| 摘要 |
1,240,488. Electro-medical apparatus. INTERNATIONAL BUSINESS MACHINES CORP. Sept.26, 1968 [Oct.24, 1967], No.45668/68. Heading G1N. To detect significant portions of an electrocardiogram, an electro-encephelogram or other complex waveform a signal derived from the waveform, e.g. by differentiation, is applied to a threshold circuit the threshold level of which is increased each time it is exceeded by the signal and thereafter allowed to diminish towards a minimum value. The threshold circuit triggers a waveform sampler which may be coupled to a recorder so that the significant portions of the waveform are recorded. The provision of a variable threshold level ensures that the system will record a small pulse occurring after a quiet interval whilst not responding to every noise pulse in a noisy part of the signal. In Fig. 1 the differentiated waveform is supplied via a filter 17, which eliminates h.f. noise, to separate positive and negative low-level threshold circuits 31, 33. The level at which each of these responds is determined by the voltage on capacitor C1. If either level is exceeded the corresponding threshold circuit provides an output pulse and also operates a monostable 35 or 37 to add a fixed amount of charge to the capacitor. Other fixedlevel threshold circuits may be provided, as 19, 21, which respond only to large deviations of the differentiated waveform from zero and instruct the sampler to record the corresponding portion of the waveform in detail. |
