1 System structure of infrared analyzer
The system structure block diagram of the infrared analyzer is shown in Figure 1. TMS320F2812DSP sends a certain frequency modulation signal to control the infrared light source. The infrared light emitted by the infrared light source passes through the gas chamber filled with the gas to be measured and is absorbed by the specific gas. It is selectively transmitted by the filter and reaches the corresponding infrared detector. The detector measures the intensity of the absorbed light energy. Reflects the strength of the gas’s absorption of infrared light, which also reflects the concentration of the gas. The weak signal output by the infrared detector passes through a precise pre-amplification and two-stage amplifying filter circuit to obtain a stable signal. The signal is converted by A/D and sent to the DSP for analysis and processing. After filtering and nonlinear correction, the final The measured data will be transmitted, saved, or displayed refreshed according to the system settings and current instrument status. Note that there are at least 2 measurement channels of the detector here. Among them, 1 is the measurement channel and 1 is the reference channel. This can achieve the effect of differential measurement and form the suppression of system noise and interference. The other sensors and The A/D channel is used to measure temperature, humidity and gas pressure, and participate in the calculation of concentration compensation.
2 System hardware design
In the hardware design of the instrument, the choice of infrared light source, detector, DSP system and peripheral circuit, signal amplification circuit is the key. The infrared light source of this instrument selects IRL715 infrared light source, the wavelength range of this light source is from visible light wavelength to 5μm, and the working life can reach 40 000 h under the driving of 5 V voltage. The detector chooses TPS2534G2 with two measurement channels. The DSP adopts the TMS320F2812 digital signal processor of American TI Company, which provides a 32-bit fixed-point DSP with a computing bandwidth of up to 150 MIPS, which greatly improves the control accuracy and data processing capacity of the control system. Its peripheral circuits mainly include: data acquisition, Switch output, man-machine interface. Storage system and USB communication interface. The signal amplifier circuit uses two AD8552 operational amplifier circuits in series. The AD855X series has the function of automatic offset adjustment, which is the best choice for low-frequency weak signal detection amplifier systems. Because this instrument focuses on the application of high-speed DSP system in infrared analysis instrument, the following is a special description of the DSP peripheral circuit.
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