Ifm Electronic Gmbh

Ifm Electric Gmbh

Peter Kimbel

Manfred Maurus

Heinz Walter

Oliver Blankenhorn

Fabian Kuhnhäuser

Alexander Oppe

Simon Büchele

The invention relates to a method for monitoring the function of a capacitive pressure measuring cell () comprising a measuring capacitor (C) and a reference capacitor (C) as well as a temperature element, wherein a pressure measurement value p is obtained by forming the quotient Q from the capacitance values of the reference capacitor (C) and the measuring capacitor (C). The method is characterized by the following method steps:

Method for monitoring the function of a capacitive pressure measuring cell

A method for operating a pressure measuring cell of a capacitive pressure sensor. The pressure measuring cell includes a pressure-dependent measuring capacitor and a reference capacitor, with an internal alternating square wave excitation voltage applied. The pressure measured value is obtained from capacitance values of the measuring capacitor and the reference capacitor. The measurement signal is an alternating square-wave signal supplied to an evaluation unit. The alternating square-wave signal is supplied to an amplifier unit where signal amplification is performed by amplitude adjustment for the internal excitation voltage and offset compensation is performed by a further square-wave signal and gain correction is performed by multiplicative influencing of the quotient of the capacitance values of the reference capacitor and the measuring capacitor, and the offset correction is performed by virtue of the square-wave signal being supplied to the amplifier unit and thus being added to the square-wave signal.

Method for operating a pressure measuring cell of a capacitive pressure sensor

The invention relates to a method for monitoring the function of a capacitive pressure measurement cell () which has a measuring capacitor (C) and a reference capacitor (C), to which an internal excitation voltage Uin the form of an alternating square-wave signal is applied. According to the invention, in order to allow the detection of a disturbing influence on the measurement result owing to, in particular, moisture-induced leakage currents, it is proposed that the corresponding voltage values U, Ube sensed from the voltage signal Uduring the falling and/or rising signal curve at least two defined times t, t, and the two pairs of values t; Uand t; Uare used to determine a linear equation U=f(t), wherein the linear equation U=f(t) within the falling or rising signal curve is used to calculate the time tat which the voltage value Uset as a threshold value or switchover point in the comparator-oscillator (SG) is reached, wherein —either the time tis compared with the actual switchover time of the comparator-oscillator (SG) and an error signal is generated in the event of significant deviation, —or the time tis used to define a hypothetical switchover point of the comparator-oscillator (SG), from which a hypothetical working frequency is calculated, and an error signal is generated if there is significant deviation of said hypothetical working frequency from the actual working frequency of the comparator-oscillator (SG).

Method for monitoring the function of a capacitive pressure measurement cell

The disclosure relates to a method for operating a capacitive pressure measurement device. In order to achieve an insensitivity to external signal sources, the disclosure proposes continuously varying the working frequency of the pressure measurement device so that a resonance formation with externally injected (interfering) frequencies is avoided.

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Tettnang, Germany

Peter Kimbel