Introduction to the ControlLogix While / Do Statement The ControlLogix While / Do Statement allows you to execute a block of code while a specific condition is true. This statement is available in Structured text. You can use this statement to perform large calculations on arrays. Some vendors might use Read More »
Introduction to ControlLogix For / Do Statement The ControlLogix For / Do Statement is similar to what you might think of as a FOR / NEXT loop. Basically, it is a construct that executes the same code a number of times. It does this by incrementing a tag. For example, Read More »
Introduction to ControlLogix CASE / OF Statement The ControlLogix CASE / OF Statement allows a specific block of code to execute. The block of code that executes depends on the value of a tag. This can also be an expression that returns a value. You can use this statement in Read More »
Introduction to ControlLogix IF / THEN Statement The most common instruction is the ControlLogix IF / THEN Statement. This is for Structured Text routines. Structured Text is an easy way to program complex algorithms. Additionaly, some vendors prefer to use all structured text routines. One of the reasons to use Read More »
Introduction to Independent PID with ControlLogix In this section we’ll set up an Introduction to Independent PID with ControlLogix. Realize the equation is different than the dependent mode. For detailed information on the PID instruction, visit the ControlLogix Instruction Set Reference Manual. The PID instruction is in chapter 13. With Read More »
Introduction to Feed Forward for PlantPAx PID With Feed Forward for PlantPAx PID, we can adjust the control variable directly. For example, if the load increases from a tank, we can immediately provide a higher setpoint to the inflow. This can drastically improve response time. Additionally, it will usually reduce Read More »
Introduction to Cascading PID with PlantPAx In this section, we’ll cover Cascading PID with PlantPAx. We’ll do this by simulating a level in a tank. The tank controller will change the setpoint of a flow controller. The goal is to maintain a constant tank level. It’s important to realize that Read More »
Introduction to PID Zero-Crossing Deadband PID Zero-Crossing Deadband is a method to prevent too much action on the control variable. Particularly, if your process variable is noisy. Too much action on a field device will cause premature wear. This requires extra maintenance, and possibly more downtime. The disadvantage to deadband Read More »
Introduction to PID tuning with Ziegler-Nichols method (rule based variation) In this section, we’ll tune a PID with the Ziegler-Nichols Method. This will be a rule based variation. Previously, we discussed a trial and error based method. Recall that we increased Kc until the loop was unstable. At this point, Read More »
Introduction to PID Feed Forward PID Feed Forward allows you to immediately compensate for a change before Proportional, and Integral have a chance to act. It does this by BIASing the control variable. For example, consider a tank where we need to maintain a constant level. As soon as we Read More »
