Sensors (Input Devices)

NOTE: Most sensors and other output devices will indicate whether their termination is NPN or PNP.  Some will give you a choice of which type of output that you prefer for your circuit. 

Switch Transistor NPN Basic switching logic component for semiconductors.  Consists of three terminations called Base, Emitter, and Collector.  When a voltage is applied to the Base, a current can now flow from the Collector to the Emitter.  It is “ON”. Remove the voltage and it is “OFF” Used in sensors to control when a signal is passed on from one device to another, or to a detector. 
Switch Transistor PNP Basic switching logic component for semiconductors. Also consists of three terminations called Base, Emitter, and Collector. However, when a voltage is applied to the base, then no current can flow from the collector to the emitter.  It is “OFF”. Remove the voltage (usually connect it to ground) and it is “ON” Used in sensors to control when a signal is passed on from one device to another, or to a detector. 

Name: Hall Effect Sensor 

Type: Proximity 

How it Works: The Hall effect is a property of semiconductors, where a current is flowing in the material.  Magnetic proximity causes a voltage potential perpendicular to the current flow. 

Use Case: Current sensing, magnetic sensing 

Name: Through-Beam Photoelectric Sensor 

Type: Presence 

How it Works: Photoelectric sensors of the through-beam type have a transmitter and receiver separated by a gap. If an object interrupts the gap the receiver reports loss of signal. Many types of transmitters and receivers are used at varying frequencies depending on the needs. 

Use Case: Presence or absence of an object.  Object counting on a conveyor 

Name: Retro-Reflective Photoelectric sensor 

Type: Presence 

How it Works: A retro-reflective Photoelectric sensor has the transmitter and receiver in the same housing. Transmitted light reflects off a target and back toward the receiver. Interruption of the light beam by an object shows as loss of signal by the receiver 

Use Case: Presence or absence of an object.  Object counting on a conveyor 

Name: Diffuse light sensor 

Type: Proximity 

How it Works: Diffuse light sensors have transmitter and receiver in a single housing but separated. The light path reflects off the object and continues to the detector. It is a V-shaped light path, so closer objects have a narrower spacing between the transmitter and receiver and vice versa. 

Use Case: Position of a reflective object. 

Name: Triangulation sensor 

Type: Proximity 

How it Works: A triangulation sensor typically uses a collimated light source like a laser.  As a detectable object moves in front of the sensor, light from the transmitter is reflected to the receiver.  Depending on where the reflected light is brightest determines the distance to the object 

Use Case: Distance of a reflective object. 

Name: Time of Flight sensor (TOF) 

Type: Proximity 

How it Works: Often referred to as TOF sensors, these shoot out a pattern of laser pulses and measure the time to receive those signals back. Counting the return time, since light has a fixed speed, results in a “point cloud” that define the size, shape and distance of objects. 

Use Case: Collision avoidance, mapping, speed measurement 

Name: Color sensor 

Type: Light 

How it Works: Color sensors consist of a “pure white” source and a detector which looks for a reflection in the Red, Green and Blue spectra.  The percentage contribution of each of the three colors indicates the color of the object. 

Use Case: Color detection, color matching 

Name: Thermocouple sensor 

Type: Temperature 

How it Works: A thermocouple consists of a junction of two different metals which creates a voltage differential that changes with temperature. Wide variety of metal combinations available. 

Use Case: -270˚ C to + 2320˚ C 

Name: RTD (Resistance Temperature Detector) 

Type: Temperature 

How it Works: RTDs are often pure metals whose resistance is positively correlated to temperature. Platinum is the high performance standard 

Use Case: -200˚C to +850˚C 

Name: Thermistor (Thermal Resistor) 

Type: Temperature 

How it Works: Thermistors are usually metal ceramic hybrids whose resistance is non-linear with respect to temperature.  It can have a positive or a negative temperature coefficient 

Use Case: Temperature “sweet spot” is around 50˚ C and range is limited 

Name: Ultrasonic sensor 

Type: Proximity 

How it Works: Ultrasonic sensors are used to measure the distance to an object.  A piezoelectric source generates a signal that travels at the speed of sound. It bounces off the object and the time to arrive at the detector is measured and used to calculate distance. 

Use Case: Detect objects that are transparent 

Name: Gyroscope 

Type: Rotation rate 

How it Works: Gyroscopes are usually MEMs devices. They contain a pair of oscillating “fingers”, whose angular momentum changes based on rotational speed. Amplitude changes are proportion to the rate of rotation. 

Use Case: Measuring/Stabilizing rotational movements. Navigation 

Name: Accelerometer 

Type: Acceleration 

How it Works: Accelerometers are usually a MEMs device.  They have a cantilever as the detector with an electrostatic feedback on the end. Deflection of the cantilever is proportional to acceleration.  The feedback acts like a servo to counter the cantilever deflection.  The servo charge required is proportional to the acceleration. 

Use Case: Measuring/stabilizing linear movements. Navigation 

Name: Windshield Rain Detector 

Type: Rain 

How it Works: To detect rain on a windshield requires a light sensor.  It is a small squarish sensor directly behind the rear-view mirror and it measures the transmitted ambient light. As raindrops accumulate it reduces the amount of light entering the sensor causing it to trigger the wipers. 

Use Case: Detecting rain on windshield 

Name: Irrigation Rain Sensor 

Type: Rain 

How it Works: An irrigation rain sensor uses either a cup or an absorbent sponge to capture water.  In either case, if the sensor is “full” it will make the irrigation system inactive until the indicator is dry. 

Use Case: Controlling irrigation 

Name: Soil moisture sensor 

Type: Moisture 

How it Works: There are many types of soil moisture technologies.  In general, a probe pair or antenna is embedded in the soil. Changes to some electrical property in the soil due to moisture are measured: i.e., capacitance, impedance, speed of a travelling wave, etc. 

Use Case: Measure soil moisture over a wide area, especially for golf courses, sports arenas and farming. 

Name: Phototransistor 

Type: Light 

How it Works: A phototransistor is very much like a regular transistor where the base charge is supplied by a base material that converts photons to charge. 

Use Case: Simple light detection, light beam interrupter 

Name: Flow Meter  

Type: Flow 

How it Works: Flow meters measure the volume of liquid or gasses flowing through the sensor.  This can be done through physical means (pressure drop, paddlewheels) or through some property of the measured substance (doppler, magnetic resonance) 

Use Case: Many varied uses: Water treatment plants, oil & gas refineries, chemical plants 

Name: Infrared Reflection 

Type: Heart Beat 

How it Works: To measure heartbeat an infrared source illuminates the skin and the reflected signal is captured by a photodiode. Each beat changes the profile of the reflected signal triggering the detector. 

Use Case: Diagnosis of heart irregularities, measurement of heart rate during exercise 

Name: Infrared Transmission 

Type: Alcohol 

How it Works: Alcohol testers or breathalyzers measure the absorption of ethanol as the sample passes between a sender/receiver pair. The IR signal is absorbed by ethanol and the degree of absorption is a measure of the percentage content of ethanol 

Use Case: Breathalyzers 

Name: Passive Infrared 

Type: PIR 

How it Works: PIR sensors consist of a pair of Infrared detector chips side-by-side.  Built-in circuitry looks at the differential output from this chip pair and if there is a difference it means that in infrared source (usually a person) has moved into range. 

Use Case: Motion detection/camera trigger/light switch 

Name: Gas Presence 

Type: Various depending on gas 

How it Works: Common gas detectors include CO2, CO, O2, CH4, H2S and others. Types of detectors are targeted to either Toxic or Combustible gases. Toxics use Metal Oxide detectors or electrochemical sensors and Combustibles use infrared or catalytic sensors. 

Use Case: Safety, Agriculture, Explosive potential, Oil & Gas operations 

Name: Ionizing Smoke Sensor 

Type: Smoke Sensor 

How it Works: Ionizing smoke detectors cause the air between two conductive plates to conduct a slight current.  As particles are generated by smoke, they reduce the current.  When the current gets low enough, it triggers an alarm. 

Use Case: Fire detection.  Best with lots of dark particles (fast burning fires) 

Name: Photoelectric Smoke Sensor 

Type: Smoke Sensor 

How it Works: Photoelectric smoke detectors sample the air with a light source. Reflectivity of the air increases as the number and size of particles increases. Above a threshold an alarm signals. 

Use Case: Fire detection. Best with small white particles, smoldering fires. 

Name: LM35/LM35C Semiconductor 

Type: Temperature 

How it Works: This semiconductor device is packaged in a TO-92 and is pre-calibrated in degrees centigrade.  Its standard range is -55 to 150˚C. Also available as LM35C designation rated -40 to 110˚ C. Mfg: TI 

Use Case: General purpose temperature measurement. Also available in 8 pin SM and a TO-220. 

Name: LDR (Light dependent resistors) 

Type: Light 

How it Works: Metal alloy has a high resistance. When exposed to a strong light source, the resistance drops dramatically.  The change in resistance is non-linear and dependent on the wavelength of light. These can have significant latency. 

Use Case: General purpose light detection. Street lamps, light meters 

Name: Humidity sensor 

Type: Humidity 

How it Works: Humidity sensors measure some changing electrical property of the air related to the % of water vapor present.  The three types of sensors are capacitive, resistive and thermal Capacitive: An open metal oxide capacitor is exposed to air and its capacitance varies due to moisture content. Resistive: Two metals strips are encased in a salt, the ions in the salt react to moisture changing the resistance. Thermal: One thermal sensor is encased in dry nitrogen and the other is exposed to air. The difference in current flow is due to difference in humidity. 

Use Case: HVAC, food processing, pharmaceuticals, meteorology, agriculture. 

Name: Resistive element 

Type: Flex 

How it Works: A resistive element is sandwiched between two flexible strips.  As the “flex strips” bend, the resistance changes in proportion to the amount of bending. 

Use Case: Data glove as an input to a VR system, measuring bending in human joints for medical diagnostics. Security in door by measuring movement at the hinge 

Name: Capacitive 

Type: Touch or Tactile 

How it Works: Glass film with embedded electronics around the edge can measure and locate when a finger touches the screen.  Allows for multi-touch operation. 

Use Case: Mobile phones and computer screens. One-touch faucets, automotive controls. Robotics, CMMs 

Name: Phototransistor 

Type: Light (Solar) 

How it Works: Usually, a phototransistor 

Use Case: Detect the presence or absence of light 

Name: MEMS, SW420 Semiconductor 

Type: Vibration 

How it Works: This is a vibration sensitive switch with a single NC contact. Once it senses vibration the switch opens. The increase in resistance is sensed and an LED is illuminated as an alarm. 

Use Case: Machinery vibration, anti-theft device 

Name: Optical Encoder 

Type: Rotation 

How it Works: Using an internal IR light source, detector and a code wheel, an optical encoder can precisely indicate position or speed when attached to a rotating shaft. The output is digital, either serial or parallel and can detect with a resolution of 10 arcsec. 

Use Case: Motor speed control: both servo motors and synchronous motors driven by VFD. High accuracy environments. 

Name: Magnetic Encoder 

Type: Rotation  

How it Works: Similar in principle to an optical encoder but more compact.  It relies on a series of radial “spokes” of alternating N-S poles with a magnetic detector to produce multiple sine waves during a single revolution.  These sign waves can be interpolated to produce high output counts with a typical accuracy of 1 arc minute. 

Use Case: Motor speed control: both servo motors and synchronous motors driven by VFD. High shock environments. 

Name: Absolute Optical sensor 

Type: Angular position 

How it Works: Using an internal IR light source, detector and a Gray-coded code wheel, an absolute optical encoder can precisely indicate angular position when attached to a rotation shaft. The output is digital, either SSI or parallel and can detect a resolution of 10 arcsec very repeatably. 

Use Case: Position indication of aiming devices, telescopes, antennas or measuring depth of holes in Oil/Gas industries, by tracking drill pipe lengths. 

Name: Linear Optical sensor 

Type: Linear position 

How it Works: These are linear analogs of the rotary optical encoders where the code wheel is replaced with a code track. Resolutions in the 10’s of microns are readily available 

Use Case: Used mostly in the machining market for tool or workpiece positioning. 

Name: Electrostatic, or Piezoelectric sensor 

Type: Noise (clapping) 

How it Works: Otherwise known as microphones, these devices consist of a flat disc that changes its electrostatic potential when activated, or in the case of piezoelectric it generates a voltage proportional to the energy in the sound wave. 

Use Case: Electrostatic: most widely used as a microphone due to flat frequency response over a wide range and long term stability. Piezoelectric: Low frequency sound-level meters. 

#Arduino #RaspberryPi #Robots #Automation #AllSensors #MakerCircuits #Mechatronics 

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