Level indicators for boats include non-invasive, digital, float type, and mechanical
Non-Invasive level indicators.
There are two types of these, the first being a capacitive type of sender consisting of foil strips stuck to the tank wall. Tanks up to 750mm high can be accommodated. This type is only suitable for polyethylene tanks. The display is a simple 5 LED type with a low level alarm red light.
The latest non-invasive technology consists of three sensors which “shake” the tank wall and read the response via an accelerometer. These units are suitable for stainless steel, mild steel, aluminium, fibreglass and plastic tanks. They are simple to fit and provide either an output for the LED display supplied or an optional analogue gauge.
Greater control and flexibility, ideal for monitoring multiple tanks.
The term digital applies to many types of level indicators. Any gauge that does not have an analogue (needle type) display can be regarded as digital. Displays can be LED lights or a liquid crystal displaying a percentage or a value.
Digital displays can receive an input from many different types of sender giving either a European, US or voltage output. Some gauges can display the level of up to 8 tanks whilst accepting input from 5 different types of sender. This is particularly useful on large boats with many different types of tanks. The latest type of level measuring is now displayed either by a laptop computer or chart plotter using a converter between the sender and the display.
Float type senders controlling analogue gauges are probably the most common type of level indication in a boat.
Float type senders are available in either a lever type or a plain straight shaft. European output is 180Ω full and 0Ω empty. US output is 30Ω full and 240Ω empty. It is important to make sure that the sender matches the gauge.
Lever Arm Type Sender
Shaft Type Sender
The lever arm type tends to fail more regularly than the shaft type because there are more moving parts and the part that changes the impedance is constantly submersed in the fuel or water. The shaft type is totally sealed with a magnet in the float switching reed switches in the shaft.
Mechanical level indicators combine the sender and gauge in one unit.
Mechanical level indicators combine the sender and gauge in one unit which suits many boat owners who do not want to consume valuable battery power. The gauge is driven magnetically by a square spiral shaft which is rotated by the rising and falling of the float. These units are made in 50mm increments starting at 200mm long.