The same transducer is used to both transmit and receive the ultrasonic signals. Just after the emission of the ultrasonic burst, the transducer is switched from the emitting mode to the receiving mode. The incoming echoes are then amplified, using a time depend amplification (Time Gain Controlled - TGC - amplifier), in order to compensate the attenuation of the ultrasonic waves during their propagation in the analyzed liquid. Following the amplification, gates are formed by sampling the echo signal. The depth of each gate is computed by measuring the time delay between the emission of the ultrasonic burst and the reception of the echo part corresponding to the considered gate. The thickness of all the gates is defined by the burst length and/or the bandwidth or the receiver. In order to compute the velocity in each gates, many emission are sent. These emissions form an array of time series data values, from which the mean Doppler frequency is computed by a powerful auto-correlation algorithm. The resulting velocity information is then displayed on the computer connected to the DOP3000 and can be stored using one of the many recording modes available.
The investigated liquid must contain particles. The size of the particles must be smaller then the wave length in order to avoid any diffraction of the ultrasonic beam. Hopefully this is often the case and most of liquid contains enough very small gas bubbles, dust or impurities. And when it is not the case, we can provide seeding solutions.
The ultrasonic probe can be placed directly in contact with the liquid or coupled to the wall of the container by means of an ultrasonic gel. The coupling medium guarantees a path for the ultrasonic waves.
One of the most important parameter is the choice of the ultrasonic probe. This choice is generally based on:
In order to cover a wide range of applications, the included digital ultrasonic synthesizer (available in option) allows to generate any emitting frequencies between 0.45 MHz and 10.5 MHz, and our standard and custom probes can be delivered in many different housings.
Available in option, The DOP3000 is not only capable of measuring instantaneously velocity profiles, but also Doppler energy profiles, echo profiles, spectral density (FFT), histogram, flow rate and even the ultrasonic field generated by an attached transducer. The optional variable spatial resolution filter allows to adapt the size of the sampling volume to the application and therefore improves the signal to noise ratio of the measurements.
All the ultrasonic parameters (ultrasonic frequency, pulse repetition frequency - PRF, time gain controlled amplification - TGC..) and the processing conditions (number of gates, filters...) can be either defined by the user, or automatically computed by DOP3000 software, thanks to its new assosted mode. The optional smart trigger capability of the instrument, available in option, allows to synchronize the acquisition to any periodic or non periodic event. Up to 32’000 profiles can be recorded in binary or ASCII format.
Operating in a Windows XP® environment, the software of the velocimeter communicates with the DOP3000 hardware through an USB port and is easier than ever to use and to tune to fit your applications as well as possible. The measured profiles are displayed on the screen of the attached PC and can be recorded on its harddrive.