The anti-interference ability, the article leads for ultrasonic flowmeter
is an important feature, because in the work environment of ultrasonic flowmeter there are usually all kinds of noise sources, the noise will produce different degree of interference and influence, interference by way of coupling into the ultrasonic flowmeter, the results of measurement are usually deviated from the true value, or to work properly, the normal operation of the ultrasonic flowmeter and cause instrument measurements have different levels of error.
If we want to guarantee the normal work of the ultrasonic flowmeter, be about to find out the source of the noise interference and coupling transmission problem, to reduce the influence of noise measurement method for the instrument to low, to ensure production stability and precision of measurement data.
Second, the classification of noise and interference of three elements about the classification of productive noise, many here we according to its source can be divided into the following: 1.
Mechanical noise due to mechanical impact, friction, rotational generated by noise, such as machine tools, textile machines, electric saw, the sound of the ball mill, etc.
A sudden change in the fluid dynamic noise gas pressure or volume or flow generated by the voice.
Such as air compressor, exhaust fan, injector, boiler water, the sound of the whistle, etc.
Electric magnetic noise due to alternating force interaction in the motor, such as generator, transformer humming.
According to the distribution of noise with time, noise can be divided into continuous and intermittent noise again.
Continuity and noise can be divided into steady state noise (
Sound pressure level fluctuation is less than 5 db)
And non steady state noise.
The latter in the pulse noise (
The duration of the sound is less than 0.
5 seconds, the time interval is greater than 1 second, the change of sound pressure level more than 40 db)
Not only affect the work, also can cause greater harm to human body.
Noise interference formed three factors to affect the normal work of the ultrasonic flowmeter is susceptible to noise source, is sensitive to the noise of the ultrasonic flowmeter circuit and the coupling between the two channels.
Three, interference coupling coupling refers to the interference signal into the inside of the ultrasonic flowmeter, based on the analysis of interference problem, to make clear interference sources, susceptible circuit and the coupling between them.
Interference sources and susceptible circuit is objective existence, it is difficult to eliminate, thus cutting coupling is very important.
There are several ways to interference of the coupling.
1 inductive coupling inductive coupling refers to the mutual inductance between two circuits, when a circuit of current change, cause induced voltage in another circuit.
Figure 1 to 2 electromagnetic coupling circuit equivalent circuit diagram.
Path between two points mutual inductance, mutual inductance coefficient for m, when the circuit 1 interference current is ni changes, through the electromagnetic coupling interference voltage in circuit 2 nnujmi & omega;
Therefore, voltage nu?
Is proportional to the current n.
2 capacitive coupling capacitive coupling refers to the parasitic capacitance between two circuits, produce electrostatic induction, make a circuit of the electric charge change affect another circuit.
Wire 1 is in the circuit shown in figure 2 the interference sources, wire two is the transmission of ultrasonic flowmeter, c1 and c2 respectively wire 1 and 2 of parasitic capacitance, c12 for wire parasitic capacitance between 1 and 2, 2 r for wires to ground resistance, when the conductor interference voltage u1 is 1, 2 of the wires interfering voltage as 'accordingly, capacitive coupling interference with the coupling capacitance increases with the increase of c12.
3 leakage current coupling leakage current due to poor insulation, high potential to low potential through the insulation resistance circuit leakage caused by interference.
Circuit shown in figure 3 for the coupling of the leakage current equivalent circuit diagram of interference sources ne?
Through leakage resistance Mr Iz leakage current to the circuit, the interference voltage of 3.
4 common impedance coupling common impedance coupling is due to two or more of the communist party of China with a circuit impedance, when a circuit of current through the interference voltage in another circuit.
There are three common impedance coupling.
Power resistance common impedance coupling.
Several electronic circuit with a power supply or the sensor power supply, high voltage circuit or high current output current flows through the power supply, and because of the existence of power resistance on power resistance pressure drop is converted to interference sources.
Common ground impedance coupling.
On the common ground of ultrasonic flowmeter, a current flows through a variety of signal, because ground impedance, the grounding line voltage to form interference.
Signal output circuit impedance coupling.
A few road load when the ultrasonic flowmeter signal circuit, any change of a load output by common impedance coupling and influence the output circuit.
5 radiation coupled radiation coupling refers to a radio device continuously outward emission of electromagnetic field, the instrument if put in the launch site, sensing and launch electromagnetic field than inductive electromotive force and form the interference.
Picked up by six conduction coupled conduction coupling refers to through the wires to the noise, then through wire transfer to the circuit of ultrasonic flowmeter and formation of the interference.
Common power line noise, it is the alternating magnetic field induction to form induced voltage power supply circuit, then through the power transmission circuit interference everywhere.
Four, the article conclusion used in ultrasonic flowmeter, the noise source to the coupling way of ultrasonic flowmeter is varied, also not obvious, noise also is varied, sometimes interfere with the scenery, so be careful analysis of the coupling way, to eliminate interference.
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