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S5-90U/S5-95U
15.6.1 Analog Input Modules
Analog Input Modules - Connecting Current and Voltage Sensors to Analog Input Modules
Analog input modules convert analog process signals to digital values that the CPU can process (via
the process input image PII).
Observe the following rules to connect current and voltage sensors to analog input modules.
•
When you have multi-channel operations, assign the channels in ascending order. This
shortens the data cycle.
•
Use terminals 1 and 2
- for the connection of a compensating box (464-8MA11)
or
- for the supply of two-wire transducers (464-8ME11).
Terminals 1 and 2 cannot be used with the remaining analog input modules.
•
Short-circuit the terminals of unused inputs (except for 464-8ME11).
•
The permissible potential difference between the common references of the inputs must not
exceed 1 V. To prevent this, set the reference potentials of the sensors to a common reference
potential.
•
If insulated sensors are used, either the sensor or the module must be earthed.
Analog Value Representation of Analog Input Modules
Each analog process signal has to be converted into a digital format, to be stored in the process
input image (PII). The analog signals are converted into a binary digit that is written in one of the
following ways.
•
in one byte (466-8MC11)
or
•
in two bytes (the remaining analog input modules).
Each position has a fixed value in powers of two.
Analog values are represented in two's complement.
The following table shows the analog value representation of the different analog inputs in 2-byte
format. The specific analog value representations are given in the description of the individual
modules.
Tabelle 15-7. Representation of an Analog Input Value as Bit Pattern
Bit Number
Analog Value Represent.
Key
S
Sign bit
X
Irrelevant bits
E
Error bit
OV
Overflow bit
EWA 4NEB 812 6115-02b
High Byte
7
6
5
4
3
2
11
10
9
8
7
S
2
2
2
2
2
0="+", 1="-"
0=no wire break; 1 = wire break
0=Measured value 4095 units at the most
1=Measured value greater than or equal to 4096 units
Low Byte
1
0
7
6
5
4
6
5
4
3
2
1
2
2
2
2
2
2
Module Spectrum
3
2
1
0
0
2
X
E
OV
15-37
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