| 摘要 |
PURPOSE:To automatize the protection of a detector and to prolong its life, by providing a voltage restriction device on the output side of an operational amplifier and restricting the output voltage and also, carrying out feedback of restricted output voltage. CONSTITUTION:In case of measuring the concentration of oxygen, an output of an operational amplifier 11 is supplied to a voltage limiting device 12 as it is when the concentration is in a range of normal measurement. The output voltage of the amplifier 11 is proportional to the output electric current and current-voltage conversion having a good linearity is carried out. Next, when the concentration is increased abnormally, an output current of an electrode 10 is increased in porportion to its concentration and the output voltage of the amplifier 11 is increased. And, the output voltage of the device 12 is restrained in some fixed value and also, feedback quantity to the amplifier 11 is restricted. Accordingly, input impedance of the circuit observed from the electrode 10 is increased and the output current of the electrode 10 is restricted and then, the electrode is protected. |
