The design and analysis of an improved high air flow meter with analog/digital filters

High-air-flow meters in the range of 0.0 SLM (standard liters per minute) to 200.0 SLM, which use a built-in microbridge sensor in flow housing, induce a significant amount of turbulence noise in the output signal. The sensor output signal is analyzed, and an analog/digital design is introduced to reduce the noise and to realize the industrial standard output range of 1.00 VDC to 5.00 VDC. Tests were performed with an A/D data acquisition system and Fourier analyzer for flow data analysis. The flow data file was used for offline time- and frequency-domain analysis and digital filter design simulation. The magnitude, mean, and autocorrelation of the noise induced on the output signal were calculated and measured. An analog Butterworth filter implemented on this high-flow meter in real time showed increased SNR, overshoot of 10%, and the response time of 400 ms. The digital forward linear predictor was implemented with TMS320C25 digital signal processor (DSP). Noise was reduced, overshoot was zero, and the response time was 195 ms.< >