- Email: [email protected]
Mechatronic sensors in integrated vehicle architecture
54
Sensors
Mechatronic Erich Zabler, Robert
Bosch GmbH,
and Acmators
A, 31 ( 1992) 54-59
sensors in integrated vehicle architecture
Frieder D-7505
Heintz, Ertlingen
Rainer
Dietz and Giinter
Gerlach
(FRG)
Abstract At present, electronic controls and systems are in the process of becoming essential and integral parts of our vehicles whereas they were previously replacements for corresponding mechanical systems predominantly separately acting or fulfilling add-on functions. From this viewpoint, the electronic systems in the vehicle will be interconnected with each other to a much greater degree than was previously the case; for this reason, they must also be reclassified and subdivided. Accordingly, electronic signal-processing components, for example, which were previously located in central control units, will be moved to the periphery where they are mechanically and electrically integrated with the sensor or actuator directly at the point at which they are actually required (mechatronics). The varied advantages of such sensors which are also capable of digital communication by means of new connection systems (bus systems) can be seen in the concrete example of an ‘intelligent’ short-circuit-ring displacement sensor. The accuracy of this sensor can be increased considerably by simultaneously simplifying its design; the highly accurate measured signal can be transmitted in a digital form.
Introduction: decentralized with electronics on site
hardware concept
To the new hierarchical arrangement concepts provided for electronic units in automobiles [l] corresponds a modular concept on the hardware side (Fig. 1). The mechanic@ parts are becoming independent components by addition of electronic circuitry. This trend is currently named mechatronic. Those units are also able to communicate via busses. Besides actuators and other electronic subunits, sensors in particular have to be adapted to this new concept. Then they are named ‘smart’ or ‘intelligent’. In this paper the typical structure and advantages of these sensors are pointed out by an interesting example suited for a new mechatronic architecture in modern cars.
Intelligent sensors
Figure 2 illustrates once more mechatronic. Today a transition the sensor from the corresponding into more modem structures of sors integrated with their inherent ing circuitry is observed. This 0924-4247/92/$5.00
the trend called from separating electronic unit ‘intelligent’ sensignal processtype of sensor
may not only contain components of a first signal conditioning stage but also digital circuits for a subsequent processing, compressing and coding of the information content to a protocol, which may finally be transferred via a bus to other units. The most important advantages which can be achieved by this method are as follows: - On the system level: Multiple usage of sensors Software/hardware relief of control units System partitioning, standardized interface - On the signal level: Utilization of small measuring effects and carrier frequency effects Convenient and flexible signal output Digitalization, bus capability, noise immunity - On the accuracy level: Correction of static and dynamic errors Ease of adjustment Usability of multisensor structures @ 1992 -
Elsevier Sequoia. All rights reserved
I
ClaSrCBus I
s2&--
I
I
Fig. 4. Basic ‘smart sensor’ circuit.
c4aaaB Bus: c-mmunicatm
I
I
I
I
NevioaaonTalaphone %s.$y
tt11
ttu
Fig. 1. Decentralized
hardware
1
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concept.
Fig. 5. Programming
Fig. 2. Integration
process of vehicle sensors.
It is the basic idea of all intelligent sensors [2] that, according to Fig. 3, the dependence of the output signal x, on the measured quantity x, as well as on the disturbing influences can be described mathematically. The function might be named ‘sensor model’. The mathematical algorithm of such a model is always identical for all sensors of a certain type and therefore programmable in a fixed manner, whereas the free parameters and constants of this model are specific for the unit and different. As shown in Fig. 4 they are always stored in an individually programmable memory part of the microcomputer (PROM). First, both the measur-
Fig. 3. General sensor model
a ‘smart sensor’.
ing signal x, and the influence signals y are digitalized. Subsequently the measuring signal is set free from errors of any kind in the microcontroller by means of the programmed sensor model and the individual correcting parameters before it may be transferred in a digital or analog form. However before the sensor will operate in the described manner it is necessary to measure in a prephase its natural uncorrected characteristic very exactly by means of reference sensors and a host computer. As shown in Fig. 5 this calibration computer calculates the needed correcting parameters which are then written into the PROM.
Contactless displacement sensors based on the shading ring principle
The idea of intelligent sensors is often explained in connection with sensors of very tiny dimensions which are manufactured in film or even semiconductor techniques, e.g., like micromachined sensors. In these cases the inherent electronics for signal conditioning might be integrated elegantly on site to the sensors either in a hybrid or even in a monolithic form. This paper shows an example where a more conventional sensor gains a lot of advantages us-
Fig. 6. Principle of a short-circuit ring sensor.
ing just this principle. In contrast to other sensors like pressure transducers and accelerometers, a miniaturization is rather limited for displacement sensors. The dimension of such a sensor normally depends directly on the measuring range. Figure 6 explains the basic principle of a contactless working short-circuit ring (SCR) sensor [ 31. Here the inductance of a coil, e.g., mounted on an E-shaped core, varies strongly by the motion of a short circuit ring made of copper or aluminium. Since this ring might not be penetrated by any alternating magnetic field it has a shading or limit-
ing effect on the magnetic field as seen in the lower picture. Figure 7 shows a special version as it is used, e.g., in electronically controlled diesel injection pumps, Tolerances of the iron sheets and temperature influences are eliminated to a high degree by means of a fixed and adjusted reference inductance Lz. For purposes of signal processing the ratio between the measuring inductance L, and reference inductance L2 is evaluated. The linearity of such a sensor is improved by narrowing the air gap between the core legs in the region of large displacements, i.e., towards the open end of the core. This increases the field strength towards the open end as can be seen in the picture with the calculated field forces.
Conventional and new electronic signal processing Sensors of this type are conventionally evaluated by electronic circuits as shown in Fig. 8. To achieve an analog output signal the sensor coils are connected as for an inductive voltage divider. For this purpose one of the two supply terminals is fed with a controllable alternating voltage in such a way that the voltage detected at the third terminal, the pick-up terminal, will disappear wherever the short circuit ring is just positioned. Simpler, however, is the design of a frequency analog, i.e., quasi-digital, circuit. In this case the variable inductance L is part of a relaxation oscillator. It converts the measured inductance L in a
Da&n and Field Diagram Core
M%lsW~KlsIlt SCR
~Measurement coil L, (s)
Fig. 7. Semi-differential SCR sensor: (a) version as control rod displacement sensor (electronic diesel control); (b) core design and field diagram.
Fig. 8. Conventional processing circuits: (a) voltage analog (semidifferential sensor); (h) period analog (simple SCR sensor).
proportional period duration T of a square wave oscillation. If an additional reference inductance is evaluated, the oscillator can easily be switched alternatively between the two inductances. Thus a pulse-length-modulated output signal is created. A so-called semi-differential sensor of this type is currently operated without any electronics on site (Fig. 9). It represents an exchangeable, separately adjusted unit. The corresponding signal processing circuit is located in the central electronic unit provided for the whole system. In such a configuration, unfortunately, both remaining errors caused by the sensor and by the electronic circuit are added. If, however, according to the rules of intelligent sensors, the sensor elements and the inherent evaluation circuitry are integrated then the deviations of both the sensor and the electronics might be adjusted and compensated (Fig. 10). A reference inductance is no longer necessary. As a first conversion stage we selected the very simple period analog circuit, as already shown in Fig. 8(b). Its output can be digitalized in an extremely simple manner by counting methods. No longer has a special contour of the E-core legs for linearizing to be provided. All these deviations are now precisely eliminated on site by computations
Fig. 9. Conventional sensor circuit.
lx fc
- Clock generator = Cfods frequency (10 MHz)
SC = Sgnd T sPedad
in a microcontroller. There is only the additional need of a very simple and cost-effective temperature sensor, which is mounted on the sensor’s core being in very good thermal contact. In Fig. 11 a photograph of the simplified sensor is shown. Using all the enumerated advantages of a sensor provided with electronics on site, the accuracy of this sensor principle was aimed to be essentially increased. The following requirements have been rated for the potential application of the sensor: 22 mm - Measurement range: - Measurement time: 0.5 ms 0.1% of measure- Accuracy: ment range (corresponding to 10 bit or 22 um) -40.. . + 120 “C ~ Temperature range: - Resolution (for 2 ms measurement time) : 12 bit (corresponding to approx. 5 urn) Since in practice the sensor is part of a very fast servocontrol system, the measuring time must not exceed 0.5 ms at any rate. Figure 12 shows the sensor characteristic measured without any correction: the temperature dependence for a fixed position shows nearly a linear and very flat run. But if these measuring values are presented for constant temperature the dependence of the displacements s versus period T appears slightly curved because a linearization mechanism is not yet applied. This curvature is mathematically modelled by a fifth-order multinomial. Over the whole operating range the inductance is varying between 4.8 and 19 mH, the period between 25 and 125 us according to a frequency variation from 8 to 40 kHz.
eond@hg (25-125ps)
Fig. 10. Circuit diagram for integrated ‘smart’ displacement sensor.
Fig.
11. Simplified design of a ‘smart’ SCR sensor (prototype).
of about 5 mm as an example corresponding period duration T of 50 us.
to a
Measuring results
Fig. 12. Determination of two-dimensional sensor characteristics s(r,, O,,). Approximation curves (a) period T(B, s = S, = const.) and (b) displacement s(r, 0 = Bi = const.).
m-O.....32
Fig. 13. Employed
interpolation
In comparison with a conventional-type sensor and signal processing the prototype of the described intelligent sensor enabled us to increase the accuracy at least by a factor of four, at some operating points even by the factor seven. The intended accuracy of 22 urn has been achieved, indeed, partially exceeded (Fig. 15). As with any digital process we have also to tolerate a quantization error by the here-employed counting method. For a synchronized count this error would not exceed _+10 urn according to the double-hatched zone in the Figure, Since the sensor signal and the pulse generator output are totally asynchronous, quantization errors of a double value can sometimes occur also but only with a low probability, as shown by the zone with the single hatching.
principle.
If we only stored the multinomial coefficients determined for different temperatures, we would indeed save memory, but we would not be able to meet the required measuring time of only 500 us. Therefore the sensor model has been stored in a PROM as a two-dimensional matrix of discrete displacement values depending on period duration on the one hand and on operating temperature on the other hand. As Fig. 13 shows it contains 65 support points along the period axis for each of 33 different temperature points. For the precise determination of the error-free measuring quantity s only a standardized interpolation must be executed. The important remaining requirement for such a sensor, as well as for the electronic components, is a good reproducibility versus time which means a high aging stability. Tolerances of the circuit components, e.g., of the used quartz, are corrected simuntaneously with the sensor.
i3mer
Fig. 14. The @C program
sequence.
30
pm 20
10
0
-10
-a
Signal processing Figure 14 illustrates the method of the employed signal processing [4] taking a measuring distance
Fig. 15. ‘Smart’ displacement temperature.
sensor deviation
as measured
at room
59
This kind of error might, however, be decreased at any time either by prolongation of the measuring time and, e.g., by evaluating a statistical mean value or by increasing the counting frequency. The deviations shown in this Figure are indeed primarily valid for room temperature, but in the meantime it is proven that the temperature influence also does not exceed a deviation of about are + IO Pm, even when these measurements rechecked after a longer time.
Conclusions
The accuracy of the sensor is essentially increased by means of electronics on site and the sensor shape can be simplified simultaneously. By simplification of the sensor shape there will be enough space available to add electronics on site to the sensor. Even mounting influences and influences of surrounding parts could be eliminated now because a late adjustment of the sensor after being built into the pump is possible. The sensor has a bus capability and can be monitored automatically. The really essential improvement of the sensor properties certainly justifies a small increase in its cost. Finally, additional tasks could also be taken over by the here-employed microcontroller, e.g., controlling the injection pump. For further investigation and development we are planning to simplify the calculation algorithm,
saving measuring time and reducing the programmable memory needed to store the correction tables. In order to lower the costs of the electronic circuitry we are designing an ASK to replace the standard microcontroller, which provides many functions and instructions. not needed here. A higher clock frequency will then increase the achievable resolution or shorten the measuring time by about a factor of four. Furthermore, we are making some effort to decrease the number of measuring cycles which are necessary in the prephase to determine the required correction parameters. These investigations will be made on a larger number of sensors in order to get statistical relevant results especially with regard to potential mass production and application.
References 1 T. Goelzer and R. Leonhard, A new architecture for car electronics, Tech. Pap. Int. Symp. Vehicle Ekctronics Integration ATA-EL 91, Turin, Italy, 1991, pp. 11-29. 2 F. Heintz and E. Zabler, Application possibilities and future chances of ‘smart’ sensors in the motor vehicle, SAE Tech. Pap. 890304 (1989). 3 E. Zabler and F. Heintz, Shading-ring sensors as versatile position and angle sensors in motor vehicles, Sensors and Actuators, 3 (1982/83) 315-326. 4 H. Friedrich, Entwicklung und Programmierung eines intelligenten Kurzschlussring-Wegsensors [Development and programming of an intelligent short-circuit ring displacement sensor], Dipfomarbeit, Fachhochschule Karlsruhe, 1990.
Sensors
Mechatronic Erich Zabler, Robert
Bosch GmbH,
and Acmators
A, 31 ( 1992) 54-59
sensors in integrated vehicle architecture
Frieder D-7505
Heintz, Ertlingen
Rainer
Dietz and Giinter
Gerlach
(FRG)
Abstract At present, electronic controls and systems are in the process of becoming essential and integral parts of our vehicles whereas they were previously replacements for corresponding mechanical systems predominantly separately acting or fulfilling add-on functions. From this viewpoint, the electronic systems in the vehicle will be interconnected with each other to a much greater degree than was previously the case; for this reason, they must also be reclassified and subdivided. Accordingly, electronic signal-processing components, for example, which were previously located in central control units, will be moved to the periphery where they are mechanically and electrically integrated with the sensor or actuator directly at the point at which they are actually required (mechatronics). The varied advantages of such sensors which are also capable of digital communication by means of new connection systems (bus systems) can be seen in the concrete example of an ‘intelligent’ short-circuit-ring displacement sensor. The accuracy of this sensor can be increased considerably by simultaneously simplifying its design; the highly accurate measured signal can be transmitted in a digital form.
Introduction: decentralized with electronics on site
hardware concept
To the new hierarchical arrangement concepts provided for electronic units in automobiles [l] corresponds a modular concept on the hardware side (Fig. 1). The mechanic@ parts are becoming independent components by addition of electronic circuitry. This trend is currently named mechatronic. Those units are also able to communicate via busses. Besides actuators and other electronic subunits, sensors in particular have to be adapted to this new concept. Then they are named ‘smart’ or ‘intelligent’. In this paper the typical structure and advantages of these sensors are pointed out by an interesting example suited for a new mechatronic architecture in modern cars.
Intelligent sensors
Figure 2 illustrates once more mechatronic. Today a transition the sensor from the corresponding into more modem structures of sors integrated with their inherent ing circuitry is observed. This 0924-4247/92/$5.00
the trend called from separating electronic unit ‘intelligent’ sensignal processtype of sensor
may not only contain components of a first signal conditioning stage but also digital circuits for a subsequent processing, compressing and coding of the information content to a protocol, which may finally be transferred via a bus to other units. The most important advantages which can be achieved by this method are as follows: - On the system level: Multiple usage of sensors Software/hardware relief of control units System partitioning, standardized interface - On the signal level: Utilization of small measuring effects and carrier frequency effects Convenient and flexible signal output Digitalization, bus capability, noise immunity - On the accuracy level: Correction of static and dynamic errors Ease of adjustment Usability of multisensor structures @ 1992 -
Elsevier Sequoia. All rights reserved
I
ClaSrCBus I
s2&--
I
I
Fig. 4. Basic ‘smart sensor’ circuit.
c4aaaB Bus: c-mmunicatm
I
I
I
I
NevioaaonTalaphone %s.$y
tt11
ttu
Fig. 1. Decentralized
hardware
1
tt11
ttu
ttu
concept.
Fig. 5. Programming
Fig. 2. Integration
process of vehicle sensors.
It is the basic idea of all intelligent sensors [2] that, according to Fig. 3, the dependence of the output signal x, on the measured quantity x, as well as on the disturbing influences can be described mathematically. The function might be named ‘sensor model’. The mathematical algorithm of such a model is always identical for all sensors of a certain type and therefore programmable in a fixed manner, whereas the free parameters and constants of this model are specific for the unit and different. As shown in Fig. 4 they are always stored in an individually programmable memory part of the microcomputer (PROM). First, both the measur-
Fig. 3. General sensor model
a ‘smart sensor’.
ing signal x, and the influence signals y are digitalized. Subsequently the measuring signal is set free from errors of any kind in the microcontroller by means of the programmed sensor model and the individual correcting parameters before it may be transferred in a digital or analog form. However before the sensor will operate in the described manner it is necessary to measure in a prephase its natural uncorrected characteristic very exactly by means of reference sensors and a host computer. As shown in Fig. 5 this calibration computer calculates the needed correcting parameters which are then written into the PROM.
Contactless displacement sensors based on the shading ring principle
The idea of intelligent sensors is often explained in connection with sensors of very tiny dimensions which are manufactured in film or even semiconductor techniques, e.g., like micromachined sensors. In these cases the inherent electronics for signal conditioning might be integrated elegantly on site to the sensors either in a hybrid or even in a monolithic form. This paper shows an example where a more conventional sensor gains a lot of advantages us-
Fig. 6. Principle of a short-circuit ring sensor.
ing just this principle. In contrast to other sensors like pressure transducers and accelerometers, a miniaturization is rather limited for displacement sensors. The dimension of such a sensor normally depends directly on the measuring range. Figure 6 explains the basic principle of a contactless working short-circuit ring (SCR) sensor [ 31. Here the inductance of a coil, e.g., mounted on an E-shaped core, varies strongly by the motion of a short circuit ring made of copper or aluminium. Since this ring might not be penetrated by any alternating magnetic field it has a shading or limit-
ing effect on the magnetic field as seen in the lower picture. Figure 7 shows a special version as it is used, e.g., in electronically controlled diesel injection pumps, Tolerances of the iron sheets and temperature influences are eliminated to a high degree by means of a fixed and adjusted reference inductance Lz. For purposes of signal processing the ratio between the measuring inductance L, and reference inductance L2 is evaluated. The linearity of such a sensor is improved by narrowing the air gap between the core legs in the region of large displacements, i.e., towards the open end of the core. This increases the field strength towards the open end as can be seen in the picture with the calculated field forces.
Conventional and new electronic signal processing Sensors of this type are conventionally evaluated by electronic circuits as shown in Fig. 8. To achieve an analog output signal the sensor coils are connected as for an inductive voltage divider. For this purpose one of the two supply terminals is fed with a controllable alternating voltage in such a way that the voltage detected at the third terminal, the pick-up terminal, will disappear wherever the short circuit ring is just positioned. Simpler, however, is the design of a frequency analog, i.e., quasi-digital, circuit. In this case the variable inductance L is part of a relaxation oscillator. It converts the measured inductance L in a
Da&n and Field Diagram Core
M%lsW~KlsIlt SCR
~Measurement coil L, (s)
Fig. 7. Semi-differential SCR sensor: (a) version as control rod displacement sensor (electronic diesel control); (b) core design and field diagram.
Fig. 8. Conventional processing circuits: (a) voltage analog (semidifferential sensor); (h) period analog (simple SCR sensor).
proportional period duration T of a square wave oscillation. If an additional reference inductance is evaluated, the oscillator can easily be switched alternatively between the two inductances. Thus a pulse-length-modulated output signal is created. A so-called semi-differential sensor of this type is currently operated without any electronics on site (Fig. 9). It represents an exchangeable, separately adjusted unit. The corresponding signal processing circuit is located in the central electronic unit provided for the whole system. In such a configuration, unfortunately, both remaining errors caused by the sensor and by the electronic circuit are added. If, however, according to the rules of intelligent sensors, the sensor elements and the inherent evaluation circuitry are integrated then the deviations of both the sensor and the electronics might be adjusted and compensated (Fig. 10). A reference inductance is no longer necessary. As a first conversion stage we selected the very simple period analog circuit, as already shown in Fig. 8(b). Its output can be digitalized in an extremely simple manner by counting methods. No longer has a special contour of the E-core legs for linearizing to be provided. All these deviations are now precisely eliminated on site by computations
Fig. 9. Conventional sensor circuit.
lx fc
- Clock generator = Cfods frequency (10 MHz)
SC = Sgnd T sPedad
in a microcontroller. There is only the additional need of a very simple and cost-effective temperature sensor, which is mounted on the sensor’s core being in very good thermal contact. In Fig. 11 a photograph of the simplified sensor is shown. Using all the enumerated advantages of a sensor provided with electronics on site, the accuracy of this sensor principle was aimed to be essentially increased. The following requirements have been rated for the potential application of the sensor: 22 mm - Measurement range: - Measurement time: 0.5 ms 0.1% of measure- Accuracy: ment range (corresponding to 10 bit or 22 um) -40.. . + 120 “C ~ Temperature range: - Resolution (for 2 ms measurement time) : 12 bit (corresponding to approx. 5 urn) Since in practice the sensor is part of a very fast servocontrol system, the measuring time must not exceed 0.5 ms at any rate. Figure 12 shows the sensor characteristic measured without any correction: the temperature dependence for a fixed position shows nearly a linear and very flat run. But if these measuring values are presented for constant temperature the dependence of the displacements s versus period T appears slightly curved because a linearization mechanism is not yet applied. This curvature is mathematically modelled by a fifth-order multinomial. Over the whole operating range the inductance is varying between 4.8 and 19 mH, the period between 25 and 125 us according to a frequency variation from 8 to 40 kHz.
eond@hg (25-125ps)
Fig. 10. Circuit diagram for integrated ‘smart’ displacement sensor.
Fig.
11. Simplified design of a ‘smart’ SCR sensor (prototype).
of about 5 mm as an example corresponding period duration T of 50 us.
to a
Measuring results
Fig. 12. Determination of two-dimensional sensor characteristics s(r,, O,,). Approximation curves (a) period T(B, s = S, = const.) and (b) displacement s(r, 0 = Bi = const.).
m-O.....32
Fig. 13. Employed
interpolation
In comparison with a conventional-type sensor and signal processing the prototype of the described intelligent sensor enabled us to increase the accuracy at least by a factor of four, at some operating points even by the factor seven. The intended accuracy of 22 urn has been achieved, indeed, partially exceeded (Fig. 15). As with any digital process we have also to tolerate a quantization error by the here-employed counting method. For a synchronized count this error would not exceed _+10 urn according to the double-hatched zone in the Figure, Since the sensor signal and the pulse generator output are totally asynchronous, quantization errors of a double value can sometimes occur also but only with a low probability, as shown by the zone with the single hatching.
principle.
If we only stored the multinomial coefficients determined for different temperatures, we would indeed save memory, but we would not be able to meet the required measuring time of only 500 us. Therefore the sensor model has been stored in a PROM as a two-dimensional matrix of discrete displacement values depending on period duration on the one hand and on operating temperature on the other hand. As Fig. 13 shows it contains 65 support points along the period axis for each of 33 different temperature points. For the precise determination of the error-free measuring quantity s only a standardized interpolation must be executed. The important remaining requirement for such a sensor, as well as for the electronic components, is a good reproducibility versus time which means a high aging stability. Tolerances of the circuit components, e.g., of the used quartz, are corrected simuntaneously with the sensor.
i3mer
Fig. 14. The @C program
sequence.
30
pm 20
10
0
-10
-a
Signal processing Figure 14 illustrates the method of the employed signal processing [4] taking a measuring distance
Fig. 15. ‘Smart’ displacement temperature.
sensor deviation
as measured
at room
59
This kind of error might, however, be decreased at any time either by prolongation of the measuring time and, e.g., by evaluating a statistical mean value or by increasing the counting frequency. The deviations shown in this Figure are indeed primarily valid for room temperature, but in the meantime it is proven that the temperature influence also does not exceed a deviation of about are + IO Pm, even when these measurements rechecked after a longer time.
Conclusions
The accuracy of the sensor is essentially increased by means of electronics on site and the sensor shape can be simplified simultaneously. By simplification of the sensor shape there will be enough space available to add electronics on site to the sensor. Even mounting influences and influences of surrounding parts could be eliminated now because a late adjustment of the sensor after being built into the pump is possible. The sensor has a bus capability and can be monitored automatically. The really essential improvement of the sensor properties certainly justifies a small increase in its cost. Finally, additional tasks could also be taken over by the here-employed microcontroller, e.g., controlling the injection pump. For further investigation and development we are planning to simplify the calculation algorithm,
saving measuring time and reducing the programmable memory needed to store the correction tables. In order to lower the costs of the electronic circuitry we are designing an ASK to replace the standard microcontroller, which provides many functions and instructions. not needed here. A higher clock frequency will then increase the achievable resolution or shorten the measuring time by about a factor of four. Furthermore, we are making some effort to decrease the number of measuring cycles which are necessary in the prephase to determine the required correction parameters. These investigations will be made on a larger number of sensors in order to get statistical relevant results especially with regard to potential mass production and application.
References 1 T. Goelzer and R. Leonhard, A new architecture for car electronics, Tech. Pap. Int. Symp. Vehicle Ekctronics Integration ATA-EL 91, Turin, Italy, 1991, pp. 11-29. 2 F. Heintz and E. Zabler, Application possibilities and future chances of ‘smart’ sensors in the motor vehicle, SAE Tech. Pap. 890304 (1989). 3 E. Zabler and F. Heintz, Shading-ring sensors as versatile position and angle sensors in motor vehicles, Sensors and Actuators, 3 (1982/83) 315-326. 4 H. Friedrich, Entwicklung und Programmierung eines intelligenten Kurzschlussring-Wegsensors [Development and programming of an intelligent short-circuit ring displacement sensor], Dipfomarbeit, Fachhochschule Karlsruhe, 1990.