How To Use Your Float Switch | Blog

A black and white diagram of a float switch.

Normally Open and Normally Closed Explained

We recently discussed how to configure a float switch, defining Normally Open and Normally Closed circuits. In short, Normally Open (NO) refers to a de-energized switch when the float is at rest. Normally Closed (NC) is the opposite, an energized switch when the float is at rest.

Here’s how it works:

A company in Florida operates a variety of historical trains, built in the 1940’s and 1950’s, which are used for special occasions. On the bottom of each of these trains is a 16-inch high water tank whose level must be monitored by the engineer during operation.

A flange mounted, 4-point level detection probe with a 90-degree bend is mounted through the side of each water tank. Each of the switches is set in the NO position. The level switches are connected to four indicator lights that illustrate the rise and fall of the water.

When the tank is full of water, all of the switches are energized and all four indicator lights are illuminated. As the water level decreases, dropping below each switch point, the respective float will revert back to a de-energized (NO) state and the associated light will turn off.

Through this use of float switches in a basic point level detection application, a level measurement vital to the train operation is monitored.

This simple use of float switches illustrates how an open or a closed switch is put into practice. Replace the lights with pumps, valves, alarms, motors, and so on, and you can see how complex the application might be.

We can’t tell you all the components you could ever use in a control application, but we can certainly help you configure your float switch to match. Let us know if you have any questions, and we will be glad to help!

Explore APG Float Switches

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