If you’re in the process of selecting a float switch for your application, you’ve likely come across the question of what the specific gravity (SG) of the liquid being measured is.

The SG is a characteristic that relates to the ratio of the object’s density to that of water and is an important consideration because the entire operation of a float switch is based on its ability to accurately measure the presence or absence of liquid.

This accuracy means everything when it comes to the proper operation of a float switch so care must be taken to select the proper float switch and settings for your application.

The good news is, you don’t need to worry about getting this right on your own.

SMD Fluid Controls manufactures a variety of fluid switches, float switches, temperature gauges, and liquid level sensors. In addition to standard off-the-shelf products, we also offer custom sensors designed to meet application specific needs. Our pros are here to help you every step up of the way to ensure you have the proper switch you need to get the job done.

In case you would like to know more, here’s a closer look at how gravity and float level transmitters work.

Floats are calibrated to a specific reference point where it will measure the liquid level in a vessel. The size and material of a float can change its specific gravity. If it is not properly set, the float can fail to alert or activate the switch.

How do you know the setting is correct?

This is where gravity and understanding your specific needs come into play.

In order to differentiate between two liquids, you’ll need to understand their specific gravity. If water and oil are being held in the same tank for example, but measurement of only the water is necessary, knowing their specific gravity and that of the float being used will make measuring that single liquid possible.

Finding the Specific Gravity

Engineering Toolbox offers an easy to use reference table for selecting specific gravity for common liquids and fluids.

Once you have selected a float that has the proper SG and will not sink (remember temperature changes in liquid should also be considered as they can change the SG) you’ll need to consider how much of the float will be exposed.

This calculation is a way of better understanding the level of liquid present and can be found by dividing the SG of the float by the SG of the liquid.

After establishing this, think about the reference point you’ll use to physically compare and measure the liquid. This is where you will calibrate your measurement.

Still have questions? Speak to one of our pros today!


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