Campbell 4WPB100 Manual do Utilizador descarregar pdf (Página 8)

4WPB100, 4WPB1K PRT Bridge Terminal Input Modules

Figure 2 Circuit Schematic

2. Wiring

The Terminal Input Module is connected to the appropriate channel. The dashed

lines in Figure 2 indicate the sensor wiring. When making 4-wire half bridge

measurements, the 4WPB is connected to a differential channel, and the sense

leads from the PRT to the next differential channel. The black excitation wire is

connected to the excitation channel. In the following examples the 4WPB is

connected to differential channel 1 and the PRT to differential channel 2; the

excitation wire is connected to excitation channel 1 (Figure 3).

Ex1

AG or

PRT

4WPB100

Datalogger

Figure 3 Wiring for Example Programs

3. PRT in 4-Wire Half Bridge

A 4-wire half bridge is the best choice for accuracy where the Platinum

Resistance Thermometer (PRT) is separated from other bridge completion

resistors by a lead length having more than a few thousandths of an ohm

resistance. Four wires to the sensor allow one set of wires to carry the excitation

current and a separate set of sense wires that allow the voltage across the PRT to

be measured without the effect of any voltage drop in the excitation leads.

Figure 2 shows the circuit used to measure the PRT. The 10kΩ resistor allows

the use of a high excitation voltage and low voltage ranges on the measurements.

This ensures that noise in the excitation does not have an effect on signal noise

and that self heating of the PRT due to excitation is kept to a minimum. Because

the fixed resistor (R

) and the PRT (R

) have approximately the same resistance,

the differential measurement of the voltage drop across the PRT can be made on

the same range as the differential measurement of the voltage drop across R

1 2 3 4 5 6 7 8 9 10 11 12 13

Sem comentários

Campbell 4WPB100 Manual do Utilizador Página 8