Glossary

DC bus is a type of circuit or protocol that serves as a common communications pathway shared by several components and which uses a direct current voltage level as a reference. It may also be used to describe a power distribution system shared by multiple components within a machine or power distribution system.

Deceleration is the rate at which something decreases its velocity. Deceleration is usually measured in units of velocity change for each unit of time (Inches/ second (velocity)/ second (time)) and in this example would be written as in./sec/sec or in./sec2.

Decentralized control is a control system in which the logic functions and input/output functions are located at individual pieces of equipment or sub systems and function essentially independent of each other. Normally the independent systems will have some means of communicating vital information with each other.

Detent torque is the maximum torque that can be applied to an un-energized step motor without causing continuous rotating motion.

Deterministic scan time is the frequency with which a Programmable Logic Controller (PLC) executes a program, including scanning all the inputs and outputs on the system. This time is usually measured in milliseconds. PLCs will normally read or “scan” the instructions in the logic program in set, sequential manner. The time required to read a specific instruction and all of the following instructions, returning to the initial instruction is generally referred to as scan time.

Device level network is a means of putting sensors, actuators and other components on a common network cable that is connected to a PLC. It eliminates point -to-point wiring between the PLC and each device.

Diagnostic code is a code (usually alpha numeric or numeric) that is displayed on some type of operator interface or within a program that indicates the status of a monitored component. Usually diagnostic codes are used to indicate the location and nature of a fault or error condition that requires rectification.

Digital motion control is a motion control system that utilizes binary coding for all logic and control functions. Analog inputs can normally be used on a digital system, but they must be converted through an analog to digital converter before being processed.

Digital servo is a servo motor (see AC servo and Analog servo) which utilizes binary coding for all parameter generation and feedback.

Digital signal is a signal that communicates information in electrical pulses that represent binary 1s and 0s. It is widely believed that digital signals can transmit more information more reliably in a given unit of time than analog signals.

Drive is an electronic device that translates a given command from a motion controller into the electrical current that turns a motor.

For a repetitive cycle, Duty Cycle is the ratio of on time to total cycle time. Duty cycle (o) = [On time / (On time + Off time)] x 100o

Dynamic braking is 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.