ADLINK USB-2401 - Manual (Page 44)

34 Operation
Figure 3-9: 2-wire RTD Connection
3.3.6 Wire Resistance Mode
The USB-2401 can source precision 0.05 mA excitation current to
the resistor to be measured and use a 2.5V input range to acquire
cross-voltage on the resistor. The formula of voltage to resistance
conversion is:
Since the excitation current can only drive the cross-voltage up to
1.5V with good linearity, the maximum equivalent value of the
resistor is limited to 30kΩ.
ADC
MUX
0.5mA
RTD
X
X
X
X
SC+
SC-
EXC
GND
USB-2401
0.00005
V(volt)
) ( = Ω R