Glossary of Sensors, Switches & Automation Terms

Thanks to the Sensor, Switch, Smart Camera, and Machine Vision device OEM's who've helped us compile our listing here.

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Target - Two definitions: 1) A part/object that will be "detected" by a sensor or a switch. 2) A "standardized object", with defined characteristics (i.e. shape, thickness, material, color, etc.) that will be used to establish the rated sensing range/capabilities of a given sensor.

Target travel, directional approaches - Sensors can detect targets moving from two different approaches; radial or axial, the illustration below shows both.

Teflon - ... also see Teflon coating/coated

Teflon coating/coated - ... also see Teflon

Thermal drift chart - A chart illustrating sensor operating variance due to changes in temperatures.

Three-wire proximity switch - An AC or DC proximity sensor with three leads, two of which supply power and a third that switches the load.

Threshold - The voltage in a photoelectric control circuit that causes the output of the sensor to change state. This voltage level is directly related to the amount of light that has reached the photoelectric receiver. The threshold is the value of received signal representing a margin of 1x. The sensitivity control (where one is available) adjusts the threshold voltage level.

Through-beam sensing mode - See Transmitted beam

Time delay before availability - See False pulse protection

Total travel - The sum of the pretravel and the overtravel. transducer A device that converts energy of one form into another form. Used where the magnitude of the applied energy is converted into a signal that varies proportionately to the applied energy’s variations.

Transient - A very short pulse of voltage (or current) that is many times larger in magnitude than the supply voltage. Transients are usually caused by the operation of a heavy resistive load or of any size inductive load like motors, contactors, and solenoids.

Transient protection - Circuitry to guard against spikes induced on the supply lines by inductive sources, such as heavy motors or solenoids turning on and off.

Transistor - A tiny chip of crystalline material, usually silicon, that amplifies or switches electric current.

Translucent - Term used to describe materials that allow light to pass through.

Transmission - Passage of light through a medium. If the light is scattered, it is “diffuse transmission.”

Transmitted beam - A photoelectric sensing mode in which the emitter and receiver are positioned opposite each other so the light from the emitter shines directly at the receiver. An object then breaks the light beam established between the two.

Triac - A solid-state switching element used for AC control voltage. Typically has low current capacity and high leakage current.

Trigger - A pulse used to initiate control signal switching through the appropriate circuit paths.

Two-wire sensor - A sensor designed to wire in series with its load, exactly like a limit switch. A 2-wire sensor with a solid-state output remains powered when the load is “off” by a residual “leakage current” that flows through the load.

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