Campbell Scientific CR3000 Micrologger - Manual (Page 302)

Section 8. Operation
302
Table 63. Resistive-Bridge Circuits with Voltage Excitation
Resistive-Bridge Type and
Circuit Diagram
CRBasic Instruction and
Fundamental Relationship Relationships
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 Where X = result of the CRBasic bridge measurement instruction with a multiplier of 1 and an offset of 0.
3 See the appendix Resistive Bridge Modules (p. 563) for a list of available terminal input modules to facilitate this measurement.
Table 64. Resistive-Bridge Circuits with Current Excitation 1
Resistive-Bridge Type and
Circuit Diagram
CRBasic Instruction and
Fundamental Relationship Relational Formulas
Basic Circuit
2
Fundamental Relationship
3
:
Full Bridge
2
CRBasic Instruction: BrFull()
Fundamental Relationship
3
:
1 See Sensors Requiring Current Excitation (p. 330) for precautions to consider when measuring resistances > 1000 Ω or sensors with
leads > 50 feet.
2
Key: I
x
= excitation current; IxR = Current Return; V
1
= sensor return voltage; R
s
= "variable" or "sensing" resistor.
3
Where X = result of the CRBasic bridge measurement instruction with a multiplier of 1 and an offset of 0.
CRBasic Example 66. Four‐Wire Full‐Bridge Measurement and Processing
'Declare Variables
Public X
Public X1
Public R1
Public R2
Public R3
Public R4