Following is a definition of terms frequently used in the instrumentation, industrial automation and test & measurement communities.
M: Mega; one million. When referring to memory capacity, two to the twentieth power (1,048,576 in decimal notation).
Machine Language: Instructions that are written in binary form that a computer can execute directly. Also called object code and object language.
Mandrel (Balancing Arbor): An accurately machined shaft on which work is mounted for balancing.
Manual Reset (Adjustment): The adjustment on a proportioning controller which shifts the proportioning band in relationship to the set point to eliminate droop or offset errors.
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 Elongation: The strain value where a deviation of more than ±5% occurs with respect to the mean characteristic (diagram of resistance change vs strain).
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.
Maximum Power Rating: The maximum power in watts that a device can safely handle.
Mean Temperature: The average of the maximum and minimum temperature of a process equilibrium.
Measurand: A physical quantity, property, or condition which is measured.
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.
Medium Effect (f m): For solvents other than water the medium effect is the activity coefficient related to the standard state in water at zero concentration. It reflects differences in the electrostatic and chemical interactions of the ions with the molecules of various solvents. Solvation is the most significant interaction.
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.
Mica: A transparent mineral used as window material in high-temperature ovens.
Microamp: One millionth of an ampere, 10-6 amps, µA.
Microcomputer: A computer which is physically small. It can fit on top of or under a desk; based on LSI circuitry, computers of this type are now available with much of the power currently associated with minicomputer systems.
Micron: One millionth of a meter, 10-6 meters.
Microvolt: One millionth of a volt, 10-6 volts.
Mil: One thousandth of an inch (0.001″).
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 0.375 to 0.010 inches. It is ideally suited for high-temperature and severe-duty applications.
Minor Scale Division: On an analog scale, the smallest indicated division of units on the scale.
Modem: Modulator/Demodulator. A device that transforms digital signals into audio tones for transmission over telephone lines, and does the reverse for reception.
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.
Mounting Error: The error resultant from installing the transducer, both electrical and mechanical.
MSD (Most-Significant Digit): The leftmost digit of the display.
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.