Fuel Tank Level Sender: Electrical

Electrical and electronic topics for small boats
jimh
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Fuel Tank Level Sender: Electrical

Postby jimh » Wed Feb 07, 2018 8:21 am

This thread will offer a summary of three tank level senders which provide the standard resistive output by rather ingenious electrical methods.

CENTROID PRODUCTS

The CENTROID PRODUCTS sender is designed with no moving parts. It senses the fuel tank level measuring the capacitance between two concentric tubes which are immersed into the tank. As the liquid level rises, the capacitance between the tubes is affected, and this is translated into a signal which can be connected to a standard fuel level gauge (a milliamp meter, typically). The electronics are encapsulated in epoxy and should be maintenance-free.

In addition to no moving parts, the sensor has another benefit: it can detect water in your fuel! The presence of water apparently has quite an effect on the capcitance, causing the indicator to significantly change its response.

The sender is fabricated with the standard five-hole bolt pattern typically found on boat fuel tanks. When installing the sender, the length of the tubes is custom fit to your tank. You use a tubing cutter to trim them to the right length depending on the depth of your tank.

Each unit is calibrated to a particular installation. The empty calibration can be done before installing the unit into the tank. The full calibration is set once you top off the tank.

The claimed advantage of this sender include a reduction in gauge bouncing when fuel is sloshing around. The sender is compatible with most electric fuel gauge meters, but some VDO-brand meters need a special model.

For more information see the CENTROID PRODUCTS website:

http://www.centroidproducts.com/tableofc.htm

I have not tried one of these myself, but I like the concept of no moving parts and individual calibration.

WEMA

Electrically-operated electrical remote fuel tank level senders are also made by WEMA, now taken over by KUS-USA. Information is available on their website at:

https://kus-usa.com/products/liquid-level-sender/

and in particular:

Liquid Level Sensors - SSS/SSL Diesel, Fuel or Water Level Sensor
https://kus-usa.com/product-tag/marine-level-senders/
and
https://kus-usa.com/product/sss-ssl-sender/

These senders apparently provide the equivalent to the more or less standard 240 to 33 ohm variable resistor or rheostat sensor used in traditional mechanical senders that control current flow through a remote gauge powered from the 12-volt battery.Their operation is accomplished with a series of small magnetic switches that connect various fixed resistors into the circuit. Unlike the CENTROID, there is a moving part in the WEMA sensor: a float collar that rides up and down on a central tube. There is no direct mechanical linkage from the float collar to the internal parts; I presume a magnetic field from the float collar operates the reed-switches.

The WEMA sensor model SSS or SSL uses a five bolt SAE mounting pattern with a 2.125-inch bolt circle. This mounting appears to be the standard configuration for electrical-electronic senders of this type.

SSI TECHNOLOGIES

An electronic fuel tank level sender gauge suitable for marine fuel tanks is made by SSI TECHNOLOGIES, INC., of Janesville, Wisconsin. Their Fluid -Trac® two-wire liquid level sensor with resistor emulation can be used to replace the conventional mechanically linked standard 33 to 240-Ohm resistive float senders often seen in small boat fuel tanks. The device is certified by the American Boat and Yacht Council (ABYC). It has no moving parts and does not protrude into the fuel tank. The device operates with digital signal processing and includes filtering to reduce the influence of fuel sloshing on the output signal. The device also appears to be able to compensate for fuel level measurements in tanks with unusual shapes. These digital algorithms are set at the factory and are not user adjustable.

The Fluid-Trac sensor appears to operate using ultrasonic distance measurement. It measures the distance from the sensor to the top of the liquid in the tank. The device is claimed to have a fundamental accuracy of two-percent. Variations in the distance from sensor to fuel from sloshing are treated as noise and are filtered out. The response time can be set (by the factory) to as long as a four-minute average in situations where there is high sloshing.

The mounting of the sensor can be accomplished with either the standard SAE five bolt pattern or with a 1 and 3/16-inch threaded mounting.

More information is available from SSI TECHNOLOGIES:

https://www.ssi-sensors.com/level-sensors

The Fluid-Trac sensor costs approximately $95. It can be ordered from U.S. Marine Products as well as from other distributors.