Campbell 4WPB100 Manual de usuario descargar pdf (Pagina 10)

4WPB100, 4WPB1K PRT Bridge Terminal Input Modules

With the PRT at 0°C, R

. Thus, the above result becomes R

, the

reciprocal of the multiplier required to calculate temperature, R

. By making

a measurement with the PRT in an ice bath, errors in both R

and R

. can be

accounted for.

To perform the calibration, connect the PRT to the datalogger and program the

datalogger to measure the PRT with the 4-wire half bridge as shown in the

example section (multiplier = 1). Place the PRT in an ice bath (at 0°C; R

Read the result of the bridge measurement. The reading is R

, which is equal

to R

since R

. The correct value of the multiplier, R

, is the reciprocal

of this reading. For example, if the initial reading is 0.9890, the correct

multiplier is: R

= 1/0.9890 = 1.0111.

4. Programming Examples

The following examples simply show the two instructions necessary to make the

measurement and calculate the temperature. The result of the 4-wire half bridge

measurement as shown is R

, the input required for the PRT algorithm to

calculate temperature.

‘Full Bridge’ is shown as the name for measurement Instruction 9

(used with the CR10/10X, 21X, and CR7). When Instruction 9 is

used with the first measurement range not set to the maximum

input range, it becomes a 4-wire half bridge measurement.

NOTE

All the examples are for a 100 ohm PRT in the 4WPB100. The excitation

voltages used were chosen with the assumption that the temperature would not

exceed 50°C. Tables 1 and 2 list 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 3.1.

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Campbell 4WPB100 Manual de usuario Pagina 10