FR2475315A1 - LOW-PASS FILTER WITH DIELECTRIC REMANENCE COMPENSATION, IN PARTICULAR FOR ELECTRONIC SCALES - Google Patents

Abstract

THE INVENTION RELATES TO A LOW PASS FILTER WITH DIELECTRIC REMANENCE COMPENSATION. IN THIS FILTER, TO COMPENSATE THE DIELECTRIC REMANENCE OF THE CAPACITOR C1, AT LEAST ONE ADDITIONAL CAPACITOR C2 AND AN ADDITIONAL RESISTOR R2 ARE PROVIDED, WHICH EXERCISE IN THE ASSEMBLY AN OPPOSITE EFFECT, WITHOUT SIGNIFICANTLY MODIFYING THE BEHAVIOR OVER THE TIME OF THE LOW WIRE . APPLICATION ESPECIALLY TO ELECTRONIC BALANCES.

Description

The present invention relates to a low-pass filter comprising at least

  least one component of the RC type (resistance-capacitance) and an operational amplifier connected downstream, intended to smooth a continuous voltage with superposed disturbing signals, in particular in

electronic scales.

  When the time constant of such a low pass filter must be of the order of one second, it is necessary to use relatively large capacitors having capacitances of about 1 vF. In the presence of such capabilities, the remanence of the dielectric is already felt. This dielectric remanence has been described, for example, in Grimsehl's "Lehrbuch der Physik" (Book of Physics), Volume II, 15th edition, 1961, page 73, published by Editions Schallreuter. Since, in general, this dielectric remanence decreases with a time constant of about 10 seconds, it is felt as a parasitic modification of the behavior in time of the low-pass filter and it causes, for example after a jump voltage at the input of said filter, too low voltage variations at the output of the latter, at a time when the transient phenomenon of said low-pass filter should be completed for a long time as a function of its time constant. When such a low-pass filter is connected, for example, to the input of a high resolution analog-digital converter, an electronic balance, in order to eliminate the disturbing signals superimposed on the DC voltage in front of

  be measured, there is a change in the

  chage when applying a weight on the scale, and this at a moment where the transient phenomenon of the filter

  Low pass should be completed a long time ago.

  The subject of the present invention is therefore a low-pass filter which, comprising at least one component of the RC type and an operational amplifier connected downstream, is improved so that the

  dielectric remanence exerts no disturbing influence

on its output signal.

  According to the essential features of the invention to compensate for the dielectric remanence of the conden-

  of the low-pass filter, another conden-

  and another resistance, which exert an opposite effect in the assembly without appreciably

  time behavior of said low-pass filter.

  In an advantageous embodiment according to the invention, the other capacitor and the other resistor are connected in parallel with the resistance of the component.

RC type.

  In another advantageous variant, the condensation

  additional resistor and resistor are connected to the feedback loop of the operational amplifier

connected downstream.

  According to another embodiment, the condensation

  additional power and resistance are connected

  parallel with the series resistance of a second amplifier

operational controller inverter.

  Advantageously, in all embodiments, the material constituting the dielectric of the additional capacitor has a higher remanence than the dielectric of the capacitor of the

low pass filter.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting examples and in which: FIG. 1 is a schematic representation of a first embodiment of the low-pass filter according to the invention; FIG. 2 diagrammatically illustrates a first variant embodiment of said filter; FIG. 3 schematically illustrates a second variant embodiment of said filter, and FIGS. 4a and 4b are diagrams highlighting the time course of the voltages respectively prevailing at the input and at the output of said low-pass filter. The filter passes FIG. 1 is a component of the type RC which comprises a resistor R1 and a capacitor C1. An operational amplifier V1 provides a non-inverting decoupling of the

  A. Without the presence of an additional capacitor

  C2 and an additional resistor R2, a voltage jump at the input E of the low-pass filter assembly (as shown in the diagram of FIG. 4a) would generate a voltage output at the output A than that illustrated in the diagram of Figure 4b for the real RC type component. The difference with respect to the ideal RC type component, illustrated on a very large scale - in FIG. 4b for the sake of clarity, is due

  the dielectric remanence of the capacitor Cl.

  The additional capacitor C2 and the additional resistor R2, connected in parallel with the resistor R1, have the effect of making the voltage of the capacitor C1, and thus the output voltage, increase more rapidly. As a result, the shape of the voltage at the output of the low-pass filter thus connected approximates the rate of voltage of an ideal RC-type component. In this case,

  appropriate choice of the value of the additional resistance

  In the case of R2, the behavior of the circuit can, directly after the voltage jump at the input, be optimally adapted to ideal behavior, while

  this behavior, a few seconds after the jump of

  at the input, is essentially determined by the value of the additional capacitor C2 and the effect of its dielectric. When the dielectric of this capacitor C2 consists of a material which has greater remanence than that of the dielectric element of the capacitor C1, it is possible to obtain

  a sufficiently large dielectric remanence, even ..

  when the capacitance of said capacitor C2 is of low value. It is generally possible, by a suitable choice of the value of the additional resistance R2, the value of the additional capacitor C2 and the dielectric thereof, to adapt the rate of the voltage at the output of the low-pass filter. according to the invention at the rate of the voltage prevailing at the output of an ideal RC component without dielectric remanence, and that so satisfactorily that, even in the presence of high resolution measuring devices, no disturbing influence

  dielectric remanence is noticeable.

  FIG. 2 schematically illustrates an alternative embodiment of the low-pass filter according to the invention. The additional capacitor C2 and resistor R2 are connected, with another additional capacitor C3, to the feedback loop of the operational amplifier V1. The operating mode of this arrangement corresponds to that illustrated with reference to FIG. that is, immediately after a voltage jump at the input E, the too small voltage increase of the real RC component is compensated by a gain, slightly greater than unity, of the operational amplifier VI, given that

  that only a part of the output voltage of this amplifier

  operational indicator is returned to its

  only by capacitive voltage divider C2 / C3. In this arrangement, the additional resistance R2 and the remanence of the capacitor C2 determine the behavior more

  long after a voltage jump.

  The second embodiment, illustrated in FIG. 3, differs from the first variant by

  the fact that the additional capacitor C2 and the resistor

  additional capacity R2 are connected in parallel with the

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  resistance-series of a second operational amplifier

  inverter V2, whereas in FIG.

  Additional reactor C2 and additional resistor R2 are connected in parallel with the resistor 1 'of the RC type component. The second operational amplifier V2 is, in any case, present most often in the circuit, for example in the form of a measuring range amplifier, equipped with an adjustable resistor R3, or as an integrator comprising a capacitor C3 at the

  place of said resistor R3 in the feedback loop.

  The additional connection in parallel with a resistor R4 has exactly the same effect as an additional connection in parallel with the resistor RM. Since, in general, the resistor R4 has a lower value than the resistor R1, this variant embodiment sometimes has the advantage that the

  resistance R2 must not be necessary either-

too much value.

  It goes without saying that many modifications can be made to the low-pass filter described and

  represented, without departing from the scope of the invention.

Claims (5)

CLAIMS -   1. Low pass filter, comprising at least one   RC-type component (resistance-capacitance) and an ampli-   downstream, in order to smooth a continuous voltage with superimposed interfering signals, in particular in electronic scales, filter   characterized in that, to compensate for the dielectric remanence   that capacitor (C1) of said filter, there is provided at least one additional capacitor (C2) and additional resistance (R2), which exert in the circuit an opposite effect without substantially modifying the   time behavior of said low-pass filter.   Low-pass filter according to Claim 1, characterized in that the additional capacitor (C2) and the additional resistor (R2) are connected.   in parallel with the resistor (R1) of the RC type component.   3. Low-pass filter according to claim 1, characterized in that the additional capacitor (C2) and the additional resistor (R2) are connected to the feedback loop of the operational amplifier. (Vl) connected downstream.   4. Low-pass filter according to Claim 1, characterized in that the additional capacitor (C2) and the additional resistor (R2) are connected in   parallel with the series resistance (R4) of a second amplifier   inverter operational controller (V2).   5. Low-pass filter according to any one of   Claims 1 to 4, characterized in that the material   chosen to constitute the dielectric of the additional capacitor (C2) has a greater dielectric remanence than that of the dielectric element of the capacitor (C1) of said filter.