Abstract: In order to improve the performance of thermal conductivity detector (TCD) for gas chromatography, a precision constant current source circuit and a difference voltage detection circuit were designed. The constant current source was designed with a field effect tube IRF460, operational amplifiers AD8672 and a linear optical coupler HCNR201. The difference voltage detecting circuit was designed with two pieces of AD8597. The noise model of the difference voltage detecting circuit was established and the theoretical value of minimum noise was calculated. The experimental results showed that the baseline noise of TCD came up to 4 μV, that the baseline drift of TCD came up to 15 μV in 50 min, that the fluctuation of constant current source was about 1 μA, which were superior to current technical specification of existing TCD. The introduced design scheme and noise analysis method have reference value for new TCD design.

Key words: constant current source, design, thermal conductivity detector (TCD), weak signal detection, gas chromatograph (GC)