Temperature Compensated Transmission Line Liquid Level Sensor
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing liquid level sensing technologies are costly, prone to mechanical failure, and expensive to produce, especially when measuring large ranges of liquid levels, and are sensitive to environmental factors like salinity and temperature.
Innovation Solution
A liquid level sensor comprising a periodic signal generator, a coupled transmission line probe, a temperature-compensated peak detector circuit with a differential amplifier, a microcontroller with ADC, and calibration buttons, using off-the-shelf transmission lines and allowing for easy calibration and replacement of sensing elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical float sensors are used to measure liquid levels, then continuous level measurement is achieved, but the device becomes bulky and expensive with moving parts that may break or deteriorate over time
Solution Approach 1:
The patent replaces mechanical float sensors with an electrical transmission line-based sensing system. The transmission line probe measures liquid level by detecting changes in electrical characteristics (impedance, capacitance) when liquid contacts different portions of the probe, eliminating all moving parts while maintaining continuous measurement capability.
Solution Approach 2:
The patent introduces a transmission line as an intermediary between the measurement system and the liquid. This transmission line acts as a mediator that interacts with the liquid through electromagnetic fields rather than direct mechanical contact, allowing level measurement without mechanical components that can fail.
2Measurement precision
If resistive sensors with conductive probes are used in conductive liquids, then level measurement is achieved, but corrosion and electrolysis occur causing sensor deterioration
Solution Approach 1:
The patent replaces resistive conductive probes with a transmission line system that measures liquid level through electromagnetic characteristics rather than electrical conduction. This eliminates the corrosive interaction between conductive probes and conductive liquids, as the measurement is based on dielectric properties rather than ionic conduction.
Solution Approach 2:
The patent changes the measurement parameter from electrical resistance (which causes electrolysis in conductive liquids) to electromagnetic impedance and capacitance characteristics of the transmission line. This parameter change allows level measurement in conductive liquids without the harmful electrochemical reactions.
3Length of stationary object
If capacitive sensors with large plates are used to measure large ranges of water level, then measurement range is increased, but manufacturing cost and complexity increase prohibitively
Solution Approach 1:
The patent segments the measurement function into distributed sections along the transmission line probe. Each section of the transmission line contributes to the overall capacitance change proportionally to the liquid level, allowing large measurement ranges to be achieved with a slender probe rather than requiring large capacitive plates.
Solution Approach 2:
The patent transitions from two-dimensional capacitive plates to a one-dimensional transmission line structure. This dimensional change allows the sensing function to be distributed along the length of the probe, enabling large measurement ranges with minimal material and lower manufacturing cost.
4Length of stationary object
If TDR technology with transmission lines is used to measure liquid level, then unbounded sensor length is achieved, but the electronics to measure time delay of reflected pulses becomes prohibitively expensive
Solution Approach 1:
The patent replaces complex TDR electronics with a simpler capacitive sensing approach using the same transmission line probe. Instead of measuring time delay of reflected pulses, the system measures the capacitive coupling between the transmission line and the liquid, which can be done with simpler, less expensive electronics while maintaining the ability to measure unbounded sensor lengths.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces the cost and size of the sensor electronics, enables measurement of a wide range of liquid levels, and is easy to calibrate, providing reliable data while being resistant to temperature fluctuations and suitable for various fluids and probe lengths.
Implementation Method 1
uses transmission lines to measure the time delay of pulse reflections from the liquid to air boundary
Implementation Method 2
When liquid level changes across a capacitive plate, the capacitance changes proportionally
Implementation Method 3
Liquids tend to have a higher dielectric constant than air or gasses. Water in particular has a very high dielectric constant of 80, and is easily measured with dielectric techniques
Data Source
AI summary
A sensor having a transmission line acting as a probe and an electronic circuit measures liquid levels. The sensor circuit uses a periodic signal generator to produce a carrier wave, which stimulates the transmission line, through a complex network coupling element. The complex impedance network forms a voltage divider with the transmission line, wherein the output of the voltage divider, is demodulated with an AM demodulator, such as a thermally compensated peak detector. This demodulated signal is related to the dielectric constant, and thus the liquid level of the material surrounding the partially submerged transmission line probe. The liquid level and the demodulated signal may be offset, scaled and linearized with a microcontroller containing signal processing routines, linearizing equations, stored calibration constants and look up tables.