Fuel Gauge Calibration

[lustyd]

I thought this may be of interest to some here. I just connected my fuel sender to a Victron Cerbo GX in order to display fuel levels on the plotters, phones, and my Garmin watch. Now that we're calibrated, I have fuel litres remaining on the displays as well as percentage full, which is very useful for range calculations. It also enables the plotter to understand range left, since I hooked up NMEA 2000 from the Cerbo.

Obviously we all know fuel tanks aren't a regular shape, but I bet not many would have guessed on a 125l tank that 20 litres is a quarter of a tank on the standard guage.

Calibration on the Cerbo was very easy, I just put in the uncalibrated and actual percentages and now I can see actual litres remaining rather than the wooly guess we had before.

The process I followed was to suck all fuel out via the air bleed screw on the filter housing. This left it empty as far as the engine is concerned, rather than actually emptying the tank - important difference. I then topped up by 10l at a time, noting down the percentages and sender readings from the Cerbo display on my phone. Finally put it all in a spreadsheet and added the percentage column to do the calibration. All in it was about 3 hours work including three trips to the fuel dock.

 

[wonkywinch]

The "round" function in Excel is handy ;-)

ROUND function - Microsoft Support

Or more simply, use the "format cells" box and set the number of decimal points for your "Sender Reading" column.

 

[lustyd]

Why? That’s the record of the actual number so there’s no point rounding it. I’m quite good with data and data tooling…

 

[wonkywinch]

Why? That’s the record of the actual number so there’s no point rounding it. I’m quite good with data and data tooling…

Garbage in garbage out?

The data after the decimal point is meaningless surely? Even 1/10th of a litre can be filed in the "don't need to know" box.

 

[lustyd]

Garbage in garbage out?

The data after the decimal point is meaningless surely? Even 1/10th of a litre can be filed in the "don't need to know" box.

No, not meaningless at all. The data is there to record values. This includes the minimum and maximum that the sender outputs. Had the sender had a range of only 40 ohms in this tank, I would have needed to work out the percentages based on those values. As it was, I didn't need to do that so the percentages are entirely separate.

Hiding detail unnecessarily is much, much worse than rounding too early. Only round numbers which need to be human readable. If you feel the need to hide them as it affects you somehow then go ahead, I was just providing the data collected. The Cerbo goes to 3 DP so I did too. I am an expert in data and analytics though, so follow best practices.

 

[yotter]

Looks pretty good, I intend to expend my Victron installation on the new boat and the Cerbo GX looks pretty capable, I like the idea of fuel tank calibration, rather than using the random gauge and shaped tank.

 

[lustyd]

Looks pretty good, I intend to expend my Victron installation on the new boat and the Cerbo GX looks pretty capable, I like the idea of fuel tank calibration, rather than using the random gauge and shaped tank.

It's very good so far. We've had the Cerbo for years and I only just realised I could just hook up resistive senders to it when I was adding the NMEA2k link to it, so aside from a bit of cable it was a free upgrade for us to add fuel level. The tracking over time on VRM is handy for seeing diesel usage for heating right now, and we'll be able to record fuel usage for trips when we get moving again.

 

[yotter]

Sounds intesting, I keep an eye on the VDO gauge as a guide, but allow 2.5 litres an hour for our VP2030 and that seems pretty accurate. Perhaps I am just looking for a way to use more Victron kit. I know I could use my phone to monitor but like the idea of the Touch 50 or Touch 70, any recommendations which to get, they seem pretty inexpensive in the great scheme of things

 

[lustyd]

We don’t have a Victron screen at all. It shows enough on a plotter via ethernet and nmea2k and we have phone access to the cerbo on wifi which literally shows the same as the screen but with less power.

Yes we do 2l/hour but this shows the litres in the tank so feels more accurate. Filling up is now 125l-current fuel so we know how much will fit in. Before we sort of guessed, including on passage when I was deciding whether to put the jerry cans in the main tank.

We’ll see though, only just done it