircraft has its distinct tail stinger or "MAD boom". On the S-3B, a similar MAD boom is installed and is electrically extended away from the aircraft during MAD operations. Additionally, the SH-60B extends a towed device called a "MAD bird" to reduce aircraft magnetic noise. With continuing advances in both compensation and sensor technology, the detection ranges for MAD sensors may be enhanced for the search and localization phases of ASW missions. Currently all naval ASW aircraft use variations of the AN/ASQ-81 MAD system. A few P-3C aircraft use an advance MAD system, the AN/ASQ-208, that usesÂ digitalprocessing.
4 'IMRT Sensors' - a smart dose of medicine for cancer treatment
MRT, developed about 10-years ago, works by 'painting' small areas of different intensity radiation over the tumour. It involves the use of aÂ servo-controlled deviceÂ called a multi-leaf collimator, that has about eighty "moving fingers" that can "allow or stop" the radiation from the treatment machine reaching the patient. It's precise control allows a three dimensional pattern of dose to be scaled up. By painting the dose distribution in this manner, a high tumour-killing radiation dose is conformed to the tumour while an acceptably low and safe radiation dose goes to the surrounding tissues and vital organs. This is very different from conventional radiotherapy in which no such painting is done and the high dose can extend beyond the tumour and damage healthy tissue.
Intensity Modulated Radiotherapy (IMRT), is a radiation therapy for cancers that improves clinical outcomes by a providing more accurate targeting of tumours then with standard radiotherapy, and minimising the amount of radiation absorbed by healthy tissues. The good news about IMRT is that it results in patients only receiving a high radiation dose where they need it, thereby preserving healthy tissues. But like most good things in life, it doesn't come with a free lunch - there's a catch. It becomes increasingly more difficult to verify that patients are receiving the prescribed dose of radiation during the course of treatment, because of the complex computer simulations required by IMRT. There's a need to validate the simulations by verifying exactly how much radiation is reaching the patient, and where it's going, and up to now, that's been a problem.
By making the project on the term paper on the topic we learn what is sensors .what are its types .what are its characterstic and where do it find applications in the daily life .