Table 6-3: StrainCalc() configuration codes
BrConfig Code
Configuration
5
Full-bridge
strain
ga
u
ge.
Half
the
bridge
has
two
ga
u
ges
parallel
to
+ɛ
and
-ɛ,
and
the
other
half
to
+
ν
ɛ
and
-
ν
ɛ
1:
6
Full-bridge
strain
ga
u
ge.
Half
the
bridge
has
two
ga
u
ges
parallel
to
+ɛ
and
-
ν
ɛ
,
and
the
other
half
to
-
ν
ɛ
and
+ɛ
1
:
1
Where
•
ν
:
Poisson's
Ratio
(0
if
not
applicable).
• GF:
Ga
u
ge
Factor.
• V
r
:
0.001
(Source-Zero)
if
BRConfig
code
is
positive
(+).
• V
r
:
–0.001
(Source-Zero)
if
BRConfig
code
is
negative
(–).
and where:
• "source":
the
result
of
the
full-bridge
measurement
(X
=
1000
•
V1
/
Vx)
when
multiplier
=
1
and
offset
=
0.
• "zero":
ga
u
ge
offset
to
establish
an
arbitrary
zero.
6.3.3 AC excitation
Some resistive sensors require ac excitation. Ac excitation is defined as excitation with equal
positive (+) and negative (–) duration and magnitude. These include electrolytic tilt sensors, soil
moisture blocks, water-conductivity sensors, and wetness-sensing grids. The use of single polarity
dc excitation with these sensors can result in polarization of sensor materials and the substance
measured. Polarization may cause erroneous measurement, calibration changes, or rapid sensor
decay.
Other sensors, for example, LVDTs (linear variable differential transformers), require ac excitation
because they require inductive coupling to provide a signal. Dc excitation in an LVDT will result
in no measurement.
CRBasic bridge-measurement instructions have the option to reverse polarity to provide ac
excitation by setting the
RevEx
parameter to True.
6. Measurements
68
Summary of Contents for CR1000X
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