Campbell CR800 Series, Operator'S Manual

Page: 268 / 598

Section 7. Installation
268
d. Calculate RS
10
:
RS
10
= X
10
• Rf = 103900
6. Calculate RS
10
/RS
0
, K, and temperature:
a. RS
10
/RS
0
= 1.039
b. K = (RS
10
/RS
0
)- 1 = 0.039
c. T = g * K^4 + h * K^3 + i * K^2 + j * K = 9.99 °C
d. T = (SQRT(d * (R S
10
/RS
0
) + e) - a) / f = 9.99 °C
1
A Campbell Scientific terminal-input module (TIM) can be used to complete the resistive bridge
circuit. Refer to the appendix Passive-Signal Conditioners — List
(p. 563).
4
Get this value from a PRT-resistance-to-temperature table
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,
' Integ,Mult,Offset)
BrHalf3W (X,1,mV25,1,Vx1,1,2033,True,0,250,1,0)
'Calculate RS0:
RS0 = Rf * X
NextScan
EndProg