Campbell Scientific 3WHB10K 3-Wire Half-Bridge Terminal Input Module - Manual (Page 6)

3WHB10K 3-Wire Half Bridge Terminal Input Module
2
3. Wiring
Shield
A
B
H
L
G
10 k Ω
Datalogger
Vx
H
L
or AG
or G
FIGURE 3-1. 3-Wire Half Bridge Used to Measure PRT
TABLE 3-1. 3WHB10K Connections to
Campbell Scientific Dataloggers
Function
Label/Lead
CR10X,
CR510 CR23X,
CR1000,
CR800, CR850,
CR3000
21X, CR7,
CR9000X
Excitation Black Wire E1 EX1 Excitation 1
V1 Reference H SE1 SE1 1H
V2 Sense L SE2 SE2 1L
Ground G AG
4. Programming Examples
The following examples simply show the two instructions necessary to 1)
make the measurement and 2) calculate the temperature. The result of the 3-
wire half bridge measurement as shown is R
s
/R
o
, the input required for the
PRT algorithm to calculate temperature.
All the examples are for a 100 Ohm PRT in the 3WHB10K. The excitation
voltages used were chosen with the assumption that the temperature would not
exceed 50°C. Table 4-1 lists excitation voltage as a function of maximum
temperature and the input voltage ranges used with the different dataloggers.
Calculation of optimum excitation voltage is discussed in Section 5.1.
The multiplier shown is for a 100 Ohm PRT. The multiplier for a 1000 Ohm
PRT is 10.