Two types of sensor are available; infrared and ultrasonic. Each has its merits in different applications. Broadly speaking the infrared sensors are used in clean liquids and the ultrasonic types are used in dirty or coloured liquids.

For secondary settlement tanks (also known as clarifiers, final tanks or humus tanks) the IR40 should be used whereas the IR15 should be specified for use in most primary tanks. Some primary tanks may require the US100, depending on the suspended solids content of the supernatant, as do most thickener tanks. Up flow clarifiers in water treatment plants typically require the IR100 sensor since the blanket is usually very light.

Highly coloured liquids such as in tanneries and some food manufacturing plants can only use the ultrasonic sensor. Most industrial effluent treatment plants where the supernatant is discharged to a river or the sewer use the IR40 sensor.