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A brief analysis of the turbine flowmeter (requires the top comment) 1 The working principle of the turbine transmitter The turbine flowmeter consists of a turbine, a bearing, a preamplifier, and a display instrument, as shown in Figure 1: The measured fluid impacts the turbine blades, causing the turbine to rotate. The rotational speed of the turbine changes with the change of flow rate. That is, the greater the flow rate, the greater the rotational speed of the turbine. The rotational speed of the turbine is then converted into electrical pulses of the corresponding frequency through the magnetoelectric conversion device. After being amplified by the preamplifier, it is sent to the display instrument for counting and display. The instantaneous flow rate and cumulative flow rate can be calculated based on the number of pulses per unit time and the number of accumulated pulses. The working principle of the turbine transmitter is that when the fluid flows along the axis of the pipe and impacts the turbine blades, a force proportional to the product of flow rate qv, flow velocity V and fluid density ρ acts on the blades, pushing the turbine to rotate. As the turbine rotates, the blades periodically cut the lines of magnetic force generated by the electromagnet, changing the magnetic flux in the coil. According to the principle of electromagnetic induction, a pulsating potential signal will be induced in the coil, and the frequency of this pulsating signal is proportional to the flow rate of the fluid being measured, that is,: Among them, qv is the total volume of fluid, and N is the total number of pulsations generated by the transmitter. ； ξ is the flow coefficient. ξ is an important characteristic parameter of the turbine transmitter. Different instruments have different ξ, and it changes with the wear and tear of the instrument over a long period of time. ； Its meaning is the number of pulses output by the transmitter when the unit volume flow passes through the transmitter. The pulse signal output by the turbine transmitter is amplified by the pre-amplifier and sent to the display instrument, so that the flow rate can be measured. 2 Selection of turbine flowmeter (1) The flowmeter body is best made of 316 stainless steel to prevent corrosion. If it is an explosion-proof area, it must also be explosion-proof. (2) Bearings generally have three specifications: tungsten carbide, polytetrafluoroethylene, and carbon graphite.: Tungsten carbide has the highest precision and is used as a standard part for industrial control ； Polytetrafluoroethylene and carbon graphite can prevent corrosion and are generally given priority in chemical industry sites. The life of the bearing is directly and inversely proportional to the square of the flow rate, so the best flow rate is 1/3 of the maximum flow rate. (3) The induction probe detects the movement of the rotating body and converts it into a pulse digital electrical signal. Its electromagnetic coil voltage output value is close to a sinusoidal curve. The frequency range of the pulse signal changes linearly with the measured flow rate. The typical ranges are 10:1, 25:1 and 100:1. The resistance of the electromagnetic coil is generally less than 2000Ω. If it is greater than this value, it may be damaged. 3 Installation of turbine flowmeter (1) The power cord of the transmitter should be a metal shielded wire, and the grounding should be good and reliable. The power supply is DC 24V, 650Ω impedance. (2) The transmitter should be installed horizontally, avoid vertical installation, and ensure that there are suitable straight pipe sections in front and behind it, generally 10D in front and 5D in back. (3) Ensure that the flow direction of the fluid is consistent with the direction of the arrow on the instrument housing, and do not install it backwards. (4) The measured medium must not corrode the turbine, especially the bearings, otherwise measures should be taken. (5) Be careful not to collide with the magnetic induction part. 4 The configuration and calibration standard of the turbine flowmeter is the ten-point water calibration method, but the calibration values are different for different viscosities, so a viscosity calibration curve is usually required. 5 Turbine flowmeter display instrument The task of the display instrument is to convert the number of output pulses per unit time and the total number of output pulses into instantaneous flow and total flow, and display them. The pulse signal output by the preamplifier has irregular amplitude and waveform. After entering the display instrument, it first needs to be shaped by the shaping circuit into a regular rectangular electrical pulse signal with a certain amplitude. Then it passes through the frequency/current conversion circuit to change the frequency signal into the corresponding current signal (4~20mA) and then converts it into an instantaneous flow value. The total amount is obtained by the conversion and accumulation circuit. Some display instruments display locally, and some send DCS display. 6 Notes (1) Before installing the turbine flowmeter, the pipeline must be cleaned. When the measured medium is not clean, a filter must be added. Otherwise, the turbine and bearings are easily stuck and the flow rate cannot be measured. (2) When disassembling and assembling the flow meter, do not collide with the magnetic induction part. (3) Set the instrument coefficient before putting it into operation. Check carefully to make sure that the instrument wiring is correct and the grounding is good before power can be supplied. (4) When installing a turbine flowmeter, the front and rear pipe flanges must be level, otherwise the pipe stress will have a great impact on the flowmeter. 7 Development Prospects With the continuous development of science, today's turbine transmitters have developed into miniaturized, highly integrated modules, designed with powerful functional software and equipped with RS232 standard computer communication interface, which facilitates maintenance and repair. It can be connected and communicated with DCS. DCS replaces display instruments, such as HOFFER flowmeter, which is more convenient and practical in industrial production processes. In short, the turbine flowmeter is a velocity flow meter that is widely used in chemical production due to its advantages of high measurement accuracy, fast response speed, wide measurement range, low price, and easy installation.