Siemens SIMATIC ET 200X, Manual

Page: 297 / 362

Technical Specifications
7-109
ET 200X Distributed I/O Device
EWA 4NEB 780601602-06
Connecting Pt 100 resistance thermometers
The resistance thermometers are measured in a four-conductor connection.
Constant current is fed to the resistance thermometers via connections I
C+
and
I
C–
. The voltage generated at the resistance thermometer is measured via
connections M
+
and M
–
. This ensures highly accurate measurement results with
the four-conductor connection. The figure below shows how resistance
thermometers are connected to an EM 144 AI 2
RTD expansion module.
1L+
Socket X1
Socket X2
1M*
* Made available by the ET 200X for the connected sensor
M+
M–
I
C+
I
C–
I
C
Connection of socket X2:
see socket X1
1
2
3
4
1
2
3
4
Figure 7-28 Connection of resistance thermometers to EM 144 AI 2 x RTD (EM with order number
6ES7 144-1JB31-0XB0)
In the case of a two- or three-wire connection, you have to create appropriate
bridges in the connector to form connections between M
+
and I
C+
and M
–
and
I
C–
on the expansion module. However, you must reckon with a lost of accuracy in
the measurement results.
7.21.8 Connecting loads to the analog outputs
When you use expansion modules with analog outputs, you can supply
loads/actuators with current or voltage.
Abbreviations used
The following abbreviations are used in the figures in this section:
Q
I
: Analog output current
Q
V
: Analog output voltage
1M: Frame connection/reference potential of the analog circuit
R
L
: Load/actuator
Connecting loads to a voltage output
You have to connect loads to a current output at Q
V
and the reference point of the
analog circuit 1M (see Figure 7-29).