Electrochemical Measurement Principle (EC)
The basic principle of an electrochemical sensor is to have two electrodes at a minimum (sensing and counter electrode) which are in contact with each other in two ways: on the one hand via an electrically conductive medium (electrolyte, i.e. liquid as an ion conductor), on the other hand via an external electric circuit (electron conductor). The electrodes are made of a special material and have a catalytic effect so that certain chemical reactions take place at the so called 3-phase boundary where gas, catalyst and electrolyte are present. Actually a two-electrode sensor (sensing and counter electrode), has many disadvantages. If there are higher gas concentrations, it leads to higher currents in the sensor and to a voltage drop which changes the preset voltage of the sensor. This can lead to unusable measurement signals or, in the worst case, the chemical reaction inside of the sensor stops during the measurement. Therefore, a third electrode is added to the sensor which is used as a reference, situated away from the current flow. The potential of the electrode is constant. With the reference electrode the sensor voltage is continuously measured at the measuring electrode and can be corrected by the control gain of the sensor. This leads to an enhanced measurement quality (e.g., in terms of linearity and selectivity) and a longer lifetime. Electrochemical sensors are usually sufficient and adequate to perform measurements by heating applications. ecom analysers do determine the concentration of the following gas components with electrochemical sensors: oxygen (O2) – out of which the CO2 content is determined, carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), sulphur dioxide (SO2), hydrogen (H2) as well as hydrogen sulphide (H2S). Due to their very high solubility in water, the measurement of hydrogen chloride (HCl) as well as ammonia (NH3) with electrochemical sensors is pretty reduced.