ControlLogix CASE / OF Statement

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 »

case of

ControlLogix IF / THEN Statement

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 »

if then

Independent PID with ControlLogix

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 »


Feed Forward for PlantPAx PID

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 »

Disturbance Offset

Cascading PID with PlantPAx

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 »

Cascading PID

PID Zero-Crossing Deadband

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 »

Zero Crossing Deadband

PID with Ziegler-Nichols Method

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 »

time constant

PID Feed Forward

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 »

Cascading PIDE (Enhanced)

Introduction to Cascading PIDE (Enhanced) In this section we’ll discuss Cascading PIDE (Enhanced). We’ll set this up using the simulator. We’ll need two simulation units with a 1000uF capacitor across the PV of the flow simulator. Be sure to wire the PV of the flow simulator to the CV of Read More »

Flow and Level

Tuning Simulator with Enhanced PID

Introduction to Tuning the Simulator with an Enhanced PID (PIDE) Instruction There are a few things to keep in mind when tuning the simulator with the Enhanced PID (PIDE) Instruction. First of all, the PIDE uses Function blocks. You will need to make sure you have activated the Function Block Read More »