Siemens Simatic S7-400 - Manual (Page 302)

Analog Modules
5-86
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Wiring for Resistance and Temperature Measurement
The following conditions apply when measuring the resistance and temperature
with the SM 431; AI 8 x 14 Bit:
Table 5-53 Channels for Resistance and Temperature Measurement with the SM 431; AI 8 14 Bit
Measuring Type Parameter Permissible
for Channel n
Condition
Resistor
(four-conductor terminal) 0, 2, 4 or 6 You must disable the ( “Measuring Type” parameter for
channels n+1 (1, 3, 5, 7).
Resistor
(three-conductor terminal) 0, 2, 4 or 6
( , , , )
The reason The connections of channel n+1 are used
to supply the resistance that is connected to
channel n
Thermal resistor
(linear, four-conductor termi-
nal) 0, 2, 4 or 6
channel n.
Thermal resistor
(linear, four-conductor termi-
nal) 0, 2, 4 or 6
Wiring for Junction Compensation for Thermocouples
If you select “RTD on Channel 0” as a reference junction for reference junction
compensation for thermocouples, the following applies:
Table 5-54 Thermocouple with Reference Junction Compensation via RTD on Channel 0
Reference Junction
Parameter
Permissible
for
Channel n
Condition
RTD on Channel 0 2 to 7 You must connect and parameterize on channel 0 a
resistance thermometer with linearization, a 3- or
4- conductor connection in the climatic range (channels
0 and 1 are thus assigned).
The reason: If channel 0 is to be used as the reference
junction, a resistance-type sensor must be connected
there to record absolute temperatures in the climatic
range.
Unused Channels
Unused channels can usually be left open. Put the measuring range module in
position “A”. You can improve the noise immunity of the module in a measuring
environment with serious interference by short-circuiting the channels.
Disable the “Measuring Type” parameter for unused channels. In this way you
shorten the scan time of the module.