ZMT32
Issue 1 - June 2008 4 www.zetex.com
© Zetex Semiconductors plc 2008
where R
B
(T
n
) is the bridge resistance at temperature T
n
where V
OFF(Tn)
is the output offset voltage at temperature T
n
Magnetic field tests
For these tests a rotating magnetic field is generated and the output signals of both bridges are measured at
four different field angles for right rotation as well as for left rotation. Using these measured output signals
the diameter and the center coordinates of the best circle are calculated. They correspond to the output
voltage range and the offset voltage. Furthermore the field angles for both rotation directions and angular
hysteresis are calculated
Method
The data pairs are transformed onto a unit circle starting from their position in the data collection
for determining direction information or angle information.
It must be evaluated with four pair values (cos, sin) on a right rotation (magnetic field rotation)
and four pair values (cos, sin) on a left rotation (magnetic field rotation).
The field rotation steps are:
Æ start in 180° position
§ right rotation to 22.5° with measurement of sensor outputs
§ right rotation to 67.5° with measurement of sensor outputs
§ right rotation to 112.5° with measurement of sensor outputs
§ right rotation to 157.5° with measurement of sensor outputs
§ right rotation to 0° (360°) , stop , reversal
§ left rotation to 157.5° with measurement of sensor outputs
§ left rotation to 112.5° with measurement of sensor outputs
§ left rotation to 67.5° with measurement of sensor outputs
§ left rotation to 22.5° with measurement of sensor outputs , end position
General description of tests with external magnetic field.
%100
)T(R
)T(R)T(R
TT
1
TCR
0B
1B2B
12
B
×
−
×
−
=
)TT(
VV
TCV
12
)1T(OFF)2T(OFF
OFF
−
−
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=α=
1O
2O
V
V
arctan]anglemeasured[
