Fuel Gauge
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Picture: Simple swivel arm float - the round indicator was not used. |
General
The developed fuel gauge (currently undergoing flight testing) is used to accurately measure and display the amount of fuel in a tank. Tanks are rarely simple cylindrical bodies and fuel gauges cannot always provide linear values due to their mode of operation (e.g. float on the swivel arm). As a result, simple fuel gauges only display correct values in the full and empty positions at best. However, this is only the case if the fuel level sensor is able to detect these end positions. In many cases, the fuel gauge can only measure in partial ranges, i.e. it does not reach the entire full or empty position for design reasons, for example. The tank indicator largely solves these problems (bulky tank containers, non-linear tank sensors and non-detectable empty and full ranges).
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Picture: Arduino Uno in case and control unit with pushbutton and LCD display |
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Picture: Tank inside installation unit of the sensor |
Function modes
1. the fuel gauge can work without a sensor. To do this, the available fuel quantity is entered into the control unit. The microcomputer calculates the remaining quantity and the expected flight time according to the operating time (from main switch on). The new tank quantity (e.g. refueling) is entered by pressing the Vol button. Then press + (tank quantity is increased by 5 liters) and - (tank quantity is only reduced by 1) to set the exact tank quantity. Press Set to exit the setting for the current tank quantity. After each liter used, the current tank quantity is saved in whole liters. This means that the current tank quantity is available again when the system is restarted. This mode is not recommended. Calculating the tank quantity on the basis of average consumption is too inaccurate.
2. in standard mode (with connected sensor - 0-200 Ohm) the fuel quantity is displayed exactly in this range (movement range of the float arm in practice only 40-180 Ohm). Due to a possibly bulky tank container and a non-linear tank arm, the quantity must be calculated using the small computer (arduino). To do this, the corresponding tank content must be entered once for the max. 11 possible swivel arm positions (can be selected as required). The interpolation is irrelevant given the number of positions and the fact that the exact quantity is displayed again when a position is reached. See programming for details.
3. the quantity that can no longer be detected by the transmitter (e.g. the swivel arm of the transmitter is at the bottom, but there are still 5 litres in the tank (Pos 1 = 5 litres) is calculated down from Pos 1 - as in the "without sensor" function mode. As a rule, a responsible pilot will never emty out his tank to this level, but in these special cases it is extremely reassuring not to be in the dark. For early warning, a warning quantity can be set above which the red LED lights up. In the event that the swivelling arm cannot extend far enough upwards, i.e. the tank is overfilled for the swivelling arm, the correct measurement starts when the last (top) position of the swivelling arm is reached. An "overfilled" tank is no problem, so you can wait until the top measuring position is reached. In any case, the tank content below Pos. 1, which can no longer be measured, is more critical.
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Picture: bulky tank |
Hardware
Fuel tank sensor
Figure 1 shows a simple swivel arm float, but other tank sensors, such as rod sensors in or on which a float follows the fill level, should also be suitable, provided that they generate an electrical resistance that can be measured against mass. The prototype works from approx. 40 to 180 ohms, it should also be possible to use a different ohmic range, in which case the values to be programmed will be different. The sensor must be suitable for fuel (both the float and the risk of explosion of the resistance pick-up), should be able to map the fill level as far as possible (min - max), be easy to install and not hinder refuelling after installation. In the prototype (see Fig. 1), the bracket was modified so that the tank opening is not affected. The bracket was therefore mounted on the existing inner flange so that no holes had to be drilled in the tank itself. It is important that the fuel level is taken as close to the centre of the tank as possible so that fluctuations and wobbling of the fuel due to changes in position during flight do not affect the fuel level indicator too much. Therefore, the position of the float rod is important, as well as its length and offset in the case of swivel arm sensors.
Micro computer
An Arduino Uno was used which is programmed accordingly. This evaluates the float level (electrical resistance) in relation to the programmed positions (P1 to P11 are possible) and transfers the available litres and the remaining flight time to a display.
The display
An Arduiono-compatible LCD display was selected as the prototype type. A round display is more elegant if round instruments are installed. However, even if absolute precision of the display were guaranteed, these have the disadvantage that they are difficult to read, especially when things get tight, i.e. the tank level is below the warning threshold. In principle, the low fill level is of interest, and all the more so as the tank is nearing the end. A numerical display is simpler as a prototype. The programming could also show precise quantity indications with simple round instruments if the scaling is used again from the beginning when a warning level is reached (already realised by an LED). I.e. in standard mode, the entire scale shows from full to warning level, from the warning level an LED lights up and the scale is then used from the warning level to empty - so it jumps back to the beginning (LED lights up). Everything is conceivable, we are working on it. As a prototype, however, the LCD display is the simpler way.
Programming
The device must be programmed to the respective sensor and tank for the first time.
Electrical installation
The device is connected the the board electrical system.
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