Objective To study the protective earth requirement for touched metal parts of medical electrical equipment to improve the manufacturer's understanding on national standards.Methods The isolation methods for the touched metal parts in national standards were studied,and the principle of protective earth combined with insulation separating was analyzed.The characteristics of the second isolation method was discussed,and the respiratory system structure and electroshock protection of the anaesthetic machine were taken as examples.Results The touched metal parts with no measures for grounding,double isolation or reinforced insulation was determined by structure detection to meet the requirements of national standards in case basic insulation ceased to be effective and the parts were uncharged.Conclusion The necessities to girt the touched metal parts with measures for grounding,double isolation or reinforced insulation should depend on the understanding on national standards and electrical construction of the equipment under test by structure detection.

This paper analyzes the shortcomings of the existing pure tone audiometers, and proposes a system to realize pure tone audiometry and speech audiometry with a new DSP processor. The pure tone test signal produced by the system has accurate frequency, high signal-to-noise ratio, and small harmonic distortion. The noise generator that comes with DSP adds a band-pass filter to realize the generation of narrow-band noise. At the same time, due to the modular structure of software design, the system has good ease of use and scalability. The test results show that the hearing test system has excellent performance and can be better used in hearing medical diagnosis.
Audiometry, Pure-Tone/methods* ; Hearing ; Noise ; Signal-To-Noise Ratio