| 摘要 |
PCT No. PCT/EP89/00355 Sec. 371 Date Feb. 10, 1994 Sec. 102(e) Date Feb. 10, 1994 PCT Filed Apr. 3, 1989 PCT Pub. No. WO89/10025 PCT Pub. Date Oct. 19, 1989An Atomic Absorption Spectrometer in which background absorption is compensated by means of a magnetic field causing a periodic line shift due to the Zeeman Effect, including a line emitting light source, an atomizing device, an optical system, by means of which the measuring light beam can be passed through an atom cloud of the atomizing device, an electromagnet, a converter circuit for converting the mains a.c. voltage into d.c. voltage applied to a capacitor, the winding of the electromagnet being located in the diagonal of a bridge circuit which is supplied with the d.c. voltage of the circuit and comprises a diode in diametrically opposite branches and a first and second controlled switch in the other two branches, the first one of the controlled switches being periodically maintained conductive by controls at the frequency of energizing and de-energizing the electromagnet, during an active time period encompassing the build-up and maintenance of the magnetic field, the first controlled switch being non-conductive during the remaining time, the second one of the controlled switches being controlled by means of a two-step current controller for regulating a predetermined current flowing through the winding of the electromagnet during the active time period of the first controlled switch, the second controlled switch likewise being non-conductive during the remaining time so that there results an essentially trapezoidal current waveform, and the winding of the electromagnet being connected in series with the diodes to the capacitor of the converter circuit in the non-conductive state of both of the controlled switches. |
