Section 7. Installation
296
7.7.17.7
Example: 100 Ω PRT in Four
-Wire Full Bridge with Current
Excitation (PT100 / Full-Bridge Resistance() )
FIGURE 72: PT100 Resistance() Four-Wire Full-Bridge Schematic
Procedure Information
Four-Wire Half-Bridge Equations for PRT Example
X = V1 / IX
X = ((R3 • (R1 + R2))
– (R2 • (R3 + R4))) / (R1 + R2 + R3 + R4)
R3 = ((
–R2 • R4) – (X • (R1 + R2 + R4))) / (X – R1)
RB = X / ((R3 / (R3 + R4))
– (R2 / (R1 + R2)))
Definitions:
•
X is the output of the Resistance() equation
•
V1 is the voltage output of the bridge at terminals U3 and U4 (this value
is used only internally in the CR3000).
•
IX is the magnitude of the current (I) excitation.
•
R1, R2, R4 are resistor values in the bridge.
•
R3 is the resistance of the PRT.
•
RB is the resistance of the whole bridge as measured between the IX
excitation line and the
ground line.
Bridge Resistor Values (mΩ)
R1
R2
R4
5000000
100000
5000000
Summary of Contents for CR3000 Micrologger
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