PERIODIC TERMS

In the mathematical expression of the orbit of a satellite, terms which vary with time in both magnitude and direction in a periodic manner.

Related Terms

TWA

Time Weighted Average

1. The time interval between a change in the input signal to a process control system and the response to the signal.
2. The time interval, after a response to one signal or event, during which a system is unable to respond to another. Also known as insensitive time.

POINCARE SURFACE OF SECTION

A method of displaying the character of a particular trajectory without examining its complete time development, in which the trajectory is sampled periodically, and the rate of change of a quantity under study is plotted against the value of that quantity at the beginning of each period. Also known as surface of section.

PLANNING HORIZON

In a materials-requirements planning system, the time from the present to some future date for which plans are being generated for acquisition of materials.

PHASE PORTRAIT

A graph showing the time derivative of a system's position (or some other quantity characterizing the system) as a function of position for various values of initial conditions.

PHASE PLANE ANALYSIS

A method of analyzing systems in which one plots the time derivative of the system's position (or some other quantity characterizing the system) as a function of position for various values of initial conditions.

PERS SUNSHINE RECORDER

A type of sunshine recorder in which the time scale is supplied by the motion of the sun.

PERMANENT BENCHMARK

A readily identifiable, relatively permanent, recoverable benchmark that is intended to maintain its elevation without change over a long period of time with reference to an adopted datum, and is located where disturbing influences are believed to be negligible.

PEEL-OFF TIME

In seismic prospecting, the time correction applied to observed data to adjust them to a depressed reference datum.

PAYOUT TIME

A measurement of profitability or liquidity of an investment, being the time required to recover the original investment in depreciable facilities from profit and depreciation; usually, but not always, calculated after income taxes.

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