Universal I/O Circuit Mitigates Capacitor Soakage in Building Automation
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Solution Overview
Problem
Building automation systems face issues with capacitor soakage, which affects resistance measurements due to dielectric absorption caused by stray capacitance from sensor leads, leading to inaccurate readings.
Innovation Solution
A universal input/output circuit that drives a known current through the resistance between terminals, reconfigures the circuit using switches, and maintains constant voltage by connecting the digital-to-analog converter directly or via a sample-and-hold element to the amplifier, ensuring the voltage remains the same before and after reconfiguration, thus mitigating capacitor soakage effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a capacitive element is in parallel with a resistive sensor for circuit operation, then the circuit can function with standard components and configuration, but dielectric absorption causes inaccurate resistance measurements due to remaining electric charge on the capacitor
Solution Approach 1:
The patent applies preliminary action by performing a discharge operation before the resistance measurement. The circuit first applies a test current to the capacitive element, measures the resulting voltage, calculates the capacitance value, and then uses this information to compensate for dielectric absorption effects during the subsequent resistance measurement. This preliminary characterization of the capacitor allows the system to account for and correct the measurement errors that would otherwise occur.
Solution Approach 2:
The patent implements feedback by using the measured capacitance value to adjust and compensate the resistance measurement process. The system continuously monitors the capacitive element's characteristics and uses this information to correct the resistance readings in real-time, thereby eliminating the adverse effects of dielectric absorption on measurement accuracy.
2Device complexity
If sequential readings are used to minimize the number of components, then the circuit can use a single A/D converter for multiple sensors, but the circuit can only obtain readings one sensor at a time requiring time allocation for each sensor
Solution Approach 1:
The patent applies universality by designing a single A/D converter that can be reconfigured through a switching network to serve multiple sensor inputs. The same converter is time-multiplexed across different sensors, allowing the system to maintain low component complexity while still acquiring data from multiple sources. The converter alternates between different input channels based on the sequential reading schedule.
3Reliability
If a unity gain amplifier is used to match impedance between D/A converter and actuator, then the output impedance matching is achieved, but the amplifier is required adding to the circuit components
Solution Approach 1:
The patent merges the amplifier function with the existing operational amplifier already present in the circuit for other purposes. Instead of adding a separate unity gain amplifier, the design repurposes an available operational amplifier to perform the impedance matching function. This integration approach maintains the necessary impedance matching while avoiding the addition of redundant components.
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
The solution effectively maintains constant voltage between terminals, eliminating adverse effects of capacitor soakage and ensuring accurate resistance measurements, allowing for reliable operation of field devices in building automation systems.
Implementation Method 1
the analog-to-digital converter is configured to convert a first analog voltage at the first connection point into a digital representation of said first analog voltage
Implementation Method 2
the digital-to-analog converter is configured to convert said digital representation at its input port into a second analog voltage
Implementation Method 3
An amplifier is required because the impedance at the output of the D/A converter does not match the impedance at the input of the actuator. The amplifier preferably is a unity gain amplifier which amplifies an electric current without changing voltage.
Data Source
AI summary
A universal input/output circuit for building automation is provided that may avoid issues related to capacitor soakage, thereby giving more accurate measurements of electric resistance. To mitigate capacitor soakage, the voltage between the input/output terminals is held constant. A programmable source drives a current through a resistor that connects to the input/output terminals. The circuit then measures a value of electrical resistance. The measurement yields a voltage signal which is transferred from the input of an analog-to-digital converter to the input of a digital-to-analog converter. A unity gain amplifier applies the output voltage of the digital-to-analog converter D/A to one of terminals. The circuit is configured such that the voltage signal at the output of the amplifier matches or substantially matches the voltage obtained from the resistance measurement.