MXPA96005535A - Posic codifier - Google Patents

Abstract

The present invention relates to a linear position encoder, a support is provided on which a pair of quadrature windings (13 and 15) are mounted. The windings are configured to have a sinusoidal magnetic sensitivity characteristic along the length of the support (5). Mounted on a movable element (not shown) there is a resonant circuit (10) that includes a coil (14) and a capacitor (17), which are magnetically coupled with the coils (13 and 15). When the circuit (10) is excited, it induces currents in the windings (13 and 15) that depend on the position of the circuit (10) within a period T of the windings (13 and 15). An excitation and processing unit (11) is provided to energize the circuit (10) and to process the induced signals in the windings (13 and 15). In one variation, the encoder can measure the rotary position in place of the translation

Description

POSITION ENCODER FIELD OF THE INVENTION The present invention relates to linear, rotary and radio position encoders, in general. The invention has a particular, though not exclusive, relevance to linear, rotary and non-contact radio position encoders. The invention is particularly suitable for use in systems where there may be electromagnetic interference.

DESCRIPTION OF THE PREVIOUS TECHNIQUE Many types of non-contact linear position sensors have been proposed. A system similar to ~ "** and present invention is the" inductosyn "type system described in the Patent of the United States of America Number 4,005,396. In particular, U.S. Patent No. 4,005,396 discloses a system employing a plurality of square wave windings mounted on the surface of a stationary element, and a coil connected to an alternating current power source mounted on an element. moe. The square wave windings each include a plurality of "high" and "low" parts, and have different periods. The system determines the position of the moe element relative to the stationary element by using the variation in mutual inductance between the coil and the plurality of square wave windings. More specifically, when the power source energizes the coil, a large current is induced in a square wave winding if the coil is adjacent to a high part thereof. Only a small current is induced in a / - coiled if the coil is adjacent to a lower part of it. Accordingly, the position of the moe element 0 along the length of the stationary element can be determined from the signals on the windings. However, this system _ has a number of drawbacks. First, the system is not "balanced", that is, it is not immune to electromagnetic interference. The present inventors have realized that this is because the ground connection is through a base plate or the like, and there is no symmetry in the system. Actually, United States Patent Number 4,005,396 recognizes the problem of interference, and tries to solve it by providing an additional winding designed to detect electromagnetic interference. The signal is then used from this extra coil to adjust the signals from the square-wave windings. However, this solution requires an additional "interference" coil, which increases the complexity of the system and, consequently, the manufacturing cost. Secondly, the system is sensitive to variations in the energy level of the energy source, 5 and is relatively sensitive to changes in the separation between the moe element and the stationary element. The present inventors have realized that this is because the system relies on the amplitude modulation of the signal from the power source, and no calculation of the radium-electric type. However, this document offers a solution to the problem of separation, which involves limiting the movement of the moe element by providing guide rails, along which the moe element travels. Although this solution can '* work in some applications, it will not work for all applications. For example, it will not work in an elevation system, since it is impractical to limit the elevation, so that there is no significant lateral movement inside the elevation arrow. 20 Third, the use of square-wave windings gives rise to the problem that if the measurements are made close to the windings (ie, in a separation typically less than 1/8 of the winding period), then the shape of the winding as it is perceived by the lifting device results in harmonics, for example, third, fifth, seventh, seventh, etc. , harmonics, which distort the measured results obtained. The present applicant has already proposed a rotary position encoder in Patent Publication Number WO 94/25829 which employs an excitation coil, two receiving coils, and a resonant circuit mounted on the rotating element. The configuration is such that, in response to an excitation current in the excitation coil, the resonant circuit produces signals on the reception coils, whose amplitudes depend on the orientation of the rotating element. Accordingly, by proper processing, the orientation of the rotating member can be determined. However, the description of this reference ^ f'4 does not extend beyond the encoding of rotating placement.

SUMMARY OF THE INVENTION In one aspect, the invention provides an apparatus 20 for indicating the relative position of first and second members, wherein one of the members carries a transmitting circuit that is coupled by electromagnetic induction with a receiver circuit carried by the other of these members, to cause a signal representing the relative positions of the first and second members to appear, wherein at least one of the transmitter or receiver circuits comprises a plurality of electrically separate conductors, located one above the other, and each comprising , a first portion extending away from a position on the member in a repetitive pattern of convolutions, and a second return portion having; similar convolutions, the convolutions of the first and second portions being substantially 180 ° out of phase, to define a repetitive pattern of first and second type cycles, which provide opposite electrical responses to a far field, whereby, an induced response in the cycles of a first type by an alteration from the bottom, it is at least partially balanced by the response induced in the cycles of the second type, and in which the convolutions formed by each conductor are spatially separated in the direction of the measurement; of the convolutions of other drivers. In a variant of this apparatus, the transmitter or the receiver is of a simpler structure, and only has an alternation of the cycles of the first and second types. The present apparatus lends itself to the determination of the relative position of a first member containing passive devices, or devices energized by external magnetic induction from an energizing cycle, and does not require external connections or an electrical or mechanical contact with the second member. , which leads, in this case, a receiver circuit. Conveniently, the first member carries a resonator LC, and the second member carries an excitation group powered by an alternating current signal, which drives the resonator, and also carries a receiver circuit including conductors arranged in quadrature sine-wave tracks . This configuration can allow both the interpolation using the received signals to give a high precision of the measurement, and can make it possible for the sine signals to be received even where the space between the receiving circuit and the track is small. The use of balanced or crossed conductors to form the transmitter or receiver circuit reduces the sensitivity to the far field, or to other external disturbances, such as metal bodies located near the receiver circuit. The invention also provides an apparatus for indicating the position of a first member in relation to a second member, which includes an input member carried by the first member, and an output member carried by the second member, and coupled with the member. of input to cause a signal to appear in the output element, indicating the relative positions of the first and second members, characterized in that at least one of the input element and the output element includes at least one conductor having a first portion extending away from the position on the second member in a pattern of sinusoidal convolutions, and a second return portion having similar convolutions, the convolutions of the first and second portions being substantially 180 ° out of phase. The quadrature output signals derived from the tracks with the sinusoidal conductors can be processed radiometrically to give an outputwhose value is insensitive to separation *. between the first and second members. The invention also provides a position encoder having coils or windings of balanced transmitters and / or receiver. In another aspect, the invention provides a position encoder having transmitter or receiver windings that have a magnetic field pattern or sensitivity to the magnetic field (as the case may be), which varies sinusoidally in the direction of the measurement, regardless of the distance from the coil of the transmitter or the receiver. When used as a translation position encoder, the invention may include an elevation having an element for indicating its position on a lifting arrow, this element being an apparatus indicating the relative position as mentioned above. The translation position encoder can be used to determine the relative position of other fixed and movable members in engineering and metrology, for example, the position of a movable printer head of a dot-matrix or ink-jet printer, or a similar device, in relation to the support structure, inside from which reciprocates the head of the printer. The invention also provides a liquid level sensor that includes a float, a support on or within which the float is slidably guided, and a linear position encoder in the shape of the relative position measuring apparatus as mentioned above. The invention is also applicable to arrow position encoders, for example, for a valve or choke having a rotary arrow, and an encoder for each arrow, the encoder being a rotary encoder as mentioned above. This encoder is conveniently used for the monitoring of arrows of a limited angular travel, for example, less than 180 °, and in particular, no more than 120 °. These limited travel arrows can be used to control, for example, gate valves, which can be activated or deactivated within a 90 ° rotary movement, and vehicle choke arrows, where angular movement is normally not greater of 120 °. The invention is applicable to an industrial process control, for example, to a fluid flow meter that includes a thinned tube and a float in the tube that moves to a longitudinal position determined by the fluid flow, providing an indicator apparatus of the relative position as mentioned above, to indicate the relative position of the float and the tube. This apparatus can additionally be provided with elements, by means of which the rotation of the float can be monitored or compensated, which can contain one or more resonators.

BRIEF DESCRIPTION OF THE DRAWINGS Now the manner in which the invention can be put into effect will be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 schematically shows a lifting system having a position encoder embog the present invention. Figure 2a is an isometric view of a linear positioning encoder embog the present invention, which is used in the lifting system shown in Figure 1. Figure 2b is an end view of a thin ribbon cut from a 5 position coding track that is part of the encoder of Figure 2a. Figures 2c and 2d are layers of printed conductors, from which a practical coder track can be formed. Figure 2e is a diagrammatic view of track 10 of the resultant two-layer printed coder. Figures 2f, 2g and 2h show alternative configurations of the conductors that make up the track of the encoder. Figure 3 shows a single period of one? ~ - "spiral winding", and the effect that far-field electromagnetic interference has on it. Figure 4a schematically illustrates a part of the linear positioning encoder shown in Figure 2a, and contains a graph of its magnetic sensitivity 20 against the positions of the resonator; Figure 4b is a diagram showing an energizing pulse, and Figure 4c is a diagram showing the current induced in the resonant circuit in response to the excitation current. Figure 5a is a schematic representation of the preferred excitation and processing circuit, used to determine for the positioning encoder of Figures 2a and 4a, the position of the resonant circuit. Figure 5b is a graph showing the output voltage versus time for an integrator that is part of the circuitry of Figure 4a. Figure 6a is a three-dimensional graph of the sensitivity of spiral coils to an external magnetic field, to change the position of the resonator. Figure 6b is a two-dimensional graph of the peak magnitude of the sensitivity as a function of the separation between the resonant circuit and the support. Figure 7 shows schematically an example of an absolute position encoder embog the present invention. Figure 8a shows another absolute position encoder embog the present invention, and the processing circuitry required to determine the position of the resonant circuit, and Figure 8b shows yet another form of the absolute position transducer and processing circuitry. Figure 9 shows another absolute position encoder embodying the present invention, and the processing circuitry required to determine the position of the resonant circuit.

Figure 10 shows another absolute position transducer embodying the present invention. Figure 11 illustrates schematically an alternative linear position encoder embodying the present invention. Figures 12a and 12b show alternative forms! of a three-phase spiral winding, together with the associated excitation and processing circuitry, but different in the manner in which the energy is applied and the position signal is received; and Figure 12c shows a four-phase spiral winding and its associated processing circuitry. Figure 13a schematically shows a liquid level sensor embodying the present invention. Figure 13b illustrates the manner in which the transducer shown in Figure 13a can be formed around a support in a helical shape. Figure 14a schematically illustrates a transducer suitable for use in a rotary position encoder embodying the present invention. Figure 14b schematically illustrates a resonant circuit that is suitable for use in the rotary embodiment illustrated in Figure 14a. Figure 15 schematically illustrates a linear position encoder that includes a single period of quadrature coil windings. Figure 16 is a graph of a typical resonance characteristic for a resonant circuit. Figures 17, 18 and 19 schematically illustrate other forms of a linear position encoder. Figure 20 is a schematic representation of the preferred processing and excitation circuitry used to determine, for the position encoder shown in Figure 19, the position of the generator harmonica. Figure 21 is an isometric view of a preferred float configuration used in the liquid level sensor system shown in Figure 13. Figure 22 is a plan view of another "? float configuration that can be used in the liquid level sensor system shown in Figure 13a. Figure 23 schematically illustrates a fluid flow rate sensing system, which employs a transducer in accordance with the present invention. Figure 24a schematically shows a float that is suitable for use in the fluid flow rate system shown in Figure 23. Figure 24b schematically illustrates a preferred shape of the float used in the fluid flow rate system shown in FIG. Figure 23. Figure 24c shows in section another fluid flow velocity system, which employs two transducers incorporating the present invention. Figure 24d schematically illustrates the shape of the float used in the detection system. , fluid flow velocity shown in Figure 23, when the float is spherical. Figure 25 is an isometric view illustrating the manner in which orthogonal excitation coils can be formed around the support in the liquid level detection system shown in Figure 13. Figures 26a and 26b are respective views of a track. of position encoder and resonator coils I balanced in accordance with another embodiment of the invention. Figure 27 is a diagrammatic view of the balanced transmitter and the tracks of the quadrature position encoder, together with a balanced lift coil 20. Figure 28 shows part of a two-dimensional displacement transducer according to another embodiment of the invention. Figures 29a and 29b are diagrams showing the relationship between an apparent measurement position and an actual measurement position for a single coil, and the use of a pair of coils to adjust the position of the apparent measurement, allowing the reduction of the adverse effects of the tilt of the coil. Figures 30a and 30b are views of alternative forms of a radial position transducter. Figure 31 shows a modified form of the transducer shown in Figure 30b, which is suitable for use in a linear position encoder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 schematically shows a lifting system having an elevator 1 that travels up and down an elevation arrow 3. Attached to one of the side walls of the lift shaft 3, there is a support of transducer 5 of an electrically insulating material connected to the wall by fixing points 7. Mounted on the support 5, there is a transducer (not shown) which is connected to an excitation and processing unit 11. In this embodiment, a resonant circuit 10 on top of the elevator, in such a way that, when excited, it generates signals in the transducer (not shown), which depend on the position of the elevator inside the arrow 3. These signals are then processed by the excitation unit and processing 11, which determines the position of the elevator and the output signals 12 to the lift controller (not shown). The processing circuitry can also determine the speed and acceleration of the elevator from the indications passing through the position, whose information can be used by the elevation controller (not shown) to optimally control the elevation. To operate effectively in the lifting environment, the sensor system must be relatively insensitive to the separation between the support of the transducer 5 and the resonant circuit 10, since the elevators are susceptible to lateral movement. Actually, the system should typically be tolerant to changes in lateral movement of approximately + 8 millimeters in l ([~ any direction.The current lifting systems use a combination of rope and pulley sensors, optical fin sensors, and encoders of the arrow on the motor and the winding gear, however, these sensors have the following disadvantages. In the rope and pulley system, the rope is connected to the elevator, and runs on a pulley wheel having a rotary encoder mounted on it. This system suffers from sliding of the rope on the pulley, and a poorly defined dynamic if the length of the lifting arrow is large. Mechanical wear is also a problem. In the optical fin system, a fin on each floor interrupts an optical beam break sensor mounted on the elevator. This system can be used to compensate for the slippage of the rope and pulley system. However, since the elevation control is mounted on the elevation arrow, and needs to communicate with the sensor, a link is required ? of additional communication between the arrow and the elevator. The coding system of the arrow suffers from the drawback that it is indirect, since it acts on the motor and the winding gear, and not on the lift directly. Therefore, as the system changes, due, for example, to the stretching of the support ropes they load, and at the same time, the system will also lose precision. * Figure 2a is an isometric view of a linear position sensor embodying the present invention, and that can be used in the elevator system shown in Figure 1. As shown in Figure 2, there is a pair of windings conductors in quadrature phase 13 and 15, and an excitation cycle 16 mounted on a support 5. In a simple form, as shown in Figure 2b, the windings 13, 15 and the excitation cycle 16 could take the form of insulated wires of copper or another conductor adhered, for example, by means of an epoxy adhesive, in the required pattern on a glass fiber substrate 5 or other flat insulating sheet material. In a more developed form, as shown in Figures 2c to 2e, conductive patterns are formed in successive printed circuit layers, which are shown in Figures 2c and 2d, each conductor layer having a printed pattern as shown, and extending between track holes. When they overlap, two layers and connected through the track holes, as shown in Figure 2e, you get a track of the sine or "spiral" configuration required. The same principle can be used to provide additional layers, for example, of other "spiral" conductors, or thick position indicator tracks, as described in more detail below. Each coil 13 and 15 starts from one end 5a of the support 5, and follows a sinuous path along the same, until it reaches the other end 5b, where it returns along the support 5 following a sinuous path to the end initial 5a. The forward and return sinusoidal trajectories formed by each winding 13 and 15 have the period Ts, and they are in the reverse phase, that is, they are substantially 180 ° out of phase. The windings 13 and 15 shown in Figure 2 and described above, will hereinafter be referred to as "coiled windings", since they visually resemble a flattened helix. The spiral windings 13 and 15 are isolated from each other, either by using track holes to the other side of the support 5 at the crossing points, or by using a laminated structure of conductor insulation. If a laminated structure is used, the support 5 must be non-magnetic, and preferably non-conductive, for reasons that can be seen later. Spiral windings 13 and 15 can be formed using any conductive wire, but are preferably formed by etching or other conventional printed circuit board technique. The excitation cycle 16 runs around the periphery of the support 5, and may include a single conductor cycle, or alternatively may include many turns of conductive wire. Each end of the spiral windings 13 and 15, and the excitation cycle 16, is connected to the drive and processing unit 11. As will be appreciated by those skilled in the art, in practice, the excitation and processing circuit 11 may be provided by a power source and a single integrated semiconductor chip. Figure 2a also shows a wire coil 14 and a capacitor 17, which together form the resonant circuit 10, which is mounted on top of the elevator 1 shown in Figure 1. As represented by the arrows 19, the resonant circuit 10 is free to move along the length of the support 5, that is, along the x-axis of Figure 2a. Preferably, the axis 21 of the coil 14 is orthogonal to the surface of the support 5, on which the spiral windings 13 and 15 are mounted, since this provides the greatest magnetic coupling between the and * winding coils 13 and 15 and the coil 14. The configuration of the excitation cycle 16 is designed to give a constant coupling with the resonant circuit 10, regardless of its position along the length of the support 5. The wire used to form the coil 14 can be of any material conductor, but preferably it is Litz wire, which is a multi-wire wire that has a low AC resistance. The Litz wire is available from Elektrisola Dr. Gerd Schildbach Gmbh & Co., of Inderhuvttenwiese D-5226 Reichshof-Eckenhagen, Germany. Figures 2f, 2g and 2h show alternative configurations of the windings. In Figure 2f, the windings have, when viewed globally, a hexagonal configuration; in Figure 2g they are triangular, and in Figure 2h they are square waves. The operation of the sensor system shown in Figure 2 will now be briefly described. When determining the position of the coil 14 along the x axis relative to the support 5, a burst of excitation current is applied to the cycle of excitation 16. The frequency of the burst should be such that it causes the circuit 10 to resonate. When the burst ends, the circuit 10 continues to resonate for a short period of time, and induces a current in each spiral winding 13 and 15. The magnitude of the induced current depends on the position of the resonant circuit 10 along the x-axis. Accordingly, by suitable processing of the induced currents in the spiral windings 13 and 15, the position of the resonant circuit 10 can be determined within a period of the windings 13 and 15. As will be seen later, two spiral windings are required. in the quadrature phase to give unambiguous readings over the entire TB period of the spiral windings 13 and 15. In the present embodiment, the absolute position is determined by using a counter inside the excitation processing unit 11, which counts the periods through which the resonant circuit has moved from a reference point. Preferably, the reference point is defined by an additional drive cycle (not shown) at a selected position on the support 5, since this allows the excitation processing unit 11 to recover the absolute position after the excitation has been removed. energy simply by moving the resonant circuit 10 until the signal level is augmented in this additional cycle. Additionally, better accuracy can be achieved by averaging the values obtained over several of these excitation and processing stages. Although the operation of the circuit described above is in some respects similar to that of a variable phase transformer of the "inductosyn" type to detect the linear displacement, the use of the spiral windings 13 and 15 provides several advantages. In particular, since the windings 13 and 15 are not of a digital nature, that is, they are continuously varying along the length of the support 5, the resolution of the system is theoretically infinite. However, in practice, the output signals are digitally processed, and the resolution of the analog-to-digital converter (CAD) in the processing circuitry that digitizes the signals from the windings 13, 15, will determine the resolution of the system. Another advantage of the spiral windings is that, since the sinusoidal forward and backward trajectories forming each coil 13 and 15 are in opposing phase, the induced currents flowing in any cycle and their adjacent cycle are in opposite directions, such that the corresponding magnetic fields are of opposite polarity, and are effectively balanced. Consequently, they are relatively immune to electromagnetic interference. This is because, as shown in Figure 3, any current induced in a cycle A of a coil due to electromagnetic background radiation 23 is canceled by the current induced by the same background electromagnetic radiation in the adjacent cycle. B of the winding. Yet another advantage of spiral windings is that their sensitivity to the magnetic field measured at any distance from the windings in a line parallel to their axis is sinusoidal. As a result, the system can be more tolerant to changes in the spacing between the resonant circuit 10 and the support 5, that is, the movement along the y-axis, than the systems inductosyn of the prior art. In particular, the sensitivity of the spiral winding remains sinusoidal, even for small separations between the resonant circuit 10 and the windings 13 and 15. Additionally, the system is relatively insensitive to dirt, dust, grease, etc., which may affect the proper operation of optical type position sensors. It should be noted that, since the excitation cycle 16 generates a uniform magnetic field along the length of the windings 13 and 15, and since the windings are balanced, the excitation cycle and the windings 13 and 15 are effectively orthogonal In other words, the excitation cycle 16, in theory, will not induce current in the windings 13 and 15, and in that way, the system could be operated in a continuous wave (OC) mode, i.e. the excitation y1 reception of the signals at the same time. However, in practice, due to the imperfections in the coiled coils, especially at their ends, some current will be induced in them by the current of the excitation cycle. Accordingly, the preferred mode of operation, in this mode at least, is impulse-echo, that is, transmit and then receive and process after the excitation has been removed. The principle of operation of the system shown in Figure 2 will now be described in more detail, with reference to Figures 4, 5 and 6. Figure 4a is a schematic diagram showing part of the spiral windings 13 and 15, the cycle of excitation 16, and the resonant circuit 10. As illustrated by the arrows 19, the resonant circuit 10 is free to move in any direction along the axis of the spiral windings 13 and 15, that is, along the x-axis . Figure 4a also shows a graph of the sensitivity function S (x) of each spiral winding at the magnetic flux density generated by the resonant circuit 10 as a function of the position x of the resonant circuit 10 along the support 5. As the resonant circuit 10 moves along the spiral windings 13 and 15, the corresponding sensitivity functions S13 (x) and S15 (x) vary in a sinusoidal manner in the quadrature phase, and are given by: S13 (X) = A COS (27TX) (1) T "0 S15 (x) = A sin (2px) (2) T., (where x and Ts are as defined above, and A 5 is the peak amplitude of the sensitivity function). r * ~ * Figure 4b shows the burst of the excitation current that is applied to the excitation cycle 16 shown in Figure 4a. Each burst includes a number of cycles of an excitation current. The number of cycles 0 transmitted depends on the resonant frequency and the quality factor (Q) of the resonant circuit 10. In this mode, a burst of 65 cycles of a triangular wave signal having a 6μs period is applied to the coil of excitation 16, which is sufficient to cause loop 10 to resonate. Figure 4c shows that the current Ir in the resonant circuit 10 increases in its magnitude, and begins to level just before the excitation current is removed. After the burst ends, the circuit 10 still resonates, but the amplitude of the Ir current decreases exponentially with time. To allow the time of the signal to be set, the excitation and processing unit 11 waits for a short period of time, approximately 4 cycles of excitation in this mode, before processing the signals on the windings 13 and 15. Consequently, after the burst of excitation current has been removed, the current flowing in circuit 10 can be represented by: Go =? Re rsen (2trfrt) (3) where fr is the resonant frequency of circuit 10, which in this mode is approximately 166 Khz, and where the exponential term containing time t and decay time T represents the exponential decrease in current amplitude over time . The Ir current flowing in the resonant circuit creates a magnetic flux density Br, in the direction of the axis of the coil 14 that is part of the resonant circuit, and can be represented by: -t Br = K1íre rsen (2pfrt) (4) where 1 ^ is a constant of proportionality that depends on the physical nature of the coil 14, that is, the number of turns, the radius, etc. The density of the alternating magnetic flux Br induces an electromotive force (FEM) in each spiral winding 13 and 15, which is proportional to the change index 0 of the magnetic change density Br, and which is modulated in its amplitude by the sensitivity function respective S13 (x) and S15 (x) of the corresponding spiral winding 13 and 15. Accordingly, when the resonant circuit 10 is in the position shown in Figure 4, the electromotive force induced in the winding. { *** spiral 13 will be given by: -t EMF13 = 27rfrK2Íre tS13 (d) cos (2pfrt) (5) 0 and the electromotive force induced in the spiral winding will be given by: -t EMF15 = 2rfrK2Ire tS15 (d) cos (27rfrt) (6) 5 where K2 is a constant of proportionality that depends on Kj, and the area enclosed by each spiral winding.

In the present embodiment, each spiral winding 13 and 15 having a peak-to-peak separation of about 35 millimeters, and a period of 200 millimeters, and coil 14 of the circuit 10 having a length of 100 millimeters (i.e. in the z of Figure 4a), a width of 50 millimeters (i.e., in the x direction of the, Figure 4a), and a separation of 10 millimeters from the support 5, and the excitation cycle 16 having a width of 45 millimeters (ie, in the z-direction of Figure 4a), a peak electromotive force of approximately 180 mV per ampere of excitation current can be induced in the spiral windings. To determine where the resonant circuit 10 is along the length of the spiral windings, ie to determine the value d within the period Tg, the signals from the spiral windings 13 and 15 are processed in the excitation and processing unit 11. Figure 5a schematically shows the excitation and processing circuitry that can be used to calculate the position of the resonant circuit 10 within the period Ta of the spiral windings 13 and 15. As shown in Figure 5a, there is a signal generator 41 that generates the excitation current that is applied to the excitation cycle 16 by means of the switch 42, the amplifier 23 and the transformer 24a. As mentioned above, in the present embodiment, the excitation current is a triangular wave having the period 6μs, and it is applied to the excitation cycle 16 in a burst of a duration of 384μs. After the excitation signal of the excitation cycle 16 has been removed, that is, when the switch 42 is opened, the signals from the spiral winding 13 are fed to a terminal of a two-way switch r ~ 26 by means of a transformer 24b that removes the common mode noise, and a mixer 27a that demodulates the 0 input signals. In a similar manner, the signals from the spiral winding 15 are fed to the other terminal of the two-way switch 26 by means of another transformer 24c and the mixer 27b. Each mixer 27a and 27b demodulates the input signals, multiplying them with 'r * "" a changed phase version 39 of the transmission signal.

In particular, a phase version changed from + 90 °, or a phase version changed -90 °. A phase change of -90 ° is required, since the resonant circuit 10 imparts a phase change of -90 ° on the excitation signal. The ratio for 0 the + 90 ° alternative will be described later. Accordingly, the signals at the output of the mixer 27a are given by: V13 = K3S13 (d) + K3S13 (d) cos4pfrt (7) 5 and the signals from the output of the mixer 27b are given by: V15 = K-jS ^ td) + K3S15 (d) cos4trfrt (8) Then these signals are multiplexed by switch 26, and filtered by the low pass filter ^ 29 to remove the high frequency components, to give: V13 = K4cso (2pd) (9) T " V15 = K4sen (2trd (10) The filtered signals are then converted into "" digital signals by means of an analog-to-digital converter of the double-inclined type, which has been adapted to be used as an input of the two signals in quadrature, and which produces the ratio of the two filtered signals . This is achieved in the following way. First, the signal V13 from the spiral winding 13 is applied to the integrator 31 (having the RC time constant) for a fixed time t0. The output of the integrator 31 will increase with the inclination V13 / RC if V13 is positive, and will decrease with the inclination V13 / RC if V13 is negative. While the integrator 31 is increasing or decreasing, as the case may be, a counter (not shown) on the microprocessor 33 counts up at a fixed speed fc. Then, at the end of the fixed time t0, the microprocessor 33 stores the value N13 reached by the counter (not shown), and operates the I switch 26, in such a way that the signal V15 from the spiral winding 15 is applied to the integrator 31. As the switch 26 is operated, the microprocessor 33 activates the change block of < + 90 ° phase 35 if the sign of the signal from the winding 15 is the same as the sign of the signal from the winding 13, and otherwise, it maintains the phase change of -90 °. This ensures that the integrator 31 always increases in the opposite direction in response to V15 than it does in response to V13. Therefore, if the signals from the two coils are both positive, then the phase change of + 90 ° will be applied, and V15 will be reversed, and in this way, the integrator 31 will decrease with the inclination of V15 / RC. While the integrator 31 decreases, the counter inside the microprocessor 33 counts up at the same speed fc as during the increase stage. When the output of the integrator 31 reaches zero, the output of the comparator 37 leverages and stops the counter in the microprocessor 33. Figure 5b shows in more detail the signal output from the integrator 31, when the signals of both windings are positive. The value of N13 is given by the time t0 multiplied by the velocity fc at which the counter counts up. However, from Figure 5b, it can be seen that at t0, the voltage Vm is given by t0 by the speed at which the integrator voltage increases. Therefore, N13 is given by: Nl3 = fct0 = fcVm (BS) "(ID /. V13 In a similar way, the value of N15 is given by the time taken for the integrator 31 to count down to zero, ie, t? multiplied by the speed fc to which the counter counts up. However, from Figure 5b, you can see that t? is equal to Vm divided by the speed at which the integrator voltage decreases, ie: N 15 = fct! = fcVm (RC) (12) V 15 Therefore, by dividing N13 by N15, the resulting digital signal is equivalent to V15 V13 '1 ° which is equal to: Therefore, the value of d can be • •! : 'determine, by means of the microprocessor 33, performing an inverse tangent function, and' using an appropriate change, depending on the sign of the demodulated signals coming out of the mixers 27a and 27b. In a more particular way, d is determined from the following equation: V 15 - d = [atan + p (if V15 <0)] _ (14) 2 p Vi3 As experts in this field will realize, equation 14 can be implemented by using N15 to direct a look-up table, since the value N15 will be directly related to the position of the resonant circuit 10. In this embodiment, the sign of the signals coming out of the mixers 27a and 27b is determined by comparing them with the earth using the comparator 37.

To accomplish this, the switch 28 controlled by the microprocessor 33 is provided, which allows signals from the center 29 to bypass the integrator 31. Assuming that it takes approximately 400 microseconds to the processing circuit to determine the position of the circuit 10 within one period of spiral winding, then you can take a reading about every millisecond. Therefore, if the absolute position is lost, the speed of the elevator can still be determined, since it is not moving faster than 100 s -1, or false errors will otherwise occur. The excitation and processing circuit shown in Figure 5a and described above, is given by way of example only, and should not be construed as limiting in any way. In the above embodiment, the resonant circuit 10 is energized by a burst of excitation current from the local oscillator 41, which is tuned to the resonant frequency of the circuit 10. The resonant frequency fr is preferably of the order of lOKhz at 1 MHz. Much lower than this, that is, approximately 100Hz, results in low induced electromotive force amplitudes in the windings, and a poor response time. Much higher, that is to say, approximately 100MHz, results in a loss of accuracy, due to the cross coupling between the spiral windings 13 and 15, and a greater complexity and expense in the processing electronics. It was previously mentioned that the system shown in Figure 2 is relatively tolerant to changes in spacing or gap between the spiral windings 13 i. and 15 and the resonant circuit 10. Now the reason for this will be explained with reference to Figures 6a and 6b. Figure 6a is a three-dimensional graph of the sensitivity function S (x, y) for a period of a spiral winding. The x-axis of Figure 6a represents the position of the resonant circuit 10 along the spiral winding 13, the y-axis represents the distance of the resonant circuit 10 r • from the spiral winding 13, and the z-axis represents the magnitude of the function of sensitivity (S (x, y) of the spiral winding 13 to the magnetic flux density generated by the resonant circuit 10. Figure 6b is a two-dimensional graph of the peak magnitude S (y) of the sensitivity function as a function of the separation between the resonant circuit 10 and the support 5. The peak value S (y) of the sensitivity function is shown to decrease as the resonant circuit 10 moves away from the spiral winding 13, ie, by increasing y. However, Figure 6a shows that the sensibility function S (x, y) varies sinusoidally by changing the position of the resonant circuit 10 along the support, independently of the separation and between the resonant circuit 10 and the drowsiness. 5. In other words, with the sinewave coil windings, the problem of harmonic distortion that is common with the devices of the prior art is eliminated or at least minimized. Accordingly, the sensitivity function of the spiral winding 3 can be represented by: S13 (x, y) = S (y) eos (2px (15) tß The sensitivity function for the spiral winding 15 shown in Figure 1 also has a peak magnitude given by S (y). Therefore, when the radiometric calculation shown in equation 13 is performed, the dependence on the separation y will be eliminated. The inventors have established that the operation of the system does not compromise with separations between zero and at least a quarter of the spiral period Ts. The coiled windings used in the present embodiment have a period of 200 millimeters. Therefore, the system can withstand separations of up to 50 millimeters, and therefore, will satisfy the requirement of lateral movement of +8 millimeters with ease. Additionally, it is possible to use the magnitude of the signals induced in the spiral windings to determine the separation between the resonant circuit 10 and the support 5. however, since the magnitude is affected by other system variables, such as the excitation energy. , etc., the calculations of the separation may not be accurate. \ Theoretically, the spiral windings can have any period Ts, and consequently, the sensor can be of any length. However, as the period Ts of the windings increases, the resolution at which the detector can detect changes in the position decreases. The reason is that small changes in the position of the resonant circuit 10 within the period Ts of the spiral windings will only produce small changes in the sensor signals, whether these small changes are detected or not depends on the resolution of the analog-to-digital converter used in the processing circuitry, the ratio of the signal to the noise of the received signal, and the spatial accuracy of the windings.Normally, for a given application, the resolution of the analog-to-digital converter is set by other parameters of the system, or by cost, and typically can be an 8-bit analog-to-digital converter.The inventors have established that for an 8-bit analog-to-digital converter, the resolution achieved with the spiral sensor is approximately 1/400 of the period Ts of the spiral windings, therefore, when the system designer specifies the resolution qu that; it requires, effectively specifies, the period of the spiral windings. In the first mode, a counter was used to allow the system to keep track of the absolute position of the resonant circuit. Another solution to this problem is to provide a coarse and fine set of spiral windings along the length of the sensor. An example of this configuration is shown schematically in Figure 7, which shows part of a support 2.4 meters long 5, which has a set of winding spirals of fine quadrature 15 and 15, with the period of 200 millimeters, and a set of spirals of coarse quadrature 43 and 45, with a period of 2.4 meters mounted on them. The signals from the fine spiral windings are used to determine the position of the resonant circuit within the fine spiral period, and the signals from the coarse windings are used to determine to which period of the fine windings the resonant circuit is adjacent. As shown in Figure 7, the thin and thick set of windings 13, 15 and 43, 45 are superposed one on top of the other, and as in the first embodiment, tracks or the like are used at the conductor crossings. This configuration is preferred because it maximizes the symmetry of the system, which in turn maximizes linearity and immunity to interference. For this solution to work, coarse windings must be able to distinguish between periods of fine windings. If this is not possible, then one or more windings of intermediate frequency should be used. Figure 8 shows alternative solutions to the ambiguity problem of the period. In particular, Figure 8a shows a first spiral winding 13 having the period T1 # and a second spiral winding 47 having a slightly longer period T1 +? T1. Additional quadrature windings will also be required, but for clarity, they are only shown at the processing end 5a of the support 5. The difference in the phase between the output signals from the two sets of quadrature windings 13, 47, indicates a which period the resonant circuit is adjacent, and the signals from one of the sets of spiral quadrature windings can be used to determine the position within that period in the manner described above. For example, signals I- and Q- from the first set of quadrature coil windings can be used to determine the position of resonant circuit 10 within the period, and signals 11 and Q1; I2 and Q2, from all windings, can be used to refer to a look-up table (TDC) of the phase differences, to whose outputs is adjacent which period of the resonant circuit 10. The look-up table will be specific for a particular sensor, where the windings have a period T ± and a period Tx r - +? Tlf and it will have to be recalculated for another sensor where these periods change. However, after a certain number of spiral winding periods, this solution will fail, since the pattern will repeat itself. Figure 8b shows a way to extend the pattern period. In particular, in Figure 8b, a third spiral winding 48 having a period T1 +? T2 different from 5 is used; winding period 47. The outputs from the three spiral windings (and the outputs from the corresponding quadrature windings (not shown) as well) can then be used to infer the correct period. Another solution Q for the ambiguity problem of the period is illustrated in Figure 9, which uses a set of gray code windings 51, similar to those used in U.S. Patent Number 4,005,396, in combination with windings square spirals 13 and 15. Gray code windings 5 are shown adjacent spiral windings 13 and 15 for clarity. Preferably, gray code windings 51 are superimposed on spiral windings 13 and 15 for maximum symmetry and minimal susceptibility to background interference. In this embodiment, the signals from the gray code scale are applied to a period decoder 53, which determines which period of the spiral windings is adjacent to the resonant circuit (not shown), and the fine placement within a only period is detected as described above. However, this embodiment suffers from the drawback that it is relatively complicated and expensive to manufacture, because many additional wires are required to provide the gray code windings 51. The inventors provide other solutions for the problem of phase ambiguity, such as providing a digital bar code type identifier along the length of the sensor track, which can uniquely identify at which period the resonant circuit 10 is adjacent. In Figure 10, this bar code is provided by the separate lower track 44 shown, which is a pseudo-random digital data track encoding the periods of the spiral windings 13 and 15. As in the embodiment of Figure 9, the bar code identifier is shown adjacent to the track for simplicity, but preferably it is superimposed on the windings 13 and 15. In the above embodiments, two were provided winding spirals in quadrature phase 13 and 15 to generate quadrature signals, from which the position of the circuit 10 can be determined unambiguously within a period Tg. Figure 11 shows another way in which quadrature signals can be generated, but this time only using a spiral winding 13. In particular, Figure 11 shows a spiral winding of multiple periods 13, an excitation cycle 16, and two circuits resonators 10a and 10b having different resonant frequencies f1 and f2, respectively. The two resonant circuits 10a and 10b are fixed one in relation to the other, with a separation of a quarter of the period of the spiral winding Tg. As indicated by the arrow 19, the two resonant circuits 10a and 10b are free to move along the length of the support (not shown) in any direction. When an excitation current is applied that has a frequency f? to cycle 16, circuit 10a will resonate and generate a signal in spiral winding 13, depending on sin [2pd / Ts], where d is the position of circuit 10a within a spiral period. In a similar manner, when an excitation current having the frequency f2 is applied to the driving cycle 16, the circuit 10b will resonate and generate a signal in the spiral winding 13, depending on sin [2tr (d + Ta / 4) / Ta], that is, cos [27rd / Ts]. Accordingly, quadrature signals are generated, from which the position of the circuit 10a (and consequently, of the circuit 10b) can be determined within a period "__ spiral. In the above embodiments, the excitation signal is applied to an excitation cycle 16 around the periphery of the support 5. One drawback of using this excitation cycle is that it does not balance, and consequently, will suffer from, and generate, an electromagnetic interference. The circuit 12a shows a three-phase spiral winding system using only one of the windings to excite the resonant circuit 10, as a result of which the excitation cycle is also balanced, In particular, Figure 12a shows three windings spirals 53, 55 and 57, each at 120 ° out of phase with the other two, and a vector representation of the signals induced in the windings by the resonant circuit 10. In this embodiment, the winding 53 uses to excite the circuit resonant 10, and the winding signals 53 and the subtraction of vectors from the winding signals 55 and 57 are used to determine the position of the resonant circuit The vector subtraction of the winding signals 55 and 57 produces a signal that is in the quadrature phase with the winding signal 53, and is represented by the vector representation of the dotted arrow 59. However, in this embodiment, when The resonant circuit 10 is adjacent to a junction of the winding 53, the excitation signal i_ is applied to the winding 55, rather than to the winding 53. In addition, the winding signal 55 and the signal representing the subtraction of the winding vectors. the signals of the windings 53 and 57 are used to determine the position of the resonant circuit. In this way, the system ensures that the resonant circuit 10 is energized for all positions along the support, and ensures that the excitation and reception windings are balanced. In Figure 12b, three coiled coils 53, 55, 57, a respective phase of a three-phase alternating current is fed at one end by means of the excitation and processing unit 11. The coils are connected to one another at the other end, to provide the neutral line of the three-phase system , and the signal appearing in the neutral line is returned to the processing unit 11. The resonant circuit 10 unbalances the neutral line, and gives rise to a signal, whose amplitude depends on the separation of the resonant circuit 10 from the coils 53, 55, 57, and whose phase depends on the position of the circuit 10 within a period of the windings. Figure 12c shows yet another configuration that the spiral windings can take. In particular, in Figure 12c, there are four spiral windings 63, 65, 67 and 69, each separated from the other by 1/8 of the period of the windings. As in the other modalities, it is - * > provides an excitation cycle 16 around the periphery of the support 5 and the excitation cycle 16, and the ends of the spiral windings 63, 65, 67 and 69 are feed to the drive and processing unit 11. The inventors have established that, by using this four-phase system, any generated spatial harmonics generated in the windings are suppressed. l < In the above embodiments, the spiral windings 13 and 15 remain essentially in a single plane. However, it is also possible to wind the spiral windings around a support in a helical pattern to achieve the same advantages as the flat pattern. This The form of the invention is particularly suitable for use in detecting the fluid level. Figure 13a schematically shows a liquid level sensor employing spiral wound windings incorporating the present invention. In Figure 13a, a support 1305 has a cylindrical shape around which the spiral windings 1313 and 1315 are wound in a helical shape. As will be appreciated by those skilled in the art, support 1305 must be transparent to the magnetic field generated by resonant circuit 1310, or otherwise, will affect the correct operation of the sensor. Figure 13a also shows the excitation cycle 1316, which "*" energizes the resonant circuit 1310 mounted on the float 1320. Preferably, the float 1320 is toroidal and fits over the support 1305 and the coils 1313 and 1315 , and can freely float up and down the cylindrical support 1305 as the liquid level (not shown) rises or falls inside the container (not shown), as illustrated by arrow 1319. In this embodiment, the float 1320 is also limited, such that it does not rotate around support 1305. As will be appreciated by experts in this field, if float 1320 could rotate, then the position indicated by processing unit 1311 will change by the same height. If a flat spiral had been used along the float of the support 1305, then this rotary problem would not cause the same problem. This problem is discussed in more detail later. Figure 13b illustrates the manner in which the spiral windings 1313 and 1315 should be wound around the support 1305. Essentially, the spiral windings 1313 and 1315 are formed of four wires 1313a, 1313b and 1315a, 1315b, starting on the exterior of the support 1305, separated at 90 ° intervals, and rotated in a helical pattern along the length of the support 1305. At the far end (not shown) of the support 1305, the wires separated by 180 ° are connected to each other, such / < * ~ that the wires 1313a and 1313b form a spiral winding 1313, and the wires 1315a and 1315b form the second quadrature spiral winding 1315. Additional windings can be wound around the support 1305 to provide a period encoder, when there is a plurality of spiral winding periods. The operation of this modality is similar to the operation of the first modality. An advantage with this helical design is that it is much easier to manufacture than the flat design, since the wires simply wrap around the support. Figures 14a and 14b show the manner in which the "spiral" transducer can be modified to be suitable for use in a rotary position encoder. In particular, Figure 14a shows a fixed circular support 1405 on which the spiral windings 1413 and 1415 are wound in a circular shape. In this embodiment, there are three periods of each spiral winding 1413 and 1415 around a support. As in the linear mode, conductor crossings are avoided by using tracks to the other side of the support, or by using a laminated structure of conductor insulator. There is also an excitation cycle 1416 mounted on the support 1405 which is used to excite the resonant circuit mounted on the element /? movable, which will be free to rotate around the axis of the support. To maintain linearity in the system, the resonant circuit must be as symmetric as possible. Figure 14b shows the rotating element 1401, which will rotate in relation to the support 1405 shown in Figure 14a around the center point 1491, as indicated by the arrows 1419. Mounted on the rotating member 1401, there is a resonant circuit 1410 which is designed to maximize the linearity of the system. The operation of this rotating mode is similar to the operation of the linear modes. In the above embodiments, spirals of multiple periods were provided along the support of the position encoder. However, in some applications, a shorter length support may be sufficient, in which case, only one spiral coil period set will be provided. Figure 15 shows a support 1505 carrying an excitation coil 1516 and two spiral windings 1513 and 1515 in the quadrature phase, which occupy a single period Tg. The windings are connected to an excitation and processing unit 1511 as before. Although this form of the device may be suitable for some applications, it is less preferred, because the end defects reduce the accuracy. In the above embodiments, a resonant circuit was mounted on the movable object. This has the advantage that it still generates a magnetic field after the excitation signal has been removed, which means that no energy source is required on the movable object. However, it is also possible to fix the position of the resonant circuit and allow the support to move. Additionally, it is also possible to determine the position of a plurality of movable objects by means of the y ~ ^, use of a resonant circuit having a different resonant frequency in each object. Figure 16 shows the resonant characteristic of a resonant circuit.

Ideally, if the resonant frequencies are going to be very close to each other, then this feature should have a high maximum value, a low minimum value, and a narrow peak width < 5W, or in other words, the resonator must have a high quality factor (Q). One method to improve this feature is to employ a quartz or ceramic type resonator in series with the coil 14 and the capacitor 17. In this embodiment, the value of the inductance of the coil 14 and the capacitance value of the capacitor 17 they are preferably selected in such a way that their impedance is canceled at the resonant frequency of the quartz or ceramic resonator, since this maximizes the sharpness of the resonant characteristic. The quartz or ceramic resonators are preferably suitable for surface mounting on printed circuit boards, as this minimizes the space required for this. The suitable ceramic resonators are supplied by AVX Kyocera, Stafford House, Station Road, Aldershot, Hants, United Kingdom, or Murata, distributed by Cirkit, Mercury House, Calleza Park, Aldermaston, Reading, Berkshire, United Kingdom. In Figure 17, the configuration of the support 1705, the excitation coil 1716, and the windings l '., 1715 and 1713, is as before. However, in this embodiment, there are two movable objects (not shown), each having a respective resonant circuit 1710A and 1710B, which has different resonant frequencies. The position of each moving object associated with the resonant circuits The respective 1710A and 1710B can be determined by exciting each resonant circuit at a time, or by exciting all the resonant circuits at the same time, using a "white noise" signal, that is, a signal containing all frequencies, and using techniques signal processing well-known for determining the position of each movable object. Although the resonant frequencies associated with each object may have any value, they are preferably selected to be relatively close to each other, such that the bandwidth of the system is not too large. Otherwise, electronics will become complex and, therefore, more expensive. Of course, if there is no problem by having an energy source on the movable object, then the capacitor 17 which forms part of the resonant circuit 10 can be replaced with a power source. This embodiment is illustrated with respect to the flat spiral design of Figure 18, but is equally applicable to the other embodiments. In particular, Figure 18 schematically shows a set of flat quadrature spiral windings 1813 and 1815 that are mounted on a support 1805, and a coil 1814 mounted on the movable object (not shown) with an alternating current source 1861 connected to the ends of the coil 1814. The mode shown in Figure 18 can be easily adapted for use in a system of multiple objects. In this adaptation, each object would have its own energy source with a particular frequency. In the above embodiments, the signals on the spiral windings are only processed after the excitation signal has been removed. The reason for this is to reduce the interference caused by the cross coupling with the excitation signal. However, if a harmonic generator is used instead of the resonant circuit, then it is possible to distinguish the signals generated by the harmonic generator from the excitation signal. Accordingly, if a separate excitation coil is provided, then it will be possible to determine the position of the harmonic generator while the excitation signal is still being applied to the excitation coil. This is possible because the harmonic generator has a non-linear magnetic characteristic that produces, in response to an excitation signal, a magnetic field with components that include harmonics of the excitation frequency. These higher frequency harmonics can be distinguished from the excitation signal and, therefore, they can be used to determine the position of the harmonic generator while the excitation signal is still being applied to the excitation coil. Figure 19 shows a modality in which a harmonic generator 1901 is mounted on the movable element (not shown) instead of a resonant circuit. This embodiment is described with reference to a flat spiral design, but is also applicable to the other embodiments described above. Figure 19 shows a support 1905 on which the spiral windings 1913 and 1915 and an excitation cycle 1916 are mounted. The excitation cycle 1916 must be capable of exciting the harmonic generator 1901 to its non-linear region when it is in any of its permitted positions, that is, along the entire length of the support 1905. The excitation cycle 1916 mounted around the periphery of the support 1905 shown in Figure 17 is an example of an appropriate excitation cycle. Figure 20 shows an example of the signal generator that generates the excitation signal, and the processing circuitry in the excitation and processing block 1911 shown in Figure 19. In particular, a pseudo-square wave generator 2063 generates a excitation signal lM having a fundamental frequency f, but without harmonics 3f, 9f, 15f, etc., which is applied continuously to the excitation cycle 1916. The signals from the spiral wound in quadrature 1913 and 1915 (and from other windings) 1971 if an absolute position is required) they are fed to an analog multiplexer 2026 controlled by the microprocessor 2033. The signal from each coil is amplified by the amplifier 2073, and mixed in the mixer 2027 with a signal 2039, whose frequency is three times the frequency of the fundamental frequency f of the 5 excitation signal, that is, the third harmonic. Accordingly, the component of the received signal having the frequency 3f (which is the component of interest generated by the harmonic generator 2001) will be demodulated, while the other components will not. The demodulated component of the high frequency components is then removed by the low pass filter 2029, converted into a digital signal in the analog to digital converter 2075, and fed into the microprocessor 2033, where it is temporarily stored. Once the signals have been processed from all the windings in this manner, the microprocessor 2033 calculates the absolute position of the movable object using equation 14 above. The harmonic generator 1901 is typically made of a non-linear magnetic material that can be driven through its saturation point to its non-linear region by the excitation signal, for example, Voile Fused Spline Strip Sch eltze 6025. alternatively, a coil connected with a non-linear electrical element, such as a diode, can also be a suitable harmonic generator 1901 (in which case, the processing circuitry would be tuned to the second harmonic of the excitation signal). A problem with the modality of the harmonic generator described above is that the presence of other earthy materials within the system can also generate background harmonic signals. However, this distortion can be minimized by: (i) reducing the coercivity and the permeability of the harmonic generator 1901, in such a way as to generate harmonics at lower levels of the transmitter field than the surrounding ferrous materials, for example, well below 50 A / m; and / or (ii) r ~ use materials with a liquid saturation point, so that high levels of high frequency harmonics that are not typically found in ferrous materials can be measured. Suitable materials having these characteristics are thin amorphous metals and long melt-spun metals (Metglass) supplied by Allied Signal of 6 Eastman Road, Persippany NJ 07054, New Jersey, USA; and magnetic materials ch? sporrotcados, such as alcncionor, of nickel. Additionally, the material form factor must be high to enable high permeability to be achieved. This can be achieved by using long, thin samples or very thin flat samples. Magnetic materials excited into the nonlinear region with a single frequency alternating current field without a direct current component (c.d.) produce harmonics of the impulse current. However, if very low permeability materials are used, then the field of the earth may be sufficient to degrade the generation of harmonics, forcing the harmonic generator out of the nonlinear region. A possible solution is for the system to apply a polarized field in direct current to counteract the field of the earth. The required direct current polarization can be determined by minimizing the detected level .- of even harmonics, or maximizing the detected level of harmonics nones. Another possibility with the use of a harmonic generator is to excite it with two different excitation frequencies Fj and F2. In this mode, the harmonic generator will generate a magnetic field that has inter-odulation components, that is, components in F1 ± F2. and- The modality of the harmonic generator is highly suitable for measuring the position of a float, since it is highly resistant to dirt, salt water, etc., which can cause electrical damping of an inductor / capacitor resonator, and can operate with large gaps between the float and the support. In addition, the harmonic generator has the advantage over the resonant circuit, that it will be coupled with the spiral windings regardless of their orientation. This is true even when the harmonic generator consists of amorphous metal having a preferred magnetic axis, since it is possible to layer the material in alternating orientations, thus obtaining a properly isotropic device. Another more complex alternative for the resonant circuit is an electronic transponder energized by the magnetic field generated by the coil of , ^ transmission, which generates a signal or code that can be distinguished from the excitation signal. This modality offers greater flexibility to the user at the expense of greater complexity and cost of the system. There are other simpler alternatives that could work in place of the resonant circuit. For example, a piece of magnetic material that concentrates the magnetic field of alternating current generated by the excitation coil, for example, ferpta, or a conductor that distorts the magnetic field of alternating current generated by the excitation coil, for example, an aluminum sheet. However, these modalities do not allow the position of more than one movable element to be detected. In the modalities where a resonant circuit is used, its shape, mass, resonant frequency, etc. , will be dictated by the particular application, and will also dictate to some degree the accuracy of the system. The inventors have established that a high degree of accuracy is achieved when the diameter of the coil forming part of the resonant circuit is approximately twice the width of the spiral windings, and approximately equal to half the period of the spiral windings. Figure 21 is an isometric view of a resonator design with air core that is appropriate for the float resonator shown in Figure 13a. The float 2120 is a tube of non-magnetic material, preferably non-conductive, for example, plastic or glass, has a length 1, and has an internal diameter large enough to fit over the support 1305 and the spiral windings 1313 and 1315 shown in FIG. Figure 13a. A coil of wire 2114 is wound around the outer side of the float 2120, such that its magnetic axis is directed radially with respect to the float 2120. In this embodiment, this is achieved by winding a first portion 2114a of the coil 2114 around the float in a first plane established at a first angle with the plane of the pipe itself, and then a second portion 2114b of the coil 2114 is wound around the float 2120 in a second second plane established at a second angle with the plane of the pipe itself , such that the combined effect of the two portions 2114a and 2114b of the coil 2114 results in a coil having a radial axis. A capacitor (not shown) will be connected to the two ends of the coil 2114 to form a resonant circuit with the coil 2114. However, in some applications, a low length 1 of the float will be a prerequisite. In this embodiment, the design shown in Figure 21 will not be appropriate, and an alternative design as shown in Figure 22 will be required. In particular, Figure 22 ^ shows in plan a flat disc-shaped float 2220, which has again an internal diameter large enough to fit over the support 1305, and coiled spirals 1313 and 1315 as shown in Figure 13a. Two 2214a and 2214b portions of a coil 2214 are mounted on the float 2220 in the manner shown, so that the axis of the coil 2214 is radial with respect to the float 2220. The ends of the coil 2214 are connected "with a capacitor 2217, thus forming a resonant circuit. The coil portions 2214a and 2214b are preferably wound around ferrite rods 2281 and 2283, since this concentrates the magnetic field produced by the coil 2214 when the resonant circuit is resonating. In the above modalities, the axis of the resonant circuit was assumed as fixed. However, in some applications, such as fluid flow meters, the resonant circuit can rotate. Figure 23 shows the manner in which a transducer shape of the present invention can be used in a fluid flow velocity sensor. The fluid is passed upwards through a vertical tube 2385 made of a non-magnetic material, preferably non-conductive, which is internally thinned as shown. The vertical position taken by a float 2320 depends on the speed of the fluid flow. Figure 24a shows in more detail the float 2320 shown in Figure 23. Inside the float 2320 there is a resonant circuit 2410, whose axis is horizontal. However, the float 2320, which in this case is generally conical, tends to rotate in the fluid flow, such that it will change the axis 2421 of the resonant circuit 2410. In accordance with the foregoing, the signal from the transducer will vary for a given height with time. In the present embodiment, float 2320 remains vertical, due to its generally conical shape, and only rotates about its vertical axis. When the 2410 circuit is resonating, and when the float is rotating, the electromotive force induced in both spiral windings on the transducer will be modulated in its amplitude by cosU, where) is the angular orientation of the float, and is zero when the axis 2421 of the 2410 circuit is perpendicular to the surface of the support 2305. However, the effect of rotation on the induced signals can be removed by the radiometric calculation performed in equation 13 above, since the electromotive force induced in both spiral windings is affected by the same modulation. Accordingly, rotating the float 2320 about a vertical axis will not prevent the determination 5 of its vertical position. However, if for any reason the float stops rotating, when the axis of the circuit ^ _, resonant is orthogonal to the surface of the support 2305, that is, when O = 90 ° or 270 °, then the height can not be determined , since there is no longer a link between the resonant circuit 2410 and the spiral windings (not shown). Figure 24b shows how the float 2320 shown in Figure 24a can be modified to solve the above problem. In Figure 24b, the float lr ^ ~ 2320 has the resonant circuits 2410a and 2410b having a horizontal axis, but perpendicular, and each preferably having a different resonant frequency fj and f2. Therefore, in this mode, there will always be an output signal in the coil windings (not shown), due to the magnetic field from at least one of the resonant circuits, from which the height of the float can be determined, independently of the angular orientation thereof. Additionally, as experts 5 will realize in this field, it is also possible to determine the angular orientation O of float 2220, from the signals generated in any of the spiral windings. This will be apparent to those skilled in the art, since the signal induced in a spiral winding due to a resonant circuit (after demodulation and filtering) is given by: and the signal induced in the same spiral wound due to the other resonant circuit (after the demodulation and filtering) is given by: Vrf "2 = (S (x, y) sin -BC (19) Therefore, the angular orientation O can be calculated from an inverse tangent function of the ratio Vf2 / Vfl. Also, the rotation speed of the float can also be determined by tracking? as it changes. This is convenient, since the rotation speed also depends on the speed of the fluid flow. Figure 24c shows in cross-section an alternative solution to this problem. In particular, Figure 24c shows the tube 2385, through which the fluid flows, the float 2320 inside the tube 2385, and two supports 2405a and 2405b remaining in orthogonal planes adjacent to the tube 2385, each having a set of windings spirals (not shown) mounted on it. In this embodiment, only a horizontal axis resonant circuit (not shown) is mounted on the float 2320. As experts in this field will realize, / '"* - there will always be an output signal from the spiral windings on at least one of the supports and, therefore, the height of the float can always be determined, regardless of its angular orientation, as in the modality shown in the Figure 24b, it will also be possible to determine the angular orientation of the float 2320 as well, however, as will be appreciated by those skilled in the art, in this embodiment, the signals from the two holders 2405a and 2405b will have to be used to determine the angular orientation. In the above embodiments, which describe a fluid flow velocity sensor, the float was specially designed to rotate only about a vertical axis Figure 24d shows another embodiment of a fluid flow velocity sensor, wherein the float 2420 is spherical and, therefore, can rotate around any axis, in this mode, a single set of winding spirals is mounted (not shown) on a support 2305 adjacent to the tube 2385. The float 2420 is free to float inside the tube 2385, which thins as before, and contains three resonant circuits 2410a, 2410b and 2410c having orthogonal axes, and having preferably different resonant frequencies. In this mode, there will always be some coupling between at least one of the resonant circuits 2410a, 2410b or 2410c, / 'inside the float 2420, and the set of coiled windings (not shown). Therefore, the height of the float 2420 can always be determined, regardless of its angular orientation. In addition, it is also possible to determine the rotation speed of the float 2420 around its axes, since the signals induced in the spiral windings (not shown) in the three resonant frequencies, will depend on the rotation speed of the float 2420. around the axis of the corresponding resonant circuit. One of the main advantages of the spiral detection system over existing fluid flow velocity sensors (which use a magnetic float and a magnetic tracking device) is that it does not exert any force on the float. Therefore, the system is more accurate than existing fluid flow velocity detection systems. In addition, by measuring both the height and the speed of rotation of the float, there is a greater dynamic range, on which a precise indication of the flow is possible.

In the embodiment illustrated in Figure 13a, it was assumed that float 1320 could not rotate about a vertical axis. However, if the float 1320 can rotate, then, to ensure that the resonant circuit is always energized regardless of the angular orientation of the float, either of two orthogonal excitation coils and a shaft resonator have to be provided. • "" "horizontal, or provide a single excitation coil and two resonant circuits of horizontal axes, but orthogonal, so that the angular orientation of the float can be determined.The angular orientation of the float must be determined so that it can be made a suitable correction of the indicated position, Figure 25 illustrates the manner in which two orthogonal excitation cycles 2516a and 2516b can be mounted around the support 1305 used in the liquid level detection system shown in Figure 13a. it requires that the two excitation coils 2516a and 2516b lie in orthogonal planes, but it is preferred, since this simplifies the processing required to determine the position and angular orientation of the float 13 shown in Figure 13a.Figures 26a and 26b show a additional form of the windings and the resonant circuit In Figure 26a, a support 2605 carries the windings 2653, 2655 and 2657 disp in a three-phase configuration. The associated resonant circuit 2610 shows the coils 2614 arranged in a spiral configuration, to form a balanced resonant circuit, with a multiplicity of cycles that extend along the direction of the measurement. This multi-cycle configuration has the advantage of averaging the signal over a number of windings, and thereby minimizing errors due to manufacturing defects in the windings 2653, 2655 and 2657. 10 In Figure 27, a transmitter track formed by spiral windings 2713 and 2715, which are fed with alternating current signals, as shown, which are in a quadrature relationship. The spiral rising coil or receiver 2714 receives \ ¿-. a signal whose magnitude depends on the position along the transmitter track inside a convolution pattern. The spiral configuration for the 2714 receiver coil is preferred, because it provides an average signal that reduces the effects of any manufacturing defects in the windings 2713 and 2715 of the transmitter. However, instead, if desired, a single coil of the receiver could be used. The alternating current sources 2741a and 2741b provide the quadrature signals that apply to the windings 2713 and 2715 as mentioned above, and are operated alternately, such that a succession of sine and cosine signals is received at receiver 2714. Figure 28 shows one of the windings that would be used in a bidemensional position encoder that use the spiral windings incorporating the present invention. In particular, Figure 28 shows a spiral winding 2815, whose coil density varies in a sinusoidal manner along the x-axis of Figure 28. As a result, the sensitivity of winding 2815 to a nearby source of magnetic field will vary from a sinusoidal way with the distance x, A spiral winding in quadrature phase (not shown) whose coil density varies in a sinusoidal manner with the distance along the x-axis will also be required. This provides a linear displacement device of one dimension. However, if an additional set of quadrature windings superimposed on the winding 2815 and the corresponding quadrature winding (not shown) are provided, whose winding densities vary in a sinusoidal manner per unit distance in the y direction, then a two-dimensional transducer is provided. For more clarity, in Figure 28 some of the windings are not shown. Figure 28 also shows a resonant circuit 2810, whose position can vary in the x and y directions. If an excitation coil (not shown) is provided to excite the resonator 2810, then the position of the resonator in the x and y direction with respect to the origin 0 can be determined from the signals induced in the four spiral windings in the manner described above. . The inventors have also established that, by careful design of the resonant circuit, it is possible to reduce (within limits) the apparent effect of the inclination of the resonant circuit. Figure 29a schematically shows a wire coil 2914 having the shaft 2921 that is part of the resonant circuit that is mounted on the movable member (not shown). Figure 29a also shows the support 2905, on which the spiral windings (not shown) are mounted. The system is designed to give the position of the resonant circuit along the length of the support. If the resonant circuit is inclined, that is, the axis 2921 of the resonant circuit is shifted through T radians, the position encoder must give the position at point 2988. However, through experimentation, the inventors have established that this is not the case. In fact, the position encoder indicates that the resonant circuit is adjacent to point 2989, which is approximately half the way between the actual position 2987 and the expected position 2988. This means that the resonant circuit appears to be at point 2990, and it seems to move along an apparent measurement plane 2992, which is different from the actual plane 2991, where the resonant circuit remains. Furthermore, the inventors have discovered that, by using a resonant circuit 5 comprising two coil portions connected in series, and spatially spaced along the direction of the measurement, it is possible to move the apparent plane of the measurement 2992 from or to support 2905. This has important implications in applications, such as the detection of the position of the head of the inkjet printer, where it may be impossible to place the coils in the required measurement plane, due to space constraints. Figure 29b shows a modality in which the -1 ^ resonator comprises two electrically connected coils, and wherein the distance between the respective axis 2921 is 2D. The two coils are fixed to the movable object, such that, if the movable object is tilted, then the two resonant circuits will tilt around point 2982.

The inventors have established that the apparent plane of measurement 2992 may vary as illustrated by arrow 2993, by changing the 2D distance between coils 2914a and 2914b. Preferably, the distance between the two coils is not an exact multiple of the coiling period. In a experiment, (i) each coil portion 2914a and 2914b comprised forty turns of 0.2 millimeter copper wire wound around a ferrite coil having a square section of 8 millimeters and a length of 18 millimeters; (ii) a suitable capacitor was selected to make the resonant circuit resonate at 150 KHz; (iii) a real separation of 25 millimeters * - was selected between the center of the coils and the surface of the support 2905; (iv) a spiral period of an inclination of 50 millimeters and 20 millimeters of peak to peak was used; (v) a spacing between coils (ie, 2D) of 116 millimeters was used. The results obtained show that the effective plane of measurement 2992 was located 120 millimeters above the track, and the position indicated by the position encoder system is point 2987 to within + 0.4 millimeters, with angular changes up to + 4 °. For the same angular changes, and a single coil, the position encoder indicates point 2987 within + 8 millimeters. This represents an improvement in the precision of a factor of 20. In a second experiment with a similar setting, but with a separation (2D) between the 100-millimeter coils, it was found that the apparent plane of the 2992 measurement is 10 millimeters above track. In a third experiment with a similar setting, but with a separation (2D) of 96 millimeters, it was found that the apparent plane of measurement 2992 was on the surface of support 2905. Therefore, in an inkjet printer application , where the nozzle from which the ink is projected onto the paper is susceptible to bending, it would be convenient if the apparent plane of the measurement were made equal to the plane of the paper. This can be achieved by selecting one! I / - adequate D separation, With this configuration, the accuracy of the system is increased, since on the apparent plane of the measurement, the position does not change much for small changes in the inclination. Figure 30a shows a manner in which the spiral windings shown in FIG.

Figure 2, to produce a suitable transducer for use with a radio encoder. In particular, the y? > Figure 30a shows a winding 3013 starting at point 3008a, and winding in a clockwise coil, to point 3008b, where it changes direction, and winding in the reverse direction to point 3008c , where it changes again, etc. By Accordingly, with this configuration, the winding 3013 has a sinusoidal magnetic sensitivity function that varies as a function of the radius. In other words, the winding has a magnetic detection pattern of "multiple" poles in any radial direction. I also know will require a second quadrature spiral wound 3015, but only its start is shown for clarity. The operation of this modality is similar to the operation of the linear modalities, and will not be described again. Figure 30b shows a modification of the spiral transducer system shown in Figure 30a. In particular, in the configuration of Figure 30b, each part * - from a complete winding several revolutions before changing direction. In addition, the direction of the windings between the change of direction is varied, from such that the magnetic sensitivity of the coil is sinusoidal in any radial direction. If the movable element can only move along the x-axis shown in Figure 30b, then only a linear coder is required. In this mode, it is possible to modify the windings by cutting them notionally along the dotted lines 3081 and 3083, and connecting the corresponding parts of the remaining windings. Figure 31 shows the resulting winding pattern if this is done. In particular, the The density of the winding 3113 varies in a sinusoidal shape with the distance along the length of the support 3105. The dotted lines generally indicated by the reference numeral 3185 represent the connections with the corresponding parts of the winding. There will also be a winding of quadrature, but for clarity, it is not shown.

The transducer of the present invention can be applied to a number of applications. The modalities have already described the use of the transducer in applications such as the control of the position of a float, of the detection of the fluid level and the detection of the fluid flow velocity. Other applications include the detection f of the position of the valve, the placement of the print head in a printer, input devices of graphic pen, cranes, a sensor of rotation of choke, sensors rotation ABS, shock absorbing sensors / travel height and store position detection tracks. Additionally, the spiral winding transducer can also be used in other encoder systems, for example, in a measuring head of yy '-i5 Hall effect. In this system, the head reads a direct current magnetic scale to indicate the position. However, if sine and quadrature tracks are used, and they also track if the absolute position is to be determined, then multiple read heads must be provided.

In this way, a lower degree of symmetry is achieved and the spiral transducer system is used at a higher cost. The lower symmetry means that the final performance is not so good. Additionally, Hall sensors also have inherent defects that are annoying to compensate in direct current systems. By using alternating current fields, these effects are effectively eliminated. When used in said application, the spiral windings can be used to generate a spatial sinusoidal field pattern by applying a current to it. The spatial pattern of the field can be controlled by configuring separate conductors that produce sinusoids with different inclinations. The spatial phase of the field pattern can be altered by making conductors have different phases and the same inclination, and altering the proportion of currents in each one. Normal sine and cosine tracks, as well as multi-phase tracks, are possible. Then the magnetic Hall effect sensor is used to measure the magnetic field ! «... 'generated by the spiral coils. Additionally, the resonant circuit mounted on the movable element can also relieve the information back to the processing circuit. For example, this information could be the temperature or the pressure of a fluid in a flow meter. This is achieved by allowing a property of the resonator to vary, depending on the measured quantity. For example, the frequency of a resonator could be changed with the temperature, by adding a resistor network that contains a thermistor to the resonant circuit. Another possibility is to change the resonant frequency with pressure using, for example, a piezoelectric cell, whose capacitance changes with the pressure as part of the resonant circuit. This property measurement system has the advantage that no electrical connections are required up to the measuring device. '-,

Claims (41)

NOVELTY OF THE INVENTION Having described the foregoing invention, it is considered as a novelty and, therefore, the content of the following is claimed as property: CLAIMS

1. An apparatus for indicating the relative position of first and second members in a measurement direction, where they are relatively movable, wherein one of the members carries an electrically resonant circuit that electromagnetically couples with an excitation circuit, and a receiver circuit carried on the other of these members, whereby, upon energizing the excitation circuit, the resonant circuit induces, by electromagnetic induction, a signal in the receiver circuit representing the relative positions of the first and second members, wherein the receiver circuit includes at least one conductor that includes a first portion extending away from a position on the member in the direction of measurement for at least one period of a repetitive pattern of convolutions, and a second return portion having similar convolutions, being the convolutions of the first and second portions substantially to 1 80 ° out of phase, to define at least two cycles of first and second types that provide electrical responses opposed to a far field, whereby, an induced response in the cycles of the first type by an alteration from the bottom is at least I partially balanced pqr the response induced in the cycles of the second type. i '!

2. The apparatus according to claim 1, characterized in that the first and second portions are formed with generally square convolutions.

3. The apparatus according to claim 1, characterized in that the first and second portions are formed with generally triangular convolutions.

The apparatus according to claim 1, characterized in that the first and second portions are formed with convolutions defining generally hexagonal cycles.

5. The apparatus according to claim 1, characterized in that the first and second portions are formed with generally sinusoidal convolutions.

The apparatus according to claim 1 of any of the preceding claims, wherein the receiver circuit includes a plurality of said conductors, which are electrically separated from each other, and are located one above the other, and wherein the convolutions that form Each conductor are spatially separated in the direction of the measurement. ,:.

The apparatus as claimed in claim 6, wherein the receiver circuit includes two electrically separated conductors, whose cycles are separated by a quarter period of the repetitive pattern.

The apparatus according to claim 6, wherein the receiver circuit includes three electrically separated conductors, whose cycles are separated by one sixth of a repetitive pattern period.

The apparatus according to claim 6, wherein the receiver circuit includes four conductors, whose cycles are separated by one eighth of a repetitive pattern period.

The apparatus according to claim 1 of any of the preceding claims, wherein the first and second portions extend away from said position by a plurality of repetitive pattern of convolutions.

11. The apparatus according to claim 10, wherein a conductive thick-placing element is provided to identify within which period of the repetitive pattern of convolutions the relative position is being measured.

12. The apparatus as claimed in claim 11, wherein the conductive element of the coarse placement is located on, but is electrically separated from the other., the plurality of electrically separated conductors.

The apparatus according to claim 11 or 12, wherein a set of electrically separated conductors having relatively short convolutions is provided, and wherein the thick-placing conductive element includes at least a second set of conductors electrically separated that have relatively long convolutions.

The apparatus according to claim 11 or 12, wherein a first set of electrically separated conductors is provided, which have convolutions of a first period, and wherein the conductive thick-placing element includes at least one second set of electrically separated conductors that have convolutions of a second period, whose value is slightly greater than, or less than, that of the first period.

15. The apparatus according to claim as claimed in claim 11 or 12, wherein the thick-placing conductive element is a digital period identifier.

16. The apparatus according to claim 1 in any of the preceding claims, wherein the receiver circuit is carried on a flat surface of a support.

The apparatus according to claim 16, wherein the resonant circuit includes a coil and a capacitor, and wherein the axis of the coil is generally perpendicular to the support.

18. The apparatus according to claim 16, when dependent on claim 10, wherein the resonant circuit includes a conductor having convolutions similar to those of the receiver circuit, and whereby, the signal induced in the receiver circuit is averaged over a number of these convolutions.

19. The apparatus according to claim as claimed in claim 16, 17 or 18, which is a linear position encoder.

20. The apparatus according to claim as claimed in claim 16 or 17, which is a rotary position encoder.

21. The apparatus according to claim as claimed in claim 16 or 17, which is a radial position encoder.

22. The apparatus according to claim 1 in any of claims 1 to 16, wherein the receiver circuit is carried on a cylindrical surface! of a support.

23. The apparatus according to claim 22, which is a linear position encoder.

24. An apparatus as claimed in any of claims 1 to 5, wherein the member carrying the electrically resonant circuit carries two different electrically resonant circuits, which are both inductively coupled to the excitation and receiver circuits, and which are separated in the direction of measurement by a quarter of a repetitive pattern period.

25. The apparatus according to claim 7, which includes a plurality of movable members, each having an electrically resonant circuit of different resonant frequency, and each inductively coupling with the excitation and receiver circuits, by means of which, when energized at the appropriate frequency by the excitation circuit, and 82 each resonant circuit induces a signal in the receiver circuit, which represents the relative positions of the corresponding movable member in relation to the member leading to the receiver circuit.

26. The apparatus according to claim 1 in any of the preceding claims, wherein v the excitation and receiver circuits are configured to operate in a pulse-echo mode.

27. The apparatus as claimed in any one of claims 1 to 24, wherein the excitation and receiver circuits are configured to operate in a continuous wave mode.

28. The apparatus according to claim 1 in any of the preceding claims, which includes a demodulator that is coupled to the phase of the signal induced in the receiver circuit by the resonant circuit.

29. An elevator having an element to indicate its position on its elevation arrow, this element being as defined in any of claims 1 to 28.

30. A liquid level sensor, which includes a float, a support on or within which the float is slidably guided, and an apparatus as claimed in any of claims 1 to 28, to indicate the relative position of the float and the support.

31. A valve or choke having a rotary arrow and a position encoder for the arrow, the position encoder being as claimed in claim 20.

32. A valve or choke according to claim 31, where the angular travel of the arrow is less than 180 °.

33. The valve or choke according to claim 31, wherein the angular travel of the arrow is not greater than 120 °.

34. A fluid flow meter including a thinned tube and a float in the tube that travels to a longitudinal position determined by the flow of fluid, and an apparatus in accordance with claim 1 of any of claims 1 to 28. , to indicate the relative position of the float and the tube.

35. A fluid flow meter according to claim 34, wherein the float can rotate, and carries a plurality of electrically resonant circuits, each including a coil and a capacitor, and wherein the axes of the coils of the plurality of resonant circuits are in mutually perpendicular planes.

36. A fluid flow meter according to claim 34, wherein the float can rotate, and wherein two substantially flat receiver circuits are provided in mutually perpendicular planes.

37. The apparatus according to claim claimed in any of claims 1 to 28, wherein the resonant circuit I includes at least two coils connected in series, spaced apart from each other along the direction of the measurement by a distance that can be varied to reduce the effect of the tilt.

38. A method for determining the relative position of first and second members, which includes the steps of: energizing the excitation circuit of an apparatus in accordance with that claimed in any of the preceding claims, by applying to this excitation circuit, of an alternating current at suitable frequencies to energize the electrically resonant circuit mounted on the other member; and detecting the output signals produced in response to the same in the receiver circuit, and deriving the relative position of the first and second members from the same.

39. A method according to claim 38, wherein the frequencies of the alternating current are in the range of 10 KHz to 1 MHz.

40. A method according to claim 38 or 39, in where the excitation circuit is energized using a burst of excitation current, and wherein the signals induced in the receiver circuit are detected after the excitation current has been removed.

41. An apparatus for indicating the relative position of first and second members in a measurement direction, where they are relatively movable, wherein one of the members carries a harmonic generator that is electromagnetically coupled to an excitation circuit, and a circuit receiver carried by the other of the members, by means of which, when energized by the excitation circuit, the harmonic generator induces, by electromagnetic induction, a signal in the receiver circuit, which represents the relative positions of the first and second members, wherein the receiver circuit includes at least one conductor that includes a first portion extending away from a position on the member in the direction of the measurement for at least one period of a repetitive pattern of convolutions, and a second portion of return that it has similar convolutions, being the convolutions of the first and second substantial portions being 180 ° out of phase, to define at least two cycles of first and second types, which provide electrical responses opposed to a far field, whereby, an induced response in the cycles of the first type by an alteration from the bottom, it balances at least partially by the response induced in the cycles of the second type.