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A theodolite is used to measure the horizontal angle between indicators on the two ends of the subtense bar. The distance from the telescope to the subtense bar is the height of an isosceles triangle formed with the theodolite at the upper vertex and the subtense bar length at its base, determined by trigonometry.
A theodolite (/ θ i ˈ ɒ d ə ˌ l aɪ t /) [1] is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying , but it is also used extensively for building and infrastructure construction , and some specialized applications such ...
A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. [1] The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common.
Sensor, hypernym for devices that measure with little interaction, typically used in technical applications. Spectroscope is an important tool used by physicists. SWR meter check the quality of the match between the antenna and the transmission line .
Schematic diagram of an opto-isolator showing source of light (LED) on the left, dielectric barrier in the center, and sensor (phototransistor) on the right [note 1]. An opto-isolator (also called an optocoupler, photocoupler, or optical isolator) is an electronic component that transfers electrical signals between two isolated circuits by using light. [1]
The sensor circuit is supplied with constant current. A distinguishing feature of the IEPE principle is that the power supply and the sensor signal are transmitted via one shielded wire. Most IEPE sensors work at a constant current between 2 and 20 mA. A common value is 4 mA. The higher the constant current the longer the possible cable length.
More advanced current probes combine a Hall effect sensor with a current transformer. The Hall effect sensor measures the DC and low frequency components of the signal and the current transformer measures the high frequency components. These signals are combined in the amplifier circuit to yield a wide band signal extending from DC to over 50 MHz.
A VR sensor used as a simple proximity sensor can determine the position of a mechanical link in a piece of industrial equipment. A crankshaft position sensor (in an automobile engine) is used to provide the angular position of the crankshaft to the engine control unit. The engine control unit can then calculate engine speed (angular velocity).