Section 7. Installation
271
where,
VS
max
= 25 mV (maximum voltage in the
±
25
input range)
R1 = 5000000 mΩ (5 kΩ)
R2 = 100000 mΩ (100 Ω)
R4 = 5000000 mΩ (5 kΩ)
RS
max
= 123240 mΩ (PT100 at 60 °C)
2
so,
VX
max
= 44972562111243 mV
4. Calibrate the PT100:
If the PRT accuracy specification is good enough, and you trust it, assume
RS
0
= 100000 mΩ. Otherwise, do the following procedure:
a. Enter
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
into the CR800. It is already programmed with the excitation voltage from
step 3.
b. Place the PRT in an ice bath (0 °C).
Summary of Contents for CR800 Series
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Page 446: ...Section 8 Operation 446 8 11 2 Data Display FIGURE 100 CR1000KD Displaying Data ...
Page 448: ...Section 8 Operation 448 FIGURE 102 CR1000KD Real Time Custom ...
Page 449: ...Section 8 Operation 449 8 11 2 3 Final Storage Data FIGURE 103 CR1000KD Final Storage Data ...
Page 450: ...Section 8 Operation 450 8 11 3 Run Stop Program FIGURE 104 CR1000KD Run Stop Program ...
Page 452: ...Section 8 Operation 452 FIGURE 106 CR1000KD File Edit ...
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