JYTEK USB-62401, User Manual

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32 Operation
Figure 3-6: Thermocouple Connection
3.3.5 RTD Input Mode
The resistance temperature detector (RTD) measures temperature by
correlating the resistance of the RTD element with temperature. The
USB-62401 can generate a steady 0.5 mA excitation current source to
each channel in RTD input mode to measure cross-voltage on the RTD.
The actual input range is ±2.5V with a formula of voltage to RTD resis -
tance conversion of:
Since the excitation current can only drive cross-voltage up to 1.5V with
good linearity, the maximum equivalent value of the RTD resistor is lim -
ited to 3kΩ.
The USB-62401 can support two, three, and four-wire RTD measure
-
ment. Adopting three- and four-wire connections rather than two-wire
can eliminate connection lead resistance effects from measurement.
Three-wire connection is sufficient for most purposes and most univer -
sal industrial applications. Four-wire connections are used for the most
precise application requirements.
0.0005
V(volt)
) ( = Ω RTD