Manual / Guide · 1964

TR-20 Computer Operator's Reference Handbook

This handbook serves as an operator reference guide for the EAI TR-20 desktop analog computer, covering operating considerations, computing components, and patching procedures. It describes the operational amplifier, attenuators, quarter-square multiplier, diode function generators, variable diode function generators, signal comparators, function switches, and repetitive operation mode. Appendices provide computer symbols, circuits using computational components, amplifier circuits for simulating transfer functions, and a bibliography.

Manufacturer: EAI
System: TR-20
Year: 1964
Type: Manual / Guide
Language: English
Learning track: machine reference
Pages: 96
Credit: Copyright Electronic Associates, Inc. 1964. Publ. No. D800 2003 0A.

TR-20
EAI
operator reference
patching and programming
computing components
analog simulation

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TR-20 COMPUTER OPERATOR'S REFERENCE HANDBOOK Publ, No. D800 2003 OA ELECTRONIC ASSOCIATES INC. 8 LONG BRANCH, NEW JERSEY ® ELECTRONIC ASSOCIATES, INC. Long Branch, New Jersey TR-20 COMPUTER OPERATOR'S REFERENCE HANDBOOK Publ, No, D800 2003 OA © ELECTRONIC ASSOCIATES, ING. 1064 ALL RIGHTS RESERVED PRINTED IN U,B.A, September 1964 NOTICE In order to enable us to process your requests for spare parts and replacement items quickly and efficiently, we request your conformance with the following procedure: 1. Please specify the type number and serial number of the basic unit as well as the identification of the part when inquiring about replace- ment items as potentiometer assemblies or cups, relays, transformers, precision resistors, etc. Qe When inquiring about items as servo multipliers, resolvers, networks, cables, potentiometer expansions, etc., please specify the serial num- bers of the major equipment with which the units are to be used, such as: Console Type 231R, Amplifier Group Type 4.028, serial #000, etc. If at all possible, please include the purchase order or the EAI project number under which the equipment was originally procured, Your cooperation in supplying the required information will facilitate the processing of your requests and aid in assuring that the correct items are supplied. It is the policy of Electronic Associates, Inc. to supply equibment patterned as closely as possible to the indi- vidual requirements of the individual customer. This is accomplished, without incurring the prohibitive costs of custom design, by substituting new components, modifying standard components, etc., wherever necessary to expedite conformance with requirements. As a vesult, this instruction manual, which has basically been writ- ton to cover standard equipment, may not entirely concur in its content with the equipment supplied, It is felt, however, that a technically qualified person will find the manual a fully adequate guide in understanding, oper- ating, and maintaining the equipment actually supplied, Electronic Associates, Inc. reserves the right to make changes in design, or to make additions to or improve- ments in its product without imposing any obligation upon itself to install them on products previously manufac- tured. Printed in U.S.A. M226 EASTERN REGIONAL OFFICE Long Branch, New Jersey Telephone: Area Code 201 229-1100 TWX-LG BR 201-222-2795 Cable-PACE Long Branch, N.J. N.Y, DISTRICT OFFICE 111 Main Street P.O. Box 218 North Syracuse, N.Y. Telephone: Area Code 315 GL8-2188 SOUTHWESTERN REGIONAL OFFICE 108 Prentice Bldg. Dallas 6, Texas Telephone: Area Code 214. EMerson 1-6165 EUROPEAN CONTINENTAL REGIONAL OFFICE SOUTHEASTERN DISTRICT OFFICE Centre Intemational, 22nd Floor Place Rogier, Brussels 1, Belgium Cable: PACEBELG Brussels Telephone: Brussels 18-40-04 Telex: 2.21-106 SALES OFFICES R&D& SPECIAL PRODUCT SALES Long Branch, New Jersey Telephone: Area Code 201 229-1100 TWX-LG BR 201-222-2795 Cable-PACE Long Branch, N.J. NORTHEAST DISTRICT OFFICE 711 Main Street Waltham, Massachusetts Telephone: Area Code 617 TWinbrook 9-0420 WESTERN REGIONAL OFFICE 1500 East Imperial Highway El Segundo, California Telephone: Area Code 213 EAstgate 2-3124 TWX 213-322-2144 7902 Old Georgetown Road Bethesda 14, Maryland Telephone: Area Code 301 652-3625 652-3626 UK & SCANDINAVIAN REGIONAL OFFICE Electronic Associates, Lid. Burgess Hill Sussex, England Telephone: Burgess Hill (Sussex) 5101-5 Cable-LON PACE Telex: 87183 EAI-ELECTRONIC ASSOCIATES SARL 11, rue du Faubourg Poissonniere, Paris 9, France Telephone: PRO 93-69 MANUFACTURING PLANTS ELECTRONIC ASSOCIATES, INC. Manufacturing Division Long Branch, New Jersey EAL COMPUTATION CENTER AT LOS ANGELES, INC. 1500 East Imperial Highway El Segundo, California Telephone: Area Code 213 EAstgate 2~3220 EAI RESEARCH AND COMPUTATION DIVISION Integrated Controls Department 4151 Middlefield Road Palo Alto, California M226a-3 ELECTRONIC ASSOCIATES, LTD. Burgess Hill Sussex, England COMPUTATION CENTERS UK COMPUTATION CENTER Electronic Associates, Ltd. Burgess Hill Sussex, England Telephone: Burgess Hill (Sussex) 5101-5 Cable ~ LONPACE Telex: 87183 PRINCETON COMPUTATION CENTER P.O. Box 582 CUSTOMER SERVICE Princeton, New Jersey Telephone: Area Code 609 WAlnut 4-2900 PARTS SALES Long Branch, New Jersey Telephone: Area Code 201 229-1100 TWX-LG BR 201-222-2795 Cable-PACE Long Branch, N.J. CENTRAL REGIONAL OFFICE 101 South Pine Street Mount Prospect, Illinois Telephone: Area Code 312 CLearbrook 5-6070 TWX-ARL HTS 3315 SAN FRANCISCO DISTRICT OFFICE 4151 Middlefield Road Palo Alto, California Telephone: Area Code 415 321-0363 TWX: 415 492-9211 EAI-ELECTRONIC ASSOCIATES GMBH Martinstrasse, 14 Aachen, W. Germany Telephone: 26041 AUSTRALIAN REGIONAL OFFICE EAI-Electronic Associates, Pty., Ltd. 87 Alexander Street Crows Nest Sydney, N.S.W. Australia Telephone: 43-1557 Cable-PACEAUS, Sydney SERVICE ENGINEERING Long Branch, New Jersey Telephone; Area Code 201 2291100 TWX-LG BR 201-222-2795 Cable-PACE Long Branch, N.J. EUROPEAN COMPUTATION CENTER Centre International, 22nd Floor Place Rogier, Brussels 1, Belgium Cable: PACEBELG Brmssels Telephone: Brussels 18-40-04 Telex: 2.21-106 CHAPTER I CHAPTER IT CONTENTS INTRODUCTION THE TR-20 COMPUTER AND COMPUTING COMPONENTS 1, 2, GENERAL DESCRIPTION este eveaeceoos oseeaseeee eee bGeae saa o 6 OPERATING CONS IDERATIONS oo beooCHRHet HHO KRCHSeE SHEE O HORSE ES a. Insertion or the Pre-Patch Panel ......ssceeeaee b, Feedback for the Amplifiers ....ccescoereecsoece c, Application of Power ..ccscccsssesescevceccseces d. Amplifier Balance .......... see e ccc ee cnc cncacees @, Overloads .rcsincscccsncccccsscrcsscesscscvences READOUT FACILITIES AND MANUAL MODE CONTROLS ........ a, Readout Facilities ... ccc cesses eccerccscccscnves b, Manual Mode Control ....cecccrsececscersoersaees ATTENUATORS eeeoeeos aes sees se csevuvueseoesoeseoe dee eonsee nose THE OPERATIONAL AMPLIFIER ...ccecesceesceveecves see a. General Considerations ...csccccscescccccucvccee b, Inversion .eccsecvcrcccccnscsscecevvestsevvesess c, Multiplication by a Constant .....cceccceccccees G, Summation .oicicecccsocccccevensccsccecesseetees é. Integration with Respect to Time ......... veaaes £, Other Mathematical OperationS .,..cceccececesene g. Patching the Amplifier as a Summer/Inverter .... h, Patching the Amplifier as an Integrator .....+¢. 12 12 13 15 16 17 17 19 19 21 21 21 22 22 ii 10, QUARTER-SQUARE MULTIPLIER ......ecceees [> b. [a CONTENTS (Cont) General Description ......cccnecs Multiplication ...cccucecccrceecs Division ..ccccsvesecrreceerceees x2 DIODE FUNCTION GENERATOR @eeeeeoeareoeseocvreooeeseneoeoeobeas ° [ b, fo General Description ...... se ccosenes Generating the Square of an Input Voltage (Single Polarity) ....cceeeees sect eeeee eeeeeeoeereaneeceaeoeaose Generating the Square of an Input Voltage (Bi-Polar). LOG X DFG AND 1/2 LOG X DFG beoocoeonorneveseescesv oe oeeeoeraese a, b, General Description ......ccc0ee : Patching wrvesscecscucsccscacvcnes e@eaoeooneoeas eaceoeootone eooeoeceerseoeeneopeseve VARIABLE DIODE FUNCTION GENERATOR GROUPS 2,645 AND 2,713. a. lo Cc. d, General Description ..scccovsess eoocoececocensoueevoovere Setup Procedure (Fixed Breakpoint VDFG's) ...csesuees Setup Procedure (Variable Breakpoint VDFG's) ........ Paralleling Fixed Breakpoint VDFG'sS .......cceeeees we SIGNAL COMPARATORS AND FUNCTION SWITCHES .....ccccsoeoeces [@ |o {fo Relay Comparator ,roseveresececes eeoceoseseeoeceeooer eos Electronic Comparator ....... se seevcce Dual Function Switch Group 2,127 epeseeteceooeseoee he ane oes 26 26 26 26 28 28 29 29 29 29 32 32 32 34 34 4.6 47 47 47 50 APPENDIX APPENDIX APPENDIX APPENDIX ll. Ir IIL Iv CONTENTS (Cont) REPETITIVE OPERATION eae bao Gb bbb KE HG oO RBH OEE HHS a. General Description ...sevcosevencecvcencvvevssesr b, Using Repetitive Operation .........cc cee ees ae COMPUTER SYMBOLS . CIRCUITS USING COMPUTATIONAL COMPONENTS .......0.0. aoe AMPLIFIER CIRCUITS FOR SIMULATING TRANSFER FUNCTIONS BIBLIOGRAPHY ....... BEEF ESTE OHO HOAs ee wD eee sooe eseoee 54 AI-1 AII-1 AIII-1 AIV-1 iii/iv Figure Number 10. ll, 12, 13, 14, 15. 16, 16a, 17. 18, 19, 20, ILLUSTRATIONS Title The TR-20 Desktop Analog Computer with Display Units ., Inserting the Pre-Patch Panel eesestbeeveseetcacszaeeeescee ee as The 6,712 Dual DC Amplifier, Showing Use of Bottle PLUGS secccccescveccveveccversccesvcecsecvesccesecccs The TRe20 Control Panel ...cccccccsccccvcccccscvscccece Readout Circuit, Simplified Schematics ...ccccccccscees An Attenuator .eccocccccccnvccccccsvccscccessecsccerees Schematics and Symbols for Attenuators ...coccoeccecces Operational Amplifier, Simplified Block Diagram ....... Patching an Amplifier as an Integrator, Showing Simplified Schematic of an Integrator Network ...... Patching an Amplifier to a Rep-Op Integrator, Showing Simplified Schematic of Integrator Network... Division Circuit for a Quarter-Square Multiplier ...... 2 X DFG Patching BeRCHBTOCHECHHBEHOCESHHTHEBEOCHOK HOHE TOE ROES x2 Generating + 10 for -10 < X < +10 eeeeeveeeesoceeon eee ees Patching the Log X DFG'S .csceccccccscescveccesscosecce VDFG Mounting LocationS ,,..cccccosscscccscsrevcceccons FVDFG Patching ..ccccccccccccrccccvcvesevrersevesvecees Sample Function and Setup Information ....ccccctcacvees Breakpoint Setup Patching ..ccocccscccsvecccrccecvececs + Variable Breakpoint Diode Function Generator Sample Curves eeveceeoeoeo oe sone eeeceeoeeoeeonoeaeeeoeeoeeees _ Breakpoint Location Plot Patching ...ccscacossscccccsons Page 10 11 14 18 18 20 23 25 27 30 30 31 32 33 35 36 38 40 42 Figure Number 21. 22. 23, 24. 25. vi ILLUSTRATIONS (Cont) Function Setup Patching .........000. eee ceeaneeaee Relay Comparator, Simplified Diagrams and Setup Patching ...cecceceseens co eeeeees eee eee ese veseeens 40.538 Electronic Comparator Unit ..ccecccesaseseece Comparator Unit, Functional Block Diagram .......e0. Electronic Switch Unit, Functional Block Diagram ... 48 49 51 52 ea ee ee [E Al fe CHAPTER I INTRODUCTION Many problems encountered in scientific or engineering work involve mathematical equations or sets of equations whose solution in most cases is difficult or practi- cally impossible to obtain by the classical approach to equation solution, The TR-20 Analog Computer provides the technical worker with a general purpose computer which permits the rapid solution of linear or non-linear equations, Although the analog machine is correctly termed a computer, it does not perform its computations by serial calculations as does the desk calculator or digital computer. Instead it performs the required mathematical operations in a parallel manner on con- tinuous variables. In the TR-20, as in most modern analog computers, the continuous variables are direct current voltages, The electronic analog computer makes it pos- sible to build an electrical model of a physical system, where the voltages on the computer represent the dependent variables of the physical system, Except for a constant of proportionality, or scale factor, each voltage will behave with time in a manner similar to the physical system variable, Thus, if the vertical position of the center of gravity of an automobile oscillates with time during a disturbance, then the voltage representing the height of the center of gravity above the surface will also oscillate; if the temperature of the coolant at the exhaust port of a con- denser rises exponentially to a steady value, then so will the voltage representing it on the computer, It can be said that the actual system and the electrical model are analogous in that the variables which demonstrate their characteristics are described by relations which are mathematically equivalent, The actual system has thus been simulated because of the similarity of operation of the electrical model and the physical system, This capability of the analog computer is of great value in performing scientific research or engineering design calculations because it permits an in- sight into the relationship between the mathematical equations and the response of the physical system, Once the electrical model is completed, well-controlled experiments can be performed quickly, inexpensively, and with great flexibility to predict the behavior of the primary physical system. Although the analog computer utilizes electronic components in its operation, it is not essential that the user have an extensive knowledge of electrical circuits. The TR-20 is basically a set of mathematical building blocks, each able to perform specific mathematical operations on direct voltages and capable of being easily interconnected, By appropriately interconnecting these building blocks, an elec- trical model is produced in which the voltages at the outputs of the blocks obey the relations given in the mathematical description of a physical problem, Since our interest is frequently in the dynamic behavior of physical systems, the mathematical equations are usually differential equations having time as the in- dependent variable. In order to solve such equations, the standard components of the computer must perform the following operations: inversion, algebraic summation, integration with respect to time, multiplication and division, and function generation, | fee ee The sequence of steps for constructing a dynamic model on an analog computer requires first a mathematical description of the physical system, usually in equation form, From this description the operator derives the information necessary to set up a computer program for interconnecting the computing components and determines the required initial conditions and forcing functions, The computing components are interconnected with wires called patch cords, The input and output terminations of the computing components are brought out to a patch bay which is usually fitted with a removable Pre-Patch Panel so that patching may be accomplished away from the com- puter. The problem is placed on the computer by inserting the patch panel and ad- justing the problem parameters to the value of the first case to be investigated, Selected voltages are applied to various components in the form of inputs or initial conditions, These voltages are derived from a precise reference voltage, Once the computing elements have been patched, adjusted, and energized, the computer is switched into the operate mode, The voltages on the computer change with time in accordance with the equations that govern the physical system variables. The be- havior of the computer model is viewed through an output device such as an X-Y plotter, oscilloscope, strip-chart recorder, or digital voltmeter, This TR-20 Reference Handbook has been prepared to serve as a working guide to the analog programmer or computer operator, The information contained presupposes a knowledge of the analog computer, its basic principles of operation, and programming procedures, (Instructional information in these areas can be obtained from "Basics of Analog Computer Programming" by the EAI Education and Training Group.) Reaaers interested in more detailed circuit information are referred to the TR-20 Maintenance Manual, CHAPTER IT THE TR-20 COMPUTER AND COMPUTING COMPONENTS 1, GENERAL DESCRIPTION The PACE® TR-20 (Figure 1) is a general purpose analog computer composed of solid- state computing components, The TR-20 is compact in size and is able to operate with stability and precision in a normal office or classroom environment, Reliable, with simplicity in functional design, the TR-20 is easy to use and can be a powerful aid to the individual engineer in the rapid solution of scientific and engineering prob- lems, Table I lists the currently available computing components and accessories for the TR-20, The TR-20 utilizes a building block concept, in which individual computing components may be easily interconnected to solve the required equations by forming electronic models analogous to the system under study. Each building block, either individually or in combination with others, is capable of performing one or more mathematical operations. The computing components in the TR-20 occupy the area above the slanting control panel area. This area is divided into three rows; the top row contains the coefficient attenuators; the middle row houses the integrator networks, comparators, and other non-linear computing components; the bottom row provides space for twenty (10 dual units) operational amplifiers, The computing components are constructed on plug-in chassis, and the front of each computing com- ponent consists of a color-coded plastic patching block that contains the input and output terminations for the unit, The computing components are inter-connected by placing patch cords or bottle plugs between the appropriate input and output ter- minations. Most TR-20's are equipped with a removable pre-patch panel that allows problem patching away from the computer, ‘The pre-patch panel consists of a rigid aluminum frame with individual rows that contain patching blocks identical with the patching blocks that form the front panels of the components. Contact between the pre-patch panel and the computing components is accomplished by means of gold-plated contact springs. Below the patching area is the monitoring and control panel area which contains con- trols and components that permit (a) switching the computer on and off, (b) mode control of the computer, and (c) measuring stationary problem voltages, A hinged cover plate directly below the control panel covers the amplifier balancing potenti- ometers and the variable diode function generators, 2, OPERATING CONSIDERATIONS The TR-20 is completely tested and calibrated at the time of manufacture and is shipped with all components in place, After performing the preliminary check-out procedure outlined in the TR-20 Maintenance Manual, the computer is ready for oper- ation, It should be noted that the low voltage levels used in the TR-20 eliminate any shock hazard to the operator when patching components with the computer turned on, Current- limiting circuits protect the reference supplies from damage during short-term over- loading if they are inadvertantly patched to ground or to each other, A patching con- nection that is dangerous to a component usually triggers the ovetload alarm system. 3 Figure 1. The TR-20 Desktop Analog Computer with Display Units TABLE I, TR-20 COMPONENTS MODEL GROUP COMPONENT NUMBER COMPUTING COMPONENTS 1 Dual DC Amplifier 6.712 2a . Dual Integrator Network (Non Rep-Op) 12,1116 2b Dual Repetitive Operation Integrator Network 12,1115 3a Quarter-Square Multiplier 7,045 3b Bi-Polar Quarter-Square Multiplier 7.117% 4a x? Diode Function Generator 16,101 4b Log X Diode Function Generator 16,126 4c 1/2 Log X Diode Function Generator 16,133 4d Sine/Cosine Function Generator 16 ,313/1016 , 004* 5a Variable Diode Function Generator Group 2.713 Consists of: -Variable Diode Function Generator 16,154-1 +Variable Diode Function Generator 16,156-1 VDFG Readout Module 16,310 5b Variable Diode Function Generator Group 2.645-0 Consists of: +Variable Diode Function Generator 16,304-1 -Variable Diode Function Generator 16,.306-1 VDFG Readout Module 16.308 5c Variable Diode Function Generator Group 2,748 Consists of: +Variable Diode Function Generator 16.165-1 VDFG Readout Module 16,310 6a Attenuator Group 42,183 6b Attenuator Group 42,187 6c Attenuator Group 42,188 6d Attenuator Group 2,128 MODEL GROUP COMPONENT NUMBER COMPUTING COMPONENTS (Cont) Consists of: Attenuator Panel 42,185 Readout Module 12,265 7a Reference Network 12,266 7b Tiepoint Network 12,267 7c Dual Function Switch Group 2,127 Consists of: Function Switch Assembly 20.366 Readout Module 12, 264 8a Relay Comparator 6.143 8b Electronic Comparator 40,538 POWER AND REFERENCE SUPPLIES 9 Regulated Power Supply 10,179 10 Reference Regulator 43.037 11 Dual DC Amplifier 6,282 OPTIONAL COMPONENTS AND ACCESSORY EQUIPMENT 12 Repetitive Operation Expansion Group 2.715 Consists of: High Speed Repetitive Operation Control Panel 20.532 Repetitive Operation Timing Unit 36,082 12,1115 Dual Repetitive Operation Integrator Networks MODEL GROUP COMPONENT NUMBER OPTIONAL COMPONENTS AND ACCESSORY EQUIPMENT 13 Display Unit** 12,987 14 Reactor Kinetics Group 2.475% 15 Transport Delay Simulator 2.448% 16 Audio Overload Alarm 13,017 l7 Slave Cable 510.038 18 Patching Kit 100,007 19 Service Shelf 51.039 20 AC Power Cable 51,040 21 Pre-Patch Panel 5,235 22 Rep-Op Slave Panel 20,567 AUXILIARY EQUIPMENT l VARIPLOTTER® 1110* 2 Repetitive Operation Display Unit 34,035* The operator should be familiar with the following paragraphs before attempting to use the computer, *These Components described in separate manuals. *kThis Component not required if the Electronic Comparator, Model 40,538 is provided. a. Insertion of the Pre-Patch Panel Before inserting the pre-patch panel, the operator should verify that the patch blocks on the pre-patch panel are aligned in the same order as the computing components. Hold the pre-patch panel at a slight angle and place it in the patch bay groove; see Figure 2, Move the pre-patch panel to the right until it contacts the right~ hand side of the patch bay. Gently, push the pre-patch panel forward until it is flush with the computer. Turn the locking lever down; the pre-patch panel will slide to the left. To remove the pre-patch panel, apply a light pressure to the panel to keep it from falling forward when dis-engaged, and lift the locking lever. b. Feedback for the Amplifiers All operational amplifiers should be provided with feedback whenever the computer is turned on, Bottle plugs, connected as shown in Figure 3a, provide feedback and prepare the amplifiers for use as standard inverters or summers, c. Application of Power Connect the computer line cord to a receptacle following the precautions given in the TR-20 Maintenance Manual, and place the OFF-ON switch to the ON position. Place the RESET-HOLD-OPER switch to the RESET position. Initially, the amplifier over- load alarm system will be triggered due to transients; after a few seconds, the over-~ load indication should cease, d. Amplifier Balance Under normal circumstances, the amplifiers will remain balanced for periods of weeks. However, at intervals it is desirable to check this condition, If an amplifier is found to be unbalanced, an adjustment should be made. If the check indicates that the amplifier balance is within tolerance, no adjustment is necessary, The amplifier must have some sort of feedback in order to be balanced. Normally, this requirement is satisfied by the circuit in which the amplifier is used. The amplifier may be balanced while normal inputs are applied. Each amplifier has a balance potentiometer located behind a hinged cover plate below the Control Panel (Figure 4). The balance controls are labeled with the number of the amplifier they serve. To set a balance control, proceed as follows: (1) Place the computer in the reset mode. Place the Voltmeter Function switch in the BAL position. Rotate the AMPL SEL switch to the number of the ampli- fier to be balanced. (2) Vary the appropriate Amplifier Balance control until the Volt meter reads within two or three divisions of zero. (The amplifier overload alarm system may be triggered during the balancing process. ) Figure 2. Inserting the Pre~Patch Panel SJ FOR SPECIAL INPUT RESISTORS INPUTS GAIN | { GAIN 10 { GAIN 0.1 GAIN I AMPL 6.712 OUTPUTS AMPLIFIER | AMPLIFIER 2 G. PATCHING WITH BOTTLE PLUGS LL b. AN INVERTER cr xX oy GAIN OF t AA Ga Ol 4 Y > I z WAG GAIN OF | A 10 yy —e 10 Wie ~(X+Y¥) C. A SUMMER panne — OIC KE YEZ)—A d. A HIGH-GAIN AMPLIFIER PATCHED FOR GAINS OF 0.1 AND | Figure 3, The 6.712 Dual DC Amplifier, Showing Use of Bottle Plugs 10 NULL POT REFERENCE SELECTOR SWITCH VOLTMETER RANGE SWITCH BALANCE POTS COMPUTER MODE CONTROL SWITCH VOLTMETER FUNCTION SWITCH Figure 4, The TR-20 Control Panel 11 When the computer is first turned on, a check of amplifier balance will show de- flections that are slightly high, but they will return to normal levels after a warm-up period. For unusual problems that might be especially sensitive to ampli- fier unbalance or integrator drift, the amplifier can be balanced at more frequent intervals in order to keep the meter deflection below one division. e. Overloads The computer is equipped with an overload alarm system that indicates the presence of an overloaded amplifier. The visual overload alarm is located on the left side of the control panel. The lamps are illuminated whenever their associated ampli- fier is overloaded. Lamps 1 to 20 serve the 20 operational amplifiers; lamps 21 and 22 serve the amplifiers associated with the plus and minus reference amplifiers respectively, The computer may be equipped with an audio overload alarm that is located in the rear of the cabinet; it sounds an audible alarm when an amplifier is F overloaded, 3 The overload alarm system indicates that something is wrong with the problem patching, the problem operation, or the computing components, Usually, no harm is done to the equipment by short-term overloads, unless they are caused by excessively high voltages other than those normally obtainable from the computer itself. However, several other reasons exist for clearing overloads soon after they are noticed. (1) If an overload is indicated for amplifier 21 or 22, the value of the plus or minus reference voltage may be other than +10.00 volts, adversely affecting problem solution, An overload in either of these amplifiers generally indicates a patching error, and should not be allowed to continue over an extended period of time. (2) Overload of unassigned amplifiers does not damage the amplifiers or affect the problem solution, However, the fact that one or more overload lamps are lit, however, may cause the operator to overlook an overload occurring in an assigned amplifier, thus causing an erroneous problem solution and defeating the purpose of the alarm system, 3. READOUT FACILITIES AND MANUAL MODE CONTROLS L The operating controls for the readout and mode control circuits are grouped on the sloping control panel area below the computing component cradles as shown in EB Figure 4. The functions of the controls are: 12 Control Power ON-OFF Switch, S4 Mode Control Switch, $5 Voltmeter Function Switch, S1 Voltmeter Range Switch, S2 NULL POT and Reference Selector Switch, +10/OFF/-10 (S3) VM Jack Amplifier Selector Switch, S6 (AMPL SEL) AMPL OUT Jack Overload Indicators, OVLD IND a. Readout Facilities Function Controls application of primary ac power to the power supply of the computer. The voltmeter is illuminated when power is applied. Controls the operational mode of the computer, Positions are RESET, HOLD, and OPERATE, Controls voltmeter operation. Positions are POT BUS, NULL, VM, AMPL, and BAL. Selects sensitivity for voltmeter. Full scale ranges of 0,1, 0.3, 1, 3, 10, and 30 volts are provided. Used in conjunction with the voltmeter to mea- sure voltages by the null comparison method. Provides for external inputs to the voltmeter when the Voltmeter Function Switch is in the NULL or VM position Selects an amplifier for output monitoring or balancing. Connected to the wiper of the AMPL SEL switch; facilitates connecting any amplifier output to external monitoring or measuring equipment. Indicate an overload in the associated ampli- fier when illuminated. The readout facilities consist of a sensitive voltmeter, selector switches for connecting the voltmeter to various points in the computer, and a precision ten-turn potentiometer that is used to measure voltages by the null-comparison method. The function of the related controls is described below, The BAL position of the Voltmeter Function Switch (S1) is used when balancing the dc amplifiers, The AMPL SEL switch (S6) is used to select the stabilizer output of the amplifier to be balanced, (Figure 5a). The balance potentiometer of the amplifier is rotated until the meter reads zero. Positions 1 to 20 of the AMPL SEL switch are connected to the stabilizers of the 20 operational amplifiers; positions 21 and 22 are connected to the stabilizers of the plus and minus reference amplifiers respectively, The diodes in parallel with the meter protect the meter movement. 13 14 STAB. OUT, AMF. H ML 1 oop 8 lererara janes] 10500 H ee o Lie RB R7 50-0-50 pa i 8.2K 1K \ or A Mi | BUS ac VW AN {mi} STAB, OUT, AMP, fu VOLTMETER cr “ "REF AMP, ———O FUNCTION SWITCH al , [22] $! " ,~REF AMP. ————O CR2 AMPL SEL ‘4 > $6 (a) BAL POSITION (9 AMP. * 1 OUTPUT as 9 [ste Oo [2] O——W-4 u # 4 2 ——o ’ . : : Bs £0-0-80 ° 1050.0 POT BUS} O ° O-—-W¢ amp, #20 OUTPUT BAL VOLTMETER On ~ + REF ———=—0 FUNCTION SWITCH sl ° -REF —O VOLTMETER RANGE SWITCH AMPL SEL s2 56 (b) AMPL POSITION £3] [vw] AMPL. on ohO i O——-wws——4 ul POT BUS | O ° BAL | Ca] OW 50-0-50 ya 10500 oe VOLTMETER ‘ aL FUNCTION SWITCH One = sl OFF! ° VOLTMETER RANGE SWITCH $2 (c} VM POSITION Figure 5, Readout Circuits Simplified Schematics VOLTMETER ar ne ; FUNCTION SWITCH ; $1 1K 2.2K 3 Sor e (d) NULL POSITION Po eee ~~ +10V ! OFF \ READOUT SWITCH | +19} © VOLIMETER =) 0. jtlov o—— -10v FUNCTION SWITCH r $1 1 | 83 Z R ° fo) i 2 eK Re POT BUS Exel fo) | | | li NULL POT | | + 1 | 1! | | Loi | | | { Por Bus 4 TO OTHER | ATTENUATORS | cowRot PANEL 20.734 : | (e) POT BUS POSITION The AMPL position of the Voltmeter Function switch establishes the circuit shown in Figure 5b where the output of the selected amplifier provides the input to the voltmeter. The Voltmeter Range switch is used to select a convenient full-scale range for the voltmeter, Note that the wiper of the AMPL SEL switch is connected to the AMPL OUT jack so that amplifier outputs can be monitored with external equipment. The VM position of the Voltmeter Function switch connects the VM jack to the Voltmeter Range switch (Figure 5c). Voltages patched into the VM jack are read on the voltmeter. . The NULL position of S1 provides a means of accurately measuring unknown voltages with respect to the computer reference voltage, The circuit arrangement is shown in Figure 5d.. The voltage to be measured is patched to the VM jack and connected to one side of the meter, The wiper of the NULL. POT is connected to the other side of the meter, The Reference Selector switch $3 is switched to the position that supplies reference voltage with the same polarity as the voltage to be measured.- The NULL POT is varied until the meter reads zero. The position of the turns-counting dial on the NULL POT indicates the magnitude of the unknown voltage; the position of S3 indicates the polarity of the unknown voltage. This null comparison method of voltage measurement provides a measurement accurate to within +0.1% of full scale. An important feature of the method is that no current is drawn from the source being measured once a balance is attained, Thus the re- sistance of the source has no effect in the measurement. A large source resistance, however, will decrease the sensitivity of the meter to unbalanced conditions. The POT BUS position of S1 is used when setting attenuators (Figure 5e). The readout circuit is connected to measure the voltage on the pot bus by the null comparison method, When the pushbutton switch associated with an attenuator is depressed, +10 volts is connected to the top of the attenuator, and the wiper is connected to the pot bus. The Reference Selector switch, S3 must be in the +10 position, The NULL POT is set to the desired attenuator coefficient. The attenuator is adjusted until the meter reads zero. The attenuator is then set to the same co- efficient as the NULL POT. b. Manual Mode Control The Mode Control switch ($5) on the Control Panel provides a means of starting and stopping computer solutions and of establishing initial conditions. The switch controls the operation of a circuit which actuates the reset and operate relays of the integrators,. The switch positions are RESET, HOLD, and OPER (operate). All computing components except the integrators are operational in all three modes. The integrators are controlled as follows: 15 RESET In the reset mode, the output voltages of the integrators are set to the values required by initial conditions of the problem. All other inputs to the integrator are disconnected. HOLD In the hold mode, the inputs to the integrators are removed; integration ceases and all vari- ables are held at the present values. OPER In the operate mode, the integrators accept inputs and integration with respect to time takes place. 4, ATTENUATORS One of the simplest and most useful operations performed on an analog computer is accomplished by using a potentiometer to multiply a voltage by a positive constant that is less than one. This corresponds to attenuation of the voltage, therefore potentiometers are often called attenuators. Both terms are used interchangeably here. Four types of attenuator groups are available for use in.the TR-20, All groups use ten-turn, 5000 ohm potentiometers, The groups are listed below. GROUP NO. OF POTS TYPE OF POT DIAL REMARKS — —————————————— = = 42,183 2 Carbon Uncalibrated Does not have Readout . Switches 42.187. 2 Carbon Uncalibrated Has Readout Switches 42.188 2 Wirewound Calibrated Has Readout Switches 2.128 : ae (42.183 & Has Readout Switches 12,265) 4 Wirewound Calibrated Pots located in Con- trol Panel area The Type 42.183, Type 42.187, and Type 42.188 Groups have similar patching termina- tions. The top potentiometer is terminated on the left side of the patching module and the lower end of this potentiometer is grounded. The lower potentiometer is terminated on the right side of the patching module and both ends of the potentio- meter are available for patching. The Type 2.128 Group consists of a patching module (Type 12.265) that mounts in the non-linear row of computing components, and Quad Coefficient Assembly, Type 42.185 that mounts in the control panelarea. The lower end of each potentiometer is grounded, The potentiometers are termina- ted in order, top to bottom, on the patching module. 16 When an input voltage Een is applied to an attenuator as shown in Figure 6, the Ry output voltage Ey is K times Ee where K= “/R T£ the attenuator is unloaded, T the mechanical ratio of Ry iRe is the same as the electrical ratio Eo rE and the attenuator could be set to the exact ratio by means of the vernier dial attached to the wiper shaft. Normally, however, the attenuator is loaded and the two ratios are not equal, The most common use of the attenuator is to feed an amplifier; thus the wiper is loaded by the amplifier input resistor, Im order to account for loading, it is more convenient to set the attenuator under loaded conditions by monitoring the wiper voltage and adjusting the wiper until the desired output is obtained. Figure 7a shows the circuit used in the TR-20 to permit setting grounded attenuators under load, A pushbutton switch is located next to each attenuator; depressing the switch connects the wiper to the pot bus, removes the voltage applied at the patch panel, and applies +10 volts to the top of the attenuator. The wiper voltage, on ‘the pot bus, can be measured by the null-comparison method by using the NULL POT on the control panel. The ungrounded attenuators are connected in the circuit configuration shown in Figure 7b, Depressing the pushbutton switch applies +10 volts to the top of the potentiometer and connects the loaded wiper to the pot bus for measuring purposes, Note that the lower end of the attenuator is not grounded and voltages may be patched to both ends of the attenuator, The patching block has a ground termination near the low end of the ungrounded potentiometer to make it convenient to ground the low end if so desired, The Type 42,183 Attenuator Group does not include the pushbutton switches, The wiper of each attenuator is brought out to a termination next to the attenuator to facil- itate readout under loaded conditions, Figure 7 contains schematics and symbols for two potentiometer types. The address or number of the potentiometer (i.e., 1 or 2) is placed within the circle; the coefficient setting (K) is written near the symbol. The high and/or low end of ungrounded potentiometers is also indicated. 5. THE OPERATIONAL AMPLIFIER a, General Considerations When a high-gain de amplifier is used in conjunction with input and feedback networks to perform mathematical operations, the resulting system is generally referred to as an operational amplifier, The operational amplifier is the basic and most versatile unit in the analog computer, It can be used for inversion, summation, multiplication by a constant, integration, and used in conjunction with special networks for squar- ing, extracting square root, generating logarithmic functions, etc, 17 | ___} . Ll ¢, Ry _ €y = R Cin = Ke in | R; T t Figure 6, An Attenuator +10V nent eaptctnadl | +10V ———O__ i . | § | Hea | _ ATTEN. 42.168 | * } TO SWITCHES OF < é Pot bus 4 » TO READOUT ALL ATTENUATOR CIRCUITS GROUPS (a) ATTENUATORS, SIMPLIFIED SCHEMATIC E in xX HI oF Ry - Rr Rr Ein =KE jn Ry K(X-Y) + 43 8 1 3o% LO - , oF xX —_ K HI Ein +) KEin K O— K (X-Y) +Y LO Y ——— (b) GROUNDED (c) UNGROUNDED Figure 7. Schematics and Symbols for Attenuators 18 Recall that the amplifier is designed to have three essential characteristics (see Figure 8): (1) The amplifier output (e,) is related to the summing junction voltage (eo) by the gain of the amplifier: e, = “Ae, (2) The input stage of the amplifier draws negligible current: i,~0 (3) The open loop gain of the amplifier is extremely high: A>>1 (on the order of 3 X 10’ at de). Therefore, the amplifier output voltage is related to the input voltage by the equation: in ey (Ee (EQ. 2-1) Equation 2-1 illustrates one of the most important characteristics of the oper- ational amplifier: the input-output relationship of the operational amplifier is solely dependent on the ratio of the feedback to the input impedance, Using Equation 2-1 as the basis of discussion, the following sub-paragraphs describe the various uses of the operational amplifier. b. Inversion When the same value resistor is used for both the feedback and the input impedance, the amplifier output voltage has the same amplitude as the input voltage but is opposite in polarity, In the TR-20 the value of Ry and R, | used for the inverter is normally 100,000 ohms (100K), therefore: 100K, _ Re eo 7 RL fin 7 TOOK Sin ~ 7 Sin 0 in Thus a +10 volt input results in a -10 volt output, and the amplifier is said to have a gain of minus one, The accuracy of the output to input ratio depends solely on the accuracy of the ratio R,/R,_- ce, Multiplication by a Constant A change in the ratio of the resistors results in multiplication by a constant. For example, with R. equal to 100K and Ra equal to 10K, the amplifier output is: _ 100K _ £9 ~~ 10K “in — 10e + 19 20 Figure 8, Operational Amplifier, Simplified Block Diagram An input of plus one volt results in an output of minus ten volts, This operational amplifier has a gain of ten, The multiplying constant can be made smaller than one by using a LOK feedback resistor with a 100K input resistor, 2 -. 1K, 0 100K “in = -O,le, in An input of minus ten volts produces an output of plus one volt, d, Summation When multiple input resistors are used with a feedback resistor Res the basic re- lationship is extended to: R R R £ £ £ = wh + — eve ~e ae f a R “9 + + R .)