Campbell CR800 Series, Operator'S Manual

Page: 273 / 598

Section 7. Installation
273
CRBasic Programs and Notes
PT100 BrFull() Four-Wire Full-Bridge Calibration
'This program example demonstrates the calibration of a 100-ohm PRT (PT100) in a four-wire
'full bridge with voltage excitation. See previous procedure and schematic.
'
'Declare constants and variables:
Const R1 = 5000000 'Value of R1 bridge resistor
Const R2 = 120000 'Value of R2 bridge resistor
Const R4 = 5000000 'Value of R4 bridge resistor
Public X1 'Raw output from the bridge
Public X2 'Calculated intermediate value
Public RS0 'Calculated PT100 resistance at 0 °C
BeginProg
Scan (1,Sec,0,0)
'Measure X1
'BrFull(Dest,Reps,Range,DiffChan,ExChan,MeasPEx,ExmV,RevEx,RevDiff,SettlingTime,
'
Integ ,Mult,Offset)
BrFull (X1,1,mV25,1,Vx1,1,2500,True,True,0,250,1,0)
'Calculate X2:
X2 = (X1/1000) + (R2/(R1+R2)
'Calculate RS0:
RS0 = (R4*X2) / (1-X2)
NextScan
EndProg
PT100 BrFull() Four-Wire Full-Bridge Measurement
'This program example demonstrates the measurement of a 100-ohm PRT (PT100) in a four-wire
'full bridge with voltage excitation. See previous procedure and schematic.
'
'Declare constants and variables:
Const R1 = 5000000 'Value of R1 bridge resistor
Const R2 = 120000 'Value of R2 bridge resistor
Const R4 = 5000000 'Value of R4 bridge resistor
Const RS0 = 100000 'Resistance of PT100 at 0 °C from calibration program
Public X1 'Raw output from bridge
Public X2 'Calculated intermediate value
Public RS 'Calculated PT100 resistance
Public RS_RS0 'Calculated ratio RS/RS0
Public DegC 'Calculated temperature of PT100
BeginProg
Scan (1,Sec,0,0)
'Measure X
'BrFull(Dest,Reps,Range,DiffChan,ExChan,MeasPEx,ExmV,RevEx,RevDiff,SettlingTime,
' Integ ,Mult,Offset)
BrFull (X1,1,mV25,1,Vx1,1,2500,True,True,0,250,1,0)