Manual / Guide · 1964

How to Use Rotary Stepping Switches

AE handbook on rotary stepping switches (Type 44/45) and circuits.

Author: Automatic Electric Co.
Year: 1964
Type: Manual / Guide
Credit: Internet Archive (archive.org)

$1.45 ROTARY HOW TO USE STEPPING SWITCHES Photographs on the front and back cover are of AE's Type 45 Rotary Stepping Switch Today's rotary stepping switches are the result of decades of service usage and experience. Here, in one book, are the major "DO's" and "DON'T's" of their successful application. wired for hermetic seaJing. AUTOMATIC ELECTRIC Subsidiary 01 GENERAL TELEPHONE & ELECTRONICS C·1057-40M -3· Merit Printed in the U.S.A. GENERAL ~ I I 1-,. HOW TO USE ROTARY STEPPING SWITCHES V. E. JAMES, Editor i· I i ! I ! I' \ 1 ! r • AUTOMATIC ELECTRIC COMPANY II ! I I Ii /. ~~ • Northlake,III;no;s TABLE OF CONTENTS Editor's Preface All rights reserved, including· the right of reproduction in whole or in part, in any form. Copyright, 1964, AUTOMATIC ELECTRIC COMPANY. Published by AUTOMATIC ELECTRIC COMPANY, Northlake, Illinois. First Edition, March 30, 1964. Printed in the United States of America. Printed by MERIT PRINTING CORPORATION. Library of Congress Catalog Card Number: 64-19348 ......................... v I. THIS IS A ROTARY STEPPING SWITCH 1 II. ROTARY STEPPING SWITCH NOMENCLATURE..... Mechanical Components . . . . . . . . . . . . . . . . . . . . . . . . . Types of "Drive" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Direction of Stepping " 5 5 10 12 III. BASIC OPERATING CIRCUITS FOR INDIRECTLY DRIVEN ROTARY STEPPING SWITCHES Pulsed Stepping Self-Interrupted Stepping Considerations of Maximum Circuit-Closure Time " Pulse-Inversion Circuit. . . . . . . . . . . . . . . . . . . . . . . . . .. 15 16 18 19 20 IV. "HOMING" OF ROTARY STEPPING SWITCHES Direct-Drive Indirect-Drive Self-Interrupted Stepping and Homing of the Type 45NC. 22 22 23 25 V. BASIC THINGS YOU CAN DO WITH ROTARY STEPPING SWITCHES. .. .. .. . . .. . . . . Select Indicate Count. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Time Intervals and Pulses . . . . . . . . . . . . . . . . . . . . . . .. Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Monitor Circuit Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. PrograIll Other " 27 27 31 31 35 37 44 50 51 52 VI. POWER REQUIREMENTS OF ROTARY STEPPING SWITCHES. . . . . . . .. .. . . . . ... 58 VII. BASIC THINGS YOU SHOULD NOT ASK ROTARY STEPPING SWITCHES TO DO 61 VIII. SOME COMMONLY ENCOUNTERED APPLICATION PROBLEMS (and how to avoid them) 65 :r I ( \ iii r IX. GUIDE TO PROPER PREVENTATIVE MAINTENANCE Lubrication . . . 71 73 77 81 84 85 86 X. SOME THINGS TO REMEMBER TO DO . 88 EDITOR'S PREFACE XI. SOME THINGS TO REMEMBER TO AVOID . 90 XII. HOW TO DETERMINE IF THE ROTARY STEPPING SWITCH IS THE ANSWER TO YOUR NEEDS . 91 XIII. HOW TO GET WHAT YOU WANT WHEN YOU ORDER 94 The purpose of this small volume is to help the engineer become better informed about rotary stepping switches. Much of the information presented herein has appeared over the years in other places. This is an attempt to gather this information together, combine it with much that has never been previously published, and to present it in one easy-to-use format. We hope that it will serve as a "Primer" to those engineers whose formal education bypassed the study of electromechanical switching devices, and as a "Reference Booh" to those who lmow the rotary stepping switch but who have been led to overlooh (or have forgotten) its versatility, economy, longevity and simplicity. Type 45 Rotary Stepping Switch "Compact" Types Series OCS Relay Mechanical Maintenance Readjusting the Drive Spring Readjusting the Interrupter Contact Springs . . . . XIV. SOME ADDITIONAL CIRCUITS YOU'LL FIND USEFUL Circuits Concerned With Rotary Stepping Switches . 103 Remote impulse control . 103 . 105 Remote switching of groups of impulses Local sequential stepping switch control without relays. 109 Bi-directional decade . 111 Lock pulsing . 112 Remote selection (lout of 100) . 113 Digital Calendar . 118 Circuits Using the Series OCS (cam-switching) Relay . 119 Impulse operation of OCS . 119 Mechanically latched on-off function . 120 Pulse dividing . 121 Binary readout . 122 Decimal-to-binary conversion . 124 Binary-to-decimal conversion . 127 Circuits Using the Codel Relay . 130 Four-bit memory device . 130 Shift register . 133 "Carry" to second register . 135 , r If the rotary stepping switch in its present quite mature form didn't already exist, it would have to be invented and perfected out of economic necessity. This could only come about after the expenditure of much development time and expense, much burning of the "midnight oil", and considerable design refinement. Even then, the resulting product would be quite inferior to today's well "shahen down" and fully-developed product because today's mtary stepping switch profits from decades of service usage, application eXIJerience, and design refinement. The manufacturer of equipment XV. SOLID-STATE CONTROL OF STEPPING RATE OF THE ROTARY STEPPING SWITCH . 137 Index of Illustrations and Circuits Bibliography iv \ . 145 . 152 v I. THIS IS A ROTARY STEPPING SWITCH F R A M E - - - - ·; using these very modern components would then advertise, "This uses rotary stepping switches, with latest model of the resulting economy, simplicity, ruggedness, and reliability". OFF-NORMAL CONTACT SPRING ASS EM. 'DRIVE SPRING It is obvious that any circuit component can be misunderstood, misapplied, and mistreated. That's why, in addition to describing the proper and beneficial ways to use rotary stepping switches, this booh offers many words of caution on improper usage. I wish to express my appreciation to the staff engineers of the Industrial Products Division, Automatic Electric Company, who served as my "Editorial Board": J. D. Ashby, D. A. Dibbern, R. A. Gibson, H. P. Hohberger, G. L. McDermott, L. B. Mitchell, and H. E. Nelson. Weare grateful to our many fine customers whose products are shining examples of how to use rotary stepping switches wisely and well. Thanhs are also due to Joe Kurnich, H. A. Bersted, L. E. Clayton, Howard Bourne, Stanley Kubicz, Jade Lacher and the many others who helped with the manuscript and with the tas7~ of transforming it into booh form. V. E. JAMES La Grange Park, m. February, 1964 vi Ij I ~ OFF-NORMAL CAM WIPER, OF WIPER ASSEM; OR "ROTOR'> I Fig. 1. Automatic, Electric Company's Type 45 Rotary Stepping Switch. This is a rotary stepping switch, as manufactured by Automatic Electric Company. It is a direct descendant of a famous telephone ancestor, the "rotary line switch", used to electrically connect one pair of wires in a dial telephone exchange to another particular pair of wires selected by the mechanical action of the unit from a large group of pairs. This function is accomplished by moving a pair of spring contacts or "wipers" in an arc and into contact with certain stationary "contacts" to which the selected pair of wires is connected. The stationary contacts are assembled in the form of a ''bank'' which may contain 10, 25, or 100 pairs (or sets) of contacts. Each of these stationary contacts in the banI, is permanently connected to two wires that provide an electrical path to a particular group of telephone subscribers, or to a particular subscriber in a group, depending on the location of the rotary line switch in the system. r They are used to switch, select, count, indicate, monitor, time, control, test and program in a wide variety of industrial products and applications. When properly engineered, specified and applied, they can handle situations with severe ambient temperatures, shock and vibration. They are not as sensitive to radiation effects as some other devices now in common use. To understand some of the reasons for this popularity, we must first agree on common definitions. What is a rotary stepping switch? It is more than just a "switch". A switch (elech'ically speaking) is something that causes a change in an electrical circuit. It may be used to turn a light or an appliance on or off, in one of its simplest forms, by closing a circuit ("make"), or by opening a circuit ("break"). In slightly less simple forms it may interrupt one circuit before establishing another ("break-before-make"), or it may establish a new circuit before disrupting the old one ("make-before-break"). - 11 ri 01 In --- Make - Break Break-before-Make Make-before-Break Fig. 2. Nomenclature for basic switch contact forms. It is more than just a "rotary switch". A commonly accepted definition of a rotary switch is a circularly arranged grouping of individual contacts, to which a movable member successively connects as it is rotated. The most common understanding of this designation (outside of the telephone field) is that of a hand operated (rotated) switch such as the station-selection switch on your television set. Consequently, the term "rotary switch" is not generally satisfactory for use in designating an electromagnetically stepped device. 2 t It is more than just a "stepping switch". By mechanically ratcheting a movable contact from one "permanent" contact position or "point" to another, under the actuating power derived from an electromagnet, a vertically-moving "stepping switch" results, as shown below. Today's rotary stepping switches are faster, stronger, and more versatile than any of their telephone ancestors. They must be so, because they have become one of the most widely-used components in indush'ial control, and, as such, must work harder, faster, longer and with closer-spaced consecutive operations than required in telephone exchanges. 1 =£!9 ~ RATCHET 0T. MAG. PAWL I .,.,ru",~ o o o o BANK CONTACTS DETENT Fig. 3. Schematic of "stepping switch" with vertical (up-and-down) motion. What IS a rotary stepping switch, then? It is precisely what its name implies: it rotates, it steps, it switches. More fully, a rotary stepping switch is a mechanism consisting essentially of one or more wiping springs fixed on a shaft moved by a pawl and ratchet which is actuated by an electromagnet in response to momentary pulses of current. At each pulse, the pawl engages the ratchet, moving the wipers (to which circuits are connected) one step forward into contact with stationary terminals to which a selected circuit is connected. (Look at Figure 1, page 1, again.) These stationary terminals are assembled in one unit in the form of a semi-circular (or arc) "bank", and may number up to 250 or more individual contacts. Bank levels, equal in number to pairs of wipers, are separated from each other by an insulating material. 3 A rotary stepping switch performs the same basic switching functions as a "switch" (see Figure 2, page 2). That is, it can "make" or "break" a circuit. It can transfer a circuit with a "break-before-malce" action. In rotary stepping switch nomenclature, this is called "nonbridging" and designated "NB" (see Figure 4C, below). If the transfer action is "make-before-break", it is called "bridging", and designated "Br". 0 000 ''''-0'''''-- : '\ 0 I I ,. 0 DIRECTION OF ROTATION 0 Jlmade". 0 SO 0,;-<2,0'--_ I I~O;--- . ) 0 01 RECTION . OF ROTATION 0 o 00 (A) Circuit to be closed, or 1./ 000 ~/ o o N' 1 0 , 0 DIRECTION OF ROTATION 0 o o ec) Circuit to be transfer- red, or "broken" and then "made" called "nonbridging" transfer. Designated "NB". Mechanical Components The descriptions used in designating rotary stepping switch parts, for re-ordering or for describing as part of a circuit function, are confusing to many. This is because they grew out of telephone practice, but do not represent uniformity even in that area. The rotated contacting member, or "finger tip", is called a wiper. The rotated group of wipers and supporting mechanism, including the ratchet wheel, is called a wiper assembly. (Some call it a "rotor".) (B) Circuit to be opened, or "broken". INDICATOR WHEEL 0 0 DIRECTION 0 81'. q.......OF / 0 ROTATION 1 \ J .-/ OFF-NORMAL CAM LOBE a a a 00 (D) Circuit to be transferred, of a "rna ke·beforebreak" type, called "bridg· ing". Designated "Br". Fig. 4. Schematics of the four basic switching actions of rotary stepping switches. Notice in the above make-before-break schematic (Figure 4D) that the tip of rotatable member (the wiper) is indicated as being of sufficient length to touch the contact moved to, before leaving the contact last rested upon. This additional length of wiper tip is the physical component that gives bridging, or make-before-break, action to rotary stepping switch operation. That is why care must be taken in preparing schematics of bridging levels. The additional designation of "Br." on the schematic is also a recommended practice. 4 II. ROTARY STEPPING SWITCH NOMENCLATURE RATCHET Fig. 5. Typical rotary stepping switch wiper assembly. As discussed in the previous chapter, wipers are of two basic kinds, those which close ("make") the circuit, and those which open ("break") the circuit. The former is by far the most common. There are two lands of wiper tips: bridging and non-bridging, both of which are often supplied on the same wiper assembly (Figure 5). Bridging wipers have long flat tips which, during rota5 tion, permit the wiper to engage the next bank contact before breaking away from the previous contact. Bridging wipers are used when the circuit through them must be continuous and unbroken. Nonbridging wipers have shorter tips that leave one bank contact before engaging the next, avoiding the electrical interconnection between circuits of adjoining bank contacts. The arrangement of contacts in a single arc, each electrically insulated, to which the wiper will be sequentially connected as it rotates, is called a physical bank level, or more simply, a level. The total accumulation of levels into an assembly is called a bank. ~ANK CONTACT i r It is customary at AE to designate the existence of even a single level of ''breal{'' contacts in the banl{ of a rotary stepping switch by adding the suffix "Ne" to the rotary stepping switch Type. Thus "Type 45NC" designates a Type 45 Rotary Stepping Switch with one or more levels of normally-closed bank contacts, regardless of how many other levels of the more common "make" contacts (normally-open) are present on the same rotary stepping switch. TERMINAL SPRING Fig. 6. A physical bank level <Compact rotary stepping switch). .~ 1 Fig. 8. A typical Type 45NC Rotary Stepping Switch. Fig. 7. Typical bank assembly of wiper and bank parts (compact rotary stepping switch). 6 A rotary stepping switch is composed of the following essentials: frame (the "platform" on which all parts are assembled and which is in turn fastened to the chassis of whatever equipment is using it), coil (the electromagnet commonly called the "Motor Magnet" or "MM"), armature assembly (which includes the pawl spring), drive spring, wiper assembly, bank, interrupter contact springs, and offnormal contact springs. The purpose of the interrupter contact springs and off-normal contact springs will be covered in detail later. 7 The Series oes Relay is part switch and part relay. It is built on a ratcheting switch-type mechanism, but operates cams which move contacts to "on" and "off" positions, like the conventional relay. It is largely used to replace mechanical interlock relays. For method of "homing" the Series oes Relay (that is, of restoring it to a normal position at the completion of a switching operation) see Figure 64, page 119. For other suggested uses, see subsequent Figures 65, 66, 67, 68 and 69. The coil or "motor magnet" consists of a coil of wire wOllild on a piece of cylindrical iron called a coil core. In the lliloperated position, the magnetic circuit is completed through the frame, coil core, "armature air gap", and armature. As the armature is attracted (operates), the air gap is reduced to zero, until the armature seats against the end of the coil core. The rotary stepping switch is then said to be operated. The distance through which the armature was attracted from the unoperated position to the operated position is called the armature "stroke". Other details of the rotary stepping switch can be identified from the sketch below: INTERRUPTER CONTACT SPRINGS FRAME DRIVE SPRING SET SCREW BANK ASSEMBLY"WIPER BRUSH SPRINGS CAM POS.T SHAFT SUPPORT BRACKET INDICATING POINTER SHAFT AND HUB BEARING ASSEMBLY LOCKNUT DRIVING SPRING ARMA TURE AND STOP ASSEMBLY WIPER ASSEMBLYRATCHET WHEEL .~ I STOP SPRING DETENT POSITION INDICATOR WHEEL I -; j f Fig. 9. Type 45 Rotary Stepping Switch-assembly details. 8 Fig. 10. Series OCS Relay with 3 cams. 9 Types of "Drive" There are two types of driving mechanisms used in rotary stepping switches: indirect and direct. When the armature-pawl combination acts directly on the ratchet, under the magnetic attraction generated by the electromagnet, the rotary stepping switch is said to be directly driven. When the pawl is caused to act on the ratchet wheel from mechanical force resulting from potential energy stored mechanically in some form of a drive spring, the mechanism is said to be an indirectly driven rotary stepping switch. -, -0 r", r ARMATURE MOTOR MAGNET r I ROTARY ARMATURE ...... I I RELEASE-ARMATURE RESTORING SPRING " \ ROTARY-ARMATURE RESTORING SPRING II I " PAWL RATCHET (PART OF WIPER ASSEMBLY) / / WIPER-ASSEMBLY RESTORING SPRING Fig. 11. Direct drive mechanism. '" , STOPPING TEETH \\ \ III RATCHET DOG _ _ BANK ASSEMBLY ,/.:::.=';;;,', I.' I r-- BANK ASSEMBLY I """---..A~-<-",,-v-o,t::~::ET (PART OF UPPER ASSEMBLY) RATCHET STOP SPRING Such a switch is the AE "Minor Switch". (The "Strowger" twomotion switch is called a "Major Switch" in telephone parlance.) Fig. 13. Indirect drive mechanism. Examples of indirectly driven rotary stepping switches are the Automatic Electric Company Types 45, 40, 44, 80 and 88. The Type 45 is known as a large switch, the Types 40, 44, 80 and 88 as "compact" switches, because of their relative size. The principal parts of a Type 44 rotary stepping switch are used as the basis for Figure 13 above. Fig. 12. The directly driven Minor Switch. 10 It can be proven quite readily that the indn-ectly driven rotary stepping switch is more consistent in performance, has longer life, is more efficient and is capable of faster stepping than the directly driven rotary stepping switch. However, that is not the purpose of this book, and the subject is covered fully in AE Sales Circular 1641. 11 from the farthest point (by forward stepping) to the starting position. On the Type 45 (26 position) rotary stepping switch, this becomes about .430 seconds (430 milliseconds), and for a Type 45 (52 position) this becomes about .870 seconds (870 milliseconds). This is s?mething to be kept in mind when designing circuits, and can be sunply restated: No switch is as fast in restoring from a "farthest point" as a Minor Switch, with its single step "flyback" or release to the .home position. In every other respect than this, the advantages are WIth the unidirectional, spring driven, indirect drive type of steppers. Direction of Stepping Rotary stepping switches are classed either as unidirectional or dual-directional. Dual-directional is sometimes designated as "aroundand-return" or as "bidirectional". Unidirectional rotary stepping switches step in one direction only. Wipers are so arranged that, when all bank contacts have been traversed, the mechanism is in its reset or "normal" position. Such a rotary stepping switch must be stepped to its normal position after each use. Dual-directional rotary stepping switches step in one direction to the selected contact. "\iVhen the selected circuit is no longer needed, the switch is reset by operation of a release magnet which returns the wipers to the normal position along a path which is opposite to the direction in which the original stepping took place. AE rotary stepping switches of both the "full size" (Type 45) and the "compact size" (Types 40, 44, 80, and 88) are all unidirectional. The "Minor Switch", and some other AE rotary stepping switches, are of the dual-directional types. Dual-directional, two coil * springreleased types of switches have one large advantage over the other types: the release step is just one large step (release armature operation) from wherever the switch is positioned in a reverse direction back to the staJ:ting point. This action is very fast (about 80 milliseconds, maximum, for an eleven position Minor Switch) and provides a time advantage over any other method of resetting to the starting point. The maximum attainable self-interrupted stepping rate of the unidirectional rotary stepping switches is somewhere around 60 steps per second under ideal conditions. This means that an II point switch (Type 44), equivalent in capacity to the Minor Switch in number of points or bank positions, would require about 11/60 of a second, or approximately .180 seconds (I80 milliseconds) to restore :'One coil steps the switch forward. The other coil (when energized at a different time) removes a holding detent from the ratchet wheel, causing the switch rotor to "fly" bac7? to the home, or normal position, from the force of the tensioned restoring spring. 12 Schematically, the dual-directional Minor Switch can be pictured as operating in this manner: RELEASE MAGNET ~ RELEASE ARM. RESTORING SPRING (LEAF TYPE) . o o o oo . . .I - - _C:..;.O:..;.N;..:TACTS ROTARY , .~ ~' o PAWL o o I o o I I r '~ WIPER ASSEM. RESTORING ARMATURE RESTORING (LEAF SPRING SPRING TYPE) Fig. 14. Schematic of Minor Switch. 13 In Figure 14, the switch moves one tooth notch each time the rotary magnet is energized, and is held in this position by the detent of the release magnet armature when the rotary armature re-positions at the end of the energized period of the rotary armature. Successive steps take place in the same manner. When the release magnet is energized, the detent is removed from the holding position and the rotor returns to its home position (against the stop) from the force of the restoring spring. The same kind of a picture presentation can be made for the unidirectional rotary stepping switch: III. BASIC OPERATING CIRCUITS FOR INDIRECTLY DRIVEN ROTARY STEPPING SWITCHES There are basically two ways of stepping an indirectly driven rotary stepping switch: pulsed and self-interrupted. II'~RATE .... ...------- >---1 ~RJ:l----4li--I I H II lMPULSINC DEVICE'. VAR. Fig. 16. Basic circuit for a rotary stepping switch. * ~ ~ TO CIRCUlrs TO BE CONTROLLED Fig. 15. Schematic diagram of pulse-controlled operation, unidirectional rotary stepping switch. Each time the Motor Magnet is energized, the armature is attracted against the tension of the driving spring, and the pawl slips over the adjacent tooth. 'When the Motor Magnet is de-energized, tlle driving spring pushes the armature pawl against the ratchet tooth it rests upon and moves the wiper assembly the prescribed distance, carrying the wipers forward to the next bank contact. The detent prevents movement in the unwanted direction while the armature is being attracted to the "cocked" position. The wiper is always moved in the same rotary direction in successive steps. 14 When a circuit of proper voltage and power capabilities is closed to the motor magnet coil of the indirectly driven rotary stepping switch, the armature is attracted and held in the "cocked" position. (See also Figure 15.) When tlle coil circuit is de-energized, the potential energy stored in tlle drive spring pushes the pawl against the associated ratchet wheel tooth, causing the wiper assembly to take a step. A set of stopping teeth engages the ratchet wheel about one-half the way down, securely preventing overthrow of the wiper assembly, and accurately positioning the wipers on the banks without strain on the pawl. The illustrations in Figure 17, page 16, show how the armature "stopping" teeth mesh with the ratchet wheel during one cycle of operation. Repetitive pulses (circuit closures) will cause the switch to take as many steps as tlle number of discrete pulses received. >(- A varistor is shown for contact protection in Figure 1 6. A capacitorresistor net is equally effective, and will be indicated in most of the subsequent figures. 15 It will also be noted that the pulse rate versus the per cent make relationships become more critical as the pulse speed increases. In ot~er words, the per cent make latitude to which the rotary stepping sWItch can accommodate narrows with pulse rate increase. Average Characteristic -i' Motor magnet operate time Motor magnet release time Maximum theoretical impulse speed Minor Switch Type 44 Type 45 16 ms 11 ms 16 ms 3 ms 18 ms 5 ms 35.5 pps 53 pps 43.5 pps Fig. 18. Maximum theoretical impulse speeds. If the switch is being pulsed from a cam or controllable pulse generator, the ideal per cent mal,e is indicated in Figure 19 by the dashed line through the pulse envelope and should be held closer to the top line than the bottom. All of this applies to an "externally pulsed" switch and does not enter directly into the capabilities of a switch being driven "self-interruptedly". Fig. 17. Pawl and "stopping" teeth action. Pulsed Stepping The length of time the circuit is closed (and opened) in a series of fast pulses is very important. To be effective, a pulse to the switch must consist of an "on" time interval (coil current flowing) long enough to fully attract the armature into a "cocked" position, storing potential energy in the drive spring while doing so. The "off" time interval must be adequate for the drive spring to move the armature, and associated wiper assembly to the next bank contact position (Figure 18). For a series of nearly constant speed pulses this can be expressed as "per cent make" (closed circuit) and "per cent break" (open circuit) as related to the overall span of a single pulse. At ten pulses per second pulsing rate, a "per cent make" of 80 % and a "per cent break" of 20 % would represent a pulse "on" time of 80 milliseconds and a pulse "off" time of 20 milliseconds. At a pulsing speed twice as fast (20 pulses per second), the respective per cent make and break intervals would be 40 milliseconds and 10 milliseconds. From the following table and the average "per cent make" curves, it will be seen that the switch must neither be starved (given too short a pulse) nor kept energized too long (given too long a pulse), if the desired speed response is to be obtained. 16 o o "... f- o f-~ 0. -- -- ..... -- _.. -- o co -- -- -- -- IDEAL PULSE o " w '" 0 <'" :;: I [' I I tI >- / 0 ,y zw "' U .0 Fig. 19. Typical pulse range curves. 'l' ~ ~ / o v/ M o N ? 1.-0- '/ _ _ COMPACT SWITCHES & SERIES OCS RELAY I/. ;.r - f - TYPE 45 ROTARY SW. I I I I I I 5 10 15 20 25 30 35 I I I I 40 45 PULSES PER SECOND 17 Self-Interrupted Stepping Considerations of Maximum Circuit-Closure Time Self-interrupted operation is used to step the switch rapidly from one point to another without use of discrete pulses from outside the switch. Under self-interrupted operation, a circuit is closed to the coil through its own interrupter contact springs. When the coil is energized, the armature is attracted in the usual way, but before fully seating on the coil core it is caused to open its own circuit, de-energizing itself. This causes the armature to fall away, driving the wiper assembly one step, but as it does so the interrupter contacts are caused to reclose. The armature is again attracted, re-cocking the switch and causing re-opening of the interrupter contacts. Thus the switch is made to run "self-interruptedly" until the circuit is opened permanently, by opening of tlle circuit at the off-normal springs, or at a bank level being used to furnish the self-interrupting potential. Examples of both kinds of circuits follow later on in this book. Rotary stepping switch coils, operating at tlle voltage for which they were designed, will stand continuous pulsing indefinitely. Use of a Limiting Resistor -f: (EXTERN ALl) - - Fig. 20. Schematic diagram of self-interrupted operation, unidirectional rotary stepping switch. 18 SPGS. I L \ T (EXTERNAL) ...I ,- - - - -- - - - t . I II STEP SWITCH II L '-- r-• I ..J --1 I FF-NORMAL SPRINGS Fig. 21. Current-limiting resistor for long pulse duration, to avoid overheating coil. Please note: Switches "doffed in" are external to the stepping switch and are controlled manually, or otherwise not associated with the switch mechanism. When the rotary stepping switch in Figure 21 is completely actuated, the current-limiting resistor is inserted in series with the rotary stepping switch coil (because a short is removed from the limiting resistor by operation of the interrupter springs-"INT. SPGS"). In this condition the power consumed is reduced to a point where the wattage dissipated by the switch coil is of a non-damaging value. Opening the "step" external control contacts will cause tlle switch to be de-energized and advance one step. The interrupter contacts, when they reclose on tllis release, again short the limiting resistor for the successive step, if any. As depicted, tlle current-limiting resistor is not in effect when the switch is stepping self-interruptedly. CONTACTS TO CIRCUITS TO BE CONTROLLED '---<>--,- INT. ~I SWITCH Self-interrupted operation of the switch is sometimes referred to as "buzzing", or "door-bell" operation. For schematic representation, see Figure 20, below. ~ VAR. LIMITING RESISTOR , ~ When coils are to be held energized for long periods of time, a limiting resistance should be inserted in series with the coil. f l J The limiting resistor used in a circuit of this type must, of course, be of sufficient wattage (about 10 watts capability) to operate in a relatively cool condition and must not be of high enough resistance to reduce tlle total circuit (coil) current to less than one-third of the normal current which tlle rotary stepping switch would otherwise draw. 19 Explanation of "Homing" in Figure 21 A It happens that Figure 21 can also be used to show the homing technique for indirectly driven stepping switches using interrupter and off-normal contact springs. In Figure 21, the contacts in tlle circuit identified as "home" are presumed to be on some remote relay or manually operated device, by means of which the circuit indicates whether the switch is to take individual steps (or self-interrupted steps) to drive the switch to the home or normal position. With the "home" contacts in tlle position depicted, closure of the "step" contacts provides a circuit to the rotary stepping switch motor magnet as described under "Use of a Limiting Resistor". When the "home" contacts are in the position other than pictured in Figure 21, and the stepping switch is off-normal, a circuit is closed from tlle stepping switch off-normal contact springs through the "home" contact, and the interrupter contact springs of the stepping switch to the motor magnet of the stepping switch. The stepping switch will operate in a self-interrupted manner until such time as the off-normal contact springs transfer to the position shown in the sketch. At this point self-interrupted motion stops. The switch is "home", or at normal. Pulse-Inversion Circuit for Direct Drive In some cases it is a must that the stepping switch move to the next bank position on pulse initiation. To make an indirectly driven stepping switch do this (circuit-wise like a Minor Switch), a relay is introduced into the circuit, as shown in Figure 22. IMPULSING DEVI CE INT. SPGS MOT. MAG. Fig. 22. Pulse-inversion circuit for rotary stepping switch "direct drive," to step switch on pulse closure. remains operated until the contacts of the impulsing device open ... When these contacts do open, Relay A restores and reconnects the rotary stepping switch motor magnet to the impulsing lead. The next closure of tlle contacts of the impulsing device will cause the circuit operation described above to be repeated. Closure of the impulsing device's contacts provides the circuit to the motor magnet of the rotary stepping switch. The stepping switch energizes, and when its armature is completely operated, the interrupter springs will close the circUit to the coil of Relay A. Relay A operates and, by means of its make-before-break contacts, locks itself to the pulse and opens the circuit to the rotary stepping switch motor magnet. The rotary stepping switch is de-energized immediately and restores to the unoperated condition, advancing the wipers one step. When the rotary stepping switch is intlle de-energized position, the interrupter springs open the operating circuit for Relay A. Relay A 20 21 IV. "HOMING" OF ROTARY STEPPING SWITCHES Homing of the Indirectly Driven Rotary Stepping Switch Rotary stepping switches usually incorporate facilities which, through various arrangements, will cause the wipers to restore to a normal position at the completion of a switching operation. This is called homing, and may be done in two ways on indirectly. driven rotary stepping switches, and by the integral design of directly driven rotary stepping switches. C HOMING LEVEL C OTHER LEVELS )0: INT. CONTACT SPGS. o 60 0 N Homing of the Directly Driven Minor Switch ROT. A o HOMING LEAD T r·-, I OPERATE RLS. I --I 1-I I I I L_-l B (SHOWN OPERAIED) OFF- NORMAL SPGS. Fig. 23. Restoring Minor Switch to normal. The release facility of the Minor Switch is an integral part of the switch design and no optional method exists. The circuit of the release coil (Figure 23) is prepared through the off-normal springs when the wipers are stepped off the home position. The wipers are stepped against tlle pull of the homing spring; a detent on tlle ratchet dog holds them in position against this pull. When the switching circuit is released, Relays A and B restore, and ground, through the now-closed off-normal springs, energizes the release magnet (RLS.). The release armature operates and witlldraws the ratchet dog from the ratchet, causing the coil spring to pull the wipers to their home position. When the wipers reach the home position, the off-normal springs open and remove ground from the release magnet. 22 Fig. 24. Restoring an indirectly driven rotary stepping switch to normal by means of a wired switch level. Figure 24 illustrates tlle method of restoring an indirectly driven rotary stepping switch to its home position by means of a wired bank level. All bank contacts of one level, except the home position, are strapped and wired to a homing lead. A bridging wiper is associated Witll. this level and ~s connected to the motor magnet (MM) through tlle mterrupter sprmgs. Upon completion of a switchino- operation via the operate lead, the wipers will be resting on ba~k contac~ ot~ler ~an. the home. position. Relay B, which was operated during tIlls sWItchmg operation, releases and grounds the wired contacts of ~he homing lev.el. This ground is extended, through the wiper and Il1terrupteI~ sprm~s, to the motor magnet as long as the wiper is en~aged WItl: a wIred contact. Thus, the motor magnet will step the sWItch, se!f-mterruptedly, until its wipers reach the home position (tlle unwIred contact number 11 in Figure 24). 23 , i I \ ,r SPARK SUPPRESSOR r-wvv---il l Self-Interrupted Stepping and Homing of the Type 45NC Rotary Stepping Switch LEVEL OF NORMALLY ~CTSr \ EX_TE_RNAL SWITCH , II I ~ /'" OPERATE INt HOMING OFF- A o CONTACT SPGS. NORMAL SPGS. Fig. 25. Restoring an indirectly driven rotary stepping switch to normal by means of off-normal springs. The motor magnet (MM) in Figure 25 is connected through the interrupter springs and off-normal springs to a homing circuit. This circuit can be under the control of a relay, such as Relay A, which is held operated during the switching procedure. The off-normal springs close when the switch wipers step off the home position to prepare a circuit to the motor magnet coil. The release of the operate circuit releases Relay A which grounds the homing circuit to magnet coil MM. Motor magnet MM now steps the wipers self-interruptedly to the home position. At this point the off-normal springs open and remove ground from motor magnet MM. The switch remains in its home position. 24 ~, MOT. MAG. INT. SPGS. "t:= •.- ---.J Fig. 26. Homing by means of a normally-closed level. When equipped w!th at l~ast one "nonnally-closed" level, the Type 45N? Rotary Steppmg SWItch can be stepped self-interruptedly to ~ deSIred. c~ntact, or homed, without the use of relays (thus eliminatmg the timing prob!ems inherent in that method of homing). Figure 26 shows schematically how this is accomplished. Besides savinothe cost of an associated relay, the wiring costs are reduced sinc~ potentials need not be connected to unwanted positions (as is r:quired for nOl~ally-open contact levels used for this kind of an application). In FI~re 26, the closure of switch "X' will cause the switch to ~:un s:l£~~te~rupte~y to this point, then stop. Also, closure of the hommg sWItch WIll cause the switch to run self-interruptedly to the home position, and then stop. Homing of the Series oes Relay Homing of the cam-switching Series oes Relay is discussed fully on page 119. 25 v. BASIC THINGS YOU CAN DO WITH ROTARY STEPPING SWITCHES To make use of rotary stepping switches we must analyze what they can do for us. As its name indicates, the rotary stepping switch is used to close circuits, open circuits, and transfer circuits. Therefore, the broadest category of what it can do is switch. This can be pinned down to eight broad functions: select, indicate, count} time intervals and pulses} control} monitor} test and program. A. Select Courtesy of elECTRONICS WORLD. Since rotary stepping switches take one step for each incoming pulse, they can be used to select any specific contact point in the bank of contact points. This can be done under manual control, or automatically. If, for example, with the wipers standing in the "home" position, five inlpulses are sent to the motor magnet, the wipers will end up in bank contact position No.5. In this position, as many functions can be performed through the wiper circuits as there are bank contact levels being contacted. A typical circuit of this type, operating under control of a dial, is given on the next page. 26 27 II''''' Dial Selection Selecting a Circuit, Absence-of-Potential Searching VAR. D I MPULS;;;;.E_ _..... LEAD j MOT. HI'Ii MAG. INT. '---<0--....,. CON TACT SPGS. ! II °0 o o o o o o 00 ; Fig. 27. Wiper disconnect circuit during stepping, to avoid energizing circuits wiped over. NOTE: Relay D must have a vendor-chosen Jow-resistance coil. . In this circuit the select lead is held open during the series of pulses (by slow-to-release Relay D) until the wiper has reached the desiJ:ed contact, after which Relay D restores to establish the chosen circuit(s). The wiper circuit(s) is (are) held open during stepping to avoid maldng undesired connections. Caution Relay D must be engineered to have an operate time equal to or less than the operate time of the rotary stepping switch and must have a release time slightly longer than the release time of tlle rotary stepping switch. Using telephone-type relays such as AE's Class A and B relays, it is suggested that tlle Series ASR or BSR type of relay be used with an 11/16" long copper slug for impulse rates of approximately 10 pulses per second (telephone dial speed). 28 KEY 1[ START GROUND -=- Fig. 28. Self-interrupted searching for absence-of-potential (ground). The arrangement shown in Figure 28 searches for