Explanation of basic knowledge of turbine flowmete

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Introduction to basic knowledge of turbine flowmeter

turbine flowmeter is composed of turbine, bearing, preamplifier and display instrument

the measured fluid impacts the turbine blades to make the turbine rotate, and the speed of the turbine changes with the change of flow, that is, the flow is large, and the speed of the turbine is also large. Then the speed of the turbine is converted into electrical pulses of corresponding frequency by the magnetoelectric conversion device, amplified by the preamplifier, and sent to the display instrument for counting and display. According to the number of pulses and cumulative pulses in unit time, the instantaneous flow and cumulative flow can be calculated

the working principle of turbine transmitter is that when the fluid flows along the axis of the pipe and impacts the turbine blade, a force proportional to the product of flow QV, flow velocity V and fluid density acts on the blade to drive the turbine to rotate. While the turbine rotates, the blades periodically cut the magnetic lines of force generated by the electromagnet, changing the magnetic flux of the coil. According to the principle of electromagnetic induction, a pulsating potential signal will be induced in the circle, and the frequency of this pulsating signal is directly proportional to the flow of the measured fluid, that is:

where QV is the total volume of the fluid, and N is the total number of pulsations generated by the transmitter; Is the flow coefficient

is an important characteristic parameter of turbine transmitter, which varies with different instruments and changes with the wear of instruments used for a long time; It means 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 front amplifier and sent to the display instrument to realize the flow measurement

2 type selection of turbine flowmeter

(1) the flowmeter body should preferably be made of 316 stainless steel to prevent corrosion. If it is an explosion-proof area, it must also be an explosion-proof result

(2) bearings generally have three specifications: tungsten carbide, polytetrafluoroethylene and carbon graphite: tungsten carbide has the highest accuracy, and it is used as a standard part of industrial control; Polytetrafluoroethylene and carbon graphite can prevent corrosion, which is generally preferred in chemical sites. The service life of the bearing is positively 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. The voltage output value of its electromagnetic coil is close to the sinusoidal curve. The frequency range of the pulse signal changes linearly with the measured flow. The typical range is 10:1, 25:1 and 100:1. The resistance of the solenoid coil is generally less than 2000, which may be damaged

3 installation of turbine flowmeter

(1) the power line of the transmitter adopts metal shielded wire, and the grounding should be good and reliable. The power supply is 24V DC with 650 impedance

(2) the transmitter should be installed horizontally, avoiding vertical installation, and ensuring that there are suitable straight pipe sections in front of and behind it, generally the first 10d and the last 5D

(3) ensure that the flow direction of the fluid is consistent with the arrow direction of the instrument housing, and do not install it upside down

(4) the measured medium shall not corrode the turbine, especially at the bearing, otherwise measures shall be taken

(5) pay attention not to collide with the magnetic induction part

4 configuration and calibration of turbine flowmeter

the standard calibration method is the ten point water calibration method, but the calibration value is different with different viscosity, so the viscosity calibration curve is usually done

5 display instrument of turbine flowmeter

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 for the production of the next generation USB type-C connector and total flow, and display it

the amplitude and waveform of the pulse signal output by the front amplifier are irregular. After entering the display instrument, it needs to be shaped into a regular rectangular electric pulse signal with a certain amplitude through the shaping circuit, and then through the frequency/current conversion circuit, the frequency signal is changed into the corresponding current signal (4 ~ 20mA), and then the instantaneous flow value of energy is converted. The total amount is converted and accumulated by these chemical materials, including the additives of medical materials Catalysts produced in the process or production, or materials that are inadvertently polluted, are obtained by the circuit. Some display instruments display locally, and some send them to DCS for display

6 precautions

(1) clean the pipeline before installing the turbine flowmeter. When the measured medium is unclean, add a filter. Otherwise, the turbine and bearing are easy to get stuck and the flow cannot be measured

(2) when disassembling the flowmeter, the magnetic induction part cannot be collided

(3) set the instrument coefficient before operation. Check carefully to ensure that the instrument wiring is correct and well grounded before power transmission

(4) when installing the turbine flowmeter, the front and rear pipe flanges should be horizontal, otherwise the pipe stress has a great impact on the flowmeter

7 development prospects

with the continuous development of science, today's Turbine transmitter has developed into a small-scale small enterprise. It is generally 1800 yuan per cubic meter, a highly integrated module, designed with powerful functional software, and equipped with RS232 standard computer communication interface, which provides convenience for maintenance and overhaul. It can connect and communicate with DCS, which replaces the display instrument, such as Hoffer flowmeter, which is more convenient and practical in the current production process

in a word, turbine flowmeter is a kind of speed flow instrument, which is widely used in chemical production because of its high measurement accuracy, fast reaction speed, wide measurement range, low price, convenient installation and other advantages

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