Design parameters for continuous flow apparatus

The thermal conductivity (TC) detector consists of four filaments embedded in a stainless-steel or brass block which acts as a heat sink. The TC detector is extremely sensitive to temperature changes and should be insulated to prevent temperature excursions during the time in which it takes to complete an adsorption or desorption measurement. Long-term thermal drift is not significant because of the calibration procedure discussed in the next section and therefore, thermostating is not required. 

Splitting the flow serves as a means of diluting the adsorption and desorption concentration peaks in order to continuously adjust the signal height using needle valve N 3. The electronic attenuator shown in Fig. 15.8 adjusts the signal by factors of two for each step. 

Needle valve N4 allows a slow bleed of adsorbate to the out septum and then to a sample cell positioned at the outgassing station. The slow flow of gas through this part of the circuit provides a source of adsorbate for the purpose of signal calibration and as a purge for the outgassing station holding cell S2. 

The septum labelled in is used to inject known quantities of adsorbate into the flow to simulate a desorption signal for the purpose of calibration. 

In order to measure the saturated vapor pressure the system is purged with pure adsorbate. Toggle valves Vg and Vjo are opened to purge gauge G2. With toggle valves Vg and Vg closed, needle valve N3 is adjusted until 

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