GB1262697A - Improvements in or relating to mass spectrometers - Google Patents

Abstract

1,262,697. Mass spectrometers. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 18 Nov., 1970 [19 Nov., 1969], No. 56648/69. Addition to 1,114,005. Heading H1D. The auxiliary ion beam control means 21, producing an effect compensating for irregularities in the magnetic field of the magnetic analyser 11 caused by eddy currents during scanning, which in the parent Specification is controlled in dependence on the variation of the current in the electromagnet 11C is now controlled by an additional unit 52 in accordance with a time variant function. The auxiliary beam control means 21 shown is an einzel lens (Fig. 2, not shown) but may alternatively be a single plate lens, or two plates arranged one on each side of the beam, or a coil. Alternative locations for the means 21 are between an output slit 9 of the e.s. analyser 7 and the e.m. analyser 11 (Fig. 3, not shown) or between the e.m. analyser 11 and an input slit 13 of the detector 17 (Fig. 4, not shown). In the latter ease, the e.s. analyser may be omitted. The time-variant function is produced by a function generator in the control unit 52, the form of the function being determined by trial and error. If the required focusing effect is constant throughout the scan, the function generator may comprise simply a battery and potentiometer. A connection 54 from control unit 51 triggers unit 52 at the commencement of a scan. Unit 52 preferably includes means to vary its output in accordance with variations in the accelerating voltage employed in the spectrometer.