Ifm Electronic Gmbh

Ifm Electric Gmbh

Manfred Maurus

Peter Kimbel

Heinz Walter

Oliver Blankenhorn

Fabian Kuhnhäuser

Alexander Oppe

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

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.

Capacitive pressure measurement device with varying frequency

The disclosure relates to a method for monitoring the operation of a pressure measuring cell of a capacitive pressure sensor, wherein the pressure measuring cell comprises a pressure-dependent measuring capacitor and a pressure-dependent reference capacitor and the pressure measuring value is obtained as a measuring signal from the capacitance values of the measuring capacitor and the reference capacitor, wherein the measuring signal is supplied to an evaluation unit in the form of an alternating square-wave signal, the pulse height of the signal depending on quotients of the capacitance values of the reference capacitor and the measuring capacitor and the period of the signal being determined by the capacitance value of the measuring capacitor such that, in the nominal pressure range of the pressure sensor, there is a fixed correlation between the pulse height and the period, wherein the pairs of values of pulse height and period (h1, d1), . . . , (hn, dn) are stored as nominal values in an adjustment procedure for determined pressure values p1, . . . , pn, and wherein, for the currently measured pressure value px, with the pair of actual values (h, d), the pair of nominal values (h, d) is determined, and if there is significant deviation between the pair of actual values and the pair of nominal values, an error signal is generated.

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Bad Waldsee, Germany

Manfred Maurus