1998 File under Discrete Semiconductors, SC17 Philips Semiconduct
|
|
|
Top Searches for this datasheet
1998 File under Discrete Semiconductors, SC17
Philips Semiconductors
Magnetic field sensors
GENERAL INTRODUCTION Contents Operating principles Philips magnetoresistive sensors Flipping Effect temperature behaviour Using magnetoresistive sensors Further information advanced users effect Linearization Flipping Temperature compensation.
General
Fig.1 Philips magnetoresistive sensors.
1998
Philips Semiconductors
Magnetic field sensors
range magnetoresistive sensors characterized high sensitivity detection magnetic fields, wide operating temperature range, stable offset sensitivity mechanical stress. They therefore provide excellent means measuring both linear angular displacement under extreme environmental conditions, because their very high sensitivity means that fairly small movement actuating components example, cars machinery (gear wheels, metal rods, cogs, cams, etc.) create measurable changes magnetic field. Other applications magnetoresistive sensors include rotational speed measurement current measurement. Examples where their properties good effect found automotive applications, such wheel speed sensors motor management systems position sensors chassis position, throttle pedal position measurement. Other examples include instrumentation control equipment, which often require position sensors capable detecting displacements region tenths millimetre even less), electronic ignition systems, which must able determine angular position internal combustion engine with great accuracy. Finally, because their high sensitivity, magnetoresistive sensors measure very weak magnetic fields thus ideal application electronic compasses, earth field correction traffic detection. sensors used maximum advantage, however, important have clear understanding their operating principles characteristics, their behaviour affected external influences their magnetic history. Operating principles Magnetoresistive (MR) sensors make magnetoresistive effect, property current-carrying magnetic material change resistivity presence external magnetic field (the common units used magnetic fields given Table Table Common magnetic units
General
handbook, halfpage
Permalloy
Current
MLC127
Fig.2 magnetoresistive effect permalloy.
Figure shows strip ferromagnetic material, called permalloy (20% Ni). Assume that, when external magnetic field present, permalloy internal magnetization vector parallel current flow (shown flow through permalloy from left right). external magnetic field applied, parallel plane permalloy perpendicular current flow, internal magnetization vector permalloy will rotate around angle result, resistance permalloy will change function rotation angle given
material parameters achieve optimum sensor characteristics Philips Ni19Fe81, which high value magnetostriction. With this material, order more information materials, Appendix obvious from this quadratic equation, that resistance/magnetic field characteristic non-linear addition, each value necessarily associated with unique value (see Fig.3). more details essentials magnetoresistive effect, please refer Section "Further information advanced users" later this chapter Appendix which examines effect detail.
kA/m 1.25 mTesla air) Gauss basic operating principle sensor shown Fig.2.
1998
Philips Semiconductors
Magnetic field sensors
General
this basic form, effect used effectively angular measurement some rotational speed measurements, which require linearization sensor characteristic. series sensors, four permalloy strips arranged meander fashion silicon (Fig.4 shows example, pattern KMZ10). They connected Wheatstone bridge configuration, which number advantages: Reduction temperature drift Doubling signal output sensor aligned factory.
handbook, halfpage
MLC128
Fig.3
resistance permalloy function external field.
handbook, full pagewidth
,,,,,,,,,, ,,,,, ,,,,,, ,,,,, ,,,,,, ,,,,, ,,,,,, ,,,,, ,,,,, ,,,,,, ,,,,, ,,,,,, ,,,,,, ,,,,, ,,,,,, ,,,,, ,,,,, ,,,,,,
MBC930
Fig.4 KMZ10 chip structure.
1998
Philips Semiconductors
Magnetic field sensors
further resistors, included, shown Fig.5. These trimming sensor offset down (almost) zero during production process.
General
some applications however, effect used best advantage when sensor output characteristic been linearized. These applications include: Weak field measurements, such compass applications traffic detection; Current measurement;
MLC129
Rotational speed measurement. explanation characteristic linearized, please refer Section "Further information advanced users" later this chapter. Philips magnetoresistive sensors
handbook, halfpage
Based principles described, Philips family basic magnetoresistive sensors. main characteristics sensors given Table
Fig.5
Bridge configuration with offset trimmed zero, resistors
Table
Main characteristics Philips sensors FIELD RANGE (kA/m)(1) -0.5 +0.5 -0.05 +0.05 -2.0 +2.0 -2.0 +2.0 -7.5 +7.5 100(3) -0.2 +0.2 -0.2 +0.2 SENSITIVITY LINEARIZE Rbridge -EFFECT 16.0 22.0 16.0 16.0 APPLICATION EXAMPLES compass, navigation, metal detection, traffic control current measurement, angular linear position, reference mark detection, wheel speed angular measurement compass, navigation, metal detection, traffic control
SENSOR TYPE KMZ10A KMZ10A1(2) KMZ10B KMZ11B1 KMZ10C KMZ41 KMZ50 KMZ51 Notes
PACKAGE SOT195 SOT195 SOT195 SOT195
air, kA/m corresponds 1.25 Data given operation with switched auxiliary field. Recommended field strength.
1998
Philips Semiconductors
Magnetic field sensors
Flipping internal magnetization sensor strips stable positions. reason sensor influenced powerful magnetic field opposing internal aligning field, magnetization flip from position other, strips become magnetized opposite direction (from, example, `+x' `-x' direction). demonstrated Fig.6, this lead drastic changes sensor characteristics.
General
field (e.g. `-Hx') needed flip sensor magnetization, hence characteristic, depends magnitude transverse field `Hy': greater field `Hy', smaller field `-Hx'. This follows naturally, since greater field `Hy', closer magnetization's rotation approaches 90°, hence easier will flip into corresponding stable position `-x' direction. Looking curve Fig.7 where kA/m, such transverse field sensor characteristic stable positive values reverse field kA/m required before flipping occurs. kA/m however, sensor will flip even smaller values `Hx' approximately kA/m).
MLC130
handbook, halfpage
(mV)
(kA/m)
reversal sensor characteristics
Fig.6 Sensor characteristics.
MLC131
handbook, full pagewidth
(mV) kA/m
kA/m (kA/m)
Fig.7 Sensor output `Vo' function auxiliary field `Hx' several values transverse field `Hy'.
1998
Philips Semiconductors
Magnetic field sensors
Figure also shows that flipping itself instantaneous, because permalloy strips flip same rate. addition, illustrates hysteresis effect exhibited sensor. more information flipping, Section "Further information advanced users" later this chapter Appendix magnetoresistive effect. Effect temperature behaviour
General
handbook, halfpage
MBB897
bridge
Figure shows that bridge resistance increases linearly with temperature, bridge resistors' temperature dependency (i.e. permalloy) typical KMZ10B sensor. data sheets show also spread this variation manufacturing tolerances this should taken into account when incorporating sensors into practical circuits. addition bridge resistance, sensitivity also varies with temperature. This seen from Fig.9, which plots output voltage against transverse field `Hy' various temperatures. Figure shows that sensitivity falls with increasing temperature (actual values given every sensor datasheets). reason this rather complex related energy-band structure permalloy strips.
Tamb
Fig.8 Bridge resistance KMZ10B sensor function ambient temperature.
1998
Philips Semiconductors
Magnetic field sensors
General
MLC134
handbook, full pagewidth
(mV/V)
Tamb
125o
operating range
(kA/m)
Fig.9
Output voltage `Vo' fraction supply voltage KMZ10B sensor function transverse field `Hy' several temperatures.
1998
Philips Semiconductors
Magnetic field sensors
Figure similar Fig.9, with sensor powered constant current supply. Figure shows that, this case, temperature dependency sensitivity significantly reduced. This direct result increase bridge resistance with temperature (see Fig.8), which
General
partly compensates fall sensitivity increasing voltage across bridge hence output voltage. Figure demonstrates therefore advantage operating with constant current.
MLC135
handbook, full pagewidth
Tamb
(mV/V)
125o
operating range
(kA/m)
Fig.10 Output voltage `Vo' KMZ10B sensor function transverse field `Hy' several temperatures.
1998
Philips Semiconductors
Magnetic field sensors
Using magnetoresistive sensors excellent properties magnetoresistive sensors, including their high sensitivity, stable offset, wide operating temperature frequency ranges ruggedness, make them highly suitable wide range automotive, industrial other applications. These looked more detail other chapters this book; some general practical points about using sensors briefly described below. ANALOG APPLICATION CIRCUITRY many magnetoresistive sensor applications where analog signals measured measuring angular position, linear position current measurement, example), good application circuit should allow sensor offset sensitivity adjustment. Also, sensitivity many magnetic field sensors drift with temperature, this also needs compensation. basic circuit shown Fig.11. first stage, sensor signal pre-amplified offset adjusted. After temperature effects compensated, final amplification sensitivity adjustment takes place last stage. This basic circuit extended with additional components meet specific requirements modified obtain customized output characteristics (e.g. different output voltage range current output signal). Philips magnetoresistive sensors have linear sensitivity drift with temperature temperature sensor with
General
linear characteristics required compensation. Philips series well suited this purpose, their positive Temperature Coefficient (TC) matches well with negative sensor. degree compensation controlled with resistors special op-amps, with very offset temperature drift, should used ensure compensation constant over large temperature ranges. Please refer part this book more information temperature sensors; also Section "Further information advanced users" later this chapter more detailed description temperature compensation using these sensors. USING MAGNETORESISTIVE SENSORS WITH COMPENSATION
COIL
general magnetic field current measurements useful apply `null-field' method, which magnetic field (generated current carrying coil), equal magnitude opposite direction, applied sensor. Using this `feedback' method, current through coil direct measure unknown magnetic field amplitude advantage that sensor being operated zero point, where inaccuracies result tolerances, temperature drift slight non-linearities sensor characteristics insignificant. detailed discussion this method covered Chapter "Weak field measurements".
handbook, full pagewidth
offset adjustment KTY82-210 TLC2272
sensitivity adjustment
KMZ10B
op-amp
op-amp (with resistive load greater than
MBH687
Fig.11 Basic application circuit with temperature compensation offset adjustment.
1998
Philips Semiconductors
Magnetic field sensors
Further information advanced users EFFECT sensors employing effect, resistance sensor under influence magnetic field changes moved through angle given shown that
General
handbook, halfpage
,,,,,, ,,,, ,,,, ,,,,
Barber pole Magnetization
MLC125
Permalloy
where regarded material constant comprising called demagnetizing anisotropic fields. Applying equations equation leads
Fig.12 Linearization magnetoresistive effect.
which clearly shows non-linear nature effect. More detailed information derivation formulae effect found Appendix LINEARIZATION magnetoresistive effect linearized depositing aluminium stripes (Barber poles), permalloy strip angle strip axis (see Fig.12). aluminium much higher conductivity than permalloy, effect Barber poles rotate current direction through (the current flow assumes `saw-tooth' shape), effectively changing rotation angle magnetization relative current from 45°.
Wheatstone bridge configuration also used linearized applications. pair diagonally opposed elements, Barber poles +45° strip axis, while another pair they -45°. resistance increase pair elements external magnetic field thus `matched' decrease resistance equal magnitude other pair. resulting bridge imbalance then linear function amplitude external magnetic field plane permalloy strips, normal strip axis.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, halfpage
equation linear where H/Ho shown Fig.7. Likewise, sensors using Barber poles arranged angle -45°, equation derives
MLC126
This mirror image characteristic Fig.7. Hence using Wheatstone bridge configuration ensures bridge imbalance linear function amplitude external magnetic field. FLIPPING
Fig.13 resistance permalloy function external field after linearization (compare with Fig.6).
sensors using Barber poles arranged angle +45° strip axis, following expression sensor characteristic derived (see Appendix effect):
described body chapter, Fig.7 shows that flipping instantaneous also illustrates hysteresis effect exhibited sensor. This figure Fig.14 also shows that sensitivity sensor falls with increasing `Hx'. Again, this expected since moment imposed magnetization `Hx' directly opposes that imposed `Hy', thereby reducing degree bridge imbalance hence output signal given value `Hy'.
handbook, full pagewidth
(mV)
MLC132
kA/m kA/m kA/m
(kA/m)
Fig.14 Sensor output `Vo' function transverse field `Hy' several values auxiliary field `Hx'.
1998
Philips Semiconductors
Magnetic field sensors
following general recommendations operating KMZ10 applied: ensure stable operation, avoid operating sensor environment where likely subjected negative external fields (`-Hx'). Preferably, apply positive auxiliary field (`Hx') sufficient magnitude prevent likelihood flipping within intended operating range (i.e. range `Hy'). Before using sensor first time, apply positive auxiliary field least kA/m; this will effectively erase sensor's magnetic `history' will ensure that residual hysteresis remains (refer Fig.6). minimum auxiliary field that will ensure stable operation, because larger auxiliary field, lower sensitivity, actual value will depend value KMZ10B sensor, minimum auxiliary field approximately kA/m recommended; guarantee stable operation values sensor should operated auxiliary field kA/m. These recommendations (particularly first one) define kind Safe Operating ARea (SOAR) sensors. This illustrated Fig.15, which example (for KMZ10B sensor) SOAR graphs found data sheets.
General
greater auxiliary field, greater disturbing field that tolerated before flipping occurs. auxiliary fields above kA/m, SOAR graph shows that sensor completely stable, regardless magnitude disturbing field. also seen from this graph that SOAR extended values `Hy'. Fig.15, (for KMZ10B sensor), extension kA/m shown. TEMPERATURE COMPENSATION With magnetoresistive sensors, temperature drift negative. circuits manufactured SMD-technology which include temperature compensation briefly described below. first circuit basic application circuit already given (see Fig.11). provides average (sensor-to-sensor) compensation sensitivity drift with temperature using KTY82-210 silicon temperature sensor. also includes offset adjustment (via R1); gain adjustment performed with second op-amp stage. temperature sensor part amplifier's feedback loop thus increases amplification with increasing temperature. temperature dependant amplification temperature coefficient first op-amp stage approximately:
MLC133
handbook, halfpage
(kA/m)
,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,,
temperature dependent resistance KTY82. values taken certain reference temperature. This usually other applications different reference temperature more suitable. Figure shows example with commonly-used instrumentation amplifier. circuit divided into stages: differential amplifier stage that produces symmetrical output signal derived from magnetoresistive sensor, output stage that also provides reference ground amplification stage. compensate negative sensor drift, with above circuit amplification again given equal positive temperature coefficient, means KTY81-110 silicon temperature sensor feedback loop differential amplifier.
SOAR
(kA/m)
Fig.15 SOAR KMZ10B sensor function auxiliary field `Hx' disturbing field `Hd' opposing `Hx' (area
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
KTY82-110
offset
KMZ10B
MLC145
Fig.16 KMZ10B application circuit with instrumentation amplifier.
amplification input stage (`OP1' `OP2') given
given negative `TC' magnetoresistive sensor required amplification input stage `A1', resistance `RA' `RB' calculated (12)
where temperature dependent resistance KTY82 sensor bridge resistance magnetoresistive sensor. amplification complete amplifier calculated positive temperature coefficient (TC) amplification
(13)
(10)
where TCKTY temperature coefficient sensor temperature coefficient amplifier. This circuit also provides adjustment gain offset voltage magnetic-field sensor.
(11)
1998
Philips Semiconductors
Magnetic field sensors
WEAK FIELD MEASUREMENTS Contents: Principles weak field sensing Philips sensors weak field measurement Application examples Test modules. Principles weak field sensing Measurement weak magnetic fields such earth's geomagnetic field (which typical strength between approximately A/m), fields resulting from very small currents, requires sensor with very high sensitivity. With their inherent high sensitivity, magnetoresistive sensors extremely well suited sensing very small fields. Philips' magnetoresistive sensors nature bi-stable (refer Appendix `Standard' techniques used stabilize such sensors, including application strong field x-direction (Hx) from permanent stabilization magnet, unsuitable they reduce sensor's sensitivity fields measurement, y-direction (Hy). (Refer Appendix Fig. A2.2). avoid this loss sensitivity, magnetoresistive sensors instead stabilized applying brief, strong non-permanent field pulses very short duration µs). This magnetic field, which easily generated simply winding coil around sensor, same stabilizing effect permanent magnet, only present very short duration, after pulse there loss sensitivity. Modern magnetoresistive sensors specifically designed weak field applications incorporate this coil silicon. However, when measuring weak fields, second order effects such sensor offset temperature effects greatly reduce both sensitivity accuracy sensors. Compensation techniques required suppress these effects. OFFSET COMPENSATION `FLIPPING' Despite electrical trimming, sensors have maximum offset voltage ±1.5 mV/V. addition this static offset, offset drift temperature variations about (µV/V)K-1 expected assuming ambient temperature resulting offset order mV/V.
General
Taking these factors into account, with external field sensor with typical sensitivity mV/V (kA/m)-1 have offset equivalent field A/m, which itself about four times strength typical weak field such earth's geomagnetic field. Clearly, measures compensate sensor offset value have implemented weak field applications. technique called `flipping' (patented Philips) used control sensor. Comparable `chopping' technique used amplification small electrical signals, only stabilizes sensor also eliminates described offset effects. When bi-stable sensor placed controlled, reversible external magnetic field, polarity premagnetization (Mx) sensor strips switched flipped between output characteristics (see Fig.17).
offset
MLC764
Fig.17 Butterfly curve including offset.
This reversible external magnetic field easily achieved with coil wound around sensor, consisting current carrying wires, described above. Depending direction current pulses through this coil, positive negative flipping fields x-direction (+Hx -Hx) generated (see Fig.18). Although principle flipping frequency need exact figure, design hints given Section "Typical drive circuit".
1998
Philips Semiconductors
Magnetic field sensors
General
Flipping causes change polarity sensor output signal this used separate offset signal from measured signal. Essentially, unknown field `normal' positive direction (plus offset) measured half cycle, while unknown field `inverted' negative direction (plus offset) measured second half. This results different outputs symmetrically positioned around offset value. After high pass filtering rectification single, continuous value free offset output, smoothed pass filtering. Figs Offset compensation using flipping requires additional external circuitry recover measured signal.
MLC762
,,,, ,,,, ,,,,
coil sensor
current pulses
Fig.18 Flipping coil.
handbook, full pagewidth
CLOCK
FLIPPING SOURCE PREAMPLIFIER OFFSET FILTER
PHASE SENSITIVE DEMODULATOR
MBH617
Vout
Fig.19 Block diagram flipping circuit.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
flipping current time offset time internal magnetization
time
time
MBH618
Fig.20 Timing diagram flipping circuit output voltage; filtered output voltage; output voltage filtered demodulated.
1998
Philips Semiconductors
Magnetic field sensors
SENSOR TEMPERATURE DRIFT sensitivity sensors also temperature dependent, with sensitivity decreasing temperature increases (Fig.21).The effect sensor output certainly
General
negligible, produce difference factor three within +125 temperature range, fields kA/m. This effect compensated flipping action described last section.
MLC134
handbook, full pagewidth
(mV/V)
Tamb
125o
operating range
(kA/m)
Fig.21 Output voltage `Vo' fraction supply voltage KMZ10B sensor, function transverse field `Hy', several temperatures.
1998
Philips Semiconductors
Magnetic field sensors
simplest form temperature compensation current source supply sensor instead voltage source. this case, resulting reduction sensitivity temperature partially compensated corresponding increase bridge resistance.
General
Thus current source only improves stability output voltage `Vo', reduces variation sensitivity factor approximately (compared factor three using voltage source). However, this method requires higher supply voltage, voltage drop current source.
MLC135
handbook, full pagewidth
Tamb
(mV/V)
125o
operating range
(kA/m)
Fig.22 Output voltage `Vo' KMZ10B sensor function transverse field `Hy' using current source, several temperatures.
1998
Philips Semiconductors
Magnetic field sensors
optimal method compensating temperature dependent sensitivity differences measurements weak fields uses electro-magnetic feedback. seen from sensor characteristics Figs sensor output completely independent temperature changes point where external field applied (the null-point). using electro-magnetic feedback set-up, possible ensure sensor always operated this point. achieve this, second compensation coil wrapped around sensor perpendicular flipping coil, that magnetic field produced this coil same plane field being measured. Should measured magnetic field vary, sensor's output voltage will change, change will different different ambient temperatures. This voltage change converted into current integral controller supplied compensation coil, which then itself produces magnetic field proportional output voltage change caused change measured field.
General
magnetic field produced compensation coil opposite direction measured field, when added measured field, compensates exactly change output signal, regardless actual, temperature-dependent value. This principle called current compensation because sensor always used `zero' point, compensation current independent actual sensitivity sensor sensitivity drift with temperature. Information measured magnetic signal effectively given current compensating coil. field factor compensation coil known, this simplifies calculation compensating field from compensating current therefore calculation measured magnetic field. this field factor precisely known, then resistor performing current/voltage conversion must trimmed. Figure shows block diagram compensated sensor set-up including flipping circuit.
handbook, full pagewidth
flipping field
earth's field
compensation coil compensation field flipping coil sensor KMZ10A1
MLC757
Fig.23 Magnetic field directions flipping compensation coils.
1998
Philips Semiconductors
Magnetic field sensors
influence other disturbing fields also eliminated provided they well known, adding second current source compensating coil. Such fields might those arising from set-up housing, ferromagnetic components placed close sensor magnetic fields from electrical motors.
General
brief summary Table compares types compensation their effects, they assessed their suitability given application. Because these options encompass range costs, individual requirements application should carefully analysed terms performance gains versus relative costs.
handbook, full pagewidth
CLOCK
FLIPPING SOURCE
PRE-AMPLIFIER WITH SUPRESSION OFFSET
PHASESENSITIVE DEMODULATOR
CURRENT REGULATOR VOLTAGE CURRENT OUTPUT
MBH619
Fig.24 Block diagram compensation circuit.
Table
Summery compensation techniques TECHNIQUE EFFECT avoids reduction sensitivity constant stabilization field avoids reduction sensitivity constant stabilization field, well compensating sensor offset offset drift temperature reduction sensitivity drift with temperature factor accurate compensation sensitivity drift with temperature
Setting Flipping Current supply Electro-magnetic feedback
1998
Philips Semiconductors
Magnetic field sensors
Philips sensors weak field measurement Philips Semiconductors present four different sensors suitable weak field applications, with primary device being KMZ51, extremely sensitive sensor with integrated compensation set/reset coils.(see Fig.25) This sensor ideal many weak field detection applications such compasses, navigation, current
General
measurement, earth magnetic field compensation, traffic detection integrated set/reset coils provide both flipping required weak field sensors also allow setting/resetting orientation sensitivity after proximity large disturbing magnetic fields. Philips also KMZ10A KMZ10A1, similar sensors which have integrated coils therefore require external coils. Table provides summary main single sensors Philips' portfolio weak field measurement.
handbook, full pagewidth
flip conductor
barber-pole
(field measured)
compensation conductor
MBH630
Fig.25 Layout Philips' KMZ51 magnetoresistive sensor.
Table
Properties Philips Semiconductors single sensors weak field applications KMZ10A KMZ10A1 SOT195 ±1.5 ±0.5 KMZ50 ±0.2 KMZ51 ±0.2 UNIT (mV/V)/ (kA/m) mV/V µV/V/K kA/m
Package Supply voltage Sensitivity Offset voltage Offset voltage temperature drift Applicable field range (y-direction) Set/reset coil on-board Compensation coil on-board Note kA/m. 1998
SOT195 16(1) ±1.5 ±0.5
Philips Semiconductors
Magnetic field sensors
Typical drive circuit principles application circuit required achieve performance mentioned, using KMZ51, described below (based simplified circuit Fig.26). fully compensated circuit described; various elements which omitted also indicated, application dictates that given functional block needed. figures quoted oscillograph (see Fig.27) were obtained using circuit shown Fig.35. FLIPPING CIRCUIT WITH COMPENSATION Although circuit described here uses KMZ51 sensor with integrated coils, circuits KMZ10A KMZ10A1 would essentially similar. However, these cases drive circuitry flipping compensation coils would probably have adapted provide different drive capability, coil field factor vary these sensors differing current density external wire-wound coils. (The field factor KMZ51 A/m.mA-1). This depends number windings naturally larger chip-coil distance external coils.
General
energy that needs expended generate same physical effect using discrete coils much higher than with KMZ51 integrated solution, point where applications with supply become unfeasible. Also, there competitive products that also have integrated coils, which have worse field factor than that produced patented design KMZ51. These require expensive DC-DC converters drive necessary current through coils.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
block SIGNAL AMPLIFIER
block CONTROLLED AMPLIFIER
block FILTER
block COMPENSATION COIL
IC6A KMZ51
IC2A
Vout IC2D IC6B COMP
IC2C
IC2B
Uref
Uref
IC2B
block Uref FLIPPING GENERATOR
OFFSET COMPENSATION flipping pulse
Uref Uref GENERATOR
OP-AMP SUPPLY
IC1B
FLIP IC1A
block
Note: values should identical
MBH620
Fig.26 Application circuit using KMZ51 sensor.
`flipper' circuit (Block generates flipping current, with flipping frequency determined about this case. previously stated, frequency critical selected minimize need post filtering and/or provide required response time. flipping frequency drives synchronous rectifier well flipping coil. signal passes from high low, C4/R17 together produce pulse that switches This charges short positive pulse passed flipping coil. low-to-high signal transition, 1998
C5/R18 forces conduct, making discharge providing negative pulse through coil. oscillograph current through flipping coil shown Fig.27c, with duration about maximum current amplitude around other diagrams show responses offset compensation (Fig.27b), measuring magnetic pulses (Fig.27a).
Philips Semiconductors
Magnetic field sensors
General
handbook, halfpage
MBH629
handbook, halfpage
MBH666
pulse response mag. pulse: 0.25 positive flip current
0.25
t/µs t/µs
0.25
offset compensation response
-0.25
-0.5
negative flip current
Fig.27 Oscillograph flipping current sensor.
This circuit actually produces necessary supply drive flipping coils, which needed some applications such electronic compass (see Section "Application examples"). Another separate clock clock generated system could also used drive TR2. resistors, reduce supply voltage set-up down level required sensor bridge, this case reducing down about flipped output signal sensor bridge amplified pre-amplification circuit (Block factor 100, providing signal about mVPP (given field about sensor plane). course, this voltage would only visible un-compensated mode; when circuit being used compensated mode, this voltage will approximately mVPP.
Referring block diagram, Fig.26, integrator around IC2B Block provides filtering remove offset. fact, this set-up performed with pass filter rather than high pass filtering. low-pass filter extracts offset uses negative feedback IC2A. does measured signal which, because flipping, signal modulated flipping frequency. This main advantages: op-amp Block only amplifying wanted signal, allowing gain higher with overload clipping) components. offset op-amp Block will also compensated, eliminating need special offset amplifiers, reducing overall system costs. design this filter affects system performance significantly. this example, flipping frequency with filter roll
1998
Philips Semiconductors
Magnetic field sensors
Block (rectification) performs synchronous rectification flipped signal, recover measured field information. this block performs alternate amplification, depending whether sensor operating with normal inverted characteristic. When flipping signal LOW, switch closed op-amp acts inverting amplifier amplification); flipping signal HIGH, then open amplification modifications made input signal. With this rectification, offset-compensated measured signal recovered from original sensor signal. Block smoothes rectified signal that single continuous output signal generated. long compensation coil used, recommended that this filter also used, ensure stable operation. compensation used, then possible less expensive components. This block, well rectifier Block even omitted entirely example, output signal then passed microcontroller which easily perform rectification smoothing, especially also being used generate flipping frequency. components Block drive compensation coil ensure that Vout proportional compensation current. application does need highest accuracy, reduced circuit complexity used. FLIPPING CIRCUIT WITH OFFSET COMPENSATION this case, Block should removed. CIRCUIT WITH FLIPPING COMPENSATION stabilization magnet periodic re-setting used instead flipping, then Block (flipping filter), Block (rectifier) Block (smoothing) omitted. flipping generation circuitry also simplified leaving R18, TR1) omitted stabilization magnet used. GENERAL REMARKS circuitry described above operates with inexpensive op-amps such LM324 LM532, keeping costs low. However, this represents just possible system solution and, depending required functions, further reductions cost achieved replacing op-amps with transistor solutions. designs that utilize some blocks circuit, such offset compensation, this should certainly considered. very simple set-up used microprocessor already available within system (Fig.28). Application examples
General
handbook, halfpage
KMZ51 compensation coil
flipping coil
PORT
MBH622
Fig.28 Set-up weak field measurement using microprocessor.
this section, look three weak field measurement applications: Electronic compass Earth geomagnetic field compensation CRTs Traffic detection. Note: topics related measurement weak currents described detail Chapter "Current measurement". ELECTRONIC COMPASS typical application weak field measurement that electronic compass. Here, sensors aligned same plane degrees another. This provides dimensional compass, with sensors measuring y-components measured (earth) field.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
COMPASS
COMPASS
SENSITIVE DIRECTION SENSITIVE DIRECTION
MBH623
Fig.29 Simplified block diagram electronic compass.
Both sensors deliver single sinewave when rotated Earth's geomagnetic field (see Fig.29). This dimensional compass sensitive angle between Earth's surface measurement plane sensors: change this angle will change alignment between sensitivity axis sensor Earth's field, therefore affect sensor output. This effect, similar that seen conventional compasses, clearly observed automotive applications, when going downhill. High precision systems eliminate this problem using three dimensional compass gravity sensor. Table Typical disturbances compass systems different angles ANGLE LOCATION Hamburg Anchorage Singapore Tokyo 9.7° 12.5° 1.5° 5.7° 18.8° 23.8° 31.2° 2.9° 11.2° 26.9° 33.3° 42.1° 4.3° 16.5°
influences. basic high-end compass example described below.
Simple 8-segment compass
main function simple compass application purely indicate direction etc.). This basic functionality typically found simple navigation aids where, example, drivers require only indication their orientation accurate indication their direction. such simple application set-ups, accuracy produced sensor electronics need only order such simple compass application, compass required only display eight major compass directions. this case, output signals compared with each other achieve three digital signals (Fig.31). These provide basic information while third, inverted sensor signal determines whether sensor signal changing positively negatively this included comparison, distinguish between eight positions compass. Simple comparators used obtain three digital signals, which drive display unit multiplexer. Note: Figure shows principles typical compass sensor set-up maximum clarity, compensation flipping coils shown separately. course KMZ51, which compensation flipping coils incorporated into sensor housing, would used real-life application.
Various levels complexity incorporated drive circuit, include various compensation techniques described earlier this chapter, depending level accuracy required expected environmental
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
Front View
View
,,,,, ,,,,, ,,,,, ,,,,, ,,,,, ,,,,, ,,,,,
Compensation coils Flipping coil sensor coordinates Sensors earth's field coordinates KMZ10A1 (2x)
MLC758
Fig.30 Compass sensor system.
handbook, full pagewidth
Signals Sensor signal (U1)
Sensor signal (U2)
Sensor signal (inverted) Signal
MLC760
Signal
Signal Display
Fig.31 Evaluated signals.
1998
Philips Semiconductors
Magnetic field sensors
High-end compass
Compass resolution increased from basic eight adapting evaluation circuit using microcontroller calculate arctan function ratio signals determine angle. resolution compass then depends microcontroller converters used. microcontroller also enables additional functionality, such storing reference direction eliminating magnetic influences from encapsulation other magnetic components.
coordinates measurement measurement
General
earth's field vector
Simple alignment using opposite directions
Electronic compasses need calibrating eliminate effects these extraneous fields produced, example, compass casing. simplest method known Bi-directional Calibration. Requiring external calibration devices, this technique output measured twice with each measurement shifted 180°. From this, components extraneous field determined simply compensated applying appropriate current coils, synthesizing compensation field.
interference field vector
coordinates
MLC761
Fig.33 Measured fields vector space.
Continuous alignment
With high-end compass applications, microcontroller also used adjust calibration compass continually. This especially useful automotive compasses, eliminating need manual re-adjustment according variable vehicle load.
Compass test units
measured coordinates field
test purposes, Philips designed board (Figs with following parameters: Supply:
earth's field
interference field
Current: (typ.) (x,y): (Vx, Vref) Load:
coordinates
(x,y): 62.5 mA/Gauss) (Ix, Vref) Noise: 0.05 Range:
MLC759
Load: (<500 Bandwidth: compass sensor test unit rotated Earth field rotational unit, resulting test-diagram shown Fig.36. Note: Uref internally generated board, does need provided externally.
Fig.32 Two-dimensional vector space.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
Vref
compass test unit
MBH624
Fig.34 test unit.
1998
This text here white force landscape pages rotated correctly when browsing through Acrobat reader.This text here _white force landscape pages rotated correctly when browsing through Acrobat reader.This text here inThis text here white force landscape pages rotated correctly when browsing through Acrobat reader. white force landscape pages
ook, full pagewidth
1998
IC6A KMZ51 IC2A IC2C signal amplifier offset compensation IC2B IC1A IC1B controlled rectifier amplification IC7A KMZ51 IC3A IC3C IC1C IC1D
Philips Semiconductors
Magnetic field sensors
compensation IC6B coil COMP IC4B Uref
IC2D filter
IC5A
voltage/current interface IC5B
IC7B COMP IC4C
IC5D
IC3B flip pulse generator
IC3D
IC3D
IC4D
IC6C FLIP
IC4A
IC1P
FLIP IC7C
MBH621
General
Fig.35 Circuit diagram electronic compass.
Philips Semiconductors
Magnetic field sensors
General
handbook, halfpage
Voy/V
0.25
-0.25
0.25
Vox/V
-0.25
MBH625
Fig.36 Typical test-diagram.
EARTH GEOMAGNETIC FIELD COMPENSATION CRTS Earth's geomagnetic field always caused problems monitor manufacturers, influences trajectory electrons tube producing horizontal tilt geometry convergence error shifts. With introduction wide screen picture tubes, this problem become unacceptable, especially with geometric test patterns 16:9 aspect ratios. With continuing goal improving picture quality allowing varying magnetic fields every part world, compensation circuit required reduce this effect. simple one-dimensional solution wrap DC-current carrying coil around neck generate magnetic field opposite Earth's field, cancelling twist electrons path reducing approximately number convergence errors.
This coil also additional advantage compensating other extraneous electromagnetic field sources emanating from such loudspeakers. including magnetoresistive sensor detect Earth field, output from sensor used drive compensation field, making adjustment automatic. Although residual picture twist North/South trapezoid errors still seen, simple DC-shift compensation current will eliminate picture twist addition vertical sawtooth (ramp) current, derived from vertical deflection, will remove trapezoid.
1998
Philips Semiconductors
Magnetic field sensors
General
Although highly sophisticated computer systems used analyse various inputs traffic systems, currently this input information gained from inductive systems which have number disadvantages. sensitivity offered inductive measuring systems requires large areas road lifted re-surfaced during installation. With their high power consumption, fact they produce very little information regarding type traffic passing over them, makes them both costly inefficient. They also rather unreliable road thermal stress.
MBH627
handbook, halfpage
Fig.37 Geometry error horizontal picture tilt.
handbook, halfpage
practically every vehicle manufactured contains high number ferromagnetic components, measurable magnetic field specific individual model from every manufacturer detected, using weak field measurement techniques with magnetoresistive sensors. Even with greater aluminium manufacture vehicle been demagnetized, will still create measurable change geomagnetic field strength flux density. comparison with inductive methods, with high sensitivity magnetoresistive measuring provide information passing vehicle type. Also, sensor size placement, systems easily quickly installed stretch road, even side road, necessary. Combined with almost negligible power consumption, this makes magnetoresistive control systems inexpensive highly efficient method monitoring traffic levels.
MBH628
Fig.38 Geometry error North/South trapezoid.
Measurements roads
field test with three-dimensional sensor modules set-up, firstly measure signals different vehicles; secondly, relative occurrence signal values three vehicle categories (car, truck). first test, module placed road, under vehicle comparison, second module placed side road. second test, which performed `live' street Hamburg, Germany, module could only positioned side road. local geomagnetic field calibrated zero, that only disturbance field caused passing vehicle would recorded. Figure shows spectra produced Opel Kadett.
TRAFFIC DETECTION number vehicles using already congested roads steadily increases, traffic control systems becoming necessary avoid time consuming traffic jams. These systems monitor traffic flow, average speed traffic density, allowing electronic road signs control flow speed traffic known trouble spots. They also have advantage indicating possible incidents, where traffic speeds fall significantly below average certain sections road. Simple modifications these systems allows them used improve safety, also monitor ground traffic airports.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
(A/m)
sensormodules
time
MBH631
Fig.39 Spectra Opel Kadett from ground sensor.
sensor modules also proved sensitive enough detect distinguish motorbikes (even with engine, frame wheels being made aluminium), which produced following roadside spectra.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
(A/m)
sensormodules
time
MBH632
Fig.40 Spectra motorbike.
roadside test Hamburg, road chosen random maximum signal value recorded different vehicles, being grouped into cars, vans trucks. relative occurrence signal values shown following diagram.
handbook, full pagewidth percentage
cars
percentage
vans
trucks (est.)
max. signal (A/m)
,,,,
max. signal (A/m)
MBH633
sensormodules
Fig.41 Distribution graphs maximum signal versus occurrence.
1998
Philips Semiconductors
Magnetic field sensors
signals each group seem have Gaussian distribution with characteristic maximum (although fact there were only three trucks, values this group estimate).
General
Although there number possible sensor solutions, traffic systems using magnetoresistive technology have none drawbacks existing radar, microwave, I/R, pressure, acoustic inductive systems (see Table They meet functional environmental restraints, such large temperature ranges, insensitivity climatic changes, power consumption and, most all, cost, high reliability ruggedness. They also perform range signalling functions including detection presence, recognition, classification, estimation speed deviation from path.
Airport ground traffic control
With constant growth traffic around world, serious consideration improvement safety ability improve handling capacity airports, control traffic around runways. Using traffic control system, possible introduce automatic guidance systems prevent runway incursions even heavily congested airports under visibility conditions, accordance with regulations set-down internationally recognized authorities. Table
Disadvantages various sensors airport ground traffic control units Radar Microwave barriers Cannot installed flush with ground Creates obstacles surveyed area Produce interference Inductive sensors sensitivity short range Poor target information High power consumption Unreliable harsh environments Repairs require traffic stopped diverted signalling Greatly affected weather conditions Complex target identification
High costs Reduced efficiency with large number targets Line sight only Complex target identification resolution Slow response times Pressure sensors Frequent mechanical breakdowns when used harsh environments Associated ageing problems Poor target identification
Acoustic sensors Signal interference when used outdoor weather conditions Trade-off between sensitivity range Large power consumption
1998
Philips Semiconductors
Magnetic field sensors
CURRENT MEASUREMENT Contents: Principles Some practical sensing set-ups Measurement examples using Philips' sensors. Principles principle measuring current with magnetoresistive sensor straightforward. current, flows through wire, generates magnetic field around which directly proportional current. measuring strength this magnetic field with magnetoresistive sensor, current thus accurately determined. EXAMPLE Table
General
Values magnetic field generated current carrying wire various distances currents CURRENT 1000 DISTANCE MAGNETIC FIELD 3.18 15.9 kA/m
Table clearly indicates that current measurement involve measurement weak strong magnetic fields. sensitivity magnetoresistive sensors easily adjusted, using different set-ups different electronics (refer selection guide General section), individual sensor optimized specific current measurement application, clear advantage over Hall effect sensors. accuracy achievable current measurement using magnetoresistive sensors highly dependent specific application set-up. Factors which affect accuracy mechanical tolerances (such distance between sensor wire), temperature drift sensitivity conditioning electronics. However, with Philips magnetoresistive sensors accuracies within about possible. There general difference set-up used when using sensors current measurement, effects disturbance fields such Earth's geomagnetic field. currents, disturbing fields eliminating using filtering techniques (similar those described Chapter "Weak field measurements"), while currents, compensation techniques must used (for example using sensors). Some practical sensing set-ups
handbook, halfpage
MGG423
Fig.42 Diagram showing field direction current carrying wire.
relationship between magnetic field strength current distance given (14)
DIRECT MEASUREMENT WITH SINGLE SENSOR Philips' sensors used number standard set-ups current measurement. simplest places single sensor close current carrying wire, measure directly field generated current (see Fig.43). Figure shows sensitivity sensor varies with distance from wire.
Some calculated values typical conditions given Table
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, halfpage
(mV)
current 1.15 0.35
KM110B/2
MGG424
Fig.43 Simple set-up measuring current using KM110B/2 sensor with external magnet.
current sensivity (mV/A) conductor width housing
MGG425
wire
(mm)
distance from sensor crystal surface
Fig.44 Sensor sensitivity versus distance wires with diameters ranging from
1998
Philips Semiconductors
Magnetic field sensors
surprisingly, sensor sensitivity rises distance decreases. relatively large values (say mm), increase sensitivity substantially linear, closer spacings, when magnetic field generated current longer uniform over sensor, rate increase drops off. higher currents, similar drop from linearity would observed quite large distances, this magnetic field generated current saturating sensor. this case, optimal linear relationship simply restored using less sensitive sensor (refer Table `General introduction' summary Philips sensors their main characteristics). sensor also laid directly onto conductor Fig.44 also shows sensitivity sensor three widths conductor.
General
IMPROVING ACCURACY WITH FERRITE CORE second set-up, shown Fig.45, more sophisticated arrangement which magnetic field generated current-carrying wire compensated secondary circuit wrapped around ferrite core. `null-field' point, detected sensor located between ends core, magnitude current secondary circuit measure current main circuit. This arrangement provides more accurate means measuring current, reducing inaccuracies result tolerances, temperature drift slight non-linearities sensor characteristics, lending itself more precision applications.
handbook, full pagewidth
ferrite
sensor
MLC141
Fig.45 Current measurement using compensating coil.
1998
Philips Semiconductors
Magnetic field sensors
Both these first set-ups allow current measurement without breaking conductor interfering with circuit way, providing distinct advantage over resistor based systems. They used, example, measuring current headlamp-failure detection system motor vehicles clamp-on (non-contacting) meters, used power industry. applications where analog signal measured, such these measurement set-ups, good evaluation circuit should used allow temperature drift compensation offset sensitivity adjustment. This applies generally measurement circuits using magnetoresistive sensors. This discussed more detail Chapter "Weak field measurements". COMPENSATING EXTERNAL MAGNETIC FIELDS measurement set-up, there always other magnetic fields present besides that generated current, such earth's magnetic field, these interfere with measurement. more accurate measurement set-up uses magnetic field sensors, compensate these external fields (see Fig.46). first sensor detects both interference field current-field positive direction, second sensor detects interference field negative direction current-field positive direction. These signals added, cancelling interference field, leaving signal that representative only current-field. This set-up works with homogeneous interference fields like that from earth. Inhomogeneous fields, which will produce different interference fields inside sensors, will still affect current measurement. This error minimized keeping distance between sensors small integrating both sensors onto single piece silicon. Large magnetic fields which fall outside range sensors also produce errors, size external fields must limited.
General
Another advantage using sensors, fixed distance apart, that measurement less sensitive sensor-conductor distance. conductor moved closer first sensor, then distance from second sensor correspondingly increased effect compensated. small differences distance between conductor sensors, sensitivity nearly constant conductor need fixed place. This method lends itself measurement current free cables.
handbook, halfpage
sensor
Hdisturb
sensor
MGG426
Fig.46 Diagram showing sensors measure current.
Table summarizes various advantages disadvantages one-sensor two-sensor measurement set-ups described above.
1998
Philips Semiconductors
Magnetic field sensors
Table Summary advantages disadvantages typical measurement set-ups
General
CURRENT MEASUREMENT WITH MAGNETIC FIELD SENSORS PROS galvanic connection breaking conductor small physical dimensions reduced sensitivity sensor-conductor distance reduced interference effects from homogeneous fields Measurement examples using Philips' sensors measurement, Philips' KMZ10A/B/C KMZ51 sensor types used. KMZ10A/B/C have stabilized with auxiliary magnets, example KM110B/2. KMZ51 sensors contain internal conductors (`coils') compensate offset temperature drift need auxiliary magnet, allowing simple circuitry with reduced need adjustments. these sensors measure fields above about ±230 (approx. times earth's magnetic field), they must used measurement set-up that reduces effects interference fields, described above. following examples demonstrate Philips' magnetoresistive sensors being used real-life situations. CURRENT MEASUREMENT USING DUAL KM110B/2
SENSORS
CURRENT MEASUREMENT WITH MAGNETIC FIELD SENSOR PROS galvanic connection breaking conductor small physical dimensions CONS effects interference from external fields sensitive sensor-conductor distance
CONS interference effects from inhomogeneous fields errors generated from large external fields
KM110B/2 sensors, placed outlined above, in-phase current measurement antiphase external field compensation, eliminating effects from stray fields improving sensitivity (see figs 48).
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, halfpage
auxiliary magnet KM110B/2
wire 1.15
MGG427
Fig.47 Diagram showing set-up current measurement.
handbook, full pagewidth
KMZ110B/2 IC1A IC1B +10V KMZ110B/2
MGG428
Vout
IC1A IC1B NE532
Fig.48 Circuit diagram.
1998
Philips Semiconductors
Magnetic field sensors
This circuit shown Fig.48 pre-tested design currents, delivering very high sensitivity. KM110B/2 sensors connected parallel, with aligned such that signals produced external disturbing fields minimized. output signal then amplified signal components considerably reduced with filtering, through R1-C2 R2-C3. This circuit gives following characteristics: Amplification: Sensitivity: V/mA Noise level: 0.37 Max. output: measured current) adjusted about this changes data Amplification: Sensitivity: V/mA Noise level: 0.015 Max. output: measured current) SENSITIVE MEASUREMENT USING WEAK FIELDS WITH DUAL KMZ51 SENSORS This section describes practical set-up that used measuring currents metal tracks PC-board. Using paired sensor approach again, following set-up also used measure currents producing only weak magnetic fields. this case, conductor also locked mechanically sensors, eliminating variations movement conductor allowing small currents measured accuracy approximately with galvanic connection. Note: since this involves measurement weak magnetic fields, techniques must used suppress influence sensor offset temperature drift. more detailed information these techniques, refer sections Flipping Compensation Chapter "Weak field measurements". Generally there several sensor set-ups which used compensate external field. there components both sides PCB, set-up Fig.49 used.
General
handbook, halfpage
KMZ51
MGG429
Fig.49 Sensor positioning current measurement with double-sided PC-boards.
current carrying track centre board with sensors' sensitive direction marked with `S'. This set-up clearly follows conditions described Section "Compensating external magnetic fields" earlier (see also Fig.46). components only placed side PCB, then track carrying current measured must laid such that conditions described Section "Compensating external magnetic fields" adhered Figure illustrates three possible set-ups sensor current-carrier, used Philips Semiconductors' demonstration board.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
Setup
KMZ51 KMZ51
,,,,,,,,, ,,,,,,,,,
current carrying track sensors
Setup
,,,,,,,,, ,,,,,,,,,
current carrying wire
current carrying track
sensors
Setup
,,,,,
sensor
MBH688
Note: size current-carrying tracks greatly exaggerated
Fig.50 Sensor positioning single-sided PCBs: track directly under sensor, same side PCB; track opposite side PCB; wire sensor.
circuitry used condition sensor output usable signal (see Fig.51) same three set-ups. basic principle have sensors electrically parallel, effectively merging output signals. This gives following advantages that Only conditioning circuit required both sensors sensors themselves automatically compensate disturbing fields.
1998
This text here white force landscape pages rotated correctly when browsing through Acrobat reader.This text here _white force landscape pages rotated correctly when browsing through Acrobat reader.This text here inThis text here white force landscape pages rotated correctly when browsing through Acrobat reader. white force landscape pages
book, full pagewidth
1998
IC5A IC2A IC2C LM324N LM324N IC2D LM324N KMZ51
Philips Semiconductors
Magnetic field sensors
IC4B COMP
COMP
IC5B
IC3D LM324 optional with reduced range
IC5B COMP IC4B COMP
IC4A KMZ51
4066 IC1A
4066 IC1B
IC3C LM324N
IC3D LM324N Vref (generated board)
IC2B LM324N
IC3B LM324N
BA5321 BA5321
BST62 BST52
IC4C FLIP
LM324N IC3A
IC1P
4066 IC1D
4066 IC1C
FLIP IC5C
MGG430
General
Fig.51 Circuit diagram: Philips Current Measurement Testboard KMZ51.
Philips Semiconductors
Magnetic field sensors
After output signals sensors have been merged, basic conditioning circuitry similar that used weak field measurement. basic principles electronics described more detail Chapter "Weak field measurements"; however, figures quoted that example compass application this circuit optimized current measurement, with following characteristics: Table Maximum level compensation current disturbing fields Icomp(max.) Time constant ±230
General
sensitivities ranges three different sensor set-ups shown Fig.50 are: Set-up V/A; range: ±1.1 Set-up V/A; range: ±1.8 Set-up V/A; range: ±0.35 Note: this example uses analog circuit, clarify principles current measurement including flipping magnetic compensation. large part functionality circuitry could easily handled microprocessor (see Fig.52 typical circuit diagram).
handbook, full pagewidth
KMZ51 KMZ51
PORT
MBH752
Fig.52 Circuit diagram using sensors microprocessor.
1998
Philips Semiconductors
Magnetic field sensors
HIGH CURRENT MEASUREMENTS Interest sensors contactless measurement high currents been steadily increasing help customers apply this technology, Philips prepared module testing, based KM110B/2 magnetoresistive sensor (equipped with stabilization magnet). consists KM110B/2 sensor, conditioning electronics U-core. wire carrying current measured should through U-core, short distance should maintained between wire sensor. Figure shows influence wire position sensitivity. wires thin, spacer above sensor prevent errors measurement. Cables conductors with large diameters less sensitive this effect. Ring cores with generally less sensitive wire position more difficult obtain mount, U-core used these test modules.
General
Figure shows conditioning electronics this set-up. principle, similar basic conditioning circuit `General introduction' (see Fig.11), although been optimized this particular application following characteristics: Supply voltage Current range: Frequency range: 1000 Temperature range: Sensitivity: mV/A Sensitivity temperature drift (temperature range -20/+85 °C): 0.8% Quiescent output voltage Quiescent output voltage temperature drift (temperature range -20/+85 °C): Equivalent current drift: typical response this sensor circuit set-up shown Fig.55 shows excellent linearity, even large currents.
handbook, full pagewidth
30.8 10.2
sensitivity
25.3
14.9
U-core type U30/25/E16 3122134 9076 (mm)
MGG433
Fig.53 Influence wire position.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
offset SA5230D amplification
KMZ110B/2
KTY85120
MGG431
Fig.54 Circuit diagram current sensor based this module.
Other current ranges obtained varying following:
MGG432
handbook, halfpage
Sensor (KMZ10C with auxiliary magnet, delivering current range about Core type Sensor position relative core. Varying these parameters described general produces higher current ranges. Sensitivity also increased winding wire repeatedly through core applying higher amplification range. Modules have also been prepared with higher current ranges ±300 using stronger auxiliary magnets. More information available request. These just possibilities offered magnetoresistive sensors current measurement. With their inherent simplicity application ability compensate easily disturbing fields, sensors easily most flexible choice.
current
Fig.55 Typical response current sensor based this module.
1998
Philips Semiconductors
Magnetic field sensors
LINEAR POSITION PROXIMITY MEASUREMENT Contents: Principles standard set-ups Position measurement applications Reference set-ups. Principles standard set-ups sensitivity magnetoresistive sensors lends itself linear position measurement systems, with number possible applications. Simple basic set-ups used one-point position measurement linear position measurement set-up easily modified produce proximity switch sensor. underlying principle very similar that used angular measurement, that magnet target moved, internal magnetization vectors permalloy strips sensor change, aligning themselves with external magnetic field thus changing their resistance.
General
When magnetoresistive sensor placed permanent magnetic field, generally exposed fields both y-direction. magnet oriented such that axis auxiliary field x-direction parallel permalloy strips sensor, then movement y-direction seen fluctuations transverse field, which equated position magnet with respect sensor. linear region sensor's sinusoidal output defined roughly length magnet. Outside this area, axial field produced magnet becomes weaker near poles, also changes direction, both which cause sensor flipping. (For further information sensor flipping, please refer Appendix Chapter "Weak field measurements"). Figure shows simplest arrangements using sensor/magnet combination measure linear displacement.
handbook, full pagewidth
MBB898
Fig.56 Sensor output field permanent magnet.
1998
Philips Semiconductors
Magnetic field sensors
strong magnetic field used sensor placed very close magnet, there danger that auxiliary field will exceed field required flip sensor characteristic, producing hysteresis sensor output (shown hysteresis loop ABCD Fig.57
General
This actually used positive effect under certain circumstances, where temporary fluctuating external fields interfere with measured signal. this case, long sensor used region between strength magnetic field from permanent magnet will block extraneous fields.
handbook, full pagewidth
MLC136
Fig.57 Sensor output strong magnetic field.
1998
Philips Semiconductors
Magnetic field sensors
orienting sensor's axis with respect axis permanent magnet, shown Fig.58, possible sensor along with comparator, proximity switch. this arrangement sensor negative output, both axial arrangements magnet, which then passed onto inverting input comparator.
General
halfpage handbook, (mV)
ambiguous range
handbook, halfpage
permanent magnet
(mm)
MGG441
Fig.59 Sensor output function distance.
MGG440
Fig.58 Proximity sensing using magnetoresistive sensor.
resulting output clearly indicative distance between magnet sensor (see Fig.59). Sensor switching levels very important this application; below certain level, strong external magnetic fields disturb sensor sufficiently produce ambiguous results.
Besides being used general position sensing measurement, incorporating back biasing magnet, single-point measurements possible using non-symmetrical region material within target such hole, pin, region non-magnetic material integrated into metal plate's structure. resulting disturbance magnetic field produces variation sensor output. Figure shows basic set-up crossover point, where hole sensor match precisely, sensor output clearly independent separation distance.
handbook, full pagewidth
,,,,,,,, ,,,,,,,,
steel MAGNET
signal
MLC258
Fig.60 One-point measurement with KM110B/1.
1998
Philips Semiconductors
Magnetic field sensors
obvious advantage this technique that precise location sensor/magnet combination irrelevant sensor basically acting `null-field' detector this point, set-up also independent temperature effects. This makes system very simple design Position measurement applications output from KMZ10B KMZ10C sensor measured function sensor displacement, parallel magnetic axis. This done using varying magnet/sensor separation distances three different sized FXD330 magnets: single placed end-to-end make single long magnet. different set-ups were used, first with magnetic field parallel sensor second with magnetic field perpendicular sensor. MAGNETIC FIELD PARALLEL PLANE SENSOR this set-up magnet oriented with sensor that broadside-on, with poles lying plane containing sensor chip. With this arrangement, auxiliary field supplied axial field (Hx) magnet, which remains reasonably constant over region interest.
General
handbook, halfpage
0.35
MGG442
Fig.61 Position measurement with sensor broadside-on FXD330 magnet.
following plots show sensor output function distance three magnet set-ups, with both KMZ10B KMZ10C.
handbook, full pagewidth
length magnet
MGG443
(mV)
(mm)
KMZ10B KMZ10C
magnet cross-section SOAR limits
Fig.62 Sensor output function displacement.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
length magnet (mV)
MGG444
(mm)
KMZ10B KMZ10C
magnet cross-section SOAR limits
Fig.63 Sensor output function displacement.
handbook, full pagewidth
length magnet (mV)
MGG445
(mm)
KMZ10B KMZ10C
magnet cross-section SOAR limits
Fig.64 Sensor output function displacement.
1998
Philips Semiconductors
Magnetic field sensors
first graph shows that separation distance increases, curve flattens out. This because sensor moved closer magnet, transverse field magnet greater effect sensor, giving rise increased rotation internal magnetization. gradient curve direct indication sensitivity sensor, then practical application designs, sensor/magnet separation important factor. From these curves also clear that KMZ10C sensor, with shorter magnets close separation distances, switching hysteresis becomes major factor limits sensors linear region. MAGNETIC FIELD PERPENDICULAR SENSOR When sensor oriented that plane perpendicular magnetic axis, impossible magnet provide auxiliary field. this case additional auxiliary magnet required, placed sensor shown Fig.65.
General
handbook, halfpage
0.35
MGG446
Fig.65 Sensor perpendicular magnetic field using FXD330 magnet.
With this set-up, following plots were obtained using same FXD330 magnets with parallel arrangement.
handbook, full pagewidth
length magnet (mV)
MGG447
(mm)
magnet cross-section KMZ10B KMZ10C
Fig.66 Sensor output function displacement.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, full pagewidth
length magnet
MGG448
(mV)
(mm)
magnet cross-section KMZ10B KMZ10C
Fig.67 Sensor output function displacement.
handbook, full pagewidth
length magnet (mV)
MGG449
(mm)
magnet cross-section KMZ10B KMZ10C
Fig.68 Sensor output function displacement.
1998
Philips Semiconductors
Magnetic field sensors
most noticeable difference these curves, compared parallel results, lack hysteresis switching. This partly auxiliary magnet stabilizing sensor fact that orientation target magnet means does produce magnetic field x-direction cannot therefore adversely affect sensor. interesting feature these curves curvature changes near ends magnet. This slight flattening possible reversal curve seen more clearly when single FXD330 magnet used with KMZ10B sensor very small separation distances mm). reason change curvature that small distances from target magnet, radial field
General
ends magnet stronger than field required induce maximum response sensor. This effectively saturates sensor output fall even increases. slightly different approach used very high resolution measurements. Using compact RES190 magnet with dimensions placed back sensor rather than directly above (see Fig.70), output sensor plotted separation distances Figure clearly shows that this set-up very well suited high resolution high sensitivity measurement position very short distances, using linear part response curve.
handbook, full pagewidth
length magnet (mV)
MGG450
(mm)
magnet cross-section KM110B/2 sensor
Fig.69 Sensor output function single FXD330 magnet.
1998
Philips Semiconductors
Magnetic field sensors
General
handbook, halfpage
0.35
MGG451
Fig.70 Sensor KM110B/2 perpendicular magnet field using RES190 magnet.
handbook, full pagewidth
MGG452
(mV)
-400
-300
-200
-100
(µm)
Fig.71 Sensor output function displacement using RES190 magnet.
1998
Philips Semiconductors
Magnetic field sensors
Reference set-ups
General
following common set-ups (Fig.72 Fig.73) that could used linear position measurement real-life applications, together with typical response curves.
handbook, full pagewidth
(mA)
KM110BH/2270 magnets
steel magnets: NdFeB 11.2 steel: position (mm)
MGG457
Fig.72 Angle sensor hybrid KM110BH/22/70 linear position measurement set-up using magnets typical response curve.
handbook, full pagewidth
(mV)
KMZ10B magnets
position (mm)
steel magnets: NdFeB 11.2 steel:
MGG458
Fig.73 KMZ10B linear position measurement set-up using magnets typical response curve.
1998
Other recent searches
WM8714 - WM8714 WM8714 Datasheet
VS003E4 - VS003E4 VS003E4 Datasheet
OP750A - OP750A OP750A Datasheet
OP750B - OP750B OP750B Datasheet
OP750C - OP750C OP750C Datasheet
OP750D - OP750D OP750D Datasheet
LC503THR1-15Q - LC503THR1-15Q LC503THR1-15Q Datasheet
HFA1112 - HFA1112 HFA1112 Datasheet
GM431 - GM431 GM431 Datasheet
Privacy Policy | Disclaimer
© 2012 Datasheet Archive
