Fluid Property Sensor Heat Loss Compensation
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Solution Overview
Problem
Conventional Pirani sensors face challenges in accurately measuring fluid properties due to significant parasitic heat losses from the measuring element's suspension and radiation, which complicate the detection of small changes in thermal conductivity, pressure, or flow, especially under varying ambient temperatures.
Innovation Solution
The improved fluid property sensor employs a measuring element with a first heating element to compensate for parasitic radiative heat losses and a second heating element to compensate for conductive heat losses, both independently controlled by a processor to minimize base power and enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the dimensions of the measuring element's suspensions are reduced to minimize base power, then parasitic heat losses decrease, but mechanical stability deteriorates
Solution Approach 1:
The patent divides the suspension system into multiple discrete suspension elements (suspension pins or suspension beams) that collectively support the measuring element. This segmentation allows optimization of each suspension component's geometry to achieve both low thermal conductivity (reducing parasitic heat losses) and adequate mechanical strength, resolving the contradiction between minimizing energy loss and maintaining structural stability.
2Reliability
If conventional temperature compensation is used with additional measuring resistors, then ambient temperature influence is compensated, but compensation accuracy is limited to a single operating point
Solution Approach 1:
The patent employs temperature-dependent correction values that are stored in memory and applied based on the actual ambient temperature conditions. Instead of using fixed compensation parameters valid only at a single operating point, the system dynamically adjusts compensation parameters according to temperature, thereby maintaining high measurement precision across a wide temperature range.
3Measurement precision
If the measuring element is made more sensitive to detect small changes in thermal conductivity, then measurement precision improves, but the sensor becomes more susceptible to parasitic heat losses
Solution Approach 1:
The patent extracts and separates the parasitic heat loss components from the measurement signal by providing correction values that account for suspension heat losses and radiation heat losses independently. This allows the measurement system to focus on detecting only the thermal conductivity changes of the measured gas, thereby maintaining high detection sensitivity while eliminating the masking effect of parasitic heat losses through mathematical correction.
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
This approach significantly reduces parasitic heat losses, improving the signal-to-noise ratio and accuracy of the sensor, allowing for more precise measurements of fluid properties, including vacuum pressure and flow rates, even at lower pressures.
Implementation Method 1
A filament suspended in a gas will lose heat to the gas as the gas's molecules collide with the wire and remove heat. Measuring the heat loss is an indirect indication of pressure.
Implementation Method 2
conventional Pirani sensors also experience conductive heat loss from the filament into the filament's suspension and radiation heat losses from the filament
Implementation Method 3
A first heating element extends at least partially proximal to the measuring element and is electrically connected to a first power source
Implementation Method 4
conventional Pirani sensors also experience conductive heat loss from the filament into the filament's suspension
Data Source
AI summary
A method comprises suspending a measuring element within a fluid and applying measuring power to the measuring element. Radiation loss compensation power is applied to a heating element. The radiation loss compensation power is selected to compensate parasitic radiative heat loss from the measuring element. Heat transfer from the measuring element into the fluid is evaluated and a property of the fluid is derived. A sensor which implements the method uses a resistive measuring element which is electrically connected to an evaluation circuit. The heating element is electrically connected to a power source. A processor receives an input from the evaluation circuit and calculates a property of the fluid while the power source provides radiation loss compensation power to the first heating element.