Marking of electric equipment

Download Marking of electric equipment

Post on 10-Mar-2017

213 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • Marking of Electric Equipment T E D P O W E L L

    ONE of the perplexing problems with which electrical technicians were faced during the gruelling war years was the frequent use of arbitrary methods in identifying components, blueprints in

    coding and equipment

    wiring, and the electri-

    Standardization of electric equipment marking is of vital interest to technicians who must install and operate the apparatus. Although many standards have been formulated, more are needed and those that do exist require greater utilization* During World War II it was brought out that existing standards do not encompass the field of name plate marking, and at that time there

    was a vital need for such a practice.

    all rotate or produce a phase-rotated output in the proper direction with the system energized.

    SELSYN WIRING

    DIAL AND MARKINGS

    cai field. The problem still exists.

    One of the simpler types of marking ambiguities, which was accentuated during the war, is the method of indicating mechanical rotation. The general terms right-hand, left-hand, clockwise, or counterclockwise sometimes are employed with no additional information. The terms left-hand and right-hand are not generally as effective as the terms clockwise and counterclockwise for rotation designations because they tend to become confusing in the case of units located overhead or mounted diagonally. The position from which rotation is viewed in relation to the machine must be considered in marking. Indicating arrows help to eliminate ambiguity in most cases.

    A-C MOTOR AND GENERATOR MARKINGS A similar problem is encountered in polyphase motor

    and generator markings. A 3-phase motor's or generator's leads usually have so-called phase markings on the three or more connections. Theoretically, when these marked leads are connected to a correspondingly marked power supply, the motor should rotate in the proper direction, and the generator should produce a properly phase-rotated output. In actual practice, however, the technician cannot rely on the aforementioned to be true because the markings of individual manufacturers are different and because they fail to indicate the actual phase rotation of the windings.

    Technicians generally must employ time-consuming trial-and-error checks with energized equipment in order to determine the actual phase-rotation. Standard notation of phase rotation and corresponding marking of motor and generator leads with associated mechanical rotation information supplied as previously mentioned would be of great help in installation work, and units manufactured by several companies could be installed in the same system with the assurance that they would

    Ted Powell of Maspeth, N. Y., was electrical test supervisor of the ship repair force, New York Naval Shipyard, Brooklyn, N. Y. Q { /

    The wide military and industrial application of self-synchronous systems to remote indication and control purposes, and the gener

    ally slight familiarity of the average engineer and technician with this device, has resulted in some confusion. Six different factors may be present to cause reversed rotor or dial rotation, reversed dial readings, or reversed control signals, even though all installation wiring apparently has been installed properly according to the blueprints. They might be listed as follows:

    1. Reversed readings caused by dial calibrations engraved in both clockwise and counterclockwise directions.

    2. Reversed dial rotations caused by gear trains between the rotors and their indicating dials in multiple-dial indicating instruments.

    3. Reversed dial readings caused by fixed-dial-and-rotating-pointer indicators in a fixed-pointer-and-rotating-dial indicator system.

    4. Reversed dial calibrations or dial rotations in multiple concentric dial indicators caused by reversed calibration of fixed or rotating dials, or by reversed rotation of dials in triple-concentric dial-type "match-the-pointer" or "relative-and-true" bearing indicators. In such instruments, a concentric ring-dial or "bug" dial reads simultaneously against an inner rotating calibrated dial and an outer fixed calibrated dial.

    5. Reversed dial rotation caused by the clockwise "phase" rotation (signal rotation) of some signal windings and the counterclockwise rotation of other windings.

    6. Reversed dial rotation caused by the connection of both rotating-field-and-stator-Y-winding and stator-field-and-rotating Y-winding indicators in the same system.

    Standardization of dial rotation and calibration would permit different manufacturer's units to be interchanged much in the manner which is possible with most motors, generators, or power transformers.

    COMPONENT NAME PLATE MARKINGS The lack of detailed information on circuit name

    plates was another problem which confronted wartime technicians. This was especially true of electronic servomechanism drives in installation, test, and maintenance.

    APRIL 1947 PowellMarking of Electric Equipment 349

  • Whenever operational troubles developed, the lack of full information was often a handicap, especially when detailed data was lacking on the blueprints as well as on the equipment and component name plates. Swift and efficient meter and test equipment checks were made more difficult as a consequence.

    Some of the necessary values usually absent were the ohmic resistance of windings; relative phasing and polarity markings for transformer and saturable-core reactor windings; wattage and accuracy values of resistors; working voltage and.accuracy values of capacitors; and coil current and voltage values and the air-gap contact-point settings for relays. Marking standards might be set up which would require the indication of all pertinent values for circuit components.

    EQUIPMENT WIRING MARKINGS

    Arbitrary and unrelated wiring codes are employed too often for the wiring of most electric equipment. This presents a problem when prints and conversion charts must be referred to continually. Obvious coding systems, which indicate circuits and equipment involved without the need for code charts, are used with considerable success by the military services. A simple type of related coding system is one in which the first letters of major equipment items are prefixed or suffixed to all their allied electric apparatus and wiring in a particular setup.

    Where elaborate installations are involved, an organized and systematic number and letter coding system is advisable for the cables, wiring conductors, and terminal connections at the connection boxes, connector plugs, and control switches. Such practice is typical of military installations because of the need for rapid identification when repair is required following battle damage. In commercial work this is not practical now because of the high initial cost. Consequently only partial marking or no marking at all is done, and subsequent repair and alteration is relatively difficult.

    Where wiring coding is practical, the box, plug, and switch coding numbers might be integrated with the cable numbers. Minor differences in the numbers could indicate the components involved and they could be located easily.

    TERMINAL BLOCK MARKINGS

    Another nonstandardized identification procedure which results in many production difficulties is the marking of instrument wiring terminal-block barriers. The blocks, which may be mounted either vertically or horizontally, may have wire number markings above or below the terminal posts, to either side, to both sides on the same block, split with half the number above and half to the side, or split with half above and half below. Some sort of standard for all wiring terminal-post markings might save production and test man-hours and reduce probability of wiring errors.

    WIRING AND COMPONENT COLOR CODING Ordinarily, color coding is effective under certain

    conditions. However, when applied indiscriminately in involved equipment and wiring applications, it may become a curse instead of a blessing. Similiarly, the color coding of conductors, capacitors, and resistors used in electronic devices results in maintenance and repair problems.

    Careful study of statistics concerning the optical characteristics of the human eye reveals some rather interesting facts. The human eye behaves differently under various lighting conditions, particularly with respect to color sensitivity and evaluation characteristics. To complicate matters further, the percentage of people with subpar vision in the large industrial areas is surprisingly high. The average man does not possess good color sense. In some groups tested, four out of five men actually had some form of color blindness which ranged from slight weakness in one color to total color blindness.

    Women, however, generally appeared to possess unusually good color vision and in some groups tested the reverse ratio was indicatedonly one woman in five was found to have appreciable color blindness of any type.

    The production man does not always work under favorable conditions. It is difficult to concentrate on and evaluate 40 to 60 multicolored cable conductors in the field. This is especially true when workers have walked over them, or handled them with dirty or perspiring hands. Swirling welding fumes, dusty air, dim and yellowish lights, excessive heat and humidity, and crowded working areas aggravate the conditions still further.

    Wartime experiences showed that not much trouble with color codes was experienced on the assembly lines where most of the workers were women working under favorable conditions, and considerable trouble was encountered in the field where men did installation and test work under adverse conditions.

    In the matter of color coding of circuit components such as resistor and capacitor units, somewhat similar problems present themselves. After a component has been handled, knocked about, struck by tools, scorched by hot soldering irons, and operated at normal or above normal temperatures, whatever color code dots and stripes it may originally have had, fade or disappear and leave a miniature mystery. A numerical value rating method, using stamped numbers and letters in the body of the component or attached metal, fiber, or plastic tags might aid identification.

    Cable color coding generally has worked out fairly well in smaller cables with about two dozen or less conductors, but it has presented something of a problem in the larger multiconductor cables where three colors per conductor are involved. The adoption of number

    350 PowellMarking of Electric Equipment ELECTRICAL ENGINEERING

  • and letter codes, or a combination of number and color code systems to decrease the number of colors involved appear to be possible solutions to this circuit and component identification problem.

    BLUEPRINT MARKINGS

    Because the design and drafting sections of industries suffered particularly during World War II from the universal skilled-manpower shortage, management of necessity allowed them to slide by with inadequate blueprints. The importance of detailed blueprints which are understood readily cannot be overemphasized in. modern industry.

    The lack of application of standardization of blueprint symbols has been pointed out by many engineers and technicians in recent years. For example, in a modern military ordnance installation, blueprints using four different types of symbol systems are found. Blueprints for the hydraulic servomechanism power drives use standard power symbols for the motors, controllers, and limit-switch circuits. The fire-control radar blueprints use standard radio symbols. The servomechanism drive blueprints for the light antiaircraft machine-gun cannon mounts use a combination of power and radio symbols. The sound-powered telephone, firing, cease-firing, shell-loading signal lights, and the lighting circuit blueprints use military symbols. Standard drafting room practice as set up by the American Standards Association is not followed very closely. The fact that many organizations are not familiar with established standards cannot be overlooked.

    To a certain extent, the lack of standardization of blueprint type nomenclature also presents a minor problem. The designations for some of the many types of prints used in the electrical and electronic fields (isometric, deck, level-or-floor, general arrangement, elementary, schematic, elementary-schematic, detail, assembly, exploded-view, quarter-section cut-away, and action-flow or functional schematic) apparently differ among industries and some sort of standardization of blueprint type terminology might prove beneficial.

    Another blueprint problem is the lack of sufficient information markings. In elementary (or schematic) blueprints, phasing, voltage ratios, and ohmic resistance values of inductive units; accuracy and wattage ratings of resistors; voltage and accuracy ratings of capacitors; coil resistance, coil current, and contact-point air-gap settings of relays; "multiplication-table" type charts of cold-circuit ohmmeter readings and hot-circuit voltage and current readings at terminal blocks and tube sockets; and so forth, are omitted. In general arrangement, isometric, and deck blueprints, necessary mechanical information concerning installations is often lacking.

    A factor which tends to cause some trouble in handling and identifying blueprints, is the practice of using arbitrary and unrelated number and letter codes for the prints. I t is usually quite practical to apply serial codes which indicate the type of equipment involved and the date when introduced. The military services use with considerable success codes permitting systematic and efficient filing and rapid identification out in the field.

    Printing Electronic Circuits A new method of printing wiring

    and circuit components on an insulated surface, developed by the National Bureau of Standards in co-operation with electronic manufacturers for the tiny generator-powered radio proximity fuse, is applicable in the design of devices where extreme ruggedness and small size are imperative. The principal effect of the printing methods, which include hand spraying and photography, is to reduce electronic circuit wiring to two dimensions. Illustrated is a size comparison between a conventional 2-stage amplifier and a miniature amplifier for use with subminiature tubes. Their characteristics are identical.

    A P R I L 1947 PowellMarking of Electric Equipment 351