Compact Sensor Ideal for Confined Spaces
Designed specifically for cramped areas like motorcycle petrol tanks, this sensor offers remarkable suitability. Unlike traditional sensors featuring moving components like floats and float arms, which pose challenges in fitting within tanks, this sensor presents a unique advantage. It operates seamlessly without any moving parts, ensuring ease of installation in limited spaces.
Cost-Effective Sensor Circuit
Crafted from readily available, inexpensive components, the sensor circuit offers an affordable solution. Assembling this circuit incurs minimal expenses, making it a budget-friendly choice for various applications. Its simplicity and cost-effectiveness make it an attractive option for those seeking an economical sensor solution.
Measuring Petrol Level with Diode-Based Sensor Circuits
The operating principle of this system relies on the measurement of forward voltages in identical diodes, ensuring their uniformity through initial checks. As a diode’s forward voltage decreases with rising junction temperature, a nearby resistor, slightly protruding from the petrol surface, experiences heating. Optimal performance is achieved when both diodes, one acting as a reference, are at the same level. If submerged in petrol, the diodes prevent the resistor’s influence by cooling it. An opamp compares voltages across the diodes, adjusting for a smaller current passing through the reference diode. When petrol levels drop, the opamp output triggers the output transistor and connects a sense resistor parallel to the sensor output. Multiple sensor circuits, each with its switched sense resistor, can work together, generating an output signal for driving meters or similar devices.
Practical Implementation of the Sensor Strip
The author designed a ‘sensor strip’ comprising five PCBs, each hosting two sensor circuits. Installed at an angle in the petrol tank, this setup achieves a resolution of approximately 1.5 liters per sensor. Commonly, tanks have an electrical fitting near the bottom for connecting a reserve level indicator lamp. This sensor strip can effectively replace this fitting, offering a reliable solution.
Considerations and Recommendations for Optimal Performance
Experimentation with sense resistor values is necessary, avoiding values lower than 100 Ω. It’s crucial to enclose the diodes and heater resistor within a tube with a small opening at the bottom. This design prevents splashing petrol from cooling the heater resistor, which could lead to inaccurate readings. Additionally, the circuit should be powered with a regulated supply voltage of 5 to 6 V to prevent excessive heating of the resistors. After confirming proper functionality, coating the circuit board with epoxy glue enhances protection against petrol exposure.
Enhancing the System with LED Display
For visual representation, an LM3914 can be utilized to construct a 10-LED display, acting as a precise level indicator. Various suitable circuit examples can be found in previous issues of Elektor magazine, offering a comprehensive solution for visualizing petrol levels.
Note: This sensor circuit is not suitable for use in conductive liquids.