Use the PCS 7 APL Polygon Block for a Nonlinear Signal Characteristic
Use the Polygon block when an input must be converted according to a defined nonlinear characteristic. The official PCS 7 APL V7.1 Function Manual documents up to 16 input/output interpolation pairs, linear interpolation between adjacent pairs, and extrapolation beyond the end points using the nearest end segment. The source question does not state its installed APL version, so confirm the block interface and limits in the manual for the actual project.
Table of Contents
- When to use Polygon
- Configure the characteristic
- Engineering procedure
- Example decision
- Verification
- Limitations and Operational Precautions
- Engineer FAQ
- Technical References
- Related Articles
- Related Tags
When to use Polygon
The APL V7.1 function manual describes Polygon as converting an input according to a nonlinear characteristic. It maps an input In to output Out using up to 16 interpolation coordinate pairs. This is suitable when the required relationship is defined by a nonlinear curve; it is not evidence that the block is appropriate for every nonlinear control task.
Configure the characteristic
In the cited V7.1 manual, define N coordinate pairs (Ini, Outi) consecutively without gaps and set N. Between points, interpolation is linear. Outside the first and last points, the documented block extrapolates using the first two or last two points. These edge behaviors matter: define the point range and decide whether extrapolation is acceptable for the process.
Engineering procedure
- Confirm that the installed APL version includes the Polygon block and read that release's function manual.
- Determine the required input/output characteristic from approved process or instrument data.
- Enter the coordinate pairs in order, without gaps, and set the corresponding number of points N.
- Place the block in the documented cyclic interrupt OB for the applicable library version and connect the input and output consistently.
- Review the linear segments between each pair and the extrapolated behavior at both ends before using the output in control logic.
Example decision
A nonlinear sensor or actuator conversion may be represented by a curve of measured or specified input/output pairs. The APL V7.1 manual's mechanism is linear interpolation between those pairs; the curve's values must come from the project's validated engineering data. No example measurements are supplied here.
Verification
Test the configured curve with representative values at every entered point, between points, and beyond the first and last points. Compare calculated output against the approved characteristic and confirm any downstream limits or interlocks address unacceptable extrapolated values.
Limitations and Operational Precautions
The official manual opened during research is for APL V7.1 (Function Manual 03/2009, A5E02102723-01); it cannot establish interface or limits for an unspecified newer/older library. A V9.0 SP2 manual was identified in search but direct PDF retrieval returned 403. Confirm current block inputs, point count and OB requirements in the actual installed APL manual before implementation.
Engineer FAQ
Does Polygon use a smooth curve? The cited V7.1 manual describes linear interpolation between adjacent points, not a smooth spline.
Should extrapolated values be trusted outside the configured range? They follow the end-segment extrapolation rule in V7.1; whether those values are physically valid must be established from the process specification.
Technical References
- PCS 7 Advanced Process Library V7.1 Function Manual, section 10.12, “Polygon - Converting the first signal (non-linear),” especially pp. 1136–1138. This official PDF was opened and read.
- PCS 7 Advanced Process Library V9.0 SP2 Function Manual, search identified its Polygon section; direct access returned 403, so it was not used to generalize V7.1 details.