Daisy Chain: A term used to describe the linking of serval RS-232C devices in sequence such that a single data stream flows through one device and on to the next. Daisy chained devices usually are distinguished by device addresses, which serve to indicate the desired destination for data in the stream.

Damping: An indication of the rate of decay of a signal to its steady state value. Related to setting time.

Damping Ratio: Ratio of actual damping to critical damping. Less than one is an underdamped system and greater than one is an overdamped system.

Dead Band: A range of input signals for which there is no system response.

DeadBand: The region or band of no response where an error signal will not cause a corresponding actuation of the controlled variable.

Decompression: The slow release of confined fluid to gradually reduce pressure on the fluid.

Delivary: The volume of fluid discharged by a pump in a given time, usually expressed in gallons per minute(gpm).

De-vent: To close the vent connection of a pressure control valve permitting the valve to function at its adjusted pressure setting.

Decibel: A logarithmic measurement of gain. If G is a system'sgain (ratio of output to input), then 20 log G = gain in decibels (db).

Detent Torque: The minimal torque present in n unenergized motor. The detent torque of a step motor is typically about 1% of its static energized torque.

Digital Signal: A voltage or current that varies between two distinct and fixed levels.

Diode Rectifier: A device used to convert Ac voltage in to DC pulses.

Direct Current (DC): A steady level of electrical current, produced by a power source e.g. battery, thermocouple etc. that flows in only one direction in a circuit.

Direct Digital Link(DDL): A digital feedback system used with servo valve to allow the valve to communicate with a digital host device such as a PLC or personal computers. The host device serially transmits command signals to the valve, and position information is sent back to the host which respond with an error correction signal.

Dither: A low amplitude, AC signal superimposed on the torque motor or solenoid input to improve system resolution. Direct is expressed by the direct frequency (H_z) and the peak-to-peak dither voltage.

Direct Drive Servo: A high-torque, low speed servo motor with a high resolution encoder or resolver intended for direct connection to the load without going through a gearbox.

Drain: A passage in or a line from a hydraulic component which return leakage fluid independently to reservior or to a vented manifold.

Double Acting Cylinder: A cylinder in which fluid force can be applied to the movable element in either direction.

Duty Cycle: For a repetitive cycle, the ratio of on time to total cycle time.
Duty Cycle= On Time / (On Time + Off Time).

Dynamic Breaking: A passive technique for stopping a permanent magnet brush or brushless motor. The motor windings are shorted together through a resistor which results in motor braking with an exponential decrease in speed.