Process sensors help, including temperature sensors, pressure sensors, level sensors and flow sensors flow meters. By Mark T. Hoske, Control Engineering March 4, Fujitsu Components America, Inc. By using this website, you agree to our use of cookies. This may include personalization of content and ads, and traffic analytics.
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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. An Automatic Flight Control System consists of several sensors for various tasks like speed control, height monitoring, position tracking, status of doors, obstacle detection, fuel level, 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 signals to different parts like engines, flaps, rudders, motors etc. The combination of Sensors, Computers and Mechanics makes it possible to run the plane in Autopilot Mode. All the parameters i. This is an extremely simplified version of Flight Control System. In fact, there are hundreds of individual control systems which preform unique tasks for a safe and smoot journey.
But in this tutorial, we will be concentrating on the Sensors part of a system and look at different concepts associated with Sensors like types, characteristics, classification etc.
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. 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 better understood if we take an example in to consideration. 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. This voltage can be calibrated to the amount of light falling on the LDR. Hence, a Light Sensor. Now that we have seen what a sensor is, we will proceed further with the classification of Sensors.
There are several classifications of sensors made by different authors and experts. Some are very simple and some are very complex. The following classification of sensors may already be used by an expert in the subject but this is a very simple classification of sensors.
In the first classification of the sensors, they are divided in to Active and Passive. Active Sensors are those which require an external excitation signal or a power signal. Passive Sensors, on the other hand, do not require any external power signal and directly generates output response. The other type of classification is based on the means of detection used in the sensor.
Some of the means of detection are Electric, Biological, Chemical, Radioactive etc. The next classification is based on conversion phenomenon i. Some of the common conversion phenomena are Photoelectric, Thermoelectric, Electrochemical, Electromagnetic, Thermooptic, etc.
The final classification of the sensors are Analog and Digital Sensors. Analog Sensors produce an analog output i. Digital Sensors, in contrast to Analog Sensors, work with discrete or digital data. The data in digital sensors, which is used for conversion and transmission, is digital in nature. 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.
We will see about few of the above-mentioned sensors in brief. More information about the sensors will be added subsequently. A list of projects using the above sensors is given at the end of the page. One of the most common and most popular sensors is the Temperature Sensor.
A Temperature Sensor, as the name suggests, senses the temperature i. Temperature Sensors can be analog or digital. In an Analog Temperature Sensor, the changes in the Temperature correspond to change in its physical property like resistance or voltage.
Temperature sensors are used to measure the thermal characteristics of gases, liquids, and solids in many process industries and are configured for both general- and special-purpose uses. More information about temperature sensors may be found in our related guide All About Temperature Sensors. Key specifications include sensor type and minimum and maximum detectable energies.
Radiation detectors are used for surveys and sample counting. More information about radiation sensors may be found in our related guide All About Radiation Detectors. Proximity Sensors are electronic devices used to detect the presence of nearby objects through non-contacting means. A proximity sensor can detect the presence of objects usually within a range of up to several millimeters, and, doing so, produce a usually dc output signal to a controller.
Proximity sensors are used in countless manufacturing operations to detect the presence of parts and machine components. Proximity sensors are generally short-range devices but are available too in designs that can detect objects up to several inches away. One commonly used type of proximity sensor is known as a capacitive proximity sensor. This device uses the change in capacitance resulting from a reduction in the separation distance between the plates of a capacitor, one plate of which is attached to the object being observed, as a means of determining motion and position of the object from the sensor.
Key specifications include sensor function, minimum and maximum working pressures, full-scale accuracy, along with any features particular to the device. Pressure sensors are used wherever information about the pressure of a gas or liquid is needed for control or measurement.
More information on pressure sensors may be found in our related guide Common Types of Pressure Sensors. Key specifications include sensor type, sensor function, measurement range, and features that are specific to the sensor type.
Position sensors are used wherever positional information is needed in a myriad of control applications. A common position transducer is a so-called string-pot, or string potentiometer.
More information about position sensors may be found in our related guide All About Position Sensors. See also proximity sensors. Photoelectric sensors are electrical devices that sense objects passing within their field of detection, although they are also capable of detecting color, cleanliness, and location if needed.
These sensors rely on measuring changes in the light they emit using an emitter and a receiver. They are common in manufacturing and material handling automation for purposes such as counting, robotic picking, and automatic doors and gates. Learn more in our related article on Photoelectric Sensors. Particle sensors are common in bin and baghouse monitoring.
Key specifications include transducer type, minimum detectable particle size, operating temperature range, sample volume, and response time.
Particle detectors used in nuclear engineering are referred to as radiation detectors see above. More information about particle sensors may be found in our related guide All About Particle Sensors. Typical applications of motion detection are detecting the stalling of conveyors or the seizing of bearings.
Key specifications include the intended application, sensor type, sensor function, and minimum and maximum speeds. More information about motion sensors may be found in our related guide All About Motion Sensors. Metal Detectors are electronic or electro-mechanical devices used to sense the presence of metal in a variety of situations ranging from packages to people.
Metal detectors can be permanent or portable and rely on a number of sensor technologies with electromagnetics being popular. Key specifications include the intended application, maximum sensing distance, and certain feature choices like handheld and fixed systems. Metal detectors can be tailored to explicitly detect metal in specific manufacturing operations such as sawmilling or injection molding.
Typical level sensors use ultrasonic, capacitance, vibratory, or mechanical means to determine product height. Key specifications include sensor type, sensor function, and maximum sensing distance. More information about level sensors may be found in our related guide All About Level Sensors. Some leak detectors rely on ultrasonic means to detect air leaks, for example. Other leak detectors rely on simple foaming agents to measure the soundness of pipe joints. Still, other leak detectors are used to measure the effectiveness of the seals in vacuum packages.
More information about leak sensors may be found in our related guide All About Leak Sensors. Key specifications include maximum response time and minimum and maximum operating temperatures. More information about humidity sensors may be found in our related guide All About Humidity Sensors.
More information about gas and chemical sensors may be found in our related guide All About Gas and Chemical Sensors. A force sensor typically relies on a load cell, a piezoelectric device whose resistance changes under deforming loads.
Other methods exist for measuring torque and strain.
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