April 2012
Column
AutomatedBuildings.com

Daikin Integration to BACnet, Modbus, KNX, WIFI, Mobile Apps
Intesis

(Click Message to Learn More)


Back to BAS Basics
Actuation

Paul Ehrlich, Ira Goldschmidt & Angela Lewis
Building Intelligence Group

As published
Engineered Systems 
April Issue - Column

Articles
Interviews
Releases
New Products
Reviews
Belimo
Editorial
Events
Sponsors
Site Search
Newsletters
Distech Controls
Archives
Past Issues
Home
Editors
eDucation
Reliable Controls
Training
Links
Software
Subscribe
Control Solutions, Inc

This month we are going to go “back to basics” and discuss some of the fundamental concepts involved with the design, maintenance and upgrades for building automation systems. 

In any control loop we have a number of fundamental elements. The key elements are identified in figure 1:

Figure 1

        
Let's focus on the details of how the control output is actuated.  The controller is going to produce some form of analog signal that needs to be converted into a physical action, which will in turn position the control valve. 

Signaling:  The analog output from the controller is typically a 0 – 10 Volt DC or 4 – 20 mA.  Other alternatives include digitally communicated values, or the use of set of binary outputs (one to drive open and the other closed).  

Control Solutions, Inc Positioning and Feedback:  The challenge with controlling a mechanical device is that the positioning of the valve may not react smoothly and linearly with the control signal.  Much of this is due to friction, flow and hysteresis.  As a result changes in control output will not always result in a linear change to the output. The impacts of hysteresis will always exist but can be minimized by providing feedback on position within the controlled device.  Without position feedback control loops will tend to be more unstable.

Actuation:  The actuator needs position the control output (in this case a valve) in responses to the output signal from the controller.  There are several challenges with actuating a mechanical device.

The most common options for actuation include:

A good control design and deployment will have accurate and stable control.  While it is possible to do this with pneumatic actuation, it is more complicated and prone to error.  This is why we prefer to see systems deployed with electronic actuation.


footer

SkyFoundry
[Click Banner To Learn More]

[Home Page]  [The Automator]  [About]  [Subscribe ]  [Contact Us]

Events

Want Ads

Our Sponsors

Resources