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Gas Detector FAQS and Maintenance CruzPro Ltd.
13 Burgundy Park Avenue
Henderson, Auckland 0612
New Zealand
Tel: 64-9-838-3331
Fax: 64-9-838-3332
Internet: http://www.cruzpro.com
FU60 digital fuel gauge / consumption calculator

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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 non-linearities 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 non-volatile memory look-up 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 flow-rate 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 re-starting 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 re-start 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 over-read 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 non-linearity's and odd fuel tank shapes. Dynamic (time-varying) 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.

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