Stability requirements for power supply of medical instruments and equipment

With the rapid development of science and technology, the precision of modern medical instruments and equipment has been further improved, becoming a comprehensive combination of electronic, acoustic, optical, magnetic, computer and other technologies. Due to the unstable interference of the power supply, the phenomenon of instruments and equipment not working properly and even causing malfunctions and damage to the system is becoming increasingly serious. Strict preventive measures must be taken to ensure the stable operation of the equipment, thereby ensuring the normal operation of medical work order. 

1、 The impact of power interference on medical equipment. The types of power interference include voltage drop, power loss, frequency offset, electrical noise, surges, harmonic distortion, and transients. There are mainly three types of interference: 1. Differential mode interference: refers to the interference superimposed on the sine wave of the line voltage, which is the interference between current carrying conductors. Such as overvoltage and undervoltage, transient mutations, spikes, etc. in the power grid. 2. Common mode interference refers to the interference generated between the power grid and the neutral line, which is the interference between the current carrying conductor and the earth, coupled into the circuit by radiation or interference, such as peak interference, radio frequency interference, steady-state voltage between the neutral line and the earth line, etc. 3. Serial mode interference: refers to interference caused by external magnetic and electric fields.

There are two main types of power sources for medical instruments and equipment: 220V (usually referred to as mains power) and 380V (power supply). Generally, power fluctuations should be within the range of± Within a range of 5%. Electrocardiograph, monitor, ultrasonic diagnostic apparatus, acupuncture and moxibustion electrotherapy apparatus or silver needle instruments that directly contact the human body, especially the instruments and equipment that detect the bioelectrical signals of the human body, because the signal acquisition is extremely weak, once disturbed, the detection results such as waveforms, graphs, and images will be superimposed with a kind of distortion similar to some pathological changes, causing misdiagnosis, as well as micro electric shock, which may cause life danger in serious cases. If it is a medical instrument equipment with a computer system, when the peak interference amplitude in common mode interference reaches 2-50V and lasts for several microseconds, it may cause computer logic errors, loss, etc.

2、 Common technical methods to ensure stability. 1. The simplest method to suppress mutual interference between instruments and equipment by using dedicated independent circuits is to use split phase power supply and independent circuit power supply. That is, in a three wire power supply line, one phase is used as the power supply for sensitive equipment, the other phase is used as the power supply for external equipment, and the other phase is used as the power supply for commonly used testing instruments or other auxiliary equipment. This measure is often applied in the power supply system of large medical equipment. 2. Equipment such as CT, DR, MR, ultrasound diagnostic equipment, etc. that require high power fluctuation during the installation of AC voltage stabilizers should be equipped to ensure that the working voltage of the equipment is basically stable and purified to achieve voltage stabilization accuracy. 3. To prevent data loss during power outages, it is necessary to ensure uninterrupted power supply for server equipment such as hospital PACS systems, CRs, inspection instruments, etc. equipped with UPS. 4. To ensure the reliability of instrument equipment signals and casing grounding, the protective grounding is to connect the metal casing of the instrument equipment to the zero wire of the power supply, and immediately burn the fuse in case of a short circuit to achieve the purpose of cutting off the power supply. Protective grounding is the process of connecting the metal casing of an instrument to a ground wire. When the casing is charged due to interference, the current flows into the ground along the ground wire, achieving the goal of protecting personal and instrument safety. Signal grounding is the process of bridging a discharge resistor between a floating ground and a common ground, with a resistance value that does not affect the equipment's leakage current requirements. 5. Shielding is commonly used to effectively suppress electromagnetic interference caused by the propagation of radiation electromagnetic energy inside and outside the equipment through space, using methods such as electric field, magnetic field, and electromagnetic field shielding. For example, electrocardiograph, monitor, acupuncture and moxibustion electrotherapy instrument and other medical equipment that can radiate electromagnetic waves should be used far away from ultrashort wave therapy machine, high-frequency electric knife, X-ray machine and other medical equipment. Use high permeability metal shielding materials to enclose electromagnetic interference sources and electromagnetic sensitive circuits, so that the external electromagnetic field strength of the shielding is lower than the allowable value, such as in nuclear magnetic resonance (NMR) equipment rooms.