Allen-Bradley SLC 500 Series User Manual

Publication 1747-RM001G-EN-P - November 2008
4-18 Math Instructions
Application Example 2 - Scaling an Analog Input to Control an
Analog Output
Calculating the Linear Relationship
Use the following equations to calculate the scaled units.
The above offset and rate values are correct for the SCL instruction. However,
if the input exceeds 13,107, the instruction overflows and sets S:5/0 math
overflow bit. For example:
To avoid an overflow, we recommend shifting the linear relationship along the
input value axis and reduce the values.
Scaled value = (Input Value X Rate) + Offset
Rate = (Scaled MAX. - Scaled MIN.) / (Input MAX. - Input MIN.)
(32,764 - 0) / (16,384 - 3277) = 2.4997 (or 24,997/10000)
Offset = Scaled MIN. - (Input MIN. x rate)
0 - (3277 x 2.4997) = - 8192
17 mA = 13,926 x 2.2997 = 34,810 (actual overflow)
34,810 - 8192 = 26,618
32,764 10V
(Scaled MAX.)
Scaled Value
0 0V
(Scaled MIN.)
3,277 4 mA
(Input MIN.)
Input Value
16,384 20 mA
(Input MAX.)

Allen-Bradley SLC 500 Series Specifications

General

Brand	Allen-Bradley
Model	SLC 500 Series
Category	Controller
Language	English