Spectrum Controls 1746sc-INI4i, User Manual

Page: 37 / 56

Chapter 5: Programming Examples 4-7
User’s Manual Pub. 0300266-04 Rev. A
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
low
) × (
∆
S) ÷ (
∆
U)} + S
low
D = {(S - S
low
)  (
∆
U) ÷ (
∆
S)} + U
low
Where S = signal value (in engineering units, such as psi).
S
low
= low limit of signal value.
S
high
= high limit of signal value.
∆ S = S
high -
S
low
D = data value (user-defined scale).
U
low
= low limit of user-defined scale.
U
high
= high limit of user-defined scale.
∆
U
=
U
high -
U
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
low
= 3.5
S
high
= 20.5
∆ S = 17
U
low
= 100
U
high
= 9999
∆ U = 9899