System Design Of Flow Velocity Measurement Of Gas-solid Two-phase Flow

There are many parameters that need to be measured in the industrial field. Among them, the velocity of gas-solid two-phase flow is a very important parameter. Nowadays, there have been many methods to measure the velocity of gas-solid two-phase flow, such as mechanics method, optics method, acoustics method, thermal method, electromagnetism method, NMR method, correlation method and so on. Every method has its own characteristic. Correlation method’s feature is salient and has been widely used. It belongs to a kind of non-contact method, so this article used this method.Correlation method is based on capacitor sensor. When using excitation voltage to drive the capacitor, it will generate weak signal. This article try to find a method to measure this weak signal. What’s more, this article try the best to design an integral intelligent instrument, including TFT display module,4～20mA output module,485 MODBUS communication module,4～20mA measurement module, digital signal output module, storage module and so on. This article take the cost of the instrument into consideration on basis of fulfilling the measurement function to make the instrument applied in the industrial field.Above all, to fulfill the instrument’s function well, this thesis uses two CPU structure. One CPU is used to sample and handle the data, and another is used to fulfill the whole instrument function. The thesis mainly do the job as below.(1) Fulfill the measurement circuit of capacitor weak signal. The weak signal from capacitor sensor is picked up by differential DC charging/discharging circuit whose cost is very low. Follow the detection circuit is low pass filter circuit, cut DC off circuit, programmable gain amplifier circuit and AD sampling circuit.(2) Fulfill the design of sampling and handling data. The core control chip of the circuit is LPC4330 which is based on the ARM Cortex M4. This chip has two cores. One is ARM Cortex MO and another one is Cortex M4 which is DSP core. The cortex MO core can handle large numbers of 10 task and the DSP core can handle large numbers of digital signal process task. What’s more, the Micro SD memory circuit is used to store he sampled data.(3) Fulfill the integral function of an intelligent instrument. This part uses the processor LPC2478 which is based on ARM7 core. LPC2478 owns TFT controller, so it can fulfill the TFT display function. What’s more, this part has isolated 4-20mA output circuit, MODBUS 485 communication module,4～20mA measurement module, digital signal output module and so on. Note that, LPC2478 communicate with LPC4330 through UART, in this way then can exchange their data.(4) Fulfill the software design and program of the whole system, including the driving software of each module, digital signal process algorithm, correlation algorithm and digital filter algorithm, and so on.Through the repeatedly debugging and experiments, the function above can work normally. The measurement accuracy of gas-solid two-phase flow’s velocity is relatively high. The resolution of capacitor reaches fF class.