| 摘要 |
The presence of a serviceable electrochemical gas sensor (1) in gas detecting apparatus is determined on the basis of the noise in the output of a sensor amplifier. A microcomputer (22) calculates mean, rms or variance values for the noise in the output of the amplifier (20) for successive periods. Each of these values is compared with the threshold and if it falls below the threshold, counter is incremented. When the counter reaches a target value, it is determined fault condition as arisen and an alarm (23) is operated. <IMAGE> |
