CN103308706A - Method and device for detecting rotating speed of vane pump - Google Patents

Abstract

The invention discloses a measuring method of the rotating speed of a water pump applicable to being driven by a three-phase asynchronous motor. The measuring method comprises the following steps of converting a current signal at the input end of the motor into a voltage signal by a current transformer, carrying out data acquisition on the voltage signal, carrying out fast Fourier transform, obtaining exciting component frequency of stator current, obtaining the frequency of feedback load component of rotor current in stator current by a frequency refining analysis method, and according to the two frequencies and the principle of the asynchronous alternating-current motor, calculating the practical rotating speed of a water discharging pump. The measuring method disclosed by the invention is wide in application range and fewer in measuring error in a process of testing pump revolution speed, and is especially suitable for a pump with an invisible shaft, and the testing cost is almost not increased.

Description

A kind of vane pump rotating speed detection method and device thereof

Technical field

The present invention relates to a kind of vane pump rotating speed detection method and device thereof, particularly a kind of method by measurement pump inlet pressure fluctuation realizes the centrifugal pump monitoring of working condition.

Background technology

Rotating speed is an important performance characteristic of centrifugal pump.Centrifugal pump mostly adopts Asynchronous Motor Driving at present, and the rotating speed of pump and the synchronous rotational speed of motor are variant, needs to adopt various velocity gauges to measure the actual speed of pump in experiment and engineering application.What adopt the earliest in the laboratory is the daylight lamp velocimetry, owing to by range estimation, measuring out of true, this method is seldom used.The tachometric survey instrument and the method that extensively adopt now have two kinds, a kind of is the photo-electric reflection type knotmeter, this metering system is more convenient accurately, but be not suitable for underwater survey, in addition, when using the method measurement, rotating shaft or with certain parts of rotating shaft synchronous rotary (such as shaft coupling etc.) must be as seen, therefore the method is not suitable for the pump of some impellers and motor direct connection yet, another kind of measuring method commonly used is based on the inductive coil method of asynchronous motor leakage flux induction, but along with improving constantly of motor and parts manufacturing and mounting process level and material property, the leakage flux of motor more and more is difficult to detect.Simultaneously because the interference of the impact that the rotor winding distributes, power frequency component, and the mixing of other noise, the waveform of the signal that gathers with inductive coil is very poor, needs filtering and amplification, and hardware cost and system complexity are higher.Also have some scholars to propose to utilize the sound principle of interference, realize the revolution speed measurement by the pressure fluctuation of measuring pump discharge, but adopt this method the high frequency dynamic pressure transducer to be installed at pump discharge, its realization equipment is complicated, and cost is high.

Summary of the invention

The invention provides a kind of measuring method and device thereof that is applicable to use the vane pump rotating speed that three-phase induction motor drives, its scope of application is wide, and measuring error is little, and increases testing cost hardly.

Principle of the present invention:

Most employing threephase asynchronous machine of vane pump drives, and what this motor adopted is electromagnetic induction principle, the three-phase current in stator, can produce the rotating magnetic field that alternately changes, pass into electric current in the rotor winding, under the effect of rotating magnetic field, the rotor of induction motor rotates gradually.But rotor speed is lower slightly or a little more than the rotating speed of rotating magnetic field all the time, revolutional slip is described the degree that rotor speed (actual speed n) and rotating magnetic field rotating speed (synchronous rotational speed n0) differ, a basic variable quantity of this parameter characterization running state of induction machine represents with s

$s=\frac{n_0-n}{n}$

When the load of induction motor changes, rotor speed and revolutional slip also will change with load variations, and the electromotive force in the rotor conductor, electric current and electromagnetic torque corresponding change also can occur thereupon to adapt to the needs of load.The rotating magnetic field that alternately changes that produces in the stator is with relative velocity " cutting " the rotor winding of Δ n size, the at this moment frequency of rotor current

$f_2=\frac{p(n_0-n)}{60}=\frac{{\mathrm{pn}}_0}{60}\&CenterDot;\frac{n_0-\mathrm{<figure-callout\; id="0"\; label="n\; n"\; filenames="DEST\_PATH\_HSB00001112071000021.png,DEST\_PATH\_HSB00001112071000022.png"\; state="\{\{state\}\}">n</figure-callout>}}{n_{}}={\mathrm{<figure-callout\; id="1"\; label="sf"\; filenames="DEST\_PATH\_HSB00001112071000021.png"\; state="\{\{state\}\}">sf</figure-callout>}}_1$

In the formula: f1 is the stator current frequency, and p is motor progression.

When induction motor moved in on-load situation not, the rotating speed of rotor was no better than synchronous rotational speed, and the rotating magnetic field that at this moment alternately changes is with the conductor of zero speed cutting rotor, so the induction current of rotor is very little, usually processes with zero current.Induction motor is in the on-load situation, and the distribution of the magnetomotive dfundamental-harmonic pair air-gap field of rotor can exert an influence, and is called rotor reaction.The rotor reaction meeting causes that the size of air-gap field and space phase change, thereby causes that stator-induced electromagnetic kinetic potential and stator current change.Induction motor a compensation rotor magnetomotive " load component " also will occur, namely in the stator current after loading

${\stackrel{\&CenterDot;}{I}}_1={\stackrel{\&CenterDot;}{I}}_m+{\stackrel{\&CenterDot;}{I}}_{1L}$

In the formula: I ₁Be stator current; I _mBe exciting curent; I _1LBe load component.

Mmf equation during according to motor load can obtain:

${\stackrel{\&CenterDot;}{I}}_1+\frac{{\stackrel{\&CenterDot;}{I}}_{1L}}{k_i}={\stackrel{\&CenterDot;}{I}}_m$

I ₂Be rotor current; k _iBe current ratio.

${\stackrel{\&CenterDot;}{I}}_{1L}=-\frac{{\stackrel{\&CenterDot;}{I}}_2}{k_i}$

The current signal that stator current comprises two frequencies is respectively excitation electric force signal and and the current signal of opposite direction identical with rotor current frequency size.Guaranteeing under the sufficiently high data acquiring frequency current signal that collects to be carried out spectrum analysis, just can obtain the excitation components frequency of stator current and the frequency of the feedback " load component " of rotor current in stator current.

Be that motor speed is:

n＝n ₀-60f ₂/p

Namely under the condition of known motor number of pole-pairs, can calculate the actual speed of rotor, i.e. motor speed.

Technical scheme:

1. by current transformer the input end of motor current signal being transformed into can be for gathering the voltage signal of applying for card and gathering.

2. by signal pickup assembly this voltage signal is gathered.

3. carry out frequency analysis by FFT transfer pair signal, calculate the excitation components frequency of stator current.

4. the frequency band in the 0-5Hz is carried out refinement by zoom-fft, calculate feedback " load component " frequency of rotor current in stator current.

5. go out the actual speed of water pump according to the level Logarithmic calculation of these two frequencies and motor.

Description of drawings

Fig. 1 is the rotary speed test system schematic diagram.

Fig. 2 is signal processing flow figure.

Fig. 3 is the actual signal sampling

Fig. 4 is FFT result figure

Fig. 5 is ZOOM-FFT result figure

Fig. 6 is error analysis contrast chart.

Embodiment

As shown in Figure 1, utilizing current transformer during measurement is little electric current with the current transitions of input end of motor, pull-up resistor of secondary circuit access at current transformer, current signal is transformed into voltage signal. adopt the difference input with the voltage signal leading-in end daughter board at load two ends, and according to coefficient of mutual inductance and actual current size, select to adjust the pull-up resistor size, guarantee that maximum magnitude is no more than [5V, 5V], the signal condition module that has the function of low-pass filtering by the cable access, by conditioning module and access capture card, used herein is data collecting card PXI6251.

Utilize Labview to write data acquisition program, gathering the voltage signal at load two ends. its collection result is as shown in Figure 3, fast fourier transform (the FastFourierTransform that utilizes Labview to provide, FFT) and zoom FFT function (Zoom-FFT), the program of writing according to Fig. 2 calculates excitation components frequency and feedback " load component " frequency of rotor current in stator current of stator current, and calculate corresponding rotor speed according to these two frequency meters, its result is as shown in Figure 3.

Here for the result adopts the transducer drive motor, compare with the tachometer value that uses light electric tachometer directly to measure by a plurality of results, the result as shown in Figure 5, its error is less than 5%, precision is higher.

Claims (1)

1. measuring method and the device of a pump rotary speed that drives by threephase asynchronous machine.It is characterized in that, by current transformer the input end of motor current signal is gathered; By pull-up resistor and signal condition module with current signal be transformed into filter away high frequency noise-the 5-5V voltage signal, by data acquisition card this voltage signal is carried out data acquisition; The signal handler of writing by Labview carries out the signal processing, wherein obtain the excitatory component frequency of stator current by fast fourier transform, frequency by the acquisition of frequency Zoom Analysis Method and the feedback " load component " of rotor current in stator current, according to this two frequency values and asynchronous AC motor principle, calculate the actual speed of water pump.

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