Balluff Gmbh

Sie Sensorik-industrie-elektronik Gmbh

Balluff Sie Sensorick Gmbh

Frank Winkens

Wolfgang Frank

Juergen Glock

Circuit arrangement measuring at least one measurement capacitor having inverting amplifier with high open-circuit voltage gain, input connected to connection of at least one measurement capacitor and to connection of negative feedback capacitor, another connection of at least one measurement capacitor connected to a reference potential and another connection of negative feedback capacitor connected to output of inverting amplifier; rectifier circuit fed voltage at the output of inverting amplifier and generates at its output voltage corresponding to voltage at output of inverting amplifier; a holding capacitor buffering voltage supply of inverting amplifier and rectifier circuit, a supply voltage connection of inverting amplifier supplied with a periodic control voltage with respect to reference potential and other supply voltage connection of inverting amplifier supplied via a diode with external supply voltage, periodic control voltage generated by signal source having a control input via which level of periodic control voltage can be infinitely variably set and this control input connected to an output of a control device which compares voltage generated at output of rectifier circuit with a desired voltage and, depending on comparison, emits output signal fed to control input of signal source, until level of periodic control voltage fed to supply voltage connection of inverting amplifier reaches value at voltage generated at output of rectifier circuit matches desired voltage, if voltage present at output of rectifier circuit matches desired voltage, at least voltage present at output of control device is a measure for at least one measurement capacitor.

Circuit arrangement for measuring at least one capacitor

A capacitive fill level sensor for measuring the fill level of a medium in a container has an electrode unit, which contains a strip-shaped measurement electrode, a strip-shaped counter electrode and a strip-shaped shielding electrode, the shielding electrode at least partially surrounding the measurement electrode. A first AC voltage source having a predefined frequency and amplitude is provided, to which the shielding electrode is connected such that a shielding capacitor formed between the shielding electrode and the measurement electrode has a shielding capacitance that is proportional to the length of the shielding electrode. A second AC voltage source of equal frequency and a predefined second amplitude is provided, the second amplitude being in phase opposition to the first amplitude, to which AC voltage source the counter electrode is connected, such that a measurement capacitor formed between the counter electrode and the measurement electrode has a measurement capacitance that is proportional to the fill level. The measurement electrode voltage present at the measurement electrode is used to determine the fill level.

Capacitive fill level sensor

The invention proposes a circuit arrangement for determination of a measuring capacitance (), comprising a reference circuit portion for defined periodic charging and discharging of a predefined reference capacitance (), and a measuring circuit portion for defined periodic charging and discharging of the measuring capacitance () to be determined, and at least one circuit portion () intended to determine at least one value (M) characteristic of the charging time curve of the reference capacitance () and for deriving at least one value (M) characteristic of the charging time curve of the measuring capacitance (), as well as a circuit portion () for comparing the at least one value (M) characteristic of the charging time curve of the reference capacitance () with the at least one value (M) characteristic of the charging time curve of the measuring capacitance (), and for deriving from that comparison the value of the measuring capacitance ().

Circuit arrangement for determination of a measuring capacitance

The invention relates to a sensor for the contactless detection of the level of a liquid and adhering high-conductivity medium, especially blood, through a non-metal container wall. The sensor has a pulse generator () that generates brief pulses which, via a low-ohm resistor (), namely, the measuring resistor, actuate an electrode () installed on the outside of the container wall. A fast-action difference amplifier that has a high common-mode rejection () and that taps a voltage drop at the measuring resistor () caused by the level-dependent pulse current, then said difference amplifier amplifies this voltage drop by a fixed factor and feeds the signal to a downstream peak detector () with filtering in order to obtain a level-dependent direct voltage and also feeds it to a downstream voltage comparator () which, by comparing the output voltage of the peak detector () to an adjustable setpoint voltage (), generates a switching signal that changes from 'low state' to 'high state' as soon as a rising filling level causes the measuring electrode () to be sufficiently covered and conversely when the filling level sinks below the electrode () or reacts inversely to the change in the filling level as soon as the polarity of one of the stages consisting of the pulse generator (), the difference amplifier (), the peak detector () and the voltage comparator () is inverted.

Sensor for the contactless detection of the level of a liquid and adhering high-conductivity medium, especially blood, through a non-metal wall of a container

A sensor according to the invention has an amplifier that is capacitively loaded vis-&#xe0;-vis the ground by a container and by a medium contained therein and that has a capacitive feedback that is dimensioned in such a way that the amplifier only oscillates when the critical filling level has not been reached. According to the invention, the capacitive feedback is influenced by the container in such a way that the capacitive load of the amplifier input caused only by the container is countered. In this manner, it is achieved that the sensor responds only to the capacitance of the medium, largely independently of the magnitude of the container capacitance. A sensor according to the invention is also characterized by such an operating frequency that, on the basis of the conductivity of the medium, it is possible to distinguish between a massive and an apparent filling of the container with the medium simulated by wetting or foam formation, but it largely avoids those problems encountered with sensors having a very high operating frequency of more than 50 MHz.

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Ludwigshafen, Germany

Frank Winkens