Datasheet

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last update
November 30, 2010
reference
smtutin
page
20/27
8 RESITIVE BRIDGE MODES (MODE 9 – 14)
8.1 Mode 9. Ub2: resistive bridge, ref. is V
bridge
, +/- 4% imbalance
In this mode, a resistive bridge can be measured where the ratio of the bridge output voltage V
CD
and the
bridge supply voltage V
AB
represents the physical signal.
The measurement range of the bridge imbalance is +/-4% in this mode.
The connection of the bridge to the UTI is shown in Figure 13. The driving voltage across the bridge V
EF
is
a square wave with amplitude V
DD
. The frequency of this signal is 1/4 of the internal oscillator frequency.
Because force/sense wires are used, the bridge is measured in a 4-wire setup, as shown in Figure 13 (a).
The signals measured in the various phases are given in Table 16
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Figure 13. Connection of the resistive bridge to the UTI for the Ub2 mode in a 4-wire setup (a) and a 2-
wire setup (b)
During phase 2, the voltage across the bridge V
AB
is measured. A very accurate on-chip voltage divider
divides this voltage by 32. This divider does not need calibration. After division, V
AB
is processed in the
same way as V
CD
.
Phase Measured voltages Output periods
1 V
offset
Toffset=N*K
2
*Voffset
2 V
ab
/32+V
offset
Tab= N*K
2
*(Vab/32+Voffset)
3 Vcd+V
offset
Tcd=N*K
2
*(Vcd+Voffset)
Table 16. Measured voltages of Ub2 mode
E
A
C
D
B
F
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