Device for the Individual Adjustment of the Intensity of Several Spectral Lamps

The invention relates to a device according to for the individual adjustment of the intensity of several spectral lamps.

Absorption spectrometers, in particular, frequently contain several spectral lamps for the generation of measuring radiation which is suitable for the sample to be investigated in each case. When the lamps are activated individually in sequence, their respective operating parameters can be regulated, in a simple fashion, directly by means of the central power unit, as a function of a measurable variable derived from the measuring ray path. However, if all the lamps are activated simultaneously and combined into a common measuring ray bundle with the aid of reflecting mirrors, several regulators, arranged after the common power unit, are required for individual adjustment of the operating parameters of the individual lamps. Individual control of these regulators as a function of a signal derived from the measuring ray bundle is not possible, since the parts of the radiation belonging to the individual lamps in the common measuring ray bundle cannot be separated. Stabilization of fluctuating emission intensities of individual lamps or, e.g., controlled matching of the radiation composition to various samples is thus not possible.

The invention therefore has the object of specifying a device with which the intensity of several spectral lamps, operated parallel to one another, can be matched, in a simple fashion, to the various requirements as a function of a regulation variable derived from the total measuring ray bundle.

Exemplary embodiments of the invention are represented schematically in the drawing and are described below. In detail,

FIG. 1 shows a device having several control loops connected in parallel, and

FIG. 2 shows a device having an alternately tuneable control loop.

In FIG. 1, radiation from two different hollowcathode lamps 1, 2, e.g. for the elements Se and Hg, are combined into a common ray path 4 with the aid of a beam-splitting mirror 3. A lens 5 collects the radiation and passes it through an optionally engageable spectral filter 6 into an absorption cell 7. A semi-transparent mirror 8, which reflects part of the total radiation towards a photomultiplier 9, is inserted into the ray path in front of the absorption cell 7.

The operating voltage of the hollow-cathode lamp 1 is generated by a power amplifier 10 and modulated, e.g., with a frequency of 2 kHz. In the same manner, the hollow-cathode lamp 2 is supplied by the power amplifier 20, which modulates the emission of the lamp with 9 kHz, for example. By means of the modulation in each case, the components of the radiation in the measuring ray path belonging to both lamps receive an identifier, which is also contained in the electrical signal generated by the photomultiplier 9. Both components of the signal can be separated by frequency filters 11 and 21. Phase-locked loops (PLL) 12 and 22 and automatic gain controls (AGC) 13 and 23 ensure phase-locked control of the power amplifiers 10 and 20 in phase with their modulation frequencies.

In FIG. 2, the elements which correspond to FIG. 1 are provided with the same reference numbers as there. The frequency filter 110, arranged after the photomultiplier 9, is electronically tuneable in this case. It obtains the control signals for this from the circuit arrangement 120, e.g. a microprocessor.

The power amplifier 130 has two outputs having different frequency-modulated supply voltages for the lamps 1 and 2. The gain control signal coming from the regulator 13 is also fed, synchronously with the tuning of the frequency filter 110 by means of the circuit arrangement 120, to the correspondingly modulated output signal of the power amplifier 130. The supply voltage at the other output, or further outputs which may be present, of the power amplifier 130 remains unregulated during this time.

Taking into account the very fast switching times for the tuning of the frequency filter and for the transient oscillation of the gain control loop compared to the general fluctuations of the emission intensities of the lamps, this is acceptable. The advantage is in a further reduction of the expense of the electronic components. Of course, a control signal for the measurement switching circuit (not shown) arranged after the absorption cell 7 can be taken from the circuit arrangement 120. The signal evaluation can be further simplified by the use of digital frequency filters, known per se.