Campbell CR300 series - Page 113

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. RevDiff and MeasOff
parameters are discussed in Minimizing offset voltages(p. 199). Much of the offset error inherent
in bridge measurements is canceled out by setting RevDiff and MeasOff to True.
CRBasic Example 1: 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
18. Measurements97