Airflow Velocity Sensor Probe Self-Calibration
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Solution Overview
Problem
Current air velocity sensors face challenges such as self-heating issues due to ambient temperature sensing, requiring expensive custom RTDs and frequent calibration, which leads to inconvenience and downtime, especially in remote locations.
Innovation Solution
A handheld air velocity sensor system with a bridge circuit assembly featuring a digitally controlled resistive element and separate temperature sensor, housed in a probe tip, allowing for self-calibration and remote data processing, reducing the need for frequent factory calibration and enabling easy replacement of probe tips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the velocity sensor is heated to sense airflow, then measurement capability is improved, but self-heating causes temperature errors
Solution Approach 1:
The patent divides the sensor into two separate RTD elements: one RTD specifically for velocity measurement that is heated, and another RTD for temperature compensation that remains unheated. This segmentation allows the velocity-sensing RTD to be heated sufficiently for accurate airflow detection while the temperature-compensation RTD remains at ambient temperature, eliminating self-heating errors in the temperature measurement.
Solution Approach 2:
The patent introduces a temperature compensation RTD as an intermediary element that measures the actual temperature of the heated velocity sensor. This intermediary RTD provides temperature data that is used to compensate for self-heating effects in the bridge circuit, allowing accurate temperature correction without requiring the temperature-sensing RTD itself to be heated.
2Temperature
If the ambient sensor resistance is made much larger to reduce self-heating, then temperature error is reduced, but sensor selection is limited and cost increases
Solution Approach 1:
The patent segments the temperature sensing function into two separate RTD elements with different resistance values optimized for their specific functions. The velocity RTD uses standard low-resistance values (e.g., 10 ohms) that are easy to manufacture, while the temperature compensation RTD uses higher resistance values suitable for its unheated operation. This segmentation allows both sensors to use standard, cost-effective resistance values rather than requiring custom high-resistance sensors.
Solution Approach 2:
The patent changes the operational parameters of the two RTD elements differently: the velocity RTD is operated at high temperature (heated to 50-150°C above ambient) with low resistance, while the temperature compensation RTD is operated at ambient temperature with high resistance. This parameter differentiation allows both sensors to use standard resistance values while achieving their respective measurement objectives without self-heating errors.
3Measurement precision
If factory calibration is performed frequently, then measurement accuracy is maintained, but downtime and cost increase
Solution Approach 1:
The patent enables the sensor to perform self-diagnosis and self-characterization by using the temperature compensation RTD to continuously monitor the actual temperature of the velocity sensor. This self-service capability allows the system to automatically detect drift and compensate for it, reducing the need for frequent manual factory calibration and minimizing downtime.
Solution Approach 2:
The patent implements a feedback mechanism where the temperature compensation RTD continuously provides temperature data back to the measurement system. This feedback loop allows real-time compensation for self-heating effects and drift, maintaining measurement accuracy without requiring frequent external calibration interventions.
4Ease of repair
If the probe tip is made replaceable, then ease of maintenance is improved, but device complexity increases
Solution Approach 1:
The patent segments the sensor device into two main parts: a reusable handle containing the electronics and a replaceable probe tip containing the RTD sensors. This segmentation allows the probe tip to be easily replaced if damaged or contaminated, while the expensive electronic components in the handle are preserved. The modular design simplifies maintenance by allowing field replacement of only the probe tip rather than the entire sensor assembly.
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 solution reduces downtime, lowers costs by using standard components, and improves measurement accuracy by factoring in humidity, while allowing for flexible and remote calibration of air velocity sensors.
Implementation Method 1
Velocity of the fluid or gas is related to the power dissipation in the sensor. The nonlinearity results from power dissipation in the sensor, which raises the sensor temperature and changes its resistance
Implementation Method 2
The bridge circuit comprises two circuit legs, with the first leg sensing the ambient temperature and including a resistive temperature detector (RTD) RD, an offset resistance RC, and a reference resistance RA. The second leg of the bridge circuit is the heated velocity sensor, comprising a second reference resistor RB and the heated RTD RE
Implementation Method 3
The operational amplifier applies a DC voltage to enable the velocity sensor to be heated to a target temperature within the overheat temperature range
Implementation Method 4
The apparatus also includes a gas flow temperature sensor for measuring the temperature of the gas or air flow to be measured
Data Source
AI summary
There is disclosed a handheld air flow velocity measurement probe that includes a bridge circuit assembly having an airflow velocity sensor that is a resistance temperature detector (RTD) and a digitally controlled resistive element to dynamically adjust and maintain the resistance of the velocity sensor within the overheat temperature predefined range. The velocity measurement also uses a separate temperature sensor to sense the temperature of the air or gas flow. A humidity sensor is also included remote from the other sensors to measure humidity in the gas flow to be measured. All of the above described components are housed at a probe tip instead of a base as in most standard handheld probes and the digital interface at the probe tip allows the user to replace a bulky, expensive telescoping antenna with stackable extender scheme.