Abstract: A data collection system in which a number of remote terminals (RT) transmit data packets for reception by one or more fixed data collectors (FDC) or a portable data collector (PDC). Each remote terminal (RT) transmits data in two frequency sub-bands to which the fixed and portable data collectors are respectively tuned. Channel capacity is improved in at least the fixed data collector (FDC) sub-band by the use in the remote terminal of minimum shift keying (MSK) encoding and pseudo-random variation of a frequency error applied to the packet transmission frequency for successive packets. In the fixed data collectors dual fast-Fourier transform signal processing enables the interpretation of simultaneous packets with different error frequencies. The use of a single design of remote terminal (RT) in conjunction with portable data collectors (PDC) simplifies system set-up, with the portable collectors providing coverage for those areas where a fixed data collector (FDC) network has yet to be established.

Abstract: A radio antenna for mounting in the lid of a water meter box and forming part of a remote meter reading system comprises an annular conductive plate and a circular conductive plate which are coaxial with and parallel to each other and spaced apart to define a slot, the circular plate serving as a ground plate. The antenna has an input in the form of a conductive pillar interconnecting the two members, with a drive input at a selected point along the length of the pillar and a second input on the ground plate. A variable tuning capacitance is disposed between the plates diametrically opposite the conductive pillar. The ground plate also serves for locating the lid in undergrowth or under snow using a metal detector.

Abstract: A density sensor comprises a cavity arranged to receive the gas whose density is to be sensed. The cavity is divided into two chambers by a flexibly mounted diaphragm. A piezoelectric excitation device at one end of the cavity is used to excite the gas in the cavity into resonant vibration in a mode having an anti-node at the diaphragm, which causes the diaphragm to vibrate with the gas. Another piezoelectric device senses the vibration, whose frequency is a function of the known mass of the diaphragm and the density and speed of sound in the gas. This last parameter can be sensed by exciting the gas in the cavity into resonant vibration in a second mode having a node at the diaphragm, so that the diaphragm does not take part in the vibration. Alternatively, it can be sensed by providing a second cavity, also arranged to receive the gas but not having a diaphragm, and resonantly vibrating the gas in the second cavity.

Abstract: A transponder includes a receiver for receiving a radio interrogation signal. The transponder also includes a phase locked loop decoder for deriving a reference signal from the received interrogation signal, and a radio transmitter for transmitting a transponder reply signal. The phase locked loop has an output which feeds the AC reference signal to the transmitter. The transmitter includes a frequency doubler which generates a transmitter radio frequency at double the frequency of the reference signal. The transmitter radio frequency is therefore controlled by the radio frequency of the interrogation signal. The phase locked loop includes a divide-by-N counter, where N is a predetermined integer parameter. The parameter N determines the derivation of the reference signal frequency from the interrogation signal frequency.

Abstract: A distributed temperature sensor comprises an elongate ultrasonic waveguide having a number of zones along its length, each zone having a grating formed on it. This is typically achieved by incorporating uniformly spaced notches or bands (or collars) throughout the zone. The grating spacing in each zone is different, so that each grating reflects a characteristic frequency. This frequency varies as the temperature of the zone varies, so if wide-band ultrasonic pulses are launched into the waveguide, the temperature of each zone can be determined from the reflected frequencies.

Abstract: A water level measurement system for use with a pressurized power plant boiler comprises a tubular pressure vessel for attachment to one end of the boiler such that the water level in the pressure vessel is the same as in the boiler. The pressure vessel has a central rod-like conductor which together with the vessel forms a coaxial RF waveguide. A pair of spaced reference discontinuities are provided in the conductor above the maximum level of the water, so that an RF pulse injected into the waveguide is reflected successively by both discontinuities and the surface of the water. The level of the water can then be determined independently of changes in the dielectric constant of the vapor above it, from the ratio between the time intervals between the first and second reflected pulses and between the first and third reflected pulses. The conductor is mounted at the top of the pressure vessel by way of a pressure seal and a ceramic insulator.

Abstract: In pressure sensor systems based upon a micromachined silicon pressure sensor comprising a resonantly vibratable beam supported on a diaphragm, the beam is excited into resonant vibration by directing an optical excitation signal at the beam resonant frequency, via an optical fibre 26, onto a part of the sensor other than the beam, preferably the diaphragm. To detect the vibrations, the underside of the beam 16 and the adjacent upper surface of the diaphragm 18 are together arranged to define a Fabry-Perot cavity, and a continuous optical detection signal is directed at this cavity, also via the optical fibre 26. The optical detection signal is thus modulated at the vibration frequency of the beam 16 by the cavity, and the modulated signal is reflected back into the optical fibre 26.

Abstract: A relative position transducer for determining the angular position of a first member angularly movable relative to a second member includes a coded track on the first member, a read head mounted on the second member, drive means for oscillating the read head to scan over and read a limited region of the coded track, and a microcomputer for interpreting the code read by the read head as the position. A first sensor detects when the read head is in a predetermined reference position and a second sensor detects the end points and direction of the read head scan. The sensor outputs are connected to the computer for correct interpretation of the read head output. An interplation is used to improve the accuracy of the position determination.

Abstract: In an optically-excited micromachined silicon pressure sensor comprising a resonantly vibrating beam mounted on a diaphragm, vibration of the beam is sensed optically via the same optical fibre through which the optical excitation signal is applied to the sensor. The end of the fibre and the beam are arranged to define a cavity or gap whose width varies with vibration of the beam and which behaves as a Fabry-Perot cavity: thus light from the fibre is directed onto the beam and then reflected back to the fibre, the reflected light being modulated at the frequency of vibration of the beam. In order to overcome the difficulty of setting the gap or cavity width at an optimum value for light of a given wavelength, light of two different wavelengths is used to sense the vibrations, the wavelengths being selected such that the phase difference produced by the gap for one wavelength differs from that for the other wavelength by roughly 90.degree..

Abstract: A vortex flowmeter is provided with a vortex-inducing bluff body in the form of a first, upstream, cylinder having a semi-circular or semi-ellipsoidal front surface and a planar rear surface, and a second, downstream, cylinder having a planar front surface and a planar or concave rear surface. The rear surface of the upstream cylinder is parallel to the front surface of the downstream cylinder, and separated from it by a gap whose width is preferably about 25% of the diameter of the upstream cylinder.

Abstract: Separate pulse inputs from respective metering circuits, representing the reactive R and in-phase W power components, are converted to a pulse output V representing the vector sum of those components. The two inputs are applied to increment respective registers, the output V is held in a third register, and a fourth register is provided to store the REMAINDER value (W.sup.2 +R.sup.2)-(V+1).sup.2. The meter includes a processor for incrementing the REMAINDER value by 2W+1 for each increment of W and 2R+1 for each increment of R and for incrementing V whenever the REMAINDER value is zero or positive and at the same time reducing the REMAINDER value by 2V.sub.1 +1, where V.sub.1 is the incremented value of V. The FRACTIONAL error in the value of V is determined by means of a look-up table.

Abstract: In a micromachined silicon pressure sensor comprising a resonantly vibratable beam supported on a diaphragm, the beam is indirectly excited into resonant vibration by directing an optical excitation signal at the beam resonant frequency onto a part of the sensor other than the beam, preferably the diaphragm. Preferably, the optical excitation signal is of a wavelength to which the sensor is fairly transparent, and is directed through the beam and diaphragm to be absorbed by a suitable coating on the underside of the diaphragm. The optical excitation signal produces local heating, and the resulting expansions and contractions at the beam resonant frequency propagate through the sensor structure to excite the beam into resonant vibration. Another optical signal is used to detect the frequency of vibration of the beam, and a positive feedback loop maintains the frequency of the excitation signal equal to the detected beam vibration frequency.

Abstract: A solid state sensor, micromachined in silicon, comprised first and second beams which can be optically excited into resonant vibration. The first beam is arranged to be acted upon by a diaphragm, so that the tension in it, and therefore its resonant frequency, is affected by the pressure applied to the diaphragm. The second beam is provided for temperature correction purposes, and to this end is positioned close to the first beam but free at one end, so that it is insensitive to the pressure applied to the diaphragm, while being subject to the same temperature variations as the first beam. Additionally, the second beam is positioned sufficiently close to the first beam that it can be optically excited simultaneously with the first beam via a single optical fibre.

Abstract: A coriolis-type mass flow sensor suitable for aerospace use comprises a tuning fork which is immersed in the fluid whose mass flow is to be sensed, such that its tines extend across (i.e. perpendicular to) the direction of flow of the fluid. The whole tuning fork is elongated in the direction of flow of the fluid, so that the fluid flows over (and between) the tines: typically, the fork may be up to 15 cm long in the direction of flow. The tines are excited to vibrate perpendicularly to the direction of flow of the fluid by several piezoelectric drive devices held under compression in, and distributed symmetrically about the midlength of, the yoke from which the tines project, while the vibrations are sensed by respective piezoelectric pickup devices within each end of the yoke. The phase difference between the vibrations sensed by the two pickup devices is a function of the mass flow of the fluid.

Abstract: A coriolis-type mass flow transducer comprises a straight tube 10 through which a fluid whose mass flow rate is to be measured is arranged to flow while the tube is set into transverse resonant vibration in its second overtone mode. Mass flow is determined by measuring the phase difference between the vibration at two points along the tube 10. Such a transducer exhibits an offset at zero flow, which can vary with time. These variations are minimized by minimizing the damping effects on the tube 10 of bellows 6, 7 used to connect tube 10 in a flow line, and then corrected by measuring the amplitude ratio of the vibrations at the two points, and correcting the initially-determined offset in dependence upon changes in this amplitude ratio.

Abstract: An ultrasonic distributed temperature sensor comprises an elongate ultrasonic waveguide in the form of steel or nickel wire 0.16 cm in diameter and up to 10 meters long, which is strung around the area whose temperature is to be monitored, eg an aircraft engine. The wire is provided with discontinuities in the form of annuli welded on to it to form annular flanges, which serve to partially reflect ultrasonic pules launched into one end of the wire. These flanges, known as "posi-notches", divide the waveguide, and thus the area to be monitored, into a number of zones, the size of each zone being determined by the spacing of the adjacent flanges defining it. In operation, the temporal spacing of each pair of successive partially reflected pulses is a measure of the average temperature of the zone defined by the flanges producing that pair of pulses.

Abstract: A liquid bottle is efficiently carried by a bicycle having a tubular frame that includes a forwardly extending first tube projecting forwardly from near the seat to the steering column, and a second tube projecting downwardly and rearwardly from the steering column at an angle .alpha. relative to the first tube and toward the pedal rotor bearing, the two tubes defining an upright frame plane that extends forwardly.

Abstract: Amplitude-balanced input signals (I.sub.1 and I.sub.2) from two pick-up coils spaced along a vibrating tube mass flow transducer are used to form sum and difference signals (S and D). These are multiplied by quadrature and in-phase signals (Q and I) respectively in multipliers, the multiplying signals being generated by a phase-locked loop locked to the sum signal (S). The in-phase signal (I) provides the drive signal for a drive coil (12) of the transducer. The product signals (P.sub.S and P.sub.D) from the two multiplier are smoothed in low pass filters to provide sum and difference voltages (V.sub.S and V.sub.D). Mass flow rate is proportional to the phase difference (represented by the ratio of these voltages) divided by the frequency of the I signal. The density of the fluid in the transducer is indicated by the frequency of the I signal.

Abstract: An ultrasonic fire detector comprises an elongate ultrasonic waveguide, e.g. in the form of a wire, which is arranged to be strung around the area to be monitored for fire. An ultrasonic pulse generator launches longitudinal ultrasonic pulses into one end of the waveguide, for reflection from the far end. The waveguide is arranged such that local heating due to a fire changes its acoustic impedance at the location of the local heating, the change in acoustic impedance being sufficient to produce partial reflection of the ultrasonic pulses. Detection of the partially reflected pulses thus indicates the presence of a fire, and their time of arrival gives the location of the fire along the waveguide. The acoustic impedance change can be produced by providing the waveguide with notches filled with low melting-point alloy, by applying a temperature-induced stress to the waveguide, or simply by the temperature gradient caused by the fire.

Abstract: A rotary displacement transducer comprises a shaft rotatably supported in a housing, and to which the rotary displacement to be sensed is applied. The shaft is axially fixed in the housing, and has a precision screw thread formed over part of its length. An internally threaded sleeve coaxially surrounds the shaft in threaded engagement with the precision screw thread, the sleeve carrying a collar having two diametrically opposed radial projections. The first projection carries a roller which engages in a slot in the housing to prevent the collar and sleeve rotating as the shaft is rotated, so that rotation of the shaft causes the sleeve and collar to move axially of the shaft by an amount dependent on the rotary displacement to be sensed. The axial movement of the collar is sensed by a linear displacement transducer of the LVDT type coupled to the other radial projection on the collar.