Industrial Electronics Glossary

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ladder diagram An industry standard for representing relay control logic. The name comes from the fact that the overall form of the diagram looks like a wooden ladder.

LAN Local Area Network. A network limited to a local geographical area such as an office or a factory.

LASCR Light-activated SCR. A SCR that can be activated into conduction when a sufficient level of light is received on its junction.

latching relay A relay that maintains a given position by mechanical or electrical means until released mechanically or electrically.

leading-edge triggering A programming technique of triggering some step by means of an off-to-on transition of an input signal.

LED Light-emitting diode. A two-lead solid-state PN junction device that produces a small amount of light when forward biased.

light operated Pertaining to a photoelectric control that energizes its output when the light intensity on the photodetector is at a high level.

limit switch An electrical switch that is actuated by motion of a machine or equipment contacting the switch.

linear stepper motor A stepper motor whose motion is in a straight line instead of rotary.

lockout A safety procedure that ensures that the source of supply voltage for a machine is disconnected and locked in the off position so that personnel can safely work on the equipment.

logic General term for relay circuits, digital circuits, and programmed instructions to perform required decision-making and computational functions.

loop 1. (closed-loop system) A control system that has an output device and a process variable signal supplied by a sensor that is used as feedback. 2. A sequence of instructions that executes repeatedly until a terminating condition is satisfied. 3. A closed-loop or open-loop system.

LRA locked-rotor amperage (current) The amount of current a motor winding draws when power is initially applied and the rotor has not begun to rotate. This would be the same amount of current the winding would draw if the rotor stopped rotating.

LSB Lease significant bit The bit that represents the smallest value within a string of bits.

LVDT Linear variable differential transformer. A linear position sensor that uses a transformer whose output is proportional to the position of its core.

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