Datasheet
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last update
November 30, 2010
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8.5 Mode 13. Brg2: resistive bridge +/- 4% and 2 resistors
In this mode, a resistive bridge with a maximum imbalance of +/-4% and two resistors can be measured.
One of the resistors can be temperature dependent, so the bridge output can be digitally corrected for
temperature effects. Both the voltage across the bridge and the current through the bridge are measured.
The connection of the elements to the UTI is shown in
Figure 15.
The voltage V
EF
is a square wave with amplitude V
DD
at 1/4 of the oscillator frequency. The
voltage across R
ref
should be between 0.1 V and 0.2V.
The voltages to be measured are indicated in
Table 24.
Figure 15. Connections of the sensors to the UTI
The voltage across the bridge
V
EA
is divided by 32 before it is processed in the same way as the other
measured voltages. The bridge imbalance
V
CD
/V
EA
is obtained from:
M
T T
T T
V
V
phase phase
phase phase
CD
EA
=
−
−
=
1
32
3 1
5 1
(6)
The specifications of this mode are listed in
Table 25
For the measurement of the signal
V
BF
, due to the effect of the internal connection wires of the UTI, an
error of 1.2% will be caused on the result of
V
AB
/
V
BF
. This measured error depends on the supply current of
the resistive bridge and the temperature.
Phase Measured voltages Output periods
1 V
offset
Toffset=N*K
2
*Voffset
2 V
ab
+V
offset
Tab= N*K
2
*(Vab+Voffset)
3 Vcd+V
offset
Tcd=N*K
2
*(Vcd+Voffset)
4 V
bf
+V
offset
Tbf= N*K
2
*(Vbf+Voffset)
5 V
ea
/32+V
offset
Tea= N*K
2
*(Vea/32+Voffset)
Table 24. Measured voltages during the measurement of Brg2 mode
Parameter (V
DD
= 5 V) Typical value
K
2
56 s/V
V
0
0.54 V
Bridge excitation AC Vdd
excitation current (max E - F) 20 mA
Bridge resistance 250-10k
Bridge output Voltage <+/- 0,2V
Accuracy Vcd/Vea 11 bits (over =/- 0.2V)
Linearity Vab/Vbf 12 bits (over +/- 0,2V)
Offset
<10 V
Resolution (SF=0)
< 7 V
Table 25. Specifications of the Brg2 mode
E
C
D
A
B
F