Ambient sensors thermistors

A compact sensor of greatly reduced dimensions (outer diameter x length 36 x 46 mm) has been constructed and is shown in Fig. 2. In order to conveniently accommodate enzyme columns and to ensure isolation from ambient temperature fluctuations, a cylindrical copper heat sink was included. An outer Delrin jacket further improved the insulation. The enzyme column (inner diameter x length 3x4 mm), constructed of Delrin, was held tightly against the inner terminals of the copper core. Short pieces of well-insulated gold capillaries (outer diameter/inner diameter 0.3/0.2 mm) were placed next to the enzyme column as temperature-sensitive elements. Microbead thermistors were mounted on the capillaries with a heat-conducting epoxy. Two types of mini system has been constructed as discussed below. 

Thermoelectric-, pyroelectric-, and thermoconductivity-based devices are other representatives of thermometric gas sensors (Korotcenkov 2011). In particular the thermal conductivity technique for detecting gas is suitable for the measurement of high (vol. %) concentrations of binary gas mixes. The heated sensing element is exposed to the sample and the reference element is enclosed in a sealed compartment (see Fig. 1.14). If the thermal conductivity of the sample gas is higher than that of the reference, then the temperature of the sensing element decreases. The higher their thermal conductivity, the lower the concentration which can be measured (Table 1.14). Power loss of a single filament thermistor by heat conduction via the ambient gas can be expressed as... 

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