Industrial Electronics Glossary

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M (mega) 1. A prefix used with units of measurement to designate a multiple of 1,000,000 ( I million). 2. An amount of memory equal to 270 = 1,048,576 bits, bytes, or words in denoting size of a block of data memory.

master control relay (MCR) A hard-wired relay that controls voltage to a PLC system or other automated system so that voltage can be de-energized by any series-connected emergency stop switch. Whenever the master control relay is de-energized, its contacts open to remove the source of power from all I/O circuits, sensors, and actuators.

microprocessor A central processing unit that is manufactured on a single integrated circuit (or on only a few integrated circuits) by utilizing large-scale integration technology.

microstepper The process of dividing steps of a stepper motor into substeps.

mnemonic A term (or abbreviation) that is simple and easy to remember used to represent a complex or lengthy set of information. For example, the mnemonic for the Timer On Delay instruction for a PLC is TON, the mnemonic for an Up Counter instruction is CTU, and the mnemonic for the subtraction instruction is SUB.

modem modulator/demodulator. Equipment that connects data terminal equipment to a communications line.

module An interchangeable plug-in circuit within a larger (modular) assembly.

MOS Metal-oxide semiconductor. A semiconductor device in which an electric field controls the conductance of a channel under a metal electrode called a gate.

MSB Most significant bit. The bit representing the greatest value within a string of bits.

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