Manual Reset (Switch): The switch in a limit controller that manually resets the controller after the limit has been exceeded.

Mass Flow Rate: Volumetric flowrate times density, i.e. pounds per hour or kilograms per minute.

Mass Storage: A device like a disk or magtape that can store large amounts of data readily accessible to the central processing unit.

Maximum Excitation: The maximum value of excitation voltage or current that can be applied to the transducer at room conditions without causing damage or performance degradation beyond specified tolerances.

Maximum Operating Temperature: The maximum temperature at which an instrument or sensor can be safely operated.

Mean Temperature: The average of the maximum and minimum temperature of a process equilibrium.

Measurand: A physical quantity, property, or condition which is measured.

Measured Media: The physical quantity, property, or condition which is measured. (eg: pressure, load, weight, acceleration)

Measuring Junction: The thermocouple junction referred to as the hot junction that is used to measure an unknown temperature.

Mechanical Hysteresis: The difference of the indication with increasing and decreasing strain loading, at identical strain values of the specimen.

Melting Point: The temperature at which a substance transforms from a solid phase to a liquid phase.

Membrane: The pH-sensitive glass bulb is the membrane across which the potential difference due to the formation of double layers with ion-exchange properties on the two swollen glass surfaces is developed. The membrane makes contact with and separates the internal element and filling solution from the sample solution.

Method of Correction: A procedure whereby the mass distribution of a rotor is adjusted to reduce unbalance, or vibration due to unbalance, to an acceptable value. Corrections are usually made by adding material to, or removing it from, the rotor.

MFLOPS: Million Floating Point Instructions Per Second.

Mica: A transparent mineral used as window material in high-temperature ovens.

Microamp: One millionth of an ampere, 10-6 amps, µA.

Micron: One millionth of a meter, 10-6 meters.

Microvolt: One millionth of a volt, 10-6 volts.

Mil: One thousandth of an inch (.001").

Milliamp: One thousandth of an amp, 10-3 amps, symbol mA.

Millimeter: One thousandth of a meter, symbol mm.

Millivolt: Unit of electromotive force. It is the difference in potential required to make a current of 1 millampere flow through a resistance of 1 ohm; one thousandth of a volt, symbol mV.

Mineral-insulated Thermocouple: A type of thermocouple cable which has an outer metal sheath and mineral (magnesium oxide) insulation inside separating a pair of thermocouple wires from themselves and from the outer sheath. This cable is usually drawn down to compact the mineral insulation and is available in diameters from .375 to .010 inches. It is ideally suited for high-temperature and severe-duty applications.

MIPS: Million Instructions Per Second.

Modem: Modulator/Demodulator. A device that transforms digital signals into audio tones for transmission over telephone lines, and does the reverse for reception.

Modulation: The process by which some characteristic of a higher frequency wave is varied in accordance with the amplitude of a lower frequency wave.

Molality: A measure of concentration expressed in mols per kilogram of solvent.

Monovalent Ion: An ion with a single positive or negative charge (H+, C1-).

Motherboard: The pc board of a computer that contains the bus lines and edge connectors to accommodate other boards in the system. In a microcomputer, the motherboard contains the microprocessor and connectors for expansion boards.

Mounted Resonant Frequency: The frequency at which the internal spring/mass system of an accelerometer resonates, producing a 90 degree phase shift in output signal vs. applied acceleration.

Mounting Error: The error resultant from installing the transducer, both electrical and mechanical.

MR: Magneto Resistive or Magneto-Resistance.

MRI: Magnetic Resonance Imaging.

MSD (Most-Significant Digit): The leftmost digit of the display.

MTBF: Mean Time Between Failures.

Mueller Bridge: A high-accuracy bridge configuration used to measure three-wire RTD thermometers.

Multiplex: A technique which allows different input (or output) signals to use the same lines at different times, controlled by an external signal. Multiplexing is used to save on wiring and I/O ports.