Method and circuit arrangement for intermittent application of a voltage to an electrode
AssigneeEndress + Hauser Flowtec AG
InventorPeter Hafner
Life of this patent
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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.
Claims15
An apparatus for cleaning an electrode used to generate a measurement signal, the apparatus comprising:
- a voltage source;
- one normally open switch including a first terminal coupled to the voltage source and a second terminal;
- another normally open switch including a first terminal coupled to the second terminal of the first normally open switch and a second terminal coupled to the electrode;
- means for selectively closing the normally open switches for a predetermined time to couple the voltage source to the electrode to clean the electrode;
- and
- an impedance converter including an input having a relatively high input impedance and an output having a relatively low output impedance, the electrode being coupled to the input of the impedance converter, and the output of the impedance converter being coupled to the first terminal of the other normally open switch so that substantially no potential difference exists between the first and second terminals of the other normally open switch, thereby increasing the accuracy of the measurement signal from the electrode.
An apparatus for cleaning an electrode used to generate a measurement signal, the apparatus comprising:
- a voltage source;
- means for generating an output signal from the electrode, the generating means being coupled to the electrode;
- an impedance converter including an input having a relatively high input impedance and including an output having a relatively low output impedance;
- a normally open switch including a first terminal coupled to the voltage source and a second terminal coupled to the input of the impedance converter;
- means for selectively closing the normally open switch for a predetermined time to couple the voltage source to the input of the impedance converter;
- a current limiting resistor coupled to the output of the impedance converter;
- and
- a pair of diodes coupled together in antiparallel, the pair of diodes including a first common terminal coupled to the current limiting resistor and to the input of said impedance converter and including a second common terminal coupled to the electrode to increase the accuracy of the measurement signal generated by the generating means.
Dependencies are inferred from the claim text.