Float Switches- Normally Open verses Normally Closed
And why you should care…
Float switches, in very basic terms, are used to detect the presence or absence of liquid (or another substance) in a tank. By measuring the level, it’s possible to determine how much is present or not present and based on that data, perform a function like sending out an alert about the levels before dangerous issues occur. It may also engage a piece of equipment.
Digging further into the functions of float switches are the various ways in which you can configure and position a float switch to operate. Depending on the application and use, you may need a closed float switch or a configuration that’s open. Understanding the differences and why one is better than the other for particular uses is key.
Closed Float Switches
Float switches that are configured to stay closed until liquid flips open the circuit, are referred to as a, “normally closed float switch.” Once liquid reaches a certain level it then forces the circuit open and activates the next step, which could be a power shut off, or alarm sound off. As water levels rise in the tank, the float is lifted too and the circuits open. Common uses for a closed float switch would be to measure water, stop overfills and when avoiding high water levels is desired.
Open Float Switches
When a float switch circuit is open, it is referred to as a, “normally open float switch” and is set to close when liquids reach a certain level. In the standard position when dry, this switch is above the liquid line and not floating. A common use for an open float switch would be in sump pumps, lift station pumps, and general pumping applications to signal a high level of liquid present and help operators to control the pumps.
A main concern when selecting between the two options are predicting whether or not the float switch will fail. However once you’ve made the best float switch configuration selection, the best protection you can have is a plan for back-up (that’s an entirely new post).
At SMD Fluid Controls, we focus on making sensors to measure anything. Our wide variety of options include off-the-shelf products as well as custom-designed sensors for a wide variety of uses from HVAC and chemical processing to aerospace, and so much more.
We’d love to tell you more about our liquid level sensors, float switches, sump switches, optical sensors, or other products as well as custom design and manufacture services.