Extreme Stability, Microscopic Insight: How High-Voltage Doorknob Capacitors Become the Stabilizing Force of MRI Magnet Power

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The core performance of a nuclear magnetic resonance (NMR) instrument lies in its ability to generate and maintain a highly uniform and stable static main magnetic field. Whether based on superconducting magnets or electromagnets, the excitation power supply and field compensation coils require extremely stable, pure, and high-voltage DC power. Any slight voltage fluctuation or ripple noise can cause magnetic field drift, leading to spectral line broadening, reduced resolution, and even the inability to resolve fine molecular structures. High-voltage doorknob capacitors are the cornerstone components that ensure the extremely low noise and long-term stability of the high-voltage power supply systems of these precision instruments.

NMR instruments place stringent demands on high-voltage power supplies:

NMR instruments, particularly high-field systems, pose significant challenges to their magnet power supply systems:

Unparalleled stability: Voltage and current fluctuations in the power supply output must be kept to extremely low levels (typically requiring better than 10⁻⁶). Even small fluctuations can directly cause variations in the main magnetic field, manifesting as peak broadening or frequency shifts in the NMR spectrum, severely impacting the accuracy of both quantitative and qualitative analysis.
The Core Function of Doorknob Capacitors: High-Voltage Filtering and Energy Storage:

In the DC-DC converter and output stage of an MRI magnet power supply, high-voltage doorknob capacitors play two crucial roles:

DC link support and filtering: They are the core of π-type or LC filter networks. Their excellent high-frequency characteristics (low equivalent series resistance (ESR) and low equivalent series inductance (ESL)) effectively filter out high-frequency ripple generated by switching power supplies, outputting a smooth, water-like high-voltage DC voltage, providing "clean" energy for the magnet system.

Transient energy buffering: During transient changes in system load, capacitors act as miniature local energy reservoirs, instantly sourcing or absorbing charge, effectively suppressing minor dips or overshoots in the bus voltage and maintaining instantaneous stability of the magnet current.

Xian Xiwuer Electronic & Info. Co., Ltd. is a wholly state-owned company with a registered capital of 91.46 million RMB Yuan, owning a total assets of 315 million RMBYuan, under the jurisdiction of Xi'an State-owned Assets Supervision & Management Committee. There are about 400 employees, with an annual sales income of 250 million RMB Yuan.

The main products include Zinc Oxide Varistors, thermistors, H-V ceramic capacitors, SPD, and Solar Energy Surge Protective Devices. The company has advanced production equipment, including 18 large sintering furnaces, 8 automatic assembly lines, the largest energy impulse current generator and a series of special test equipment and environmental test equipment. In the same industry in China, the company has the largest production capacity and the highest degree of automation with the most complete testing methods.

Our employees are 8 with master's degrees and more than 80 engineers with senior technical titles. 12 technicians have been awarded Experts with Outstanding Contributions by the Xian municipal government, and 1 expert has been enjoying a special allowance from the State Council.

The company has five sites for business production and operation, covering an area of 50,000 square meters. Its construction area is up to more than 54,000 square meters.

· No.99, Fengqing Road, Lianhu District, Xi an(ceramic capacitor)

· No.1118, Ziqaing Road, Xincheng District, Xi' a (Headquarters, varistors, thermistors)

· No.11, Longshou South Road, Lianhu District, Xi' a (Registration, photovoltaic lightning protection box)

· Block A, No.18, Gaoxin Road, High-tech District, Xi' an

· Jinghe New Town Xi Xian New Area(the new plant)

• Xian Xiwuer Electronic and Info. Co., Ltd. is a wholly state-owned company with a registered capital of CNY 101.465 million (exchanged to USD 15.85 million), owning total assets of CNY315 million (traded to USD 49.22 million). It was established in 1976. Currently, it has about 460 employees, with an annual sales income of CN280 million (exchanged to USD43.75 million). The company has four production and business bases covering an area of 43052 square meters, and a construction area of more than 50000 square meters. The company has 8 persons with master's degrees, more than 80 engineers with senior technical titles 12 technicians who have been awarded Experts with Outstanding Contributions by the Xian municipal government, and 1 expert who has been enjoying a special allowance from the State Council.

• The main products include

            • Smart Embedded Epoxy Pole；

            • Integrated Instrument Transformer

• Capacitive Voltage Divider；

• High Voltage Capacitor Rod；

• High Voltage Film Capacitor；

• High Voltage Resistor；

• Primary and Secondary Integrated Intelligent assembly and components with the function of voltage measurement, current measurement, protection, temperature monitoring, and power supply；

• Medium-High Voltage components/parts/ assembly；

• Surge Protective Device for Power Supply System；

• Chips for lightening devices；

• Zinc Oxide Varistor；Thermistor.

Major Customers: ABB, Schneider, GE, ZTE, XD Electric, XJ Electric, PingGao Electric and etc.

• The company has the provincial Technical R&D Center. The company has developing and manufacturing experiences of the key products HV Ceramic Capacitor, SPD, Varistor, Thermistor and for nearly 20 years. There have been 32 patented technologies, 4 invention patents, and 4 national key new products. The company is in the leading position in the same industry. The company has grown very fast with a unique management system which is the fundamental guarantee to the continuous development of the enterprise under the state-owned system. In Northwest China, the company is the first to implement ISO 9001 standards and the first to promote the use of ERP management systems, having achieved ISO9001, ISO14001, and ISO45001 approval, thus standardizing and improving the management level of the company.
• Through continuous technological innovation, product R&D, and quality improvement the main technical performance and reliability of the products are at the internationally advanced level the same level as Panasonic and Siemens. The products have UL, VDE, TUV, CAS, CE, CQC, RoHS, and REACH certifications. The company has advanced production equipment among which the key production equipment and modern assembly lines are imported from Japan, the U.S.A, Germany, Korea, and Belgium including 26m large sintering tunnel furnaces8 automatic assembly lines, the largest energy impulse current generator and a series of special test equipment and environmental test equipment. In the same industry in China, the company has the largest production capacity and the highest degree of automation with the most complete testing methods. The company has two routine test laboratories with the most advanced lightning testing equipment and environmental testing equipment which comply with national standards for laboratory construction. They are the significant laboratories supported by Shaanxi Province with professional testing technicians undertaking part of the supervision and inspection of electronic products in Shaanxi Province at the same time.
• We believe we are able to supply satisfied goods and services to customers at home and abroad with the most reasonable price and the shortest delivery time. on the basis of our excellent quality assurance capacity, technical development capacity, and rich manufacturing experiences.

Through continuous technological innovation, product R&D, and quality improvement, the main technical performance and reliability of the products are at the international advanced level, at the same level as Panasonic and Siemens. The products have UL, VDE, TUV, CAS, CE, CQC, RoHS, and REACH Certification