Voltage controlled electronic filter

• US 4,063,450 A
• Filed: 07/02/1976
• Issued: 12/20/1977
• Est. Priority Date: 07/02/1976
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Lyons, Prentice Coleman
• Primary Examiner(s): Myracle, Jerry W.
• Application Number:
  US05/702,316
• Time in Patent Office: 536 Days
• Field of Search: 73/67.2, 73/71.2, 73/116, 328/166, 328/167, 330/109
• US Class Current: 73/579
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence
• CPC Class Codes: H03G 5/16 Automatic control
• CPC Class Codes: H03H 11/1252 Two integrator-loop-filters

Abstract

The response characteristics of an electronic filter are automatically adjusted as a function of the magnitude of an applied DC voltage to permit the same filter to be used for varying applications. Embodiments for varying the center frequency and Q of the filter are disclosed. The filter has particular utility in vibration monitoring systems wherein the center frequency may be selectively set at a value which is characteristic of the frequency of particular vibration signals of interest. In a disclosed vibration monitoring system incorporating the voltage controlled filter of this invention, which is particularly useful for monitoring vibration levels in gas turbine engines, the magnitude of the DC control voltage is varied as a function of gas turbine rotational velocity. In an alternate embodiment of the vibration monitoring system an adjustable feedback circuit is provided which may be set to reduce variations in phase shift as the center frequency of the filter is varied or alternatively to automatically track a particular center frequency.

Claims

1. An electronic filtering system comprising:

an active filtering network having adjustable response characteristics;

means for varying the Q of the filtering network as a function of the magnitude of an applied DC voltage, and

means for maintaining the gain of the filtering network constant as the Q is varied.

2. An electronic filtering system comprising:

an active filtering network having adjustable response characteristics;

means for varying the center frequency of the filtering network as a function of the magnitude of an applied DC voltage;

wherein the filtering network comprises a cascade of two integrators which includes first and second operational amplifiers interconnected by a first resistor, and a third operational amplifier; and

the center frequency varying means comprises a first two input analog multiplier having one input connected to the output of the third operational amplifier, the other input connected to a DC control voltage and an output connected to the input of the first operational amplifier through a second series resistor, and a second two input analog multiplier having one input connected to the output of the second operational amplifier, the other input connected to the DC control voltage and an output connected through a third series resistor to the input of the third operational amplifier.

3. The electronic filtering system of claim 2 further comprising means for varying the Q of the filtering network.

4. The filtering network of claim 3 wherein the Q varying means comprises:

a third two input analog multiplier having one input connected to the DC control voltage through a first voltage dividing means, the other input connected to the output of the first operational amplifier and an output connected through a fourth series resistor to the input of the first operational amplifier, and

a fourth two input analog multiplier having one input connected to the DC control voltage through a second voltage dividing means, the other input for receiving input signals to the filtering network and an output connected through a fifth series resistor to the input of the first operational amplifier.

5. A system for monitoring vibration levels in gas turbine engines comprising:

transducer means for producing AC output signals having a frequency content and amplitude proportional to the velocity of measured vibration levels,

bandpass filtering means having a center frequency which may be varied as a function of an applied DC voltage for receiving the signals output from the transducer means and outputting vibration signals within the filter pass band, and

means for automatically controlling the center frequency of the bandpass filtering means as a function of the rotational velocity of the gas turbine engine.

6. The vibration monitoring system of claim 5 wherein the center frequency control means comprises:

tachometer means for producing an AC signal whose frequency is proportional to the rotational velocity of the gas turbine,

means for converting the AC signal to a DC control voltage having a magnitude proportional to the frequency of the converted AC signal, and

means for applying the control voltage to the bandpass filtering means.

7. The vibration monitoring system of claim 6 wherein the frequency control means further comprises voltage divider means for selectively attenuating the DC control voltage.

8. The vibration monitoring system of claim 6 further comprising:

means for amplifying the AC signals output from the transducer means,

means for integrating the amplified AC signals, and

switch means for alternatively connecting the input of the bandpass filtering means directly to the output of the amplifying means or to the output of the integrator means.

9. The vibration monitoring system of claim 5 further comprising;

variable feedback means for reducing variations in phase shift of the output of the filtering means as its center frequency is varied.

10. The vibration monitoring system of claim 9 wherein the variable feedback means may be set at a value which causes the center frequency of the filtering means to automatically track a predetermined frequency.

11. The vibration monitoring system of claim 9 wherein the variable feedback means comprises:

a 90°

phase shifter having an input connected to the output of the filtering means, and

a two input phase detector having one input connected to the output of the 90°

phase shifter, the other input connected to the output of the transducer means, and an output connected through a variable voltage divider to the voltage control input of the bandpass filtering means.