Abstract: A device for measuring or controlling a property of a flow medium comprises a conduit which carries a flow medium. A choke element located in the conduit has a first open operating position and a second closed operating position. A driver drives the choke element from one operating position to the other. A pressure sensor measures the difference in pressure before and after the choke element in said conduit. A processor responsive to the pressure difference calculates a flow or thermal property of the flow medium. The processor comprises an input for receiving a continuous control signal which indicates a desired value of a flow or thermal property of the flow medium and a converter for converting the continuous control signal into a pulse-pause signal for controlling the driver.

Abstract: A heat circuit comprises an initial conduit containing a flow medium and a return conduit. A choke element located in a conduit such as the initial conduit of a heat circuit serves to control the flow of the flow medium. The choke element has several active positions in which openings having differently sized cross-sections are inserted into the path of flow. The choke element is moved by a drive so that a particular position of the choke is active. A differential pressure sensor measures the presure difference before and after the choke element. A computer resposive to the differential pressure sensor controls the drive so that a particular cross-section of the choke element takes effect and the flow of the medium is measured with sufficient precision over a wide measuring range. The inventive arrangement may also include a temperature sensor for measuring the temperature difference between the initial and return conduits.

Abstract: To the phase locked loop for controlling the oscillator that regenerates a bit-rate clock signal from a data signal by means of a phase comparison circuit followed by a low pass filter, the output of which controls the oscillator frequency, a digital frequency comparison circuit is provided for assuring that the oscillator frequency will be brought into the capture range of the phase locked loop. The output of the digital frequency comparison circuit is converted from digital to analog form for being used in combination with the low pass filter output to control the oscillator. Frequency and phase control signals are applied to opposite electrodes of a variable capacitance diode in the frequency determining circuit of the oscillator.

Abstract: For producing the bone substitute material from collagen and hydroxyapatite, an aqueous solution of cleaned collagen is mixed with a cross-linking agent causing only a partial cross-linking, and the mixture is lyophilized.The quantity of the cross-linking agent is chosen such that the collagen retains its resorbability and its absorptivity vis-a-vis bodily fluids, the material further showing no undesirable side effects.Preferably less than 1% by weight of formaldehyde, one of the preferred cross-linking agents, is added, with reference to the dry weight of collagen, and sintered apatite grains with a diameter of 50-300 .mu.m are used.Such a bone substitute material is stronger and less tearable as previously known materials and insures a good promotion of the growth of own bone tissue and the substitution by it.