Siemens S5-135U/155U - Manual (Page 403)

9-21
System Manual
C79000-G8576-C199-06
9.3.11 Connecting Resistance Thermometers in the Extended Pt 100
Range
The series-connected resistance thermometers (up to 8 Pt 100s) are fed with a
current of 2.5 mA (I
C+
/I
C-
) by a constant current generator. The voltage at the
Pt 100s is picked off at measurement inputs M+ and M-.
In this mode, the temperature range of approximately -100
°
C to +100
°
C has
a more accurate resolution. The mode is printed on the cover of the module
as follows: “resistance thermometer compensated low range.”You should
only use the 6ES5 498-1AA11 range card (
" 50 mV / 500 mV).
Unused inputs must be connected in parallel to a wired input. In the
following figure, for example, these are the inputs CH4 to CH7.
M+
M–
Ch0
M+
M–
Ch1
M+
M–
Ch2
M+
M–
Ch3
M+
M–
Ch4
M+
M–
Ch5
M+
M–
Ch6
M+
M–
Ch7
Ic–
Ic+
L+
L–
6ES5498-
1AA11
6ES5498-
1AA11
24V
M24V
2.5mA
Figure 9-10 Connecting Resistance Thermometers in the Extended Pt 100 Range
Analog Input/Output Modules