JP2002501619A - Method and apparatus for continuous non-invasive monitoring of noise - Google Patents

Abstract

  (57) [Summary] Preferably, the extra bandwidth of the fiber optic sensor is dedicated to determining the integrity of the sensor. The apparatus preferably comprises means for finding the amplitude of the noise in the selected frequency range, which preferably includes one or more types of signal processors. After appropriately determining the amplitude of the noise from the output of the sensor, it is preferable to compare the calculated amplitude to a predetermined upper and lower noise limit. If the noise amplitude is outside these limits, a flag or interrupt is set to notify the system processor or other monitoring device about the sensor failure.

Description

Description: METHOD AND APPARATUS FOR CONTINUOUSLY NON-INVASIVE MONITORING OF NOISE TECHNICAL FIELD OF THE INVENTION The present invention relates to monitoring devices for sensors, and more particularly, to an apparatus and method for continuously monitoring for possible failures of a fiber optic gyroscope. Background of the Invention Fiber optic gyroscopes (FOGs) with little or no mechanical components have become much used instead of earlier mechanical gyroscopes. Although fiber optic gyroscopes have virtually eliminated the need to monitor for potential failure of unreliable mechanical components, the performance of fiber optic gyroscopes must still be monitored to ensure reliability. Prior art methods of monitoring mechanical gyroscope operation are not effective with modern gyroscope technology and require a method of monitoring the performance of modern fiber optic gyroscopes. Typical ship operators perform complex validity tests to determine if the gyroscope attitude readout is accurate. When performing the validity test, the operator usually checks each time the posture is read out for a large change. This is because, for example, normal posture reading at 0.001 second intervals should not change significantly. To test the performance of the gyroscope, the pilot typically reads and calculates the differential output to determine if a large change has occurred. However, reading the attitude display often requires the use of a computer or calculator for each query to perform a separate, time-consuming analysis. In addition, if the gyroscope fails completely, the monitor often displays zero output. When reading the zero output, the pilot often does not know the critical distinction whether the readout indicates a correctly functioning zero attitude shift or the monitor is malfunctioning. Therefore, there is a need for a failure monitor that does not need to read the attitude display. Fiber optic gyroscopes are generally optical inertial rotation sensors that use the well-known Sagnac effect to detect rotation about an axis. Generally, the FOG activates an interferometer from an external light source and directly measures the phase shift of the lightwave after the light has passed through a closed optical path (optical fiber). As the light wave travels through the optical fiber, the effective sensitivity of the gyroscope increases with multiple turns of the fiber. More specifically, in an interferometer fiber optic gyroscope, an electromagnetic wave (light wave) from a single light source is split and made to travel in opposite directions through a coiled optical fiber, where the pair of waves is Finally, the light enters the photodetector. The relative properties of the beam usually do not change due to potential changes in fiber properties (ie, thermal, mechanical, etc.). This is because, due to the principle of reciprocity, if both beams are subjected to the same environmental change, both beams are affected substantially equally. According to general relativity, when the gyroscope rotates, the effective optical path length of the first light wave generally increases in one rotation direction and decreases in the opposite rotation direction. The second lightwave generally has the opposite effect on the effective optical path length. The effective optical path length difference between a pair of light waves introduces a phase shift (Sagnac effect) between these waves. The longer the length of the coiled optical fiber, the greater the phase shift difference between the two beams. The resulting phase shift usually forms an interference pattern. This interference pattern is detected by an interferometer, which is then used to determine the gyroscope angular velocity. In order to accurately measure the rotational speed, an AC bias (dither) is often introduced mechanically or electro-optically into the light beam, which affects the behavior of the beam. A ship's FOG readout signal generally contains not only inertial speed information (the speed at which the ship is rotating) but also signal components that are directly related to sensor dithering. To obtain accurate results in low noise systems, dither signals are often minimized or reduced. Devices that analyze gyroscope system noise must substantially compensate for the effects of dither. Most current systems for monitoring gyroscope operation modify the gyroscope function non-invasively. Non-intrusive changes in gyroscope functionality usually reduce the effectiveness of the intended operation of the gyroscope. Prior art devices can monitor individual components of the gyroscope, whereas prior art monitors use gyroscope noise (US Pat. Nos. 5,331,404, 5,469,257, 5,416,584) and input signals (US). No. 5,204,631), dither (US Pat. Nos. 5,325,173, 5,331,401 and 5,331,402), phase angle (US Pat. No. 5,347,359), or amplitude (US Pat. No. 5,452,862). Often affects. Further, as described in the above-mentioned patents, prior art devices positively affect the gyroscope signal, but do not monitor gyroscope stability by analyzing gyroscope noise. There is a need for a non-intrusive system for continuously monitoring gyroscope components for failure. Some prior art devices substantially allow the gyroscope to safely start during its operation without continuously monitoring the gyroscope. The primary purpose of these prior art devices is to provide a start-up procedure that substantially minimizes delays during start-up and has minimal adverse effects, but these devices do not monitor the FOG for faults during operation. . If a failure occurs during steady-state operation of the device, i.e. after startup, the monitoring function is generally unavailable. For example, in the case of prior art monitors, the pilot would typically have to turn the power of the aircraft on and off to replay the starting procedure and retest the gyroscope, which is clearly an undesirable choice. US Pat. No. 5,363,194 to KiIlpartrick et al. Discloses a laser gyroscope microprocessor limited to providing start-up control methods and apparatus. U.S. Pat. No. 5,363,194 discloses a system for safely and quickly starting a laser gyroscope. The microprocessor performs tests on the gyroscope and provides a health signal during the timing sequence. If all systems in the gyroscope start correctly, the system will report a healthy state "OK" to the process block. The present invention, when acceptable, performs a built-in test (BIT) function that sets the state of the gyroscope to a healthy state. Each BIT routine indicates the status of a particular component that has been tested by the microprocessor. These built-in test functions include a read intensity monitor reading function, an optical path length inspection function, a control length controller inspection function, a dither error inspection function, a branch current inspection function, a LIM inspection function, It includes a function to check the temperature. These events are all in the gyroscope and are monitored during a certain time frame. At the end of that time frame, a health signal is transmitted. The built-in test function and the self-test function are periodically executed. Further, after each BIT, data is lost as the device interferes with gyroscope function. The system does not continue to monitor the gyroscope after the startup process has been completed. Thus, Killpartrick's devices do not provide continuous monitoring. Many devices non-invasively affect gyroscope function by substantially modifying the gyroscope signal, while other devices non-invasively reduce gyroscope noise. Blake et al., U.S. Pat. No. 5,469,257, discloses a method for reducing noise in an output signal from an optical system. The noise reducer incorporates a device that adjusts the amplitude or phase of the noise indicating signal. The wave emitted from the light source is delayed when it reaches the output of the optical system. Further, the phase adjustment non-invasively affects the phase of the bias modulation signal. There is a need for a system that non-invasively monitors gyroscope signals without interrupting the data acquisition process. Moeller et al., U.S. Pat. No. 5,331,404, discloses a low noise fiber gyroscope system that includes excess noise subtraction. This patent discloses a system and method for non-invasively subtracting excess noise from a sensitive gyroscope system. The resulting signal is polarized, detected and amplified with a further delayed noise signal. By modulating the amplified noise signal with a portion of the amplified gyroscope signal and subtracting the amplitude modulated noise signal from the amplified gyroscope signal to produce a reduced noise gyroscope signal; Excess noise components in the amplified gyroscope signal are reduced. Moeller's device also non-invasively reduces the noise component of the amplified gyroscope signal by amplitude modulating the noise component. Other devices non-invasively introduce or modify various signals of the gyroscope system. No. 5,416,584 to Kay discloses a non-intrusive system that injects sinusoidal noise into the dither of a ring laser gyroscope to prevent dynamic lock-in. Kay's device also non-invasively introduces a frequency bias into the light beam of the ring laser gyroscope. The primary purpose of Kay's device is to reduce lottery in ring laser gyroscopes, not gyroscope monitoring. Ogawa et al., U.S. Pat. No. 5,341,210, discloses a digital ramp phase type interferometric gyroscope. A ramp signal is generated by repeatedly storing step values. A step value is continuously generated corresponding to the input angular velocity until the accumulated value exceeds a certain threshold. The ramp signal is used to modulate the phase of the light beam to cancel the phase difference between the beams. Perform subtraction and comparison steps to add the corrected signal to a reference value to generate a corrected threshold and phase difference. Thus, Ogawa's device corrects several values: threshold and phase differences beyond the non-intrusive monitoring capabilities. The Negishi patent, US Pat. No. 5,285,257, discloses an optical rotation detection device that performs synchronization detection in a phase in which AM noise is minimized. One device modulates the phase of light propagating in the sensing loop, and another device depolarizes the light propagating in the sensing loop. The output signal is further controlled and processed. The signal control / processing means non-invasively controls the phase of the output signal. Hobbs, US Pat. No. 5,204,631, discloses a system and method for automatic thresholding of a signal in the presence of Gaussian noise. A sub-circuit is used to set and adjust the threshold signal based on statistics regarding the input signal and a predetermined acceptable false alarm rate. A second comparator is used that compares the threshold signal with the input signal and outputs a signal corresponding to their difference. The threshold signal is adjusted non-invasively to account for false alarm rates. The frequency of the false alarm rate is converted to a current and an output corresponding to the adjusted threshold is provided. Again, this prior art device changes the gyroscope data, the threshold signal, non-invasively. Summary of the Invention The fault monitor preferably tests the optical and electrical circuits of open-loop and closed-loop fiber optic gyroscopes so that they operate continuously and are transparent to the system in use. For example, the monitor properly reports a failed light source, fiber splice, optical phase modulator, or photodetector assembly. More specifically, fiber optic gyroscopes generally exhibit spectrally and temporally continuous noise at their output. This noise is often present throughout the gyroscope's bandwidth, and if the gyroscope's bandwidth is larger than the bandwidth required to measure its angular input, extra noise is needed to determine the gyroscope's integrity. Can be appropriately allocated to the noise monitor. Preferably, the noise monitor comprises means for determining the amplitude of the noise within the selected frequency range. In a preferred embodiment, a suitable signal processor determines the amplitude of the noise. In operation, the noise monitor preferably subtracts the successive values of the accumulator output from the previous value to form the absolute value of each difference and stores the amplitude sum in an accumulator register. Next, it is preferable to compare the calculated amplitude with predetermined upper and lower noise limits at predetermined time intervals. Accumulated amounts of these out-of-limit noises generally indicate excessively high or excessively low data contingency, and thus indicate a failed gyroscope. If the noise amplitude is outside these limits, a flag preferably notifies the system processor that a gyroscope failure has occurred. The flag preferably generates an interrupt and sends it to the processor, or the flag is periodically polled by the system processor. BRIEF DESCRIPTION OF THE FIGURES Preferred exemplary embodiments of the present invention are described below with reference to the accompanying drawings. In the drawings, the same numbers indicate the same elements. FIG. 1 is a block diagram of an exemplary device for fault monitoring. FIG. 2 is a block diagram of a detailed exemplary device for fault monitoring. FIG. 3 is a schematic graph showing an intensity response curve as a function of input speed for the present invention. FIG. 4a is a block diagram of an exemplary device for an open loop fiber optic gyroscope. FIG. 4b is a block diagram of an exemplary device for a closed loop fiber optic gyroscope. Detailed Description of Preferred Exemplary Embodiments The method and apparatus according to various aspects of the present invention monitor substantially continuously a portion of the noise bandwidth output from the sensor 5 to properly determine the integrity of the fiber optic sensor 5. The fiber optic sensor 5 is a device suitable for detecting a changed signal, including an open loop fiber optic gyroscope and a closed loop fiber optic gyroscope. In a preferred embodiment, sensor 5 is a closed loop fiber optic gyroscope. The method of performing the noise monitoring is described in detail below, but in general, the sum of the input differences of the rotational speed values is compared to a fixed upper limit level 90 and a lower limit level 100 to determine if a fault in the sensor 5 has occurred. Preferably, it is determined whether it is present. Referring briefly to FIG. 1, an exemplary apparatus 1 for noise monitoring according to various aspects of the present invention preferably includes an amplitude detection device 10, a comparison device 20, and an indication device 25. Referring briefly to FIG. 2, it is preferred to compare the speed signal 40 received by the amplitude detection device 10 with the preset limits 90, 100 in the comparison device 20, as described in more detail below. . Preferably, the indicating device 25 is activated when the speed signal 40 is outside the preset limits 90,100. With continued reference to FIG. 2, the amplitude detection device 10 includes a detector, such as a signal processor, capable of calculating the amplitude of a noise signal. An exemplary amplitude detection device 10 according to the present invention preferably includes a photodetector 35, an accumulator 50, a subtractor 60, an absolute value circuit 70, a bit accumulator 80, an accumulator register 85, and a clear circuit 87. . Detector 35 preferably includes a detector, such as a photodiode, capable of detecting an optical signal and converting the signal to a digital word. According to a preferred embodiment of the present invention, detector 35 comprises an Epitax model ETX300T. Accumulator 50 preferably includes a device capable of accumulating signals, such as a gyroscope accumulator. Preferably, the subtractor 60 includes a device capable of subtracting the signal. The magnitude circuit 70 preferably includes a device capable of calculating the magnitude of the signal. Bit accumulator 80 preferably includes a device capable of storing bits of the signal. Accumulator register 85 preferably includes a device that can register signals. The clear circuit 87 preferably includes a device that can clear the accumulator. The aforementioned components of the amplitude detection device 10 may be implemented in the form of a gate array, an application specific integrated circuit (ASIC), or various microprocessors preferably implemented in a microprocessor that algorithmically implements each of the functions discussed above. Includes circuitry. With continued reference to FIG. 2, the comparison device 20 includes a device that can compare the signal to a preset level. An exemplary comparison device 20 according to the present invention includes a comparison device 20 that determines whether the signal 40 exceeds a fixed upper limit level 90 and a lower limit level 100. The limit levels 90, 100 include velocity values at which the level of comparison can be determined, such as a fixed integration rate noise value. With continued reference to FIG. 2, the indicating device 25 preferably includes a device that can notify the system when an event occurs. An exemplary pointing device 25 according to the present invention preferably includes a fault flag 120. In a preferred embodiment, device 1 monitors FOG. This is because, due to the electronics of the FOG, the FOG generally has a high signal resolution, so that a measurably large signal can be extracted from the available bandwidth of the sensor 5. Because of the presence of noise in this large output signal, the fiber optic gyroscope will exhibit spectrally and temporally continuous noise at its output, and therefore use that noise to monitor gyroscope integrity. Can be. This noise is present throughout the gyroscope's bandwidth, so if the gyroscope's bandwidth is greater than the bandwidth required to measure its angular input, extra bandwidth will determine the gyroscope's integrity. Can be devoted to The noise in the output signal generally includes dark current noise (a DC current that does not become dominant in the FOG unless it is at a high temperature where shot noise can occur), background radiation noise (which is not a problem except for satellites), Noise due to the statistical nature of the photodetection process), and thermal noise (noise generated in a load resistor equally positioned between the two leads of the photodiode, which predominates at low optical power). In. Many of the other operations of the gyroscope contribute to gyroscope noise and are optionally used to monitor the gyroscope according to the present invention. For example, optical gyroscopes often include light sources that exhibit "excess" noise, which is white noise (broadband) as a significant noise source for monitoring. Since the amplitude of the electromagnetic wave emitted by the light source changes due to the noise, it is preferable to control the light source noise in the FOG. Therefore, when the amplitude of the electromagnetic wave changes, a clear change occurs in the phase shift between the light waves. Thus, excess noise limits the ultimate sensitivity of the device and saturates rather than improves the performance of the gyroscope system as the source power increases. A broadband light source is required in a gyroscope for several reasons, including Rayleigh backscattering and the Kerr effect. Broadband light sources have a number of different frequencies that optically interfere with each other (cause beats) and therefore generate relative intensity noise (white band noise), which is a significant noise source for monitoring. Excess noise often occurs due to intensity fluctuations in a broadband light source. However, there is a need for a broadband light source with a stable spectrum in a fiber optic gyroscope to minimize zero rotation drift due to coherent Rayleigh backscatter noise and Kerr effect. For example, intensity noise generally occurs in broadband light sources. This is because the illuminants in the light source emit light waves of optical frequency, which mix with each other to leave relatively low frequency intensity fluctuations. Alternatively, excess noise (or relative intensity noise) in the system may include flicker noise (1 / f noise) or current noise resulting from electrical circuit and carrier density variations of the light source. Noise in the gyroscope is also increased by the lack of bias stability. This often results in polarization and backscatter errors, and is also an incorrect indication of rotational speed. Therefore, high performance gyroscopes generally require high bias stability (characterized by the 1 / f power spectrum). For example, the attitude nose reference system requires a bias accuracy of 1 to 10 degrees, the optimal stability is defined by a bias accuracy of 0.01 to 0.001 degrees and inertial navigation, and the aiming satellite is 0.0001 to 0 degrees. 0.001 degree bias accuracy is required, and undersea navigation requires a bias accuracy of 0.00001 degree or more. Referring to FIG. 2, the monitoring device 10 is preferably configured with means for finding the amplitude of noise within a selected frequency range. This means preferably comprises a suitable signal processor, which preferably comprises semiconductor processing electronics with digital signal processing integrated circuits. Alternatively, it is preferable to determine the amplitude of the noise using an analog circuit. More specifically, it is preferable to convert the digital output of the optical gyroscope to an analog voltage, and then to pass it through a bandpass filter of a selected noise bandwidth. In this way, the measured value of the filter output instead of the amplitude is used for comparison. Thus, analog filtering is generally a simpler method for detector 35 with its own analog output. Referring now to FIG. 3, an intensity response curve 200 as a function of input rotational speed 40 for the present invention is suitably depicted in a schematic graph. Preferably, the y-axis represents photodiode light intensity 205 and the x-axis represents input rotation speed 40 so that the phase shift varies linearly with input rotation speed 40. However, the gyroscope output is not linear. This is because the detector output is a cosine function of the phase difference between the two beams, and thus has a minimum 210 and a maximum 220. A properly operating gyroscope will generally exhibit predictable noise amplitude within definable upper and lower limits. However, the frequency range in which it is preferable to monitor noise should not be affected by gyroscope input motion. To monitor the noise amplitude, it is preferable to select a frequency range at or near the upper end of the gyroscope's inherent bandwidth. For fiber optic gyroscopes, the bandwidth is determined by the electronics design and selected to include the high end frequency band of the response spectrum that is outside the frequency range of virtually all possible mechanical inputs Is preferred. With continued reference to FIG. 3, the detector current is preferably insensitive to small phase shift changes near the quiescent rotational speed 225 where the maximum intensity 205 is. When the input rotational speed 40 occurs, the intensity 205 decreases. Because the slope of the response curve is substantially minimal within region 250, the change in intensity 205 is minimal for input rotational speed 40 near zero input rotational speed 225. Similarly, the current of the detector 35 is insensitive to the input rotational speed 40 corresponding to the other minima 210 and maxima 220 of the response curve 200. Also, distinguishing between the input rotational speeds 40 in the two different directions is difficult due to the symmetry of the response curve 200. Injecting a bias into the lightwave (bias modulation) causes the gyroscope to operate near the finite slope 240 of the response curve 200. Preferably, the demodulator system 400 of FIGS. 4a and 4b is used to modulate the FOG with a square wave, preferably alternating between the maximum slopes 240 of the response curve 200. Further, the gyroscope input rotational speeds 40 are preferably symmetrically spaced near the operating point, thereby increasing the sensitivity of the detector 35. Therefore, the high sensitivity is preferably the result of a gyroscope operating near the finite slope 240 of the response curve 200. More specifically, referring to FIG. 4a, a method for determining a rotational speed output 40 from an open loop fiber optic gyroscope is schematically illustrated. Light from light source 405 is split by a conventional beam splitter such that the two beams enter the first end of fiber coil 410 and the two beams travel in opposite directions. When the two beams exit the second end of the fiber coil 410, a modulator 415 at the second end of the fiber coil 410 modulates the optical phase shift between the two beams, then The beams recombine at photodetector 420. The modulator 415, together with the bias modulation generator 440, modulates the light beam by generating a bias modulation signal at a selected frequency. This frequency is preferably related to the length of the fiber coil 410. For example, a system having a 1000 m long fiber coil 410 would add 100 kHz. Further, in a preferred embodiment, bias modulation generator 440 generates a constant current in the form of a square wave having a peak-to-peak signal. After the two modulated beams recombine, the beam strikes photodetector 420, which generates an AC output current, and thus the intensity of the AC output current is the intensity of the light beam incident on photodetector 420. based on. The output current from photodetector 420 is amplified in preamplifier 425 and then enters demodulator 430. The gyroscope direction and rotation determination is made by demodulator 430, ie, using phase sensitive demodulation. Phase sensing demodulation is a procedure that reads the amplitude of the sine function of the AC voltage along with the phase of the AC voltage. If the AC voltage is in phase or out of phase with respect to a given reference signal, the phase of the AC voltage needs to be determined. In the preferred embodiment, the predetermined reference is an output signal directly from bias modulation generator 440. Thus, by comparing the modulated amplitude and phase of the AC voltage with the amplitude and phase of the reference bias modulation signal, respectively, the degree and direction of rotation is easily determined. Referring to FIG. 4b, a method for determining the rotational speed output 40 from a closed loop fiber optic gyroscope is schematically illustrated. The same components and procedures described above for the open loop fiber optic gyroscope are included in the closed loop fiber optic gyroscope of FIG. 4b. However, the closed loop fiber optic gyroscope of FIG. 4b adds additional components, a first integrator 450, a second integrator 460, and a feedback modulation generator 470. Operationally, referring to FIG. 4b, the modulator signal from demodulator 430 enters first integrator 450 and then to second integrator 460 and a feedback modulation generator, thereby providing steady state feedback modulation. Waveforms occur. Finally, the ramp feedback modulation waveform enters the modulator with the signal from the bias modulation generator. In a preferred embodiment, the feedback modulation waveform is a variable representing a ramp "saw" voltage waveform. However, the ramp does not increase indefinitely since the waveform resets itself every two. Fortunately, a reset of two is relatively equal to no reset at all, and the system goes unnoticed since after each reset the system starts at the beginning of a new cycle. Since the relationship between the voltage and the degree of the phase shift is constant, the amplitude of the waveform measured by the optical phase shift is generally 2. The frequency of the ramp waveform before resetting is a measure of the input speed. In a preferred embodiment, the ramp voltage waveform is a serrodyne ramp. In an open loop system (FIG. 4a), the output of demodulator 430 will generally deviate from zero (eg, become slightly positive). However, in a closed loop system (FIG. 4b), the feedback modulation generator 470 generates a ramp feedback modulation waveform in response to a slight increase in the output of the demodulator 430, and the demodulator process described above. The ramp feedback modulation waveform is sent to modulator 415 until the output of 430 goes to zero, in other words, to a steady state. If the output of the demodulator 430 is zero, the input to the first integrator 450 becomes zero, so that the first integrator 450 outputs a steady finite digital number. The output of the first integrator 450 is a constant digital number, and thus the output of the second integrator 460 is a ramp since the time integral of the constant is a ramp. Thus, the finite digital number is the rotational speed output 40 of the closed loop FOG. For example, if the gyroscope is undergoing a constant rotational speed of about 10 degrees / second, a steady state exists. In a preferred embodiment, modulator 415, demodulator 430, bias modulation generator 440, first integrator 450, second integrator 460, and feedback modulation generator 470 are a gate array, application specific integration. Suitably, it includes various circuits implemented in the form of circuits (ASICs) or, preferably, microprocessors that algorithmically implement each of the functions discussed above. The photodetector 420 preferably includes a detector that can detect an optical signal and convert the signal to an analog circuit, such as a photodiode photodetector. According to a preferred embodiment of the present invention, photodetector 420 includes an Epitax model ETX300T. Further, in a preferred embodiment, a known preamplifier 425 is incorporated after the photodetector 420 in demodulator system 400 and before demodulator 430. Referring to FIG. 2, a rotational speed signal 40, preferably in the form of a digital word that is at least 8 bits wide, is preferably sent to a gyroscope accumulator 50, which causes the gyroscope accumulator 50 to It is preferable to store words. The higher bits representing the greater velocity change are preferably substantially ignored by the gyroscope accumulator 50 since the velocity change is minimal. Preferably, the subtractor 60 and the absolute value circuit 70 each subtract successive speed values of the output of the accumulator 50 from each other, and preferably form the absolute value of each difference. Preferably, bit accumulator 80 stores the sum of the speed value differences in accumulator register 85. The data in accumulator register 85 is preferably sent to comparison device 20. The comparison device 20 compares the data from the accumulator register 85 at fixed time intervals with a fixed upper boundary level 90 and a lower boundary level 100 (fixed integration rate noise value). The clear circuit 87 preferably clears the bit accumulator 80 about every 100 milliseconds based on the monitor update clock 110 to account for other updates and new comparisons based on the new speed signal 40. Further, the clear circuit 87 preferably determines the frequency of failure analysis and possible future reporting. It is preferred that the accumulation of noise at the critical levels 90, 100 indicates a high or low signal contingency, and thus indicates a failed gyroscope. If the noise amplitude is outside these limits, a signal is preferably sent to the indicating device 25. The pointing device 25 preferably includes a gyroscope fault flag 120 that notifies a system processor that a gyroscope fault has occurred. The system processor preferably generates an interrupt in software. The flag 120 preferably generates an interrupt to the processor, or alternatively, the flag 120 is periodically polled by the system processor. As mentioned above, the noise monitor 1 operates substantially continuously and is transparent to the system in use. This is because monitoring is preferably performed in a frequency domain that is not affected by external variables. Thus, since the present invention analyzes the sensor noise and not the signal, it is possible to monitor the integrity of the sensor 5 with a measurable noise amplitude and a definable output noise spectrum. In a preferred embodiment, by monitoring the noise, the noise monitor 1 allows the light of the fiber optic gyroscope to include, among other things, a failed light source, fiber splice, fiber coupler, optical phase modulator, photodetector assembly, etc. It is preferred to test circuits as well as electronic circuits. More specifically, dimming the light source generally reduces noise, since noise is approximately proportional to optical power. Thus, modern light sources are typically subject to larger noise variations, thus simplifying detection of altered noise indicative of a failed gyroscope. Further, a failed splice often results in a loss of noise detected by the present invention. Darkening an integrated optical chip or fiber generally results in less light to the photodiode, resulting in a significant loss of noise. Also, if the phase modulator is unable to perform its intended function due to broken electrode wires and / or similar failures, the noise value will be altered, and thus, if the photodiode malfunctions, the electronic amplifier will be substantially disconnected. You will receive different (generally more) noise. Also, if the associated electronics are unable to generate the proper bias modulation amplitude, the noise will generally be higher or lower. Thus, monitoring noise is a fairly effective and useful tool for determining the integrity of a fiber optic gyroscope. It will be apparent to those skilled in the art that the above detailed description of the preferred embodiment of the invention represents a method and apparatus for continuous noise monitoring that falls within the scope and spirit of the invention. Further, those skilled in the art will appreciate that various modifications and changes can be made without departing from the scope and spirit of the invention. For example, while the invention has been described with reference to a fiber optic gyroscope, the invention applies to any sensing device. Those skilled in the art will appreciate that the present invention is not limited to the details shown herein, but is claimed in any form or modification that falls within the scope of the appended claims. Therefore, the scope of the invention is set forth in the following claims.

Claims (1)

[Claims] 1. A device for continuously monitoring sensor failures,   An amplitude detection device for detecting the amplitude of a signal containing data;   A comparison device communicating with the amplitude detection device;   An apparatus comprising: an indication device in communication with the comparison device. 2. The apparatus of claim 1, wherein said sensor is a fiber optic sensor. 3. The apparatus of claim 1, wherein said sensor is a closed loop fiber optic sensor. 4. The amplitude detection device,   A detector for providing the data;   An means for communicating with the detector and storing the data provided by the detector; An accumulator,   A subtractor that communicates with the accumulator and subtracts the data continuously;   An absolute value circuit that communicates with the accumulator and calculates an absolute value of the data;   In communication with the absolute value circuit and provided by the detector and the absolute value circuit A bit accumulator for storing the data,   Communicates with the bit accumulator and by the bit accumulator An accumulator register for recording the accumulation of the supplied data;   Communicate with the bit accumulator and cycle the bit accumulator 2. The apparatus of claim 1, further comprising: a clear circuit for clearing. 5. The comparison device includes a fixed upper limit level and a fixed lower limit level. The comparison device stores the accumulator register at the critical level. The device of claim 1, wherein the device is compared to: 6. The indicating device stores the data in the accumulator register as the A contract that includes a gyroscope fault flag to signal when it is outside the critical level An apparatus according to claim 1. 7. The amplitude detection device configured to determine a direction and rotation of the sensor; The apparatus of claim 1, further comprising a demodulation device in communication with the chair. 8. The demodulation device,   Modulation configured to modulate the optical phase shift of waves propagating in opposite directions Vessels,   A photodetector configured to generate an AC output voltage and in communication with the modulator;   The photodetector configured to read the amplitude and phase of the AC output voltage; A demodulator communicating with the   Configured to generate a constant voltage and communicate with the modulator and the demodulator. And a bias modulation generator. 9. A first integrator;   A second integrator in communication with the first integrator;   A second integrator configured to generate a feedback modulation waveform; 9. A feedback modulation generator in communication with said modulator. 3. The demodulation device according to claim 1. 10. The feedback modulation waveform is used to reset the lamp 10. The device of claim 9, comprising a pressure waveform. 11. A method for continuously monitoring sensor failures,   Providing an amplitude detection device for detecting the amplitude of a signal containing data When,   Providing a comparison device in communication with the amplitude detection device;   Providing an indicating device that communicates with the comparison device;   Indicating a failure. 12. The method of claim 11, wherein the sensor is a fiber optic sensor. 13. The method of claim 11, wherein the sensor is a closed loop fiber optic sensor. . 14． The step of providing an amplitude detection device,   Providing a detector that provides the data;   Providing an accumulator in communication with the detector;   Storing the data provided by the detector;   Providing a subtractor in communication with the accumulator;   Subtracting successive data;   Providing an absolute value circuit in communication with the accumulator;   Calculating the absolute value of the data;   Providing a bit accumulator in communication with the absolute value circuit;   A switch for storing the data supplied by the subtractor and the absolute value circuit; Tep,   Providing an accumulator register in communication with the bit accumulator; Tep,   Recording the accumulation of the data provided by the bit accumulator Steps to   Providing a clear circuit in communication with the bit accumulator;   Periodically tagging the bit accumulator. 12. The method according to claim 11. 15. The step of providing the comparison device comprises a fixed upper limit level and Providing a fixed lower limit level, wherein the comparing device is provided. Comparing the accumulator register with the limit level The method of claim 11, comprising steps. 16. Providing the indicating device comprises providing a gyroscope failure flag Providing the gyroscope failure flag. The data in the accumulator register is outside the limit level The method of claim 11, comprising the step of notifying when. 17． Determining the direction and rotation of the sensor using a demodulation device And a communication link between the demodulation device and the amplitude detection device. 12. The method of claim 11, wherein the method comprises providing 18. Determining the direction and rotation of the sensor comprises:   Modulating the optical phase shift of a counterpropagating wave using a modulator When,   Generating an AC output voltage;   Reading the amplitude and phase of the AC output voltage using a demodulator; ,   Generating a constant voltage and sending it to a demodulator and said modulator 18. The method of claim 17, wherein 19. The step of determining the direction and rotation of the sensor includes feedback Generating a modulated waveform and sending the waveform to the modulator. The method according to claim 17. 20. The feedback modulation waveform is used to reset the lamp 18. The method according to claim 17, comprising a pressure waveform.