Siemens SIMATIC S5-100U System Manual page 274

Analog Value Processing
11.2.1 Voltage Measurement with Isolated/Non-Isolated Thermocouples
Module 464-8MA11/8MA21 is recommended for voltage measurement with thermocouples. With
floating sensors (e. g., isolated thermocouples), the permissible potential difference V
terminals of the inputs and the potential of the standard mounting rail must not be exceeded. To
avoid this, the negative potential of the sensor must be connected to the central ground point (see
Figure 11-1). Jumper terminals 1 and 2 together if you do not use compensation boxes.
Reference junction
Figure 11-1. Voltage Measuring with Isolated Thermocouples (6ES5 464-8MA11/8MA21)
With non-floating sensors (e. g., non-isolated thermocouples), the permissible potential difference
V must not be exceeded (see maximum values of the individual modules).
CM
Reference junction
Figure 11-2. Voltage Measuring with Non-Isolated Thermocouples
11-2
1 3 5
2 4 6
+ -
+ -
+ -
Compen-
sating box
1 3 5
2 4 6
+ - + -
+ -
Compen-
sating box
(Module 6ES5 464-8MA11/8MA21)
7 9
8 10
Thermal
coupling
7 9
8 10
V
CM
Thermal
coupling
EWA 4NEB 812 6120-02b
S5-100U
between
CM