A sensor is a device that detects a physical change or event in its environment and converts it into a signal that can be interpreted by either a human or a machine. Although sensors vary in complexity, such as a thermometer (an example of a simple sensor), most sensors are electronic. Sensors measure a wide variety of stimuli and are used to measure temperature, gauge distance, detect smoke, regulate pressure, and many more things. The effectiveness of a sensor can generally be gauged by three criteria:
- Their sensitivity to the measured stimuli
- Their ability to ignore outside stimuli that may occur around the measured one
- Their (hopeful) lack of influence on the measured stimuli
Most sensors have a linear transfer function, meaning that the relationship between the input stimuli and the output data will be constant. In measuring sensitivity, many data can be expressed as a ratio between the output signal and the measured property. For example, in a sensor measuring temperature with a voltage output, the sensitivity could be expressed as a constant of Volts/Kelvin (voltage over temperature).
With the invention of the Internet of Things (IoT), the demand for sensors has been greatly increasing, as they are a necessary part of automation technology.
Electronic sensors can be divided into two categories: analog and digital. Analog sensors convert data into an analog signal and are much more precise than digital sensors, which are limited to a finite set of possible values. The scale of values on an analog scale is continuous, meaning that an analog sensor can detect any change in the physical variable, no matter how slight. In contrast, digital sensors are limited to fixed data, in this case ones and zeroes, even though they still reflect the same trend of variation.
There is an abundance of different kinds of electrical sensors. Depending on the type of sensor, its electrical output can be a voltage, current, resistance, or another electrical attribute that varies over time.
A variety of types of sensors are used throughout numerous industries. Some of the most widely used types of sensors are listed below.
Vision and imaging sensors are electronic devices that sense when an object, color, or other presence enters their field of view. Once this stimuli is received, vision and imaging sensors convert the data into an image that can be displayed. Integral specifications for these sensors include the type of sensor and intended use, as well as any features of the accompanying transducer—a device that converts energy into a readable signal.
Temperature sensors are electronic devices that detect limits related to thermal properties, and in turn deliver signals to the inputs of control and display devices. These sensors typically rely on an RTD or thermistor to measure temperature and convert it to an output voltage. Key specifications for temperature sensors include the type of sensor or detector, maximum and minimum temperature readings, and dimensions of diameter and length. Temperature sensors are used to monitor the thermal qualities of liquids, gases, and solids in a wide breadth of industries and can be configured to a tailored purpose.
Radiation sensors are electronic devices that detect radioactive signals, such as alpha, beta or gamma rays, and convert them into a signal for counters or display devices. Key features include minimum and maximum measurable quantity. These sensors are mostly used for surveying and sample counting.
Proximity sensors are electronic devices that can detect the presence of an object and display that object's proximity to the sensor, without making physical contact with it. These sensors usually have a range of up to several millimeters, and in turn produce a common dc output signal to a controller. Proximity sensors are widely used in the manufacturing industry to detect the presence of parts and machine components. Key specifications include maximum sensing distance, minimum and maximum operating temperatures, and the dimensions of diameter and length. Though proximity sensors are often short-range devices, there are models designed to detect objects up to several inches away.
Pressure sensors are electro-mechanical devices that can detect the pressure in gases or liquids, measured in forces per unit area. These sensors, in turn, deliver that data to control or display devices. Pressure sensors commonly require a diaphragm and strain gage in order to observe and measure the force that is exerted against a unit area. Integral specifications for this sensor type include minimum and maximum working pressures and full-scale accuracy. Pressure sensors are utilized in any situations where pressure of a liquid or gas must be monitored.
Position sensors are electronic devices with the ability to sense the positions of valves, doors, throttles, and other such hardware, and deliver those signals to the inputs of display devices. Key specifications include sensor type, sensor function, and range of measurement. Position sensors are used in a variety of control applications where knowing positional information is necessary.
Photoelectric sensors are electronic devices that can sense when an object passes through their field of vision. These sensors have also been used to color, cleanliness and location, among other things. Photoelectric sensors work by measuring changes in the light that they admit, and they require an emitter and a receiver to do so. This type of sensor is most commonly used in manufacturing and automation.
Particle sensors are electronic devices used to observe dust and other airborne particles and send those signals to control and display devices. These sensor types are commonly used in bin and baghouse monitoring. Key features include minimum particle size, sample volume, and response time. Radiation sensors, discussed above, are a type of particle sensor specific to radioactive particulates.
Motion sensors are electronic devices that are able to detect the movement or lack of movement of parts, people, and other objects. Typical uses for motion sensors are technology monitoring or security purposes. Key specifications include minimum and maximum detectable speed and intended use.
Metal sensors, more commonly referred to as metal detectors, are electric or electro-mechanical devices that detect the presence of metal. This sensor type is extremely common and is used to detect metals in packages and people, among other applications. Most metal sensors rely on electromagnetic technology and come in models that can be permanent, such as a large archway, or portable, such as a metal-detecting wand.
Level sensors are electronic devices that are used to detect the level of a solid, liquid, or gas within a container. These sensors typically rely on ultrasonic, capacitance, vibratory, or mechanical technology to determine the height of the measure substance and deliver the data to control or display devices. Level sensors can also be of the contact or non-contact type (more information on these types of sensors can be found below).
Leak sensors are electronic devices used to detect the undesired flow of a liquid or gas. Leak detectors rely on different types of technology depending on their intended application. For example, ultrasonic technology might be more commonly used to monitor unwanted air leaks, while other leak sensors might utilize simple foaming agents to determine the weak points of pipe joints.
Humidity sensors are electronic devices that are able to sense the amount of water that is in the air. This information is then delivered to the inputs of control or display devices. Key specifications for humidity sensors include maximum response time and minimum/maximum operating temperature.
Gas and chemical sensors are permanently housed or portable electronic devices that detect the presence of, or measure the amount of various gases and chemicals in the air. These types of sensors are most commonly used for monitoring of confined spaces, leak detection, and analytical instrumentation among other things, and are oftentimes equipped to detect multiple types of gases or chemicals.
Force sensors are sensors capable of measuring variables that relate to forces such as weight, torque, load, etc. and provide that information to the inputs of control or display devices. Force sensors typically utilize a load cell, a piezoelectric device that changes its resistance under deforming loads, though they use different methods to measure torque or strain. These sensors are used in load management applications of all kinds, including truck scales and bolt tensioning devices.
Flow sensors are electronic devices capable of sensing the movement of solids, liquids, or gases and provide that data to the inputs of control or display devices. Flow sensors can be fully or partially electronic, with technology ranging from ultrasonic devices that observe flow from outside of a pipeline to a paddlewheel that spins as water passes over it. These types of sensors are used extensively in the processing industry.
Flaw sensors are used in a myriad of manufacturing processes to identify aberrations and inconsistencies on surfaces or in underlying materials. Depending on the application, flaw detectors might utilize ultrasonic and acoustic technologies among other methods to identify flaws.
Flame sensors or detectors are optoelectronic devices that can sense the presence or quality of fire. Flame detectors commonly rely on ultraviolet or infrared technology to detect the presence of fire and are often used to control combustion and in safety applications.
Electrical sensors are electronic devices that can detect an electrical current or voltage and send those signals to the inputs of control or display devices. Key specifications for this sensor type include minimum and maximum detectable values, operating temperature range, and sensor function. Electrical sensors commonly rely on hall effect detection to identify the presence of electrical currents or voltage. These sensors are employed across a wide range of industries for a variety of purposes, including to monitor railway, fan, pump, and heater systems.
A contact sensor refers to any type of sensor that relies on physical contact or touch from the object being observed in order to produce a signal and deliver it to a control or display device. Simple contact sensors can be found in alarm systems used to monitor windows or doors. More complex contact sensors have been used in applications from temperature monitoring to proximity detection in robotics and automated machinery.
In contrast to contact sensors, non-contact sensors are electronic devices that do not require physical contact from an observed object or phenomenon in order to detect it. A familiar example of a non-contact sensor would be the motion sensors that are used to turn on security lights. Non-contact sensors rely on a variety of technologies, including infrared energy, microwave energy, ultrasonic waves, and others, depending on their purpose.