VTI Instruments Corp.
44
EX1629 Basic Operation
The quarter-bridge strain conversion is calculated according to:
sense
backhalf
diff
V
V
V
excitation
unstrained
diff
V
V
V
V
r
r
r
V
GF
V
2
1
4
Setting this conversion automatically configures the input path for quarter-bridge mode, in which
the required completion resistor is enabled and the back-half resistors are connected. This
configuration is illustrated in Figure 2-3.
Any of these quarter-bridge conversions also apply to the following bridge configuration, where
the dummy gage is utilized for temperature compensation of the active gage:
V
EXC
R
R
V
O UT
R ( )
g
R (Dummy)
g
R ( )
g
R (Dummy)
g
+
–
+
–
F
IGURE
3-2:
Q
UARTER
-B
RIDGE WITH
D
UMMY
G
AGE
This is simply a quarter-bridge configuration where the completion resistor is external to the
instrument (since only one leg of the bridge is active, it is a quarter-bridge, not a half-bridge which
would contain two strain gage resistors). To configure a channel for this use, the channel’s EU
conversion should be set to quarter-bridge (any of the 120, 350, or User configurations can be
used, since the nominal resistance only effects which completion resistor is selected), the input
multiplexer should be set to half-bridge, and then the completion resistor should be set to full.
While this configuration appears similar to a half-bridge configuration, it is different in that the
quarter-bridge conversion equation is used. This configuration may be used with any external
completion resistor.
Half-Bridge Bending
This conversion applies to the following bridge configuration:
V
OUT
V
EXC
R
R
+
–
+
–
R (+ )
g
R (- )
g
F
IGURE
3-3:
H
ALF
-B
RIDGE
B
ENDING
C
ONFIGURATION
Содержание EX1629
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