DE LOS CONSEJOS LOCALES DE TUTELA CAPÍTULO ÚNICO

present in the machine and available as data for the program, and which usually are not subject to change with time. 2. A value that remains the same throug­ hout the distinct operation; opposite of variable. 3. A character or group of characters usually representing a value. A key or standard, used by the computer to identify, locate, measure, or test in order to make a de­ cision.

constantan Alloy containing copper and nickel. Tra­ dename. See copper versus copper-nickel.

constant current power supply A regulated po­ wer supply which acts to keep its output current con­ stant in spite of changes in load, line, or temperature.

constant-delay (filter) See Bessel.

constant failure rate period That possible period in the life of a non-repaired item during which the fai­ lure rate is approximately constant.

constant-head meter A flow measurement device that maintains a constant pressure differential by vary­ ing the cross section of a flowpath through the meter.

constant instruction An instruction not intended to be executed as an instruction, written in the form of a constant. Related to dummy instruction.

constant level tank A tank, the level of liquid in which is controlled for example by a weir, the length of which shall be as long as possible to ensure stable flow conditions in the circuit being supplied with li­ quid.

constant multiplier A computing element that mul­ tiplies a variable by a constant factor.

constant of a measuring 91 contact separation constant of a measuring instrument The factor

or coefficient by which the indication must be multip­ lied to obtain the value of the measured quantity.

constant power motor (constant horsepower motor) A multispeed motor that develops the same related power output at all operating speeds. The tor­ que then is inversely proportional to the speed.

constant-rate injection method 1. A method of

measuring the discharge in which a tracer of known concentration is injected at a constant and know rate at one cross-section and its dilution is measured at an- other section downstream where complete mixing has taken place. Pertains to liquid flow measurement in open channels. Measurement of flow by dilution met- hods. 2. A method of measuring the flow-rate in which a tracer of known concentration is injected at a constant and known flowrate at one cross-section and its dilution is measured at another cross-section downstream where adequate mixing has taken place. Pertains to measurement of fluid flow in closed con­ duits.

constant rate injection method A method of mea­ suring the flow-rate in which a tracer of known con­ centration is injected at a constant and known flow- rate at one cross-section and its dilution is measured at another cross-section downstream where adequate mixing has taken place. Pertains to measurement of fluid flow in closed conduits.

constant storage A part of storage designated to store the invariable quantities required for processing.

constant torque motor Multispeed motor that is capable of developing the same torque for all design speeds. The rated power output varies directly with the speed.

constant – voltage charge (storage battery) A charge in which the voltage at the terminals of the bat­ tery is held at a constant value.

constant – volume gasthermometer A device for detecting and indicating temperature based on Char­ les’ Law – the pressure of a confined gas varies direct­ ly with absolute temperature; in practical instruments, a bulb immersed in the thermal medium is connected to a Bourdon tube by means of a capillary; changes in temperature are indicated directly by movement of the Bourdon tube due to changes in bulb pressure.

constant voltage power supply A regulated po­ wer supply which acts to keep its output voltage con­ stant in spite of changes in load, line, or temperature. Thus, for a change in load resistance, the output cur- rent changes by whatever amount necessary to accom­ plish this.

constraint rule A rule that limits a search by a desig­ nated portion of the problem space. Note: Constraint rules may be effective control mechanisms in expert systems and rule-based systems.

constructional hardware Mechanical structures, or group of structures, for mounting measurement, con­ trol and monitoring equipments. For example, racks, panels, cabinets, shelves, etc.

consultation (in artificial intelligence) The onli­ ne interaction between a knowledge-based system and a user seeking assistance, usually consisting of a ques­ tion-answer dialog.

contact One of the current-carrying parts of a relay, switch, or connector that are engaged or disengaged to open or close the associated electrical circuits.

contact-actuation time The time required for any specified contact on the relay to function. When not otherwise specified, it is the initial actuation time. For some purposes, it is preferable to use either the final or effective actuation time.

contact alignment A term which refers to electrical contacts and the sidewise movement or play in mating contact pins or other devices for plugs or other contact insertions or surfaces.

contact arc The electrical (current) discharge that oc­ curs between mating contacts when the circuit is be­ ing disestablished.

contact area The common surfaces between conduc­ tors or connectors of electricity flow.

contact arrangement 1. The combination of con-

tact forms that make up the entire relay-switching structure. 2. See contact configuration.

contact bifurcated Contacts used in printed circuits with slotted flat springs which increase flexibility of the spring and provide extra points of contact.

contact bounce An unwanted making and breaking of the connection while opening or closing a contact.

contact bounce time The time interval from initial actuation of a relay contact to the end of bounce brought about during pickup or dropout or from exter­ nal causes.

contact chatter 1. The undesired vibration of mating

contacts during which there may or may not be actual physical contact opening. If there is no actual opening but only a change in resistance, and it appears as “grass” on the screen of an oscilloscope having ade­ quate sensitivity and resolution. 2. A sustained rapid physical opening and closing of contact points caused by mechanical vibrations.

contact configuration A standard or designed ar­ rangement of various contacts general multiple-con- tact connectors, i.e., including the spacing, number, orientation location of the contacts in the connector.

contact current-carring rating of a relay The current that can be carried continuously or for stated periodic intervals without impairment of the contact structure or interrupting capability.

contact discharge method A method of testing, in which the electrode of the test generator is held in contact with the EUT (equipment under test), and the discharge actuated by the discharge switch within the generator. Pertains to electrostatic discharge test met- hods.

contact emf A small voltage established whenever two conductors of different materials are brought into contact.

contact force The amount of force exerted by one of a pair of closed contacts on the other.

contact gap Also called contact separation. The dis­ tance between a pair of mating relay contacts when they are open.

contact interrogation signal A signal whose value indicates wheather a contact is open or closed.

contact pressure The amount of pressure holding a set of contacts together.

contact rating The electrical power-handling capabi­ lity of relay or switch contacts under specified envi­ ronmental conditions and for a prescribed number of operations.

contact resistance Total electrical resistance of a contact system, such as the resistance of a relay or a switch measured at the terminals. Usually this resis­ tance is only a fraction of an ohm.

contact retention The minimum axial load a contact in a connector can withstand in either direction while remaining firmly fixed in its normal position in the in­ sert.

contact sense module A device which monitors and converts program-specified groups of field-switch contacts into digital codes for input to the computer.

contact stabilization 92 continuous dying contact stabilization (water quality) A modifica­

tion of the activated sludge process whereby previous­ ly aerated activated sludge is brought into contact with raw sewage for a short period of time (for ex- ample 15 to 30 min.). The sludge, after contact, is settled out and returned to a separate tank where it is aerated for a longer period of time (for exampe 6 to 8 h.).

contact symbology diagram Commonly referred to as a ladder diagram, it expresses the user-program­ med logic of the controller in relay-equivalent symbo­ logy.

contact thermography A method of measuring sur­ face temperatur in which the surface of an object is covered with a thin layer of luminescent material and then viewed under ultraviolet light in a darkened room; the brightness viewed indicates surface tempe­ rature.

contact-type membrane switch A disk-shaped momentary-contact switch of multilayer construction; the active element consists of two conductive buttons separated by an insulating washer; finger pressure on one face of the disk brings the buttons into contact, completing the electrical circuit; when the pressure is released, the contacts separate, breaking the electrical circuit.

contact wetting The coating of a contact surface with an adherent film of mercury.