FR2458946A1 - INTEGRATING CELL FOR FORMING A FILTER, THIS FILTER AND ITS APPLICATION TO THE DETECTION OF VIBRATION LEVELS - Google Patents

Abstract

INTEGRATING CELL WITH ADJUSTABLE TIME CONSTANT ENTERING THE CONSTITUTION OF A FILTERING CIRCUIT. IT CONTAINS A CAPACITOR 7 CONNECTED IN FEEDBACK BETWEEN AN OUTPUT TERMINAL 6 AND THE REVERSE INPUT 3B OF AN OPERATIONAL AMPLIFIER 3, A RESISTOR 5 CONNECTED BETWEEN AN INPUT TERMINAL 1 AND ONE OF THE CONDENSER TERMINALS, A SWITCH 8 INTERPOSED IN SERIES BETWEEN RESISTOR 5 AND TERMINAL 3B, THIS SWITCH BEING CONTROLLED BY A PERIODIC SIGNAL OF RECTANGULAR PULSES WITH ADJUSTABLE CYCLICAL RATIO. APPLICATION TO A DEVICE FOR DETECTION OF VIBRATORY LEVELS OF ROTATING MACHINES OPERATING AT VARIABLE REGIMES.

Description

The present invention relates to an integrating cell

  in the constitution of a filter circuit, of the type comprising a capacitor connected between an output terminal and a stabilized potential point and a resistor connected between an input terminal and one of the terminals of the capacitor. The invention also relates to a filter comprising at least

a cell of this type.

  The invention also relates to a detection device

  vibratory levels, making use of this filter, and

in a rotating system.

  The object of the invention is in particular to propose a cell enabling the formation of a filter with a cut-off frequency

controllable.

  This object is achieved, in accordance with the invention, by virtue of

  that this cell comprises a switch in series with the resistor

  said switch being controlled by a periodic signal of adjustable period, for successively establishing and interrupting the connection, via the resistor, between said input terminal and the

  capacitor, depending on the value of the control signal.

  Advantageously, the stabilized potential point is the inverting input terminal of an operational amplifier on

  which is mounted, in feedback, the capacitor.

  The controllable frequency filter according to the invention is characterized, in accordance with the invention, in that it comprises at least one integrating cell as defined above and a periodic control signal generator whose output terminal is connected to the control terminal of the

said cell.

  Advantageously, the lowpass filter is constituted by an integrator cell provided with a second resistor connected in parallel with the capacitor and switching means for establishing or interrupting the connection between said second resistor.

  and said capacitor on the adjacent side or stabilized potential point.

  Advantageously, the filter comprises two cells of

  series-mounted scrapers, in feedback on a first

  input of an operational amplifier mounted in

  pourer and a second input is connected to the output of a first integrator cell, via an inverter cell, the second integrator cell being connected, by its output, to said first input of the adder, whereby a bandpass filter is obtained between a third input of the adder and the output of the first integrator cell, a low pass filter between said third input and the output of the first integrator cell, and a high pass filter between

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  this same third input and the output of the adder.

  Advantageously, the low pass filter comprises a sequence

  of at least three integrator cells connected in series, against

  reaction on the adder amplifier, said first adder, the inverting amplifier is an amplifier mounted in addition and each integrator of the suite is connected by its output to an input of an adder, the next integrator, of the following , being connected to the other adder, the first integrator - the one

  whose input is connected to the output of the first adder -

  being connected by its output to the other adder.

  The device for measuring vibration levels applying this filter is characterized, according to the invention, in that this device comprises a movement detector of the casing of the rotating system, a filter as defined above,

  whose input terminal is connected to the output terminal of the detector

  the control signal generator is a device measuring the frequency of rotation of at least one element of the rotating system and providing a control signal whose frequency is a multiple of this rotation frequency, and a device measuring the amplitude of the signal filtered by the

filtered. -

  Advantageously, the measuring device is a detection device

  peak generator comprising a signal storage capacitor

  and a discharge circuit of said capacitor, this circuit comprises

  resistor in series with a switch controlled by said control signal to provide or interrupt the discharge of the capacitor through the resistor, in accordance with the

value of said control signal.

  Other features and advantages of the invention

  will be better understood by reading the following description

  several embodiments and with reference to the accompanying drawings in which

  FIG. 1 is an electrical diagram of an integrated cell

  according to one embodiment of the invention

  FIG. 2 is a diagram of a control signal used in

  for the cell of FIG. 1 - FIG. 3 is an electrical diagram of a first-order low-pass filter according to one embodiment of the invention - FIG. 4 is a circuit diagram of a universal filter according to a mode embodiment of the invention;

  FIG. 5 is a block diagram of a device for

  vibration level detection according to one embodiment of the invention; FIG. 6 is an electrical diagram of the generator circuit 28 of FIG. 5, according to one embodiment of the invention; FIGS. 7a to 7c show diagrams of signals present at different points of the circuit of FIG. 6, according to one embodiment of the invention; FIG. 8 is an electrical diagram of the amplitude measuring circuit 29 of FIG. 5, according to one embodiment of the invention; FIGS. 9a to 9c represent diagrams of signals present at different points of the circuit of FIG. 8,

  according to one embodiment of the invention.

  The cell shown in FIG.

  Operational amplifier grater. This cell includes a

  input terminal 1, an output terminal 2, and an operational amplifier

  rational 3 whose non-inverting input 3a is connected to the ground 4, whose inverting input 3b is connected to the input terminal 1 via a resistor 5, and whose output terminal 6 is connected at the output terminal 2 of the cell. A capacitor T

  is connected as a negative feedback between output 6 and the input

  jug 3b of the operational amplifier 3.

  An electronic switch 8 is interposed between the resistor 5 and the junction point 9 between the capacitor 7 and the inverting input terminal 3b. This switch 8 receives a control signal 10 represented symbolically by an arrow on

  Figure 1, a signal whose shape is shown in Figure 2.

  This signal is binary, its value "1" corresponding to the closing F of the switch 8 and its value "0" corresponding to the opening

0 of this switch.

  The signal 10 is a periodic signal of rectangular duty cycle pulses: 8 = SF T The time constant of the integrator of FIG. 1 is equal to RC, where R and C are the values, respectively, of the resistor 5 and of the capacitor 7. By varying the duty cycle OF of the signal 10, it is thus possible to vary at will the

  time constant of the integrator.

  This process can be advantageously applied to the

  Adjustable cutoff frequency filter (s). FIG. 3 represents a first-order low-pass filter using a cell similar to that of FIG. 1. In FIGS. 1 and 3, the analogous elements bear the same references. It can be seen that the filter of FIG. 3 is obtained by connecting a so-called gain stabilization resistor 11 between the output 6 of the amplifier 3 and the junction point 12 between

  the input resistance 5 and the switch 8.

  It can be seen that the cutoff frequency at 3dB of the filter

  of Figure 3 is f = BF, ob RI is the value of the resistance

c -

  11, 8, F and C 2 er1C being already defined above in

  reference to FIGS. 1 and 2. By modifying OF, it is therefore possible to modify

  proud at will the cutoff frequency fc of the low pass filter of

Figure 3.

  FIG. 4 shows the diagram of a second-order filter - using four operational amplifier cells, two cells of which are similar to that of FIG. 1. This filter comprises a first cell 13 formed by an operational amplifier 13a mounted as an inverter adder receiving on a first input terminal 13b the signal to be filtered; a second and a third input terminal 13c, 13d of the cell 13 are connected to the output, respectively 14a, 15a of an integrator cell 14 and a cell 15 formed by an operational amplifier 15b mounted in

  Inverter amplifier. The other integrating cell 16 is

  placed between the output 13e of the adder cell 13 and the input 14b of the first integrator cell 14, and is connected,

  by its output 16a at the input 15c of the amplifier cell 15.

  The switches 8 of the integrator cells are, in this example, each constituted by an n-channel field effect transistor 17, preferably of the type 2N4091, whose control electrode - or gate - 1Ta is connected, via a terminal 14c, 16b periodic signal generator of rectangular pulses cyclic ratio OF adjustable at will or slaved to an external parameter. This generator is not shown in Figure 4, but an example of this generator will be given below

  as part of the description of a particular application

  of an integrating cell filter according to the invention.

  The filter of Figure 4 comprises three output terminals 18, 19 and 20 electrically equivalent to the terminals, respectively 14a, 13e and 15c already described. On each of the output terminals 13, 19 and 20 is available a signal consisting of the signal applied to the input terminal 13b and filtered, respectively, low pass, high pass and band pass. To protect the grid

  1Va of field effect transistors 17 against positive voltages

  a diode in the opposite direction 21 between the terminal

  14c, 16b and said gate 17a.

  To ensure the operation of each transistor 17 over the entire dynamics of the input signal of the integrator 14, 16, the terminal 17b of the transistor 17 is connected to the junction point 22 between two series diodes 23 mounted in the same direction, and which

  the electrode opposite said point 22 is grounded 4.

  Thus, each integrator cell 14, 16 is analogous to the cell of FIG. 1, the components 5 and 7 having, in this example, the same value for the two cells 14, 16. By varying the duty cycle of the signal applied to the terminals 14c and 16b, the filter cut-off frequencies are varied

  pass (exit 18) and go high (exit 19) as well as the frequency

  center of the bandpass filter (output 20). It will be noted that the gain stabilizing resistor 11 of the cell of FIG. 3 corresponds, in the circuit of FIG. 4 for each cell 14, 16 to the input resistances, respectively 24 and 25, the resistance 24 corresponding to the cell. 13 and the resistance 25

in cell 15.

  The filters with a cut-off frequency or adjustable central frequency according to the invention find particular application in the detection devices - or indicators - of vibratory levels of rotating systems - or rotating machines - operating at variable speeds and / or having several members rotating at different speeds.

  different speeds. A reactor - or jet engine -

  The airplane is an example of these rotating systems.

  As shown in FIG. 5, a detector 26 provides an analog signal proportional to the acceleration or speed or position of a point in the housing of the rotating system to be monitored. This signal is applied to the input of a narrowband bandpass filter 27 such as that of FIG. 4, whose central frequency fc is driven by a control pulse signal such as the signal supplied by a generator. 28; the frequency F of this signal 10 is a multiple of the rotation frequency N of a rotating element of the system to be monitored; this is written F = pN, where p is a positive number. To ensure correct operation of the filter 27, it is necessary to have F "fc, for example F = 5 to 10 times fc, for this purpose the values

  (R) of the resistance 5, (C) of the capacitor 7 and 9 are

  selected according to the frequency F of the control signal and the center frequency of the filter 27. In the case of the circuit of FIG. 4, this central frequency fc is equal to

  at BF o B, F, R and C have already been defined above.

  2efRC The filtered signal leaving the filter 27 is applied to a device or circuit 29 measuring the amplitude of the

filtered signal.

  FIG. 6 gives an exemplary embodiment of the generator

  28. This generator comprises a sensor 30 of the rotational frequency

  rotation of the system to be monitored, an amplification

  differential sensor 31 receiving the signal from the sensor 30, a

  Schmitt circuit 32 transforming the curved pulse signal 33 emitted by the amplifier 31 into a rectangular signal 34, and a monostable circuit - or flip-flop 35 transforming the signal 34 into a calibrated signal as a frequency F as the signals 33 and 34

(Figures 6 and 7a to 7c).

  The sensor 30 is, in the example shown, of the type

  with an air gap variation it comprises a wheel made of ferro-

  magnetic key 37 keyed on a rotating element 38 of the system to be monitored, coaxially with the axis of rotation of this rotating element; the wheel 37 is provided with protuberances 37a regularly distributed around its circumference; these protuberances pass close to the adjacent end of a core of ferromagnetic material 39a of a coil 39; the terminals 39b, 39c of the coil 39 are

  each connected to a respective input 31a, 31b of the amplifier

  Differential encoder 31. By using a differential amplifier, common mode noise signals are eliminated. The

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  monostable circuit 35 provides a signal 36 whose R value (duration of each rectangular pulse) is constant and therefore

  independent of the frequency F = 1 of this signal 36.

  FIG. 8 shows an exemplary embodiment of the measuring circuit 29 of FIG. 5. This circuit is essentially a peak detector of the filtered signal 40 supplied by the filter 27. The signal is substantially sinusoidal if the bandwidth of the filter 27

  is narrow and if it exists, in the signal 41 provided by the detection

  26, a component at the frequency fc = OF = KN where K is a constant coefficient. The circuit of FIG. 9 comprises (a) a detector circuit 42 receiving, at its input terminal 42a, the filtered signal 40 (b) a peak value storage capacitor 43 connected.

  between the ground 4 and the emitter 44a of a transistor 44 made

  part of the detector circuit 42

  (c) a discharge circuit 45 of the capacitor 43.

  (d) an output amplifier circuit 46 having an input terminal

  46a is connected to the hot spot 43a of the capacitor 43.

  The detector circuit 42 comprises an amplifier

  Rational 47 on which is mounted, in feedback, the base-transmitter circuit of transistor 44 whose collector 44b is connected to a direct voltage source + V. The input 42a is connected to

  the non-inverting input 47% of the operational amplifier 47.

  The discharge circuit 45 comprises a resistor 48 mounted between the point 43a and the ground 4, in series with the emitter-collector circuit of a transistor 49 whose base 49a is connected

  at the output terminal of the circuit 28 so as to receive the signal

  General 36; for this purpose, the output terminal of the circuit 28 is connected to a control terminal 45a of the circuit 45. Resistors

  50, 51 are connected between the base 49a and respectively

  The transistor 49 is selected and arranged to operate as a switch connecting the ground 4 and insulation of this mass the resistor 48, depending on whether

  the signal 36 has the value "l" or the value "0" respectively.

  The circuit 46 is constituted by an amplifier

  52 mounted as a non-inverting, high-current follower amplifier

  input impedance and a current amplifier for a gal-

  vanometer 55 mounted in feedback on the amplifier 52 in series with a resistor 54, a resistor 53 connecting the input

52a to ground 4.

  The operation of the detection device shown

  in Figures 5 to 9 is the following.

  When a periodic disturbance of frequency N (for example an unbalance) appears on the rotating system to be monitored, it causes the presence, in the analog signal 41, of a component at this frequency N. The filter 27 eliminating the other frequency components of the signal 41, the signal 40 collected on the output terminal of this filter is a pure sinusoid of

  frequency, whose effective value can be measured by the

  positive 29. This device 29 measures the peak amplitude of the signal 41 but this signal 41 being a pure sinusoid, this peak value is proportional to the rms value and it will be sufficient to scale the dial of the galvanometer in effective value to obtain this value by simple reading. In fact, the tension appearing at

  point 43a of circuit 29 (Figure 9) is not strictly

  aunt but it has some residual ripple - hum - whose amplitude "a" is made independent of N (ie the frequency of the filtered signal 40) thanks to the

  switching transistor 49, as will be explained later.

  As shown in FIGS. 10a to 10c, the signal 40,

  alternately straightened by the base-transmitter function of the tran-

  sistor 44, is sampled by the capacitor 43 associated with the discharge circuit 45, at the rate of the signal 36. For simplicity, there is shown in FIG. 10c a signal 36 of the same frequency as the signal 40 - in fact, the frequency ( F) of the signal 36 is significantly greater than that (N) of the signal 40, but if the value of the resistor 48 is not too low, the effect of the circuit 45 between two adjacent positive peaks 40a of the signal 40 is the same for two signals 36 of different frequency (F) and the same duty cycle 8F. The discharge time constant of the members 43, 45 is inversely proportional to the frequency N of the signal

  which one wants to measure the amplitude. As a result, the amplifier

  Study "a" is independent of N. The detector 26 may be a detector of a parameter such as acceleration, speed, or

  the position of a point of the casing of the rotating system. This detection

  includes a sensor of this parameter and a differential amplifier receiving the signal of this sensor to amplify this

  signal and eliminate common mode noise.

  According to one variant, the filter of FIG.

  take a sequence of more than two internally-mounted cells

  in series in feedback on the operational amplifier 13a.

  In this case, the amplifier 15b is also mounted as an add-on and each additional integrating cell is connected, by its output, to an input - which is particular to it - of one or the other of the adders according to its rank. in the following, the

  third integrating cell being connected to the second addition-

  neur 15, the fourth, the first adder 13, and so on.

  Of course, in the description given above of

  operation of the detection device, we have only considered

  the existence in the rotating system of a frequency disturbance

  quence N and we have set at least one of the parameters R, C, O, p so that we have f = N. It may be interesting to detect

  harmonics of this disturbance, at frequencies 2N, 3N, ...

  etc. In this case the frequency fc will be set to these values 2N, 3N ...

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Claims (8)

  This is the case in the constitution Jb; x-d t a circuit. flt-p: type with a capacitor   connected between an output terminal and a point with static potential   stabilized, and a resistor connected between an input terminal and one of the terminals of the capacitor, characterized in that   has a switch in series with the resistor, this inter-   switch being controlled by a periodic signal of period   in order, successively, to establish and interrupt the connection, via the resistor, between said input terminal and the capacitor,   depending on the value of the control signal.   2. Cell according to claim 1, characterized in   what the stabilized potential point is the input terminal in-   jug of an operational amplifier on which is mounted,   in feedback, the capacitor.   3. Filter, with controllable cutoff frequency (s),   characterized in that it comprises at least one integrated cell   according to one of claims 1 and 2, and a generator   of periodic control signal, whose output terminal is   connected to the control terminal of the switch of said cell.   4. Low pass filter according to claim 3, characterized   characterized in that it is constituted by an integrator cell provided with a second resistor connected in parallel with the capacitor,   and switching means for establishing or terminating the connection   25 between said second resistor and said capacitor on the   adjacent to the stabilized potential point.   5. Filter according to claim 3, characterized in that it comprises two integrator cells connected in series, in   feedback on a first input of an operational amplifier   a second input is connected to the output of a first integrator cell, via an inverter cell, the second integrator cell being connected, by its output, to said first input of the integrator, adder, whereby a band pass filter is obtained between a third input of the adder and the output of the first integrator cell, a low pass filter between   said third input and the output of the first cell   scratcher, and a high-pass filter between this same third entry l 2458946 and the output of the adder.   6. Filter according to claim 5, characterized in that it comprises a sequence of at least three integrator cells.   series-mounted feedback on the additional amplifier   said first adder, in that the inverting amplifier is an adder-mounted amplifier, and in that each integrator of the sequence is connected by its output to an input of an adder, the next integrator, of following, being connected to the other adder, the first integrator - the one whose input is connected to the output of the first adder - being   connected by its output to the other adder.   7. Application of the filter according to one of the claims   3 to 6 to the realization of a device for measuring the vibrat-   of a rotating system, characterized in that said device comprises: a motion detector of the casing of the rotating system,   a filter according to one of claims 3 to 6, the terminal of which   is connected to the output terminal of the motion detector and   whose control signal generator is a measuring device   frequency of rotation of at least one element of the rotating system and providing a control signal whose frequency is a multiple of this rotation frequency, and a   measuring the amplitude of the signal filtered by the filter.   8. Application according to claim 7, characterized   in that the measuring device is a peak detector, comprising   a signal storage capacitor and a discharge circuit of said capacitor, said circuit comprising a series resistor with a common switch from said control signal for   provide or interrupt the discharge of the capacitor through   resistance, depending on the value of said control signal.