Spectrum Controls SLC 500 User Manual page 37

Important -
The following equations show you how to convert user-defined scale units (or
any type of units) to engineering units, and vice versa:
S = {(U – U ) × (∆S) ÷ (∆U)} + S
low
D = {(S - S ) (∆U) ÷ (∆S)} + U
low
Where S = signal value (in engineering units, such as psi).
S = low limit of signal value.
low
S = high limit of signal value.
high
∆S = S S
high - low
D = data value (user-defined scale).
U = low limit of user-defined scale.
low
U = high limit of user-defined scale.
high
∆U = U U
high - low
Example. You have a sensor with a 4–20 mA range, and you want to scale your
data from 100 to 9999 counts. For a 4–20 mA input with user-defined scaling,
your module sets the signal limits to 3.5 mA and 20.5 mA (see Table 4-2). After
entering 100 and 9999 into output words 4 and 5 (or 6 and 7), respectively, the
relationship between input signal and data value (counts) would be as follows:
Figure 4-1. Graph of signal value vs data value
In the preceding example:
S = 3.5
low
S = 20.5
high
∆S = 17
U = 100
low
U = 9999
high
∆U = 9899
Chapter 5: Programming Examples
low
low
User's Manual Pub. 0300266-04 Rev. A
4-7