Thermal conductivity detector circuit and method for operating the same
A thermal conductivity detector includes a switch controllable to short-circuit the input of an amplifier to improve the thermal conductivity detector for use in gas chromatography without the need of an additional reference cell, wherein a digital signal processor calculates a transfer function of an analog signal processor from a digitized difference signal received in response to short-circuiting the input of the amplifier at a given time when solely a reference carrier fluid passes through a measuring cell, and the digital signal processor recovers a detector signal by deconvoluting the digitized difference signal with a transfer function.
1. A thermal conductivity detector comprising:
a measuring cell containing at least one thermal conductivity detector element and providing a detector signal and being passed through by a sample fluid in a reference carrier fluid stream;
an analog signal processor including an amplifier for amplifying the detector signal, a low-pass filter for providing a running average of the amplified detector signal, and a subtractor for generating a difference signal from the amplified detector signal and the running average;
a digital signal processor for digitizing and digitally processing the difference signal, said digital signal processor deconvoluting the digitized difference signal with a transfer function to recover the amplified detector signal in digitized form; and
a switch controllable to short-circuit an input of the amplifier;
wherein the digital signal processor is configured to calculate the transfer function of the analog signal processor from the digitized difference signal received in response to short-circuiting the input of the amplifier at a given time when solely the reference carrier fluid passes the measuring cell such that the thermal conductivity detector is operated in a substantially continuous manner to increase an operating speed of a gas chromatograph.
2. A gas chromatograph comprising at least one thermal conductivity detector of claim 1 .
3. A method for operating a thermal conductivity detector comprising:
passing a sample fluid in a reference carrier fluid stream through a measuring cell and generating a detector signal via a thermal conductivity detector;
processing the detector signal in an analog signal processor including amplifying the detector signal, providing a running average of the amplified detector signal by low-pass filtering, and generating a difference signal from the amplified detector signal and the running average; and
digitizing and digitally processing the difference signal comprising deconvoluting the digitized difference signal with a transfer function to recover the detector signal in digitized form;
the method further comprising, as an initial step, short-circuiting an input of the amplifier at a given time when solely the reference carrier fluid passes the measuring cell and calculating the transfer function of the analog signal processor from the digitized difference signal received in response to short-circuiting the input of the amplifier such that the thermal conductivity detector is operated in a substantially continuous manner to increase an operating speed of a gas chromatograph.