High-precision And Multi-loop PID Digital Temperature Control System Of TDLAS

The output wavelength of Distributed Feed Back laser in TDLAS technology is susceptible to temperature, for what we must control the temperature stability of laser and associated circuitry in the environment of city vehicle gas leak detection. The study is to find an anti-interference ability, high stability and accuracy of the laser temperature control programs to achieve precise laser frequency of the laser output.This work investigates the wavelength modulation and harmonic detection technology. By changing the temperature of the laser to change the output laser’s center wavelength and scanning in the vicinity of the center of the gas absorption peak,we can gain the optimum temperature. Take the second harmonic central peak of 95% as the scope of accreditation testing, the calculated temperature stabilized laser range peak to peak is 7m℃, with a standard deviation calculated stability 1m℃.A fully digital PID temperature control system is built. In the interior that is completely non-intrusive and structural integrity, the laser’s temperature stability reaches the criteria of 1m℃. But the temperature is vulnerable to outside influence, which causing the background concentration fluctuations. To improve the ability of the laser to suppress interference and to ensure maximum temperature range, we developed a multi-loop PID temperature feedforward control scheme, using a cascading temperature control that the first level temperature as a feedforward quantity is introduced to the second level temperature. Feedforward multi-loop PID control increases the laser’s temperature interference suppression about 2-2.5 times than the original single-loop PID control.A fuzzy self-tuning PID control program is developed. The range of PID parameters of different TDLAS loop is obtained by testing, and the program is achieved by PTS test systems and MATLAB.The feasibility of fuzzy PID control is verified by testing. Compared to the single-loop PID its ability increases by near 3 times.Therefore, the method effectively improve the temperature of anti-interference ability and achieve high-precision temperature control.