Page 22 ·
TECPak
User’s Manual
2-Wire versus 4-Wire Measurements
One concern in using RTDs are their relatively low resistance (typically 100
Ω
at
0°C), and small
Ω
/
°C. Because of these two factors, the resistance of the cable
used to connect to the sensor can become a significant error in the sensor
measurement. The
TECPak
offers two RTD measurement modes: a
conventional two wire measurement mode, which is subject to this error, and a
four wire measurement mode that uses separate sensor and source lines to
remotely sense the actual resistance of the RTD and eliminate the cable or
connector resistances.
When using 4-wire measurement mode, you must select ‘RTD (4-wire)’ as the
sensor type, and then connect the and Remote at one side of
the RTD, and Sensor– and Remote Sensor– to the other side of the RTD. Make
these connections as close to the sensor as possible.
The drawings below illustrate how 2-wire and 4-wire connections work. Note that
4-wire measurements require all four wires to be brought through the cable to
the mount. The
1262B
and
1263B
cables carry this connection through to the
mount, but the
1260B
and
1261B
cables do not.
RTD 2-wire Measurement
RTD 4-wire Measurement
Because the Analog Set Point input shares the measurement input with the
remote sensor input, when using RTD 4-wire measurement mode, the Analog
Set Point Input is disabled.
Mount
5300
RTD
Sensor
Sensor–
5300
RTD
Sensor
Remote
Remote Sensor–
Sensor–
Mount
