Measurement principles used in sensors

Measurement principles used in sensors

The car runs a plurality of sensors. As the sensor body of a vehicle, they convert input signals to the different electrical signals. Control devices of various systems (engine, safety and comfort) use these signals to perform the functions of control and regulation. Depending on the task, various measuring principles.

Position Sensors

Characteristics

Sensors determine the position of the one-dimensional or multi-dimensional position of the movement and the angular positions (linear and rotary values) of various types and in various ranges. These include distance, distance, displacement (Eng .: displacement), filling level and even minimal stretching, ie. all quantities that can be measured in meters and degrees.

In this area, there has long been the desire to switch to the use of proximity sensors that are not subject to wear and therefore a more durable and reliable. However, the question of costs is still forced to use the old principles of the sensor, since the majority of measurements they cope well with their tasks.

The values ​​of the provisions are «extensive measurement values», where the measurement of the measured values ​​or measurement range is largely determined by the value of the sensor (for comparison: «intense measured values» — such as, for example, pressure and temperature). Therefore, sensors for extensive quantities of medium and large scale (e.g., flow sensors and force) is less suited to miniaturization and hence economical mass production. Since this rule applies to a lesser extent on the rotation sensors (angle) than the speed sensors (movement) (the angle is not dependent on the radius or length of the knee), the first increasingly used in the car.

In the case of extensive quantities in a wide range of measurements often initially still converted into intense quantities which can be measured using microsensors. Thus, when measuring the flow moves to the density measurement of the flow (stream) (measurement of the partial flux density, for example 1: 100), wherein the conduit becomes significant flow sensor component without which the sensor can not be tested and calibrated.

The speed sensor and the distance a large measuring range (approx. 0.1 … 50 m), the measurement value is converted by the sensors of wave propagation (sound and electromagnetic waves) in delay or phase of the pulse, which can be readily measured electronically using a relatively small emitting / receiving devices. In the case of sound waves an essential component of the measuring device is a signal propagation medium (e.g., air), and the required time reference (e.g., pezoeletrichesky resonator).

Overview of the measured values

There are many applications in which the position is true of the measuring values. In other cases, the measured position of the path / angle is different measured values.

In practice, often «incremental sensor system» is designated as angle sensors, as they are primarily used to measure the number of revolutions. These angle sensors are not in the true sense. However, for the measurement of the angle of rotation increment (the amount by which the value is increased), as measured by the sensors shall be designed with a plus sign, ie, summed. These systems measure the angles used in limited quantities, as the counter can continually faked due to the impulse noise. Hard-defined (set) reference signals in the forced position can help only partially. In such systems, the measurement of the angle absolute position when disconnecting the operating voltage is lost. There also does not help nonvolatile storage of the final state, since the majority of the angular positions can be changed mechanically in the OFF state (e.g., steering wheel angle).

Although the angle of the crankshaft is measured incrementally, this measurement anew after each rotation is adjusted in the reference signal detected by the sensor, if the expected appearance of interference (problem). There also has to reckon with the fact that the engine is started is not known what position is the crankshaft; he should do with the starter only one full turn, to generate at least one reference signal. The movement of the crankshaft is very monotonous, ie it is almost always quite monotonous (without discontinuities) in only one direction (almost always forward never backwards). Therefore, it is safe to say that almost any revolution will correct result.

At instantaneous start the engine without a starter can not prevent the occurrence of defects incremented angle measurement — as well as the steering angle of the steering wheel. This requires absolute angle sensor for a range of 360 °.

Potentiometers

Cat track potentiometer — often the constructed as a corner sensor — using correspondence between the length of the wire, or a film resistor (from «Cermet» or «Conductive Plastic») for its electrical resistance parameter for measurement purposes.

Currently most budget option is the sensor speed / angle of rotation. Through delineation (to shape) measured the width of the track (also possible to perform parts) can affect the shape of the graphics performance. Connection of the sliding contact is often carried out by a second contact with a track surface, by which, however, laid conductor material with a low electrical resistance. To protect against overload in most cases the supply voltage to the measuring path through the lower pre-resistance RV (for zero and slope correction).

Depreciation and distortion measurement characteristics can be reduced by removing the minimum loaded (IA lt; 1 mA) and the conclusion in dust- and waterproof capsule. The condition is also less wear of the sliding contact and the selection of paths, providing optimum friction; wherein the sliding contacts may take the form of «spoon» and «wiper» be single or a composite, and even take the form of «broom».

However, a number of significant advantages, opposed a large number of serious shortcomings.

Benefits potentiometers

► Low cost;

► simple visual design;

► large measuring effectiveness (measuring voltage = run);

► not necessary electronics;

► good standoff voltage noise;

► wide operating temperature range (lt; 250 ° C);

► high accuracy (better than 1% of the final parameters of the measuring range);

► measurement range (perhaps almost 360 °);

► hassle entering doubles;

► Adjustable (laser ablation and so on.);

► flexible characteristic curve (variable track width);

► flexible mounting (flat or curved surface);

► large number of producers;

► fast sampling.

Disadvantages potentiometers

► Mechanical wear due to attrition;

► measurement errors due to traces of abrasion;

► problems when working in liquids;

► contact resistance, which varies from a sliding contact to the measuring path;

► disconnect sliding contact under hard acceleration or vibration;

► complex tests;

► limited capacity performance in a miniature form;

► interference (noise).

Application

Examples of potentiometers:

► sensor gas pedal or the gas pedal module to determine the desired moment of rotation for motor control;

► level sensor fuel tank;

► potentiometer threshold hydrodynamic coupling (KE and L-Jetronic) to determine the volume of air that is sucked in the engine;

► angle sensor throttle to determine its position in gasoline engines.

Magnetic inductive sensors

Of all the sensors that perform contactless position measurement, magnetic sensors are most sensitive to interference and strong. This applies primarily to sensors working on the basis of the alternating current, i.e. magnetic induction. Necessary for this way of arranging the coils need to be available more space in comparison with micromechanical sensors, i.e. the ability to install redundant sensors (performing measurements in parallel) is absent. Furthermore, the necessary contact with the coil is a factor that negatively affects the cost and reliability.

Of the large number of known devices of this type in a vehicle basically uses two of them, which have a very similar principle. Currently, however, they do not apply to macromechanical performance in the production of automotive sensors in the new developments of the company «Bosch».

Sensors eddy current If conductive, flat or curved membrane (plate) (e.g., aluminum or copper) is close to the coil, energized at high frequency eddy current (usually containing no iron), it affects both its resistance, and its inductance. The reason for this becomes eddy currents in the damper plate (spoiler) for increasing the magnetic interaction. The position of the damper plate reflects the segment of measurement s.

In general, high operating frequency (range MHz, low-frequency power is absorbed too much electric current due to low inductance) requires the direct subordination of the sensor electronics or shielded connection — often even portable. For measuring effect conversion into an electrical output voltage can be used as a damping effect (effective resistance) and the effect of the substitution field (inductance). In the first case suitable, for example, the oscillator variable amplitude oscillation, otherwise, variable-frequency oscillator or an inductive voltage divider, receives power by a constant frequency (a different location).

Eddy current principle allows different ways to adapt to the task of performing measurements. It is well suited for the determination of large segments or angles (already existed almost series development, for example, the throttle pedal and gas), and very small quantities (eg torque sensors). Since the principle of the eddy current sensor can be produced as a micromechanical, in terms of their advantages can not exclude their use in the future. Extensive use is the principle of the sensor in the measurement technology used in production and quality control as for accurate determination of small segments / distances, and for the layer thickness in the range of microns.

Ring sensors with short-circuited winding

In contrast to the sensor coil of the eddy current sensor with a short ring coil is always magnetically, tinned core straight or bent U-shaped or E-shaped. The movable spoiler is designed as a short-ring of a material which is a good conductor, such as copper or aluminum, which is movably located on one or all of the core trunnions. Due to the iron core such sensors have a higher inductance than the eddy current sensors and higher efficiency of the measurement of the very concentrated magnetic flux conduction type iron core. Thus, they can operate at low frequencies, and does not necessarily require electronic signal at the location on the sensor. The iron core protects the measuring space between the core pins from external interference fields.

The alternating field, which creates a current in the coil iron core and around it, you can not get through a short-ring, since the eddy currents are compensated in a short-circuit ring to almost zero. Eddy currents in the shorted ring act in this way — as «the magnetic insulator» — the spread of the magnetic flux F space between the coil and the cage ring (hence the English: shading ring) and make it dependent on the position’s short-ring, F = F (x).

Inductance is defined as: (1) L = F / I

Therefore, short-positions of the ring has a direct impact on the inductance L of the coil winding. The relationship L = L (x) in a wide range yavyatsya positive linear. The measurement can use almost the entire length of the sensor. It does not require a mechanical guide shorted narrow rings.

Mass short-ring, which should be moved, is very small. Create shape (shaping) the distance between pins affects the shape of characteristic curve: narrowing the distance from the spigot until the end of the measuring range of a given good linearity improves. Depending on the material and the design operation is carried out most often in the range 5 … 50 kHz. The sensor is used in the most demanding conditions, such as in diesel fuel pumps.

Due to the mode of operation in an alternating current cores plated (for example, NiFe-tinning, 0.2 mm thick). To obtain the required mechanical stability, which holds the plates to the acceleration in a stable state, they are not only glued conventional manner but additionally «punctured.» For this purpose, on the label in certain places made bulges with which they are connected to a soft annealing inside (like Lego), without destroying the electrical insulation between the shields.

Poludifferentsialny ring sensor short-circuited winding with a movable measuring and reference rigid cage ring is very accurate; it performs the analysis as an inductive voltage divider (data analysis inductance L1 / L2, or the (L1-L2) / (L1 + L2), or as a member of the oscillator circuit determining the frequency, in order to create the frequency-analogue signal (perfectly protected from interference, easily digitized).

Figure 9 shows the construction of the ring poludifferentsialnogo sensor short-circuited winding (KDKO) for diesel distribution pump. Each core pin mounted one measuring coil and a reference coil. If the coil passes an electric alternating current coming from the control unit, formed variable fields. Reference shorted ring remains stationary, while the measurement of short-closed ring fixed to the shaft of a damper (ignition timing (f). By moving the measuring short-circuited rings changes the magnetic flux, and with it, and the voltage across the coil, as the control unit maintains a constant current (podvodimy current). The switch processing signals, forms the ratio of the output voltage UA at the measuring inductance L1 to the reference voltage URef on the reference inductance L2. It is proportional to the deviation of the measurement of short-closed ring, and can be analyzed by control unit.

Sensors rotating variable fields using the coil, powered by an alternating current of angular frequency with coils or similar devices (such as winding conductive structures) can be placed two- and multipole structure of the AC as a contour and linear. These pole structures with a constant phase wiring can be moved relative to a set of receiver coils, often stationary, having the same phase wiring, due to the motion of the measured system — whether it is a rotary or translational system. Wherein during movement of the amplitude of input signals vary sinusoidally. If the receiver coils are moved to a certain part of the wiring relative to each other (e.g., T / 4 and T / 3), the sine wave shifted in phase by an appropriate angle (e.g., 90 ° or 120 °). This creates a voltage, for example:

(1) u ^ U-sincp-sinat

(2) u2 = Usin (p — 90 °) = -sinat

= Ucosp-sinat or also:

(3) U = u1-sinp

(4) Uj = Usui (p-120 °) -sinat

(5) Uj = Usui (p-240 °) -sinat

After rectification on the basis of these stresses can be very accurately calculate the angle of rotation as well. That’s how the sensors described in the classical measurement technology as sensors using synchronization methods, and in-resolver duktosina and are predominantly angle measuring sensors.

In a simple arrangement of bipolar mechanical angle of rotation and also corresponds directly to the electric phase angle. When using n pairs of combined mechanical full angle cp = 2 is converted into a phase shift and n- = 2n, so that the phase shift a corresponds to the angle of rotation only p / n, which significantly increases the resolution of the measuring system. If the measuring range is more unambiguous measurement signal provided by other means, for example, a simple protractor.

The sensor of the company «Hella» Angle sensor, developed by «Hella», does not apply to any of these technologies, but more like a inductosyn gauge. Figure 10 illustrates a sensor, such as a 6-pole structure valued (n = 6), which from an electrical point of view, transforms the rotation angle Q = 60 ° in the phase shift and the amplitude of the light signaling device = 360 °. All necessary wiring structure applied to the laminate conductive-radiating plate in the stationary stator. The rotary part can also be made in the form of stamped parts, or cantilever mounted on a plastic carrier (hot-stamping).

On the stator is a round spiral conductive paths, which induces eddy current in dependence on the angle of rotation in the meandering spiral turn in on themselves, having the same outer diameter and an operating frequency of 20 MHz. Such an eddy current is, of course, generates, as well as spiral excitation secondary magnetic field which is superimposed on the excitation field in a way that attempts to extinguish was only one equal circular current-conducting path, comparable to the coil of the stator, it would just completely extinguished the primary field. However, due to meandering structure resulting multipole field arises, which allows rotation together with the rotor, and all of its magnetic flux is nearly zero.

This multipole alternating field is read concentric receiver coils or meanders, located on the stator. They are moved during the pole pitch (e.g., 60 °) to, respectively, 1/3, i.e. electrically their signal amplitude at 120 ° per step.

Receiving coils are distributed through all the n pole pairs (series connection) and use the sum of all polar fields.

Referring to Figure 10c receiving coils are connected in a star. These electrical signals to determine the phase angle or a mechanical rotation angle f summed ASIC, which provides the necessary (right) extension, selection and formation ratio. Version ASIC 1 receives the necessary digital control signals from the microcontroller located in close proximity. Another version of the ASIC 2 has the ability to be completely independent (stand-alone) to use the sensor. ASICS enables to perform during the final adjustment of manufacturing mechanical and electrical tolerances. For use at elevated requirements for security measures it is possible to create a redundant system with two galvanically separated signal chains and two ASIC. The operating principle of the sensor may be described in the «cut» as the principle of the speed sensor. Along with minor production costs the main advantages of this sensor are: touch and does not cause deterioration of the principle of the measurement;

► complete independence from temperature (150 ° C);

► High accuracy (within a measuring range from 360 ° to ± 0,09 °);

► flexibility (consistent with all the angular range of up to 360 °);

► possibility of creating duplicate structures;

► High EMC security;

► exclusive use of standard materials without the need for ferromagnetic parts;

► flat design.

For these reasons, the sensor can be used in a vehicle in a large number of locations.

Magnetostatic sensors

Magnetostatic sensors measure the magnetic field of direct current. In contrast to the magnetic induction (coil) probes are better suited for miniaturization and cost-effectively produced by means of microsystems technology. Since the direct current field can easily penetrate through the walls of a plastic instead of a ferromagnetic metal, the advantage of magnetostatic sensors consists in the fact that the stationary part can be well protected from the rotating conductor via capsule — usually a permanent magnet or a soft magnetic wire — as well as from the weather medium. Primarily used galvanomagnetic effects (Hall effect and Gaussian) and magneto-resistive effect (AMR and GMR).

Galvanomagnetic effects Hall effect is determined primarily by using the wafer. If through such a plate on which a current flows vertically to miss the magnetic induction B, the charge carriers are deflected from a straight path by the Lorentz force vertically relative to the field and to the current I through the angle f. Thus, perpendicular to the direction of the current between the two extreme opposite points of the plate is proportional to the voltage UH will shoot a voltage proportional to the field B and the current I (Hall effect):

(2) Uh = Rh IB / d mit RH = Hall coefficient, d = thickness of the plate

At the same time the longitudinal resistance of the plate increases regardless of the direction of the field in a parabola (the effect of Gaussian magnetoresistor).

Factor RH, which is crucial for measuring the sensitivity of the plate, using the silicon is relatively small. Since the plate thickness d can be reduced by using diffusion technology, Hall voltage again reaches the technically usable. Using silicon as the main material, while the plate can be integrated switch for signal preparation, whereby the manufacture of such sensors can be very advantageous.

With respect to measuring sensitivity and temperature silicon is not the most suitable material for manufacturing the semiconductor Hall sensor. The best characteristics are, for example, semiconductors III-V, such as gallium arsenide or indium antimonide.

Hall switch In the simplest case, the Hall voltage is supplied to the threshold electronics integrated in the sensor (Schmitt Trigger), which produces a digital output signal. If the magnetic induction B, the current sensor is below a certain lower threshold parameter, then the output value corresponds, for example, logical «O» («release» state); if it is above a certain upper threshold setting, then the output signal corresponds to the logical «1» («operate» state). Since this process is guaranteed for the entire operating temperature range, and for all instances of the same type, both thresholds are relatively far from each other (approx. 50 AB). Therefore, to turn on the switch requires considerable Hall induction stroke AB.

Such sensors, still produced by bipolar technology, used, for example, fences Hall (Fig. 12), which have been integrated into the body of the distributor of ignition, driving the camshaft. This barrage of Hall sensor in addition to a more permanent magnets and magnet wires tomyagkie. The magnetic circuit has a U-shaped or forked shape, so that through the open end of the contactor can be used myagkomagnitnogo material that shields or alternately unlocks magnets, so the Hall sensor switches between states operate and release. The next way of application — the digital sensor, steering angle LWS1.

Hall sensors of this type quite inexpensive, but are only good for switching mode and too inaccurate to analyze analog values.

Hall sensors, operating on the principle of «Spinning Current)

The disadvantage of a simple silicon Hall sensor is simultaneously sensitive to mechanical stress (piezoelectric effect), which are inevitable during assembly and lead to undesirable temperature displacement characteristics. Using the principle of «Spinning Current», in conjunction with the transition to CMOS technology, this drawback was overcome. While the piezoelectric effect and there, it is compensated by the averaging time of the signal, as occurs when a fast, controlled electronically changing electrodes (rotation) with different characters. If there is a need for labor saving for manufacturing sophisticated electronics to switch the electrodes, it is possible to integrate several Hall sensors (two, four or eight) with respectively different current directions by positioning them close to each other, and their signals are summed up in the context of the message. The principle of Hall-ICs is very well suited for use in analog sensors. Temperature effect, is partially a negative effect on the measuring sensitivity is not reduced by this. Such integrated Hall-ICs are suitable mainly for measuring small intervals, during which they read through the data field strength approximating permanent magnet (eg, the force sensor iBolt, he reads the weight of the front passenger seat for optimum airbag deployment). Similar good results were still obtained only by use of the individual Hall elements, for example, combinations of III-V compounds with sequentially switched hybrid amplifier (for example, Hall acceleration sensors).

Differential Hall Effect In a double Hall sensor (differential Hall sensor) at a certain distance on the chip are two complete systems Hall. Electronics defines the difference of both the Hall voltage. These sensors have the advantage, which is that their output does not depend on the absolute value of the magnetic field strength, and they only determine the spatial variation of the magnetic induction as a differential sensor, i.e. field gradients (which is why they are often referred to as gradient probes).

Such sensors are usually used to measure the number of revolutions since the polarity of the output signal depends on the air gap between the rotor and the sensor. If the scanning gear is only one simple Hall sensor, it does not recognize, to see if the magnetic flux due to the continuation of the rotation of the gear, or by changing the distance (for example, vibration, mounting tolerances). This leads to serious errors scan, since the signal must be fed to the detector threshold. In differential sensor principle of operation of the other. They evaluate only the difference of the two signals are located at the right distance from each other Hall sensors. If the difference signal, for example, the positive, the distance between the gear and the sensor can be changed at will; the difference will be positive, even if it is in the amount will be less. The sign can be changed only in the case of continued rotation of the rotor. Serial connection detection threshold also has no problem with the definition of change of distance and spin.

To achieve maximum output choose the distance between the two, often installed along the edges (lengthwise), Hall sensor chip, is about half the incremental distance (the distance between the teeth). This maximum signal is very wide, ie He covers a wide range of vibration incremental distance. Large deviations from the incremental distance change requires a more complex construction of the sensor.

As the gradient of the probe sensor can not be installed in any position, it should be installed as closely as possible in the direction of rotation of the incremental rotor.

Corner Hall sensors in the range to 180 ° C using a rotating magnetic ring («Movable Magnet»), as well as several stationary soft magnetic conductors can get direct linear output signal for a larger range of angles. In this two-phase field, the magnetic ring is held by a Hall sensor located between the U-shaped conductors with direct conductivity. The effective magnetic flux passing through the Hall effect sensor depends on the angle of rotation p.

This principle applies to gas pedal sensor.

Derivative forms the basic principle of «moving magnet» is an angle sensor of the Hall type ARS1 with a measuring range of 90 °. The magnetic flux is constantly magnetized disk semicircular shape is given to a magnet through a pole piece, two conductors with direct conductivity and ferromagnetic axis. Thus, depending on the position of the angle of the flow is carried out to a greater or lesser degree through the two straight conductor conducting a magnetic path which is also a Hall sensor.

Thus, the magnetic band can achieve linear characteristics. In a simplified arrangement in the model type ARS2 no magnesium-tomyagkie conductors. Here, the magnet moves along a circular arc around the Hall sensor. Formed with a sinusoidal characteristic curve move only a relatively short stretch has good linearity. If the Hall sensor is located slightly outside the middle of the circle characteristic deviates significantly from the sine wave.

It shows only a short span of 90 ° and a long section with good linearity little over 180 °. The disadvantage is the low shielding against extraneous fields, remains dependent on the geometrical tolerances of the magnetic circuit, and fluctuations in the intensity of the magnetic flux in the permanent magnet depending on the temperature and aging.

Angle sensors in the range of 360 ° to analog angular sensor with a measuring range of 360 ° means that the permanent magnet is rotated, as illustrated, positioned on orthogonal two Hall sensors. In order not too dependent on the tolerance of the position of the magnet, the magnet must be large enough. In this case both the Hall sensor must be located as close to each other in terms of the same direction of the constant magnetic stray field that displays the position angle P of the permanent magnet. They are oriented at right angles relative to each other and parallel to the axis of rotation of the permanent magnet, thus gauge readings x- and y components of the field vector B, rotating over them:

(3) UH1 = Ux = B-siiKp

(4) UH2 = Ujy = B-cosp

On the basis of these two signals can calculate the trigonometric angle is the ratio f = arctg (UH1 / UH2) chip for processing data, which can be purchased commercially and through which the signal is digitized.

This arrangement of the Hall sensor allows integration with vertical Hall device (Vertical Hall Devices) in such a form as shown in the figure, so that the area of ​​the sensor chip is vertical to the axis of rotation, and the sensor, in contrast to conventional, planar Hall sensor with a sensitivity in the plane of rotation (Fig. 19). Monolithic integration ensures high accuracy necessary at right angles, as well as the desired compact design of both systems Hall. The company «Sentron» («Melexis»), Switzerland is working to create such sensors in the future will introduce them to the market.

Angle sensors of the type considered, for example, for the realization of launch systems momentary start, in which the absolute position of the rotation of the camshaft to be measured in the range of 360 °.

In principle, there is another method by which the conventional planar Hall sensor (optional) can be given sensitivity in the plane of rotation. With the method used by Melexis-Sentron (e.g., type 2SA-10) for measuring the components of the field appearing in the plane of rotation of the Bx and By on the same chip with four Hall sensors offset from each other by 90 °, are arranged on the narrow circumference. Thus each sensor is comprised of the above reasons, a pair of Hall elements rotated by 90 °. After completion of the fabrication of the chip on the surface mounted circular disc of magnetic material with a diameter of approx. 200 m, as shown in Figure 20 so that the Hall sensors clearly fall under the edge of the disc.

On the basis of their high relative magnetic insights that drive acts as a flux concentrator (IMC, a built-in magnetic concentrator) and forces all lines of the field vertically to enter into its surface. Due to this, the field lines extending horizontally without flux concentrator (in the plane of rotation) at the location of the Hall sensors, forcedly guided in the vertical direction (out of the plane of rotation) and hence may modulate the Hall elements. Since the elements located diagonally to each other, they «see» the opposite direction of the field, then for reading out one field component is determined by the difference of both opposite identical Hall voltage. At the same time due to this susche-stvuyugtsie vertical component Bz mutually eliminate its effect.

Due to the combined signals further analysis elements located diagonally to each other, it is possible to determine the parameters of the vertical field components Bz; since they ferromagnetic disc has no effect and the elements, because of their location are not losing their sensitivity is normal plane of rotation. Thus, due to this arrangement, the induction vector B acting at the location of the sensor is read in all three components. Electronic switching means necessary to analyze the sig-nel, including a digital signal processor, which is used for calculating the arc tangent function, based on the basis of the microcontroller (DSP), and the funds needed for the final adjustment of the sensor (EEPROM), can be integrated with the sensor on the the same chip inexpensively.

To measure angles up to 360 ° is sufficient to over the sensor chip with integrated signal analyzer rotates the permanent magnet, preferably a circular shape, magnetized parallel to the chip. Since the rotation angle formed by the arc tangent function of the ratio of the two resulting sinusoidal and kosinusoi Far sensor signals, the intensity of the magnetic field and, therefore, and the aging of the magnet, its temperature dependence and the distance to the surface of the sensor play no role. The sensor determines only the position of rotation of its excitement.

Maximum own sensor error specified by the manufacturer in the range of 360 ° at a rate of + 2 °. It can be reduced by calibrating the sensor by the user. In this case, the accuracy of the digital output is 10 bits at a resolution of 12 bits. On the basis of the time signal processing processor shortest sampling frequency to 20MHz clock frequency is 200 microseconds. Output signal modulated pulse frequency, can be used at up to 1 kHz. To initialize the sensor takes 15 ms. Standard setting power of the electromagnetic field is approx. 40 mT. At a density above 0.7 T flux concentrator plate goes into saturation.

The sensor may advantageously be programmed for any of the measuring range lt; 360 °, this creates additional operational reliability by controlling overrange (using, for example, as an angle sensor to the accelerator pedal operation FPM2.3).

Angles 360 ° can also be determined using the most simple devices 1C Hall (Hall switches), which are also used to measure the speed (the use of sensors in the steering wheel angle type LWS1). For this Hall sensors unilinearly and n are arranged uniformly on the circumference for reading n bits. Magnetically coded disk blocks separate field above it permanent magnets or unlock it so that the Hall sensors in the event of continued rotation of the disk sequentially issued various code word (serial code). In order to avoid serious mistakes in the testimony in the moments of transition purposefully used the Gray code. Gray code is designed so that the code words for the two neighboring positions — in contrast to the binary — only differ by 1 bit to the possible erroneous figure in the transition from one position to the next step does not exceed the angle.

To create the steering angle sensor code wheel drive, for example, is connected to the steering shaft, and the remaining portion of the sensor with the chassis. The complexity of this sensor is that the magnetically coded disk must be mounted on bearings in a floating state, which leads to implement complex and voluminous mounting by means of flexible plastic cuff. Code disk for reasons of tolerance of the air gap between the upper and lower wheels must pass very tightly. Appropriate optoe-lektronnoe solution using photocells is not entirely satisfactory, since due to the sensitivity of the sensor elements to the contamination is not possible to provide them with quality protection.

Multiple number of revolutions can be read using the optional simple 3-bit device code disk which moves over the step-down gear. The resolution of such devices is often not above 2,5 °.

Magnitorezistornye sensors

Along with the transverse direction of the Hall effect semiconductor plates longitudinal effect is observed and resistance, also called Gauss effect. Items that use this effect, known as «magnetoresistors» (trade name of the company «Siemens») and are made of III-V-semiconductor crystal indium antimonide (InSb). Unlike Hall sensors for optimal plate magnitore-sistors should be rather short and inflexible, ie First create a very low electrical resistance. To accomplish technically useful indicators in zone k, a large number of such plates should be connected in series with each other. The elegance of the design can be achieved by setting the microscopic needles nickel-antimony high conductivity in the semiconductor chip, arranging them transversely to the direction of current, and due to the additional bending resistance to the semiconductor.

The dependence of the resistance of the magnetic induction to induction target of 0.3 T square, and in excess of these indicators — increases linearly. Control range upwardly unlimited, the temporal behavior of the technical conditions of use, as well as in the Hall-sensors should be regarded as almost inertialess.

Since the parameter of resistance magnetoresistors shows strong temperature variations (approx. 50% reduction after 100 K), for the most part, they only come as a double layout in the voltage divider circuit (differential magnetoresistors). In this case both the resistance divider must be modulated magnetically counter (reverse sequence). Switching resistance divider ensures, despite very high temperature coefficient of resistance of individual really good stability symmetry point (operating point), in which both resistors have the same value divider.

To achieve good sensitivity measuring device magnetoresistors forcibly operated in the magnetic operating point of 0.1 … 0.3 T. The required magnetic bias voltage provides a small permanent magnet whose action can be enhanced by using a small plate for closing the magnetic flux.

Magnetoresistors advantage is their high level of the signal even without amplification zone is in volts and thus protects electronics and reduces the number of security measures. In addition, both passive resistive components are very sensitive to electromagnetic interference, and because of the high field prestressing-tion-almost resistant to extraneous magnetic fields. Because of strong temperature changes magnetoresistor is almost always used in the increment-governmental protractor and speed sensor or dual sensor limit (with switching characteristics).

The anisotropic magnetoresistive sensor (AMR)

Thin, thickness of 30 … 50 nm NiFe-coverings reflect electromagnetic anisotropic process. This means their electrical resistance changes under the influence of a magnetic field. Therefore, the structure of this type of resistance is called anisotropic magneto-resistive elements or sensors (abbreviated ADR). Metal alloy used is also known as Permalloy.

Technology and models on the elongated resistive strip shown in Fig. 25a, is created a small spontaneous magnetization (excitation) MS in the longitudinal direction of the conductive path without external control field (shape anisotropy). In order to ask him to-one single direction, it may be theoretically and opposite AMR sensors, as displayed, are often provided with weak input current magnet. In this state, the longitudinal resistance has its maximum refractive If the magnetization vector R under the influence of additional external field Hy and rotates, the longitudinal resistance is gradually reduced until it reaches its minimum value R ±, at 0 = 0. The resistance depends on the angle 0, which is created by magnetization MS and a current I, depending on its dynamics, and reflects the cosine (5) R = R0 (1 + p-cos20) mit R || = R0 (1 + b) ; R ± = R0

The coefficient in the highest possible fluctuation resistance. It is approx. 3% If the external field is much larger than the spontaneous magnetization (which has always been the case with the control permanent magnets), the direction of the external field and almost always determines the current angle of 0. The sum of the voltage of the field has no value, ie The sensor operates, so to speak, «saturation».

Shorted strip having a high conductivity (e.g., gold) over the layer AMP force without an external field current to flow at an angle of 45 ° relative to the spontaneous magnetization direction (longitudinal direction). With this «trick» — referred to as «sensor with diagonal stripes on the status indicator» — characteristic curve is shifted relative to the sensor characteristic curve simple resistance at 45 °. For outdoor field strength Hy = 0, it is at the point of maximum sensitivity of the measurement (the turning point).

Laying two opposing bands of resistance provides a change of its resistance to the contrary under the influence of the same field. This means that if one increases, the other decreases simultaneously.

As the thin layer sensors, they have another advantage in that, for example, they can be adjusted to a predetermined parameter by means of laser balancing (e.g., reset). The support material used oxidized silicon disk, which in principle can be integrated electronics for signal preparation. Currently, in order to save still prefer to separately produce chip electronics and sensor and install them, for example, on a common frame. Control The magnetic field is created mostly due to a magnet that moves over the sensor translational or rotational.

Along with simple bipolar elements USAID also exist psevdodatchiki Hall almost square thin-film structures NiFe, which, like conventional Hall sensors have four connections. Two for the gang and two transverse pickup (pseudo-) Hall voltage. Unlike conventional Hall psevdodatchik Hall sensors is sensitive to magnetic fields in the plane of the layer, but not vertically thereto. It displays the characteristic curves are not proportionate, and very precise sine wave, which in any case does not depend on the strength of the control field and temperature. For a field parallel to the conductive path, the output voltage disappears, only to turn up at an angle f = 90 ° describe the halftime sinus. Thus obtained a sinusoidal voltage is obtained with the amplitude (6) UH = in-8pt2f

If the external control box once turned on f = 360 °, the output voltage is also repeats two full sine period. John amplitude strongly depends on the temperature and the size of the air gap between the sensor and the control magnet; it decreases with increasing temperature and increasing air gap.

The measuring sensitivity of pseudo-Hall can be increased considerably (not too distorted sinusoidal), if initially holohedrally elements to make hollow to them was only a frame. Due to this modification, the pseudo-Hall sensor including in its geometric shape is transformed into a full-bridge of four AMP-resistance. Even additional bending resistance of the bridge is not too distorted sinusoidal waveform, if only a certain width of the track meander not less than the specified.

Simple protractor USAID for the range lt; Magnetoresistive goniometers 30 ° in the version with limited accuracy and measurement range (max. ± 15 °) using magnetoresistive mismatch voltage divider (differential sensor) consisting of longitudinal (theoretically even meander) resistivity of permalloy with high transverse gold stripes. In these sensors, the zero point is not dependent on the distance from the magnet to the sensor and has no effect on the growth characteristics of the graphics, which still depends on the temperature (TC almost -310-3 / K).

This sensor is considered as a cost-effective alternative for measuring the position of the pedal.

Simple speed sensor AMP to the millimeter range Similarly with separate differential oblique stripes on the status display, you can create the simplest velocity sensors with a measurement range is usually equal to several millimeters. To achieve good accuracy requires only a constant distance (air gap) between the sensor and the moving magnet that embodies measured to s. Changes in temperature, increasing the graphics display characteristics can be easily and well compensated with an additional thin-film metal sensor on the same substrate, which has almost the same TC, but opposite sign (e.g., Pt, Ti, Ni).

Precision multidetector (POMUX) for segments gt; 10 mm There is a «smart» multidetector with diagonal stripes on the status indicator to measure the length of the path, known under the brand name POMUX (multiplex position). It uses the fact that the point of symmetry and zero point characteristic curve is completely independent from the air gap and temperature. Its use in a car is often considered (for example, measuring stroke length), because it has excellent characteristics, namely, the extreme accuracy. He had already depicted in the form of a circle as a protractor to determine the low-frequency tuned gravitational fluctuations, with which you can determine the position of the vehicle (tilt sensor).

Protractor to 180 °

Magnetoresistive protractors version psevdodatchikov Hall using high-precision sinusoidal signal that is read at the output terminals of the four-phase, holohedrally structure of the sensor. Thus two full periods of the electric output signal corresponds to the mechanical rotation of the magnet 360 °. With the second element, at an angle of 45 °, it is further generated cosine-scanning signals. From the ratio of two signal voltages can be determined angle measurements (for example, using the arctangent function) with high accuracy in the range of 180 °, regardless of variations in temperature and fluctuations of the magnetic field intensity (distance, aging) (e.g., using a microcontroller or ASIC).

A further condition for obtaining a high accuracy of the sensor is that in both axles field must have at least the same direction (from a certain value of force (power), the amount does not matter), which can be ensured only if the two bridges are located one above the other. It was possible to find a solution in which both axles are offset by 45 °, so intertwined with each other, they can be regarded as one point and, in principle, arranged one above the other.

Protractor 360 °

The great disadvantage of goniometers AMP is their natural limit is uniquely defined by the angle measuring range 0 ° … 180 °. This limitation can be overcome by modulating the magnetic field with an alternating magnetic auxiliary field (Fig. 31). Then, in contrast to sensor signals with a periodicity of 180 ° COS and SIN, the inclinometers are modulation signals at intervals of 360 °.

Thus recognition ranges can achieve only by determining the sign of the modulation signals, and at the same time, doubling the range of unambiguity at 0 ° … 360 °. Due to the fact that the auxiliary field to the sensor is directed both axles in opposite directions, the two modulation signals are shifted in phase. For recognition of the range need only determine the sign of a stronger by the sum of the modulation signal. With this recognition becomes uncritical range and perhaps even with strong modulation signals.

The magnetic field is generated due to the support of the planar coil integrated into the sensor chip USAID. In accordance with the wiring accessory box with full bridge COS and SIN shows directions differ by 45 °.

The sensor may be installed only at the end of the rotating shaft, i.e., for example, at the end of the steering shaft to measure steering angle in systems that dispense with the determination of multiple revolutions of the steering wheel (for example, a sensor steering angle LWS4).

Goniometer in the range above 360 ​​° (multiple turns) turns Multiple rotating parts such as the steering shaft can be measured using a double arrangement «psevdouglomera Hall effect» (180 °). Both respective permanent magnet rotated by multiplitsiruemoy transmission. Since the two low earning their toothed wheel on which are arranged permanent magnets differ in the number of teeth on one (the number of teeth m and m + 1), their opposing phases (the difference between the rotation angle: 4 — O) is a unique value for the absolute position of the angle cp steering shaft. The system is designed so that this phase difference when the total number of turns of the steering shaft, is equal to four, less than 360 °, and thus ensuring the uniqueness of the measurements. Each individual sensor, moreover, gives ambiguous current resolution rotation angle. Due to this arrangement, the resolution can be obtained, for example, for the entire steering wheel angle, more precisely 1 ° (the use of this principle in a sensor steering angle

LWS3).

Superhigh magnetoresistive sensors (sensors extra large magnetic resistance) (SMR) SMR measurement technology was developed a few years ago and is now beginning to be applied in determining the angle and speed in the automotive industry. Significant advantages of the technology compared to CMP sensor technology AMR (anisotropic magnetoresistive) consist of natural-one 360 ​​° in determining the angle and the high sensitivity of the magnet when determining the number of revolutions.

Unlike the anisotropic magnetoresistive sensor, RMC composed of not only a functional magnetic layer, and the most part of complex systems layers. Basically distinguish two systems: the first — multilayers SMR is usually from 20 sequences of alternating soft magnetic and non-magnetic layers of the individual. Second — spin valves construction, consisting of antiferromagnetic, ferromagnetic and non-magnetic functional layers. The thickness of the individual layers in both systems is 1 … 5 nm, It covers only a few atomic layers.

The electrical resistance of a set of layers of CMP depends on the angle between the magnetizations of neighboring ferromagnetic individual layers. It is the maximum when antiparalellnom location and the minimum — in parallel.

SMR multilayers

The relative change in resistance (the effect CMP) is in multilayers SMR 20 … 30%, respectively, by a factor of 10 greater than the effect of AMR (anisotropic magnetoresistive sensor). To place the working point in the sensitive range of graphical features to the multilayer stack CMP tverdomagnitny add one layer that provides a suitable podmag-magnetizing field. The sensitivity of this sensor structure is about 0.8% / mT, which is higher than that of the anisotropic magnetoresistive structure with slanted stripes on the status indicator.

CMP-spin valves, spin valves are also suitable for installation work to determine the angle. Reference magnetisation required for determining the angle, which is produced in such a manner that the magnetization direction of one of the ferromagnetic layers (FM1) is fixed by adjacent antiferromagnetic interaction with sodium layer (AFM). Therefore, they are called «coupled layers.» In contrast, the magnetization of the second ferromagnetic layer (FM2), magnetically uncoupled through a nonmagnetic intermediate layer, is free to rotate by an external magnetic field. Therefore, these layers are called «free layer».

Resistance varies according cosine-function of the angle f between the external field direction and the reference direction. The decisive factor in the accuracy of measurement of the angle is the stability of the reference magnetization compared to the influence of an external field. This stability is greatly improved by the use of additional synthetic antiferromagnetic (SAF). In this case, we are talking about two ferromagnetic layers, which are connected by a very thin non-magnetic spacer layer antiferromagnetic manner and at the expense of its total net vanishing magnetic moment do not provide external field contact surface. The magnetization of one of these two layers is fixed adjacent natural antiferromagnetic-magnets (AFM). The determining process in a magnetic multilayer system is connected to the interaction with the natural layers is antiferromagnetic (AFM), and the interaction of the ferromagnetic layers to each other (PL, RL, FL).

Moreover, the process is recognized as in the AMR sensor structures by crystal and shape anisotropy of the individual magnetic layers.

Goniometer SMR as the protractor AMP comprises two bridges (jumpers integers), one of which produces a cosine signal and sine signal to the other depending on the direction of the external field. The necessary different magnetic reference direction MR produced by local heating of individual resistance measuring bridges and cooling the adjacent magnetic field corresponding orientation. Due arktangentsialnogo bridges connecting both signals the direction of the field can be uniquely determined over the entire angular range of 0 ° … 360 °.

Sensors propagation

In recent years the development focused largely on sensors that determine the near and distant surroundings, t. E the distance from other vehicles or the traffic participants and obstacles. Round view of the car (fig. 38) allows you to use the system, increase security and help drive the car (driver support system).

Ultrasonic technology to measure the distance between the vehicle and an obstacle in the area of ​​detection of 2.5 m using ultrasonic sensors. They can be used to monitor the environment of a vehicle when parking and maneuvering (Parktronic).

By analogy with the principle of sonar ultrasonic transducers send ultrasonic pulses at a frequency of approx. 43.5 kHz, and the time interval between sending the pulse and the return ehoimpulsa reflected from obstacles. The distance between the sensor and the nearest obstacle is calculated by the propagation time te ehoimpulsa and reflected sound velocity in air (approx. 340 m / s): = 0.5 l-te -c

In the front and rear area of ​​the vehicle is set to 6 sensors each. This creates a large angle to obtain the data for the analysis of the surrounding space. And geometric distance from the obstacle to the front of the vehicle is determined by triangulation method based on the measurement results (distance b, and c) the second ultrasonic sensors located relative to each other by a distance d. When approaching an obstacle the driver receives visual and / or audible.

Defining characteristics displayed asymmetrically. Selected vertical angle less than the angle with the horizontal in order to prevent that, bumps regarded as obstacles.

Radar technology to determine the surrounding area at a distance of 200 meters using radar (Radio Detection and Ranging). Radar sends out electromagnetic waves that are reflected from metal surfaces and are accepted by the receiver of the radar. Based on the comparison with the received signal sent from the standpoint of time and / or frequency, can determine the distance and relative speed of the object reflecting signal.

This technology is used in the automotive industry in the ACC (Adaptive Cruise Control, adaptive speed control). APS enables adjustment of the speed at which the speed decreases, when the vehicle moves slowly forward, and thus maintains a predetermined distance.

Measurement of transit time

All principles of the radar distance measurement is based on the direct or indirect measurement of the transit time of the signal during the time between the transmission of radar signal and receiving the echo. For direct measurement of the signal propagation time is measured time t. It is calculated by direct reflection in relation to double the distance d of the reflector and the speed of light with the following formula: m = 2 d / c

When the distance d = 150 m = 300 and 000 km / s signal transmission time is: t = 1 ms Modulation frequency

Direct measurement of the transit time is a complicated procedure. More simple is the indirect measurement of transit time. This method is known as the FMCW (Frequency Modulated Continuous Wave) (frequency simulated continuous oscillation). Instead of comparing the time of the transmitted signal and the reflected signal is compared to the FMCW radar frequency transmitted and reflected signals.

The condition is a rational measure changes over time, the carrier frequency of the transmitter.

When using the method of FMCW radar wave linearly modulated in frequency, are sent within a few milliseconds and typically have a deviation of a few hundred MHz (/ S, mapped by the solid line). The signal reflected from the vehicle in front, according to the delayed transmission time. The growing field of low frequency signal in the downlink region — high frequency proportionally. The frequency difference A / is a discrete value for the distance.

If further between cars there is a relative speed, the frequency of the received signal ^ increases due to duplicate the effect in increasing and in the area falling by a certain amount. In this way, we obtain two frequency difference A / 1 and A / 2. Their addition results in a distance, their subtraction — relative speed of vehicles in relation to each other. The signal processing in the frequency range for each object gives a frequency which is a linear combination of each member for the distance and relative speed. By measuring the frequency of the two zones with different lift can determine the distance and relative speed of a single object. For situations that involve multiple targets it requires several zones with different lifts.

Duplicating effect Despite that consistently provide distance measurement can determine the relative speed of the object being measured, the measurement value is faster, more reliable and more accurately measured through the use of back-up effect.

For an object moving relative to the direction of the radar sensor (relative velocity of the reflected signal with respect to radiation signal determines the frequency shift fD. If the relative speed difference, it is here: fD = -2fC ■ ige1 / s

Thus / c is a carrier frequency signal. Under normal for the ACC radar frequencies fC = 76,5 GHz frequency offset obtained fD = 510 ■ ige1 / m, ie, 510 Hz — 1 m / sec relative velocity (approx.)

Angle Measurement

As the third-base side need to find the value of the object’s position radar research. It can be determined only in the case when the radar beam is directed in different directions and the direction is determined by the signals with the strongest signal reflection. This will require a quick pan («scan») the beam or multibeam antenna arrangement.

The high-element sensor ACC

High frequency power produces a voltage controlled oscillator (VCO, Voltage-Controlled Oscillator), consisting of a Gunn diode in a mechanical resonator, between 76 and 77 GHz (Fig. 43). The control electronics (PLL-ASIC, PLL = Phase Locked Loop) by the oscillator VCO operates and provides stabilization and modulation frequency.

A high frequency power is distributed through the Wilkinson divider into four transmitting / receiving channel. Through the «downy» the mixer output, on the one hand, supplied to the antenna on the other hand, the received signal «admixed» in the primary frequency band.

The system consists of four antennas combined emitters operating at transmission / reception, a high frequency substrate, four rod antennas polystyrene (a plastic cone) for prefocusing and a plastic lens to focus the beam. The lens used as an element of the body and both radar and optical window screening. Radar waves simultaneously emitted four emitters antennas coherently, resulting in creating a wave transmitter. Itself split into four separate beams is first performed on the receiving side. It uses four separate overbuilt host channel.

Measurement of the position and the way with GPS

GPS is a global positioning system (Global Positioning System) satellites on the basis of which the Americans first used for military purposes, and then gradually introduced into civil use. With satellites 24

(21 operating and 3 spares) at an altitude of 20,183 km system is fully functional since 1993. Meanwhile, used even more than 24 satellites. They orbital period of 12 hours distributed in six orbits so that at every point of the Earth was seen continuously for at least four (often up to eight).

They continuously transmit (digital) signals at a frequency of 1.57542 GHz. The signals contain, put simply, the following data:

► identification code of the satellite,

► position of the satellite,

► point data (including date).

For precise determination of the transmission time available on board the satellite by two hours of cesium and rubidium, the error is less than 20 … 30 ns. The estimated transmission time is usually in the range of 70 ms. Satellites identify themselves with the help of pseudo-random (PRN-number), which consists of 1023 bits and repeats every 1 ms. It is transmitted as a carrier phase modulation.

Using the GPS receiver, consisting of GPS-antenna reception signal portion, accurate clock and a microprocessor, a user can, through this information, specify a geographical position in three-dimensional imaging. Theoretically, it is enough to three satellites. Because less complicated watch mobile receivers (quartz crystals) is still a little bit different from the satellite clock, it is necessary to draw a fourth satellite, by which the receiver clock inaccuracy is eliminated. From the measured transit time performance concludes a distance of «visible» satellites.

Positioning is carried out as follows: — then by Trillo-teratsii, according to which there is only one point in space, which distance fulfills the three conditions. Additional information is also obtained that the vehicle — in contrast to the plane — should be on the surface of the Earth.

The measurement will be more accurate, the more the satellite signal will be made, and better than satellites evenly distributed across the sky. Since the complete transfer service civilian targets (May 2000), the accuracy of determination in the plane reached 3 … 5 m, when determining the height of 10 … 20 m. With GPS modernization in the DGPS (Differential GPS, mobile stations have long-wave signals, in contact with a stationary reference station), this error can be reduced even more. So, today possible resolution to less than 1 m.

This accuracy is all the more surprising when you consider how various noise undergoes a very complex dimension. Here I would like to draw attention to the fact that the high speed of approx. 12000 km / h, which are moving satellites relativistic effects do not matter much. At high speeds, the time is slower than on Earth. When the weaker gravity that exist in orbits that time goes faster. High speed causes delay time of 7.2 microseconds per day, less gravity has six times more the opposite effect.

If the location data stored in the mobile GSP receiver, such as a car, a large volume, and often, then it is possible to easily construct a curve trajectory vychilit and vehicle speed. If the data is sent via radio transmission module is mounted on a stationary central station on it and you can always find the location of a vehicle.

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