is now widely used in all kinds of flow measurement field, especially the big diameter pipeline measurement can reflect the more superior performance measurement.
Due to the flow measurement accuracy of ultrasonic flowmeter is largely depends on the system of ultrasonic signal correctly identify.
Circuit coupled noise more than limit, it is likely to damage of signal waveform, leads to deviation and error of measurement data, serious and even cause the entire instrument can work normally.
So in the design of effective noise reduction and noise pickup is must focus on key points.
This article is aimed at in the design of ultrasonic flowmeter is improved, such as the signal filtering, shielding, adopt balance circuit and so on, in order to improve the ultrasonic flowmeter's ability to adapt to the environment.
Through a series of methods and measures for the big, improve ultrasonic flowmeter ability to adapt to the environment.
An overview, ultrasonic flowmeter, ultrasonic flowmeter is by measuring the fluid flow on ultrasound beam (
Or ultrasonic pulse)
To measure the effect of flow meter
, purpose is to solve some difficult problems measurement.
Ultrasonic flowmeter, set at a suit, computer and sensor technology of acoustic research results combined with modern electronic technology, can be used for a variety of liquid measurement.
Second, the source of the noise analysis in the ultrasonic flowmeter measurement system, a noise source material type a lot.
Flowmeter installation environment of the larger electric field and magnetic field interference;
Near the water pump installation of pumps to bring close to the ultrasonic signal noise;
Operators carry communication system;
The higher harmonic in power;
High frequency noise brought by the crystal oscillator circuit boards.
For from the outside noise interference sources, mainly adopts circuit sensitivity to noise, reduce noise pickup, cut off noise coupling path solution, for from within the system, such as the circuit noise sources, on the signal, the digital separation is taken, multipoint earthing, reasonable wiring methods to solve.
The noise of the typical path diagram as shown in figure 1.
As you can see, the generation of a noise problem must have three elements, *, first must have a noise source;
Secondly, there must be sensitive to noise receiver;
Third, there must be a source of the noise from sent to the receiver of the coupling path.
Thus to solve the noise problem must be addressed from the three aspects.
Three 3, ultrasonic flowmeter improvement measures.
1 filter for ultrasonic signal frequency is roughly 1 MHZ, composed of op-amp and capacitor devices such as the bandwidth of the active filter is small, big in a few hundred thousand Hertz, in near the frequency is not easy to use, and if the special integrated filter circuit and cost on the high side, so here USES a simple composed of LC filter inductance and capacitance.
As shown in figure 2, which is made up of L and C parallel resonance, the resonance frequency is in 1.
5 MHZ, consist of L1, C1 and L2, C2 series resonance, the formation of T network, realizes the bandpass filter.
In addition to design filter circuit in signal processing, for all the wires in and out of the shielding box are implementing measures for filtering.
Where the wire through the shield, USES the feed electricity capacity, and in the land of the wires and circuit connection and a short pin of mica capacitor.
2 block in for aluminium material is adopted in the design of housing, in its internal form a protective layer of electric field and magnetic field of the instrument.
As is known to all, the ideal shield should be a closed and continuous conductive shell, no open holes and seams.
In practical use, however, because of the need to wiring, it is difficult to achieve real shielding.
By blocking the discontinuity of analyzing the influence of magnetic field induced current, there is no using rectangular aperture walk the line, and adopt the strategy of the open holes on the surface of the shielding box of multiple, and make the in and out of the shield conductor shielding layer is 360 & deg;
Connection to the shielding box.
The advantage is directly improve the system for the electric and magnetic fields to endure, to enhance the performance.
3 the balancing circuit is used to produce the same and opposite signal circuit, the signal into two wires;
Circuit, the better, the balance characteristic of signal of scattering the smaller;
It's also the better noise suppression characteristics.
Offset the ability of interference signal, balance circuit is based on strict signal waveform and the amplitude is symmetrical, in strict accordance with gain, inverting circuit, on the basis of the theory, the ideal balanced amplifier has infinite rejection ratio on induced noise, can be completely offset the interference signal, but in practice, due to reasons such as gain error balance circuit, anti-jamming ability can't reach the ideal value, even some new distortion and noise.
But even so, relative to the single-ended circuits can only strengthen the screening and power filter is adopted to reduce interference, balance circuit is a kind of active, positive and effective anti-interference measures, in bad electromagnetic environment, the advantages are very obvious when the long distance transport.
Four, the article conclusion in the design of the ultrasonic flowmeter and the use of process, each kind of noise can have a great influence on its measurement precision, according to the above, this paper by adopting methods such as filtering, shielding, balance circuit on the meter circuit improvement, through this a series of modified products have been in the field of production, the effect is very obvious, for improve flowmeter measurement precision and stability has a great effect.
In this paper by embellish instrument technology co. , LTD. Arrange release.
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