Decade Capacitance Standard Box with Parasitic Reduction
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Solution Overview
Problem
Existing decade capacitor standards have complex structures with many wires, leading to parasitic effects and measurement errors, especially in large capacitance measurements, due to lack of compensation for open and short circuits, and complicated operation procedures.
Innovation Solution
A novel decade capacitor design using six sets of 4-value capacitors and a special changeover switch with short and open positions to encode decade capacitance values, reducing the number of wires and connections, and providing compensation for internal and external parasitics, resulting in a more accurate and compact measurement system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional decade capacitor design with 10 capacitors and rotary switch is used, then capacitance selection capability is achieved, but structure complexity and parasitic effects increase
Solution Approach 1:
The capacitance selection is segmented into 6 decades rather than using 10 capacitors directly. Each decade uses 4 capacitors with specific values (1, 2, 2, 5 units) to represent 10 capacitance steps, reducing the total capacitor count from 10 to 6 sets of 4 capacitors. This segmentation approach simplifies the overall structure while maintaining full decade selection capability.
Solution Approach 2:
Each of the 6 decades has locally optimized capacitor values (1, 2, 2, 5 unit pattern) tailored to its specific capacitance range. This local quality optimization allows each decade to achieve accurate 10-step selection with minimal capacitors, reducing global structure complexity while maintaining measurement precision across all decades.
2Measurement precision
If more capacitors and connection wires are used to achieve decade capacitance values, then capacitance selection range is improved, but parasitic effects and measurement errors increase
Solution Approach 1:
The harmful connection wires between capacitors are extracted and eliminated by using a changeover switch that directly selects capacitors from each decade. The switch connects the selected capacitor directly to the output terminal without requiring inter-capacitor wiring, thereby removing the source of parasitic effects while maintaining full decade capacitance selection capability.
Solution Approach 2:
The changeover switch, which could be seen as adding complexity, actually converts the potential harm of multiple connections into a benefit by providing a centralized, low-parasitic connection point. The switch structure allows all capacitor selections to converge at a single output terminal, transforming what would be multiple parasitic-prone connections into a single controlled connection path.
3Measurement precision
If traditional capacitor standard without compensation is used, then device simplicity is maintained, but measurement accuracy for large capacitance deteriorates
Solution Approach 1:
Open and short circuit compensation is performed preliminarily through dedicated compensation capacitors and switches before actual capacitance measurements. The compensation network is pre-configured with capacitors and switches that can be activated to cancel out parasitic effects, preparing the measurement system in advance to handle both small and large capacitance measurements accurately without complicating the main measurement procedure.
4Device complexity
If 10 capacitors with 20 wires are used for decade selection, then full capacitance range is achieved, but connection complexity and parasitic inductance increase
Solution Approach 1:
The changeover switch serves multiple functions: it selects capacitors from 6 different decades, provides open circuit position, provides short circuit position, and connects to a common output terminal. This multi-functional design eliminates the need for separate connection wires for each capacitor, reducing connection complexity from 20 wires to a single switch structure with unified output, thereby improving measurement accuracy.
Data Source
AI summary
The invention disclosed a high precision decade capacitor standard box. It comprises 6 sets of physical capacitors, 6 changeover switches, and output ports. Each set of physical capacitors include 4 physical capacitors, at least one capacitor has single-unit capacitance. The changeover switch implements the decade encoding of all the combinations of 4 physical capacitors. The changeover switch has input terminals that connect to two electrodes of physical capacitors, and output terminals that connect to the output ports of capacitor standard box to provide the selected capacitance. The capacitance values can be selected any integer from 0 to 10 times of single-unit capacitance. The decade encoding of all the combinations of 4 capacitors can reduce the number of required capacitors and wires for connecting capacitors. The open and short compensation are adopted in this decade capacitor standard, which minimizes error, improve accuracy, and is convenient for measurement, transport, and field application.