Campbell Scientific CR3000 Micrologger - Manual (Page 268)

Section 7. Installation
268
Figure 83: PT100 in four-wire full-bridge
CRBasic Example 61. PT100 in Four‐Wire Full‐Bridge
'See FIGURE. PT100 in Four-Wire Full-Bridge (p. 268) for wiring diagram.
Public BrFullOut
Public Rs_Ro
Public Deg_C
BeginProg
Scan (1,Sec,0,0)
'BrFull(Dst,Reps,Range,DfChan,Vx1,MPS,Ex,RevEx,RevDf,Settle,Integ,Mult,Offset)
BrFull (BrFullOut,1,mV50,1,Vx1,1,5000,True,True,0,250,.001,.02344)
'BrTrans = Rf*(X/(1-X))
Rs_Ro = 50 * (BrFullOut/(1 - BrFullOut))
'PRTCalc(Destination,Reps,Source,PRTType,Mult,Offset)
PRTCalc (Deg_C,1,Rs_Ro,2,1.0,0)
NextScan
EndProg
7.8.18.2.5 PT100s with Current Excitation
Example Shows:
• How to measure multiple PRTs with current excitation.
Advantages:
• Higher accuracy. Common excitation errors for all sensors in a series, which
results in smaller differential errors.
• Uses only one differential channel per PRT.
Disadvantages:
• If one series connection breaks, all sensors in the series will fail.