Industrial Automation Tech Note 27 - TNIA27
Abstract:
This document describes using Crimson® 3 programming to scale a nonlinear input signal.
Products:
CR Series HMI / G3 Series HMI / G3 Kadet HMI / Graphite® HMI / Graphite® Controllers / Modular Controller / Data Station Plus / ProducTVity Station
Use Case: Scaling a Nonlinear Input Signal
Many applications involve a nonlinear relationship between the input signal and the engineering units that it represents, such as the level of a conical or horizontally mounted cylindrical tank. This document explains how to scale the signal using Crimson programming, as well as replacing the functionality of the obsolete CSINI8L0 and CSINV8L0 modules.
Required Software:
Crimson 3.0 / 3.1
Theory
When the equation that relates the input signal to the engineering units is unknown the alternative is to divide the curve into multiple lines. The more lines that are used the closer the engineering units will be. In order to generate these lines, a series of X (input signal) and Y (engineering unit) coordinates are entered into arrays. The input signal is compared to the elements of the X array in order to find which line segment should be used to calculate the engineering units. Figure 1 is a visualization of the data points used later in the document.
Figure 1.
Application
1. Create and populate X and Y arrays.
• The arrays can be exposed for entry from the user interface or populated by a program.
|
// populate arrays with known data points X[0] = 1; X[1] = 10; X[2] = 20; X[3] = 30; |
• For a more accurate result, use more data points. Table 1 below shows the inaccuracy of using only 4 points compared to the true equation output:
|
Input |
Squared |
4 Segment Calculation |
|
1 |
1 |
1 |
|
2 |
4 |
12 |
|
3 |
9 |
23 |
|
4 |
16 |
34 |
|
5 |
25 |
45 |
|
6 |
36 |
56 |
|
7 |
49 |
67 |
|
8 |
64 |
78 |
|
9 |
81 |
89 |
|
10 |
100 |
100 |
|
11 |
121 |
130 |
|
12 |
144 |
160 |
|
13 |
169 |
190 |
|
14 |
196 |
220 |
|
15 |
225 |
250 |
|
16 |
256 |
280 |
|
17 |
289 |
310 |
|
18 |
324 |
340 |
|
19 |
361 |
370 |
|
20 |
400 |
400 |
|
21 |
441 |
450 |
|
22 |
484 |
500 |
|
23 |
529 |
550 |
|
24 |
576 |
600 |
|
25 |
625 |
650 |
|
26 |
676 |
700 |
|
27 |
729 |
750 |
|
28 |
784 |
800 |
|
29 |
841 |
850 |
|
30 |
900 |
900 |
Table 1.
2. Create the program (CalcVal).
a. Referring to Figure 2, edit the program’s prototype.
Figure 2.
1) Return Type – Data Type: Floating-Point or Integer
2) Parameters – Floating-Point or Integer (Input)
b.Write the program code:
|
// declare locals
// calculate PV change in this segment |
3. Use the program as the Source of a tag.
Referring to Figure 3.
a. Create a new Numeric Tag.
b. Change its Source to General.
c. Type in the name of the program, with the name of the source value as its argument: CalcVal(Reading).
Figure 3.
Disclaimer
It is the customer's responsibility to review the advice provided herein and its applicability to the system. Red Lion makes no representation about specific knowledge of the customer's system or the specific performance of the system. Red Lion is not responsible for any damage to equipment or connected systems. The use of this document is at your own risk. Red Lion standard product warranty applies.
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