Constant Temperature Anemometer Kelvin Sensing Circuit
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Solution Overview
Problem
Prior art constant temperature hot-wire anemometers face challenges in accurately measuring fluid flow due to resistance errors introduced by cables and connections, which cannot be easily differentiated from filament resistance, leading to erroneous gas flow calculations and requiring recalibration.
Innovation Solution
The design incorporates a Kelvin sensing technique using a conductor between electrically conductive pins, where a current source maintains constant resistance, and a voltage sensor measures voltage across the conductor, isolating resistance changes from cables and connections, allowing for precise fluid flow calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a cable and connections are used to connect the probe to circuitry, then the probe can be detachably attached for maintenance or replacement, but resistance errors are introduced that cannot be differentiated from filament resistance
Solution Approach 1:
The circuit is segmented into two separate measurement paths: one for current delivery and one for voltage sensing. The current source connects to the filament through cable connections, while the voltage sensor directly measures the voltage across the filament terminals without including cable resistance in the measurement path. This segmentation allows detachable probe attachment while eliminating cable resistance errors from the measurement.
Solution Approach 2:
A separate voltage sensing path acts as an intermediary between the filament and the measurement circuitry. This intermediary path directly measures the voltage across the filament without being affected by cable resistance, thereby mediating the measurement to exclude harmful resistance artifacts from the cable and connections.
2Adaptability or versatility
If cable and connection resistance changes occur due to temperature or physical disturbance, then the probe can operate in varying environmental conditions, but measurement accuracy deteriorates requiring recalibration
Solution Approach 1:
The voltage sensor continuously monitors the actual voltage across the filament and feeds this information back to the measurement circuitry. This feedback mechanism allows the system to compensate for any resistance changes in the cable or connections by comparing the measured voltage with the expected voltage, thereby maintaining measurement accuracy across varying environmental conditions without requiring recalibration.
3Device complexity
If traditional two-wire measurement is used, then the circuit design is simpler, but cable and connection resistance cannot be differentiated from filament resistance
Solution Approach 1:
The measurement circuit uses an asymmetric configuration where the current delivery path and voltage sensing path are different. The current source uses two wires to deliver current through the filament, while the voltage sensor uses a separate direct connection to measure voltage across the filament terminals. This asymmetric design adds minimal complexity but enables precise differentiation between cable resistance and filament resistance.
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 eliminates resistance artifacts from cables and connections, enabling accurate and precise fluid flow measurements without the need for frequent recalibration, improving measurement accuracy and efficiency.
Implementation Method 1
the amount of heat lost due to convection is a function of the fluid velocity passing over the filament. Constant temperature hot-wire anemometers, or CTAs, hold the temperature of a heated filament constant, and use empirical data, mathematical algorithms, or both to calculate the flow rate of a fluid based on the energy used to keep the filament at the constant temperature. Because filament temperature is related to the electrical resistance of filament, the CTA operates to maintain a constant resistance of the filament.
Implementation Method 2
a filament is welded between two pins of a probe. The probe is detachably attached to a cable. The cable communicates with circuitry for calculation of the gas flow rate passing over the filament.
Data Source
AI summary
A constant temperature anemometer is disclosed. The anemometer includes electrically conductive pins including a first set of pins and a second set of pins. A conductor is coupled to the electrically coupled pins. A current source is configured to provide a current through the conductor between the first set of pins. A voltage sensor is configured to measure the voltage across the conductor between the second set of pins. The current source and voltage sensor are configured to maintain a constant resistance of the conductor between the first set of pins.