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damping The reduction in amplitude of an oscillation.
dark operate Pertaining to a photoelectric control that energizes its output when the light intensity on the photodetector is at a low level.
data A general term for any type of information. In a more specific sense, the term data refers to information in a particular context such as the amount of parts a machine has made, the amount of time on a time-delay circuit, or other machine values.
dead band The values to which a system input can be changed without causing a corresponding change in system output.
delta connection A three-phase connection where windings are connected in series with the power applied. The windings are connected in the shape of a triangle or the Greek letter delta (Δ).
deviation Difference between the setpoint and process variable in a control system. Also called error.
di/dt The instantaneous rate of change in current over time.
diac A two-terminal electronic device that is specifically designed to fire in both the positive and negative directions when its applied voltage reaches a predetermined amount.
digital signal A signal that has only two distinct states: off and on.
digital-to-analog conversion (D/A conversion) A digital value whose instantaneous magnitude is converted to its equivalent analog signal. Typical digital values range from 0-4095 or 0-999 in PI-Cs and the equivalent analog value ranges from 4-20 mA or 0-10 V dc.
DIN Deutsche lndustrie Normenausschuss. A German agency that establishes European standards. diode A two-terminal solid-state semiconductor that allow current flow in one direction.
DIP Dual inline package. A configuration in which printed circuit components are built with two parallel rows of pins so that they can be easily mounted and soldered to printed circuit boards. direct current (dc) Current that flows in only one direction.
disable To inhibit logic from being activated.
discrete An electronic device that has an individually distinct identity as opposed to being part of an integrated circuit.
discrete circuit A circuit built from separate components opposed to being part of an integrated circuit.
discrete signal A signal that has only two distinct states: oft' and on.
disk drive The device that reads data from or writes data to a disk.
diskette (floppy disk) A thin, flexible disk coated with magnetic oxide and used to store data.
documentation A collection of printed pages for a PLC that may include the ladder diagram, program comments, data tables, and other diagrams to provide reference information for operation and troubleshooting.
DOS Disk operating system. A set of computer commands specifically designed to aid in setting up tiles and directories in the hard drive or floppy drive of a computer. The commands also are designed for copying or moving programs and files between memory devices.
download Transferring a program from a terminal to control unit such as a programmable controller or CNC controller.
DSR Data-Set-Ready. A signal that indicates the modem is connected, powered up, and ready for data transmission.
DTE Data-Terminal-Equipment. Equipment that is attached to a network to send or receive data or both.
DTR Data-Terminal-Ready. A signal that indicates the transmission device (terminal) is connected, powered up, and ready to transmit.
duty cycle The ratio of working time to total time for a motor or machine that operates intermittently.
dv/dt 1. The instantaneous rate of change in voltage over time. 2. A network consisting of a resistor and capacitor that can help protect a SCR from excessive du/dt, which can result from line voltage spikes.
dwell A programmed time delay.
dynamic braking A method of braking a DC motor which involves disconnecting the motor windings from applied voltage and reconnecting them across a set of resistors.
This page was last updated: Tuesday, August 19, 2008 23:33