Low Impedance Liquid Level Detection for HVAC Condensate Pumps
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Solution Overview
Problem
Conventional liquid level detection systems in condensate pumps for HVAC systems face issues with fouling, high impedance circuits, and external interference, leading to inaccurate readings and system failures due to contamination and noise.
Innovation Solution
A liquid level detection device utilizing low impedance signal electrodes and a lock-in amplifier to generate unique signals, rejecting false signals and noise by only accepting signals that match the phase and frequency of the reference signal, thus providing accurate liquid level measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high impedance capacitive sensors are used to detect liquid level, then measurement sensitivity is improved, but the system becomes vulnerable to leakage currents, contamination, and external electromagnetic interference
Solution Approach 1:
The patent changes the impedance parameter of the sensing electrodes from high impedance (typical of capacitive sensors) to low impedance. This parameter change fundamentally alters the sensor's interaction with the environment, making it resistant to leakage currents and contamination while maintaining detection capability through the low-impedance signal transmission and lock-in amplifier processing
Solution Approach 2:
The patent introduces a lock-in amplifier as an intermediary signal processing device between the low-impedance electrodes and the control system. This intermediary component selectively amplifies and detects only the signal at the reference frequency, filtering out noise and interference, thereby enabling reliable detection despite the low impedance nature of the electrodes
2Measurement precision
If capacitive plates are placed in contact with water to sense level changes, then detection capability is improved, but fouling from debris and algae buildup adversely affects sensor performance
Solution Approach 1:
The patent changes the electrical parameter (impedance) of the sensing elements from high impedance to low impedance. This parameter change fundamentally alters how the sensor interacts with the liquid environment, making the sensor surface less susceptible to fouling effects while maintaining the ability to detect liquid level changes through signal transmission and processing
3Adaptability or versatility
If multiple float switches and control circuits are added to control pump operation and alarms, then system control functionality is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical float switch system with an electronic low-impedance electrode system coupled with a lock-in amplifier. This substitution eliminates the need for multiple mechanical float switches, linkages, and specialized bi-stable snap-action switches, thereby reducing device complexity while maintaining or improving control functionality through electronic signal processing
Solution Approach 2:
The patent creates a universal control system where the low-impedance electrode array can detect multiple liquid levels and the lock-in amplifier can process various signal types. This multi-functional electronic system replaces multiple specialized mechanical switches, allowing a single system to perform pump control, alarm triggering, and HVAC shutdown functions
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 effectively rejects contamination and noise, ensuring reliable operation of condensate pumps and HVAC systems by accurately determining liquid levels without being affected by fouling or external interference.
Implementation Method 1
The level detection device of the present invention includes an electronic signal source for generating one or more signals (multi-phase or multi-frequency), a lock-in amplifier, and a reference signal directly connecting the signal source to the lock-in amplifier. The signals generated by the signal source are connected to one or more low impedance signal electrodes.
Data Source
AI summary
A liquid level detection device includes a signal source for generating one or more unique signals on low impedance signal electrodes, a lock-in amplifier, and a reference signal directly connecting the signal source to the lock-in amplifier. The unique signals generated by the signal source are connected to one or more low impedance signal electrodes. The low impedance signal electrodes may be positioned at different levels inside the tank so that at any given level of liquid in the tank, each low impedance individual electrode may or may not be in contact with the liquid in the tank. Alternatively, the low impedance signal electrodes may be attached to the external wall of the tank at different levels. An antenna is connected to an input of the lock-in amplifier. The antenna may be placed inside the tank at the lowest level for the liquid, or the antenna may be attached to the outside wall of the tank near the bottom of the tank.