Instruction Manual: Model 3500 Analog Computer (Portable)
Instruction Manual
MODEL 3500
ANALOG COMPUTER
(Portable)
Manufactured By
DONNER SCIENTIFIC COMPANY
Concord, California
A Division of
Systron-Donner Corporation
January 1960 Serial No.
—JIYSTRON —TONNER
OU
WARRANTY
Systron- Donner instruments are warranted during a period of one year from date of shipment to
original purchaser to be free from defects in material and workmanship. This warranty does not
apply to vacuum tubes, except as they are warranted by tube manufacturers. The liability of
Seller under this warranty is limited to replacing or repairing any instrument or component
thereof which is returned by Buyer at his expense during such period and which has not been
subjected to misuse, neglect, improper installations, repair, alteration, or accident. Seller
shall have the right of final determination as to the existence and cause of a defect. In no
event shall Seller be liable for collateral or consequential damages. This warranty is in lieu
of any other warranty, express, implied or statutory, and no agreement extending or modifying
it will be binding upon Seller unless in writing and signed by a duly authorized officer.
RECEIVING INSPECTION
Every Systron Donner instrument is carefully inspected and is in perfect working order at the
time of shipment. Each instrument should be checked as soon as received, If the unit is
damaged in any way or fails to operate, a claim should immediately be filed with the trans-
portation company.
REPAIRS
Whenever a Systron-Donner instrument requires service, the nearest Systron-Donner represen-
tative should be contacted; all representatives will provide immediate service or arrange
factory returns when necessary.
Please specify both model and serial number in all correspondence concerning Systron-Donner
instruments. Address all inquiries on operation or applications to your nearest sales represen-
tative or Sales Manager, Instruments, Systron-Donner Corporation, 888 Galindo Street, Concord,
California.
CONCORD. CALIFORNIA
TABLE OF CONTENTS
Page
Warranty. 2 6 wk ee ee ke ee ke ti
~ Introduction. © 2 2. ee ee eT
Computer Theory . 2... . . . . ww ee ee ew ew ee
_ (Outline of Computer Operations For Non-Electronics People)
Programming and Operation. . . . . . . .. re © |
Circuit Description . 2... . we eee ee 9
Servicing . 2. we 20
PartsList . . . ee ee
Appendix
Schematic Diagrams: Model 3500 Computer, Dwg. No. 3899
Model 3103 Amplifier, Dwg. No. 5217
Power Supply and Regulator, Dwg. No. 3920
Demonstration Problem Connections
Tech Notes No. 1 and No. 2
Potentiometer Loading Chart
Supplementary Instruction Manuals:
Model 3103/4 DC Amplifier
Power Supply and Voltage Regulator
LIST OF ILLUSTRATIONS
Figure 1 — Model 3500 Portable Analog Computer (with Auxiliary reese
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Figure 3 — Operating Controls and Indicators . . . . ..... . di
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MODEL 3500
RACK MOUNTING INSTRUCTION
Reference instruction manual:
Fig. 4, page 24
Fig. 2, page Vv
To prepare unit for rack mount - Fig. 4.
Step l. Remove (10) panel mtg. screws and cup washers
retaining:
(a) Control Panel.
(b) Patch panel.
(c) Potentiometer Panel.
retain hardware for rack mounting
Step 2. Remove (4) mounting screws and washers retaining:
(a) Rear trim strip.
Step 3. To remove side panels.
Release the (2) wing screws on rear apron allowing
it to fall back.
Remove from inside rear flange (2 per side) remaining
Side panel screws and washers. Side panel is now
removable.
To rack mount - Fig. 2
Close (2) wing screws on rear apron.
Caution - Do not remove protective mesh from fan. opening.
Assemble panels to rack per fig. 2, using all hardware from
Step 1. Unit is now ready for operation ver manual, Programming
and Operation Section, beginning page 1l.
ar
a
Model 3500
Figure 2 — Model 3500 In Rack Mount
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4 C44
INTRODUCTION
I] = General Description
The Model 3500 is a low-cost, portable, analog
computer with very high performance characteris-
tics. Its ten-amplifier capacity (five integrators
and five summers) is sufficient for handling a large
majority and a wide variety of computer applica-
tions. The computer is completely self-contained
within a small case and requires only a selection
of plugin components (resistors, capacitors, and
patchcords) to be fully operational.
The striking simplicity of the overall design
reduces all operations to fundamental steps which
can be readily understood by persons unfamiliar
with electronics, without sacrificing accuracy or
versatility. Circuit components are presented on
the problem board in a highly intelligible manner,
giving an immediate visual analogy between the
physical computing circuit and the problem diagram.
In addition to fulfilling the important need for
a portable computer easily accessible to the in-
dividual engineering-designer and scientist, the
Model 3500 is suitable for widespread applications
for automation in the monitoring and control of
industrial processes and is ideal for student lab
work and classroom demonsiration. For this latter
purpose, the computer may be mounted in a dis-
play-type rack, as shown in Figure 2, and the
operational Model 3530 Remote Problem Board set
may be employed. Each of these units commands
up to five amplifiers in the computer independently
of the second unit, thus converting the Model 3500
into separate small computers. By means of the
auxiliary Model 3520 Multiple Control Unit, two or
three portable computers may be slaved together,
increasing the amplifier capacity to twenty or
thirty. This accessory also provides automatic
reset for the computers, which enables one jo re-
peat the solution continuously as for displaying
on an oscilloscope.
The Model 3500 may be used directly as a
complete DC amplifier system by means of the
amplifier input-output connectors onthe front panel.
It can also double as a sine-cosine function gene-
rator, a low-frequency signal generator, a wave
analyzer and a precision null volt-meter. (Circuits
for these applications are described in the ap-
pendix.)
Model 3500
2
— Computer Applications
In its primary role, the basic analog computer
is used to give accurate solutions of linear (and
certain classes on non-linear) differential equa-
tions and transfer functions. With auxiliary analog
instruments, including function generators, servo
or electronic multipliers, and transport time delay
generators, general and complex non-linear equa-
tions may be solved. The operational amplifiers
in the computer perform the functions of algebraic
addition, subtraction, multiplication by a constant,
sign-changing, integration, and differentiation.
Being an analog device, whereby physical
quantities are represented by computer voltages,
the computer may be used as an accurate model
of an arbitrary physical system, thus saving im-
measurable time in engineering design, construc-
tion, and analysis. System parameters are varied
by adjusting the computer potentiometers.
This analog computer can make an invaluable
contribution for study, demonstration and research
in a wide variety of fields. A partial list of sub-
jects includes:
AERODYNAMICS
CHEMICAL KINETICS
ELECTRICAL ENGINEERING
antenna design
filter network design
servo system analysis
Lissajous figures
Modulation
damping factor
AC circuit fundamentals
Fourier Analysis
Mairix Analysis
frequency, phase, and time response
MECHANICAL ENGINEERING
simulation of dynamic systems
structural analysis
PETROLEUM ENGINEERING
MATHEMATICS
differential equations
simultaneous algebraic equations
partial differential equations
LaPlace transforms
logarithmic decrements
basic meaning of derivative and integral
of a variable
quantitative study of equations on a
parametric basis
METEOROLOGY
MEDICAL AND PSYCHOLOGICAL RESEARCH
human environment
cardio-vascular system
nervous system
orthopedics
genetics
virology
CLASSICAL PHYSICS
trajectories of freely falling bodies
equations of simple harmonic motion
damping factor
heat transfer analysis
fluid mechanics
optical ray tracing
NUCLEAR PHYSICS
radio-active decay series
electron trajectories
operation of a cyclotron
REACTOR KINETICS
STATISTICS
auto- and cross-correlation
economic forecasting
3 — Detailed Description
The basic components of the computer are the
ten high-gain DC amplifiers which rival in per-
formance those used in computers many times
more costly. They are offered with an option of
chopper-stabilization, or without stabilization. At
any time, the unstabilized amplifier can be con-
verted in the field or at the factory by adding com-
ponents to the printed circuit board. The voltage
range of these amplifiers is between +100V and
-100V with 4 milliamperes maximum output cur-
rent. (See ‘‘Specifications’’ for complete data.)
The panel meter of the Model 3500 has four
direct-reading scales and a null voltmeter function
which permits measurements and settings to the
nearest 0.1 volt (equal to an accuracy of three
significant figures). Five potentiometers are a-
vailable for initial condition adjustments or co-
efficient settings. These may be supplemented by
the optional Models 3570 or 3571 ‘‘pot’’ strips or
individual plug-in potentiometers.
A set of compute-reset contacts located on
the problem board permits two of the summing type
amplifiers to be converted to integrators and also
may be used to synchronize a Donner Model 3400
Computer or other auxiliary equipment with the
Model 3500. Plug-in problem board components
supplied for the Model 3500 include encapsulated
resistors of common values between 0.1 and 10
megohms with either 1% or 0.1% tolerance, and
0.1% polystyrene capacitors of 0.01, 0.1 and 1.0
microfarad values. (See Appendix for complete
listing.) A highly regulated power supply furnishes
all necessary power for the DC amplifiers as well
as precision reference voltages for the null volt-
meter. The Model 3500 also includes positive and
negative bias voltage supplies which are used as
sources for problem constants, amplifier balancing
and overload indication circuitry, and four diode
limiters for special computing circuits.
4 -— General Specifications
Detailed specifications for individual compo-
nents are given in supplementary manuals.
Stabilized Amplifiers (with 100K resistors)
short-term stability: +200uv
60 cps noise: 5my, r.m.s.
Frequency response:
resonant at 60kc
-3db at 85kc
drift (as unity integrator):
+150uv/second
Meter
Null accuracy: +0.1 volt
direct ranges: +3V, 10V, 30V, 100V
Input Power
115V or 230V, +10%, 50-60 cps
single phase, 225 watts
Size: 5%" h by 12%" d by 19" w
Shipping Weight: 28 lbs.
Mode! 3500
5
MODEL
3731 Electronic Function Multiplier .
3735 Electronic Function Multiplier
(High-Accuracy)
3732 Quarter-Square Multiplier
3750 Variable Base Electronic Function Generator
Fixed-Function Generators.
3770 Transportation Delay Generator.
3121. Amplifier Receptacle
3103 Dual Amplifier .
3104 Dual Amplifier .
3570 Potentiometer Strip
3571 Potentiometer Strip .
3520 Multiple Control Unit .
3530 Remote Problem Board Set .
Plug-in Components .
(See Appendix for Further details)
Model 3500
Accessories
DESCRIPTION
Provides two channels of multiplication. Each
produces output voltage equal to .01XY where both
X and Y may vary between -100 and +100 volts.
Diode-type multiplier with characteristics similar to
Model 3731.
Uses 24 biased diodes to simulate electronically
the curve of any single-valued, continuous function.
Series of plug-in circuit cards; each set at factory
to simulate a single function.
Provides two separate or cascaded channels for
accurate time delay of low frequency signals.
Three available ranges of delay cover .005 to 20
seconds.
Mounts up to five dual amplifiers for use as auxi-
liaries.
Chopper-stabilized type used in the Model 3500.
Identical to 3103, but chopper-stabilizer circuit is
omitted.
Contains 8 single-turn composition potentiometers.
Contains 8 ten-turn wire-wound potentiometers.
Controls 2 or 3 Model 3500 computers for slave
operation. Provides automatic reset.
Each board independently commands five amplifiers.
Patchcords
Resistors, 1%, deposited carbon and 0.1% wire-
wound.
Capacitors, 0.1% polystyrene
Potentiometers, individual, single turn, 0.1 megohms
(part No. 3961)
Operational relay, double-pole, double-throw (part
No. 3965)
COMPUTER THEORY
Outline of Computer Operations for Non-Electronics People
NOTE: Throughout the succeeding chapters cross-
references will be made to facilitate use of the
manual. For example, ‘‘(see 3.2)’’ indicates para-
graph reference within the same chapter; ‘‘(see
II|-3.2)”’ refers to another chapter.
1 - General
A detailed understanding of analog computers
is not necessary to solve the majority of problems
on the Model 3500. The supplementary theory book-
let furnished with the computer is intended as a
comprehensive reference, and may serve as the
basis for a course in analog computation. How-
ever, the brief outline presented here, together
with the supplementary examples in the appendix,
will acquaint the novice with the essential steps.
The steps of computer operation are:
]. Arrangement of problem equations (drawing
of preliminary diagram),
2. Magnitude and time scaling, with transfor-
mation to mochine equations, if required.
3. Preparation of a computer circuit diagram,
4, Programming the computer problem board
and setting problem parameters according
to the diagram.
5. Recording or observing the solution.
It is usually helpful to make a preliminary
shorthand diagram after step 1, which eventually
may take the place of Step 3.
2 = Computer Operations and Notation
The analog computer performs operations with
varying d.c. voltages which car se made to ob y
the same set of mathematical equations used to
describe a given physical system. Thus, it can be
used as a convenient electrical model of the sys-
tem to be studied, giving continuous, dynamic so-
lutions in real, ‘‘fast’’, or ‘‘slow’’ time. Problems
most suitable to the analog computer may involve:
]. Ordinary differential equations with con-
stont coefficients.
dy dy
o> + pape cy = f(x)
(single equations or sets)
2. Algebraic equations (roots of polynomials,
matrices, simultaneous linear equations).
3. Partial differential equations, e.g.:
a’*e sd 30
Heat Flow 573 h2 OOP
4. Boundary value problems (all initial con-
ditions not known) e.g.:
vibration problems, or bending of beam
supported at both ends.
5. Implicit solutions
F (x,y,z) = 0
6. Non-linear problems (with auxiliary squip-
ment), e.g.:
d?y dy
ia eh * sin y . y = f (x)
also discontinuous non-linearities such as
friction, back-lash, limiting.
7. Real-time physicc! simulation in which the
computer substitutes for a component in a
physical system.
8. Data processing (in-line or delayed), inte-
gration, algebraic calculations auto- or
cross-correlation.
The basic component is the operational amplifier,
symbolized . This component performs
the operations listed in Table | when connected
with passive components (resistors —AAAAv= and
capacitors a ke. as shown in the ‘‘Computer
Circuit Symbol”’ column. After one gains familiarity
with circuit connections, he may use only the simp-
lified operctional symbols (shown in the center
column) as shorthand for the circuit symbols.
Further explanation is given below. Before at-
tempting to demonstrate the examples presented in
this section, one should become acquainted with
the method of connecting and adjusting components
given in the succeeding chapters, ‘‘Programming
and Operating the Computer’’.
Model 3500
a‘p = % Dv fN X‘D
° (X"*) nw, *
= JUdIDIjJa07 *4
8 a l uy UOIIpuod jDIHU] = y
[24 7 : -
1 + apte f” 28. o— Wo | y+ xf- 1 + xf
l (Xx)
uolfosBayuy *3
Zoe
(A - X) (A)
(Z - ley_ = % | % (A = X)-
I ' (x)
i. uol}oD4YGng *q
Z0
° pwr fa
(fag + ) = 9 i" ; 1 ; (AS + X)- ¢ (A) (AG + X)-
| oN | Lino | ——(x)
{ lL ° Burwuing *>
( ul . ar ° wy .
a = °a) - X Ol-
ty W\—e Z|
[ (xOL-) (Xx)
Wenp- = %% NJot fupjsuo7
PHRPee,, OL b Aq uoljooijdisinw *g
(L fo up)
#0, wa ul
_ Gag we LeeAnn a
‘o- = 3 NY lL (X -) NY (x) xX . l-
PPP HPAL l
BulBuoys-uBig *y
NOILONN4 YFsASNVYL
TOEWAS LINDYID YAFLNdWOD
TOGWAS TIVNOILVYsdO
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NOILVLON YALNdWOD - | AVGVL
3
- Sign-Changing (Inverting)
and Multiplication by a Constant
In terms of the actual voltage change performed
by the computer circuit in examples.A and B (Table
|), the expression or transfer function is:
-R
e = : * €in
Rin
or variable.
where e,, may be constant
R¢ and R,, are fixed-value plug-in resistors con-
nected physically as explained in Chapter III, par.
4.2a. If R¢ = Rj,, then e, = e,,. When the ratio
R,/R;,, has some value other than 1, as in example
B of Table 1, multiplication or division by a con-
stant is performed. Besides the discrete ratios
obtainable with the available resistors (see Appen-
dix for a complete list of values), multiplication
or division by any value of constant may be a-
chieved by using an adjustable coefficient potenti-
ometer in conjunction with the amplifier (see 6.1).
4 ~— Summing and Subtraction
With several input sources, as in example C
(Table 1), the expression for the operational ampli-
fier circuit becomes:
eo = = (e; + e2 + etc.) if all resistors are equal,
or
R R
f f
e = - (e —+t+e + etc.)
° 1 Ry 2 R>
if resistor ratios other than 1 are selected.
By combining the summing and inverting opera-
tions (examples A and C), subtraction of two quan-
tities is made possible, as illustrated in example D.
Demonstration Problem A
After reading the following chapter on ‘‘Pro-
gramming and Operating’, connect the circuit shown
below and confirm that eg measures 68 volts.
OPERATIONAL DIAGRAM
e,=-80v-—_}
0.2 ey
@o=+60v
Actual problem board connections are shown under
‘‘Demonstration Problem A Connections’’ in the
Appendix. Note that e; and eg are obtained from
the +105 and -105 fixed bias terminals by means
of potentiometers (see I|I-4.3C). Use of the meter
is described in III-3.
-105v
+105v
CIRCUIT DIAGRAM
REb=1
+60v
Model 3500
5 = Integration
If a capacitor C is substituted for resistor Rg,
as in example E of Table 1, the amplifier elec-
tronically performs integration with respect to time
and the expression for the circuit can be written:
t
eo = foi dt + K, ifR*C = 1
°
(Normally R = 1 megohm and C = 1 microfarad)
NOTE: The value of R is always calcu-
lated in megohms (M) and C in microfarads
(mfd).
“K" is the initial condition constant which is
inserted electrically as a preliminary charge on
the capacitor when the computer is placed in
“‘Reset’’; that is, before the input voltage is ap-
plied to the amplifier by turning the function switch
to ‘‘Compute’’. (See IIl-4.3a)
Analogous to example C of Table 1, if an in-
tegrating amplifier has several inputs with different
values of R, the expression is:
t
ne + 2 + avete.) dt +k
° R,C RC
which tells us that the amplifier both sums and in-
tegrates at the same time.
Demonstration Problem B
Connect the circuit shown below:
OPERATIONAL DIAGRAM
10
0.5
eo=+10v
e,=-2v
K=0v
Substituting the given values of e, R, K, and
C into the equation in paragraph 5 yields:
t -2 10
e --f ( +—) +0 = 20+-5t=15¢
° ° 0.1 2
The result may be observed dynamically on the
100V direct-reading scale of the meter when it is
connected to the amplifier output. e, will increase
15 volts per second for over six seconds after the
computer is placed in the ‘‘Compute’’ mode until
the amplifier reaches saturation (+100 volts out-
put) at which time the overload lamp will light and
the solution is no longer valid. Refer to the ‘‘De-
monstration Problem B Connections’? diagram in
the Appendix.
Model 3500
-105v
-2v c=1
R1=0.1 |
aa AAA METER
+105v WA/VPomnnd al
CIRCUIT DIAGRAM
6 =
Coefficients
6.1 Fractional Gain: The coefficient potentiometer
is normally used as shown below as a means to
obtain a fractional part of the amplifier input
voltage.
The output voltage of the amplifier, therefore, may
be expressed as:
where a is the desired fraction (always less than
unity) established by the setting of the potentio-
meter. Whereas the gain of an amplifier is usually
limited by choice of Ry and R;,, to the integers 1,
2, 5, 10, or their reciprocals, any fractional value
of these integers may be established by the coef-
ficient a, (See III-4.3B for technique of adjustment.)
6.2 Reciprocal Coefficients: The coefficient po-
tentiometer is also commonly used in the circuit
shown below, yielding gains greater than unity.
The transfer function for the amplifier circuit is:
-]
C= —— ein if Ry = R,
n
+At
The gain of the circuit is seen to be inversely
proportional to potentiometer setting a. In this
circuit, a should not be set to a value of less than
0.1. To obtain a gain greater than 10, change the
ratio of R¢/R;,, as in par. 3.
7 — Solution of Differential Equations
By combining the basic operations described
in Table 1, the computer is able to perform one of
its basic roles, the solution of linear differential
equations. A simple, typical problem occuring fre-
quently in mechanical, electrical, and hydraulic
systems, which can be represented by a general
second order differential equation, will serve to
illustrate the common approach to problem pre-
paration:
dy dy
+ a—
dt 2 dt
The equation: + by = At
which can be abbreviated: Y + ay + by = At
Since the computer may perform successive inte-
gration, generating lower order derivatives from
the highest order derivative, the equation is nor-
mally put into the form:
yY = -ay - by + At
This equation can be represented by the following
block diagram:
(1) (2) (3)
de
=r S
hi
The computer solution is realized by interconnect-
ing components to perform the operations described
by the block diagram. The block diagram can be
translated immediately into the following computer
diagram, using operational symbols. (Remember
that each amplifier produces a sign-change!)
Model 3500
Vv
+At
L
-ay
A/a
Note that if the term ¥ is not actually of interest,
the summing and integrating operations could be
performed simultaneously by one amplifier. The
circuit diagram would then become:
=
tf
\Aa
8 — Problem Scaling I!lustrations
D> ty
The following illustrations should be studied
and then demonstrated, referring to the following
chapter on ‘‘Programming and Operating the Com-
puter’’ as necessary.
Demonstration Problem C
Consider the first-order differential equation
representing uniform linear motion:
; _ dx ‘
velocity =—— = A or x= A
dt
(eq. 1)
The computer diagram for ‘‘solving’’ this equation
would be simply:
(x) -x
A
The constant input A, representing constant velo-
city, is obtained from the fixed 105 volt bias by
setting a potentiometer for the desired fractional
output value. Using A = 25 ft./second, the com-
plete operational diagram becomes:
YA
5V
+105v ©
Model 3500
is adjusted for an output of
Amplifier
Potentiometer
25 volts (see II|-4.3c.).
used if it is desired or necessary to read x with its
true polarity. The equivalent circuit diagram for
the problem is given below, and the actual problem
board connections are shown on the ‘‘Demonstra-
may be
tion Problem C Connections’? diagram in the
Appendix.
c=1
+105 -——{ |—
METER
POT R=l
1 25v -x +)
From equation (1) we know that the solution is
Sdx = SA dt or X = At + K_= (eq. 2)
K is the initial condition, X,. For this example
set X, = 0 ft. (see II|-4.3a). As seen from equation
(2), the output can be expected to increase linearly
from zero to -100 volts in four seconds, beginning
at t = 0 when the computer is placed in the ‘‘Com-
puter’’ mode. When the amplifier output exceeds
100 volts, it may saturate (the overload lamp
lights) and the solution is not valid beyond this
point.
Magnitude Scaling
If, in Example C, A = 200 feet/second, and
we wish to compute X for a second, it will not be
possible to represent the problem quantities by
voltages of equal value since the maximum range
of the amplifiers is +100 volts. In this case, it.is
necessary to scale the magnitude of A and conse-
quently, X. Let us use A/2 = 100 volts, resulting
in an output of -X/2. (If K has some value other
than zero, it would have to be scaled down to K/2
also.) The computer equation is:
= — (eq. 3)
To achieve the 1/2 magnitude scaling, it is only
necessary to readjust potentiometer 1 for an out-
put of 100 volts. The output -X/2 will now in-
crease linearly from zero to -100 volts in only
one second, representing an actual increase in X
to 200 feet for the same period.
Time Scaling
The one second ‘‘real-time’’
computing period
of this example may not be convenient for observ-
ing the solution on the meter, oscilloscope, or
recorder — whichever is being used for monitoring.
Indeed, for some problems it may be desirable to
simulate a phenomenon lasting only a few mil-
lionths of a second. This would not be possible
without time-scaling the computer problem to within
the response range of the computer and the re-
corder. On the other hand, it may be desirable to
program a phenomenon which lasts many hours in
real time to occur within a relatively brief period
in the computer.
In the present example, let us slow up the
solution from one second to ten seconds.
Let t (real time) 0.1T (machine time)
so that dx. 10 2%
dt dT
Substituting in equation (3):
1 A
eo
2 dT 2
d a MAT (eq. 4)
an — = . 7
2 102 a“
where T = 10¢
These equations tell us that by using an amplifi-
cation factor (or ‘‘gain’’) of 1/10 of the input A/2,
the output will increase at 1/10 the former rate
and we will have achieved a time-scale transfor-
mation of 10.
It is not necessary to change the setting of
potentiometer ] to achieve the time scaling. In-
stead, change the amplifier gain from a value of 1
(1/RC = 1, where R = 1, C = 1 mfd.) to 1/10 (1/RC
= 1/10, where R = 10M, C = 1 mfd). (Refer to Table
1, step E). The operational diagram is:
+105v GQ); 0.1
5=100v “Fr-AT
If no 10 megohm resistor is available, then it will
be necessary to reset the potentiometer to 1/10
its initial output value, or 10 volts. The output
-X/2 will now increase from zero to -100 volts in
ten (T) seconds, representing a change in X of
zero to 200 feet in one (t) second of real time.
Additional demonstration problems are pres-
ented in the Appendix.
Model 3500
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DEMONSTRATION PROBLEM CG
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PROGRAMMING and OPERATION
1 — Operating Controls and Indicators
Figure 3
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Name or Panel Legend Explanation
@ POWER (switch and ‘‘on”’ indicator) Applies all operating power.
@ FUNCTION
RESET Applies initial conditions preparatory to running
the problem solution.
COMPUTE Initiates the problem solution.
HOLD Interrupts the problem solution, maintaining in-
stantaneous values.
METER RANGE
100V, 30V, 10V, 3V. Direct-reading meter ranges.
NULL Null voltmeter (0.1 volt sensitivity).
REFERENCE _ Calibrated dial which selects comparison voltage
for null voltmeter.
POTENTIOMETERS Used to select initial condition voltages for in-
tegrators and as coefficient potentiometers.
OVERLOAD Each lamp lights up when output of corresponding
amplifier exceeds 100 volts to indicate error
in solution.
BALANCE Screwdriver adjustment for balancing correspond-
amplifier.
RECEPTABLES J407 & J408____
For connecting optional remote problem boards or
for connecting amplifiers to external equipment,
Model! 3500
1]
2 = Preliminary Adjustments
2.1 Warm-Up
Turn on the panel power switch and allow the
Model 3500 to warm up for at least ten minutes
prior to making any of the adjustments described
on succeeding pages. The amplifier overload indi-
cators will light up when the computer is first
turned on. Normally, they will extinguish after one
minute. If an amplifier is unconnected, it will be
necessary to plug-in a feedback resistor between
the amplifier input and output terminals (see 4.2).
2.2 Balancing the Amplifiers
To perform correctly, each amplifier must be
balanced so that when an input of zero volts is
applied, the output will also be virtually zero. The
chopper-stabilized type amplifiers are highly stable
and will seldom require a balance adjustment. They
should be checked at weekly intervals, however,
while the unstabilized amplifiers should be check-
eddaily. Proceed as follows:
1. Connect each amplifier, in turn, as an in-
verter with a gain of 1000, if it is chopper-
stabilized, or a gain of 100 if it is un-
stabilized. The reciprocal coefficient cir-
cuit (see ||-6.2) is most convenient for
obtaining these large gains. Use the
REFERENCE potentiometer as shown
below:
BALANCE CIRCUIT
Circuit Diagram
For stabilized amplifiers, set the REF-
ERENCE dial to .010 and for unstabilized
amplifiers set the dial to 0.100 (see 3.2a).
2. Connect the meter to read the output volt-
age of the amplifier (see 3.1). Select the
3V meter range.
3. The meter reading should not exceed +0.4
volt for any amplifier, although it may vary
within this limit*. If correction is neces-
sary, turn the corresponding amplifier
screwdriver BALANCE adjustment (on the
front panel) until the average meter reading
is zero. A small screwdriver is provided for
this adjustment.
Problem Board Connections
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REE —METER+ »
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* This error represents a typical offset at the amplifier sum-
ming junction of 400 microvolts for the stabilized ampli-
fiers or 4 millivolts for the unstabilized amplifiers.
Model 3500
4. Remove the connections to the amplifier
and then repeat these steps for all remain-
ing amplifiers (or at least the ones which
are to be used). When finished, return the
METER RANGE switch to 100V.
3 — Using the Panel Meter
The panel meter may be used either as a
direct-reading meter for monitoring the outputs of
amplifiers and for general measurements, or as a
null voltmeter for measuring with 0.1% accuracy
coefficient potentiometer settings, initial condition
and other constant voltages in the computer and
in external equipment.
CAUTION! Do not leave the meter in the
NULL voltmeter function while running a
problem solution or monitoring amplifier
outputs. The meter may load the ampli-
fiers, giving erroneous results.
3.1 To Use the Meter for Direct Voltage Readings
Set the METER RANGE switch to the desired
scale. Normally, use the 100-volt range for all
initial readings and then select the appropriate
smaller scale. Connect the meter as follows:
—METER+
eo 86.
X XN
*
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— to unknown voltage
A positive voltage is indicated on the meter by
deflection to the right and a negative voltage by
deflection to the left.
Model 3500
3.2 Null Voltmeter
When the METER RANGE switch is set at the
NULL voltmeter position, the meter compares the
unknown input voltage with a known reference
voltage selected by the REFERENCE knob. This
may be represented as in the diagram below:
Unknown Known
Input Reference
Voltage Voltage
The REFERENCE potentiometer, when used in
the NULL function, selects a meter reference volt-
age between 0 and +100 volts, accurate to the
nearest 0.1 volt.
a. Reading the Dial: Each revolution of the REF-
ERENCE dial represents a ten-volt increment.
To select a reference voltage of +54.6 volts,
for example, turn the REFERENCE knob until
‘‘5’’ appears in the digit window and the pointer
indicates ‘‘46’’ on the dial face. When measur-
ing coefficient potentiometer settings (see
4.3b), the REFERENCE dial reading will be
interpreted as the ratio of reference voltage
(output at the REFERENCE POTENTIOMETER
ARM) to 100 volts, (the full voltage across the
REFERENCE potentiometer when connected).
For instance, in the previous example, the read-
ing of 5-46 will be interpreted as 54.6 V/100V,
or 0.546.
b. Null Voltmeter Connections: The diagram below
shows problem board connections for measuring
a positive unknown voltage with the null volt-
meter. (For coefficient potentiometer adjust-
ments, refer to 4.3b). To measure a negative
voltage, substitute the -NULL terminal for the
+NULL terminal.
+NULL- REF. —METER+
28
“SF to €
x
—NULL =
To measure the unknown fixed voltage e,, ad-
just the REFERENCE knob until the meter
indicates zero and then read the REFERENCE
dial.
13
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Programming The 8
Problem 8sa::
4 =
4.1 General
The computing circuit described by the final
diagram is constructed on the problem bourd by
interconnecting the various computing elements of
the computer, all of which have terminations on
the problem deard. The arrangement and marking of
the problem Loard allows construction of a physical
ly resembles the prepared cir-
circuit whic Ss
cuit ciagram. All problem board terminals of com-
puting elements are identified by their common
example, amplifiers ,
potentiometers f “S , diodes O—B-o
Auxilicry terminals such os METER, GROUND 93,
and +109V ore clearly labeled. In the illustrations
symbe!s; for
in this section, dotted lines are used to indicate
plug-in resistors &-W--g , capacitorso- - 4J--©,
and patchcords.
CAUTION!
WHEN THE COMPUTER IS ON, APPROXIMATELY
100 VOLTS D.C. EXISTS AT THE 105V TERMI-
NALS AND POSSIBLY AT MANY OTHER TERMI-
NALS ON THE PROBLEM BOARD. BE CAREFUL
NOT TO CONNECT THESE TERMINALS TO
GROUND OR THE COMPUTER CHASSIS. ALSO,
DO NOT TOUCH THE EXPOSED METAL TIPS
OF THE PATCHCORDS.
4.2 Amplifier Terminals
a. Summing Amplifiers: There are two basic ampli-
fier terminal configurations. The typical sum-
ming or inverting operational circuit is generally
represented as:
R¢( feedback)
Ry
€1 OVW
R2
eo WAV ‘ out
summing
junction
OR se |
en Sout
The terminals of amplifiers nos. 6 through 10
normally will be utilized as below:
Rf *
rN 7 / (EITHER POSITION)
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1 | Reg °
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\f additional inputs are needed, two or more
plug-in components may be stacked at the same
terminais. Amplifiers nos. 6 and 10 have extra
input terminals.
b. Integraior ~ Summing Amplifiers: For the typical
integrating circuit generally represented by:
hs
R]
0
LI Pl_.
R2 HOLD
_s OVW" CONTACT 1
INITIAL
CONDITION
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the terminals of amplifiers nos. 1 through 5 are
normally utilized as below:
Cc
e, ~--- Ow {f
Ry
oo AA, a
Sg ov e
(Refer to Dwg. No. 3899 in the Appendix for
the complete circuit diagram of an integrating
amplifier.) The initial condition voltage source
is obtained from the corresponding IC potentio-
meter in the upper-right portion of the problem
board.(See 4.3afor connections and adjustments.)
Mode! 3500
FEEDBACK RESISTOR
Any of Amplifiers nos. 1 through 5 may also be
used for normal summing and inverting (sign-
changing) operations by inserting a patchcord
across the ‘‘hold’’ contacts thus:
Re
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R
in
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CAUTION: Be careful not to connect an
amplifier output terminal to ground.
4.3 Potentiometers
The five potentiometers grouped on the front
panel are used either to establish problem coeffi-
cients or as sources of constant input voltages or
initial condition voltages for the corresponding in-
tegrator amplifiers. Normally, these potentiometers
will be adjusted by means of the null voltmeter.
In common practice, the potentiometers are patched
into the computer circuit before being adjusted.
a. Initial Conditions: For each integrator amplifier
which requires an initial condition voltage other
than zero, connect the correspondingly num-
bered ‘‘IC’’ potentiometer as shown below:
+105
IC
oe
(Terminal is internally an
wired to Amplifier 4). oO
4
Connections for a Negative IC Voltage
IMPORTANT! Note that the top patchcord is
connected to the +105 terminal to establish a
NEGATIVE initial condition. (The initial condi-
tion is produced at the output of an amplifier which
reverses the voltage polarity.)
Model 3500
If the initial condition voltage for a particular
amplifier is to be zero volts, it is only necessary
to "’ground’’ the IC terminal adjacent to the poten-
tiometer of corresponding number as shown:
OMIT |
CONNECTION
'
'
Connection for Zero Initial Conditions
The potentiometer is then free for use as a coefi-
cient ‘‘pot’’,
‘To Establish an Initial Condition Voltage
Let us assume that an initial condition of
+60.0 volts is to be applied to integrator amplifier
No. 4,
1. Place the FUNCTION switch at ‘‘Reset’’.
2. Connect potentiometer No. 4 for initial condi-
tions as above but with its top terminal patched
to the -105 (not +105) volt terminal.
3. Connect the null voltmeter as in par. 3.2b to
measure a positive voltage. Set the REFERENCE
dial at 60.0 (‘'6’’ in window, ‘‘00’’ on dial),
4. Connect the +METER terminal to one of the out-
put terminals of amplifier No. 4.
5. Turn potentiometer No. 4 until the meter reads
zero. The adjustment is now complete. Discon-
nect the meter.
(Note: Initial condition voltages may be adjusted
within an accuracy of one to two volts by reading
the amplifier output voltage on a direct-reading
meter scale.)
b. Coefficient Potentiometers. Where a coefficient
a is indicated in a problem diagram as:
15
{\
Aa
_
ea
ey
in the computer circuit diagram it would be trans-
lated as:
Rf
o-
*in
COEF in
POT b——0 ec
3 Rin °
where a is the setting of the potentiometer. Using
any potentiometer not employed for initial condi-
tions, make the following connections:
fin------ "ic
— a
OMIT o SETTING
CONNECTIONS 7
Amplifier wert”
Terminals .7 7
Cin ,? ° *
“” Potentiometer
ow Terminals
Rin ~s »
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&
REF.
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TO +105
To Adjust a Coefficient Potentiometer:
1. Place the FUNCTION switch at ‘‘Compute’’.
2.
Connect a patchcord temporarily between the
input and output terminals of all amplifiers
associated with coefficient potentiometer as
shown in the figure at the bottom of the page.
Temporarily connect the top terminal of the
potentiometer to the +105 terminal only (for the
sake of standardizing), at the same time re-
moving the connection to e;,.
Interconnect the potentiometer and the null volt-
meter as shown below.
. Adjust the meter REFERENCE potentiometer
for the desired setting.
. Turn until the
meter reads zero. The adjustment is now com-
the coefficient potentiometer
pleted. Restore the original circuit connections
as above, making sure that the temporary patch-
cord between the amplifier input-output termi-
nals is removed.
Fixed Voltage Sources: To obtain a fixed volt-
age (other than an initial condition), as for a
constant amplifier input, use the same circuit
connections shown for a coefficient potentio-
meter in par. 4.3b above, except use a +105 or
-105 terminal (choose the same polarity as the
desired voltage) for the source of e. The potenti-
ometer adjustment procedure is also identical
to that for coefficients, except the left terminal
of the REFERENCE potentiometer must be con-
nected to the same 105V polarity as the po-
tentiometer.
°in
le
(DISCONNECT) e ]
Connections During Adjustment of a Coefficient Potentiometer
Model 3500
d. Using the Auxiliary Potentiometer Strips:
When the Model 3570 or 3571 potentiometer strip
assembly is installed, its terminals are utilized
in exactly the same manner as the terminals of
the five potentiometers on the Model 3500 panel,
except that the auxiliary potentiometers are not
used to supply initial condition voltages to
amplifiers nos. 1 to 5. Connect a patchcord be-
tween one of t