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Head: The height of a column or body of fluid above a given point expressed in linear units. Head is often used to indicate gauge pressure. Pressure is equal to the height times the density of the fluid.

Heat: The form of energy that has the capacity to create warmth or to increase the temperature of a substance. Any energy that is wasted or used to overcome friction is converted to heat. Heat is measured in calories or British Thermal Units (BTUs). One BTU is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

Heat Exchanger: A device which transfers heat through a conducting wall from one fluid to another.

Horsepower (HP): The power required to lift 550 pounds one foot in one second or 33,000 pounds one foot in minute. A horsepower is equal to 746 watts or to 42.4 British Thermal Unit per minute.

Holding Torque: Sometimes called static torque, it is specifies the maximum external force or torque or torque that can be applied to a stopped, energized motor without causing the rotor to rotate continuously.

Home: A reference position in a motion control system derived from a mechanical datum or switch. Often designated as the "zero" position.

Hydraulic Balance: A condition of equal opposed hydraulic forces acting within a hydraulic component.

Hydraulics: Engineering science pertaining to the energy of liquid flow and pressure.

Hydrostatics: Engineering science pertaining to the energy of confined fluid.

Hybrid Servo: A brushless servo motor based on a conventional hybrid stepper. It may use either a resolver or encoder for commutation feedback.

Hysteresis: The differences in response of a system to an increasing or a decreasing input signal.