GB2088047A - Electronic peak averaging circuit for a pyrometer - Google Patents

Abstract

An electronic peak averaging circuit for a pyrometer viewing the surface of turbine blades in a jet engine includes a peak holding circuit 18 which identifies and holds the maximum value of the sensor waveform over a predetermined interval of time. A tracking filter 12 provides a timing signal to a pulse generator 16 that creates control pulses to dump the peak hold unit at the end of each predetermined interval. A sample and hold unit 24 connected to the output of the peak holding unit is enabled by generator 16 just prior to each dump pulse for the peak hold unit so that the output of the sample and hold retains the peak amplitude of the sensor waveform during the prior predetermined interval. A low pass filter 30 integrates the output from unit 24 to form a final output signal which is indicative of the average peak temperature. <IMAGE>

Description

SPECIFICATION Electronic peak averaging circuit for a pyrometer Technical Field This invention relates to a peak averaging circuit for use with a pyrometer, and more particularly, to a peak averaging circuit for measuring the average peak potential of an electrical signal to derive an indication of the average of the maximum or highest temperatures on the surface of turbine blades that rotate at varying velocities.

Background Art Pyrometers are known generally and are thermometers used for several years to measure the temperature of a surface. There are many different types of pyrometers; two of the better known types use an electrical signal or an optical signal.

The accurate measurement of the temperature of a surface is especially important if the surface is the surface of a turbine blade which is used in the first stage of the turbine section of a jet engine. This is because the first stage of the turbine is next to the combustion section and, as such, is subjected to the most extreme temperature of the jet engine.

Thermal stressing is a significant consideration in both the design and operation of a jet engine. Over temperature thermal stressing of the turbine blade can cause deterioration which results at a minimum in increased engine maintenance, or in the extreme, a structural failure of the turbine blade itself. Accordingly, it is important to know the temperature of the hottest surface or surfaces of the blades in the first stage of the turbine because these temperatures often define the maximum operating temperature of the jet engine.

The optical pyrometer has some significant advantages over other types of temperature indicating devices for use in jet engines to measure the temperature of turbine blades. An optical pyrometer is a noncontact device so there is no mechanical contact with the turbine blades that can cause perturbations or other mechanically related degradations of the readings.

An optical head is quite small and can be positioned so that all of the blades on one rotor pass the field of view of the optical head. An optical pyrometer has an extremely fast response characteristic so that even small hot points on the rotating surface of a turbine blade can be identified and profiled. The optical head transmits the radiant energy emitted by the high temperature surface of the turbine blade out of the engine housing by an optical fiber cable. A transducer than converts the optical signal into an electrical signal. As the turbine blades rotate, the surface of each blade passes the optical view area of the pyrometer creating a cyclic analog signal in which the ampitude variation is proportional to the temperature variation of the turbine blades being observed by the optical head of the pyrometer.

The period of the analog signal is related to the rotational velocity of the turbine blades. Because the rotational velocity of the turbine blades changes dramatically during the operation of the jet engine, i.e., a low rotational velocity when the jet engine is at idle, and a high rotational velocity under maximum thrust condition, the period of the analog signal is not constant. An electrical circuit for monitoring the high temperature of the turbine engine must then be able to track or follow this change in periodicity in order that the maximum temperature of each turbine blade in the analog signal is considered in measuring the average peak temperature of the turbine blades.

Disclosure of Invention It is an object of the present invention to provide an electronic peak averaging circuit for use with a pyrometer to measure the average maximum temperature on the surface of a set of rotating turbine blades.

A particular feature of the present invention relates to an electronic circuit which can follow an analog signal whose fundamental frequency varies over a 2 1 range. Accordingly, the circuit can be used to measure the average peak value of an analog signal from a pyrometer, or the like, in which the sensing head of the pyrometer responds to temperature variations on the surface of a turbine blade. Accordingly, as the rotational velocity of the turbine blade changes, the peak averaging circuit of the present invention accurately follows, or tracks, the changes in velocity to provide an accurate measurement of the peak value or maximum temperature, of the surface of each turbine blade.

According to the present invention, an electronic peak averaging circuit for a pyrometer used to measure the temperature on the surface of blades in the first stage of a jet engine turbine provides an output signal which is proportional to the average of the peak or maximum temperature. A peak holding circuit is connected to receive the signal from the sensing head of the pyrometer and, together with a sample and hold unit, are periodically actuated by a control circuit in order to capture the peak or maximum transition of the signal from the sensor head. A control circuit is provided for enabling the peak holding unit and the sample and hold unit at the appropriate time interval to record the maximum peak value. A self-tuning, tracking filter provides an output sinusoid which tracks the changes in periodicity of the signal waveform from the head of the optical pyrometer.

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments and accompanying drawings.

Brief Description of Drawings.

Fig. 1 is a schematic drawing depicting one embodiment of an electronic peak averaging circuit for use with a pyrometer according to the present invention; and Fig. 2 is a drawing depicting the signal waveforms at various points in the schematic drawing of Fig. 1.

Best Mode for Carrying Out the Invention Referring initially to Fig. 1, there is seen one embodiment of an electronic peak averaging circuit according to, the present invention. The circuit is particular well suited for use with an optical pyrometer to measure high temperature surfaces within a jet engine. The optical pyrometer might have one or more sensing heads 10 which would be fixedly mounted in the case or housing of the jet engine to measure the temperature of various engine components at certain critical locations. One such location is the first stage of the turbine which, because of its proximity to the combustion section, tends to be one of the hottest areas in the jet engine.Accordingly, the sensor head 10 of the pyrometer would be mounted in the engine housing immediately adjacent to the rotating blades of the turbine so that the energy radiated from the surface of each turbine blade would impinge the sensor head 10. A fiber cable (not shown), or the like, would normally lead from the location of the sensor head 10 through the engine case to a transducer (also not shown) where the optical signal is proportionally converted to an electrical signal and presented to an input lead 11.

Referring still to Fig. 1 , the electronic peak averaging circuit according to the present invention includes an input lead 11 which receives an electrical signal that is proportional to the radiant energy emitted by the surface of the turbine blade and impinging on the sensor head. A tracking filter 12 is provided and is connected to the input lead 1 1 for tracking the fundamental frequency of the input signal. The output from the tracking filter 12 is a signal which is substantially sinusoidal and has a period that essentially corresponds to that of the input signal. A pulse generator 16 is connected by a line 14 to the tracking filter 12 and uses a sinusoidal signal as a timing signal for the generation of control pulses.

A peak hold device 18 is also connected to receive the input signal on the line 11 and hold the maximum value thereof during an interval of time.

The peak holding device 18 is periodically discharged or dumped by a control signal supplied on the line 20 by the pulse generator 1 6. The output of the peak hold device 1 8 is presented via a line 22 to a sample and hold unit 24 is enabled by a control pulse from the pulse generator 16 to its control terminal on a line 26 and samples the value of the signal at its input. The output of the sample and hold unit 24 is presented on a line 28 to a low pass filter 30 which essentially integrates/averages the signal from the sample and hold circuit. Finally, the output from the peak averaging circuit is available on the line 32 and can be presented to an analog device, such as a meter, or one of the many known digital devices for reading of the average peaking engine temperature. Of course, this signal could also be used as an input to a control circuit for the jet engine.

voltage waveform; peak hold means connected to said input means and activated by control pulses from said timing means for measuring the peak value of said input waveform during a predetermined interval; and sample means connected to said peak hold means and enabled by said control pulses to sample the signal from said peak hold means, and to provide an output signal corresponding to the peak value of said signal received by said input means averaged over several predetermined intervals.

6. A peak averaging circuit according to claim 5, wherein said peak hold means is periodically discharged at predetermined intervals by dump control pulses supplied by said timing means.

7. A peak averaging circuit according to claim 6, wherein said sample means is periodically enabled by sample control pulses from said timing means, each of said sample control pulses occurring just prior to each of said dump control pulses so that the peak value within said predetermined interval is retained.

8. A peak average circuit according to claim 1, further including means connected to the output of said sample means for integrating the output signal from said sample means over a period of time.

In operation, the electronic peak averaging circuit according to the present invention tracks the fundamental periodicity of a signal waveform from an optical pyrometer so that a peak holding circuit can be enabled during the appropriate time interval to ensure that the peak value of the sensed waveform is included in the peak average.

Referring now to Fig. 2 in addition to Fig. 1 , there is seen an illustration of typical waveforms at various points in the schematic of Fig. 1. As turbine blades sequentially pass the sensing head 10 of the pyrometer, a signal waveform 50 is created (Fig. 2A) which is proportional to the radiant energy emitted from the surface of the turbine blades, this radiant energy being proportional to the absolute temperature of the surface. A signal 52 (Fig. 2B) is the output from the self-tracking filter 12, and as can be seen, this waveform has a period z which approximates that of waveform 50 from the sensing head. Using this as a variable timing signal, the pulsing generator 16 creates a series of control pulses, pulse 54 (Fig.

2C), which are presented to the sample and hold unit 24 and a series of control pulses, pulse 56 (Fig. 2D), which are presented to the peak hold unit 18. Each pulse 56 causes the peak holding circuit 18 which is sensing the voltage waveform 50 to dump or discharge for a period essentially corresponding to the width of the control pulse.

The output from the peak hold unit 18 is signal 58 (Fig. 2E) and is periodically dumped to a lower value by each pulse 56. The signal 58 then remains at this voltage level until the magnitude of the input waveform exceeds this voltage level. In other words, the peak holding circuit 18 tracks the increases in input voltage level from the time it was dumped by a dump pulse 56. This then is the input signal supplied to the sample and hold unit 24. The sample and hold unit 24 is enable by each pulse 54 just prior to each pulse 56 for dumping the peak hold unit 18. The maximum voltage level reached during the prior sample period is held during the next sample period. The output from the sample and hold unit 24 is signal 60 (Fig. 2F).

Accordingly, the waveform of the signal 60 corresponds to the peak value of each cycle of the input waveform, which is from the sensing head of the pyrometer. The low pass filter integrates signal 60 to give the average peak value and this signal is available at an output terminal 32 for an analog device, such as a simple dial meter, or for the multitude of known digital devices which would calculate the average peak temperature.

It will be appreciated by those of ordinary skill that other types of integration circuit could be used with the present invention. However, the integration period may vary depending on the particular peak average value of interest. For example, if the average peak value of the first stage of a turbine engine is the measurement of interest, then the integration period would have to be sufficiently long such that a measurement from the surface of each turbine blade in that stage is included. It should be understood that the peak averaging circuit of the present invention can be used with a number of other devices in addition to a pyrometer. In fact, the peak average circuit of the present invention can be used to measure the average peak value of almost any quasi-periodic signal that has a period which changes or varies as a function of time. In order to track to determine peak average of any periodic signal, it is essential that the peak value of such a periodic signal be measured. The present invention follows, or tracks the input signal to ensure all of the peak values are properly included. Another system which could employ a peak averaging circuit is a hydraulic or pneumatic system in which the average peak value of pressure or strain is of interest. Yet another system in which the average peak value of a signal is important is an audio system because of the possibility of overdriving system components.

Although this invention has been shown and described with respect to a preferred embodiment, it will be understood by those skilled in this art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.

Claims (5)

1. A peak averaging circuit for use with a pyrometer to measure the temperature of a surface that has a changeable rotational velocity, comprising: sensor means for responding to energy radiating from said turbine blade, to provide a signal having a waveform related to the absolute temperature of said rotating surface; timing means connected to receive said signal waveform from said sensor means, and for providing control pulses of a fundamental frequency related to the periodicity of said signal from said sensor means; and means connected to receive said signal from said sensor means for measuring the peak amplitude of the waveform of said signal from said sensor means, and for providing an output signal corresponding to the average peak value of said waveform over a predetermined interval.

2. A peak averaging circuit according to claim 1, wherein said timing means include a tracking filter means and a pulse generator means, and wherein said tracking filter means is connected to said sensor means for generating a substantially sinusoidal signal having essentially the same period as the signal from said sensor means, and wherein said pulse generator means utilizes the zero crossings of said sinusoidal signal to generate control signals.

3. A peak averaging circuit according to claim 2, wherein said means for measuring the peak amplitude of said waveform from said sensor means includes a peak hold means and a sample and hold means, and wherein said peak hold means is connected to said pulse generator means, and wherein said peak hold means retains the peak value of the signal at its input until it is periodically discharged by a control pulse supplied by said pulse generator means.

4. A peak averaging circuit according to claim 3, wherein said sample and hold means is periodically actuated by a control pulse from said pulse generator to sample the output from said peak hold means just prior to said peak hold means being discharged.

5. A peak averaging circuit for measuring the average peak value of a signal waveform, comprising: input means for receiving a signal having a waveform with a variable periodicity; timing means connected to said input means for tracking the fundamental frequency of said input voltage waveform and for providing control pulses related to the periodicity of said input