Coaxial Cable Compensation for Electrical Impedance Tomography
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Solution Overview
Problem
Existing Electrical Impedance Tomography (EIT) systems face significant signal loss due to the series and shunt components of coaxial cables, particularly when measuring low impedance loads at high frequencies, which degrades the accuracy of voltage measurements.
Innovation Solution
A system and method that modify the current applied at the input of a two-port electrical network to compensate for losses caused by the network, using measured voltage at the input and knowledge of two-port parameters obtained during calibration, to achieve a desired load current without measuring at the load end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If shielded cables are used to reduce interference between current sources, then electromagnetic interference is reduced, but parasitic capacitance increases which degrades high-frequency operation
Solution Approach 1:
The patent implements a feedback mechanism where the system measures the actual current delivered to the load through voltage measurements and uses this information to adjust the output current. The feedback loop compensates for the effects of cable capacitance by comparing the desired current with the actual current and adjusting accordingly, thereby maintaining accurate current delivery despite the presence of parasitic capacitance in shielded cables.
Solution Approach 2:
The system dynamically adjusts operating parameters including frequency and current amplitude based on measured conditions. By changing the operating frequency and current parameters in response to measured voltage and current values, the system optimizes performance across different frequency ranges while compensating for cable effects, thus maintaining reliability in high-frequency operation despite using shielded cables.
2Reliability
If active circuit is used to drive cable shield or grounded shield with current source, then shunt capacitance effect is reduced, but series cable components are not addressed
Solution Approach 1:
The patent creates a universal compensation system that handles both shunt capacitance and series impedance effects through a single integrated approach. The system performs multiple functions: it compensates for shunt capacitance through feedback control and simultaneously addresses series resistance and inductance through impedance correction algorithms. This multi-functional system eliminates the need for separate compensation circuits for different cable effects.
Solution Approach 2:
The patent introduces voltage measurements and computational algorithms as intermediaries between the current source and the load. Instead of directly compensating for cable effects at the hardware level with separate circuits, the system uses voltage sensing and mathematical correction as an intermediary layer to account for both shunt and series cable components, providing a more comprehensive solution.
3Measurement precision
If voltage measurements are made at the load end, then accurate load voltage is obtained, but cable series inductance causes significant voltage drop making measurements inaccurate
Solution Approach 1:
The system performs preliminary compensation for cable voltage drops by calculating the expected voltage loss due to series inductance and resistance before making measurements. The feedback mechanism预先 adjusts the output to account for anticipated voltage drops, and the system characterizes cable parameters in advance to use in compensation calculations, thereby improving measurement accuracy.
Solution Approach 2:
The patent replaces direct physical voltage measurement at the load with an indirect measurement and calculation approach. Instead of mechanically measuring voltage at the load end where cable drops affect accuracy, the system substitutes this with voltage measurements at the source combined with computational correction based on known cable characteristics, eliminating the need for precise load-end measurements.
4Stability of the object's composition
If current source output impedance is increased to maintain high quality current, then current stability improves, but the effect of cable impedance becomes more significant
Solution Approach 1:
The feedback mechanism allows the system to maintain high current stability while compensating for cable impedance effects. By continuously measuring actual current and voltage and adjusting the output based on these measurements, the system achieves both current stability and immunity to cable impedance variations, resolving the contradiction between high output impedance benefits and cable effect susceptibility.
Data Source
AI summary
A system and method for minimizing signal interference in coaxial cables carrying signals for electrical impedance tomography (EIT) by compensating for losses from both the series and shunt elements on the path from the source to the load, providing a compensated load current and voltage. One or a series of two-port networks is used to modify a current source with applied current to compensate for losses in the cable to attain the desired load current. The input current is adjusted using the measured voltage and the shunting output and stray impedance, preferably determined during a calibration process.