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Converting analog output data -7, Converting analog output data – Rockwell Automation 1746-XXXX SLC 500 4-Channel Analog I/O Modules User Manual User Manual

Page 45

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Publication 1746-UM005B-EN-P - June 2004

Module Operation and System Considerations 4-7

To determine an approximate current that an input value represents,
you can use the following equation:

Converting Analog Output Data

Analog outputs convert a 16-bit two’s complement binary value into
an analog output signal. Because the analog output channels have a
14-bit converter, the 14 most significant bits of this 16-bit number are
the bits that the output channel converts.

The NIO4I and NO4I support two and four current outputs
respectively, ranging from 0 mA to a maximum of 21 mA. The NIO4V
and NO4V support two and four voltage outputs respectively, ranging
from -10 to +10 Volts dc.

The following tables identify the current and voltage output ranges for
the output channels, the number of significant bits for the applications
using output ranges less than full scale, and their resolution.

Current Range

Decimal Representation
for Output Word

Number of
Significant Bits

Resolution
per LSB

0 to 21 mA - 1LSB

0 to +32,764

13 bits

2.56348

µ

A

0 to +20 mA

0 to +31,208

12.92 bits

4 to +20 mA

6,242 to +31,208

12.6 bits

×

input value

=

input current (mA)

20 mA

16,384

The Input Value is the decimal value of the word in the

input image for the corresponding analog input.

For example, if an input value of 4096 is in the input image,
the calculated input current is:

×

4096

=

5(mA)

It should be noted that this is the calculated value. The
actual value may vary within the accuracy limitations of
the module.

20 mA

16,384