Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1980-06-04
1981-10-27
Willis, Davis L.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
250345, 356434, 356436, G01N 2126
Patent
active
042975794
ABSTRACT:
In a bi-frequency infrared spectrometer having a filter wheel rotating in the path of rays, which filter wheel carries two semicircular filters transparent in different spectral ranges, the influence of the radiation from the filters themselves is eliminated in that the filter wheel has an opaque backplate on the side facing the light source, said backplate having one aperture in the area of each filter, which aperture passes through the path of rays. In this way the detector "sees", at first, only the filter with the radiation emanating from the filter itself, and is subsequently exposed to the measuring beam emanating from the light source and passing through the sample cell, when the aperture is being moved through the path of rays. A clamp circuit keeps the output signal zero until shortly before the aperture passes through the measuring beam. The detector signal is integrated by an integrator during a measuring time interval and a reference time interval. In order to eliminate the infuences of inertia and memory effects of the integrator, the detector signal is integrated with reversed sign during a certain time interval before each reference time interval and each measuring time interval. The logarithms of the output signals of the integrator are formed and are transferred to a memory after each reference time interval and each measuring time interval. The integrator is then reset to zero. The difference of the stored signals should then be a measure of the concentration of an element sought, the absorption band of which coincides with the transmission range of one of the filters. In order to get a linear relation between the output signal obtained and the concentration, even if there are deviations from Beer's Law or the measurement is affected by the radiation from instrument parts themselves or the different transmissivities of the filters, adjustable corrective voltages are applied to the integrator, and the signal is applied to the integrator through different resistances during the measuring time interval and during the reference time interval. A filter having a transfer function inverse to the transfer function of the detector is connected to receive the output of the detector.
REFERENCES:
patent: 4205913 (1980-06-01), Ehrfeld et al.
Bodenseewerk Geosystem GmbH
Willis Davis L.
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