Technical data of CPU 31xC   
6.6 Technical data of the integrated I/O 
  CPU 31xC and CPU 31x, Technical Data 
6-34  Manual, 01/2006 Edition, A5E00105475-06 
6.6.2  Analog I/O 
Wiring of the current/voltage inputs 
The figure below shows the wiring diagram of the current/voltage inputs operated with 2-/4-
wire measuring transducers. 
9
$1$
0
0
F
,
X
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&
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$1$
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3LQWR
3LQWR
3LQWR
3LQWR
 
Figure 6-1  Connection of a 2-wire measuring transducer to an analog current/voltage input of 
CPU 313C/314C-2 
 
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X
,
F
X
,
F
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0
$1$
0
0
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ZLUH
VLJQDOFRQYHUWHU
3LQWR
3LQWR
3LQWR
3LQWR
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&
ZLWK0
$1$
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&
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Figure 6-2  Connection of a 4-wire measuring transducer to an analog current/voltage input of 
CPU 313C/314C-2 
Measurement principle 
31xC CPUs use the measurement principle of actual value encoding. Here, they operate 
with a sampling rate of 1 kHz. That is, a new value is available at the peripheral input word 
register once every millisecond. This value can then be read via user program (e.g. L PEW). 
The "previous" value is read again if access times are shorter than 1 ms.