Unit Circuit Research Articles

An Electrical Analogue to Simulate the Oxygen Relations of Roots in Anaerobic Media

AbstractThe paper describes the construction and the theory underlying a simple electrical analogue which may be used to simulate the internal oxygen relations of roots in the wetland condition. The model represents an unbranched root lying within an oxygen sink and consists of twenty circuit units linked in series. Each unit which can be programmed independently, represents the major oxygen diffusion paths, impedances and sinks recognizable in a centimetre‐long segment of root/wet soil system. Simplicity has been achieved by specifying constant radius for the root (0.05 cm), constant potential activity for the external sink, by expressing respiration and radial oxygen loss as a function of root surface area, and by the non‐inclusion of oxygen storage capacity.

Time-controlled filling of liquid nitrogen traps

A bistable circuit using two silicon controlled rectifiers is switched at regular intervals to initiate a delivery of liquid gas into the cold trap of an ultra-high vacuum system. A thermistor located within a nylon neck fitting is used to terminate the delivery. The circuit and gas transfer unit are described in sufficient detail to enable this reliable automatic delivery system to be constructed without difficulty.

Fast Low-Power-Drain Logic System for Use in Nuclear Experiments on Scientific Satellites

A fast low-power-drain logic system has been developed for use in nuclear experiments on scientific satellites. The system consists of a compatible set of AND and NAND gates, pulse generators, delays and bistables. Each basic circuit unit has a response time in the 10 nanosecond range and power drain in the 2.0 milliwatt range. The basic units may be directly interconnected to form a required logic system. The basic circuit units, their use in a typical coincidence anti-coincidence system and their possible use in event priority and wide dynamic range pulse height analyzer systems is described.

Packaging an X-band microwave integrated circuit

Packaging of a hermetically sealed X-band microwave integrated circuit module is described. The module is a complete receiver-transmitter, including dipole antenna, for phased array radar applications. The principal problem areas are: 1. Interconnections between microwave thin film ceramic circuit units within the module. 2. Mechanical space limitations, imposed largely by wavelength considerations. 3. Techniques for mounting the ceramic circuit units within the module. 4. External geometry which affects mounting and external connections. 5. Dissipation of heat.

Apparatus for Direct Determination and Continuous Recording of Internal Friction at Constant Amplitude

An apparatus is described in which internal friction at constant amplitude is continuously determined in terms of directly measured electrical and mechanical parameters of the system without recourse to a secondary method of calibration. The specimen, in the form of a wire, serves as the torsion member in a torsion pendulum which is maintained in sustained oscillations by an electromechanical system employing positive feedback. Attached to the inertia member of the torsion pendulum are two coaxial coils which are located in the field of a permanent magnet. The emf generated in one of the coils (pickup coil) by the motion in the field is amplified, converted into a square wave and fed back into the other coil (the driver) through a gain control circuit. The power fed back into the driver coil is controlled by a servoloop in such a way as to maintain the amplitude of oscillation constant. The internal friction is proportional to the setting of the gain control unit in the driver circuit and is displayed continuously on a strip chart recorder. Internal friction values measured on this device agree to within better than 2% with those measured from the logarithmic decrement.

Circuit to facilitate the measurement by the four-probe method of the resistivity of silicon in the range 0.002 to 10 000 ohm cm

A simple a.c. operated four-probe device and associated circuit for the measurement of semiconductor conductivity is described. The 400 c/s measuring current can be varied from 0.12 μA to 2.5 mA which enables resistivities in the range 0.01 to 500 ohm cm to be measured with accuracy to ±4%. By taking suitable precautions this range can be extended to 0.002 to 10 000 ohm cm. The waveform of the signal at the voltage probes is monitored as an indication of the correct operation of circuit and probe unit. The limitations of the circuit and the four-probe method are discussed.

Digital circuits operating at 1 Mc/s using transistors

The paper describes circuits for performing logical operations in data processing. They operate reliably at 1 Mc/s and at a maximum ambient temperature of 45° C. The logic circuits use an alloy-junction transistor with an alpha cut-off frequency exceeding 10 Mc/s and an aluminium-bonded diode. Complete digital systems can be built using a number of logic units called ‘bricks’, in conjunction with the circulating pulse stores described in a companion paper [Showell, H. A., Barrow, C. W. M., and Collis, R. E. (Convention paper*)]. A set of simple rules determine the interconnections that can be used between units.The logic units described are gates, buffer amplifiers, inhibit-inverter amplifiers, bistable triggers and monostable triggers. D.C. coupling is used between units in order to obtain uniform operation irrespective of the time pattern of the pulse signals. Each one-microsecond digit period is terminated by a common discharge pulse of short duration that restores all transistors, by removing minority carriers from the base regions. No regenerating amplifiers are used, because the circulating pulse stores perform the dual functions of storage and of regenerating pulses, which have suffered attenuation and delay in the logic circuits.Each circuit unit is on a small printed wiring card. These are assembled in the required combinations on larger cards which form convenient plug-in packages.

Pattern recognition by means of automatic analogue apparatus

The problem of synthesizing apparatus that will automatically simulate man's ability to recognize and to learn to recognize patterns is discussed and it is concluded that analogue circuits, rather than the digital switching circuits that have been employed in the past, provide the simpler solution. A new circuit unit that possesses many of the essential functional characteristics exhibited by nerve cells in the brain is derived from earlier work on the electrical simulation of nervous-system functional activity and forms the basic element of the circuits.The new analogue apparatus consists of a number of distinct functional circuits arranged in a definite sequence, through which signals derived from the patterns to be recognized pass simultaneously on their way to the final output terminals. Classification information may be built into the apparatus initially if it is available, but if not, it can be stored automatically in a special unit during a setting-up procedure in which samples of the pattern types that the apparatus will be required to recognize are presented, together with identification signals. Low-resolution automatic pattern-recognition apparatus is described, and examples illustrate the setting-up procedure and subsequent performance of the apparatus.

Pattern recognition by means of automatic analogue apparatus

The problem of synthesizing apparatus that will automatically simulate man's ability to recognize and to learn to recognize patterns is discussed and it is concluded that analogue circuits, rather than the digital switching circuits that have been employed in the past, provide the simpler solution. A new circuit unit that possesses many of the essential functional characteristics exhibited by nerve cells in the brain is derived from earlier work on the electrical simulation of nervous-system functional activity and forms the basic element of the circuits.The new analogue apparatus consists of a number of distinct functional circuits arranged in a definite sequence, through which signals derived from the patterns to be recognized pass simultaneously on their way to the final output terminals. Classification information may be built into the apparatus initially if it is available, but if not, it can be stored automatically in a special unit during a setting-up procedure in which samples of the pattern types that the apparatus will be required to recognize are presented, together with identification signals. Low-resolution automatic pattern-recognition apparatus is described, and examples illustrate the setting-up procedure and subsequent performance of the apparatus.

Automatic testing of wired relay circuits

PRACTICALLY ALL of the telephone switching equipment in an automatic exchange is made up of wired assemblies of relays and other components interconnected by a multiplicity of wires. Many of these assemblies are made up of smaller components called “relay circuit units.” These vary in size, and after testing, are mounted in larger frameworks. A careful check of connections and electrical continuity is essential to assure that these units will function properly when connected to other circuits in a telephone exchange.

Automatic testing of wired relay circuits

PRACTICALLY all of the telephone switching equipment in an exchange is made up of wired assemblies - assemblies of relays and other components interconnected by a multiplicity of wires. These assemblies are on frameworks generally 11 feet 6 inches high. Many of these frameworks are made up of smaller components called relay circuit units composed mainly of relays. Rotary switches, resistors, capacitors, jacks, etc., necessary for the operation of switching circuits may also be included. These components vary in height up to about 24 inches and after testing they are mounted in the larger frameworks. A careful check of connections and electrical continuity is essential to assure that these units will function properly when connected to other circuits in a telephone exchange.

Quartz-Crystal Measurement at 10 to 180 Megacycles

A method is described for measuring the equivalent parameters of both the main and spurious modes of very high-frequency crystal units. The crystal is placed between the plate and cathode of an amplifier tube, and the voltage developed across it is recorded as a function of frequency. The series resistance R88. can be obtained by comparing the resulting voltage peaks with the voltage developed across a pure capacitive load. The series capacitance C8 is measured by recording the resonance curve with the crystal unit in circuit, and then recording a second resonance curve when the capacitance across the crystal unit has been increased by a known amount. The frequency difference between the two curves gives a measure for C8. Correction functions are derived for evaluating the recorded data for crystal units having high R8 and low reactance of the static capacitance Co.

The Exhibition of Apparatus at Paris

The Exhibition of Apparatus in conjunction with the Third International Congress of Radiology was held at the Porte de Versailles on the outskirts of Paris. Our friends are to be complimented on having secured a really ideal hall for teh purpose, and on having arranged the Exhibition so as to give the visitors as much comfort and as little fatigue as possible. Two points which contributed largely to this were the uniformity in design of the stands and the breadth of the gangways. So far as the exhibits are concerned, the keynote, apart from some definite advances to be mentioned below, seemed to be a kind of consolidation of the position. The broad basic Exhibition of Apparatus at Paris 485 principles of apparatus design as regards transformers, couches, screening stands, etc., were much the same as at Stockholm. For instance, there were in evidence the six-valve, fourvalve and single-valve units, the continuous potential condenser unit, the Villard circuit unit, and the 30-milliampere unit. One found Potter-Bucky couches, screening stands, and tube stands—all, broadly speaking, similar to those at Stockholm. The differences to be noted were improvements in finish and a distinct tendency towards greater solidity and robustness, so that the product bears the stamp of the engineer rather than the instrument maker—by which no disparagement of the latter is intended.

Magnetic circuit units adopted by I. E. C.

Standardized designations already adopted will obviate confusion if generally ratified; further international standardization of electromagnetic nomenclature is urged.