There are lots of final control elements to choose from, and which one will be right for your process depends on a lot of things. This article will list the most common final control element types and give you some pointers on how to choose one.

What is a final control element?

Final control elements are essential parts of a control loop, not to mention the whole process. They make sure the right quantity and quality of product passes through the process.

Let me explain the difference between monitoring systems and control systems. When we talk about monitoring systems, there are two essential items in this loop, the primary element and the controller. Primary element refers to the device that sends data from the process to the controller. The controller collects the process data for a local visualization, trend, or historical information.

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Primary element, controller, final control element

A control system has three parts in the loop: the primary element, the controller, and the final control element.  The primary element will measure the level, flow, or whatever, and send its data to the controller. The controller will compare the data with the setpoint.

If the values don’t match, then the controller sends a signal to open or close the final control element to reach the setpoint value. It happens over and over during the process operation.

So we can define a final control element as a mechanical device responsible for changing a process to achieve a setpoint in your system. Final control elements consist of valves, pumps, dampers, gates, and more.

When scaling out a final control element for your application, keep these variables in mind:

  • Fast response, to start and stop instantaneously
  • Good precision and repeatability
  • Minimal maintenance required
  • Design to work in harsh environments or with particular materials

Final control element types

Control valve as a final control element

The control valve appears in various segments as a final control element to control all kinds of gases and liquids. These come with a vast list of plugs, actuators, positioners, materials, and bodies. So you could probably mix and match a solution from the options

Variable frequency drive as a final control element

The variable frequency drive (VFD) can control the velocity of air conditioning motors. And if you have a pump or fan connected to the motor, then the VFD can help with those too.  As you can see, the variable frequency drive can bring a lot of benefits to your process.

N1030 Temperature controller with 1 relay output

Solenoid valve as a final control element

With an on/off control, you can apply an on/off valve or a solenoid valve, depending on the application. So these simple valves may provide just what you need.

Damper as a final control element

For air control, a damper comes up as a popular solution for a final control element. This device works specifically for air control in several scenarios on a variety of pipes.

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