Q.What is the difference between Floating control and Tri-state control?

A. For all intents and purposes these terms mean the same thing. The precise difference is that Floating refers to the controller (i.e, thermostat) and Tri-state refers to the controlled device (i.e, damper actuator or valve). A floating controller is used in conjunction with a tri-state actuator. The first floating controllers used the wiper attached to a bi-metal strip of a SPDT contact. The wiper moved (floated) between the two outer terminals so that at set point, the wiper did not connect with either of the outer terminals thus offering a tri-state operation (on/off/on). This is now most often done with electronic or digital controllers.

Tri-state devices have three distinct modes described below.

• Motion in one direction (CW or stem up)
• No motion (@ set point)
• Motion in the opposite direction (CCW or stem down)

So, if you have floating control then you must have a tri-state device to affect the change in the control loop. Kele has interface devices that can change an existing control scheme from proportional to tri-state (floating) signal by using a UCS-221 or a tri-state (floating) to a proportional signal by using a PWA-1T.