Overview
For example, if a 0-10V analog input corresponds to a PLC digital range of 0-4096 or 0-16383, using 0-4096 as an example: one full rotation corresponds to 360 degrees and maps to the 0-4096 range. That means a digital value of 4096 indicates a 360° rotation, and 2048 corresponds to 180°.
Angle Calculation and Integer Limits
If you only need to display the angle and the received digital value is A, the actual angle is A/4096 * 360. However, PLCs typically perform integer arithmetic, so this calculation may yield zero unless you handle it properly.
Two Handling Methods
There are two common approaches:
1. Use Floating-Point Arithmetic
Use floating-point arithmetic to compute the angle directly. This is the most accurate method, but it can be more complicated for beginners due to the required conversions.
2. Scale to Preserve Decimal Precision
Scale the value so you avoid decimals in PLC integer arithmetic but can still display decimals on an HMI. For example, compute A * 36000 / 4096: perform the multiplication first, then the division. This scales the result by 100. If A is 2048, B becomes 18000, which an HMI can display as 180.00 by placing the decimal point two places from the right.
PLC Register Mapping and Examples
Different PLC brands read analog inputs in similar ways: each analog channel maps to a dedicated register. Consult the device manual for exact register names and ranges.
For example, a Siemens first analog channel might be AIW0; a Delta first analog channel might be D1110 (approximate). For a 0-10V input, some PLCs read values from 0 to 255, but the actual range depends on the PLC model and its resolution. Current inputs are handled similarly, with different wiring requirements.
