Siemens LOGO! Series Manual page 54

LOGO! installation and wiring
2.3 Wiring LOGO!
LOGO! AM2 PT100
You can connect a maximum of two 2-wire or 3-wire PT100 sensors or one 2-wire plus one
3-wire PT100 sensor to the module. Note that the sensor type supported by the module is
only PT100 with the default temperature coefficient of α= 0.003850.
For a 2-wire connection, you need to short-circuit terminals M1+ and IC1 or M2+ and IC2.
Errors caused by the ohmic resistance of the measuring line are not compensated for this
type of connection. A line resistance of 1 Ω is proportional to measuring error of +2.5 °C.
A 3-wire technique suppresses the influence of the cable length (ohmic resistance) on the
result of the measurement.
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Manual, 04/2011, A5E03556174-01
LOGO!