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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Dark operate mode (D.O. or D/O) - The program mode of a photoelectric sensor in which the output circuit energizes (or delay logic begins) when light intensity on the photodetector has sufficiently decreased below the threshold of the photodetector.

Data Capture - The act of collecting data from a process or passing product using a Smart Sensor, Barcode Reader, or RFID Tag-reader, in order direct an automated action. Data capture sensors are widely used in W&D centers. Also see Automatic Identification (AutoID)

DC - Stands for Direct Current (DC), see definition listed below.

Delay logic - A timing function which alters an output’s response.

Delayed one-shot - Timing logic in which an input signal initiates an adjustable delay period, at the end of which the output pulses for an adjustable pulse (“hold”) time. The input signal may be either momentary or maintained. No further action occurs until the input signal is removed and then re-applied, at which time the sequence begins again.

Depth-of-field - See Maximum sensing distance

Diagnostic - Advanced warning signal of potential loss of control output due to ambient changes.

Differential, switching - See Hysteresis

Differential travel - Travel distance required to reset contacts; the angle or distance through which the actuator moves from the contact operating position to the actuator free position, or the distance between the operating point and the release point. See Hysteresis

Diffuse sensing mode - A photoelectric proximity sensing mode in which the light from the emitter strikes a surface of an object at some arbitrary angle and is detected when the receiver captures some small percentage of the diffused light. Also called the “direct reflection mode” or the photoelectric “proximity mode.”

Digital output - An output circuit or sensor output with only two operating states, either “ON” or “OFF.” These operating states often are called “Hi” or “Low.”

DIN - Stands for “Deutsches Institute für Normung” the German committee for standardization, visit Deutsches Institute für Normung

Diode - A two-layer semiconductor that allows current to flow in only one direction and inhibits current flow in the other direction.

Direct current (DC) - A current that flows only in one direction through a circuit. As ordinarily used, the term designates a practically non-pulsating current.

Direct opening action contacts - Achievement of contact separation as the direct result of a specified movement of the switch actuator through non-resilient members.

Direct scan - See Transmitted beam

Discrete sensor “Discrete” means individual or distinct, and in engineering a “discrete” variable (or measurement) refers to a true-or-false condition. As such, a discrete sensor is one that is only able to indicate whether the measured variable is above or below a specified setpoint.

Double break contacts - Contacts which break the circuit in two places. See "DPDT" and "DPST", as well as Switch Configurationfor an illustration of typical wiring/control options.

Downstream - In manufacturing, two stages of production are "Downstream" and "Upstream", and the middle point is called midstream. Materials in upstream processes have lesser value, but as they proceed increasing value is added. Materials and products pass through midstream phases, and eventually reach downstream steps, which move them closer to a finished product. If sensor and switch-related downtime occurs earlier in production process, costs are lower. When ...

DPDT switch - Abbreviation for “Double-Pole/Double-Throw” switch or relay contacts; switch with two "Single-pole/double-throw" contacts operated simultaneously by a single action. See Switch Configuration for an illustration of this and other typical wiring/control options.

DPST switch - Abbreviation for “Double-Pole/Single-Throw” switch or relay contacts. Equal to two SPST switches controlled by a single mechanism; two sets of single-pole contacts, and operated simultaneously by a single action (throw). See Switch Configuration for an illustration of this and other typical wiring/control options.

Drift - A change in operate point.

Dual output - See Cmplementary output

Dwell-time - The adjustable or fixed time length of an output pulse, independent of input signal duration.

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