Abstract: This galvanic electrode of a flow sensor of an electromagnetic flowmeter for measuring the volumetric flow rate of an electrically conductive liquid flowing in a measuring tube is practically absolutely fluid-tight inserted in the wall of the measuring tube and has a highly constant wetting surface. The electrode comprises a shank having a first portion which is fitted fluid-tightly in a hole in the wall, an end face and a second portion having a smaller diameter than the hole and the first portion. A wetting surface formed by the end face and a second portion of the electrode shank. This second portion forms a gap between the surface of the hole. The gap is sufficiently wide and the surface of the hole has a low surface tension so that the liquid will penetrate into and fill the gap, and the wetting surface will remain constant under all operating conditions of the flowmeter.

Abstract: An electromagnetic flow measuring tube is manufactured by forming an inner member which consists substantially of plastic and thereafter coating the inner member with a material which has a lower coefficient of thermal expansion and a higher mechanical strength than the material of the inner member to form an outer member which surrounds the inner member in a form-stabilizing stiffening manner. Thus, when the inner member is formed from plastic in hot condition, as for instance by injection molding, it can cool down and solidify in a relaxed condition, so that it is free of intrinsic mechanical stresses when the outer member is applied. This eliminates the danger of a detachment of the inner member from the outer member and of subsequent occurrence of cracks in the material of the inner member. Mounting flanges, stiffening webs and other structural elements are integrally formed with the plastic inner member. This permits a simple and economic manufacture of flow measuring tubes having a complicated shape.

Abstract: A method and a circuit arrangement for intermittent application of an electrical DC or AC voltage by a switch to an electrode in contact with a material, in particular for cleaning the electrode. The method is suitable in particular for use in electromagnetic flow measuring technology. The objective is to protect the electrode from parasitic capacitances present in the switch and interference voltages occurring therein. This is achieved in that at least in the period in which no voltage is applied to the electrode, the electrical potential of the electrode is coupled to the terminal of the switch which is not allocated to the electrode. Impedance converters are suitable as coupling elements.

Abstract: In an electromagnetic flow measuring arrangement an electrically conductive fluid flows through a measuring tube in which a magnetic field is generated transversely of the flow direction, whereby a voltage is induced which is proportional to the flow velocity. This voltage is tapped by means of two electrodes. The cavity of the measuring tube has an elliptical cross-section with two major axes, the first major axis coinciding with the connecting line of the two electrodes, and the second major axis coinciding with the direction of the magnetic field. The flow to be measured is proportional to the product of the measured flow velocity and the cross-section area of the cavity of the measuring tube. The flow measuring arrangement is constructed so that on changes of the cavity cross-section caused by external influences the cross-section retains substantially the profile of an ellipse and the length of the second major axis remains substantially constant.

Abstract: An arrangement for magnetic-inductive flow measurement of an electrically conductive liquid flowing in a conduit includes a magnetic field generator which generates a periodically reversed magnetic field passing through the conduit perpendicularly to the flow direction. In the conduit two electrodes are disposed. The voltage taken from the electrodes is applied to a measuring amplifier. Connected to the output of the measuring amplifier are two sample and hold circuits which are controlled by a control circuit in such a manner that they sample the output voltage of the measuring amplifier for equal induction values of opposite sign of the magnetic field and store the sampling values until the next sampling. A subtraction circuit forms the difference of the stored sampling values.

Abstract: An arrangement for generating DC magnetic fields of alternating polarity for the magnetic-inductive flow measurement by means of a field coil which is connected via alternately controlled switching members to a DC voltage source, wherein during the reversal time following the change-over of the switching members a capacitor is connected to the field coil to form a resonant circuit separate from the DC voltage source and the capacitance C of the capacitor in dependence upon the desired reversal time .DELTA.t has substantially the value ##EQU1## wherein L is the inductance and R the ohmic resistance of the field coil.

Abstract: A method of compensating interference DC voltages in the electrode circuit in magnetic-conductive flow measurement with periodically reversed DC magnetic field in which the useful signal is obtained by sampling and storing the signal voltage after each reversal of the magnetic field at opposite polarity values of the magnetic field during a sampling time interval and forming the difference of the stored sampled values, and wherein in a compensating time interval following each sampling time interval a compensation voltage is produced by sampling and storing the signal voltage, which compensation voltage is superimposed oppositely on the signal voltage for compensating the signal voltage within the compensation time interval to the value zero and is retained until the next compensation time interval, wherein each compensation time interval lies within the time interval corresponding to the switched-on magnetic field, in which also the preceding sampling time interval lies.