Glossary of Terms - M


A measurement term meaning one million.

Melting Point

The temperature at which a solid becomes a liquid.


A high temperature (1200°F) glass insulation for RTD or thermocouple lead wires.


A dedicated set of integrated circuits mounted on a single circuit card (sometimes comprised in a single IC chip), used to exercise control or perform a series of interrelated functions in some localized portion of an overall system. It comprises a central processing unit (CPU, or microprocessor), memory circuits, and input/output (interface) circuits. Input circuits accept signals from external sources (and internal sources such as a clock) and convert them to corresponding digital voltages for CPU processing. The CPU performs logical and computational operations on these signals, as directed by a control program held in memory, based on conditions at the controlled process or instrument. CPU outputs are command signals which are sent to appropriate locations in the controlled system to accomplish the objectives of the control program.


The small central processing unit (CPU) that performs the logic operations in a microcomputer system. Decodes instructions from the stored program, performs arithmetic and logic operations, generates timing signals, produces commands for external use in process or instrument control.


A measurement term meaning one thousandth.

Mineral Insulated

A term used to express a swaged or drawn thermocouple construction where a mineral oxide insulation, usually magnesium oxide or aluminum oxide, is densely compacted in a sheath for rugged bendable high temperature, sensor construction.

Mirror Scale

Analog meter scale with a mirror arc that enables alignment of the eye's line of sight perpendicular to the scale when taking a reading. Eliminates parallax, considerably improves reading accuracy.

MOV (Metal Oxide Varistor)

A device to short out voltages above its design rating. MOV clips voltage peaks

Most Significant Digit (MSD)

The leftmost digit of the display.

Mueller Bridge

A four-wire lead compensated Bridge used for laboratory calibration of RTDs (accuracies in milliohm region).


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.


One or more resistances which can be switched in series with a meter input to provide a selection of measurement ranges for the meter.