The traditional method currently used to detect the balance coefficient of elevators has a limitation in accurately obtaining the instantaneous current signal when the elevator is at the position of the balance floor. To address this issue, a novel detection method is proposed for determining the elevator balance coefficient. As the elevator runs through its full stroke, its speed waveform exhibits a symmetrical trapezoidal distribution. By accurately capturing the start and stop signals of the elevator operation, the current signal at the position of the balance floor can be determined. In this study, a combination of red light through-beam photoelectric sensors is used to record the trigger signals during the start and stop times of the traction elevator. Real-time data collection is conducted simultaneously using both the photoelectric sensor and the current transmitter. The moment when the photoelectric signal jumps is considered as the moment when the elevator starts or stops. However, the signal collected from the red light through the photoelectric sensor may be affected by the magnetic field generated by the permanent magnet motor. To mitigate the interference of clutter signals, a simple threshold filtering method is employed based on the characteristics of noisy signals. Experimental results demonstrate that this novel balance coefficient detection device enables fast and accurate measurement of the elevator's balance coefficient.
In order to measure the axial flowing velocity of a suspension carbon particles of tens of micometer-scale, the photoacoustic doppler frequency shift was calculated from a series of individual A scans using a autocorrelation method. A 532nm pulsed laser with the repetition rate of 20Hz was used as a pumping source to generate photoacoustic signal. The photoacoustic signals were detected using a focused PZT ultrasound transducer with central frequency of 5MHz. The suspension of carbon particles was driven by a syringe pump. Firstly, the complex photoacoustic signal was calculated by the Hilbert transformation from time-domain photoacoustic signal. The complex photoacoustic signal was then autocorrelated to calculate doppler frequency shift. The flow velocity was calculated by averaging the autocorrelation results of individual A scans. In comparison , the previously reported data processing methods using cross-correlation method in time domain or frequency domain require high sequential scanning rate or high laser repetition rate up to several kHz to avoid aliasing or uncorrelation between sequential waveform pairs. But it is difficult to get several kHz repetition rate for a single pulsed laser and the correlation between waveform pairs of sequential A scans were also limited by the laser repetition rate. To solve the problem, we used the autocorrelation method of individual A scans to calculated Doppler frequency shift. The time delay can be user defined to avoid aliasing. The feasibility of the proposed autocorrelation method was preliminarily demonstrated by quantifying the motion of a carbon particles suspension flow from 5 to 60 mm/s. The experimental results showed that the autocorrelation result approximately agreed with the setting velocity linearly.
Photoacoustic tomography(PAT) is a new imaging modality of biological tissues. It merges the contrast advantage of
pure optical imaging with the resolution advantage of pure ultrasound imaging. A numerical simulation method of spatial
resolution in photoacoustic tomography was studied. The full width at half maximum (FWHM) of point spread function
(PSF) was calculated to determine the spatial resolution. The effectiveness of the simulation method was indicated by
experiment. The relationship between spatial resolution and filter's cutoff frequency and active detector aperture size
was calculated. The result could be used to calculate the spatial resolution of photoacoustic imaging system.
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