General Sensor systems 1997 File under Discrete Semiconductors, S

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General Sensor systems 1997 File under Discrete Semiconductors, S

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General Sensor systems
1997 File under Discrete Semiconductors, SC17
Philips Semiconductors
Sensor systems
ANGLE MEASUREMENT Contents Principles standard set-ups Philips sensors angle measurement Real-life measurement applications Information advanced users applications Additional measurement set-ups Magnets Angle sensor eccentricity. Principles standard set-ups principle behind magnetoresistive angular measurement essentially simple: explained general section, effect naturally angular effect. resistance permalloy strip depends angle between internal magnetization vector permalloy strip direction current through When using effect sensors measuring angles, linearization using barber-pole sensor layout required original direct relationship between resistance angle Rocos2) valid.
General
achieve accurate measurement, only condition that internal magnetization vector permalloy directly follows external field. This done applying external field very much greater than internal field sensor `saturated'; with today's sensors, this normally achieved having magnetic field strength approximately kA/m sensor plane. this set-up, (Fig.3) angle measured directly detecting field-direction set-up independent Magnet field strength Magnetic drift with time Magnetic drift with temperature Ageing, Mechanical tolerances. which allows reduced system tolerances pre-trimming sensor. This solution adopted Philips KM110B modules. only precaution that need taken with this technique ensuring field directions during trimming match field directions after assembly. There ongoing development sensors that placed this `saturated' condition using steadily smaller field strengths this significantly reduces system costs, because relatively inexpensive normal ferrite magnets used rather than other, more costly permanent magnets. Note: Philips sensors modules have general been designed used with this `direct' method. However, there other techniques that used: information other methods, refer `Information advanced users applications' later this chapter angle measurement influence, fully possible, internal magnetization sensor application external magnetic field, magnetization follows closely possible external magnetic vector. recommended, typical `saturation' field kA/m applied, vector addition this external field with internal magnetization kA/m, result systematic error about This error eliminated during production Philips modules trimming.
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Permalloy
Current
MLC127
Fig.1 magnetization effect permalloy.
1997
Philips Semiconductors
Sensor systems
General
When using sensor/magnet combination angular measurement applications, magnet placed target, front sensor (which positioned that internal magnetization vector parallel that magnet reference point). When target turns, magnet rotated front sensor angle external field changes relative internal field permalloy strips. This causes internal magnetization vector sensor rotate angle aligning itself with external field (see Fig.2).
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kA/m
kA/m
MSB924
Fig.2 Internal field vectors align with stronger external field.
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Sensing accuracy with this set-up unaffected
shaft
magnet field strength magnet field strength drift with time magnet field strength drift with temperature magnet ageing mechanical tolerances
magnetic flux line
sensor
MSB927
Fig.3 Arrangement sensor magnet.
1997
Philips Semiconductors
Sensor systems
EXTENDING ANGLE RANGE From basic relationship (see Appendix magnetoresistive effect): Rocos2) easily shown that: sin2 sensor used non-linearized mode, then translates single rotation target (360°) into 720° output signal complete sine waves). This means that output signal magnetoresistive sensor offers good linearity only within angle range ±15° (where sine wave output acceptable application (for example there microprocessor system which convert output sine curve linear relationship), angle range extended ±35° (see Fig.4). Resolution reduced ends range, behaviour unaffected middle range. obtain solution angles range ±90°, sensors used (see Fig.5). they accurately positioned another mechanically, then electronically their output signals phase. Therefore output signals from sensors represent sin2 cos2 respectively, sin2/cos2 tan2, therefore easily calculated.
General
Note: sensors arranged parallel, (positioned degree another) this set-up excellent redundant set-up (although course angle measurement range will limited). With this set-up, both sensors influenced equally external magnet, redundancy achieved with only external magnet need signal conditioning reduced. Although principle set-up Fig.5 simple, factors have addressed before this solution measurement angles economically viable. Firstly, there economic combining sin2 cos2 signals into single signal representing angle answer this need, Philips developing ASIC (Fig.6) with required signal conditioning chip offering digital interfacing (solutions PWM, serial stream CAN.bus possible). Secondly, sensors have aligned mechanically exactly 45°. This achieved using advances magnetoresistive manufacturing technology, where overlapping sensor bridges etched same substrate, using photo-mask process. This process extremely high accuracy, more than sufficient this application
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magnet angle
signal
-180
-135
angle deg.
MBH659
KMZ10B
Fig.4 Angle measurement with KMZ10B.
1997
Philips Semiconductors
Sensor systems
General
handbook, full pagewidth
magnet sensor
signal
-180
-135
angle deg.
sensor a.sin2 -b.cos2
MBH658
Fig.5 Angle measurement with sensors.
sin(x) +VO1 -VO1 +VO2 -VO2 -cos(x) BUFFER ADC2 Vout ADC1 ALGORITHM ADJUSTMENT OUTPUT CURVE CHARACTERISTIC BUFFER Vout
RC-OSCILLATOR CLOCK GENERATOR
TEST/TRIM MODE
RESET
MBH735
VIA1
VIA2 OFFS1
OFFS2
VDDA
VDD1
VSSA
VDD2
Fig.6 Block diagram `one-chip' ASIC solution, UZZ9000.
1997
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Philips Semiconductors
Sensor systems
General
handbook, full pagewidth
MBH660
Fig.7 Layout KMZ41 chip.
Figure shows actual layout Philips KMZ41. provides resistor networks, connected individual Wheatstone bridges, aligned with shift their sensitive magnetic directions, producing required electrical shift. course, also possible align both bridges magnetically parallel each other they produce same output signal. that case, redundancy achieved using single sensor device. increasing number bridges, combination both principles achieved make, example, three-times redundant sensor fully redundant sensor that measure over full 90°, combination. Philips sensor modules angle measurement Based magnetoresistive sensors, Philips Semiconductors developed range ready-to-use magnetoresistive sensor modules contactless angle measurement offering following features: Offset, zero point sensitivity pre-trimmed assembly final encapsulated sensor simple calibration after assembly unnecessary) Integrated temperature compensation; protection. 1997
These ready-to-use modules with built signal conditioning electronics have several advantages: Output independent magnet tolerances, temperature coefficients, mechanical set-up other tolerances single linear output signal provided angles 180° variety output signals provided: analog (voltage current), Pulse Width Modulation (PWM) interfaces (e.g. I2C, CAN). Philips' KM110BH/2xxx family range modules using hybrid thick-film technology. circuits magnetic parameters these modules have been designed they used directly many applications, with further trimming adjustment, basis customized solutions. reduce system costs simplify application even further, family ASIC solutions development, some which contain both sensor conditioning electronics. combining both elements single encapsulation, pre-aligned systems offered which simply mounted normal PCB.
Philips Semiconductors
Sensor systems
addition ready-made modules, Philips Semiconductors willing undertake customised designs high volume applications excess 50,000 units), either specific hybrid integrated solutions. KMB110BH/21 MODULE SERIES Figure shows construction KM110BH/21 module, which based KMZ10B sensor available types: KM110BH/2130 KM110BH2190. They both based same circuit, trimmed differently: KM110BH/2130 trimmed higher amplification measures angles between -15° +15°, generating linear output signal; while KM110BH/2190 measures angles from approximately -45° +45° produces sinusoidal output. Both produce analog voltage signal. Figure shows output modules, function measured angle further details, refer Table KM110BH/2270 MODULE
General
KM110BH/2270 module, which based KMZ11B1 sensor, trimmed measure angles ranging from -35° +35° integrated input voltage stabilization. contrast other modules KM110BH/2 range, KM110BH/2270 analog current output signal mA), which converted voltage signal using simple resistor. output sinusoidal. This module extremely good resolution reproducibility (better than 0.001° hysteresis, which typically 0.02° very low. When designing encapsulation KM110BH/2270, necessary have pins hybrid bent into shape, avoid excessive force solder joints. this case, please order KM110BH/2270G. further details, refer Table
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19.05
0.25 0.05
0.25 0.05 2.54 2.54 standoff mounting
MBC703
16.933
0.08 0.76 0.08
Fig.8 Construction KM110BH/21.
1997
Philips Semiconductors
Sensor systems
General
handbook, full pagewidth
output signal
MBC705
external magnet KM110BH/2130, measurement range KM110BH/2190, measurement range
(deg)
Fig.9 Output characteristics KM110BH/2130 KM10BH/2190 modules.
Table
overview main characteristics Philips modules angle measurement KM110BH 21301 21902 sinusoidal 16.9 0.001 +125 2270 sinusoidal 23.6 20.3 0.001 +125 2430 linear 23.6 20.3 0.001 +125 2470 sinusoidal 23.6 20.3 0.001 +125 UNIT
PARAMETER
Angle range Output voltage3 Output current Output characteristic Supply voltage Substrate dimensions Resolution Temperature range
linear 16.9 0.001 +125
1997
Philips Semiconductors
Sensor systems
KM110BH/24 MODULE KM110BH/24 available versions based KMZ41: KM110BH/2430 trimmed measure angles between -15° +15°, generating linear output signal (non-linearity 1%); while KM110BH/2490 measures angles from approximately -35° +35° produces sinusoidal output. On-board protection circuitry makes these modules tolerant. Real-life angular measurement applications With angular measurement using magnetoresistive sensors, number possible applications very broad, replacing outperforming other types sensors variety applications, some which listed Table Amongst these numerous applications, undoubtedly most common automotive industry, where they used measure pedal throttle position. Table Typical applications angle sensors Automotive agricultural Pedal position Active suspension units Self-levelling systems Automatic headlight adjustment Medical Body brain scanners where accurate angle information vital build cross-sectional images Control joysticks tilting tables Games joysticks Spirit levels Valve control Material thickness Feedback systems belt control Wear detection Consumer Industrial REDUNDANT SYSTEMS
General
multiple sensors with identical behaviour implemented single piece silicon, magnetoresistive set-up ideal solution construction redundant systems, safety critical applications, example, such accelerator pedal. essential functional blocks typical redundant sensor system shown Fig.10. each sensor, signal first amplified. This stage also includes offset compensation determines characteristic output signal (sinusoidal linear). After temperature compensation, third stage provides additional trimming output signal allows inclusion diagnostic functions (for example, wire connected short circuit conditions). final stage provides additional protection, against short circuits (between supply voltage output signal, example) overvoltage (for example, module supply accidentally connected battery supply).
1997
Philips Semiconductors
Sensor systems
General
handbook, full pagewidth
redundant sensor
offset compensation temperature trimming signal compensation characteristic
signal conditioning
MSB923
Fig.10 Functional block diagram module with redundancy.
Information advanced users applications ADDITIONAL MEASUREMENT SET-UPS
Linear
linear angle measurement, strength external magnetic field used within normal sensitivity levels sensor measures resulting field strength rotating magnet. seen from Fig.11, signal linearity weak field method allows angles ±90° measured without correction sinusoidal shape wave. This technique used most competing angle measurement set-ups. However, since magnet's properties directly influence sensor output, measurement equipment must carefully calibrated after assembled calibration material ageing possible all. Only with very well defined magnetic system pre-calibrated circuit used defining such system difficult expensive, tolerances caused thermal sensitivity magnet mechanical set-up.
using set-up with magnets placed rotatable frame, angular rotations around ±85° measured through symmetrical positioning magnets, effect magnet position eliminated. Figure shows practical arrangement, which basically acts contactless potentiometer. However, response perfectly sinusoidal magnetic influences axis.
1997
Philips Semiconductors
Sensor systems
General
handbook, full pagewidth
signal
KMZ10
/degrees
weak field
strong field
MBH716
Fig.11 Sensor response different magnetic fields.
handbook, halfpage substrate
magnet RES190
,,,,,,, ,,,,,,, ,,,,,,, ,,,, ,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,,
KMZ10C steel
magnet RES190
MBH651
Fig.12 Contactless potentiometer angle measurement. 1997
Philips Semiconductors
Sensor systems
General
Extending measurement angle greater than
With second fixed magnet, possible adjust sensing distance angle range further extended, cope with angles greater than ±90°. This lead increased mechanical tolerances although using magnets same material, temperature variations disregarded. Figure shows typical set-up. MAGNETS main requirement magnet that should strong, ensure tolerances negligible, obviously cost space must also considered, according individual application requirements. Table compares three commercially available Samarium-Cobalt (SmCo) magnets suitable angle measurement applications. These magnets have tolerance their magnetization direction which affects angle measurement. This tolerance, which should taken into account mechanical calibration possible symmetry axis module rotation axis magnet should identical, although axes shifted slightly, affect sensing accuracy neglected because field lines magnet parallel. Measurements with magnets with face 11.2 oriented towards sensor allow eccentric tolerances assuming acceptable tolerance 0.25 acceptable tolerance 0.5%. Evidently, magnet smaller, these values should proportionately reduced.
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,,,,,,,, ,,,,,,,, ,,,,,,,, ,,,, ,,,,,,,, ,,,, ,,,,,,,,
adjustment mechanism e.g. screw sensor
plain bearing
adjustment magnet
,,,,
substrate
moved magnet
axis rotation
MBH656
Fig.13 Angle sensor with adjustable measuring range.
1997
Philips Semiconductors
Sensor systems
Table Typical values various dimensions Sm2Co17 magnets DIMENSIONS(1) (mm) 11.2 Notes Magnetization always parallel latter dimension. distance between magnet front sensor. Tolerance' maximum deviation which change sensor output signal <0.5% full scale output. Eccentricity' maximum deviation magnet rotational axis from sensor rotational axis which change sensor output signal <0.5% full scale output. d(2) (mm) TOLERANCE d(3) (mm) ±0.30 ±0.15 ±0.30 ECCENTRICITY(4) (mm) ±0.25 ±0.15 ±0.20
General
MATERIAL Sm2Co17
Tamb (°C)
ANGLE SENSOR ECCENTRICITY angle measurement using direct measurement technique, ideal arrangement with homogeneous parallel field. Although large magnets fulfil this requirement, there usually compromise between magnet size corresponding tolerances sensor cost considerations. sensor magnet rotation axes line, sensor output characteristics follow approximately following signal voltage relationship: Vo(0) sin2
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sensor
field lines
magnet
MBH655
Fig.14 Angle sensor with eccentric sensor position.
1997
Philips Semiconductors
Sensor systems
However, depending sensor position relation magnet angle measured (see Fig.14), offsets sensitivity changes occur. These conditions alter ideal relationship described equation above.Angle tolerance values calculated using following relationship: sin2( magnetic constant and, provided width length magnet approximately equal, calculated from following equation: Table
General
Typical values Sm2Co17 magnets (degree/mm2) 1.35 0.74
MAGNET DIMENSIONS 11.2
positions y-axis, there sensitivity change with maximum tolerance level ±45° ±135° (see Fig.15); diagonal positions, offset tolerance occurs with maximum ±90° ±180° (see Fig.16).
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V0/V0 -0.2 -0.4 -0.6 -0.8 -1.0
MBH654
0°/180°
90°/-90°
Fig.15 Response tolerances sensor position y-axes.
1997
Philips Semiconductors
Sensor systems
General
handbook, full pagewidth
V0/V0 -0.2 -0.4 -0.6 -0.8 -1.0
MBH653
45°/-135°
45°/135°
Fig.16 Response tolerances sensor position diagonals.
Table
Typical tolerance values (DEGREES)
Some typical values when shown Table adjusted angle sensor maximum tolerance 1/2CRm2 ±15° range between 15°, tolerance increases approximately linearly from zero this value. Above ±15° sinusoidal function given above effective taken into account sensors. Figure gives maximum tolerances ±15° different magnets function eccentricity radius general, tolerance about 0.3° provided corresponds about magnetic dimensions
(DEGREES) 0/90/. 45/135/.
0.134
0.87 0.25
Single sensor system
assume that single, encapsulated angle sensor with eccentricity will adjusted mechanically specified output voltage then tolerances zero. Then over useful angle range ±45°, original offset tolerances transformed into resultant tolerance: Rm2sin2
1997
Philips Semiconductors
Sensor systems
General
handbook, full pagewidth
MBH652
||/°
Sm2Co17-magnets
11.2, 5.5,
Rm/mm
Fig.17 Maximum angle tolerances
Double sensor system (KMZ41)
this case, both sensors influenced differently resulting tolerance calculated from deviations response curves. C.Rm2 sufficiently small, angle calculated from relation output signals arc-tan function, then resulting measuring tolerance described cos4 sin2( This leads worst case tolerance occurring tolerance zero 22.5°, 67.5° 112.5°. These zero positions used adjust sensor highest precision measurements. sensors adjusted this way, maximum tolerance limited Rm2.
1997

General Sensor systems 1997 File under Discrete Semiconductors, S

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