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when excitation is reversed, the differential measurement of the voltage drop across the sensor is
made with excitation at both polarities and then excitation is again applied and reversed for the
measurement of the voltage drop across the fixed resistor. The results of the measurements (X)
must then be processed further to obtain the resistance value, which requires additional program
execution time.
CRBasic Example 2: : Four-Wire Full Bridge Measurement and Processing
'This program example demonstrates the measurement and
'processing of a four-wire resistive full bridge.
'In this example, the default measurement stored
'in variable X is deconstructed to determine the
'resistance of the R1 resistor, which is the variable
'resistor in most sensors that have a four-wire
'full-bridge as the active element.
'Declare Variables
Public
X
Public
X_1
Public
R_1
Public
R_2 = 1000
'Resistance of fixed resistor R2
Public
R_3 = 1000
'Resistance of fixed resistor R3
Public
R_4 = 1000
'Resistance of fixed resistor R4
'Main Program
BeginProg
Scan
(500,mSec,1,0)
'Full Bridge Measurement:
BrFull
(X,1,mV250,1,Vx1,1,4000,True,True,0,60,1.0,0.0)
X_1 = ((-1 * X) / 1000) + (R_3 / (R_3 + R_4))
R_1 = (R_2 * (1 - X_1)) / X_1
NextScan
EndProg
6.3.2
Strain
measurements
A
principal
use
of
the
four-wire
full
bridge
is
the
measurement
of
strain
ga
u
ges
in
structural
stress
analysis.
StrainCalc()
calculates
microstrain
(µɛ)
from
the
formula
for
the
specific
bridge
configuration
used.
All
strain
ga
u
ges
supported
by
StrainCalc()
use
the
full-bridge
schematic.
'Quarter-bridge',
'half-bridge'
and
'full-bridge'
refer
to
the
number
of
active
elements
in
the
bridge
schematic.
In
other
words,
a
quarter-bridge
strain
ga
u
ge
has
one
active
element,
a
half-bridge
has
two,
and
a
full-bridge
has
four.
StrainCalc()
requires
a
bridge-configuration
code.
The
following
table
shows
the
equation
used
by
each
configuration
code.
Each
code
can
be
preceded
by
a
dash
(-).
Use
a
code
without
the
dash
when
the
bridge
is
configured
so
the
output
decreases
with
increasing
strain.
Use
a
6. Measurements
66
Содержание CR1000X
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Страница 16: ...Appendix A Glossary 176 Appendix B Index 214 Table of Contents viii ...
Страница 20: ...l Smart sensors o SDI 12 o RS 232 o Modbus o DNP3 o TCP IP o RS 485 1 Data acquisition system components 4 ...
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Страница 237: ...wiring panel 5 Appendix B Index 220 ...