Abnormal fluctuations in the cumulative value of PLC200smart
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As shown in the figure, please help analyze what causes the large fluctuations in the cumulative water volume! The PLC200smart program is used to calculate cumulative values from instantaneous values (with updates every second), and the trend graphs appear normal. However, after 2 hours of operation, the phenomenon shown in the graph occurred. What could be the cause of this? The trend graphs for temperature, pressure, and instantaneous flow rate are all stable, with no abnormal fluctuations! The error accumulation value is the value of the instantaneous flow rate at 1 hour; the instantaneous value is 135 t/h, and the accumulation is completed on a second-by-second basis! The frequency of occurrence is also not fixed and irregular
Quietly wait and pay attention for an answer, let’s learn a bit
Why isn’t anyone answering? This is a pretty typical question – is there something wrong with the program?
Upload the program from the PLC so that the issue can be analyzed and diagnosed. Typically, to enable addition of such integers or real numbers, a rising edge detection is required; otherwise, it keeps accumulating in each scanning cycle of the PLC. By incorporating rising edge detection, addition occurs only once when a rising edge is detected, thus avoiding the aforementioned problems. This is a typical example of PLC performing addition.