Several ways of outputting current signal in the pipeline of V-cone flowmeter

Flow measurement is the most common measurement of fluid physical indicators in production and life. There are many principles for flow measurement. There are ultrasonic, electromagnetic, pressure, temperature and other measurement principles. Under normal circumstances, the flowmeter signal comes from flow, pressure, temperature detection. Components, reasonable selection of the installation position of different detection components can reduce the influence of fluid disturbance and noise, and improve the detection effect.

(1) Pressure detection

The most common such flowmeters are orifice flowmeters, annubar flowmeters, venturis, etc. by throttling devices.

The pressure detection of the fluid mostly uses a diffusion silicon pressure sensor or a ceramic pressure sensor. According to the principle of vortex precession, the position of the pressure tap should be selected in the throat of the measuring tube, because the pressure of the throat is the most representative of the pressure at which the nucleus precession zone is generated.

(2) vortex signal detection

The most common ones are rotary vortex flowmeters, turbine flowmeters, etc., and can use thermal, force sensitive, capacitive, ultrasonic, optical, electromagnetic and other detection components to detect local flow velocity changes caused by vortices and pressure pulsation of fluids to achieve vortex Signal Detection.

Reasonable selection of the mounting position of the detecting element has a good effect on obtaining a vortex signal with high intensity and low noise. After testing, the vortex signal detecting component is installed near the intersection of the throat and the expansion section of the measuring tube, and the vortex precession at this position is strong and the noise is small.

The detection method of the double detection component has better measurement effect. In the two measurements of the measuring tube, a pair of vortex signal detecting elements are symmetrically arranged. The two vortex signals have a phase difference of 180 degrees, and the differential detection method can obtain doubled signals, and can effectively eliminate common mode interference, such as pipeline vibration and flow field disturbance, thereby greatly improving the signal to noise ratio. Expand the flow measurement range.

The size of the sensing element should be as small as possible to reduce the disturbance of the sensing element to the flow field. If an insertion type detection element is used, the influence of the depth of the insertion element of the detection element should be considered. The detecting element has a large size and deep insertion, and the throttling effect is increased, and the disturbance to the flow field is also increased, which also affects the stability and frequency of the vortex core precession. Tests have shown that the insertion depth increases and the meter factor K of the flow meter increases, but the linearity of the flow meter deteriorates.

(3) Fluid temperature detection

Most of the fluid temperature detection uses platinum resistance detection components. The stability and reliability of the components are good, the price is not high, the volume is small, and the installation is convenient. In recent years, the thin film platinum resistance detecting element has a small volume and a fast response, and is a good temperature measuring element.

The position of the temperature measurement point should be selected in the outlet section of the measuring tube, where the temperature of the fluid is basically the same as that of the throat, and the temperature measuring element does not interfere with the precession of the vortex core.

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