Siemens LOGO! Series Manual page 55

LOGO! AM2 RTD
You can connect a maximum of two PT100 sensors or two PT1000 or one PT100 plus one
PT1000 sensor in a 2-wire or 3-wire connection or in a mixed use of 2-wire and 3-wire
connection to the module. Note that the sensor type supported by the module is only PT100
or PT1000 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. If a PT100 sensor is connected, a line resistance of 1 Ω is proportional to
measuring error of +2.5 °C; if a PT1000 sensor is connected, a line resistance of 1 Ω is
proportional to measuring error of +0.25 °C.
A 3-wire technique suppresses the influence of the cable length (ohmic resistance) on the
result of the measurement.
Note
Fluctuating analog values are due to screening on the connecting wire from the analog
valuator device to the analog AM2 / AM2 PT100 / AM2 RTD LOGO! expansion module
(encoder wire) that has either been mounted incorrectly or not at all.
To avoid fluctuating analog values when using these expansion modules, proceed as
follows:
• Use only shielded encoder wires.
• Shorten the encoder wire as much a possible. The encoder wire must not be more than
• Clamp the encoder wire on one side only and clamp it only to the PE terminal on the AM2
• Connect ground on the encoder supply to the PE terminal on the expansion module.
• Avoid operating the LOGO! AM2 PT100 or LOGO! AM2 RTD expansion module with a
LOGO!
Manual, 04/2011, A5E03556174-01
10 meters long.
/ AM2 PT100 / AM2 AQ / AM2 RTD expansion module.
power supply that is not grounded (potential-free). If you cannot avoid this, connect the
negative output/ground output on the power supply to the shielding on the resistance
thermometer's measuring wires.
LOGO! installation and wiring
2.3 Wiring LOGO!
55