Analog Computers

English translation

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Description and Operating Instructions for the Transistorized Desktop Analog Computer EA 22

This document is an English translation of the original German-language “Beschreibung und Bedienungsanleitung für den transistorisierten Tischanalogrechner EA 22” published by GTE (Gesellschaft für technische Elektronik mbH).

Table of Contents

A. Equipment Description

  1. General Description
    • 1.1 Introduction
    • 1.2 Concept and Scope
  2. Constructive Design
    • 2.1 Rear Side of the Unit
    • 2.2 Front Side of the Unit
  3. Assignment of the Patch Jacks for the Computing Elements
    • 3.1 General
    • 3.2 Potentiometer Units
    • 3.3 Operational Units
    • 3.4 Fixed Potentiometer Strip
    • 3.5 Control Panel

B. Operating Instructions

  1. Starting Up
  2. Nulling the Amplifiers
  3. Preparing Programming on the Computer
  4. Setting Integration Constants
  5. Setting Potentiometers (with Compensation Device)
  6. Setting Potentiometers (with Digital Voltmeter)
  7. Setting Function Generators
  8. Setting the Plotter
  9. Iterative Computing
  10. Switching Off the Computer

A. Equipment Description

1. General Description

1.1 Introduction

The following is a description of the analog computer system EA 22, together with an operating manual, designed to be as clear as possible for the user and to serve as a reference guide for day-to-day operation. For users who are not familiar with analog computing, study of the following books is recommended beforehand:

  • H. Schwarz, “Elektronische Analogrechner,” Franzis-Verlag, Giloi/Lauber, “Analogrechnen,” Springer Verlag
  • D. Ernst, “Elektronische Analogrechner,” R. Oldenbourg, München

1.2 Concept and Scope

The GTE analog computer EA 22 was developed with particularly high priorities regarding both functional quality and the widest possible flexibility in its use. The high control panel quality ensures the greatest possible technical utilization of the computer elements. This was accomplished through a constructive separation of computing elements and control elements: the amplifiers are housed in the rear half of the unit facing away from the operator, while the operational units, including their patch jacks, as well as the control panels with the overload indicators and the reference voltage control knobs are located on the front side. This arrangement is so designed that the computing elements can be exchanged with the greatest possible freedom in sequence programming and with simultaneous use of interchangeable patch panels.

Maximum complement of a GTE 22 includes: 22 computing amplifiers, 20 coefficient potentiometers (5 units with 4 potentiometers each), and 10 operational units (double networks), to each of which two amplifiers belong. The remaining two amplifiers serve as free summation amplifiers at the disposal of the operator for use in precision computation or in the precision time base.

The computing amplifiers and the reference voltage unit are precision units of accuracy class 0.01%. The operational units can be supplied in accuracy classes 0.1% (A-execution) or 0.01% (B-execution), so that each analog computer EA 22 can be most economically adapted to the requirements at hand. For instance, for budget reasons the A-execution will be purchased initially; later a single unit exchange can upgrade an existing EA 22 installation to the 0.01% accuracy class.

The use of semiconductor elements in printed circuit technology, and especially the use of gold contacts for relay and patch jack connections, ensures high reliability. In the event of incorrect patching, damage to computing elements can be avoided; static amplifiers and potentiometers, which serve as reference voltage sources, are protected against short-circuit by electronic means (bypassing the fuses) and by current limiting.

2. Constructive Design

The analog computer system EA 22 is housed in a desktop enclosure whose front side accommodates the passive computing elements and the control panels and elements, while the rear section accommodates from the back the computing amplifiers, amplifier power supplies, and reference voltage units.

2.1 Rear Side of the Unit

After loosening the mounting screws of the rear enclosure walls, a magazine housing up to 22 computing amplifiers is visible at the top, with two mechanical card-extractor ejectors visible for each pair of amplifiers. A complete zero-stabilized computing amplifier is located on just a single printed circuit board. In the lower rear section, the complete power supply for the analog computer system is assembled as a compact unit that can be removed after loosening four screws and pulling two connectors. The power supply consists essentially of:

  • Network transformers with rectifiers and filter capacitors
  • A printed circuit board (400 Hz square-wave generator for Zerhacker excitation)
  • Two identical cooling fans for amplifier power supply
  • Regulation amplifiers (for +15 V and −15 V), which in turn draw from another board containing the reference voltage unit, consisting of temperature-stabilized precision Zener diodes and two zerhacker-stabilized additional amplifiers for the reference voltage
  • The power supply also includes the fuses, which are accessible without removing the rear panel

In the middle height of the rear panel, four connector strips are mounted for connecting multiple EA 22 units together or for connecting a single unit via parallel-cable to a larger installation. The rear jacks are provided for any desired patching by the customer.

2.2 Front Side of the Unit

Three areas can be distinguished here. In the upper section are the coefficient potentiometers; in the middle section are the passive operational units with their patch jacks; and in the lower section are all the control, monitoring, and display devices.

All input and output jacks needed for creating the computing circuits are located on the exchangeable operational units, arranged and on a fixed panel so that identical programming sequence is possible with exchangeable patch panels.

For storing programs and for shortening setup times when the computer is used by multiple persons, the EA 22 can supply up to 10 interchangeable programming fields. These panels, which are duplicates of the front panels of the operational units, can be inserted and removed individually, and can thus be adapted to the respective computer complement. The connections between the computer and the interchangeable programming field are made through robust gold contact springs, ensuring a secure contact connection.

In the lower control panel are first a fixed strip with overload indicators and the null-balance potentiometers for the 22 computing amplifiers, labeled 1a, 1b … up to 11b. On the right side are the operating mode controls for the various operating modes (potentiometer setting, startup, computing, hold), as well as a pushbutton for compensation setup and a digital voltmeter connection (white socket), which leads to the Verstärkerstromversorgung (amplifier power supply).

3. Assignment of Patch Jacks for Computing Elements

3.1 General

Color-coded jack identification is used throughout; it represents a notable improvement in the often confusing variety of colors used and achieves a high degree of clarity with a relatively small number of colors. The colors have the following meanings:

  • Red: Positive reference voltage (+10 V)
  • Yellow-red: Amplifier output (positive)
  • Dark blue: Negative reference voltage (−10 V)
  • Schwarz (Black): Negative reference voltage (−10 V) — appears to refer to the summing junction/input side
  • Yellow: Summing point inputs at multipliers and function generators
  • White: Patch jacks, free terminals, signal points (Steckpunkte)

3.2 Potentiometer Units

Each potentiometer unit consists of four potentiometers. The wiper (Grün = green, center = the Griff/knob end taken as the accessible contact point) is tapped off while the upper end of potentiometer 2 is always the wiper input, so that at the junction of potentiometers 1, 2 and 3 the shorting can be done easily via patch stub. Potentiometers 1 and 2 have two outputs each.

3.3 Operational Units

Up to 10 operational units (Doppelnetzwerke, double networks) can be installed; each two amplifiers belong to one unit. The various operational configurations are as follows:

a) Integrators. The yellow Doppelkurzschlussstecker (double shorting patch) covers the integrator inputs from the summing junction. The shorting patch is white and covers the inputs to the integrator below the Buchsen H and Z (Hold and compute relay contacts), where H and r are for the control inputs and s and p are on the operational unit jacks themselves, and can be connected to the operational unit jacks by patch plug.

b) Double summer/integrator. The summing junction is blocked as above.

c) Multiplier. The double shorting jack covers Buchse M with S, and the Buchse Z (compute) with the multiplier output jack. The multiplier is produced as follows: in the “normal” operating position the input resistance is 20 kΩ; at the multiplier output the computing amplifier has a feedback resistor of 100 kΩ.

The product appears at the amplifier output. At the output junction of the multiplier the feedback is fully interrupted by the double shorting plug and can be connected with any other amplifier.

d) Function generator/double summer. This unit has two summer networks and an “advance” function (Vorrangfunktion), which is a function generator with 20 diode breakpoints, two free potentiometers, and also two free Buchsen (I and O).

e) Summation amplifier with four inputs (Vierfachsummierer). With junction M, the Buchse Z is connected with an additional single patch jack.

f) Summation amplifier in all four quadrants (Vierfachsummierer in vier Quadranten).

3.4 Fixed Potentiometer Strip

This strip provides resistors for the reference voltage and the computing values for the 22 amplifiers (and their 11b designation labels). Each amplifier has fixed precision potentiometers for overload detection lamps and for the null-balance trimming.

For continuous-time computation of iterative sequences, the computing sequence including hold and startup is performed automatically. With the precision time base, integrators can compute during the holding period and measure values can be taken. A hold sequence can thus involve the display of measurements.

The operating mode sequence is as follows:

  • Startup and Hold: 1 ms to 100 s
  • Computing and Hold at 0: 1 ms
  • Startup and Hold at 0: 0.1–1.5 ms

For continuous computation the precision time base controls two relays, P (from the hold circuit), resulting in a particular start–compute–hold cycle period continuously repeated.

3.5 Control Panel

The control panel (Bedienungsfeld, section 20 on the enclosure) includes:

  • “Pot”: Potentiometer-setting mode, with compensation device
  • “Anf”: Initiates integration starting conditions
  • “Rechnen”: Compute mode; integrators start computing after startup conditions are reached; the overload control lamp lights briefly for about 2 seconds. In computing mode the reference voltage connection is maintained at about +15 V, +1 V
  • “Halt”: Hold mode – the computer can be programmed; the overload lamps can also be checked in this way
  • “Halt-0”: Holds integrators at zero; all computing amplifiers can be nulled by electronic means with the null-balance potentiometers, and thus a compensator or a digital voltmeter can be used

The operating mode switch BG 30 finally provides via pushbutton P the integration starting condition control. The precision time base ZG 22 serves for automatic control of the time period of the computer. The pre-selector in the time base holds a single Buchse P available to the user while in “Rechnen” mode, the text “Eigene” is displayed in green.

B. Operating Instructions

1. Starting Up

  • At startup, connect the computer to a 220 V power supply.
  • Additional computers and measuring instruments can be connected via parallel-cable over the rear strip (an A).
  • All other computers should have the “Halt” operating mode switch set to “Anf” and the corresponding overload lamps will then light up momentarily after about 2 seconds. When operating from a single computer, the display control is set to “Eigene” in green.

2. Nulling the Amplifiers

Although the amplifiers are factory-set precisely and are very stable, to achieve the highest accuracy all amplifiers should be nulled before first use and at regular intervals thereafter.

The nulling procedure is as follows:

  • Set the operating mode switch to “Halt”
  • Set the Betriebsartschalter (operating mode selector) to “Halt-0” Stellung
  • The first amplifier to be nulled is the 100× feedback amplifier; set one potentiometer with Factor 10 (i.e., insert the amplifier with the 100× feedback resistor into the circuit)
  • Connect the null indicator (oscilloscope or null voltmeter) to the output of the first amplifier
  • With all other amplifiers connected in parallel, adjust each individually

At the highest accuracy (100× input amplification), the null should also be checked with the diode feedback path. The repetition test with the decimal position of the potentiometers between 1 and 2 on the time base should be verified.

3. Preparation of Programming on the Computer

The analog computer must NOT be patched under power without caution:

  • All amplifiers must first be checked for correct static operation.
  • Any incorrect patching can lead to overloads; the overload indicators warn visually.
  • Short-circuit protection is provided electronically.
  • Double-check each patch connection; when programming with external patch panels, ensure they are correctly aligned.
  • Inserting individual operational units: each unit can be interchanged with any other unit without tools.
  • When using exchangeable programming panels: these duplicate the front panels of the operational units so that programs can be stored and the EA 22 reconfigured rapidly.

4. Setting Integration Constants

The constant K = 1·s^(−1) (the shorting plug connects the number 1 to the appropriate jacks) is set by the following procedure on the time base ZG 22.

If one requires large integration constants (e.g., 10 × 10^(5)), one large and one small integration constant potentiometer together with a scaling coefficient can be set using the Doppelfunktionsstecker (double function plug).

5. Setting Potentiometers (with Compensation Device)

  • Set the operating mode switch to “Pot.”
  • Set the Betriebsartschalter to “Komp” (compensation).
  • In “Komp” mode: the reference voltage is switched and the compensation of the Spannungsvergleicher (voltage comparator) is adjusted. This provides the potential comparison of the Präzisionspotentiometer-setting with electronic compensation.
  • The compensation potentiometer must be adjusted until a Diode display indicates balance.
  • Set the desired coefficient potentiometer value; press “Pot” so long until the digital voltmeter shows the balance coefficient assigned.
  • Fix the setting with the locking screw on each potentiometer.

6. Setting Potentiometers (with Digital Voltmeter)

  • Set the operating mode switch to “Pot.”
  • Connect the digital voltmeter to the white socket and yellow sockets (for Verstärkerstromversorgung).
  • The Betriebsartschalter should not be set to “Komp” but rather in a non-computing position.
  • Set the desired coefficient values; the digital voltmeter displays the coefficient values directly.
  • Fix the setting with the locking screw.

7. Setting Function Generators

  • The function generator input is set at a convenient single-diode adjustment point.
  • The Einstellhebelschalter (adjustment lever switch) is plugged in at any position and the function shape adjusted.
  • The function setting uses the fine adjustment of each potentiometer and the piecewise-linear approximation given by the diode breakpoints.
  • After setting, the function generator output can be verified by observing the output on the digital voltmeter connected to the output jacks.

8. Setting the Plotter

  • The plotter ZG 22 drives the plotter output automatically during a computing run.
  • The pre-selector controls the test mode “Rechnen,” while the plotter operates simultaneously.

9. Iterative Computing

On the analog computer EA 22 iterative computations are carried out automatically. In “Rechnen” mode, the computer runs the operating sequence startup–compute–hold in repeated cycles. With the precision time base, the integrators can also continue running during the hold period, and measurement values can be taken.

The standard control states:

  • Startup (gedrückt, pressed): Inf.
  • Rechnen: Hold state: H = 0, R = 1
  • Halten: H = 1, R = 1
  • Pause: H = 0, R = 1

In the “Pause” state, the normal integrators retain their initial conditions. This state is indicated on the computer by the illumination of the non-pressed Anf. key.

The memory integrator (speichernder Integrierer) must be connected according to Fig. 9.2: it stores a value at a relay input and presents the stored value at its output.

For iterative computations with memory integrators: when memory integrators are needed, connect the Buchse H with s and R with p for the respective memory integrators. The following table gives the relay state of the memory integrators during iterative computing:

Computing phaseOperationHR
Anf. (gedrückt)Anf.00
RechnenHalten01
HaltenRechnen11
PauseHalten01

In the “Pause” state, the normal integrators take up their initial conditions. This state is indicated on the computer by the illumination of the non-pressed Anf.-Taste.

The memory integrator must be switched according to Fig. 9.2.

10. Switching Off the Computer

The mains switch may be actuated at any time and in any operating mode.