English translation — EAI Analog/Hybrid-Rechner Newsletter Nr. 013, Oktober 1967

This document is an English translation of the original German-language EAI newsletter (EAI Electronic Associates GmbH, Aachen), issue Nr. 013, 4th year, October 1967 – February 1968.

EAI ELECTRONIC ASSOCIATES GmbH | 51 Aachen, Bergdriesch 37

Oct. 1967 – Feb. 1968 | No. 013 – 4th Year

THE FEATURED SIMULATION TOPIC

Foreword: The Analog Computer as a Cybernetic Model in Biology and Medicine

Since cybernetics introduced generalised engineering concepts such as feedback and control into biology and medicine, analog and analog/hybrid computers have gained an important place in medical and biological research. Their applications lie primarily in two areas:

The simulation and investigation of physiological and anthropotechnical models.
The analysis of measurement data such as EEG and ECG, which accumulate in ever-greater numbers through modern electromedicine.

The idea of using a practically immortal — and therefore especially versatile — test subject, whose state can be changed by turning a knob, draws a growing number of researchers toward simulation with analog computers, whose operation is particularly simple for physicians and biologists. Cybernetics, for its part, has introduced into these non-technical disciplines a way of thinking that enables the mathematical capture of complex processes. The advantages of analog computers in this regard can be summarised in three points:

The communication between operator and machine (“man–machine interface”) is particularly straightforward thanks to the direct analogy between computing elements and computing operations, and requires of the user neither electrotechnical expertise nor knowledge of difficult programming languages.
The analog program requires only a modest amount of mathematics, which — in contrast to the digital computer, where numerical methods must be used for programming — is used only to describe the process being investigated.
As a result, the researcher’s intellectual effort is largely freed from the program and program flow, allowing creative concentration on the specialist tasks at hand.

A sign that the analog computer has recently become widespread in biology and medicine is the fact that in the last five months of the previous year, 6 of the 19 sold Analog/Hybrid computers of Type 580 were destined for biomedical applications. This new computer was presented to the public for the first time in August 1967.

(Dipl.-Ing. Alberto Bento, Applications Engineer, EAI-GmbH)

SIMULATION OF THE PUMPING ACTION OF THE HEART CHAMBER

(From the article “The Analog Computer in Biology and Medicine” by Dipl.-Ing. Werner Bub, EAI-Brussels — special reprint)

The systemic blood circulation is sustained by the energy imparted to the blood by the action of the left ventricle. To illustrate its behaviour, the heart chamber is treated as an elastic bag that alternately contracts and relaxes. The arterial outflow is initially received by another elastic reservoir — the aorta — whose outflow is in turn limited by the arterial flow resistance R₀.

During the relaxation phase (diastole) of the heart chamber, it fills as a result of the residual pressure P_U of venous blood from the left atrium. The mitral valves D1 (see Fig. 1a) are open and a flow resistance R1 is active. The aortic valves D2 remain closed because the arterial pressure P_O is greater than the pressure P_K in the heart chamber. The onset of contraction (systole) is initiated by the depolarisation of the heart muscle. During the subsequent isometric contraction phase, the ventricular pressure P_K rises steeply until it exceeds the pressure in the aorta P_O, at which point the semilunar valves D2 open. The heart chamber empties, overcoming a flow resistance R2, into the reservoir C_O of the aorta. Diastole is again initiated by repolarisation of the heart muscle, and during the subsequent isometric relaxation phase the ventricular pressure P_K drops, causing the aortic valves D2 to close. The aorta empties slowly into the arteries, with pressure P_O falling only slightly.

The following equations describe the mechanism outlined above, neglecting the inertial forces that arise from acceleration of the blood:

Equation	Description
dV_K/dt = Q1 − Q2	Rate of change of ventricular volume
Q1 = (P_U − P_K) / R1	Venous inflow for P_U > P_K
Q2 = (P_K − P_O) / R2	Outflow to aorta for P_K > P_O
dQ_O/dt = …	Arterial outflow
dV_A/dt = Q2 − Q_A	Rate of change of aortic volume
P_K = V_K / C_K	Ventricular pressure
P_O = V_A / C_O	Pressure in the aorta
C_K = f(t)	Activity of the heart chamber

These equations can be illustrated by an electrical equivalent circuit (Fig. 1b). Diastole and systole are described by varying the capacitance C_K.

The above equations were reproduced on the analog computer via the patch diagram (Fig. 2). The heart valves D1 and D2 are represented by amplifiers 33 and 21. The use of an amplifier circuit rather than diodes alone — which would in principle be possible — has the advantage of achieving a practically ideal diode characteristic, without threshold voltage and forward resistance, at very high reverse resistance.

The time function C_K, which represents systole and diastole, is also generated on the analog computer.

Fig. 3a shows an oscillogram of cardiac activity as achieved with circuit Fig. 2. Beyond representing normal cardiac activity, the analog computer model can be used to reproduce certain typical cardiac defects and to study their effects.

Valvular defects can be represented by modifying the diode characteristics of the amplifier circuits 33 and 21 in Fig. 2. Insufficiency (inadequate closing capability) of the valves is reproduced by connecting a direct branch in parallel between the output of amplifier 32 and integrator 30, taking sign inversion into account. Stenosis — i.e., narrowing of the passage cross-section when the valves are open — can be achieved by reducing the set value of P 36, that is, by increasing the flow resistance R1.

The oscillogram Fig. 3b was recorded with insufficient mitral valves. Compared with Fig. 1a, a reduction in the maximum ventricular pressure P_K, and thus also in the aortic pressure P_O, is apparent. In addition, the waveform of P_K has changed somewhat. After reaching a maximum value, P_K drops slightly due to leakage through D1 before D2 opens. Diseases of the heart muscle that manifest as reduced contractility of the heart chamber can be reproduced by altering the amplitude of C_K.

NEW COMPUTING COMPONENTS FOR THE EAI ANALOG/HYBRID COMPUTER 580

Two new plug-in modules for the EAI Analog/Hybrid Computer 580 are now available. These are two combination modules, briefly described below:

1. Integration Network Module, combined with Potentiometer Programming Panel, Type 12.1615, consisting of:

An electronically controlled integration network, with all analog inputs and control facilities for an integrator as in the dual version Type 12.1611
A programming panel for 5 potentiometers

This new module allows expansion of the number of integrators from 16 to a maximum of 20. The modules are installed in the first 4 slots of the analog memory (track-store units), whose maximum number is 8. Expansion of the individual integrators to the remaining slots is possible with a minor wiring change. The new module not only expands computational capacity but also allows individual control of the operating state of certain integrators that would otherwise have to be controlled in pairs.

2. Dual Multiplier, combined with output panel for 1 Dual-VDFG, Type 7.130, consisting of:

Two multiplication networks (high-precision version, as Type 7.106)
Output panel for one Dual-VDFG
2 free diodes
Reference voltage

The new module enables expansion of the total number of multipliers from 8 to 16, and is installed in the slot of the non-linear function generators.

A console is now available for housing the output devices — X-Y plotter and 4-channel display unit — with dimensions matching the main unit, allowing convenient operation of the output devices from the computer’s control panel.

HYBRID COMPUTATION IN INDUSTRIAL PROCESS ENGINEERING

“Hybrid Computation in the Process Industries” is the title of a recently published EAI booklet containing a comprehensive summary of the various application possibilities of modern hybrid computing methods in process engineering.

The 83-page book explains the basic principles of applying hybrid computing in industrial process engineering as an aid for model-based investigation and representation of process plants in the chemical and petroleum industries, by means of analog and hybrid simulation.

The introduction briefly explains the specific role of the analog and digital computer in a hybrid system.

Part 1 of the book provides an overview of the application of hybrid computing methods to the solution of general mathematical and process engineering problems, including ordinary and partial differential equations, simulation of dynamics and control, and optimisation of processes. The application of hybrid computers is explained in detail for each section.

Part 2 addresses specific problems in chemical and petrochemical process engineering, including examples of: the simulation of a chemical tubular reactor and three types of evaporators; conversion control of polymerisation reactors; automatic identification of mathematical models in chemical reaction kinetics; and system investigation for the design of a catalysis controller. Literature references are given for each example.

The book is available from EAI at a price of DM 15.—.

(Dipl.-Ing. Alberto Bento, Applications Engineer, EAI-GmbH)

MAINTENANCE

EAI is pleased to announce that maintenance contracts are now available for all EAI and Brush equipment — previously only possible for larger EAI installations.

On request, tailor-made contract proposals will be drawn up for the EAI and Brush equipment installed at the customer’s premises. Enquiries are requested promptly for timely scheduling.

(Dieter Schwarz, Ing. grad., Customer Service Manager)

THE SIMULATED APPLE TREE

With a computer one can simulate almost anything today — but it is hardly believable that this also applies to apple, pear, or peach trees, or to any kind of fruit-bearing tree.

Automated fruit harvesting, as long as no new method is developed, is subject to a major constraint: the force required to shake off all ripe (and only ripe) fruit can in practice be controlled only very imperfectly.

Techniques such as ultrasonic and mechanical tree-shaking, or the use of blowers, have been used in the past with varying success. To obtain more precise answers, scientists at the Institute for Agricultural Engineering at Rutgers University (USA) are using a desktop analog computer, Type TR-20, from EAI-Electronic Associates Inc., to simulate fruit trees and observe their reactions to various forces acting upon them.

First, the TR-20 amplifies incoming signals from accelerometers and strain gauges attached to a real fruit tree; the signals are then recorded on magnetic tape. The computer then analyses the data, from which the equations characterising the tree are derived. The equations are patched onto the analog computer and solved, enabling observation of the changes caused by applying various variable forces to the tree.

According to the scientists, the method is expected to enable the development of optimal harvesting equipment.

(Volker Koch)

EAI SERIES 10 PROCESSOR

A Special-Purpose Analog Data Processor Assembled from Plug-In Components

General Description — Series 10 Housing:

Mounts in standard 19” rack or user’s console
Self-powered with built-in power supply
10 Vdc reference, 22 Vdc (unregulated) and 15 Vdc regulated power
All connections made with close, point-to-point screw-type 10-position terminal blocks
Two or more processors may be wired together for large systems
Provision for 10 plug-in modules
Accepts up to 10 input/output lines standard or 20 I/O lines (optional)
External test jack
Pre-wired cabling from programming area to door permits easy installation of meters, indicators and switches
Built-in meter and built-in fan

Modular Components:

Power network built into every module, no wiring required
All test points and trimming potentiometers accessible without removing module from housing

Integrator Amplifier: Hybrid amplifier with field-effect front end. Drift less than 30 µV/sec when used as an integrator. Output current capability up to 50 mA when used as an inverter or integrator.

Differential Amplifier Module: High common-mode rejection (120 dB), gain up to 1000. Input impedance 10 MΩ.

Time Division Multiplier Module: 2% maximum error in X·Y, X²/Y, and similar applications.

Universal Function Generator: Variable slope, variable breakpoint, and point-expansion capability.

Current and Voltage Converter Modules: 0.1% conversion accuracy; supplied over the ranges of 1–5, 4–20, and 10–50 milliamperes.

Relay Comparators: Typical switch times of 0.7 ms; 0.03% sensitivity and accuracy.

Universal Amplifier Module: Summing circuit coverage for up to nine inputs; useful over a wide range of transfer functions and limiting applications. Stability to 5 mV over the temperature range of 0–130°F.

Please request the multi-page Series 10 Processor datasheet.

BRUSH MARK 26C — 6-CHANNEL PORTABLE RECORDER

The Brush 6-channel recorder, Type Mark 26C, is a compact, portable multi-channel recording system.

Patented, proven pressure-fluid writing system as standard
3 channels in red and 3 channels in blue — an aid for faster identification of channels
At high resolution: consistent line widths; immediately dry trace; right-angle coordinates
Additionally 4 event markers as standard equipment: 1 marker each at left and right margin, two markers between channels
Built-in 1-second timer, which can optionally control the left inter-channel marker
Built-in, fully transistorised amplifiers with 12-stage range switch
Total measuring range from 1 mV full-scale to 500 V full-scale
DC voltages up to 500 V can be applied without risk, regardless of the position of the input attenuator
Writing pens protected against overload by electrical limiters
Amplifiers have differential inputs, high noise rejection, 10 MΩ input impedance
Contactless servo system maintains writing accuracy of 0.5% of full-scale
Frequency response flat ±2%, from DC to 40 Hz at 40 mm writing width, to 100 Hz at 10 mm writing width
8 pushbutton-controlled paper feed speeds, electrically controlled; no data loss when switching speeds (1 mm/min – 125 mm/sec)

(Erwin Roth, Sales Engineer, EAI-GmbH)

APOLLO PROJECT

A few weeks ago the EAI computing centre in Washington received the largest single contract ever awarded to an EAI computing centre. On the recently installed hybrid system Type 690, the Washington computing centre will simulate the guidance and control system of an Apollo capsule during re-entry into Earth’s atmosphere. This simulation is part of the Apollo Project, which plans to land an American on the Moon by 1970.

This contract is unique not only in terms of its scope, but also in view of the success of the Apollo programme itself and the computing capabilities that the EAI 690 system offers.

A particularly important part of the entire Apollo project is the further development of guidance proposals for the spacecraft.

The Command Module forms the re-entry vehicle of the manned lunar landing project. As such, it must return from lunar orbit, manoeuvring through a narrow corridor as it enters the Earth’s atmosphere, in such a way that temperature and deceleration forces do not exceed safety limits, and finally descend safely by parachute.

This simulation study pursues two goals: first, the perfection of the flight guidance system; second, training opportunities for spaceflight itself. Apollo astronauts will be trained at the Washington computing centre in the practical manoeuvring of the Command Module by operating the control instruments.

To make the simulation as realistic as possible, a model of the interior of a Command Module is being built in the Washington computing centre. In a soundproof room, the pilot is confronted with realistic instruments and control organs.

By operating the controls, the trajectory of the capsule is computed in the 690 system. This is a complex simulation, and the fact that this problem can be solved by the 690 demonstrates the outstanding capabilities of this system. The computed trajectory is displayed on a screen on the instrument panel, showing the deviation of the actual from the pre-programmed trajectory that the Command Module must follow during the critical re-entry phase of the lunar flight.

EAI plays a significant role in the Apollo project. At the Houston computing centre, an EAI 8900 hybrid system is used to simulate the docking manoeuvre of the lunar landing vehicle with the Command Module. NASA Huntsville uses an EAI 8900 system for simulation of the Apollo propulsion system, and NASA Ames also has an EAI 8900 hybrid system for studies of the biomedical aspects of manned spaceflight.

(Volker Koch, Ing. grad., Sales Engineer, EAI-GmbH)

EAI VARIPLOTTER X-Y PLOTTERS — NEW ADDITION

The extensive EAI VARIPLOTTER X-Y plotter programme has been enriched by an additional new item: the coordinate plotter, Type 1140 M.

This is a compact 19-inch unit specially designed for recording the solution curves of analog computers, distinguished by particularly high accuracy (static 0.075%, dynamic 0.1%, repeatability 0.05%) and high writing speed (25 cm/sec on both axes). It is therefore also well suited for many other applications in industry and research.

Operating functions are clearly arranged:

Pushbuttons select the 2 scale ranges (from 50 mV/cm to 5 V/cm at input impedances from 50 kΩ to 1 MΩ)
Switch from fixed scale value to variable subdivision controlled by 10-turn potentiometer
Zero position of the pen is set across the full plotting area via 10-turn potentiometer; the zero point can be suppressed by half the plotting format size (28 × 43 cm) on both axes
When connected directly to the analog computer, all functions of the plotter can be controlled from the computer; a computer cable provides the necessary connections

Technical specifications:

Mains connection switchable: 220 V/60 Hz or 115 V/60 Hz
Paper held by suction holes distributed across the writing surface (vacuum by fan)
EAI supplies interchangeable ink cartridges in red, green, and black

(Dipl.-Ing. Hartmut Leuschner, Sales Engineer, EAI-GmbH)

EAI ANALOG/HYBRID COMPUTER COURSES — FIRST HALF OF 1968

Locations and Dates:

Munich: 4–8 March 1968 (Registration deadline: 21 February) — Künstlerhaus, Lenbachplatz
Aachen: 1–5 April 1968 (Registration deadline: 23 March) — Hotel Quellenhof

The EAI Analog/Hybrid Computer Courses for the first half of 1968 will take place in the first week of March and first week of April in Munich and Aachen, respectively. This constitutes the 12th and 13th courses organised by EAI.

Each course is divided into two sections. Part 1 covers programming of the classical analog computer (without logic); Part 2 contains lectures on the parallel-organised hybrid computer. Lectures are held in German (Exception: Part 2 of the Munich course, which runs in English).

Participants will be given the opportunity to practise worked examples on the available Analog/Hybrid Computer after the lectures. For this reason, the number of participants is limited.

Course fees: DM 400.— per person for the 5-day course. Participation in only one of the two parts is charged at half the fee. For EAI customers who already own an EAI PACE analog computer, participation of 2 persons for 5 days is free of charge. Additional participants pay half fees.

Programme overview:

Day	Topic
Monday	1. Introduction: Principles of operation and applications of analog, digital, and hybrid computers; computing methods and operation of modern analog computers. Mode control. Reference voltage. Demonstration and practicum.
Monday–Tuesday	2. Structure of the analog computer. Linear computing components. Non-linear computing components. Further computing components. Peripheral devices.
Tuesday	3. Model representation of dynamic systems. Solution of system equations using the analog computer. Demonstration and practicum.
Wednesday	4. Programming the Analog Computer I — Amplitude and time scaling of computing equations. Programming of ordinary differential equations. Redundancy. Algebraic loops. Stability. Static and dynamic test. Static and dynamic accuracy. Demonstration and practicum.
Wednesday	5. Practical Application of the Analog Computer I — Simulation. Demonstration and practicum.
Wednesday	6. Practical Application of the Analog Computer II — Measurement data processing. Demonstration and practicum. Film screening.
Thursday	7. Programming the Analog Computer II (special computing methods without parallel logic). Automatic scaling. Differentiation. Sampling as subroutine technique. Boundary-value problems in ordinary differential equations. Inverse functions and implicit technique. Optimisation on the analog computer without parallel logic. Demonstration and practicum.
Thursday	8. Description of the parallel-organised logic (hardware). Structure of a digital augmenting system. Clocked and unclocked logic. Combinatorial elements of the parallel logic.
Wednesday (Part 2)	Introduction to interactive computing methods. Examples.
Thursday (Part 2)	Subroutine technique. Optimisation. Solution of algebraic equations.
Friday (Part 2)	Partial differential equations. Practicum. Discussion.

(Dipl.-Ing. Alberto Bento, Applications Engineer)

NEW BRUSSELS OFFICE

EAI is pleased to announce that, from 15 March 1968, EAI-Electronic Associates Inc. European Division will occupy new, modern offices in Brussels:

EAI-Electronic Associates Inc., European Division 116–120, Rue des Palais, Brussels 3, Belgium Telegram address: pacebelg-brussels Telephone: 032/16.81.15 Telex: Brussels 21,10c

Previously at: Centre International, 22nd Floor, Place Rogier, Brussels, Belgium (Telex: 2.21.10 — Telephone: 18.40.04)

PRODUCT LISTINGS (from the issue)

EAI PACE TR-20 Desktop Analog Computer
EAI PACE TR-48/58 Desktop Analog Computer
EAI 580 Analog/Hybrid System
EAI Digital Augmenting System DES 30
EAI Series 1110, 1125, 1130, 1131, 1132, 1133 XY Plotters
EAI Series 1125 Digital Voltmeters
EAI Series 1140 (Variplotter)
EAI Data Acquisition Systems
EAI Education & Training
Brush Mark 26C 6-Channel Portable Recorder
Model 6200 Display Unit (Nixie tube readout)
Model 6201 DVM Module
Model 6202 Counter Module
Model 6203 AC Converter Module
Model 6240 Rack-Mounted DVM
MC Laboratory Cables and Accessories (with MC-Knüpftülle connector system)

EAI Analog/Hybrid Computer Newsletter — Issue 013, October 1967 – February 1968