In
this post we will show a PID temperature control application programmed in
Function Block Diagram. This language is practical to be used in the process
industry, due to the facility in visualizing the process and in manipulating
the instructions of digital, analog signals, alarms, operating mode, among
others.
The
PID control will be performed with the PIDE (PID Enhanced) instruction, which
has a PID algorithm proportional to the Error delta. Thus, the regulation of
the CV variable is done with the error variation. The visualization of the
system's response is done with a Trend where the system's SP, PV and CV are
shown.
The
Process Value (PV) is simulated, based on CV, multiplying by a multiplier
coefficient and also by a 5s dead-time and a 10s lag-time, in order to simulate
the response time of a real system.
In
this case, the logic of the analog input signal, the PIDE instruction and the
response simulation were performed in the same routine to facilitate
visualization. However, in a project, it would be better to create AOI (Added
On Instructions) and use the modules created for data exchange. An AOI can be
created, for example, to simulate and test the response of a system.
Step change response:
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