A position sensor is any device that permits position measurement.
It can either be an absolute position sensor or a relative one. Position sensors can be either linear or angular. Poisitioning Sensors are finding their way into more handheld, medical and industrial devices every day. Knowing the position and orientaion of a device or tool is critical for any modern control system to work accurately. Examples are as varied as a smart phone, a drilling platform, or the attitude control of a Boeing 777.
A pressure sensor measures pressure, typically of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding and is usually stated in terms of force per unit area. A pressure sensor transducer generates an electronic signal as a function of the pressure imposed. Pressure sensors are used for control and monitoring in thousands of everyday applications.
Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, fluid level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators, piezometers, and manometers, among other names. Pressure sensors can vary drastically in technology, design, performance, application suitability and cost. A special category of pressure sensors can dynamically measure very high speed changes in pressure. Example applications are combustion pressure in an engine cylinder or a gas turbine. These sensors are commonly manufactured out of piezoelectric materials such as quartz.
A conservative estimate is that there are over 50 technologies and at least 300 companies making pressure sensors worldwide.
A photoelectric sensor, or photoeye, is a device used to detect the distance, absence, or presence of an object by using a light transmitter (often infrared) and a photoelectric receiver. They are used extensively in industrial manufacturing. There are three functional types: opposed (a.k.a. through-beam), retroreflective, and proximity-sensing.
A self-contained photoelectric sensor contains optics and electronics and requires only a power source. The sensor performs its own modulation, demodulation, amplification, and output switching. Some self-contained sensors provide such options as built-in control timers or counters. Because of technological progress, self-contained photoelectric sensors have become increasingly smaller.
Remote photoelectric sensors, used for sensing over long distances or in hard-to-reach places, contain only the optical components of a sensor. The circuitry for power input, amplification, and output switching are located elsewhere, typically in a control panel. This allows the sensor to be very small and the controls to be accessible, since they may be bigger.
When space is restricted or the environment too hostile even for remote sensors, fiber optics may be used. Fiber optics are passive mechanical sensing components. They may be used with either remote or self-contained sensors. They have no electrical circuitry and no moving parts and can safely pipe light into and out of hostile environments.
Thermal sensors range from bare thermocouples and Resistive Temperature Devices (RTDs) to more sophisticated infrared non-contact sensors that can directly, consistently, and accurately measure a material's temperature. In many systems, temperature control is fundamental. There are a number of passive and active temperature sensors that can be used to measure system temperature, including: thermocouples, resistive temperature detectors, thermistors and silicon temperature sensors. These sensors provide temperature feedback to the system controller to make decisions such as over-temperature shutdown, turn-on/off cooling fan, temperature compensation or general purpose temperature monitor.