Showing posts with label ELECTRONICS. Show all posts
Showing posts with label ELECTRONICS. Show all posts
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Characteristics of Sensors
Characteristics of Sensors:
Selecting a Sensor Based on its Traits
Sensors are used by engineers to characterize the characteristics or behavior of an object or system. Choosing the right sensor for the job is critical.
A sensor takes an input quantity and converts it to an output quantity. Sensors may be simple physical measurement systems, or complex electronic devices requiring sophisticated data acquisition systems. No matter the type of sensor, input type, or output type, every sensor has inherent characteristics that allow the user to select the right sensor for the task at hand.
Sensor Characteristics
Some sensor characteristics include:
· Input Range
· Output Range
· Accuracy
· Repeatability
· Resolution
Input Range:
Input range is the maximum measureable range that the sensor can accurately measure. For example, a compression load cell may have an input range of 0 - 5000 pounds. The load cell cannot accurately measure "negative", or tensile loads, or compressive loads greater than 5000 pounds. Generally, quantities outside of the input range can be measured, but characteristics such as accuracy and repeatability may be compromised when the input is outside of the specified range.
Output Range:
Output range generally refers to electronic sensors, and is the range of electrical output signal that the sensor returns. However, the output range could be a physical displacement, such as in a spring scale, or rotation, such as in a clock-style analog thermometer. The output range is related to the input range by the conversion algorithm specific to the sensor type, and the algorithm may include factors based on the calibration of the specific sensor.
Accuracy
Accuracy actually refers to the amount of error, or inaccuracy, that may be present in a sensor. Accuracy can be stated as a unit of measurement, such as +/- 5 pounds, or as a percentage, such as 95%. In most cases, increased accuracy results in an increased cost for a sensor.
Repeatability
Repeatability, as the name implies, refers to how often a sensor under the same input conditions will return the same value. If a sensor is designed to be used over and over again, it is important that the output value is accurate over every measurement cycle for the life of the sensor. Repeatability is determined by calibration testing of the sensor using known inputs.
Resolution:
Resolution is the smallest unit of measurement that the sensor can accurately measure. Some transducers return output signals in discrete steps, and therefore the resolution is easily defined. Resolution can be stated as a unit of measurement or as a percentage. For electronic sensors, resolution is also dictated by the resolution of the signal conditioning hardware or software.These qualities are common to all sensors, no matter what characteristic is being measured. All of these traits must be considered when selecting the right sensor for the specific needs of a test.
Selecting a Sensor Based on its Traits
Sensors are used by engineers to characterize the characteristics or behavior of an object or system. Choosing the right sensor for the job is critical.
A sensor takes an input quantity and converts it to an output quantity. Sensors may be simple physical measurement systems, or complex electronic devices requiring sophisticated data acquisition systems. No matter the type of sensor, input type, or output type, every sensor has inherent characteristics that allow the user to select the right sensor for the task at hand.
Sensor Characteristics
Some sensor characteristics include:
· Input Range
· Output Range
· Accuracy
· Repeatability
· Resolution
Input Range:
Input range is the maximum measureable range that the sensor can accurately measure. For example, a compression load cell may have an input range of 0 - 5000 pounds. The load cell cannot accurately measure "negative", or tensile loads, or compressive loads greater than 5000 pounds. Generally, quantities outside of the input range can be measured, but characteristics such as accuracy and repeatability may be compromised when the input is outside of the specified range.
Output Range:
Output range generally refers to electronic sensors, and is the range of electrical output signal that the sensor returns. However, the output range could be a physical displacement, such as in a spring scale, or rotation, such as in a clock-style analog thermometer. The output range is related to the input range by the conversion algorithm specific to the sensor type, and the algorithm may include factors based on the calibration of the specific sensor.
Accuracy
Accuracy actually refers to the amount of error, or inaccuracy, that may be present in a sensor. Accuracy can be stated as a unit of measurement, such as +/- 5 pounds, or as a percentage, such as 95%. In most cases, increased accuracy results in an increased cost for a sensor.
Repeatability
Repeatability, as the name implies, refers to how often a sensor under the same input conditions will return the same value. If a sensor is designed to be used over and over again, it is important that the output value is accurate over every measurement cycle for the life of the sensor. Repeatability is determined by calibration testing of the sensor using known inputs.
Resolution:
Resolution is the smallest unit of measurement that the sensor can accurately measure. Some transducers return output signals in discrete steps, and therefore the resolution is easily defined. Resolution can be stated as a unit of measurement or as a percentage. For electronic sensors, resolution is also dictated by the resolution of the signal conditioning hardware or software.These qualities are common to all sensors, no matter what characteristic is being measured. All of these traits must be considered when selecting the right sensor for the specific needs of a test.
INTRODUCTION TO OPTICAL SENSOR
Using Light as a Measurement Tool
Optical sensors detect the presence or behavior of light waves. This could include light in the visible spectrum, or outside the visible spectrum.
Optical sensors are a class of sensors that use light waves as an input. These light waves can be used directly to determine the proximity of an object, or indirectly to measure other properties. There are several different types of optical sensors:
· Photodetectors – Photodetectors, also known as proximity sensors, are used to determine if a moving object enters the range of a sensor. The most commonly found photodetector is the “electric eye”. This type of sensor works by projecting a beam of light from a transmitter to a receiver across a specific distance. As long as the beam of light maintains a connection with the receiver, the circuit remains closed. If an object passes through the beam of light, the continuity of the circuit is lost, and the circuit opens. An example of this type of sensor is a garage door opener safety sensor that will halt the closing of the door if an object breaks the beam.
· Infrared sensors – Active infrared sensors project a beam of light in the infrared spectrum and receive the returning reflection from objects in the sensor’s range. Infrared sensors can be used as proximity sensors, such as in automatic doors. Passive infrared sensors are used to measure the radiation of heat within its range. Examples of passive infrared sensors include “heat-seeking” missile guidance systems and infrared thermography systems.
· Fiberoptic sensors – Fiberoptic sensors can be used to measure a wide range of physical phenomena, depending on the configuration of the sensor. Optical fibers can be coated with materials that respond to changes in strain, temperature, or humidity. Optical gratings can be etched into the fiber at specific intervals to reflect specific frequencies of light. As the fiber is strained, the distances between the gratings change, allowing the physical strain to be measured.
· Interferometers – An interferometer is a device that adds waves from two light sources, generating an interference pattern. The pattern can be used to determine properties of the waves. Interferometry is used in many industries, but its most visible use is in astronomy. Two small telescopes mounted a fixed distance apart can achieve the resolution of a single telescope with a diameter equal to the distance between the two telescopes. Early interferometers were limited to large wavelength radio telescopes, but are now applied to shorter wavelengths of light. This method allows astronomers to measure the diameters of stars, and future projects using interferometers will help astronomers detect and perhaps measure extrasolar planets.
Optical sensors can in many cases provide non-contact measurement in environments where direct contact of electrical circuitry is not possible, such as in high-voltage applications. Optical sensors are used for both very low-tech and very-high tech applications.
Optical sensors detect the presence or behavior of light waves. This could include light in the visible spectrum, or outside the visible spectrum.
Optical sensors are a class of sensors that use light waves as an input. These light waves can be used directly to determine the proximity of an object, or indirectly to measure other properties. There are several different types of optical sensors:
· Photodetectors – Photodetectors, also known as proximity sensors, are used to determine if a moving object enters the range of a sensor. The most commonly found photodetector is the “electric eye”. This type of sensor works by projecting a beam of light from a transmitter to a receiver across a specific distance. As long as the beam of light maintains a connection with the receiver, the circuit remains closed. If an object passes through the beam of light, the continuity of the circuit is lost, and the circuit opens. An example of this type of sensor is a garage door opener safety sensor that will halt the closing of the door if an object breaks the beam.
· Infrared sensors – Active infrared sensors project a beam of light in the infrared spectrum and receive the returning reflection from objects in the sensor’s range. Infrared sensors can be used as proximity sensors, such as in automatic doors. Passive infrared sensors are used to measure the radiation of heat within its range. Examples of passive infrared sensors include “heat-seeking” missile guidance systems and infrared thermography systems.
· Fiberoptic sensors – Fiberoptic sensors can be used to measure a wide range of physical phenomena, depending on the configuration of the sensor. Optical fibers can be coated with materials that respond to changes in strain, temperature, or humidity. Optical gratings can be etched into the fiber at specific intervals to reflect specific frequencies of light. As the fiber is strained, the distances between the gratings change, allowing the physical strain to be measured.
· Interferometers – An interferometer is a device that adds waves from two light sources, generating an interference pattern. The pattern can be used to determine properties of the waves. Interferometry is used in many industries, but its most visible use is in astronomy. Two small telescopes mounted a fixed distance apart can achieve the resolution of a single telescope with a diameter equal to the distance between the two telescopes. Early interferometers were limited to large wavelength radio telescopes, but are now applied to shorter wavelengths of light. This method allows astronomers to measure the diameters of stars, and future projects using interferometers will help astronomers detect and perhaps measure extrasolar planets.
Optical sensors can in many cases provide non-contact measurement in environments where direct contact of electrical circuitry is not possible, such as in high-voltage applications. Optical sensors are used for both very low-tech and very-high tech applications.
INTRODUCTION TO SENSORS
How Engineers Use Sensors to Measure Object Properties and Behaviors:
Electrical and mechanical sensors are widely used to characterize the performance and properties of components and systems, but are also found in household objects.
Sensors are electrical or mechanical components that are used to measure a property or behavior of an object or system. Some sensors measure properties directly, other sensors measure properties indirectly, using conversions or calculations to determine results. Sensors are used by scientists and engineers during research and testing activities, but they can also be found in many household objects, such as temperature sensors in an oven to accelerometers in an automobile airbag system. Sensors are generally categorized by the type of phenomenon that they measure, rather than the functionality of the sensor itself.
MECHANICAL SENSORS:
Mechanical sensors measure a property through mechanical means, although the measurement itself may be collected electronically. An example of a mechanical sensor is a strain gauge. The strain gauge measures the physical deformation of a component by experiencing the same strain as the component, yet the change in resistance of the strain gauge is measured electrically. Other types of mechanical sensors include:
· Pressure sensors
· Accelerometers
· Potentiometers
· Gas and fluid flow meters
· Humidity sensors
ELECTRICAL SENSORS:
Electrical sensors measure electric and magnetic properties. An example of an electrical sensor is an ohmmeter, which is used to measure electrical resistance between two points in a circuit. An ohmmeter sends a fixed voltage through one probe, and measures the returning voltage through a second probe. The drop in voltage is proportional to the resistance, as dictated by Ohm's Law. Other electrical sensors include:
· Voltmeter/Ammeter
· Metal detector
· RADAR
· Magnetometer
THERMAL SENSOR:
Although all thermal sensors measure changes in temperature, there are a variety of types of thermal sensors, each with specific uses, temperature ranges, and accuracies. Some types of thermal sensors include:
· Thermometers
· Thermocouples
· Thermistors
· Bi-metal thermometers
CHEMICAL SENSORS:
Chemical sensors generally detect the concentration of a substance in the air or in a liquid. Some chemical sensors, such as pH glass electrodes are designed to be sensitive to a certain ion. Some other types of chemical sensors include:
· Oxygen sensors
· Carbon monoxide detectors
· Redox electrodes
OPTICAL SENSOR:
Optical sensors detect the presence of light waves. This could include light in the visible spectrum, or outside the visible spectrum, in the case of infrared sensors. Some types of optical sensors include:
· Photodetectors
· Infrared sensors
· Fiberoptic sensors
· Interferometers
OTHER TYPE OF SENSOR:
There are many other types of sensors that don't fall into one of the broad categories described here. Some of these sensors include:
· Radiation sensors, including Geiger counters and dosimeters
· Motion sensors, including radar guns and speedometers
· Acoustic, including sonar and seismometers
· Gyroscopes
While sensors are used frequently by engineers and scientists in their studies, sensors are also use in many household products. Sensors can be found in many everyday objects, including touch-sensitive buttons and screens, infrared remote controls, motion-sensitive lighting, and home thermostats.
Proximity Sensors:
Proximity sensors may be of the contact or non-contact type. Contact proximity sensors are the least expensive. Proximity sensors can have one of many technology types. These include capacitive, eddy current, inductive, photoelectric, ultrasonic, and Hall effect. Capacitive proximity sensors utilize the face or surface of the sensor as one plate of a capacitor, and the surface of a conductive or dielectric target object as the other. The capacitance varies inversely with the distance between capacitor plates in this arrangement, and a certain value can be set to trigger target detection. In an eddy current proximity sensor electrical currents are generated in a conductive material by an induced magnetic field. Interruptions in the flow of the electric currents (eddy currents), which are caused by imperfections or changes in a material's conductive properties, will cause changes in the induced magnetic field. These changes, when detected, indicate the presence of change in the test object. Magnetic inductive devices are identical in configuration to the variable reluctance type and generate the same type of signal. However, inductive pickoff coils have no internal permanent magnet and rely on external magnetic field fluctuations, such as a rotating permanent magnet, in order to generate signal pulse. Photoelectric devices are used to detect various materials at long range, using a beam of light. They detect either the presence or absence of light and use this information to read the data from the output transistor. An ultrasonic proximity sensor emits an ultrasonic pulse, which is reflected by surface and returned to sensor. Speed can be determined by measuring frequency difference (Doppler Effect). The basic "Hall Effect" sensing element is a semiconductor device which, when electrical current is sent through it, will generate an electrical voltage proportional to the magnitude of a magnetic field flowing perpendicular to the surface of the semiconductor.
The most important parameter to consider when specifying proximity sensors is the operating distance. This is the rated operating distance is the distance at which switching takes place. Common body styles for proximity sensors are barrel, limit switch, rectangular, slot style, and ring. Important dimensions to consider when specifying proximity sensors include barrel diameter, length, width, and height.
Proximity sensors can be a sensor element or chip, a sensor or transducer, an instrument or meter, a gauge or indicator, a recorder or totalizer, and a controller. A sensor element or chip denotes a "raw" device such as a strain gage, or one with no integral signal conditioning or packaging. A sensor or transducer is a more complex device with packaging and/or signal conditioning that is powered and provides an output such a dc voltage, a 4-20mA current loop, etc. An instrument or meter is a self-contained unit that provides an output such as a display locally at or near the device. Typically also includes signal processing and/or conditioning. A gauge or indicator is a device that has a (usually analog) display and no electronic output such as a tension gage. A recorder or totalizer is an instrument that records, totalizes, or tracks force measurement over time. Includes simple datalogging capability or advanced features such as mathematical functions, graphing, etc.
Electrical and mechanical sensors are widely used to characterize the performance and properties of components and systems, but are also found in household objects.
Sensors are electrical or mechanical components that are used to measure a property or behavior of an object or system. Some sensors measure properties directly, other sensors measure properties indirectly, using conversions or calculations to determine results. Sensors are used by scientists and engineers during research and testing activities, but they can also be found in many household objects, such as temperature sensors in an oven to accelerometers in an automobile airbag system. Sensors are generally categorized by the type of phenomenon that they measure, rather than the functionality of the sensor itself.
MECHANICAL SENSORS:
Mechanical sensors measure a property through mechanical means, although the measurement itself may be collected electronically. An example of a mechanical sensor is a strain gauge. The strain gauge measures the physical deformation of a component by experiencing the same strain as the component, yet the change in resistance of the strain gauge is measured electrically. Other types of mechanical sensors include:
· Pressure sensors
· Accelerometers
· Potentiometers
· Gas and fluid flow meters
· Humidity sensors
ELECTRICAL SENSORS:
Electrical sensors measure electric and magnetic properties. An example of an electrical sensor is an ohmmeter, which is used to measure electrical resistance between two points in a circuit. An ohmmeter sends a fixed voltage through one probe, and measures the returning voltage through a second probe. The drop in voltage is proportional to the resistance, as dictated by Ohm's Law. Other electrical sensors include:
· Voltmeter/Ammeter
· Metal detector
· RADAR
· Magnetometer
THERMAL SENSOR:
Although all thermal sensors measure changes in temperature, there are a variety of types of thermal sensors, each with specific uses, temperature ranges, and accuracies. Some types of thermal sensors include:
· Thermometers
· Thermocouples
· Thermistors
· Bi-metal thermometers
CHEMICAL SENSORS:
Chemical sensors generally detect the concentration of a substance in the air or in a liquid. Some chemical sensors, such as pH glass electrodes are designed to be sensitive to a certain ion. Some other types of chemical sensors include:
· Oxygen sensors
· Carbon monoxide detectors
· Redox electrodes
OPTICAL SENSOR:
Optical sensors detect the presence of light waves. This could include light in the visible spectrum, or outside the visible spectrum, in the case of infrared sensors. Some types of optical sensors include:
· Photodetectors
· Infrared sensors
· Fiberoptic sensors
· Interferometers
OTHER TYPE OF SENSOR:
There are many other types of sensors that don't fall into one of the broad categories described here. Some of these sensors include:
· Radiation sensors, including Geiger counters and dosimeters
· Motion sensors, including radar guns and speedometers
· Acoustic, including sonar and seismometers
· Gyroscopes
While sensors are used frequently by engineers and scientists in their studies, sensors are also use in many household products. Sensors can be found in many everyday objects, including touch-sensitive buttons and screens, infrared remote controls, motion-sensitive lighting, and home thermostats.
Proximity Sensors:
Proximity sensors may be of the contact or non-contact type. Contact proximity sensors are the least expensive. Proximity sensors can have one of many technology types. These include capacitive, eddy current, inductive, photoelectric, ultrasonic, and Hall effect. Capacitive proximity sensors utilize the face or surface of the sensor as one plate of a capacitor, and the surface of a conductive or dielectric target object as the other. The capacitance varies inversely with the distance between capacitor plates in this arrangement, and a certain value can be set to trigger target detection. In an eddy current proximity sensor electrical currents are generated in a conductive material by an induced magnetic field. Interruptions in the flow of the electric currents (eddy currents), which are caused by imperfections or changes in a material's conductive properties, will cause changes in the induced magnetic field. These changes, when detected, indicate the presence of change in the test object. Magnetic inductive devices are identical in configuration to the variable reluctance type and generate the same type of signal. However, inductive pickoff coils have no internal permanent magnet and rely on external magnetic field fluctuations, such as a rotating permanent magnet, in order to generate signal pulse. Photoelectric devices are used to detect various materials at long range, using a beam of light. They detect either the presence or absence of light and use this information to read the data from the output transistor. An ultrasonic proximity sensor emits an ultrasonic pulse, which is reflected by surface and returned to sensor. Speed can be determined by measuring frequency difference (Doppler Effect). The basic "Hall Effect" sensing element is a semiconductor device which, when electrical current is sent through it, will generate an electrical voltage proportional to the magnitude of a magnetic field flowing perpendicular to the surface of the semiconductor.
The most important parameter to consider when specifying proximity sensors is the operating distance. This is the rated operating distance is the distance at which switching takes place. Common body styles for proximity sensors are barrel, limit switch, rectangular, slot style, and ring. Important dimensions to consider when specifying proximity sensors include barrel diameter, length, width, and height.
Proximity sensors can be a sensor element or chip, a sensor or transducer, an instrument or meter, a gauge or indicator, a recorder or totalizer, and a controller. A sensor element or chip denotes a "raw" device such as a strain gage, or one with no integral signal conditioning or packaging. A sensor or transducer is a more complex device with packaging and/or signal conditioning that is powered and provides an output such a dc voltage, a 4-20mA current loop, etc. An instrument or meter is a self-contained unit that provides an output such as a display locally at or near the device. Typically also includes signal processing and/or conditioning. A gauge or indicator is a device that has a (usually analog) display and no electronic output such as a tension gage. A recorder or totalizer is an instrument that records, totalizes, or tracks force measurement over time. Includes simple datalogging capability or advanced features such as mathematical functions, graphing, etc.
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