Thermal Flow Meter Reach-Time Switching for Low-Flow Accuracy
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Solution Overview
Problem
Existing thermal flow meters face calculation errors when measuring low liquid flow rates due to heat transfer to the measurement tube or liquid before reaching the second temperature detecting resistance element, limiting the measurable flow rate range on the lower limit side.
Innovation Solution
A thermal flow meter with a measurement tube and temperature detection substrate featuring heating and temperature detecting resistance elements, utilizing voltage signals to measure reach times and calculate flow rates based on both reach times when flow rates are high, and solely on the first reach time when flow rates are low, with adjustable weightings to reduce calculation errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If two temperature detecting resistance elements are arranged downstream from the heating resistance element, then the measurement can be performed for higher flow rates, but the measurement precision deteriorates for low flow rates due to heat transfer to the measurement tube or liquid before reaching the second temperature detecting resistance element
Solution Approach 1:
The patent applies dynamics by making the measurement method adaptable based on flow rate conditions. The calculation unit dynamically switches between using only the first temperature detecting resistance element for low flow rates and using both temperature detecting resistance elements for high flow rates. This dynamic adjustment allows the system to maintain measurement precision across the entire flow rate range while expanding the measurable flow rate range.
Solution Approach 2:
The patent changes the measurement parameter selection based on flow rate conditions. For low flow rates, the system uses only the first reach time parameter, while for high flow rates, it uses both first and second reach time parameters. This parameter change strategy resolves the contradiction by selecting the appropriate measurement approach based on the actual flow rate, thereby maintaining precision while expanding the measurable range.
2Adaptability or versatility
If the second temperature detecting resistance element is used for low flow rate measurements, then the measurable flow rate range expands, but the calculation accuracy deteriorates due to heat transfer before reaching the second element
Solution Approach 1:
The system dynamically adapts its measurement configuration based on the detected flow rate. When the flow rate is determined to be low, the calculation unit uses only the first temperature detecting resistance element, avoiding the heat transfer issue. When the flow rate is high, it uses both elements. This dynamic adaptation enables the system to expand its measurable flow rate range while maintaining calculation accuracy through appropriate element selection.
Solution Approach 2:
The calculation unit acts as an intermediary that mediates between the temperature detecting resistance elements and the flow rate measurement. It processes the temperature signals from the resistance elements, determines the flow rate, and then selects which resistance element data to use for the final calculation. This intermediary function allows the system to expand the measurable range while maintaining precision by filtering out inaccurate measurements from low flow rate conditions.
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
Reduces calculation errors in low flow rates and expands the measurable flow rate range by accurately calculating flow rates using a combination of reach times and adjustable weightings, enhancing measurement accuracy and reliability.
Implementation Method 1
a voltage output unit configured to output a voltage signal to the temperature detection substrate, the voltage signal being for heating the heating resistance element
Implementation Method 2
a voltage detection unit configured to determine a first output voltage in accordance with a temperature of the first temperature detecting resistance element and a second output voltage in accordance with a temperature of the second temperature detecting resistance element
Data Source
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AI summary
Provided is a flow rate calculation method including: a time measurement step S103, S104 of measuring a first reach time T1 taken by a liquid heated by a heating resistance element to reach a first temperature detecting resistance element and measuring a second reach time T2 taken by a liquid heated by the heating resistance element to reach a second temperature detecting resistance element; and a calculation step S108, S110, S111 of calculating a liquid flow rate of a liquid flowing through a measurement tube based on the first reach time T1 and the second reach time T2. The calculation step includes calculating the liquid flow rate based on both the first reach time T1 and the second reach time T2 when a first flow rate FL1 is greater than a first predetermined flow rate and calculating the liquid flow rate based on the first reach time T1 without using the second reach time T2 when the first flow rate FL1 is less than or equal to the first predetermined flow rate.