Resistive Liquid Level Sensor with Low Impedance Measurement
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Solution Overview
Problem
Conventional resistive liquid level sensors are limited in measuring multiple liquid levels and temperature accurately, especially when dealing with two liquids of different specific gravities in a single tank, due to high and irregular output impedance, which affects accuracy and introduces non-linear errors, and they cannot support precision temperature measurements.
Innovation Solution
A resistive liquid level/temperature sensor and transmitter system with a continuous resistive chain network and magnetic floats of different specific gravities, coupled with a low impedance three-wire RTD and a microcontroller-based liquid level controller, enables accurate measurement and wireless transmission of both liquid levels and temperature within a storage tank.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional resistive chain network is used to measure liquid level, then the sensor can indicate liquid level, but the output impedance is very high and irregular which decreases accuracy and introduces non-linear errors
Solution Approach 1:
The patent introduces an intermediary impedance measurement circuit that acts as a mediator between the resistive chain network and the reading device. This circuit includes a current source that drives current through the resistive chain and a voltage measurement circuit that measures the voltage drop across known resistors. The intermediary circuit converts the high-impedance voltage output into a low-impedance current signal, thereby reducing the output impedance effect and improving measurement accuracy while eliminating non-linear errors.
2Adaptability or versatility
If a conventional resistive chain network is used, then liquid level can be indicated, but the analog input requires extremely high impedance which prevents support for precision temperature sensors
Solution Approach 1:
The patent implements a universal measurement interface that can accommodate both liquid level sensing and temperature sensing functions. The impedance measurement circuit is designed to work with multiple sensor types by using a current source that can drive different impedance loads. The circuit includes multiplexer functionality that can selectively measure different sensor outputs, making the system versatile enough to support both the resistive chain network for level measurement and precision temperature sensors without requiring extremely high input impedance.
3Adaptability or versatility
If conventional resistive level sensors are used, then single liquid level can be measured, but dual liquid level and temperature measurement is not achievable
Solution Approach 1:
The patent merges multiple measurement functions into a single integrated sensor system. The resistive chain network for liquid level measurement is combined with a precision temperature sensor in a unified probe assembly. The impedance measurement circuit is designed to measure both the resistive chain output and the temperature sensor output through a shared current source and voltage measurement infrastructure. This merging approach enables simultaneous measurement of dual liquid levels and temperature while avoiding the need for separate measurement systems, thereby managing complexity through functional integration.
4Use of energy by stationary object
If conventional resistive chain network is used, then power consumption is higher, but low power consumption is not achieved
Solution Approach 1:
The patent implements periodic action by using a current source that is activated only during measurement cycles rather than continuously. The impedance measurement circuit measures voltage drops at specific time intervals when the current source is active, then enters a low-power idle state between measurements. This periodic operation mode allows the sensor to maintain measurement capability while significantly reducing average power consumption compared to continuous operation of conventional resistive chain networks.
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 system provides precise measurements of two liquid levels and temperature with low power consumption, overcoming the limitations of conventional sensors by using PRODUCT and INTERFACE impedance loops and a low impedance multiplexer to calculate liquid levels and temperature, ensuring high accuracy and sensitivity.
Implementation Method 1
Magnetic floats having different specific gravities surround and slide up and down the probe. The product float rises along the probe to the product liquid level, and the interface float rises to the interface liquid level.
Implementation Method 2
The product and interface floats magnetically close respective ones of the normally-open reed switches from the resistive network.
Implementation Method 3
A low impedance three-wire RTD (resistive temperature device) is located near the bottom of the probe such that the resistance thereof is indicative of temperature.
Data Source
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AI summary
A resistive liquid level/temperature sensor and transmitter (50) including low voltage impedance measurement circuitry to convert three impedance values into indications of the temperature and the levels of two (16, 18) different liquids (e.g., oil and water) located within a storage tank (14). A resistive chain network (40, 42) including a plurality of series connected resistors (R1... R5) and a corresponding plurality of reed switches (R1... R5) extend longitudinally through a liquid level sensing probe (10) that is dipped into the liquids in the tank.