Float Level Detector

A float device measures a liquid level from above. Floats, one of the oldest and simplest methods of level measurement, are used extensively in wet-wells or sludge sumps that require a discrete high or low level indication.

They are also used for local indication of level in tanks and open channels as in Figures.

Float Level Detector

Figure: Counter weighted float-level indicator

Source: WEF,2008

Figure: Float switches

A float level meter shown in Figure 6.12 senses water level through a slide rheostat as resistance and converts the changed resistance into current.

It transmits analog output signal (DC 4 mA to 20 mA) proportional to the water level and sends the signal representing the water level continuously to the monitoring room.

The O&M issues to be cared for are as follows:

• Clean inside the stilling well regularly and keep it free from floating matter or scum to prevent malfunctions

• Check moving parts such as a counter weight, pulley and wires for corrosion or damage.

The level switch shown in above figure is used to control the pump and to issue alarms according to water level. The signals from the level switch are “on/off” digital signals, which compromise a sequence circuit.

Float switches should be located away from the tank walls to prevent the floats from banging against the concrete wall and internal contacts from failures.