| 摘要 |
<p>A bioelectrical impedance measuring system that measures and indicates the impedance of a biological subject, such as one or more human extremities. The system measures and indicates a basal impedance value of the measured subject, and also indicates short temporal variations in the basal value. In the system an excitation signal, derived from an electrical signal source, is coupled to the subject by excitation electrodes and a resulting subject output signal is sensed by receiver electrodes. The subject output signal is electronically subtracted from a reference signal derived from the signal source, and the resulting signal is used to drive a display unit. The system includes a null detector connected to the display unit input, and an automatic gain control unit responsive thereto, connected in the subject output signal path to automatically maintain the system in a nulled condition. With the output of the system adjusted to a null condition the value indicated is proportional to the basal impedance of the subject. The automatic gain control unit includes a lock function generator to hold the variable gain at an instantaneous null establishing a basal value for a desired measurement episode. Consequently, any variations in the nulled signal are indicative of variations in the impedance of the subject. A range indicator is associated with the gain control unit to verify that the subject output signal is within the dynamic range of the gain control unit.</p> |
