Float switches
Fluids levels in containers may need to be monitored and controlled for a number of different reasons. It may be important to know when a receptacle is getting low on fluid or high on fluid and appropriate action may then need to be taken.
An example of this is a submersible water pump. If it is allowed to run dry, it will quickly burn out. Finding a method of fluid level control is therefore important and some sort of device is needed to prevent this happening.
The answer is to use a float switch. Mercury tilt switches used to be used frequently but since mercury is highly toxic they are no longer favoured. A modern float switch is more commonly made from a reed switch, triggered by a float-mounted magnet. More complex switches are also available and they use a series of optical or conductance sensors.
The float switch is basically used to detect the level of liquid within a container. When a designated minimum or maximum level is reached, the float switch activates and triggers the desired response, such as turning a pump on or off or triggering an alarm.
Float switches have uses in industry but also in the home. An environmentally friendly home may use a rainwater toilet and the chances are that it will be controlled by one of these devices. The cistern of the toilet will need to be filled from the main rainwater reservoir. When the cistern is not full enough, the switch can be set to activate a pump and replenish the water supply, switching off again when the cistern is full, thus preventing water overflowing and ruining the bathroom.
In cases where the liquid being measured is turbulent, the float switch may be triggered a lot. This is known as multi-switching and may not be desirable as it can damage a pump with the repeated switching about over a short period of time. In these cases, the device can be set to stay off for a set period of time or to activate only when liquid is detected continuously for a programmed period of time.
Float switches are fairly simple devices but they are very useful
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