FU60 digital fuel gauge theory of operation and FAQS
The FU60 is a very accurate digital fuel gauge that computes fuel level, fuel usage rate and time to go before you run out of fuel
for both diesel and gasoline (petrol) engines using only a standard resistive fuel sender inside the tank. No "flow" sensor required!
If you already have a tank sender installed, then all you need do is replace your analog fuel gauge with the FU60 digital fuel computer.
The FU60 "learns" tank shape and eliminates sender errors and nonlinearities during calibration
and achieves an accuracy of better than 2% over the entire range of the fuel tank.
This is accomplished by "teaching" the FU60 all the characteristics of your tank and fuel sender
in the following manner:
First, you empty the tank. Any fuel remaining in the tank when you start the calibration
procedure will become a fuel reserve when the meter reads 000.0 later on.
You tell the FU60 to enter the calibration mode using the front panel switches
and then fill the tank stopping up to sixteen times to tell the FU60 how much fuel you have pumped
into the tank at each calibration point. The front panel keys are used to enter this
fuel information. At each calibration point the FU60 measures the sender resistance
and stores this information along with how much fuel you told the FU60 that means into a nonvolatile
memory lookup table.
After the last calibration point has been entered the FU60 calculates and matches a
mathematical curve to the data points you have entered. With this curve the FU60 can calculate fuel
remaining very accurately even between data points. The FU60 is able to measure a wide range of
different sender resistances and automatically compensates for both American and European
sender types (one goes down in resistance with decreasing fuel level, the other goes up).
Since the FU60 now knows fuel level very accurately it can compute fuel usage rate from
the equation: Gallons Per Hour = (Fuel Used) / (Elapsed Time) instead of trying to measure
flow rate. Because of the high internal accuracy of the FU60, it takes only a couple of minutes
to get an accurate fuel consumption rate figure.
There are several interesting things about this method: 1) The longer you
wait, the more accurate the answer becomes. 2) You don't need a subtractor
unit for diesel engines because it measures fuel remaining in the tank, not
the difference of what's going to and from the diesel engine. 3) Works with both
very low consumption and high fuel consumption engines. 4) Is great for giving you
a very accurate average fuel consumption calculation for the entire trip.
5) Costs a lost less than a flowrate meter.
The downside is that this technique provides an average fuel usage rate
over the measurement period not an instantaneous rate.
To get a more instantaneous computation, the FU60 provides for restarting
the Elapsed Time clock at any time by pressing one of the buttons. If you
want to check consumption vs rpm, for instance, you change rpm and restart
the elapsed time clock and wait for an accurate answer.
The FU60 is also the only fuel gauge that is accurate. Most
fuel gauges overread when used with tanks that are shaped to the hull  some
overread by a very large amount  right near the bottom, where you most
want the accuracy.. The calibration procedure used with the FU60
eliminates errors due to sender inaccuracies and nonlinearity's and odd
fuel tank shapes. Dynamic (timevarying) electronic filters minimize
fluctuations due to boat roll, etc.and the sloshing cancels out. This technique does
not work perfectly if the angle of the boat
changes permanently (powerboat going on step at plane). Careful placement
of the fuel sender can minimize even these problems.
Another advantage that allows the FU60 to be much more accurate is the fact
that the voltage driving the sender is a highly regulated. This means you
get an accurate fuel reading even if your battery voltage changes. All
analog fuel gauges pass the unregulated battery voltage through a small
meter movement to the sender. As the sender resistance changes, the meter
movement shows different fuel levels. Unfortunately they also show
different fuel levels if your battery voltage changes. If your analog fuel
gauge shows 50 gallons with a 13.8 VDC battery voltage, it will show 43
gallons if your battery voltage drops to 12.0 VDC (without using any fuel!).
The FU60 nay not be the perfect solution to everyone's fuel gauge problems  and
some people will still need a fuel flow meter, it's just that the FU60 is years ahead of your average analog fuel gauge and for many people will
also provide fuel consumption calculations. This is doubly true for people with
diesel engines where a substantial part of the fuel is returned to the tank making fuel flow
measurements very complicated and expensive.
