Abstract: A method of calibrating a process computer, of the kind including an analogue to digital converter for converting analogue input signals representative of measured process parameters into digital signals for processing within the computer, and a digital to analogue converter for converting the processed signals into analogue output signals, comprises applying a known analogue signal to the analogue to digital converter, comparing the resulting digital signal with its expected value, and computing and storing a first calibrating correction value in dependence on the difference. A known digital signal is then applied from within the computer to the digital to analogue converter, whose output is coupled back to the input of the analogue to digital converter for conversion thereby and correction in accordance with the first calibrating correction value.

Abstract: A solid sensor, for sensing a physical parameter such as pressure, comprises a resonantly vibratable beam formed across a cavity in a substrate by micro-machining, and arranged such that changes in the parameter vary its resonant frequency. The beam either consists of or has deposited on it a material exhibiting piezo-electric effect, so that vibration of the beam can be excited by using the effect. This is achieved using light, either by forming a photodiode in the substrate in or near the beam, so that illuminating the photodiode causes a voltage to be applied to the beam, or, in the case where the piezo-electric material exhibits surface piezo-electric effect, by directly illuminating the beam.

Abstract: A proximity sensor includes an electrical circuit formed by a slot in an elongate conductive strip. The strip carries a magnet having a pole piece protruding through the strip at one end of the slot. At the other end of the slot pass laminations which magnetically couple the electrical circuit and a multi-turn coil arranged on a form attached to the strip. The coil is terminated at a pair of output leads. A ferrous object passing in the vicinity of the pole piece of the magnet modifies the flux pattern at the pole face. The resultant flux changes, being tightly coupled to the electrical strip, induce a low voltage high current emf into the strip, which forms the primary turn of a current transformer. The secondary of the current transformer is formed by the close-coupled coil, which has multiple turns, dependent upon the output voltage required at the output leads.

Abstract: In a weapons training simulator, laser radiation is output via optics (28) to simulate the firing of a round, and reflected radiation received via a conjugate path to assess the effectiveness of the shot. In the event of a miss a scan of the target area is required to provide fall of shot information. The scan is performed by controlled movement of the output faces of fibre optics (23, 24, 25) flexibly coupling to fixed sources (20, 21, 22) and of the input face of a fibre optic (200) flexibly coupling to a fixed detector (201). The problem of the bulk and inertia of prior art systems is improved by the remote location of lasers, drive and control, which may be conveniently separated for service or replacement without disturbing the optically aligned input and output faces. A further improvement is that vertically aligned multiple sources may be employed without undue weight penalty, yielding elevation information from a lateral scan.

Abstract: A digital instrument is represented by an analog-to-digital converter 17 controlled by a CPU 10 to effect measurements at regular intervals. The digital measurements are stored in a history file in a RAM 14, e.g. the most recent 100 or 500 measurements. The measurements are also linearly processed by rounding and range scaling to produce 100 reduced measurements in a second file in the RAM 14. This file is cyclically read out to a digital-to-analog converter 18 to produce a voltage on a terminal 22 for application to an oscilloscope which provides a display from which features of the measurements (e.g. a trend or a periodic component) can be seen. In order to allow for flyback and reset the 100 reduced measurements are held in a file of larger capacity (e.g. 130 or 150 measurements) which is cyclically read out. As the oldest of the 100 measurements is read a driver 19 provides a trigger pulse on a terminal 23 for the oscilloscope external trigger input.

Abstract: A sensor for assessing conditions within a metallic high pressure boiler 10, has a sensitive tip section 12, which is insulated from the boiler by virtue of a ceramic spacing member 101. The joins between the member 101 and sensor body 15 and tip 12 respectively are subject to full boiler pressure. The present invention provides a pressure seal by virtue of forming a brazed seal between the parts by forming a ceramic component to be brazed in a ceramic of average gain size of substantially between 5 and 15 microns and of purity exceeding 99% with a maximum silica content of substantially 0.2%, introducing between components a eutectic of substantially the composition: 80% to 90% silver; 5% to 6% copper; less than 6% titantium; and sufficient in quantity to fill gap therebetween, and subjecting the components to a temperature in excess of eutectic liquids temperature while maintaining the components in a vacuum.

Abstract: In a fluid level measurement system for the measurement of a level of fluid in a vessel the electrical impedance of a first conduction path between a central rod electrode and a surrounding cylindrical electrode and the electrical impedance of the second conduction path between the cylinder and the vessel are established. The first conduction path is restricted to be below the minimum fluid level by an insulating coating on the rod. The second conduction path varies with the fluid level. An output signal is extracted from the electrodes potentiometrically which is indicative of the fluid level. The signal may be linearized by application to a circuit having a matched non-linear transfer function. With this arrangement, a continuous output signal indicative of the fluid level is produced which is not subject to errors due to changes in fluid resistivity.

Abstract: A battery backup circuit for a CMOS RAM is isolated from the negative, or ground, power supply rail of the memory so that the memory is held at a potential which is sufficiently different from that of the normal write-enable signal (usually zero volts) to prevent spurious signals from affecting the memory.

Abstract: An RMS converter has first and second transistors (40a and 42a) providing a signal representing double the log of the input voltage, a third transistor (40b), matched with the first (40a), providing a signal representative of the log of the output voltage and a fourth transistor (42b), matched with the second (42a). providing a signal representative of the anti-log of the ratio of those signals; the transistors in each matched pair are repetitively interchanged functionally thereby reducing errors caused by slight differences in the transistor operating characteristics.

Abstract: A cable outlet adaptor comprises (i) a bush (20) which is threaded over the cable (14) and has a cut-out (30) towards one end; and (ii) a hood (40), having a cap portion (42) and a sleeve portion (44) at a right angle thereto, and split into two sections along a median plane through both portions. The hood can be fitted, even when the cable is already terminated at both ends, by displacing the cable into the cut-out in the bush, placing the cable and bush in one half of the hood and folding the other half over so that the bush extends into the cap portion and the cable emerges from the cut-out into the sleeve portion. A spiral support spring (60) slides over the sleeve portion to hold the two halves together, and pegs (48) in the cap portion engage in holes (32) in the bush to retain the hood on the bush.

Abstract: In order to ensure that the vibrations of a system under test are in accordance with a reference spectral density Z(w), the system is driven by a signal x.sub.n (t) provided by an inverse discrete Fourier transform (IDFT) with random phases introduced by a function R.sub.n (w) and the response spectral density Y.sub.n (w) provided by a DFT is brought into agreement with Z(w) by a feedback loop. Moreover, in order to ensure that this is done in one iteration, X'.sub.n (w) is derived from x.sub.n (t) by a DFT and divided by Y.sub.n (w) and the quotient is multiplied with Z(w) to provide the new input x.sub.n (w) for the IDFT. The division cancels out the random factor which is present in both X'.sub.n (w) and Y.sub.n (w).The system thus equalizes both rapidly and stably.

Abstract: In a heterodyning arrangement to enable frequency response testing of a system at a high frequency F using a digital correlator capable of operation at a lower frequency F/h, an offset signal is generated at a frequency F(h-1)/h and multiplied with the output signal of the system under test. Two heterodynes result: a wanted signal at a frequency F/h, and an unwanted image signal at F(2h-1)/h. The value of h is selectable independently of a divisor N which controls derivation of the test frequency F from a frequency synthesizer operating at a frequency NF. Thus the frequency of the image signal can be arranged to avoid spurious non-zero responses in the digital correlation process at frequencies related to N.

Abstract: A roller-type ultrasonic inspection device for inspecting vehicle tires comprises a roller assembly 20 mounted on a non-rotatable hug 16. Two piezoelectric crystals 80,82 are mounted in the hub 16 such that their principal transmitting/receiving axes A and B converge generally radially outwardly of the hub. The angle between the axes A and B is selected such that when the roller assembly 20 is urged into rolling contact with the tread-bearing surface of a tire 90, the axes meet (allowing for refraction effects) in the body of the tire beneath the tread. This ensures that the device can detect defects in the body of the tire, and is relatively insensitive to the tread.