Abstract: A transducer for sensing density, pressure or pressure difference in fluids comprises a resonantly vibratable cylinder as its sensing element. The cylinder has a mounting ring at one end, the mounting ring being clamped against a base member by means of a spring arranged to exert a substantially constant clamping force on the mounting ring. An outer cover fits over the cylinder, the cover having a flange which is directly bolted to an upstanding annular rim of the base member and a depending skirt portion in which the spring is integrally formed by machining.

Abstract: A scanner unit on a double-sided printed circuit board has reed switches on one face and coils on the other. The copper patterns include large screening pads beneath the reed switches and the coils. These pads distribute heat evenly along the switches to minimize thermally-induced E.M.F.'s, and provide electrostatic screening. An energizing circuit for the coils provides a single, long pulse several times larger in magnitude than the minimum required for relay actuation, followed by a series of shorter pulses of the same magnitude, but having a time-average magnitude equal to the relay holding current. This avoids the need for a voltage-dropping resistor and power wastage therein.

Abstract: A pressure transducer comprises two similar resonantly vibratable cylinders, one disposed coaxially inside the other and each having its own resonant vibration excitation system. A pressure P1 is applied to the inside of the inner cylinder and to the outside of the outer cylinder, while a pressure P2 is applied between the cylinders, whereby the difference in the respective vibration frequencies of the cylinders is dependent on the pressure difference P1-P2. Either P1 or P2 can be a reference pressure, e.g., a vacuum for an absolute pressure version of the transducer. Alternatively, either P1 or P2 can be atmospheric pressure, so that the transducer operates as a gauge pressure transducer.

Abstract: A line buffer circuit for coupling an interface to a data highway without requiring separate signal paths for sense and drive functions, comprises a unity-gain voltage amplifier coupling a line in the highway to the respective interface terminal for the sense function, and a current source connected to sink current from the highway line to ground for the drive function. The current source is controlled so that the current passing through it is proportional to the magnitude of the current passing from the amplifier through the interface terminal.

Abstract: A deflection amplifier for driving a magnetic-deflection cathode-ray tube in a digital plotter has two switching circuits coupled to low- and high-voltage supplies respectively. An error amplifier compares the actual deflection-coil current, as indicated by the voltage developed across a resistor in series with the coil, with the command input voltage indicating the required current. As long as the difference between required and actual currents is less than a predetermined threshold value, only the low-voltage switching circuit operates, thereby limiting power dissipation. However, if the current difference exceeds the threshold value for at least 2.mu.s, the high-voltage switching circuit commences operation to supplement the drive provided by the low-voltage circuit. The high-voltage circuit is limited by logic circuitry to periods of operation 20.mu.s long with a 5.mu.s quiescent period between each. The low- and high-voltage supplies are bipolar, and corresponding bipolar threshold values are provided.

Abstract: A printed circuit mother board, for interconnecting the respective edge connectors of a plurality of other printed circuit boards having digital circuitry thereon, has a set of generally straight, approximately parallel tracks on each side. Each set of tracks comprises alternate signal tracks and ground tracks, and the ground tracks of each set are interconnected with each other to approximate to a ground plane. Additionally, the tracks on one side of the board are slightly laterally displaced with respect to the tracks on the other side, so that each signal track on either side is opposite a ground track on the other side. The possibility of interference between signals carried by the signal tracks is thus reduced, and the board has transmission line characteristics.

Abstract: A displacement transducer comprises a charge coupled device having a plurality of light sensitive stages arranged in a line. An obturating member connected to a member whose displacement is to be transduced is disposed between the charge coupled device and a light source. As the obturating member is moved, it varies the amount of light received by the respective stages of the charge coupled device, so that the charge distribution in the charge coupled device is representative of the position of the obturating member and therefore of the member whose displacement is to be transduced.

Abstract: The analogue storage circuit includes a charge transfer device such as a charge-coupled device (CCD) and a quantizing circuit. The charge transfer device is arranged to shift an analogue signal from its input to its output, the analogue signal being subject to a change in magnitude during such shifting.The quantizing circuit receives the analogue signal from the output of the charge transfer device and quantizes that signal at a respective one of several substantially discrete levels. The quantizing circuit is arranged to apply the quantized analogue signal to the input of the charge transfer device, whereby in operation the analogue signal is circulated round the loop defined by the charge transfer device and the quantizing circuit. The quantizing circuit is further arranged to quantize the analogue signal, upon each subsequent receipt thereof, at the same one of the discrete levels.

Abstract: An interface circuit for use in a data transmission system is designed to be used not only between a highway and a device but also to link highways and can be commanded to enter a status in which commands sent to it on one highway are modified and sent out as commands on a second highway so that a controller device on the one highway can control devices not only on that highway but also on the second highway, with extension, if desired, to a third highway or beyond. To achieve this, the interface circuit has two ports each for connection to a respective one of two substantially identical highways, and status control means responsive to signals received at either port to establish different statuses of the interface. For inter-highway communication, the status control means is responsive to a command signal of particular form at either port to produce a modified command signal at the other port.

Abstract: The analogue storage circuit comprises a nonlinear amplifier for amplifying an input voltage. The amplifier includes means for generating a sequence of predetermined voltages, each predetermined voltage being higher than the preceding one in the sequence. A plurality of voltage level responsive circuits are each connected to receive the input signal and a respective one of said predetermined voltages and are each arranged to change from a first state to a second state as the input voltage passes through a level of equality with the respective predetermined voltage in a given direction. An output circuit is provided, as well as a plurality of voltage follower circuits each having a first input connected to receive a respective one of the predetermined voltages and an output connected to the input of the output circuit.

Abstract: The data terminal is manually operable and is intended for communicating with a data processor. The terminal has a keyboard having a plurality of manually selectable keys, each of which represents a respective message to be communicated to the processor. A display is provided having a plurality of zones each corresponding to a respective key of the keyboard, and the display is arranged to display in each zone an indication of the message represented by the key corresponding to that zone. The keys are in the form of touch keys. Merely touching a key serves to manually select that key, and causes the visual appearance of the display to change, so as to indicate which key is selected. This change may for example be a reversal of the relative brightness of the corresponding zone of the display e.g. dark on light instead of light on dark. Actually depressing the key, as opposed to just touching it, produces an output signal for communicating the message represented by the selected key to the processor.

Abstract: A density transducer employs a hollow cylinder capable of vibrating in the circumferential (or hoop) mode as the density sensing element, the cylinder being open at both ends and arranged so that the fluid whose density is to be transduced can come into contact with only the internal surface of the cylinder. The opposite ends of the cylinder are each secured to a respective clamping ring, which establishes a node at its respective end of the cylinder. The clamping rings each have a piston face which faces axially away from the cylinder and is acted on by the pressure of the fluid, thereby applying a compressive axial force to the cylinder which tends to reduce the effect of variations in the pressure of the fluid on the frequency of the vibration.

Abstract: A rectifying circuit comprises a high gain A.C. amplifier having first and second rectifying means connected in respective negative feedback paths between its output and its input and arranged to pass respective feedback currents of opposite polarity. A current copying device is responsive to the current flowing in one of the rectifying means to copy this current.In a preferred embodiment, said one rectifying means comprises the base-emitter junction of a first transistor, whose collector is connected to the input of the amplifier, and the current copying means comprises a second transistor, matched with the first transistor, and having its base-emitter junction connected in parallel with the base-emitter junction of the first transistor. The rectified output signal in this embodiment is taken from the free collector of the second transistor.

Abstract: A highly linear AC to DC conversion system comprises a variable gain amplifier via which an AC signal to be converted is applied to an AC/DC converter. The output of the AC/DC converter is compared with a reference level and a control signal dependent on the difference therebetween adjusts the gain of the variable gain amplifier so as to reduce the difference. The output of the AC/DC converter is also applied to one input of a comparator, whose DC output is applied via the variable gain amplifier to the other input of the comparator. The variable gain amplifier has exactly the same gain for both AC and DC signals. It can then be shown that the DC output signal produced by the comparator is very accurately linearly related to the magnitude of the AC input signal.

Abstract: In a multi-device data transmission system with source and acceptor devices linked by a data highway and handshake lines, provision is made for automatically adjusting the delay of the handshake cycle to suit the highway length and other determinative factors. This is achieved in that the acceptors do not accept data until told so to do via one handshake line, whereas the source is only allowed to issue this command when it has been told via another handshake line that all acceptors have seen the data. The system determines its own delay in this way and automatically adapts the delay to whatever length of highway is employed, whether a fraction of a meter in a circuit board or several tens of meters in inter-rack wiring.

Abstract: In a DVOM of the dual slope type, an unknown resistance or conductance to be measured is connected to a reference signal source to generate a voltage or current which is measured by the DVOM. However, if the input impedance of the DVOM is not extremely high, it loads the unknown resistance or conductance, and renders the relationship between the value of the unknown resistance or conductance and the actual voltage or current measured by the DVOM non-linear. In order to correct for this, a proportion of this actual voltage or current is algebraically summed with the reference signal used in the DVOM for generating the second slope of its dual slope operation, the proportion being selected in dependence on the input impedance of the DVOM (which can thus now take any convenient value) to linearize the relationship between the value of the unknown resistance or conductance and the output signal of the DVOM.

Abstract: A bipolar reference voltage source comprises first and second ratio-matched transistors having respective collector load resistors and arranged to pass slightly different currents. The emitter of the first transistor is connected to two emitter resistors in series, while the emitter of the second is connected to the junction between the emitter resistors. The bases of the transistors are commoned, while their collectors are respectively connected to the two inputs of a differential amplifier. A switching arrangement has a first state in which the output of the differential amplifier is connected to the bases of the transistors, and the end of the two emitter resistors remote from the transistors is grounded, thereby producing a first reference voltage of one polarity at the output of the differential amplifier.

Abstract: A symmetrical non-linear network for use in a function generator in which one or other of a pair of transistors is brought progressively into conduction by a non-linear network, so as to present a low dynamic resistance between the terminals. The non-linear network preferably includes a pair of diodes having a lower turn on voltage than that of the associated transistors, for example Schottky diodes with silicon transistors.The invention also provides a function generator incorporating the above non-linear network for converting square waves to sine waves in which the amplitude of the input signal to the network is controlled automatically.

Abstract: This invention relates to electronic analogue to digital converters of the integrating type wherein a capacitor is successively charged by an input signal and discharged by a reference signal, the time required for discharge serving as a measure of the amplitude of the input signal.The invention provides a converter wherein the integrator has differential inputs and the control means applies successively the input signal and the reference signal to the same input of the integrator if these signals are of different polarity, but successively to different ones of the differential inputs if input signal and reference signal are of the same polarity.The invention has application in measuring positive or negative input signals whilst employing a single principal reference signal and may be used advantageously in digital voltmeters for making d.c. measurements in the presence of interference.

Abstract: In an analogue to digital converter the unknown voltage is applied continuously to an integrating circuit during each conversion period. An opposing reference voltage is switched on and off to cause the amplifier output to ramp up and down between two detection levels. One or both of these levels varies as a periodic function of time, e.g. a sawtooth waveform. Clock pulses are counted when the slope of the output ramp is of one sign only and it is shown that the ratio of the unknown voltage to the reference voltage is simply related to the number of clock pulses actually counted when the slope is of said one sign and the total number of clock pulses occurring during the conversion period.