Rockwell Automation 2706-MB1 MESSAGEVIEW 421 SOFTWARE MANUAL - Manual (Page 86)

4–38 Planning an Application
Publication 2706-817
Data entered by a MessageView terminal operator can be scaled
from engineering units such as:
•
gallons
•
pounds per square inch.
to machine control values.
Values entered at the terminal are scaled according to the formula:
x =
y - b
m
=
Entered Value - Offset
Scale
y = mx + b
y = scaled value (entered by operator)
m = scale (multiplier)
x = controller value
b = offset.
To calculate value (x) stored at the controller address, the formula becomes:
The scale and offset values are entered in the Tag Editor. Scaled
values affect the controller values as follows:
•
A scale (m) entered as a value >1 generates an x value smaller
than y - b.
•
A scale (m) entered as a value <1 generates an x value larger than
y - b.
Note: An ASCII Input device may transmit either numeric or
alphanumeric data.
•
If it sends numeric data, it may enter the data in a Numeric Entry
variable where it may be scaled if necessary.
•
If it sends alphanumeric data, it enters the data in an ASCII Entry
variable, where it cannot be scaled.
Scaling Data Entry
Variables