POSITION SENSOR SYSTEM, PARTICULARLY FOR DETECTING ROTARY MOVEMENT AND METHOD FOR DETECTING ERRORS IN A POSITION SENSOR SYSTEM

Abstract

A rotary movement position sensor is presented that includes a first sensor output, a second sensor output, a first signal processing unit, a second signal processing unit, a first system output providing the output of the first signal processing unit or of the second signal processing unit, and a second system output providing the output of the second signal processing unit or of the first signal processing unit. A swapping unit that swaps the first signal processing unit between the first sensor output and first system output to the second sensor output and second system output and simultaneously swaps the second signal processing unit from the second sensor output and second system output to the first sensor output and first system output and vice versa. A method for detecting errors in a position sensor system is also presented.

Claims

1. A position sensor system, particularly for detecting rotary movement, comprising: a position sensor, particularly for detecting rotary movement, with a first sensor output and a second sensor output; a first signal processing unit for processing, particularly amplifying and filtering, the signal of the first sensor output or the second sensor output; a second signal processing unit for processing, particularly amplifying and filtering, the signal of the second sensor output or the first sensor output; a first system output providing the output of the first signal processing unit or of the second signal processing unit; and a second system output providing the output of the second signal processing unit or of the first signal processing unit, wherein the position sensor system further comprises a swapping unit for swapping the first signal processing unit from the first sensor output and first system output to the second sensor output and second system output and for simultaneously swapping the second signal processing unit from the second sensor output and second system output to the first sensor output and first system output and vice versa.

2. The position sensor system according to claim 1, further comprising a control unit for processing the first system output and the second system output.

3. The position sensor system according to claim 2, wherein the control unit comprises a first analog-to-digital converter for the first system output, a second analog-to-digital converter for the second system output, and a digital signal processing unit for processing the signals of the first analog-to-digital converter and the second analog-to-digital converter.

4. The position sensor system according to claim 2, wherein the control unit comprises a multiplexer for multiplexing between the first system output and the second system output and a common analog-to-digital converter connected to the output of the multiplexer, and a digital signal processing unit for processing the signal of the common analog-to-digital converter.

5. The position sensor system according to claim 2, wherein the control unit detects ripples in the first system output and/or second system output caused by swapping the first signal processing unit and the second signal processing unit.

6. The position sensor system according to claim 2, wherein the control unit further determines magnitude for the ripples in the first system output and second system output.

7. The position sensor system according to claim 2, wherein the control unit determines the second derivate of the first system output and of the second system output and detects peaks in the calculated second derivates representing errors in the first signal processing unit respectively in the second signal processing unit.

8. The position sensor system according to claim 7, wherein the control unit calculates the average of the first system output respectively of the second system output.

9. A method for detecting errors in a position sensor system, particularly for detecting rotary movement, comprising: a first operating condition, in which a first sensor output is processed by a first signal processing unit and provided to a first system output and in which a second sensor output is processed by a second signal processing unit and provided to a second system output; and a second operating condition, in which the first sensor output is processed by the second signal processing unit and provided to the first system output and in which the second sensor output is processed by the first signal processing unit and provided to the second system output; and further comprising the step of alternating between the first operating condition and the second operating condition.

10. A method according to claim 9, wherein the first system output and the second system output are processed by a control unit.

11. A method according to claim 10, wherein the first system output is converted by a first analog-to-digital converter and the second system output is converted by a second analog-to-digital converter of the control unit or wherein the control unit multiplexes between the first system output and the second system output and converts the multiplexed signal by a common analog-to-digital converter.

12. A method according to claim 9, comprising the step of detecting ripples in the first system output and/or second system output caused by alternating between the first operating condition and the second operating condition, preferably over time for a static position sensor and/or over the position of the sensor.

13. A method according to claim 12, comprising the step of determining the magnitude for the ripples in the first system output and second system output.

14. A method according to claim 9, comprising the step of calculating the second derivate of the first system output and of the second system output and detecting peaks in the calculated second derivates representing errors in the first signal processing unit respectively in the second signal processing unit.

15. A method according to claim 9, comprising the step of determining the average of the first system output and of the second system output.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In the following, the invention will be further explained with respect to the embodiments shown in the figures. It shows:

[0058] FIG. 1A illustrates a block diagram of a position sensor system according to a first embodiment of the invention in a first operating condition,

[0059] FIG. 1B illustrates a block diagram of the position sensor system of FIG. 1A in a second operating condition,

[0060] FIG. 2A illustrates a block diagram of a position sensor system according to a second embodiment of the invention in a first operating condition,

[0061] FIG. 2B illustrates a block diagram of the position sensor system of FIG. 2A in a second operating condition,

[0062] FIG. 3 illustrates a block diagram of a position sensor system according to a third embodiment of the invention in a first operating condition,

[0063] FIG. 4 illustrates a diagram showing output signals of a swapped position sensor system without error in the signal path,

[0064] FIG. 5A illustrates a diagram showing output signals of a swapped position sensor system with an offset error,

[0065] FIG. 5B illustrates a diagram showing an output of a static position sensor with the offset error of FIG. 5A over time,

[0066] FIG. 5C illustrates a diagram showing the offset error of the signals of FIG. 5A over position and the magnitude of the offset error over position,

[0067] FIG. 5D illustrates a diagram showing the total error of the signals of FIG. 5A over position and the total average error,

[0068] FIG. 6A illustrates a diagram showing output signals of a swapped position sensor system with an amplitude error,

[0069] FIG. 6B illustrates a diagram showing an output of a static position sensor with the amplitude error of FIG. 6A over time,

[0070] FIG. 6C illustrates a diagram showing the amplitude error of the signals of FIG. 6A over position and the magnitude of the amplitude error over position,

[0071] FIG. 6D illustrates a diagram showing the total error of the signals of FIG. 6A over position and the total average error over position,

[0072] FIG. 7A illustrates a diagram showing output signals of a swapped position sensor system with a phase error,

[0073] FIG. 7B illustrates a diagram showing an output of a static position sensor with the phase error of FIG. 7A over time,

[0074] FIG. 7C illustrates a diagram showing the phase error of the signals of FIG. 7A over position and the magnitude of the phase error over position,

[0075] FIG. 7D illustrates a diagram showing the total error of the signals of FIG. 7A over position and the total average error over position,

[0076] FIG. 8A illustrates a diagram showing the second derivate for output signals of a position sensor system with an offset error over position,

[0077] FIG. 8B illustrates a diagram showing the magnitude of the signals of FIG. 8A over time,

[0078] FIG. 9A illustrates a diagram showing the second derivate for output signals of a position sensor system with an amplitude error over position,

[0079] FIG. 9B illustrates a diagram showing the magnitude of the signals of FIG. 9A over time,

[0080] FIG. 10A illustrates a diagram showing the second derivate for output signals of a position sensor system with a phase error over position,

[0081] FIG. 10B illustrates a diagram showing the magnitude of the signals of FIG. 10A over time, and

[0082] FIG. 11 illustrates a block diagram of a position sensor system according to the prior art.

DETAILED DESCRIPTION

[0083] FIG. 1A shows a block diagram of a first embodiment of a position sensor system 1, particularly for detecting rotary movement, in a first operating condition. The position sensor system 1 comprises a position sensor 2, particularly for detecting rotary movement, with a first sensor output 3 and a second sensor output 4. The position sensor system 1 further comprises a first signal processing unit 5 for processing, particularly amplifying and filtering, the signal of the first sensor output 3 or the second sensor output 4, and a second signal processing unit 6 for processing, particularly amplifying and filtering, the signal of the second sensor output 4 or the first sensor output 3.

[0084] The signal of the first sensor output 3 and the second sensor output 4 are either processed by the first signal processing unit 5 or the second signal processing unit 6 at a time. Thus, if the first sensor output 3 is processed by the first signal processing unit 5 the second sensor output 4 is processed by the second signal processing unit 6 and if the first sensor output is processed by the second signal processing unit 6 the second sensor output 4 is processed by the first signal processing unit 5.

[0085] The position sensor system 1 further comprises a first system output 7 providing the output of the first signal processing unit 5 or of the second signal processing unit 6 and a second system output 8 providing the output of the second signal processing unit 6 or of the first signal processing unit 5. Again, at a given time the output of the first signal processing unit 5 is provided by either the first system output 7 or the second system output 8 and the output of the second signal processing unit 6 is provided at that time by the other of the second system output 8 or the first system output 7. Thus, if the output of the first signal processing unit 5 is provided by the first system output 7 the output of the second signal processing unit 6 is provided by the second system output 8 and if the output of the first signal processing unit 5 is provided by the second system output 8 the output of the second signal processing unit 6 is provided by the first system output 7.

[0086] According to the invention the position sensor system 1 further comprises a swapping unit 9 for swapping the first signal processing unit 5 from the first sensor output 3 and the first system output 7 to the second sensor output 4 and second system output 8 and for simultaneously swapping the second signal processing unit 6 from the second sensor output 4 and second system output 8 to the first sensor output 3 and first system output 7 and vice versa. In FIG. 1A the swapping unit 9 is identified by two dashed circles, one between the position sensor 2 and the signal processing units 5, 6 and the other between the signal processing units 5, 6 and the system outputs 7, 8, i.e. at the two locations where the swapping takes place.

[0087] In the first operating condition of FIG. 1A the first sensor output 3 is connected to the first signal processing unit 5 and the output of the first signal processing unit 5 is connected to the first system output 7. Consequently, the second sensor output 4 is connected to the second signal processing unit 6 and the output of the second signal processing unit 6 is connected to the second system output 8.

[0088] The first signal processing unit 5 and the second signal processing unit 6 each comprise an amplifier 11 and a filter 12. The amplifier 12 is for example an operation amplifier (op-amp) and the filter 12 is for example a resistor-capacitor circuit (RC circuit). The first signal processing unit 5 and/or the second signal processing unit 6 can add some offset error, gain error and/or phase error, as indicated in FIG. 1A by the corresponding arrows.

[0089] The position sensor system 1 of FIG. 1A further comprises a control unit 10. The control unit 10 can be either integral with the position sensor system 1, i.e. on the same chip, or external of the position sensor system 1 and connected to the position sensor system 1 by e.g. a cable. FIG. 1A refers to an external control unit 10, as indicated by the connection points and lines between the position sensor system 1 and the control unit 10.

[0090] The control unit 10 in FIG. 1A comprises a first analog-to-digital converter 13 for the first system output 7 and a second analog-to-digital converter 14 for the second system output 8. The output of the first analog-to-digital converter 13 and of the second analog-to-digital converter 14 are processed by the same digital signal processing unit 15.

[0091] The control unit 10, especially the digital signal processing unit 15, is designed to detect ripples 18 in the first system output 7 and/or second system output 8, caused by swapping the first signal processing unit 5 and the second signal processing unit 6.

[0092] Furthermore, the control unit 10, especially the digital signal processing unit 15, is designed to determine the magnitude for the ripples 18 in the first system output 7 and second system output 8.

[0093] To further increase the accuracy of the position sensor system 1 the control unit 10, especially the digital signal processing unit 15, can determine the 2.sup.nd derivate of the first system output 7 and of the second system output 8 and detect peaks in the 2.sup.nd derivates. The peaks represent errors in the first signal processing unit 5 respectively in the second signal processing unit 6, especially offset, gain and/or phase errors.

[0094] To reduce or compensate errors in the first signal processing unit 5 and/or second signal processing unit 6 the control unit 10, especially the digital signal processing unit 15, can calculate the average of the first system output 7 respectively the second system output 8.

[0095] FIG. 1B shows a block diagram of the position sensor system 1 of FIG. 1A in a second operating condition. In this second operating condition the first sensor output 3 is connected to the second signal processing unit 6 and the second signal processing unit 6 is connected to the first system output 5. Further, the second sensor output 4 is connected to the first signal processing unit 5 and the first signal processing unit 5 is connected to the second system output 8. Thus, the swapping unit 9 has swapped the first signal processing unit 5 from the first sensor output 3 and first system output 7 to the second sensor output 4 and second system output 8 and simultaneously swapped the second signal processing unit 6 from the second sensor output 4 and second system output 8 to the first sensor output 3 and first system output 7. By swapping the signal processing units 5, 6 the swapping unit 9 changes the operating condition of the position sensor system 1.

[0096] Since the sensor output 3, 4 are processed by different signal processing units 5, 6 in the two operating conditions and because the different signal processing units 5, 6 may have different offset, gain and/or phase errors, the system outputs 7, 8 may contain ripples 18, which are detected by the control unit 10.

[0097] In FIG. 1B the swapping unit 9 is again identified by two dashed circles. The swapping of the signal processing units 5, 6 is identified by the crossings in the two dashed circles.

[0098] In the first operating condition shown in FIG. 1A the first sensor output 3 is processed by the first signal processing unit 5 and provided to the first system output 7 and the second sensor output 4 is processed by the second signal processing unit 6 and provided to the second system output 8.

[0099] In the second operating condition shown in FIG. 1B the first sensor output 3 is processed by the second signal processing unit 6 and provided to the first system output 7 and the second sensor output 4 is processed by the first signal processing unit 5 and provided to the second system output 8.

[0100] The swapping unit 8 causes an alternation between the first operating condition and the second operating condition.

[0101] The first signal processing unit 5 and the second processing unit 6 amplify and filter the first sensor output 3 and the second output 4 and thereby eventually adding offset errors, gain errors and/or phase errors.

[0102] The first system output 7 and the second system output 8 are processed by the control unit 10. The first system output 7 is converted by the first analog-to-digital converter 13 of the control unit 10 and the second system output 8 is converted by the second analog-to-digital converter 14 of the control unit 10. The signals of the first analog-to-digital converter 10 and of the second analog-to-digital converter 14 are processed by the digital signal processing unit 15 of the control unit 10.

[0103] The control unit 10 detects ripples 18 in the first system output 7 and/or the second system output 8, which are caused by alternating between the first operating condition and the second operating condition, i.e. by processing the sensor output signals 3, 4 by different signal processing nits 5, 6 in the two operating conditions.

[0104] By determining the magnitude for the ripples 18 in the first system output 7 and the second system output 8 the control unit 8 can determine the kind of error, i.e. offset error, gain error and/or phase error.

[0105] The accuracy of the error detection can be enhanced by calculating the 2.sup.nd derivate of the first system output 7 and of the second system output 8 and detecting peaks in the calculated 2.sup.nd derivates. The peaks represent errors in the first signal processing unit 5 respectively in the second signal processing unit 6.

[0106] By determining the average of the first system output 7 and of the second system output 8 the errors can be reduced or even compensated.

[0107] Advantageously, the swapping unit 9 swaps the first signal processing unit 5 and second signal processing unit 6 regularly, preferably in equal intervals.

[0108] FIGS. 2A and 2B show a block diagram of a position sensor system 1 according to a second embodiment of the invention in a first operating condition respectively in a second operating condition. The second embodiment of the position sensor system 1 shown in FIGS. 2A and 2B differs from the first embodiment of the position sensor system 1 shown in FIGS. 1A and 1B in that the control unit 10 only comprises a common analog-to digital converter 17 instead of a first analog-to-digital converter 13 and a second analog-to-digital converter 18. In order to process the first system output 7 and the second system output 8, the control unit 10 comprises a multiplexer 16 for multiplexing between the first system output 7 and the second system output 8. The multiplexer 16 is preferably by the control unit 10 and a corresponding information is used by the digital signaling processing unit 15, so that the digital signal processing unit 15 can assign the current received digital signals from the common analog-to-digital converter 17 to the first system output 7 respectively second system output 8.

[0109] FIG. 3 shows a third embodiment of a position sensor system 1 according to the invention in a first operating condition. The third embodiment of FIG. 3 differs from the first embodiment of FIGS. 1A and 1B in that the control unit 10 is an internal control unit 10. Thus, the first system output 7 and the second system output 8 are internal to the position sensor system 1.

[0110] Since all other features correspond to the first embodiment of FIGS. 1A and 1B the third embodiment is not shown in the second operating condition. Furthermore, the internal control unit 15 can also be used for the second embodiment shown in FIGS. 2A and 2B accordingly.

[0111] FIG. 4 shows exemplary outputs of the first sensor output 3 and the second sensor output 4 in an error-free situation with no offset, ideal amplitude matching and ideal 90 phase shift between Sine-signal 20 and Cosine-signal 21, resulting in no swapping ripple. The horizontal axis of FIG. 4 represents the mechanical rotation, in this case 360 and the vertical axis represents the signal level of the first sensor output 3 and the second sensor output 4. In this case the maximum signal level is 1.0.

[0112] The first sensor output 3 provides a sinusoidal signal, which starts with a signal level of 0 at 0. The sinusoidal signal of the first sensor output 3 is referred to as Sine-signal 20. The second sensor output 4 also provides a sinusoidal signal, which is phase shifted by a quarter of a phase respectively 90. Thus, the signal level of the second sensor output 4 is 1.0 at 0. The sinusoidal signal of the second sensor output is referred to as Cosine-signal 21.

[0113] The first sensor output is defined by:

[00001]$A^{*}.Math.\sin .Math..Math.\left(\frac{x*}{1.Math.8.Math.0}\right).Math.\left[x.Math..Math.\mathrm{in}.Math..Math.\mathrm{degree}\right],$

or

A* sin(x) [x in radians],

[0114] and the second sensor output is defined by:

[00002]$A^{*}.Math.\sin .Math..Math.\left(\frac{\left(x+9.Math.0\right)*}{1.Math.8.Math.0}\right).Math..Math.\mathrm{or}.Math..Math.A^{*}.Math.\cos .Math..Math.\left(\frac{\left(x\right)*}{1.Math.8.Math.0}\right).Math.\left[x.Math..Math.\mathrm{in}.Math..Math.\mathrm{degree}\right],\mathrm{or}$$A^{*}.Math.\sin .Math..Math.\left(x+\frac{}{2}\right).Math..Math.\mathrm{or}.Math..Math.A^{*}.Math.\cos .Math..Math.\left(x\right).Math.\left[x.Math..Math.\mathrm{in}.Math..Math.\mathrm{radians}\right].$

[0115] The peak amplitude respectively the signal level A is 1.0 in FIG. 4.

[0116] FIG. 5A shows an error case where the second signal processing unit 6 has an offset error of 10% relative to the maximum signal amplitude of 1.0. FIG. 5A shows the Sine-signal 22 and Cosine-signal 23 of the first system output 7 respectively the second system output 8 with the offset error over a full phase (0 to 360).

[0117] FIG. 5B shows the output of a static sensor located at 120 of FIG. 5A in the time domain. The horizontal time axis is a relative number, representing 40 swapping cycles (20 swapping periods). The deviation between the signals of the two operating conditions (swapped and un-swapped) is visible as a rectangular signal, toggling between two signal levels. This rectangular signal is referred to as ripples 18. The ripples of the swapped Sine-signal 22 are indicated by numeral 28 and the ripples of the swapped Cosine-signal 23 are indicated by numeral 29. Furthermore, FIG. 5B shows the averages for the ripples 28 of the swapped Sine-signal 22 and the ripples 29 of the swapped Cosine-signal 23.

[0118] FIG. 5C shows the offset error for the Sine-signal 22 and Cosine-signal 23 of FIG. 5A and the magnitude both signals

[00003]$\left(\sqrt{{\left(\mathrm{Sin}-\mathrm{signal}.Math..Math.22\right)}^2+{\left(\mathrm{Cosine}-\mathrm{signal}.Math..Math.23\right)}^2}\right)$

over a full phase (0 to 360). An indication of an offset error is that at any position the error of the Sine-signal 22 and Cosine-signal 23 is constant and equal.

[0119] FIG. 5D shows the total errors calculated from the un-swapped signal 31 and swapped signal 30 at the first system output 7 and the second system output 8 and the averaged total error. By averaging the errors of un-swapped signal 31 and swapped signal 30 the total offset error can be reduced.

[0120] FIG. 6A shows an error case where the second signal processing unit has a gain error of 10% relative to the maximum signal amplitude of 1.0. FIG. 6A shows the Sine-signal 24 and Cosine-signal 25 of the first system output 7 respectively the second system output 8 with the gain error over a full phase (0 to 360).

[0121] FIG. 6B shows the output of a static sensor located at 120 of FIG. 6A in the time domain. The horizontal time axis is a relative number, representing 40 swapping cycles (20 swapping periods). The deviation between the signals of the two operating conditions (swapped and un-swapped) is visible as a rectangular signal, toggling between two signal levels. This rectangular signal is referred to as ripple 18. The ripples of the swapped Sine-signal 24 are indicated by numeral 28 and the ripples of the swapped Cosine-signal 25 are indicated by numeral 29. Furthermore, FIG. 6B shows the averages for the ripples 28 of the swapped Sine-signal 24 and the ripples 29 of the swapped Cosine-signal 25.

[0122] From FIG. 6A and FIG. 6B it follows that the largest ripple 18 occurs at the signal peaks and the smallest ripple 18 occurs at the zero crossings of each signal 28, 29.

[0123] FIG. 6C shows the gain error for the Sine-signal 24 and Cosine-signal 25 of FIG. 6A and the magnitude both signals

[00004]$\left(\sqrt{{\left(\mathrm{Sin}-\mathrm{signal}.Math..Math.24\right)}^2+{\left(\mathrm{Cosine}-\mathrm{signal}.Math..Math.25\right)}^2}\right)$

over a full phase (0 to 360). The largest error of the Sine-signal 24 respectively the Cosine-signal 25 occurs at the positive and negative peaks (90, 270 for Sine-signal 24, 0, 180 for Cosine-signal 25) and the minimum errors occurs at the zero crossings (0, 180 for Sine-signal 24, 90, 270 for Cosine-signal 25). An indication of a gain error is that the errors of the Sine-signal 24 and Cosine-signal 25 are not constant over a full phase, but the magnitude of both signals is constant.

[0124] FIG. 6D shows the total errors calculated from the un-swapped signal 31 and swapped signal 30 at the first system output 7 and the second system output 8 and the averaged total error. By averaging the errors of un-swapped signal 31 and swapped signal 30 the total amplitude error can be eliminated.

[0125] FIG. 7A shows an error case where the second signal processing unit has a phase shift error of 6 compared to the first signal processing unit 7. FIG. 7A shows the Sine-signal 26 and Cosine-signal 27 of the first system output 7 respectively the second system output 8 having a phase shift error over a full phase (0 to 360).

[0126] FIG. 7B shows the output of a static sensor located at 120 of FIG. 7A in the time domain. The horizontal time axis is a relative number, representing 40 swapping cycles (20 swapping periods). The deviation between the signals of the two operating conditions (swapped and un-swapped) is visible as a rectangular signal, toggling between two signal levels. This rectangular signal is referred to as ripples 18. The ripples of the swapped Sine-signal 26 are indicated by numeral 28 and the ripples of the swapped Cosine-signal 27 are indicated by numeral 29. Furthermore, FIG. 7B shows the averages for the ripples 28 of the swapped Sine-signal 26 and the ripples 29 of the swapped Cosine-signal 27.

[0127] From FIG. 7A and FIG. 7B it follows that the largest ripple occurs at the zero crossings and the smallest ripple occurs at the signal peaks of each signal 26, 27.

[0128] FIG. 7C shows the phase shift error for the Sine-signal 26 and Cosine-signal 27 of FIG. 7A and the magnitude both signals

[00005]$\left(\sqrt{{\left(\mathrm{Sin}-\mathrm{signal}.Math..Math.26\right)}^2+{\left(\mathrm{Cosine}-\mathrm{signal}.Math..Math.27\right)}^2}\right)$

over a full phase (0 to 360). The largest error of the Sine-signal 26 respectively the cosine-signal 27 occurs at zero crossings (0, 180 for Sine-signal 26, 90, 270 for Cosine-signal 27) and the minimum errors occurs at the positive and negative peaks (90, 270 for Sine-signal 26, 0, 180 for Cosine-signal 27). An indication of a phase shift error is that the errors of the Sine-signal 26 and Cosine-signal 27 are not constant over a full phase, but the magnitude of both signals is constant.

[0129] FIG. 7D shows the total errors calculated from the un-swapped signal 31 and swapped signal 30 at the first system output 7 and the second system output 8 and the averaged total error. By averaging the errors of un-swapped signal 31 and swapped signal 30 the total phase shift error can be reduced to a constant level over a full phase.

[0130] FIG. 8A shows the 2.sup.nd derivate of the Sine-signal 22 and Cosine-signal 23 of FIG. 5A referring to the offset error. FIG. 8B shows the magnitude of the 2.sup.nd derivates of FIG. 8A

[00006]$\left(\sqrt{{f^{}\left(\mathrm{Sine}-\mathrm{Signal}.Math..Math.22\right)}^2+{f^{}\left(\mathrm{Cosine}-\mathrm{Signal}.Math..Math.23\right)}^2}\right).$

FIG. 8A is split into two graphs due to the overlapping of the 2.sup.nd derivate of the Sine-Signal 22 and the 2.sup.nd derivate of the Cosine-Signal 23.

[0131] The vertical axis on both graphs is a relative number representing the 2.sup.nd derivate of the signals. It depends on the time interval between measurements of the signal ripple 18 on the Sine-Signal 22 and Cosine-signal 24, representing the sample rate of the analog-to-digital converter 13, 14, 17 analysing the Sine-signal 22 and Cosine-signal 23. The larger the error, the larger will be these signal levels. The horizontal axis of FIG. 8A represents the position of the position sensor 2 in electrical degrees and the horizontal axis of FIG. 8B is a relative number representing 20 swapping cycles (10 swapping periods).

[0132] An offset error in the first signal processing unit 5 and/or second signal processing unit 6 is indicated by a constant 2.sup.nd derivate pulse over position. The 2.sup.nd derivate magnitude is also constant over position.

[0133] FIG. 9A shows the 2.sup.nd derivate of the Sine-signal 24 and Cosine-signal 25 of FIG. 6A referring to the gain error. FIG. 9B shows the magnitude of the 2.sup.nd derivates of FIG. 9A

[00007]$\left(\sqrt{{f^{}\left(\mathrm{Sine}-\mathrm{Signal}.Math..Math.24\right)}^2+{f^{}\left(\mathrm{Cosine}-\mathrm{Signal}.Math..Math.25\right)}^2}\right).$

FIG. 9A is split into two graphs due to the partial overlapping of the 2.sup.nd derivate of the Sine-Signal 24 and the 2.sup.nd derivate of the Cosine-Signal 25.

[0134] The diagrams of FIG. 9A and 9b otherwise correspond to FIG. 8A and 8b, especially with respect to the axis.

[0135] A gain error in the first signal processing unit 5 and/or second signal processing unit 6 is indicated by a non-constant 2.sup.nd derivate peak pulse pattern over position. The 2.sup.nd derivate magnitude is constant over position and time.

[0136] FIG. 10A shows the 2.sup.nd derivate of the Sine-signal 26 and Cosine-signal 27 of FIG. 7A referring to the phase shift error. FIG. 10B shows the magnitude of the 2.sup.nd derivates of FIG. 10A

[00008]$\left(\sqrt{{f^{}\left(\mathrm{Sine}-\mathrm{Signal}.Math..Math.26\right)}^2+{f^{}\left(\mathrm{Cosine}-\mathrm{Signal}.Math..Math.27\right)}^2}\right).$

FIG. 10A is split into two graphs due to the partial overlapping of the 2.sup.nd derivate of the Sine-Signal 22 and the 2.sup.nd derivate of the Cosine-Signal 23.

[0137] The diagrams of FIG. 10A and 10b otherwise correspond to FIG. 8A and 8b, especially with respect to the axis.

[0138] A phase shift error in the first signal processing unit 5 and/or second signal processing unit 6 is indicated by a non-constant 2.sup.nd derivate peak pulse pattern over position. The 2.sup.nd derivate magnitude is constant over position and time.

[0139] FIG. 11 shows a block diagram of a position sensor system 1 according to the prior art. The position sensor system 1 comprises a position sensor 2 with a first sensor output 3 and a second sensor output 4. The position sensor system 1 further comprises a signal processing unit 32 for processing, particularly amplifying and filtering, the signal of the first sensor output 3 and the second sensor output 4.

[0140] The signal processing unit 32 comprises a multiplexer 34 to multiplex between the first sensor output 3 and the second sensor output 4. The signal processing unit 32 further comprises an amplifier 11 and a filter 12.

[0141] The position sensor system 1 comprises a system output 33 providing the output of the signal processing unit 32.

[0142] The position sensor system 1 of FIG. 11 further comprises a control unit 10. The control unit 10 can be either integral with the position sensor system 1, i.e. on the same chip, or external of the position sensor system 1 and connected to the position sensor system 1 by e.g. a cable. FIG. 11 refers to an external control unit 10, as indicated by the connection points and lines between the position sensor system 1 and the control unit 10.

[0143] The control unit 10 in FIG. 11 comprises an analog-to-digital converter 17 for the system output 33. The output of the analog-to-digital converter 17 is processed by digital signal processing unit 15.

[0144] The control unit 10, especially the digital signal processing unit 15 must have knowledge which sensor output 3, 4 is currently processed by the signal processing unit 32. Therefore, the control unit 10, especially the digital signal processing unit 15 controls the multiplexer 34 of the signal processing unit 32 via a control line 35. This requires additional wiring between the position sensor system 1 and the external control unit 10. A further disadvantage of this variant is that in a rotating position sensor system 1, due to the sequential processing of both signals, both position sensor signals are not measured at the same position as the item to be measured will have moved by a certain amount between the measurements of the two position sensor signals, which is particularly disadvantageous for high speed systems, as this error increases with rotating speed.