Electrochemical Sensor

Many toxic gases like carbon monoxide, chlorine, ammonia can be detected by electrochemical sensors. Also these sensors can be used for detection of oxygen gas. There are two or three electrodes in the electrochemical sensor depending on the model.

Carbon monoxide gas enters the membrane and reaches these electrodes. Carbon monoxide gas and electrodes get into chemical reaction and electric current occurs. Electric current and gas concentration are directly proportional to each other. When gas concentration increases, electrical current increases as well. When electrical current reaches the alarm threshold level, sensor sends alarm signal.

Semi-Conductor Sensors

Semi-conductor sensors are generally used in domestic gas detectors. Usage of semi-conductor sensors is not recommended because these sensors react to several gases. Also these sensors are unstable in fresh air. Even substances like water vapour may cause alarm signal. For all these reasons, semi-conductor sensor is not preferred very much.

There is a metal oxide surface which is heated between 300°C-400°C inside the sensor. Oxygen gas in the air reacts with metal oxide surface and a certain semi-conductivity is supplied in normal state. If there is a gas leakage, gas molecules will displace oxygen molecules and change the semi-conductivity of metal oxide surface. The correlation of sensor’s output signal and gas concentration is logarithmic.