Design and measurement analysis of mine sewage flow meter circuit

Abstract: The design, measurement and analysis information of mine sewage flow meter circuit is provided by excellent flow meter and flow meter manufacturers and quotation manufacturers. 0 Introduction In recent years, sewage flowmeters have been rapidly applied in the industrial field, especially in the measurement of river water transportation and sewage discharge flow. mine. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the design and measurement analysis article details of the mine sewage flowmeter meter circuit. 0 Introduction In recent years, sewage flowmeters have been rapidly applied in the industrial field, especially in the measurement of river water transportation and sewage discharge flow. Slurry flow and other media. However, due to the special requirements of coal mine safety, there are few sewage flow meters that can be used in coal mines. Aiming at these problems, a sewage flow meter circuit suitable for mine flow measurement is developed. It is controlled by a new type of single-chip microcomputer, coupled with a special intrinsically safe excitation circuit, and has various functions such as real-time detection and timely display. After trial by many companies, its performance and technical indicators have basically reached the advanced level of similar products at home and abroad. 1 Design scheme 1.1 Design idea At present, the safety types of mine explosion-proof electrical products in my country are mainly explosion-proof and intrinsically safe. The intrinsic safety design is to strictly control the spark energy generated by each part of the circuit, so a special intrinsically safe excitation circuit is used in the design to prevent the excitation current from causing sparks; a new low-power single-chip microcomputer is used to control the work of the entire device to ensure Its stability and reliability; a variety of electromagnetic shielding measures are used to prevent static electricity and electromagnetic interference to ensure the stable operation of the circuit. 1.2 The hardware part of the system circuit (1) The block diagram The device adopts a high-speed single-chip module circuit (STM32F407), which has strong floating-point operation capability, ultra-low power consumption, and the power consumption is only 38.6mA. It is used to control the entire sewage flowmeter, including generating excitation pulse square wave signal, receiving the voltage signal reflecting the flow rate from the probe, and outputting 4~20 mA current signal for the analog display instrument. The CPU module has various interface circuits RS232, High-speed USB interface, etc.), operating keyboard and display interface circuit, etc. The block diagram is shown in Figure 1. (2) In order to ensure the measurement accuracy of the sensor, the probe of the sensor is required to be streamlined. When the probe is inserted, the impact on the fluid is small, and it is approximately considered to be an unobstructed flow state. Specifically, a 25.4 mm stainless steel tube is used as the probe shell, and the excitation coil core is made of soft magnetic steel. The excitation coil is connected. In order to avoid the interference caused by the inductive emission signal in the probe, shield the signal emission lead, the coil and the electrode connection. (3) Special circuit design ①Excitation signal and drive circuit In order to ensure that the probe works in an unblocked state, the size of the probe should be as small as possible, so that the generated excitation current is also small, and the subsequent receiving circuit is required to have a high enough input impedance. To ensure the sensitivity and anti-interference of the sensor; in order to prevent the AC 50 Hz power frequency interference, the square wave current is selected as the excitation current, and its frequency can be selected as 1/4 of the power frequency frequency of 12.5 Hz, which can effectively suppress the power frequency interference. The excitation signal is internally generated by the single-chip microcomputer, and the 12.5 Hz square wave signal is output from the 26th pin, which is connected to the 3-pin signal of IC5 (LMD18200T), which is the driving module circuit of the excitation coil. On the excitation coil between its 2 feet and 10 feet. A square wave current of 20~30 mA positive and negative symmetry is formed on the excitation coil L, which is synchronized with the control square wave voltage. The square wave voltage generated by the fluid motion cutting the magnetic field line is completely synchronized with the excitation current, that is, it is synchronized with the square wave voltage of the control switch network, which is convenient for the synchronous demodulation of the signal in the receiving circuit. The circuit is shown in Figure 2. ② The excitation current in the intrinsically safe excitation coil circuit sensor is a dangerous source of electric sparks. The sewage flowmeter should be used in the mine to ensure that the excitation circuit meets the intrinsic safety requirements. When the current flows through the excitation coil, a magnetic field will be generated inside the coil, and the magnetic field will store energy. When the circuit is disconnected, the energy stored in the coil will be released in the form of sparks. Therefore, the stored energy in the coil must be released in order to meet the requirements of intrinsic safety. A bidirectional diode (TVS tube P6KE6.8CA) is used in parallel at both ends of the coil as the freewheeling branch to discharge the magnetic energy stored in the coil, reduce the spark when on and off, and absorb current.release energy. for the purpose of intrinsic safety. ③The sensor amplifier circuit is shown in Figure 3. The IC2 (SL28617) preamplifier is used to amplify the voltage signal sent by the sensor that reflects the flow rate, and the gain of the operational amplifier can be changed by changing the resistance values ​​of Rin and Rfb in the figure.

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