In many of the newer coffee machines, without permanent water connections for commercial or domestic applications, a low water indicator lamp signals the minimum water level. In this case a permanent magnet is built into a float housing installed in a removable plastic water tank.
The positioning of the Reed Switch and the magnetic strength of the magnetic float guarantee the switching of the contacts when the water level drops to the level of the Reed Switch sensor position. By design, the switch sensor remains closed even after the water level continues to drop well below the minimum water level.
In the machine itself, a Reed Switch is mounted behind a plastic or aluminum cover. The magnetic contacts of our MK03 and MK04 series, for example, offer the sensing requirements suitable for this application.
The construction of the water tank is usually designed to insure that at least 2 cups of water remain once the minimum water level has been reached. The Reed Switch will only open (and thereby turn off the low water light) when the water level has been sufficiently refilled such that the magnetic float is above the minimum water level mark.
In the case of coffee machines with permanent water connections, the same sensor approach applies except for the fact that the indicator light is removed and a water-switching valve is added.
Generally speaking, this approach works well for all similar fluid level applications.
Full Application Write Up Coffee Maker Components - Liquid Level SensorCoffee & Espresso Machines - Reed Sensor