Campbell CR6 Series, Operator'S Manual

Page: 337 / 690

Section 7. Installation
337
CRBasic Programs and Notes
PT100 BrHalf3W() Three-Wire Half-Bridge Calibration
'This program example demonstrates the calibration of a 100-ohm PRT (PT100) in a three-wire
'half bridge with voltage excitation. See previous procedure and schematic.
'Declare constants and variables:
Const Rf = 10000000 'Value of bridge resistor
Public X 'Raw output from the bridge
Public RS0 'Calculated PT100 resistance at 0 °C
BeginProg
Scan (1,Sec,0,0)
....'Measure X:
'BrHalf3W(Dest,Reps,Range,SEChan,ExChan,MeasPEx,ExmV,RevEx,SettlingTime,
' fN1
(p. 584),
Mult,Offset)
BrHalf3W (X,1,mV200,U3,U1,1,2500,True,0,15000,1,0)
'Calculate RS0:
RS0 = Rf * X
NextScan
EndProg
PT100 BrHalf3W() Three-Wire Half-Bridge Measurement
'This program example demonstrates the measurement of a 100-ohm PRT (PT100) in a three-wire
'half bridge with voltage excitation. See adjacent procedure and schematic.
'Declare constants and variables:
Const Rf = 10000000 'Value of bridge resistor
Const RS0 = 100000 'Resistance of PT100 at 0 °C from calibration program
Public X 'Raw output from the bridge
Public RS 'Calculated PT100 resistance
Public RS_RS0 'Calculated ratio RS/RS0
Public DegC 'Calculated temperature
BeginProg
Scan (1,Sec,0,0)
....'Measure X:
'BrHalf3W(Dest,Reps,Range,SEChan,ExChan,MeasPEx,ExmV,RevEx,SettlingTime,
' fN1
(p. 584),
Mult,Offset)
BrHalf3W (X,1,mV200,U1,U11,1,2500,True,0,15000,1,0)
'Calculate RS and RS_RS0:
RS = X * Rf
RS_RS0 = RS/RS0
....'Calculate temperature from RS_RS0:
'PRTCalc(Dest,Reps,Source,PRTType,Mult,Offset)
PRTCalc (DegC,1,RS_RS0,1,1.0,0)
NextScan
EndProg