Design of digital lock-in amplifier for low concentration gas detection

In a measurement system, it is sometimes necessary to extract very small sensor signals from noise. This study performs a digital lock-in amplifier implemented on an ARM Microcontroller for detecting low concentration gas. This lock-in system has the ability to increase the sensitivity or signal to noise ratio. In the experiment, the lock-in system with the varies gain and cutoff frequency. The sensitivity and the signal to noise ratio can be considerably improved by means of the proposed system. The results showed that the signal to noise ratio of the original signal and the lock-in system with the unity gain were −4.73 dB and 4.08 dB, respectively. The higher gain implemented on the lock-in system would produce the higher signal to noise ratio. The lock-in system has also been tested for detecting of carbon monoxide gas resulting a signal to noise ratio of the gas sensor and the lock-in system are 3.9 and 15.6 dB, respectively.