First, the working principle

The basic principle of intelligent vortex flowmeter is Carmen vortex principle, that is, "the separation frequency of vortex street is proportional to the flow rate"

The fluid diameter of the flowmeter is basically the same as the nominal diameter of the instrument. As shown in figure 1, insert an approximately isosceles triangle cylinder into the fluid, with the axis of the cylinder perpendicular to the flow direction of the measured medium and the bottom facing the fluid.

When the measured medium flows through the cylinder, vortices are alternately generated on both sides of the cylinder, and the vortices are constantly generated and separated, forming two rows of vortices downstream of the cylinder, that is, "vortex street". Theoretical analysis and experiments prove the frequency of vortex separation.

This rate is proportional to the velocity of the medium on the column side.

F=Sr

Where: f-frequency of vortex separation at cylinder side (Hz)

V-tower side velocity (m/s) d-tower upstream width (m);

Sr—— Strouhal number is a constant that depends on the cross-sectional shape of cylinder and has nothing to do with fluid properties and velocity, and it is 0. 17 ~ 0. 18.

Figure 1 Vortex Street in a Circular Tube

The design column width d of the intelligent vortex flowmeter has a fixed ratio to the diameter d of the flow tube, so the average flow velocity v flowing through the tube has a fixed ratio to the column side flow velocity v:

Because in the above formula, d and d are known structural dimensions, and Sr is constant, the vortex separation frequency f is measured, and the average velocity in the tube is measured, thus the flow q is measured:

Q = 3600F volts (m3/h)

Where: F—— the flow area of flowmeter fluid (m2)

V—— the average flow rate of flowmeter fluid (m/s).

The staggered separation of vortices produces pulsating pressure in the wake on both sides of the cylinder and behind the cylinder. The detection probe arranged inside the cylinder (or behind the cylinder) is affected by this tiny pulsating pressure, which makes the piezoelectric crystal elements buried in the probe subject to alternating stress and generate alternating charge signals. After transforming, amplifying, filtering and shaping the alternating charge signal, the detection amplifier outputs a current (or voltage) pulse signal with the same frequency as the eddy current separation frequency. Each pulse output by the flowmeter will represent a certain volume of measured fluid. The total number of pulses output in a period of time will represent the total volume of fluid flowing through the flowmeter during this period.

Working principle of turbine flowmeter

Fluid flows through the sensor housing. Because the blades of the impeller have a certain angle with the flow direction, the impulse of the fluid makes the blades produce rotating torque. After overcoming the friction torque and fluid resistance, the blade rotates and the speed is stable after torque balance. Under certain conditions, the speed is proportional to the flow. Because the blade has magnetic conductivity and is in the magnetic field of the signal detector (composed of permanent magnet steel and coil), the rotating blade cuts the magnetic field lines and periodically changes the magnetic flux of the coil, thus inducing electricity at both ends of the coil.

The pulse signal is amplified and shaped by an amplifier to form a continuous rectangular pulse wave with a certain amplitude, which can be transmitted to a remote display instrument to display the instantaneous flow and accumulation of fluid. In a certain flow range, the pulse frequency f is directly proportional to the instantaneous flow q of the fluid flowing through the sensor, and the flow equation is:

Among them:

F- pulse frequency [Hz];

K—— Instrument coefficient of sensor [1/m3], which is given by the checklist. If the unit is [1/L]

Q—— instantaneous flow rate of fluid (under working conditions) [m3/h];

3600- conversion factor.

The instrument coefficient of each sensor is filled in the verification certificate by the manufacturer, and the K value is set in the supporting display instrument, so that the instantaneous flow and cumulative total can be displayed.