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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Octal numbering system - A "base-8" numbering system that uses only the digits "0 thru 7".

Off - 1) Term used to designate the state of a bit; the inoperative state of a device(sensor); the state of a switch or circuit that is "Open". Designated by the symbol
"0". 2) Contrasted with "On", see below.

Off delay - Timing logic in which the output energizes immediately when an input signal is present. The off-delay timing begins at the trailing edge of the input signal, keeping the output energized. If a new input signal is received during the off delay timing, the timer is reset, and the off-delay period begins again at the trailing edge of the new input signal. The output de-energizes after removal of input and trailing edge triggered timer expires.

Off state current - See Leakage current

Ohm - Unit of measurement for resistance and impedance. The resistance through which a current of one Ampère will flow when one Volt is applied.

Ohm’s law - A formula "E = I x R", where "Current" (I) is directly proportional to "Voltage" (E) and inversely proportional to total "Resistance" (R) of a circuit.

On - 1) A term used to designate the state of a bit; the operative state of a device(sensor); the state of a switch or circuit that is "closed". Designated by the symbol "1". 2) Contrasted with "Off", see above.

On delay - Timing logic in which timing begins at the leading edge of an input signal, but the output is energized only after the preset on-delay time has elapsed. The output ceases immediately at the trailing edge of the input signal. If the input signal is not present for the on-delay time period, no output occurs. If the input signal is removed momentarily and then re-established, the on-delay timing starts over again from the beginning.

On delay one-shot - Timing logic that combines on delay and one-shot timing into a single function. The input signal must be present for at least the time of the on-delay in order for a timed one-shot pulse to occur. See "One-shot", next term below.

One-shot - Timing logic in which a timed output pulse begins at the leading edge of an input signal. The pulse is always of the same duration, regardless of the length of the input signal. The output cannot re-energize until the input signal is removed and then re-applied.

On/off delay - Timing logic that combines on delay and off delay timing into a single function.

Opaque - A term used to describe a material that blocks the passage of light energy. “Opacity” is the relative ability of a material to obstruct the passage of light.

Open-collector - A term used to describe the NPN or PNP output of a DC device, where the collector of the input transistor is not connected to any other part of the output circuit except through a diode for protection. See sinking (NPN output), sourcing (PNP output).

Operating contact position - The position to which the contacts move when the actuator is deflected to or beyond the actuator operating position.

Operating distance - The target travel position where a proximity sensor output turns "On". May vary with environmental conditions such as temperature, and if target material (steel, aluminum, brass, etc.) changes. See < href="http://www.softnoze.com/glossary-s.cfm">Sensing distance, and also "Operating distance, assured" and "Operating distance, rated" below.

Operating distance, assured - Also called "Operating distance, rated", see Sensing distance, nominal

Operating distance, rated - Also called "Operating distance, assured", see Sensing distance, nominal

Operating force - The straight line force in the designed direction applied to the switch actuator to cause the contacts to move to the operated position.

Operating margin - See Margin

Operating mode - Refers to the specific intensity level (either light or dark) that initiates a photoelectrics output circuit. See light operate mode (L.O. or L/O), dark operate mode (D.O. or D/O).

Operating temperature - Actual range over which sensors can be operated. Usage outside the temperature limits will result in loss of stability, change in operate point, and possible permanent damage to the sensor. Nominal sensing distance is determined at 25°C.

Operating torque - The torque that must be applied to the actuator to cause the moving contact to move to the operated contact position.

Opposed sensing mode - See Transmitted beam

Optical cross-talk - When a photoelectric receiver responds to the signal from an adjacent emitter.

Optical power - Power or intensity of the projected light available from a particular emitter; beam intensity.

OR logic - A logic function in which the presence of any defined input condition causes a load to energize (A or B or C = output). Usually created by wiring all outputs in parallel to a load.

Oscillation - A periodic change in a variable, such as in the wave amplitude of an alternating current.

Output - An electrical device, either solid state or contact, that directs power to actuate a load or provide system status indication.

Overcenter mechanism - (Need to define and give example of, in a limit switch mechanism)

Overload protection - The ability of a sensor to withstand load currents between continuous load rating and a short-circuit condition with no damage.

Over travel - The movement of the actuator beyond the contact operating position.

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