Resistive-Bridge Type and
Circuit Diagram
CRBasic Instruction and
Fundamental Relationship
Relational Formulas
Full Bridge
1,2
CRBasic Instruction:
BrFull()
Fundamental Relationship:
These relationships
apply to
BrFull()
and
BrFull6W()
Six Wire Full Bridge
1
CRBasic Instruction:
BrFull6W()
Fundamental Relationship:
1
Key: V
x
= excitation voltage; V
1
, V
2
= sensor return voltages; R
f
= fixed, bridge or completion resistor; R
s
=
variable or sensing resistor.
2
Campbell Scientific offers terminal input modules to facilitate this measurement.
Offset voltage compensation applies to bridge measurements. In addition to
RevDiff
and
MeasOff
parameters discussed in
(p. 57), CRBasic bridge
measurement instructions include the
RevEx
parameter that provides the option to program a
second set of measurements with the excitation polarity reversed. Much of the offset error
inherent in bridge measurements is canceled out by setting
RevDiff
,
RevEx
, and
MeasOff
to True.
Measurement speed may be reduced when using
RevDiff
,
MeasOff
, and
RevEx
. When
more than one measurement per sensor is necessary, such as occurs with the
BrHalf3W()
,
BrHalf4W()
, and
BrFull6W()
instructions, input and excitation reversal are applied
separately to each measurement. For example, in the four-wire half-bridge (
BrHalf4W()
),
6. Measurements
65
Summary of Contents for CR1000X
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