Resistance transmitter concentration of oxygen, such as for example converter based on titanium oxide, can be the basis exhaust gas analyzer. Titanium oxide is a material whose resistance changes depending on the number of oxygen molecules adsorbed on the surface.
The converter is made of platinum wire or thin film resistor, whose surface is covered with titanium oxide. Depending on the oxygen content in the exhaust gas of a layer of titanium oxide changes its resistance and, therefore, the total resistance of the device.
The determination of the other gases used other substances. There are also converters for detecting propane and methane. In resistive transducers, there are two elements: one covered with a substance, and the other - uncovered. It is used as a temperature compensating element when measurements are carried out with the converter included in a bridge circuit.
There are resistive gas analyzers and gas-sensing elements based on work which is their sensitivity to changes in the thermal characteristics of the surrounding gases.
For example, the sensing element based on the change of electrical resistance of metals on temperature. The sensitive element of such transducer (katharometer) is sufficiently long metal wire connected to a source of electrical voltage. The wire is in the flow of analyzed gas. The magnitude of the flowing and the heating wire current is controlled with high precision. When you change the concentration of the surrounding gas occurs the corresponding change of the thermal conductivity of the gas. The result of this change, the heat transfer between the wire and the surrounding gas. Accordingly, changes in the temperature of the wire and its electrical resistance. This leads to a change in the value of electric current which is fixed a measuring device.