Time shift (measurement method)

Time shift (in German time shift method (ZVV)) is a measurement method based on the backscattering of light (e.g. laser light) by particles. It is used to determine the characteristic properties (size and speed) of individual particles in an aerosol or spray . The drop impulse and the volume flow at the measuring point can in turn be determined from these variables.

history

This technique was first mentioned by Semidetnov in 1985. In 2002, Damaschke et al. and in 2003 by Albrecht et al. further developed.

scope of application

This procedure is mainly used for process engineering tasks. Drops and particles that are in suspensions and emulsions or in another liquid are reliably detected. In contrast to the phase Doppler technique , the process can differentiate between bubbles and solid particles. Intensive research made it possible to construct a compact analyzer that is now useful for industrial use. This structure and the associated advantage arise from the fact that the transmitter and receiver optics are attached to a common carrier and are therefore easy to position.

properties

This is an improved time shifting method, so it is more adaptable. The forward and backward spreading method ensures this adaptability. It determines the size, speed and number of particles and thus also the volume flow. In many cases it is also possible to have the refractive index specified. This ratio can be used to determine the phase or material that is being measured.

functionality

The laser beam is focused by lenses. The light that was scattered by the particles is divided into s (perpendicular) and p (parallel) polarized light and is recorded separately by two photo detectors. The signal that comes from the detectors provides the necessary information to accurately estimate the size, speed and refractive index of the particles and droplets. The thickness of the laser beam should not exceed the size of the droplet in order to obtain the time-shift signal. If this value is exceeded, the signal is no longer suitable as a basis for determining the above-mentioned quantities. This then gives rise to the problem that the signal components of the different scatters overlap and thus cannot be recorded and differentiated individually. But it is precisely this distinction that the above method needs to determine its values.

Web links

Individual evidence

^ ^A ^b ^c W. Schäfer: Time-Shift Technique for Particle Characterization in Sprays .
^ ^A ^b Walter Schäfer and Cameron Tropea: Time-Shift Technique for Particle Characterization in Sprays . 1st edition. ISBN 978-3-8442-6708-2 .
↑ Characterization of particles and drops. Retrieved August 10, 2016 .
↑ Vincentz Network: Counting drops thanks to time difference. Retrieved August 10, 2016 .

[:0-1] A ^b ^c W. Schäfer: Time-Shift Technique for Particle Characterization in Sprays .

[:1-2] A ^b Walter Schäfer and Cameron Tropea: Time-Shift Technique for Particle Characterization in Sprays . 1st edition. ISBN 978-3-8442-6708-2 .

[3] Characterization of particles and drops. Retrieved August 10, 2016 .

[4] Vincentz Network: Counting drops thanks to time difference. Retrieved August 10, 2016 .