2-Wire Rtd Connections - Data Translation DT9871 User Manual

2-Wire RTD Connections

The 2-wire configuration is the least accurate of the RTD wiring configurations because the
lead wire resistance (R
measurement errors, particularly if the lead wire is long. If you decide to use the 2-wire
connection scheme, ensure that you use short lead wire connections.
For example, if the lead resistance is 0.5  in each wire, the lead resistance adds a 1  of error
to the resistance measurement. Using a 100  RTD (Pt100) with a 0.00385/°C European curve
coefficient, the resistance represents an initial error of 1  /(0.385 /°C) or 2.6°C. Since the
lead wire resistance changes with ambient temperature, additional errors are also introduced
in the measurement.
Figure 16 shows a 2-wire RTD connection.
RTD Channel
Return
– Sense +Sense
4 3 2
RTD
Figure 15: 3-Wire RTD Connection
) and its variation with temperature contribute significant
L

425 A
Current
1
R
L
*R is lead wire resistance.
L
Wiring Signals
49