在波长调制法的光谱吸收型气体传感器设计中,通常采用二次谐波检测技术。然而含有气体体积分数信息的被测信号和二倍频参考信号的相位差变化严重影响了二次谐波信号测量结果。采用双光路相位保持设计来解决这一问题,设计包括移相电路和双光路两部分,移相电路由数字电路组成,调整方便,用来消除电路本身固有延时; 光路部分通过增加一路不经气室吸收的参考光路,同检测光路组成双光路,保证无论光纤长度如何变化,被测信号和参考信号相位始终相同。在波长调制的基础上引入双光路相位保持设计后,随被测信号相位0～90°变化,测量结果误差值低于±10%。这种设计提高了系统检测结果的稳定性,实现了恶劣环境中,任意距离任何位置的气体体积分数检测。

The second harmonic is used when using wavelength modulation technology to design gas sensor based on optical spectrum. Whereas phase difference between gas sensing signal and double frequency reference signal has great influence on the measured result of second harmonic. A reference optic fiber is used to synchronize the phases. There are two parts in this technology: phase shift circuit and reference optic fiber. Phase shift circuit consists of digital circuit which is used to compensate circuit delay and is easy to modulate. Reference optic fiber which does not pass by gas cell is added in the optical path. It makes sure that the phases between measured signals and referenced signals are synchronized no matter how the length of the optic fibers changes. In the design of phase synchronization using double optical path based on wavelength modulation,the error of meausred result keeps lower than ±10% with phase of measured signals changing from 0° to 90°. It not only simplifies the calibration of the sensor, but also makes possible to install the sensor at any distance site.