Ladder logic 401: Data acquisition and analysis

A programmable logic controller (PLC) is designed to not only provide information on signal levels, but it can also capture data and it can be analyzed. The methods, however, can vary a great deal depending on the platform so this will focus on a generic level. First, capturing the signal levels: These assume a signed integer signal from an analog card, unknown resolution. The image above shows a random sampling of values collected from a typical analog card. Since analog/device (AD) converters don’t change values very quickly, it can be difficult to see the spikes that may occur in the signal. If values can be sampled at a higher rate than a typical proportional-integral-derivative (PID) control scheme might require, it might show some data like this. The spikes in these images illustrate what you can do if you do some simple limiting of values based on averaging. It is important to note that any modification of data collected will require a delay of the signal. After all, it takes t
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