Glossary N

Following is a definition of terms frequently used in the instrumentation, industrial automation and test & measurement communities.

N/C (No Connection): A connector point for which there is no internal connection.

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.