Siemens Aktiengesellschaft

Ludwig Kimmig

Michael Ludwig

Peter Krause

Camiel Heffels

Ralf Bitter

Thomas Hörner

Martin Kionke

Karlheinz Schmidt

A lock-in amplifier with an additional phase-sensitive detector is provided. A measurement signal is mixed in a multiplicative fashion with a reference signal, which is phase-shifted by 90 degrees, for a modulation frequency. In order to reliably filter out interference signal portions in a widest possible dynamic range and, at the same time, minimize unavoidable influence on the useful signal portion, a control device is connected downstream of the additional phase-sensitive detector. The control device determines a control variable corresponding to the strength of the interference signal from the measurement signal mixed with the reference signal phase shifted by 90 degrees and uses the control variable to change the integration duration of the integrator proportionally to the control variable, a corresponding cut-off frequency of an equivalent low pass being coordinated automatically.

Lock-in amplifier and method for filtering a measurement signal using such an amplifier

The invention relates to a NDIR-gas analyser comprising an infrared radiation source (), a measuring vessel () containing a gas mixture () having a measuring gas component () that is to be detected, and a detector device () that is arranged behind the measuring vessel that can detect the influence of ageing of the radiation source () and optionally dirt deposits in the optical radiation path without interrupting measuring. According to the invention, at least one optopneumatic detector () is arranged in the beam path of the radiation source (), said detector being filled with any gas () when arranged between the radiation source () and the measuring vessel (). The concentration of measuring gas components is lower in the detector () than in the measuring vessel () if filled with the measuring gas components, and said detector is filled with a gas when arranged between the measuring vessel () and the detector device (), the absorption spectrum of the detector being outside of the spectrum of the measuring gas components () and other transversal gases in the gas mixture (). The measuring signal () of the detector device () is corrected by the detector signal () generated by the detector ().

Non-dispersive infrared gas analyzer

A non-dispersive infrared gas analyzer for determining concentrations of carbon dioxide and/or carbon monoxide, hydrocarbons, and nitrogen oxides has two measuring cells 4, 6 consecutively traversed by a beam, with an optopneumatic detector 22 for carbon dioxide and an optopneumatic detector 23 for carbon monoxide arranged between them. Detectors 7, 8 for hydrocarbons and nitrogen oxides are arranged on the measuring cell 6 located downstream from detectors 22, 23 in the direction of the beam.

Method and device for measuring the concentration of a detector gas in a

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Ettlingen, Germany

Ludwig Kimmig