| 摘要 |
<p>The two-wire or life-zero measuring system comprises measuring means (23) fed with direct current from a rectifier (12, 13, 14) connected to the secondary winding (9) of a high-frequency transformer of which the primary winding (8) is energized with direct-current pulses at a high frequency. The current flow in the primary winding depends on the load formed by the measuring means on the secondary winding. This current is measured and is in a linear relation to the current flow in the measuring means. Voltage peaks in the primary circuit, in the secondary circuit and in the current-measuring circuit and cut off by means of Zener diodes (4,24,33). This measuring system is simple due to the two-wire measuring circuit and has an intrinsic safety partially due to the galvanic separation of the measuring circuit from the power circuit and the Zener diodes avoiding excess voltages in all circuits. The system is able to measure static and dynamic phenomena with passive measuring elements such as strain gauges or with active elements such as piezoelectric crystals controlling a current source in the secondary circuit.</p> |
