GE GFK-0804B manual Programming for an Analog Expander Unit, Analog Scaling, Analog References

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Programming for an Analog Expander Unit

Analog Scaling

The Analog Expander Unit provides two 8-bit analog inputs and one 8-bit analog output. Scaling for an analog input or output is:

Minimum: 0 volts = 0mA = 0 bits

Maximum: 9.969 volts = 19.922mA = 255 bits

Some examples of equivalent values are:

Volts 46190

9.969

7.5

5

2.5

0

0 64 128 192 255 Bits

Analog References

In a program, input 1 uses reference IR1. Input 2 uses reference IR2. The analog output uses reference OR1.

Maximum Values

The program references (IR1, IR2, and OR) used to store analog data are 16 bits each. However, the module utilizes only the lower 8 bits. Therefore, it is important not to inadvertently program a value greater than 255, which would cause incorrect results.

For example, suppose you programmed an output value of 258. This is shown below in bits. Because the module uses only the lower 8 bits, it would interpret the value incorrectly.

0 0 0 0 0 0 0 1

0 0 0 0 0 0 1 0

Higher 8 bits not used Only these 8 bits are used

1-8 Micro PLC Programmer's Guide ± April 1994 GFK-0804B