Transcript
ANMM Iasi 2003
Current sensors using magnetic materials Pavel Ripka Czech Technical University, Prague
Current Sensors: Overview • Resistive Shunt • Contactless sensors – use B – current transformers – current comparators – Rogowski coils – magnetic field sensors » » » »
in gapped core compact remote multisensor configuration
GMI current sensor Current clamps
Engineer’s wishlist
Resistive shunts
no galvanic insulation dissipated heat measured current should be interrupted
DC current sensor with gapped core Magnetic yoke Measured current n2 n1=1
I1 I2 R2
V2
IH Hall sensor in narrow airgap
Problems: bulky, sensitive to external fields offset drift – only Hall
Large currents = Large yokes
LEM
Magnetooptical current sensor
• • • • •
optical fibre x bulk glass 1% accuracy even after temp. compensation expensive > 1000 A good for high voltages
Current transformer Magnetic core
lS
I1
I2
s
Secondary
Primary N1
r1
N2
ui
Z2
r2
h I1 Y’11
L1, Rv1 Y11
C11
M
L2, Rv2
I2
C21
Y21 Y’21
Cm1 Ym1
Y12
C12
Cm2
C22
C’21
Y22
Rv1
Lr1,
L’r2, I01
Ic Z2
Ym2 C’11
I1
U1
Ui1 Cp
IR Rz
R’v2
I’2
IL Lh
U’2
Z2
AC Current clamps
Leakage Shielding
I1
Secundary winding Measudary winding Core
Flux Φ2 generated by secondary winding
Φ1 generated by measured conductor
DC current sensor using oscilloscopic clamps
AC Current Comparator Magnetic shielding
Detection ring core
I2
I1 Primary winding
1
2
Secondary winding
N2
N1
Detection winding DET
AC Current Comparator
DC Current Comparator N1
Nb
N2 Magnetic shielding Detection ring cores
I1
I2
NS
f
G
ref 2f
I
PSD
R
Out
DC Current Comparator
cover
Secondary winding
magnetic shielding Detection winding Detection cores
Modulation winding
Electrostatic shielding
Novel AC/DC Comparator Detekčn í toroidy
Magneti
Kryt
Sekundární vinutí
Primární vinutí
Vitrokov 8116 –as cast B (A/m)
0.8 10Hz 1kHz 10kHz 20kHz 40kHz
0.6 0.4 0.2 0 -0.2 -0.4 -0.6
H (A/m)
-0.8 -80
-60
-40
-20
0
20
40
60
80
Vitrokov 8116 – annealed B (A/m)
0.8 10Hz 1kHz 10kHz 20kHz 40kHz
0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -80
H (A/m)
-60
-40
-20
0
20
40
60
80
Excitation current
Nexc = 10
N1
N2
16 A p-p I1
I2
N S
f
G
I
PSD
R
Out
Testing core homogeneity Testing coil
V out
~ α
Generator
Ratio error I1
I2 R2s
N1= 10
RN1=0, 1Ω
A ’ A
V
N2=1 00
B ’ B
RN2= 1Ω
εI [%] 0.02
0.01
0
-0.01
-0.02
-0.03
-0.04 -200
-150
-100
-50
0
I1 [A]
50
100
150
200
Current transformer mode Voltmeter
Gen (sin)
I1
Shunt 1mV/A
I2
N2=100
N1=1 0 In
Lock-in
A’
Ref
B’
RN1=0,1 Ω
RN2=1 Ω A
B 40 -0.1
burden 1
εI [%]
amplitudová chyba fázová chyba
30
-0.2 20 -0.3 10 -0.4 0 -0.5 10
100
1000
f [Hz]
C
10
4
δI [mi n.]
Current transformer mode δI [min.]
εI [%]
40
Bm ls ' I sin 0 z N 2 I 2
-0.1
amplitude error phase error
30
-0.2
I
Bm ls ' cos 0 z N 2 I 2
20 -0.3 10 -0.4 0 -0.5 10
burden 1
100
1000
f [Hz]
10
4
AC/DC current comparator mode Voltmeter
Gen (sin)
I1
Shunt 1 mV/A
I2
N2=100
N1=10
Lock-in
In A’ Ref
B’
RN1=0,1 Ω
Electro nics RN2=1 Ω
A
B
Závislost chyb komparátoru s elektronikou na frekvenci pro I1=56,6 A 0.05
25 amplitudová chyba fázová chyba
0
εI [% ]
20
-0.05
15
δI [mi 10 n.]
-0.1
-0.15
5
-0.2
0
-0.25
-5 100
f [Hz]
1000
C
10
4
AC/DC current comparator mode Voltm etr
Generá tor (sin)
I1
Boční k 1 mV/ A
Lockin
I n R e f
I2
N2 = 100
N1 =1 0
RN1=0 ,1 Ω
Závislost chyb komparátoru s elektronikou na frekvenci pro I1=56,6 A
εI [%]
A ’
B ’
A
B
Ele ktr. čás t RN2= 1Ω
25
0.05
amplitude error amplitudová chyba phase chyba error fázová
0
εI [%]
20
15δI
-0.05
[min.]
10
-0.1
-0.15
5
-0.2
0
-5
-0.25 100
f [Hz]
1000
C f [Hz]
10
4
Rogowski coil measures di/dt
Digital integrator for Rogowski coil
IC for power meter
Digital power meter with di/dt sensor
Magnetic sensors for current sensing
• Magnetic field sensors – semiconductor – ferromagnetic magnetoresistors – other (GMI, optical, resonant, SQUID…)
Magnetic field sensors
Scalar
Vector
Measure the size of B (“total field B”)
Measure the projection of B into the sensitive axis • single-axis • tri-axial
B Bx2 B y2 Bz2 only resonant sensors
most magnetic sensors
Magnetic field sensors: DC and AC
AC
DC
Measure only changing field: induction coils
Measure DC and AC fields
d d Vi NAB dt dt Vi .. Induced voltage .. Magnetic flux A .. Coil area N .. Number of turns
most magnetic sensors
Current sensor specifications
• • • • • •
FS range, linearity, hysteresis TC (“tempco”) of sensitivity Offset, offset tempco and long-term stability Perming (= null change after magnetic shock) Geometrical selectivity Noise – PSD , rms or p-p value
• Resistance against environment – temperature, humidity, vibrations
Types of magnetic field sensors
• • • • • • • •
Semiconductor sensors (Hall, …) Ferromagnetic magnetoresistors (AMR, GMR, …) Resonant magnetometers (Proton, Cesium, ...) SQUIDs (LTS + HTS) Induction coils Optical (Fibre optic, bulk ) Fluxgate Other principles (GMI, magnetoelastic, …)
Basic rules
Dipole field (from small objects) B 1/r3 Long iron pipe B 1/r2 Long straight current conductor B 1/r
Linear Hall sensor
Asahi Kasei Electronics: InSb Hall element (HW series)
Hall integrated circuit
Analog electronics: • Delivers constant current • Amplifies VH • Flips contacts • Performs compensations • May compare with threshold
Honeywell Hall Sensor Using Four CrossConnected Hall Elements
Vertical Hall sensor B is parallel to the substrate
B
I V
J V2
V3
Expected Advantages: long-term stability robustness Active zone is buried into a mono-crystal, far away from the chip surface.
V1
currently not used: expensive no so good
Permalloy Flux concentrators
Used for Hall and MR Increase sensitivity Possible problems: • TC of sensitivity • perming • linearity Cylindrical Hall device with integrated magnetic flux concentrators (Sentron AG: developed, but not in production)
Feedback Hall current sensors
1 A .. 1 kA sensors
LTS 25-NP 25 A, 200 kHz error 0.02 % sensitivity TC: 50 ppm/K LEM
PCB - integrated current sensor
1 – the current lead 2 – the ferromagnetic yoke 3 – Vertical Hall sensor or MR
Sentron
Hall current sensors – compact design vnější magnetický obvod pouzdro pouzdro vodič s měřeným proudem vodič s měřeným proudem
vývody Hallova generátoru
vývody Hallova generátoru
magnetokoncentrátory
směr citlivosti
vývody Hallova generátoru
zapouzdření 1mm
Classical Hall with Flux concentrators
Inside structure of C-MOS Hall
AMR bridge sensor
Philips KMZ Full bridge made of meandered resistors with barber-pole strips
AMR current sensor (F.W.Bell)
Vout
range
5 ... 50 A
linearity
0.1 %
sens. tempco 50..100 ppm/K typ. offset (250C) 15 mA max. offset
Imeas
(-25 .. 850C)
30 .. 50mA
developed by:
GMR bridge sensor
GMR resistors configured as a Wheatstone bridge sensor (NVE) • •
R2, R3 are shielded R1, R4: field is concentrated by approx. D1/D2
250
Still has nonlinear
(NVE)
40 150 30 100
20
50
0 -2.5
10 0 -1.5
-0.5
0.5
Applied Field (mTesla)
1.5
2.5
Output (mV/V)
unlike AMR bridge
Voltage (mV)
response
50 200
GMR Contactless current sensor
Long straight current conductor B 1/r NVE GMR sensor measures current in close wire
Advantages of magnetoresistors
compared to Hall sensors: • higher sensitivity • no piezo effect • higher operational temperatures AMR very good GMR, SDT ... too much nonlinear
Fluxgate sensors
Most sensitive room-temperature magnetic sensors Based on non-linear magnetization characteristics of ferromagnetic core. Measure up to 1 mT with 100 pT resolution Classical fluxgates: precise, but expensive (CTU Prague)
Fluxgate principle • Ferromagnetic core - non-linear B-H • Excitation and sensing coil • Core is periodically saturated by Iexc, drops to 1 twice each period • Measured B0 causes 2nd harmonics in Vind
Vind Iexc(t)
(t)
B(t) N
Bo
B()
Fluxgate principle H Hexc
a)
Vi
Hm
t
t
Vi
B()
•
In absence of external field, magnetisation is symmetrical External measured field causes assymetry – detected in induced voltage
H Hexc+H0
t b)
Vi t
H0
t
•
t
Hm
Micro-fluxgate sensors
(in development) • • • • •
Shizuoka University
flat coils electrodeposited core or amorphous strips electronics on chip cheap resolution still higher than MR
Magnetic amplifier
= current sensor based on fluxgate principle
Magnetic amplifier 100mA/div
DC current2 =80mA compensates I 1=40A
= current sensor based on fluxgate principle
Fluxgate current clamps unsymmetrical core Фext
3
3
Фext2
z y
Фext1
1
Фext2
z
Фext
y
x
2
x
2
Фext
Фext1
1
Фext
Fluxgate current clamps symmetrical core Φext 2 1
z y 2
Фext
Фext
x 2
Φext 2
1
Leakage flux
Leakege Shielding Sekundární vinutí I1 Measured current Core
Flux Φ2 generated by compensation winding
Φ1 generated by measured conductor
Fluxgate current clamps jádro senzoru
core
stínění
shielding
z y x
no shielding
symmetrically shielded core
assymetrical shielding
Suppression of external currents Error caused by external 40 A current 100
Iv [mA]
unshielded
non-symmetric shielding symmetrical shielding
10
1
0.1 10
100
1000
distance [mm]
40 A current clamp
Relative error( % FS) 0.6 10mm
unshielded non-symmetric shielding symmmetric
0.4 0.2 δ [% ]
0 -0.2 -0.4 -0.6 -0.8 -40
-30
-20
-10
0 I1 [A]
10
20
30
40
Frequency characteristics B (dB)
2 0 -2 CSLA1CD CSNE151 KZB464/501 Currclamp
-4 -6 -8 -10 -12 10
100
1000
10
4
10
5
10
6
f (Hz)
Error of Hall sensors δ2 (%) 1 CSLA1CD CSNE151 0.5
0
-0.5
-1 -40
-30
-20
-10
0
10
20
30
I (A)
40
Error of fluxgate-based sensors
0.4 KZB464/501 Currclamp 0.2 %)
0
-0.2
-0.4
-40
-30
-20
-10
0 f (Hz)
10
20
30
40
Resistance against external currents Sensor type
FS
error response to 40A
CSLA1CD (Hall)
57 A
2160 mA
CSNE151 (Hall)
35 A
180 mA
KZB464/501 (Siemens)
40 A
120 mA
Currclamp (our design)
40 A clamps
14 mA
problems: low-impedance networks injected interference
Fluxgate-based DC/AC current sensor (PEI Ireland) Magnetic circuit: 7 mm/10mm ring material: electrodeposited permalloy sandwiched into PCB. excitation winding: integrated in the PCB 40 turns, R= 700 m.
Toroid with magnetic core embedded in PCB Wire carrying current to be measured.
Current sensing: Sensor Array
Array of six sensors: • increased sensitivity • resistant against external currents and fields
Sentron Hall sensors with field concentrators measure current flowing through the hole
Remote current sensing Hall with field
AMR
5 mT 6 mm 0.1 < 0.2 % 200 ppm/K
offset TC resolution perming, hyst. BW power cons.
600 nT/K
6 mm
6 mm
50 T 1 T 100 kHz 55 mW
fluxgate
flipped
concentarors
linear range size linearity sensitivity TC offset@250C
AMR
10 nT
10 nT
0. 5 mT 30 mm 1 ppm 30 5 nT 0.1 nT/K 100 pT < 1 nT 1 kHz 150 mW
GMI current sensor
Ibias= Idet~
~ Imeas =
GMI current sensor
Ibias=
demonstrator: 2 turns of 150 % GMI tape
Idet~
~ Imeas =
GMI current sensor - parameters 2 turns
200 T + feedback
FS range
2A
100 A
sensitivity
0.24 Ω/A
24 Ω/A in open loop
197 ppm/ºC
30 ppm/ºC
Z (0 A)
23 Ω
2.3 k Ω
∆Z/∆T
0.24 Ω/A
???
105 mA/ºC
???
sensitivity TC
offset drift
Future trends AMR compact current sensors circular sensor fields di/dt coreless coils with digital integrator embedded pcb sensors Optical sensors for large currents
Engineer’s wishlist
• • • •
constant high , high Bsat materials constant high , low Bsat materials low TC GMI materials trick how to linearize GMR, SDT
Resources
• •
www.nve.com (GMR) www.Sentron.ch (vertical Hall)
•
www.ssec.honeywell.com/magnetic/ (AMR)
• •
www. Micronas.com (Hall) www.Infineon.com (Siemens: Hall, GMR)
•
www.semiconductors.Philips.com/automotive/sensors_discretes (AMR)
• • •
www.Geometrics.com (resonant magnetometers) measure.feld.cvut.cz/groups/maglab (fluxgate) Magnetic sensors and Magnetometers (book) Artech, 2001,www.artechouse.com
