Measurement Computing CIO-EXP-RTD16 - Manual (Page 20)

5.6.1 Two-wire RTD Hookup
+IEXC (EXCITATION CURRENT (+))
+ SENSE
- SENSE
-
? ? ? ? ?
C A O
-IEXC (EXCITATION CURRENT (
− ))
2-WIRE
RTD
Add Jumper Wires
Between Terminals
CIO-EXP-RTD BOARD
A two wire RTD has two leads, one to each side
of the temperature sensitive resistor. The
excitation current is connected directly to the
leads at the CIO-EXP-RTD16 screw terminals. A
two wire connection is less accurate than the 4
wire type, and so is not the first choice for the
best measurements. The reason for the inaccuracy
is that there is a varying resistance associated with
the excitation current flowing in the sense leads
and this resistance is added to the measurement.
The amount of inaccuracy is determined by the
wire gauge and length.
Figure 5-4. Two-Wire RTD Connections
5.6.2 Three-Wire RTD Hookup
+IEXC (EXCITATION CURRENT (+))
+ SENSE
- SENSE
-
? ? ? ? ?
C A O
-IEXC (EXCITATION CURRENT (
−
))
3-WIRE
RTD
CIO-EXP-RTD BOARD
NOTE: The CIO-EXP-RTD uses a non-standard 3-wire hook-up.
A three-wire RTD connection allows the use of
special circuit to compensate for resistance
variations in the lead wires with temperature
changes (Figure 5-5 at right).
NOTE: The +Sense terminal is not used in this
non-standard hookup.
Figure 5-5. Three-Wire RTD Connections
16