Milk Level Sensing with Pump-Stop Hydrostatic Pressure
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Solution Overview
Problem
Existing milk level measurement devices in coffee machines face instability in pressure readings during suction, leading to measurement errors and require complex setups with reversible or dual pumps, which are costly and unreliable.
Innovation Solution
A device comprising a pressure sensor, suction pump, and valve on the suction line, controlled by a unit that stops measuring pressure during pump operation to stabilize readings, using hydrostatic pressure to calculate liquid levels accurately, and includes a table for container sizes to determine remaining liquid quantities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pressure measurement is performed during pump suction operation, then liquid level can be continuously monitored, but pressure readings become unstable and measurement errors occur
Solution Approach 1:
The system alternates between measurement mode and suction mode. During measurement mode, the pump is stopped and the valve is closed to allow stable pressure readings. During suction mode, the pump operates to move liquid. This periodic switching resolves the contradiction by ensuring measurements are only taken when pressure is stable, while still providing continuous monitoring capability over time.
2Measurement precision
If incremental measurement method is used to determine liquid consumed by pump, then liquid level can be tracked, but measurement reliability decreases due to unstable pressure values during suction
Solution Approach 1:
The system performs measurements at predetermined moments when the pump is stopped, before the next suction cycle begins. This preliminary action ensures that pressure readings are taken under stable conditions, and the measurements are then used to calculate liquid consumption incrementally, maintaining both precision and reliability.
3Measurement precision
If reversible pump or dual pumps are used to enable level measurement, then measurement capability is achieved, but device complexity and cost increase
Solution Approach 1:
The measurement function is extracted from the pump operation itself. Instead of requiring the pump to have reversible capability or having dual pumps, the system separates measurement (performed when pump is stopped) from suction (performed when pump operates). This extraction resolves the contradiction by achieving measurement capability without increasing pump system complexity.
4Measurement precision
If pressure sensor is placed in suction line during pump operation, then liquid level can be measured, but pressure signal becomes unstable
Solution Approach 1:
The pressure sensor continuously monitors the pressure in the suction line, but valid measurements are only taken during periodic intervals when the pump is stopped and the valve is closed. This periodic measurement approach allows the sensor to detect hydrostatic pressure accurately during stable periods while ignoring the unstable periods when the pump is operating.
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
Provides reliable and stable milk level measurements, independent of container shape, with stable pressure readings and efficient operation, enabling accurate milk quantity calculation and control for coffee machine operations.
Implementation Method 1
the sensor is apt to measure the hydrostatic pressure in the tube
Data Source
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AI summary
Present invention relates to a device for measuring a level of a liquid in a container (12). The device comprises a sensor (15), arranged to sense a pressure of a liquid (11) in a tube (14), a pump (19) arranged to pump the liquid from the container (12) through the tube (14), and a valve (18) located along the tube between the sensor (15) and the pump (19) and arranged to impede back flow of the liquid into the container when the pump stops pumping the liquid. The device is arranged to measure the level of the liquid into the container on the basis of the hydrostatic pressure measured by the sensor after each stop of the pump. The invention also relates to a method for measuring a level of a liquid in a container (12) by means of a pressure sensor (15).