signal and release a circuit from occupation. 4. To emply a data storage device. 5. To place one or more storage locations into a prescribed state, usually zero
clearance distance 74 closed loop control
or the space character. Contrast with set. Also called reset.
clearance distance (numerical control) The dis tance between the tool and the workpiece when the change is made from rapid approach to feed move ment to avoid tool breakage.
clearance flow (control valves) That flow below the minimum controllable flow with the closure mem ber not seated.
clear area In character recognition, a specified area that is to be kept free of printing or any other mar- kings not related to machine reading.
clear instruction That specific instruction which re- places data or information in storage or in registers, accumulators, etc. with zeros or blanks.
clear signal (data communication) The original unscrambled, normal, unprocessed or uncoded signal.
clear terminal See reset terminal.
clear to send (data communication) A code de signation (EIA RS-232) applied to a sense circuit used by a terminal or computer to detect that its modem is ready to send data.
cleaver A device used to cut or break optical fibers in a precise way so the ends can be connected with low loss.
clinging nappe A nappe held in contact with the downstream face of the weir. Pertains to liquid flow measurement in open channels.
clinker A hard compact congealed mass of fused fur nace refuse, usually slag.
clipper (data communication) A specific circuit which removes the portion of a current waveform which would otherwise extend above or below a spe cified level.
clipping level The signal level at which clipping (dis tortion) just begins to occur.
CL list A tabulation of engineering drawings, specifi cations and other reference documents needed to fa bricate and assemble a configuration item (SAMA).
clobbered When a program or data are lost because of a system malfunction.
clock (CLK) 1. A master timing device used to provi
de the basic sequencing pulses for the operation of a synchronous computer. 2. A register which automati cally records the progress of real time, or perhaps some approximation to it, records the number of ope- rations performed, and whose contents are available to a computer program. 3. A data communications clock which controls the timing of bits sent in a data stream, and controls the timing of the sampling of bits recei ved in a data stream.
clock cable Cable of specific impedance and electri cal characteristics used to distribute the clock (master) frequency where needed in digital computers.
clocked Pertaining to the type of operation in which gating is added to a basic flip-flop to permit the flip- flop to change state only when there is a change in the clocking input or an enabling level of the clocking in- put is present.
clock frequency The master frequency of periodic pulses which schedules the operation of the computer.
clock generator A test-signal generator that supplies a chain of pulses identical with those supplied by the clock circuit of a digital computer.
clocking (data transmission) The generation of periodic signals used for synchronization.
clock mode A system circuit that is synchronized with a clock pulse, that changes states only when the pulse occurs.
clock pulse, clock signal A periodic signal used for synchronization or for measuring intervals of time.
clock pulse generator A specifically designed ge nerator which generates pulses for purposes of timing or grating in a digital computer, i.e., pulses which are used as inputs to gates to aid in pulse-shaping and ti ming. Same as time pulse generator.
clock rate The time rate at which pulses are emitted from the clock. The clock rate determines the rate at which logical or arithmetic gating is performed with a synchronous computer.
clock register, timer A register whose contents are changed at regular intervals in such a manner as to measure time.
clock signal, clock pulse A periodic signal used for synchronization or for measuring intervals of time.
clock skew A phase shift between the clock inputs of devices in a single clock system; the result of varia tions in gate delays and stray capacitance in a circuit.
clock stagger 1. Time separation of clock pulses in a
multiphase clock system. 2. Voltage separation bet- ween the clock thresholds in a flip-flop.
clockwise arc (numerical control) A circular path that is described by the reference of a tool that rotates in a negative angular direction about the centre of the path.
clogging Choking, progressive or not, of a porous or fibrous layer or of an apparatus by deposits of solid or liquid particles.
clone Computer or circuit that behaves in the same way as the original it was copied from.
close at and open at (control valves) Signal span (psi, volts, amps, etc.) at which a control valve shall be closed and open. Note: This is signal to valve ope rator and is not necessarily controller output signal if a positioner and/or transducer is used.
closed action flow Action flow in a closed action path of a system in which the output variable is conti nuously influencing the manipulated variable and thus continuously influencing itself. Note: A reset circuit has an open action flow in spite of the fact, that the structure has a closed action path.
closed action path Action path which connects the output to one of the inputs of the system.
closed array An array which cannot be extended at either end.
closed circuit (fluid power systems) Circuit in which return fluid is directed to the pump inlet.
closed-circuit communication system Certain communication system which are entirely self-contai ned and do not exchange intelligence with other facili ties and systems.
closed instruction loop A group of instructions that can be repeated endlessly, there being no exit point.
closed loop 1. In a feedback loop, a signal path
which includes a forward path, a feedback path and a summing point, and forms a closed circuit. 2. A loop that has no exit and whose execution can be interrup ted only by intervention from outside the computer program in which the loop is included. 3. Pertaining to a system with feedback type of control, such that the output is used to modify the input. Refers to Ho neywell TDC 3000 control systems.
closed loop control, feedback control 1. Control
in which the controlled variable is compared with the reference variable, and the difference between them is used to adjust the controlled variable to the reference variable. 2. Control in which control action is made to depend persistently on the measurement of the con- trolled variable. 3. An operation where the computer applies control action directly to the process without manual intervention.
closed loop gain 75 coating closed loop gain In process instrumentation the
gain of a closed loop system, expressed as the ratio of the change of directly controlled variable as output to the change of reference variable as input at a specified frequency.
closed loop numerical control A type of numeri cal-control system in which position feedback, and of- ten velocity feedback as well, is used to control the dynamic behaviour and successive positions of mach ine slides or equivalent machine members.
closed loop stabilization A mode of operation in which the value of an output is compared with a refe rence value so that the difference between those valu es controls directly or indirectly the output quantity at the desired value.
closed loop voltage gain The voltage gain of an amplifier with feedback.
closed position (control valves) The position of the closure member when a continuous surface or line of contact is established with the valve seat. For non- seating valves, the closed position is obtained when the flow passageway is minimum.
closed position (fluid power systems) 1. Valve
position in which the inlet supply is not connected to an outlet. 2. Position of the valve member in which the flow path between inlet and outlet ports is closed.
closed routine A routine which is not inserted as a block of instructions within a main routine but is ente red by basic linkage from the main routine.
closed subroutine A subroutine, one copy of which suffices to be linked by calling sequences for use at more than one place in a computer program.
closed type head box Pertaining to the pulp and paper industry, a head box in which the stock chamber is closed to the external atmosphere and where the pressure can be regulated independently of the atmos pheric pressure; compare open head box. The closed type head box may or may not have an air cushion; compare hydraulic head box.
closed user group A group of specified users of a data network that is assigned a facility which permits them to communicate with each other but precludes communication with all other users of the service or services.
closed white water system See white water sys tem.
close memory Part of a directly addressable compu ter memory which provides fast cycle time and is usu ally employed for frequently used accesses.
closing pressure (pressure relief devices) Clo sing pressure is the value of decreasing inlet static pressure at which the valve disk re-establishes contact with the seat or at which lift becomes zero.
closing relay A form of auxiliary relay used to con trol the closing and opening of the closing circuit of the device so that the main closing current does not pass through the control switch or other initiating de- vice.
closure member (valves) A movable part of a val ve which is positioned in the flow path to restrict the flow through the valve. A closure member may be a plug, ball, disk, vane, gate, diaphragm etc.
cloud-velocity (gaging) A method of determining the mean velocity by measuring the time taken for a cloud of injected liquid to travel between two sec tions. Pertains to liquid flow measurement in open channels.
CL specification The configuration item (CL). Spe cification establishes the functional, performance and design criteria for the design, development, testing and production of any combination of parts, subas
semblies, units or groups that perform a specific func tion and is essential to the completeness of a system or subsystem (SAMA).
clustering In a computer, the process of grouping things with similar characteristics. A properly pro grammed computer can take a list of items and group them into clusters.