By narrowing the bandwidth of the signal and amplifying it by a lock-in amplifier, the fluctuating components of the signal can be shown on an oscillograph with lock-in amplifier.

• 锁相放大技术对被测信号进行窄带放大，锁相放大器结合示波器输出了被测信号的周期变化部分，实现了光热法测量中微弱信号的测量。