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Hall effect A condition in a semiconductor where current flowing perpendicular to a magnetic field produces a (small-voltage) potential difference perpendicular to both the magnetic field and the current flow.
hard contacts Any type of physical switching contacts as compared to soft programmed contacts in a PLC program.
HDLC High-level data-link control. A communications protocol sanctioned by the International Standards Organization (ISO) that defines procedures for the data link and physical layers for the seven-layer ISO model for communications.
hexadecimal numbering system A base 16 numbering system which uses the symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F for numerals.
holding current 1. The amount of current required to keep a thyristor in its conductive state after its firing signal is removed. 2. The current used to hold relay contacts in their activated condition.
home position A reference position for all absolute positioning movements. Usually defined by a home limit switch and encoder marker. Normally set at power up and retained as long as the control system is operational.
horsepower (hp) A unit of power. 1 hp = 33,000 ft-lb/min = 746 W.
This page was last updated: Wednesday, August 20, 2008 7:10