Related Manuals for Philips KMZ51
Summary of Contents for Philips KMZ51
- Page 1 APPLICATION NOTE Electronic Compass Design using KMZ51 and KMZ52 AN00022 Philips Semiconductors...
- Page 2 Both sensors rely on the magnetoresistive effect and provide the required sensitivity and linearity to measure the weak magnetic field of the earth. While the KMZ51 is a single axis field sensor, the KMZ52 comprises a two-dimensional field sensor, as it is required for a compass, within one package. Both devices are equipped with integrated set/reset and compensation coils.
- Page 3 Philips Semiconductors Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 APPLICATION NOTE Electronic Compass Design using KMZ51 and KMZ52 AN00022 Author: Thomas Stork Philips Semiconductors Systems Laboratory Hamburg, Germany Keywords Earth´s magnetic field Magnetoresistive sensors 8-segment compass High resolution compass...
- Page 4 KMZ51 and KMZ52 SUMMARY This paper describes how to realize electronic compass systems using the magnetoresistive sensors KMZ51 and KMZ52 from Philips Semiconductors. Therefore, firstly an introduction to the characteristics of the earth´s magnetic field is given. In the following, the main building blocks of an electronic compass are shown, which are two sensor elements for measuring the x- and y-components of the earth field in the horizontal plane, a signal conditioning unit and a direction determination unit.
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Page 5: Table Of Contents
4.1.1 The Magnetoresistive Effect ....................12 4.1.2 Optimization of Sensor Characteristic using Barber Pole Structures ........13 4.1.3 Bridge Configuration ......................13 4.2 Set/Reset and Compensation Coils....................14 4.3 Philips MR Sensors for Compass Systems..................15 SIGNAL CONDITIONING UNIT (SCU)......................16 5.1 Requirements...........................16 5.2 Offset Compensation ........................17 5.3 Sensitivity Difference (∆S) Compensation..................19... - Page 6 Philips Semiconductors Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 LIST OF FIGURES Figure 1 Earth´s magnetic field ........................... 8 Figure 2 Earth field vector ........................... 9 Figure 3 Functional block diagram of an electronic compass ................10 Figure 4 The magnetoresistive effect in permalloy ...................
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Page 7: Introduction
Following a description of Philips´ magnetoresistive sensors for compass applications, the design of each building block is covered in detail. Here, both hardware and software realisations are shown. Further sections are dedicated to special items like interference field calibration, true north calibration, tilt compensation and system accuracy. -
Page 8: Earth´s Magnetic Field
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 EARTH´S MAGNETIC FIELD The magnetic field of the earth is the physical quantity to be evaluated by a compass. Thus, an understanding of its basic properties is required, when designing a compass. Figure 1 gives an illustration of the field shape. -
Page 9: Figure 2 Earth Field Vector
Electronic Compass Design using AN00022 KMZ51 and KMZ52 The azimuth is the reading quantity of a compass. Throughout this paper, α is counted clockwise from magnetic north, i.e. north is 360° or 0°, east is 90°, south is 180°, west is 270°. -
Page 10: Building Blocks Of An Electronic Compass
90 degrees with respect to each other. Philips´ magnetoresistive sensor technology is an optimum choice for measuring weak magnetic fields like the earth´s field. The KMZ52 is a sensor device, which is perfectly matched to this application, as it comprises two extremely sensitive field sensors in the required configuration in one SO16 package. - Page 11 Electronic Compass Design using AN00022 KMZ51 and KMZ52 the compensation of sensitivity differences between the x- and the y- field sensor. Optional features for high performance systems are temperature compensation of sensitivity and compensation of the error due to non- orthogonality between the sensors.
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Page 12: Magnetoresistive (Mr) Sensors For Compass Applications
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 4. MAGNETORESISTIVE (MR) SENSORS FOR COMPASS APPLICATIONS The intention of this section is to describe the basic principles of magnetoresistive sensors, which a compass designer should know. A more detailed description of the magnetoresistive effect can be found in [3]. -
Page 13: Optimization Of Sensor Characteristic Using Barber Pole Structures
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 4.1.2 Optimization of Sensor Characteristic using Barber Pole Structures Figure 5a illustrates the sensor characteristic according to (2). For small magnitudes of Hy, the sensitivity is very low and non-linear. Furthermore, this characteristic does not allow to detect, whether Hy is positive or negative. -
Page 14: Set/Reset And Compensation Coils
Figure 8 Fields generated by set/reset and compensation coil Philips MR sensors dedicated for compass applications are available with integrated set/reset and compensation coils, saving the additional cost and effort to provide external coils. Furthermore, as integrated... -
Page 15: Philips Mr Sensors For Compass Systems
KMZ52 to form a three-dimensional sensor, in order to compensate for tilt, as will be described in section 9. Figure 9 shows a simplified circuit diagram of the KMZ51, showing the MR resistor bridge as well as the set/reset and compensation coils. Table 1 provides an overview on Philips´ compass sensor portfolio. -
Page 16: Signal Conditioning Unit (Scu)
Philips Semiconductors Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 5. SIGNAL CONDITIONING UNIT (SCU) 5.1 Requirements The SCU consists of two separate “channels” fulfilling the basic task of amplifying the x- and y-field sensor output voltages (refer to Figure 3). Considering a minimum earth field strength in the sensor plane of approximately 15 A/m and a sensor sensitivity of typically 80 mV/(kA/m) (at Vcc = 5V, refer to Table 1), an MR sensor will deliver an amplitude of approximately 1.2 mV, when rotated in that field. -
Page 17: Offset Compensation
Electronic Compass Design using AN00022 KMZ51 and KMZ52 To compensate for sensitivity differences ∆S, the SCU should allow to trim its output voltages for equal amplitudes when rotated in the earth field. If high accuracy is desired over a wide temperature range, also an automatic compensation of sensitivity temperature drift should be implemented. -
Page 18: Figure 12 Timing Diagram For Flipping Circuit
Philips Semiconductors Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 flipping current IF time internal magnetization pre-amp Vx,y Offset Vo Vx,y time filter time Vx,y time MBH618_1 Figure 12 Timing diagram for flipping circuit (a) voltage at preamp output; (b) voltage at filter output;... -
Page 19: Sensitivity Difference (∆S) Compensation
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 5.3 Sensitivity Difference (∆S) Compensation At a given temperature, ∆S can be compensated by adjusting the SCU for equal output voltage swings Vy,pp and Vx,pp during compass rotation. The output voltage swings can be equalized by adjusting the amplification of one SCU channel. -
Page 20: Non-Orthogonality Compensation
Practically, the compensation field can be generated by supplying a current through an appropriate coil near the sensor. As already pointed out, Philips MR sensors for compass applications come with an integrated compensation coil, allowing to apply the electro-magnetic feedback method without the need for any external coils. -
Page 21: Circuit Design
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 5.5 Circuit Design Figure 15 shows a circuit for one SCU channel (i.e. one field direction Hx or Hy), including pre-amplification, offset compensation by flipping and temperature compensation of sensitivity by electro-magnetic feedback. -
Page 22: Flipping Generator (Block1)
For a low-to-high transition at the output of OP1, C5/R18 forces TR1 to conduct, discharging C6 and providing a negative current pulse through the coil. KMZ51 and KMZ52 both require flip current pulses of typically ±1A for a duration of 3µs. To drive that current controlled by the OP output, TR1 and TR2 should be Darlington transistors. -
Page 23: Pre-Amplifier (Block 2)
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 5.5.3 Pre-amplifier (block 2) The flipped sensor signal is amplified here by a factor of R4/Rbridge, where Rbridge is the resistance of the sensor bridge. Due to the electro-magnetic feedback used in this circuit, the pre-amp´s output will be virtually zero, when the closed loop control has settled. -
Page 24: Scu Without Electro-Magnetic Feedback
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 5.5.8 SCU without electro-magnetic feedback If no temperature compensation of sensor sensitivity is required, the electro-magnetic feedback loop can be interrupted by omitting the compensation coil driver (block 6). Block 5 is still required as low pass filter in order to suppress flipping spikes on the signal line. -
Page 25: Direction Determination Unit (Ddu)
Philips Semiconductors Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 6. DIRECTION DETERMINATION UNIT (DDU) 6.1 8-Segment Compass If applications require a rough direction indication only, then a compass set-up is sufficient, which identifies the nearest of the eight cardinal or intermediate points (e.g. N, NW, S, SE, ...). This information can be gained from the SCU outputs without evaluating the arctan function in equation (1). -
Page 26: High Resolution Compass
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 6.2 High Resolution Compass A compass with high accuracy is required for example in navigation systems. Here, the compass together with a measurement of the travelled distance are used to determine the actual position as long as no GPS signals can be received, e.g. -
Page 27: Interference Field Calibration
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 7. INTERFERENCE FIELD CALIBRATION In practice, the earth field at the compass may be superimposed by other magnetic fields or distorted by nearby ferrous materials. An efficient compensation of such effects is required in order to achieve reliable azimuth readings. -
Page 28: Figure 21 Principle Of Bidirectional Calibration
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 such strong fields, that the amplifiers of the SCU are overdriven. In this case, accurate measurement of the interference field and thus compensation are not possible. Interference field compensation ideally means, to convert the shifted and/or deformed test diagram into a circle around the centre (0,0). - Page 29 -Hix and -Hiy at the respective sensors. Using Philips magnetoresistive sensors KMZ51 or KMZ52, this task can be fulfilled straight forward by applying appropriate currents to the compensation coils of the respective sensors. In systems using a microcontroller, the compensation can be done by subtraction of the interference field components from the respective sensor output signals.
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Page 30: True North Calibration
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 8. TRUE NORTH CALIBRATION Once the azimuth has been measured with a compass, one has to be aware, that this indicates the heading direction relative to MAGNETIC north. However, in most practical cases, the heading direction relative to GEOGRAPHIC or TRUE north is required in order to allow navigation by means of a map. -
Page 31: Tilt Compensation
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 TILT COMPENSATION As pointed out in section 2, it is the horizontal (i.e. perpendicular to gravity) component of the geomagnetic field, that points to magnetic north. To measure this horizontal component, a compass system as described so far must be positioned, such that the sensitive axes of its field sensors are also in the horizontal plane. -
Page 32: Figure 23 Tilt Error Magnitudes
Philips Semiconductors Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 shows tilt error versus tilt angle for two loactions on earth. Inclination values for locations world wide are available at [1]. 70,00 60,00 Hamburg, inclination = 68° 50,00... -
Page 33: Figure 25 Electronically Gimbaled Compass
3-axes field sensor system can be built up with a dual sensor KMZ52 for the x and y axes and a single sensor KMZ51 for the z axis. For pitch and roll sensing, gravity sensors as compact devices in IC packages are available, realized by combining micro-machining and integrated circuit technology. -
Page 34: System Accuracy
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 10. SYSTEM ACCURACY Table 2 summarizes the main error influences on a compass system together with methods for calibration, as discussed in the respective sections of this paper. In all equations, α is the real azimuth. -
Page 35: Application Examples
Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 11. APPLICATION EXAMPLES Following block diagrams represent ideas for the realization of complete compass systems. The functional blocks for signal conditioning and direction determination shown here have been described in earlier sections of this paper. -
Page 36: Figure 28 8-Segment Compass With Microcontroller
Philips Semiconductors Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 Signal Conditioning and Direction Determination Unit (SCU+DDU) (see section 5.5.9) 2-dimensional field sensor KMZ52 Microcontroller Software: compensation Flip - Flipping clock Iflip coil coil generation driver - Offset-elimination (section 5.2) -
Page 37: References
Status Report of Repeat Data At the WDC-A, (Summary of data from geophysical observatories world wide) http://www.ngdc.noaa.gov/seg/potfld/mrepeat1.shtml Data sheet: KMZ52 Magnetic Field Sensor Philips Semiconductors Data Handbook SC17 including CD-ROM: Semiconductor Sensors Philips Semiconductors, 1998 Web site of Philips Semiconductors http://www.philips.semiconductors.com/handbook/various_39.html... -
Page 38: Appendix 1 List Of Abbreviations
Philips Semiconductors Application Note Electronic Compass Design using AN00022 KMZ51 and KMZ52 APPENDIX 1 List of abbreviations magnetic field vector magnetic field strength He(x,y) magnetic field strength of earth´s field (x,y component) Hi(x,y) magnetic field strength of interference field (x,y component)