Rockwell Automation 1746-XXXX SLC 500 4-Channel Analog I/O Modules User Manual - Manual (Page 77)

Publication 1746-UM005B-EN-P - June 2004
Programming Examples 6-15
The following graph shows the shifted linear relationship. Notice that
the resulting offset value is reduced.
Calculating the Shifted Linear Relationship
Use the following equations to recalculate the linear relationship:
Scaled value = ((input value - input min.) x slope)) + offset
Slope = (scaled max. - scaled min.) / (input max. - input min.)
(31,208 - 6,242) / (100-90) = 24,966/10
Offset = scaled min.
6,242
Scaled value = ((input value - 90) x (24,966/10)) + 6242
Since the slope is greater than 3.2767, only standard math can be used
for the ladder diagram with SLC 500 fixed, SLC 5/01, 5/02, 5/03
(OS300 and 301) and 5/04 (OS400). The following ladder diagram
prevents a processor fault by unlatching the mathematical overflow bit
S2:5/0 before the end of the scan. Refer to the example ladder
diagram on the next page. Following this example is another ladder
diagram performing the same function, but using the SCP (scale with
parameters) instruction available only in the SLC 5/03 (OS302), SLC
5/04 (OS401), and SLC 5/05.
Scaled
Value
Input Value
(input min.)
100%
(input max.)
90%
20 mA = 31208
(scaled max.)
4 mA = 6242
(scaled min.)