VTI Instruments EX1629, User Manual

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EX1629 Basic Operation 49
C
OMPLETION
R
ESISTOR
/I
NPUT
M
ULTIPLEXER
D
EFAULT
S
ETTINGS
Table 3-2 contains the default input multiplexer and completion resistor values for each EU
conversion.
EU Conversion Completion Resistor Input Multiplexer
Voltage Full Full
Quarter 120 Ω 120 Ω
Back-half
Quarter 350 Ω 350 Ω
Back-half
Quarter User User Back-half
Half Bending Full Back-half
Half Poisson Full Back-half
Full Bending Full Full
Full Poisson Full Full
Full Bending Poisson Full Full
Ratiometric Full Full
Linear Full Full
T
ABLE
3-2: D
EFAULT
C
OMPLETION
R
ESISTOR
/I
NPUT
M
ULTIPLEXER
V
ALUES
G
AGE
F
ACTOR
/ P
OISSON
R
ATIO
As illustrated in the Engineering Unit (EU) Conversion subsection, there are two constants
utilized in the EU strain conversions: gage factor and Poisson ratio.
The gage factor (GF), a measure of strain gage sensitivity, is a dimensionless quantity defined as
the ratio of the fractional change in resistance to the fractional change in length along the primary
axis of the strain gage. Mathematically, this is expressed as:
ε
R
ΔR
L
L
R
R
GF
The gage factor value for a specific strain gage is provided by the strain gage manufacturer. The
default gage factor is 2.0.
The Poisson ratio (ν), in simple terms, is a measure of the extent to which a material contracts as it
is being stretched. In engineering terms, it is a dimensionless quantity defined as the ratio of
transverse contraction strain to longitudinal extension strain in the direction of the stretching force.
Mathematically, this is expressed as:
long
trans
ε
-ε
ν
The Poisson ratio value for a specific material should be obtained from a mechanical engineering
reference. The default Poisson ratio is 0.3.