Abstract: A vacuum cleaner is provided comprising a housing (1) with two filter systems (2,3) arranged in series, means (4) for generating an air flow through the filter systems, the second filter system (3) as seen in the direction of flow being a cyclone filter system, which vacuum cleaner is provided with one reservoir (5) for collecting dust from both filter systems (2,3), which reservoir can be closed off with a lid (14), is suitable for accommodating a disposable dust bag (6), and is furthermore divided into two compartments (5a, 5b) by a wall (13), each reservoir compartment serving to collect separated dust from the accompanying filter system, while the wall (13) is fastened in the reservoir (5) in such a way that it can be taken out. Preferably, the removable wall (13) is fastened to the lid (14).As a result, the user can remove all the dust from the vacuum cleaner in one operation.

Abstract: A method of and an arrangement for measuring the velocity and/or length of moving objects using the Doppler principle. Measurement of the velocity of objects over a wide range imposes stringent requirements on the bandwidth of the electronic apparatus which process the Doppler shift. The velocity and/or length are measured accurately using simple, narrow-band electronic processing circuits by imparting a pre-shift to the frequency of the electromagnetic wave directed towards the object to be measured. This pre-shift is opposite to the Doppler shift generated by the movement of the object and is realized by imaging a light beam originating from a laser onto the object via a rotating phase grating. The rate of rotation of the phase grating is controlled so that the total Doppler shift measured is always constant.

Abstract: An ionization flow meter which can determine with high accuracy the flow of a gas expressed as a gas velocity, volume flow, or mass flow and substantially independently of pressure, temperature and, as the case may be, moisture content. By applying the theory of corona discharges, data relating to the flow-determining factors such as ion mobility and gas density can be derived from the known measured voltage and current values using electronic means. For example, the slope S of the I-V characteristic curve can be determined from the measured values of voltage V and current I.