LINEAR MAGNETIC FIELD SENSORS
Low Field Measurements—When measuring 100 µgauss
resolution or less, the permalloy film must be completely
set, or reset, to insure low noise and repeatable
measurements. A current pulse of 4 amps, or more, for just
a couple microseconds will ensure this. The circuits in
Figures 8 and 9 are recommended for applications of
HMC1001/2 that require low noise and high sensitivity
magnetic readings.
For any magnetic sensor application, if temperature drift is
notanissue, thentheresetpulseneedonlybeoccasionally
applied. This will save power and enable the use of digital
filtering techniques as shown in Figure 12. Circumstances
for a reset pulse would be 1) power on or, 2) field over/
under range condition. Any other time the sensor should
perform normally.
200
1µF (1)
1µF (1)
+5V
Low Cost—For minimum field measurements above 500
µgauss, a less elaborate pulsing circuit can be used. In both
Figures 10 and 11, the pulse signal is switched using lower
costDarlingtontransistorsandfewercomponents.Thiscircuit
mayhaveamorelimitedtemperaturerangedependingonthe
quality of transistors selected. If accuracy is not an issue and
cost is, then the reset only circuit in Figure 11 will work.
10K
0.1µF
0.1µF
HMC1022
8
FMMT717
FMMT617
14
0.1µF
9,15
0.1µF
0.1µF
0.1µF
Clock
+16 to 20V
4.7µF (1)
10K
(1) Tantalum, low R
10K
S/R strap @ 4.5Ω typ.
0.022µF
0.022µF
3A peak (min.)
ZTX705
ZTX605
HMC2003*
Figure 12—5V Circuit for SET/RESET (1021/1022)
17
1
0.22µF
The circuit in Figure 13 generates a strong set/reset pulse
under a microprocessor clock driven control. A free running
555 timer can also be used to clock the circuit. The SET
current pulse is drawn from the 1 µF capacitor and a 200
ohm dropping resistor should be placed in series with the
supply to reduce noise.
Clock
S/R
10K
(1) Tantalum, low R
Figure 10—Single Clock Set/Reset Circuit (1001/1002)
S/R strap @ 4.5Ω typ.
+16 to 20V
3A peak (min.)
100K
*
HMC2003
17
0.22µF
1
0.022µF
Clock
ZTX605
S/R
10K
5V
Clock
S/R
T
PW ≈ 2 µsec
-16V
reset
*The HMC2003 has 3-axis S/R straps in series.
These are the HMC1001 and HMC1002 sensors.
Figure 11—Single Clock Reset Only Circuit (1001/1002)
10
HONEYWELL [ Honeywell ]
