Analog Computer AR 12 — Technical Description

This document is an English translation of the original German text: “Analogrechner AR 12” by Frey Analogtechnik, Prisdorf.

AR 12 — Analog Computer

The desktop analog computer AR 12 is suited for educational and simulation purposes. The AR 12 is a compact, portable computer housed in a 19-inch standard enclosure with 4 rack units of height; installation in 19-inch equipment cabinets is possible when the chassis is removed from the desk housing.

Design Concept

Easy and quick to learn — no knowledge of electronics required
Clear, well-arranged working panel
High computing accuracy
Reliability
Fully integrated, state-of-the-art technology
Plug-in card construction
High computing speed
Low price

The high computing speed permits use with an oscilloscope when the solution function is to be displayed as a stable image.

Applications

Demonstration of dynamic processes
Display of equations
Solution of oscillation problems
Investigation of parameters
Simulation of control systems

Frey Analogtechnik, Bebu 2110, Prisdorf

General Principles

The Principle of the Analog Computer

Physical and technical-mathematical processes are described by equations between computational quantities that depend on time or another independent variable.

In the electronic analog computer, each of these computational quantities is represented by a voltage proportional to it. The relationships among the computational quantities — or the voltages analogous to them — are simulated by networks in which the necessary computing operations (for example, addition, subtraction, integration, etc.) are carried out by operational amplifier circuits.

The result of this electronic computing process is that the voltages in the network change over time in the same way as their analogous computational quantities of the problem.

Computing processes in which the dependent variables depend not on time but on a single other independent variable can also be handled by setting that independent variable proportional to time — “analog.” If several independent variables occur, the problem cannot be solved with one analog computer.

Partial differential equations can only be investigated when they can be reduced to ordinary differential equations.

The analog computer is distinguished from the digital computer in that the effect of varying a parameter can be made directly visible, either on the screen of the oscilloscope or on the X-Y plotter. Its disadvantage is the lower accuracy compared to the technically more elaborate digital computer. The accuracy of the analog computer is limited by the measurement accuracy of the electrical quantities — voltages, resistors, capacitors, etc. — and lies between 0.1 and 10 percent.

Construction

The analog computer AR 12 has 12 computing amplifiers: 6 are connected as integrating amplifiers and 6 as summing amplifiers. Additionally, 5 isolated computing voltages and 5 computing potentiometers are available. The outputs of the computing amplifiers and of the computing voltages are permanently short-circuit proof.

Parameter adjustment is performed by a compensation circuit or in scale divisions. The time constants of the integrators can be switched between 1 second and 0.001 second. Initial conditions are set with FET switches.

Via a 12-position rotary switch, all outputs of the computing amplifiers, potentiometers, and computing voltages can be routed to the measuring instrument, which either measures the voltage directly or operates as a bridge measuring device using the built-in reference voltage.

For synchronisation of additional equipment, the trigger pulse of the field-effect transistors is available at the TRIG jack on the front panel.

All electronics are housed on Eurocard-format plug-in cards (10 × 15 cm) with 31-pin DIN connector strips. The boards are made of 1.5 mm epoxy resin. The amplifiers can be adjusted after removing the rear panel of the housing.

Plug-in Cards

Slot	Designation	Function
B1	RB 89	High-frequency suppression filter
(?)	SN IV APS	4-channel DC supply
66	SN IV ATD	4-channel DC supply
59	RB 91	2-channel DC supply
50	(shield plate)	—
47	RB 17	Oscillator
41	RB 24	Integrator
39	RB 24	Integrator
32	RB 23	Amplifier

Housing dimensions: W × H × D = 300 × 200 × 250 mm
Weight: approx. 12 kg

Technical Specifications

Integrators — Six units

Time constant switchable: 1 s / 1 ms
Initial condition: settable at two jacks on front panel (white jacks)
One input (yellow jack)
Three outputs (blue jacks)
Maximum input and output voltage: ±5 V
Transfer function: U_a = −(1/RC) ∫ U_e dt + U₀

Summing Amplifiers — Six units

Three inputs, gain factor 1 (yellow jacks)
Two inputs, gain factor 10 (green jacks)
One input, summing point (red jack)
Two outputs (blue jacks)
Maximum input voltage: ±5 V or ±0.5 V depending on gain factor
Maximum output voltage: ±5 V
Transfer function: U_o = −[(U₁ + U₂ + U₃) + 10(U₄ + U₅)]

Computing Amplifiers (Type AR 12-2 / AR 12-5)

Parameter	AR 12-2	AR 12-5
Bandwidth	1 MHz	1 MHz
Open-loop gain	2 × 10⁵	1.5 × 10⁵
Input impedance	7 × 10⁷ Ω	10¹¹ Ω

Computing Voltage

Stabilisation: 10⁻⁴
Adjustable with potentiometers 1–5
Voltage range: 0 < U < 5 V
Maximum floating output voltage: 5 V
Permanently short-circuit proof

Computing Potentiometers

Available with 1 turn or precision type with 10 turns
Coefficient setting using a reference voltage
Coefficient range: 0 ≤ α ≤ 1

Semiconductor Complement

21 integrated circuits
6 field-effect transistors
2 silicon transistors

Mechanical

19″ chassis in 19″ desk housing with 114 4-mm jacks
Eurocard-format plug-in cards
Power supply: 220 V, approx. 40 W; IEC standard cold-device connector

Further technical data are contained in the individual plug-in card descriptions.

Front Panel

The front panel carries the jack fields for integrators, summing amplifiers, computing voltages, potentiometers, and earth. Jacks are colour-coded:

White — initial condition inputs (integrators)
Yellow — signal inputs (gain ×1)
Green — signal inputs (gain ×10)
Red — summing point / positive pole of computing voltage
Blue — signal outputs
Black — negative pole of computing voltage / earth

Switches and Potentiometers

S1…S6 — Switches for calibrating the computing potentiometers. When set to EICHEN (calibrate), the associated potentiometer is connected to the calibration voltage.

S7 — Switch for selecting the calibration mode between POT/SPANN (potentiometer/voltage) and VERST (amplifier). When set to VERST, the amplifier selected with S14 is routed to the calibration device. When set to POT/SPANN, positions 1–5 of the rotary switch route the computing voltages, and positions 7–12 route the computing potentiometers to the calibration device.

S8 — Calibration mode selector. In position KOMP, the voltage of the computing voltage or potentiometer output selected via S14 and S7 is determined in a compensation circuit using the calibration potentiometer. In position SKT, the voltage is displayed in scale divisions on the measuring instrument.

S9 / S10 — S9 selects whether the computing process runs once (EIN, single) or repetitively (REP). S10 starts or stops the computing process.

S11 / S12 / S13 — Switching for the two time constants of the integrators. The switch must be set to 1 SEK when an X-Y plotter is connected. The S12 pushbutton increases the sensitivity of the measuring instrument after coarse balancing during the compensation calibration.

S14 — Mains switch (power on/off).

P/PREC — Rotary switch for the 12 outputs of the computing amplifiers or the 5 computing voltages and 5 potentiometers, depending on the position of S7.

The potentiometer with the digital adjustment knob serves as the calibration potentiometer of the analog computer and is active only in position KOMP of S8.

P11 / TRIG — The REP.FREQ potentiometer sets the computing time. Repetitive operation is only useful at the 0.001-second time constant. The BNC socket TRIG provides pulses synchronous with the repetition frequency for triggering an observation oscilloscope.

Jack Panel

Integrator Field (Figure 1)

The white jacks are used to set the initial conditions of the integrator. The blue jacks are the three outputs of the integrator. The yellow jack is the input.

Summing Amplifier Field (Figure 2)

The three yellow jacks are the inputs with gain factor 1. The two green jacks are the inputs with gain factor 10. The red jack is the summing point of the computing amplifier. The two blue jacks are the outputs.

In the COMPUTING VOLTAGE field, the red jacks carry the positive pole and the black jacks the negative pole of the computing voltages.

In the POTENTIOMETER field, the yellow jacks are the inputs and the blue jacks are the outputs of the potentiometers. The third terminal of each potentiometer is connected to earth and is available at the six black jacks in the EARTH field.

Starting the Computing Process

Procedure

Patch the network corresponding to the problem.
Switch power on (S14 EIN).
Set switch S9 to REP (repetitive).
Set time constant with S11 to 0.001 s.
Calibrate computing voltages and potentiometers (EICHEN).
Switch S7 to VERST (amplifier).
Switch S1 through S6 to RECHNEN (compute).
Connect TRIG jack to oscilloscope trigger input.
Set computing switch S10 to EIN (on).

Calibrating Computing Voltages

Set switch S7 to POT/SPANN.
Select the desired computing voltage with S14 rotary switch.
Set switch S8 to KOMP.
Set the desired value at the PEIC knob.
Turn the computing voltage knob until a null balance is obtained on the measuring instrument.
Press pushbutton S12 (EMPF) and repeat the null balance.

Calibrating Potentiometers

Set switch S7 to POT/SPANN.
Select the potentiometer with the S14 rotary switch.
Set switch S8 to KOMP.
Set the desired value at the P_EICH knob.
Switch the S1…S6 switch associated with the potentiometer from RECHNEN to EICHEN.
Turn the selected potentiometer knob until null balance is obtained on the measuring instrument.
Press pushbutton S12 (EMPF) and repeat null balance.
Switch S1…S6 back from EICHEN to RECHNEN.

Amplifier Offset Adjustment

Remove the rear panel.
Switch on the device — do not touch the power supply (220 V!).
Set S9 to EINM (single).
Set time constant to 0.001 s.
Set S8 to KOMP.
Set S7 to VERST.
Select integrators 1–6 sequentially with rotary switch S14 and adjust as per steps 8–11.
Short the white jacks of the selected integrator (initial condition = 0).
Connect the integrator input to an EARTH jack in the patch field.
Set S10 to EIN; turn the precision trimmer on the rear of the chassis (each amplifier has one trimmer assigned) until no deflection change is visible on the measuring instrument.
Set S10 to AUS and repeat step 10 until full balance is achieved.
Select summing amplifiers 7–12 with S14 and adjust as per steps 13–14.
For amplifier offset adjustment, connect one input to EARTH.
Perform offset adjustment with the precision trimmer; press EMPF for higher accuracy.

Layout of Precision Trimmers in Chassis (viewed from rear)

Card	RB 23	RB 24	RB 24	RB 57
	7 8 9	(Integrators)	11 12	(Summing amplifiers)
DC supply	RB 89	SN IV APS	SN IV APS	RB 91

Summing Amplifier Circuit

Jack	Colour	Gain
Summing point	Red	—
Input 1	Yellow	×1
Input 2	Yellow	×1
Input 3	Yellow	×1
Input 4	Green	×10
Input 5	Green	×10
Output	Blue (×2)	—

Integrator Circuit

S1 — FET switch for initial conditions
S2 — Reed-relay switch for time constant
Capacitor: 1.1 µF
Initial condition jacks: White (×2)
Input: Yellow (B4)
Input resistor: 655 kΩ
Outputs: Blue B2, B3, B5, B6

Plug-in Cards — Individual Descriptions

RB 23 — Amplifier Card

The RB 23 amplifier card is equipped with 6 integrated operational amplifiers. Each amplifier has an assigned precision trimmer to compensate offset voltage. The output signal of each amplifier can be switched onto a common bus via reed relays, making monitoring and measurement flexible.

The value of resistor R₀ (one per amplifier) depends on the external wiring of the amplifier. When used as an inverter:

R₀ = R_E · R_A / (R_E + R_A)

The external wiring flexibility allows numerous applications: individual amplifiers can be configured as summing, integrating, or differentiating amplifiers. Active filters can also be constructed with appropriate wiring. Types RB 23-2 and RB 23-3 are suitable for analog computing.

Technical Data (RB 23)

Parameter	RB 23-1	RB 23-2	RB 23-3
Supply voltage	±15 V, ~50 mA
Reed relay switching voltage	±15 V, ~50 mA
Output voltage	max. ±10 V
Input voltage	max. ±10 V, ~20 nA
Input bias current	80 nA	5 nA	5 pA
Input offset current	20 nA	2 nA	0.5 pA
Open-loop voltage gain	200,000	200,000	120,000 V/V
Input impedance	2 MΩ	10 MΩ	10¹¹ Ω
Temp. coeff. of input offset voltage	—	±5 µV/°C	10 µV/°C
Bandwidth at unity gain	1 MHz	1 MHz	800 kHz

Pin Assignments (31-pin DIN)

Pin	Signal
31	+15 V supply
10	SA — bus of outputs
28	A1 — output amplifier 1
27	S1 — switching relay 1
25	E1 — input amplifier 1
24	A2 — output amplifier 2
23	S2 — switching relay 2
22	E2 — input amplifier 2
20	A3 — output amplifier 3
19	S3 — switching relay 3
18	E3 — input amplifier 3
16	A4 — output amplifier 4
15	S4 — switching relay 4
14	E4 — input amplifier 4
12	A5 — output amplifier 5
11	S5 — switching relay 5
10	E5 — input amplifier 5
8	A6 — output amplifier 6
7	S6 — switching relay 6
6	E6 — input amplifier 6
4	GND (earth)
2	−15 V supply

Card dimensions: Eurocard 10 × 15 cm, 31-pin DIN strip, epoxy resin 1.5 mm thick, component height 1.8 cm, weight approx. 130 g.

RB 24 — Integrator Card

The RB 24 integrator card is equipped with 3 integrators. Transfer function:

U_a = −(1/RC) ∫ U_e dt + U₀

The time constant is normally 1 s or 0.001 s. Switching between these two time constants can be initiated by an external voltage. The switching of all three integrators is performed simultaneously via reed relays. The time constants can be varied using the 1 MΩ potentiometers on the board.

Resetting of the integrators is performed via FET transistors triggered simultaneously. The offset voltage of each integrator can be compensated by a precision trimmer.

By exchanging the integration capacitors and input resistors, other integration time constants can be set. The resistor R₀ must be chosen according to the population of the integration network. Each integrator has a reed relay assigned that switches its output signal onto a common bus for flexible monitoring.

The RB 24 is produced in three versions; types RB 24-2 and RB 24-3 are suitable for analog computing.

Technical Data (RB 24)

Parameter	RB 24-1	RB 24-2	RB 24-3
Supply voltage	max. ±15 V, ~50 mA
Time-constant/bus relay switching voltage	±15 V, ~50 mA
Output voltage	max. ±5 V
Input voltage	max. ±10 V
Input bias current	80 nA	5 nA	5 pA
Input offset current	20 nA	2 nA	0.5 pA
Open-loop gain	200,000	200,000	120,000 V/V
Input impedance	2 MΩ	10 MΩ	10¹¹ Ω
Temp. coeff. of input offset	—	±5 µV/°C	10 µV/°C
Bandwidth at unity gain	1 MHz	1 MHz	800 kHz

Pin Assignments

Pin	Signal
31	+15 V supply
10	SA — output bus
26	E1 — input integrator 1
24	A1 — output integrator 1
23	S1 — switching relay 1
22	C1 — initial condition 1
18	E2 — input integrator 2
17	A2 — output integrator 2
15	S2 — switching relay 2
14	C2 — initial condition 2
12	E3 — input integrator 3
11	A3 — output integrator 3
10	S3 — switching relay 3
5	C3 — initial condition 3
4	ZK — time constant
2	RS — reset; GND
1	−15 V supply

Card dimensions: Eurocard 10 × 15 cm, 31-pin DIN strip, epoxy resin 1.5 mm thick, component height 1.8 cm, weight approx. 140 g.

RB 37 — Oscillator Card

The RB 37 oscillator is designed for equipment requiring a low-frequency clock that does not need high frequency stability. The clock frequency can be varied via an external potentiometer. The frequency is determined by the external potentiometer, an internal 10 kΩ resistor, and the on-board capacitor C:

f = 1 / ((R_ext + 10 kΩ) × C)

The duty cycle of the rectangular output voltage is set by a 50 kΩ potentiometer. By choosing R_ext (100 kΩ – 1 MΩ) and C, the user can determine the frequency range.

Connections

Pin	Signal
31	+8 to +30 V, ~10 mA
25	FQ — frequency setting (external potentiometer)
24	AU — oscillator output
2	GND (earth)

Card dimensions: Eurocard shortened to 10 × 5 cm, 31-pin DIN strip, component height 1.8 cm, weight approx. 40 g, epoxy resin 1.5 mm thick.

RB 89 — High-Frequency Suppression Filter

When electrical loads (contactors, commutators, etc.) are switched on or off, a wide spectrum of interference frequencies with partially high amplitudes is generated. These voltage spikes cause errors in logic circuits with integrated circuits because they are often long enough to affect the switching state.

As long as no switches are in the immediate vicinity of the RB 89 filter, logic circuits are adequately protected.

The filter on the 31-pin Eurocard RB 89 consists of two interference-protection chokes with high inductance (~20 mH) and a small parallel capacitance (~10 pF), plus three capacitors. The circuit is protected by a 1.5 A fuse against overload. The maximum current through the filter must not exceed 1.5 A at 220 V. The permitted ambient temperature is approx. 70°C.

Connections (31-pin DIN)

Terminal	Signal
Input 220 V	Phase P, Neutral N, Earth E
Output 220 V	Phase P, Neutral N, Earth E

Board dimensions: Eurocard shortened to 10 × 9 cm, 31-pin DIN strip, epoxy resin 1.5 mm thick, component height 1.5 cm, total weight approx. 133 g.

RB 91 / RB 93 — Power Supply Card

The 31-pin Eurocard power supply card in Eurocard format is equipped with two separate, complete power units for supplying analog and digital circuits: a fuse, mains transformers, rectifiers, regulators, and power transistors.

The RB 91 card delivers two galvanically isolated, voltage-stabilised DC outputs, switchable with jumper bridges: 4–12 V or 4–24 V. Output voltages are set with precision potentiometers; they are floating (earth-free). Output current limiting can be set with miniature trimmers from 0.05 A; at 12 V it is set to 0.7 A and at 24 V to 0.15 A. The card is permanently short-circuit proof.

The stabilisation circuit consists of an integrated circuit and a power transistor. The integrated circuit is a monolithically integrated voltage regulator fabricated in planar epitaxial technology; it contains a temperature-compensated reference amplifier, a comparison stage, an output power transistor, and a current-limiting circuit.

The IC features very low temperature drift and high ripple rejection.

During continuous operation in the 4–12 V range, the bridges should always be switched to 12 V to avoid unnecessary heat dissipation.

When powering interference-sensitive circuits with the RB 91 dual power card, use of the RB 89 high-frequency suppression card as a pre-filter is recommended.

Technical Data — Regulator

Parameter	Value
Input voltage regulation factor	0.01% per output voltage at 12 V input
Output current regulation factor	0.01% per output voltage
Temperature coefficient of output voltage	0.01%/°C at 0–70°C
Ambient temperature (max.)	70°C
Ripple rejection	85 dB
Long-term stability	0.1% per 1,000 hours

Connection — Transformer input: 220 V
Output DC voltage 1 and 2: see board labelling

Jumper wiring: For 4–12 V — two bridges per supply; for 4–24 V — one bridge per supply (per labelling on reverse of board).

Board dimensions: Eurocard 10 × 16 cm, 31-pin DIN strip, total height 4.5 cm, total weight 0.5 kg.

SN A — Adjustable Power Supply Cards (1–24 V, 40 mA)

The SN A power supply cards (SN I AM/AP, SN II AMS/APS, SN IV AMS/APS, etc.) are complete, highly stabilised DC supplies for analog and digital circuits, equipped with transformer, rectifier, and regulator. The adjustable DC supplies provide stabilised output voltages from 4 to 24 V at 40 mA. Voltage adjustment is via 15-turn precision trimmers (P) or miniature trimmers (M). Output current limiting activates at 50 mA maximum. The output voltage is permanently short-circuit proof and earth-free.

The stabilisation circuit uses an integrated monolithic voltage regulator fabricated in planar epitaxial technology, with temperature-compensated reference amplifier, comparison stage, output power transistor, and current-limiting circuit. This IC features very low temperature drift and high ripple rejection.

The transformer input is connected to 220 V AC. For interference-sensitive circuits, the RB 89 high-frequency filter card is recommended upstream.

Available variants and connections:

Type	Channels	Output
SN I AM 1×4	1	−24 V, 40 mA
SN I AP 1×4	1	+24 V, 40 mA
SN II AM 2×4	2	−24 V, 40 mA
SN II AP 2×4	2	+24 V, 40 mA
SN II AMS 2×4	2	−24 V, 40 mA (precision)
SN II APS 2×4	2	+24 V, 40 mA (precision)
SN IV AMS 4×4	4	−24 V, 40 mA (precision)
SN IV APS 4×4	4	+24 V, 40 mA (precision)

Block Diagram Components

4.3 kΩ resistor
10 Ω resistor
1 kΩ resistor
470 µF/15 V capacitor
4.7 µF/15 V capacitor
8,200 pF capacitor
850/C800 transistor
IC (integrated regulator)
Transformer

Stabiliser Technical Data

Parameter	Value
Input regulation factor	0.01% of output voltage at 12 V input
Load regulation factor	0.01% of output voltage
Temperature coefficient of output voltage	0.01%/°C at 0–70°C
Ambient temperature (max.)	70°C
Ripple rejection	85 dB
Long-term stability	0.1%/1,000 hours

Board dimensions:

Type	Length	Width	Height	Weight
SN IV AMS/APS	15 cm	10 cm	— cm	400 g
SN II AMS/APS	10 cm	10 cm	4 cm	220 g
SN II AM/AP	8 cm	10 cm	7 cm	200 g
SN I AM/AP	4 cm	10 cm	— cm	100 g

All boards are 10 cm wide and can therefore be installed in Eurocard rack systems. Boards are made of 1.5 mm epoxy resin.

Price List (February 1973)

Item	Price (DM)
AR 12 Type 1 — Integrator RB 24-2, Amplifier RB 23-2, Potentiometer 1 turn	2,580.—
AR 12 Type 2 — Integrator RB 24-2, Amplifier RB 23-2, Potentiometer 10 turns	2,950.—
AR 12 Type 3 — Integrator RB 24-3, Amplifier RB 23-3, Potentiometer 10 turns	5,420.—
Patch cables for programming, 40 pcs.	116.—

Prices: excluding VAT, including postage and packaging.
Discount: 2% for payment within 10 days, net within 30 days.
Volume discount available for orders of three or more units of the same type.
Price indications are subject to change. Technical changes reserved.
Jurisdiction and place of fulfilment: Berlin (W).

Distributor

Astron — Jahn + Stoeckle Electronics GBR
Berlin 12, Jebenstraße 3/11
Tel. 3121203

Frey Analogtechnik, Bebu 2110, Prisdorf (Estorf)