Vortex Flowmeter traffic signal is reflected by the frequency of the vortex, so how vortex frequency detection, is the vortex flowmeter developed an important subject.

Judging from the current vortex frequency signal detection theory to the generally have two categories:

detected after a vortex in the vortex in the vicinity of the flow changes in frequency, mainly through thermal components completed,

detected after the vortex in the vortex of the force on the changes in frequency, mainly through the completion of piezoelectric-sensitive components.

Below, we will discuss ways of detecting these two specific examples.

The first detection method to cylindrical vortex of a hotline for example, that the structure shown in Figure 3-9. Cylinder with a guided surface-pressure, with the same cylinder internal cavity. Cavity by the partition divided into two Part of the partition of the central part of a - holes, holes in the detection fluid flow with the platinum resistance wire.

When the vortex in the downstream side of a cylinder, the lift due to the role, making the bottom of the cylinder pressure higher than at the top. Cylinder from top to bottom in the bottom of the fluid under pressure from the poor, from the bottom of cylinder pressure hole lead into the empty plastic, The central part of the wall through small holes, the flow platinum resistance wire, I. pressure from the top hole outflow. If the platinum resistance Sijia heat to a temperature higher than the fluid temperature, when fluid flow platinum resistance wire, it will Taking the heat, change its temperature, or change its resistance value. When a cylinder at the top of a vortex, the fluid pressure from the hole into the lead, guide pressure from the next hole outflow, and again through the platinum resistance wire, a change The resistance value. It can be seen: Value Change and the corresponding changes in flow, and also the relative frequency of the vortex should therefore be detected platinum resistance wire resistance change frequency eddy frequency and then flow by value.

Will be platinum resistance wire resistance converted into electrical signals changes in the value of the circuit as shown in Figure 3-11.

Figure 3-11 vortex flowmeter thermal detection methods circuit diagram

Figure in the A1 will be the bridge Yibi platinum resistance wire the output of differential amplification, the A2 through the power amplifier output current feedback callback bridge, the wire so that platinum resistance temperature higher than a constant temperature of fluid value.

The second detection method to 1.30, in a vortex of example. This shows that the structure shown in Figure 3-10. Column in the triangle on both sides of flexible metal with two films, and they are very tied to the capacitor, with electrodes inside plate. Electrode and metal pull between the film is full of oil, to transfer the pressure.

When this triangle Zhu Below produce a vortex, while higher than the bottom of the pressure on the pressure at the top, will be 1.30 Zhu to the bottom of the metal film, the pressure, and at the top of the pop metal films on the field, changed the two respective electrical capacitors Capacity so that corresponds to the turn of the lift, two capacitors on the power differential capacity to change. Therefore, the capacitance changes and changes in the corresponding lift, and also the relative frequency of the vortex should be, so that could change by the power capacity Frequency vortex frequency and then flow by value.

Electric capacity will be converted into electrical signals changes in the circuit diagram shown in Figure 3-22. Vortex detection sensors from two metal plates composed of membrane electrode and differential changes capacitors and place it on the bridge, electrostatic detection capacity by RF Oscillation circuit have incentives. When a vortex, the capacitance changes, leading to bridge imbalances, the potential imbalance through the RF amplifier to enlarge, and received by the detector after the vortex corresponding to the frequency signal. The signal amplification and The whole formation of rectangular waves, from the current loop as a given,

Pulsed output. Feedback loop to compensate for temperature changes arising from the bridge imbalance.

Compared to the two detection methods, a way of high sensitivity, apply a wide frequency range, the corresponding flow of a wide scope, but it fine structure, vulnerable to the effects of impurities in the fluid. The second method of solid, reliable , In the industrial application of a broader survey. However, due to lift and the square is directly proportional to flow rate, flow rate increased by 10 times, 100 times the lift will change. Therefore, if the requirements can apply to the flow meter the flow of large scope, can guarantee that it is Ling certain enough, this method is to a certain extent the difficulties