GLOSSARY
Select the first letter of the desired search item. We will then
display the matching terms that begin with that letter.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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 Ionic Activity Coefficient: See Activity coefficient.
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 (.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.
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.
N/C (No Connection): A connector point for which there is no internal
connection.
NBS: National Bureau of Standards.
NEC: National Electric Codes.
Negative Temperature Coefficient: A decrease in resistance with an increase in temperature.
NEMA-4: A standard from the National Electrical Manufacturers Association, which defines
enclosures intended for indoor or outdoor use primarily to provide a degree of protection against
windblown dust and rain, splashing water, and hose-directed water.
NEMA-7: A standard from the National Electrical Manufacturers Association, which defines
explosion-proof enclosures for use in locations classified as Class I, Groups A, B, C or D, as
specified in the National Electrical Code.
NEMA-12: A standard from the National Electrical Manufacturers Association, which defines
enclosures with protection against dirt, dust, splashes by non-corrosive liquids, and salt spray.
NEMA-Size Case: An older US case standard for panel meters, which requires a panel cutout
of 3.93 x 1.69 inches.
Nernst Equation: A mathematical description of electrode behavior: E is the total
potential, in millivolts, developed between the sensing and reference electrodes; Ex varies with the
choice of electrodes, temperature, and pressure: 2.3RT/nF is the Nernst factor (R and F are
constants, n is the charge on the ion, including sign, T is the temperature in degrees Kelvin), and
ai is the activity of the ion to which the electrode is responding.
Nernst Factor (S, Slope); The term 2.3RT/nF is the Nernst equation, which is equal (at T =
25°C) to 59.16 mV when n = 1 and 29.58 mV when n - 2, and which includes the sign of the charge
on the ion in the term n. The Nerst factor varies with temperature.
Network: A group of computers that are connected to each other by communications lines to
share information and resources.
Nibble: One half of a byte.
Nicrosil/Nisil: A nickel chrome/nickel silicone thermal alloy used to measure high
temperatures. Inconsistencies in thermoelectric voltages exist in these alloys with respect to the
wire gage.
NMR (Normal-Mode Rejection): The ability of a panel meter to filter out noise superimposed
on the signal and applied across the SIG HI to SIG LO input terminals. Normally expressed in dB at
50/60 Hz.
Noise: An unwanted electrical interference on the signal wires.
Normal (axial) Stress: The force per unit area on a given plane within a body a = F/A
Normal Hydrogen Electrode: A reversible hydrogen electrode (Pt) in contact with hydrogen
gas at 1 atmosphere partial pressure and immersed in a solution containing hydrogen ions at unit
activity.
Normal-mode Rejection Ratio: The ability of an instrument to reject interference usually of
line frequency (50-60 Hz) across its input terminals.
NPT: National Pipe Thread.
Null: A condition, such as balance, which results in a minimum absolute value of output.
O.D.: Outside diameter.
Octal: Pertaining to a base 8 number system.
Offset: The difference in temperature between the set point and the actual process
temperature. Also, referred to as droop.
ofhc: Oxygen-free high-conductivity copper. The industrial designation of the pure copper
used in a Type T thermocouple.
Ohmeter: An instrument used to measure electrical resistance.
On/off Controller: A controller whose action is fully on or fully off.
Open Circuit: The lack of electrical contact in any part of the measuring circuit. An open
circuit is usually characterized by rapid large jumps in displayed potential, followed by an
off-scale reading.
Operating System: A collection of programs that controls the overall operation of a
computer and performs such tasks as assigning places in memory to programs and data, processing
interrupts, scheduling jobs and controlling the overall input/output of the system.
Operational pH: The determination of sample pH by relating to pH measurements in a primary
standard solution. This relationship assumes that electrode errors such as sensitivity and changes in
asymmetry potential can be disregarded or compensated for, provided the liquid junction potential
remains constant between standard and sample.
Optical Isolation: Two networks which are connected only through an LED transmitter and
photoelectric receiver with no electrical continuity between the two networks.
Outboard Rotor: A two-journal rotor which has its center of gravity between the journals.
Output Impedance: The resistance as measured on the output terminals of a pressure
transducer.
Output Noise: The RMS, peak-to-peak (as specified) ac component of a transducer's dc output
in the absence of a measurand variation.
Output: The electrical signal which is produced by an applied input to the transducer.
Overshoot: The number of degrees that a process exceeds the set point temperature when
coming up to the set point temperature.
| 
