Apogee Instruments ST-110 Руководство пользователя - Страница 11
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Печатать страницуST-150
The ST-150 does not include bridge resistors and therefore requires measurement with dataloggers or controllers
that are capable of current excitation. Although the ST-150 can be used in a 2-wire or 3-wire measurement
configuration, a 4-wire configuration is recommended for highest accuracy (4-wire measurement configuration
eliminates the influence of lead wires). In the 4-wire configuration, an excitation current is applied across the PRT
with two of the lead wires, voltage is measured across the other two lead wires using a differential measurement,
and resistance of the PRT is calculated by dividing the measured voltage by the excitation current (Ohm's Law).
Current does not flow in the wires where voltage is measured, so resistance of the lead wires does not influence
the measurement. Temperature of the PRT is calculated from resistance using equations (2) and (3) on page 13. If
a half-bridge measurement is desired, the same wiring and bridge resistors detailed below in the ST-300 section
can be used to make the measurement.
White: Current excitation
Black: Ground
Yellow: High Side of Differential Channel
Blue: Low Side of Differential Channel
Clear: Ground (shield wire)
Note: as shown in the
schematic, the 4-wire PRT can
be directly measured. The black
and blue wires are electrically
connected to one side of the
PRT while the yellow and white
wires are electrically connected
to the other side of the PRT.