Patent Publication Number: US-6220098-B1

Title: Multiple sensor ultrasonic monitoring device

Description:
This application is a continuation of application Ser. No. 09/073,564 filed May 6, 1998, now abandoned. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     In general, the present invention relates to a device for detecting and monitoring ultrasonic sound waves. In particular, the present invention relates to a portable ultrasonic monitoring instrument that utilizes multiple sensors which can be interchangeably installed into a sensor socket to obtain measurements such as ultrasonic sound wave strength and surface temperature that are useful in detecting machinery defects and equipment failures. 
     2. Background of the Invention 
     The normal frequency range for human hearing is roughly 20 to 20,000 hertz. Ultrasonic sound waves are sound waves that are above the range of human hearing and, thus, have a frequency above about 20,000 hertz. Any frequency above 20,000 hertz may be considered ultrasonic. Most industrial processes, including almost all sources of friction, create some ultrasonic noise. For example, leaks in pipes, machinery defects and electrical arcing produce ultrasonic sound waves that have a frequency that is too high for the human ear to detect. In the past, analog ultrasonic sensors have been used in industrial settings to sense these ultrasonic sound waves. To monitor the ultrasonic sound waves produced by operating machinery, an operator would use an ultrasonic sensor to obtain a reading indicating the strength of the ultrasonic sound waves near the machine. If the ultrasonic sound levels generated by one machine were larger than those produced by another similar machine, the operator would investigate further to determine if a problem existed with the noisy machine. If the ultrasonic sound levels were approximately equal to those produced by a properly functioning machine, the operator would assume the machine was properly functioning and simply proceed to the next machine. Some of the prior art ultrasonic sensors used to monitor machines were semi-permanently mounted on individual machines so that ultrasonic readings could be obtained by simply checking the output of the ultrasonic sensors. However, other ultrasonic detectors were portable to allow the operator to monitor many machines. These portable ultrasonic detectors were especially useful in locating small leaks in pipes carrying pressurized gasses. Because ultrasonic sound waves attenuate very rapidly, the location of the sound waves is usually the location of the leak. Therefore, in order to locate a leak, the user simply moved the ultrasonic detector over the surface until the strength of the ultrasonic sound waves rapidly increased. The user then investigated further by placing soapy water on the location where it was suspected that there was a leak. If a leak was present, bubbles would form in the soapy water where the gas was escaping. 
     These analog ultrasonic instruments suffer from many drawbacks. For example, the analog instruments do not provide a quantitatively referenced power level of the signal to the user. Instead, the analog ultrasonic units simply provide a relative indication of the ultrasonic sound waves&#39; strength in one location compared to another location. Typically, this information is provided to the user by a needle on a dial with an adjustable volume. The volume is set so that the needle is at a reference point when an ultrasonic measurement is taken in a particular location. If the needle rises above that point when a reading is taken in another location, the ultrasonic noise level is higher at the second location than the reference point and vice versa This is undesirable because it makes it difficult to compare readings taken at one point in time to readings taken at a later point in time. Also, prior art analog instruments did not employ analog to digital converters or microprocessors, making it difficult for them to perform advanced signal analysis techniques on the ultrasonic electrical signals. 
     SUMMARY OF THE INVENTION 
     The present invention solves the foregoing problems by providing an automated ultrasonic monitoring system that utilizes multiple sensors to detect ultrasonic sound waves. The sensors can be removably installed in a sensor socket. Each sensor contains encoded identification information that allows the ultrasonic monitoring system to recognize the type of sensor installed in the socket and configure itself to operate with the sensor. This ability to recognize new sensors allows the ultrasonic monitoring system to be upgraded by simply developing new sensors and installing new firmware to identify the new sensors. Thus, the present invention is a substantial improvement over the prior art. 
     In accordance with the present invention, a portable ultrasonic sound and temperature detection and analysis device for measuring surface temperatures and detecting ultrasonic sounds produced by sources such as leaks in pipes, arcing, electrical corona and machinery defects is provided. The ultrasonic device comprises an elongate housing for enclosing the ultrasonic device. The elongate housing further has a grip that is designed to provide a handle that allows a user to carry and point the ultrasonic device like a pistol. A barrel shaped portion is attached to the grip at one end. A trigger which is used to control the functioning of the ultrasonic device is located at the junction of the barrel shaped portion and the grip. 
     The invention uses a set of sensors to produce ultrasonic electrical signals. The set of sensors includes at least a temperature sensor, an ultrasonic sensor, and a combination temperature and ultrasonic sensor. A plurality of electrical contact pads are located on a cylindrical base portion of each sensor in the set of sensors. Identification and configuration information concerning the type of sensor is encoded on each sensor in the set of sensors. An identification circuit receives and analyzes the identification and configuration information from the sensor installed in the sensor socket and configures the ultrasonic monitoring device to operate with the sensor installed in the sensor socket. The sensor socket is located in the barrel shaped portion of the ultrasonic device and is designed to interchangeably receive a sensor from the set of sensors. The sensor socket has a cylindrical shaped cavity with walls and a bottom portion for receiving the sensor from the set of sensors. A set of pins located in the bottom portion of the sensor socket provide electrical contacts between the plurality of electrical contacts on the sensor installed in the sensor socket and the ultrasonic device. A pair of spaced apart L-shaped grooves are located in the walls of the cylindrical shaped cavity. Each of the L-shaped grooves has an open receiving portion that begins at the rim of the cylindrical shaped cavity and extends a distance down the cavity walls to an ending position and a leg portion that extends perpendicularly from the ending position of the open receiving portion. A pair of protrusions are fixedly attached to the sides of each of the sensors in the set of sensors. The protrusions are shaped and positioned to be received in the L-shaped grooves in a manner that removably secures the sensor in the sensor socket. Installation guide means prevent a sensor from the set of sensors from being improperly installed in the sensor socket. Focusing means may be used to focus the area from which the sensors can receive ultrasonic vibrations. 
     The ultrasonic monitoring device is preferably powered by a rechargeable power supply located in the grip of the elongate housing that provides a power supply voltage and a ground voltage to the ultrasonic device. A battery charger jack located underneath the barrel shaped portion of the elongate housing receives a voltage that is used to recharge the rechargeable power supply. 
     The present invention further includes a variable frequency sine wave oscillator that produces local oscillator frequency signals. A mixer receives the ultrasonic electrical signals from the sensor installed in the sensor socket and the local oscillator frequency signals from the variable frequency sine wave oscillator and heterodynes the ultrasonic electrical signals to produce audible frequency range signals that correspond to the ultrasonic electrical signals but are in the audible frequency range of a human being. A low pass filter receives the audible frequency range signals from the mixer and removes any above audible frequency range signals in the audible frequency range signals received from the mixer. A headphone jack located on the base of the grip receives the audible frequency range signals from the low pass filter. A pair of headphones have a headphone plug that receives the audible frequency range signals from the headphone jack when the headphone plug is inserted into the headphone jack and broadcasts the audible frequency range signals so that they can be heard by a user of the ultrasonic device. 
     Additional features of the present invention include a temperature sense circuit that supplies a constant current to a sensor installed in the sensor socket. A temperature signal is produced that corresponds to the temperature sensed by the installed sensor. The temperature signal is supplied to a microprocessor which interprets the temperature signal as a temperature. A display is provided that displays the temperature value to the operator of the ultrasonic monitoring device. A communications port allows the ultrasonic monitoring device to communicate the temperature and other sensed values to an external device. 
     Thus, the present invention overcomes the problems associated with single sensor prior art devices. The provision of sensor socket adapted to interchangeably receive a plurality of sensors allows one ultrasonic device to be configured to perform a wide variety of monitoring tasks. Sensors tuned to receive ultrasonic sound waves of different frequencies can be installed in the socket without requiring extensive modifications. In addition, the provision of a combination temperature and ultrasonic sensor allows multiple measurements to be taken simultaneously. 
     In a particularly preferred embodiment of the present invention, the sensor socket is a cylindrical shaped cavity having walls and a bottom portion for receiving a sensor from a set of sensors. A set of pins located in the bottom portion of the sensor socket provide electrical contacts between the plurality of electrical contacts on the sensor installed in the sensor socket and the ultrasonic monitoring device. A pair of spaced apart L-shaped grooves are located in the walls of the cylindrical shaped cavity. Each of the L-shaped grooves has an open receiving portion that begins at the rim of the cylindrical shaped cavity and extends a distance down the cavity walls to an ending position and a leg portion that extends perpendicularly from the ending position of the open receiving portion. A pair of protrusions are fixedly attached to the sides of each of the sensors in the set of sensors wherein the protrusions are shaped and positioned to be received in the L-shaped grooves in a manner that removably secures the sensor in the sensor socket. The open receiving portions of the L-shaped grooves are positioned so that the sensors will always be installed in the socket with the same orientation. 
     In further accordance with the particularly preferred embodiment discussed above, output means output properties of the ultrasonic electrical signals and identification information concerning the sensor installed in the sensor socket. One of the sensors in the set of sensors is an ultrasonic waveguide probe that senses ultrasonic vibrations by being placed in contact with the object producing the ultrasonic vibrations and one of the sensors is an airborne ultrasonic sensor that senses ultrasonic vibrations being produced by an object without coming into contact with the object. The ultrasonic sensors have a piezoelectric element for converting ultrasonic vibrations into ultrasonic electrical signals corresponding to the ultrasonic vibrations. A cone may be fit over a sensor in the set of sensors as needed to focus the area in which the sensor detects ultrasonic sound waves. Preferably, at least one ultrasonic sensor is substantially resonant at 40 kHz. However, the present invention also comprehends an ultrasonic sensor that has a resonant frequency that can be adjusted to one of a plurality of resonant frequencies. Such an ultrasonic sensor includes a tuneable inductive and capacitive circuit having an adjustable resonant frequency. 
     Also in accordance with the present invention, analysis means perform time and frequency domain waveform analysis on the ultrasonic electrical signals. This analysis mainly consist of digitally performing fast Fourier transforms on the signals to produce frequency spectrums. Regions of the frequency spectrum are then examined to locate peaks and patterns occurring at frequencies that would tend to indicate a machinery defect. The exact frequencies would depend upon the speed at which the particular machine was operating. This is the type of machine specific data that would be included in the configuration information provided to the ultrasonic sensing device. Alarm means are used to inform the operator of the device when a property of an ultrasonic signal exceeds a user selected threshold value. 
     An especially preferred embodiment of the present invention further provides a combined ultrasonic sound wave and temperature sensor. A housing encloses the ultrasonic sound wave and temperature sensor. An ultrasonic sensor attached to the housing senses ultrasonic vibrations produced by an object and a temperature sensing means measures the surface temperature of an object. The temperature sensing means has a contact tip constructed out of a material having a high thermal and ultrasonic conductivity and a temperature sensing element that is constructed out of a material with a resistance that is highly dependent upon the temperature of the material. An attachment means of high thermal conductivity and low electrical conductivity couples the temperature sensing element to the contact tip. In an alternative embodiment, the temperature sensor may be a thermocouple temperature sensor. The temperature sensing means is coaxially mounted inside the ultrasonic waveguide probe. An insulating bushing is mounted inside the ultrasonic wave guide probe so that the insulating bushing surrounds the contact tip of the temperature sensing means. In an especially preferred embodiment, the insulating bushing is constructed out of Dupont Vespel. The materials for the contact tip and the temperature sensing element are selected to minimize the intrinsic thermal time constant of the temperature probe. 
    
    
     Other objects, features and advantages of the present invention will become apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings below, like reference characters refer to like parts throughout the several views, and wherein: 
     FIG. 1 is a perspective view of an operator using the ultrasonic monitoring system of the present invention; 
     FIG. 2 is a side view of the elongate housing that shows the locations of the main internal components; 
     FIG. 3 is a front view of the elongate housing that shows the bottom of the sensor socket; 
     FIG. 4 is a bottom view of the barrel shaped portion of the elongate housing that shows the location of the input and output ports. 
     FIG. 5 is a bottom view of the grip portion of the elongate housing showing the headphone jack; 
     FIG. 6 is a rear view of the elongate housing that shows the display and user input keys; 
     FIG. 7 a  is a block diagram of the electronics contained in the elongate housing; 
     FIG. 7 b  is a block diagram of an embodiment of a received signal strength indicator; 
     FIGS. 8 a  and  8   b  are pictorial representations of a preferred sensor socket; 
     FIGS. 9 a ,  9   b , and  9   c  are pictorial representations of an airborne sensor; 
     FIGS. 10 a ,  10   b ,  10   c , and  10   d  are pictorial representations of a contact sensor; 
     FIG. 11 is a pictorial representation of a focusing cone; 
     FIG. 12 is a pictorial representation of a method for using the ultrasonic transmitter to locate a hole in a pipe; and 
     FIG. 13 is a flow chart outlining a route based method of monitoring equipment using the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     The ultrasonic monitoring system of the present invention effectively locates leaks of air, steam, or other gases from pressurized systems as well as arching and electrical corona, which may produce ultrasonic sounds. Furthermore, the ultrasonic monitoring system can also diagnose and analyze steam trap operation, bearing and gear defects, cavitation and surging in pumps and compressors, lubrication problems in dynamic equipment, valve operation, steam lines, and piston friction and detonation problems in reciprocating equipment. 
     Referring now to FIG. 1, an especially preferred ultrasonic monitoring system  10  for detecting and monitoring ultrasonic sound waves  12  is shown. The ultrasonic sound waves  12  are emanating from the intersection  14  of two abutting pipes  16  and  18 . In the case of leak detection, the ultrasonic monitoring system  10  is principally used by the operator  20  to determine the location from which the ultrasonic sound waves  12  are emanating. The ultrasonic monitoring system  10  consists of an ultrasonic sensor  22  mounted in a portable elongate housing  24 . In operation, the elongate housing  24  is held by the operator  20  and pointed toward a machine or device that might contain a leak or defect that is radiating ultrasonic sound waves  12 . A pair of headphones  26  are worn by the operator  20  and attached to the elongate housing  24  via a cord  28 . The operator  20  of the ultrasonic monitoring system  10  receives an audible signal the volume of which indicates the relative strength of the ultrasonic sound waves  12  being received by the sensor  22  located in the barrel of the elongate housing  24  through the pair of headphones  26 . When the elongate housing  24  and the sensor  22  are pointed away from the source  14  of the ultrasonic sound waves  12 , the strength of the ultrasonic sound waves  12  detected by the sensor  22  decreases. When the elongate housing  24  and the sensor  22  are pointed toward the source  14  of the ultrasonic sound waves  12 , the strength of the ultrasonic sound waves  12  detected by the sensor  22  increases. This increase and decrease in the detected ultrasonic sound wave strength can be audibly represented in a variety of fashions. For example, a rise in the volume of a tone produced by the ultrasonic monitoring system  10  could indicate the detected ultrasonic sound waves are growing stronger and a fall in the volume of the tone could indicate the sound waves are growing weaker. A rise and fall in the pitch of the tone could also indicate a respective rise and fall in the strength of the detected ultrasonic sound waves. Alternatively, a Geiger counter type clicking would also serve the function of indicating the strength of the detected sound waves to the user  20  of the ultrasonic monitoring system  10 . However, in a most preferred embodiment, the ultrasonic sound waves  12  received by the sensor  22  are heterodyned to produce related electrical signals that have a frequency in the audible range of humans. These related signals have many of the distinctive properties of the ultrasonic sound waves  12  from which they were produced. Providing these related electrical signals to the headphones  26  allows the operator  20  to identify the type of noise source radiating the ultrasonic sound waves  12  by listening to the distinctive noise signals created by different types of ultrasonic sound wave sources. 
     The ultrasonic sound waves  12  received by the sensor  22 , or the data derived from the ultrasonic electrical signals produced by the sensor  22 , are preferably stored in a microprocessor based system  32 , which is releasably secured to the operator  20 . The microprocessor based system  32  is used to store and analyze the data collected by the ultrasonic monitoring system  10 , provide testing information to the operator  20  and prompt the operator  20  to take measurements from particular locations. As discussed in greater detail below, the microprocessor based system  32  in a preferred embodiment is a portable personal computer or personal data assistant. The microprocessor based system  32  is secured to the operator  20  via a utility belt  30 . The utility belt  30  also has a holster for receiving the elongate housing  24 , pockets for accessories such as small tools, tags, survey tape and soap solutions, and an ultrasonic sound wave transmitter and charger  34 . 
     The elongate housing  24  contains many of the components needed to implement an ultrasonic monitoring device  10  in accordance with the present invention. The preferred internal location of these components inside the elongate housing  24  is shown in FIG. 2. A sensor socket  36  is located in the barrel portion  38  of the elongate housing  24 . The sensor socket  36  is designed to receive a variety of different sensors  22 . When a sensor  22  is installed in the sensor socket  36 , the sensor socket  36  provides electrical contact between the installed sensor  22  and a microprocessor based control circuit  40  also located in the barrel portion  38  of the elongate housing  24 . 
     As shown in FIG. 3, the electrical contacts between the sensor  22  and the sensor socket  36  are provided by a series of electrical contacts  42  located in the sensor socket  36 . In an especially preferred embodiment, the electrical contacts  42  consist of six spring biased pins  42  that create an electrical connection between the pins  42  and corresponding contact pads  108  located on the base of the sensors  22 . The sensor socket  36  is surrounded by a plate  44  that covers and protects the front of the barrel portion  38  of the elongate housing  24 . 
     The microprocessor based control circuit  40  is internally contained in the barrel portion  38  of the elongate housing  24 . Preferably, the microprocessor  78  in the microprocessor based control circuit  40  is a sixteen bit Toshiba microprocessor having model number TMP93CS41F. The microprocessor based control circuit  40  also preferably contains a RAM chip that is 256K×8 bits and a flash memory that is 64K by 8 bits. The microprocessor based control circuit  40  can communicate to external devices by means of several input and output ports located on the lower portion of the barrel  38  of the elongate housing  24 . As shown in FIG. 4, an RS 232 port  46  is located on the lower portion of the barrel  38 . In addition to the RS 232 port  46 , an infrared communications port  48  is also located on the lower portion of the barrel  38  beneath the sensor socket  36  and provides the microprocessor control circuit  40  the ability to establish wireless communication with an external device. Preferably, the infrared communications port  48  is a low-voltage infrared receiver manufactured by Texas Instruments under Model No. TIR1000. Additionally, a signal output port  50  is located near the RS 232 port  46  and the infrared communications port  48 . The signal output port  50  provides a signal that is the detected envelope waveform of the ultrasonic electrical signal. The detected envelope waveform signal consists of any instantaneous point on the detected waveform having a DC value directly related to the signal strength in decibels at that point. This signal output may be provided to a machine analyzer so that frequency and time domain analysis can be performed on the ultrasonic envelope waveform. The final port shown in FIG. 4 is a battery charger jack  52  that is used to receive the DC voltage source that charges the rechargeable power supply  58 . 
     Referring back to FIG. 2, a trigger  54  for activating the ultrasonic monitoring system  10  is located at the junction of the barrel portion  38  and the grip portion  56  of the elongate housing  24 . The trigger  54  is positioned similar to a trigger on a real pistol and is electrically connected to the microprocessor control circuit  40 . When the trigger  54  is pressed, the ultrasonic monitoring system  10  begins collecting data. When the trigger  54  is released, the system  10  ceases collecting data. Thus, the trigger  54  simply functions as an activation switch and it is understood that there are alternative manners in which this function could be implemented. 
     The electrical components of the ultrasonic monitoring system  10  contained in the elongate housing  24  are powered by a rechargeable power supply  58  that is mounted in the grip portion  56  of the elongate housing  24 . As previously discussed, the rechargeable power supply  58  is recharged by a way of a battery charger jack  52  which is located next to the signal output port  50 . A standard adapter having a first end for plugging into a common electrical outlet and a second end for engaging port  52  provides power to the battery chargerjack  52 . A headphone jack  62  located on the bottom portion of the grip  56  extends through the handle plate  60  of the elongate housing  24 . The headphone jack  62  provides signals to the headphones  26  through a removable cord  28  that is electrically connected to the headphones  26 . Alternatively, wireless headphones may be incorporated into the present invention. FIG. 5 is a view of the bottom of the grip  56  that clearly shows the headphone jack  62  and the handle plate  60 . 
     FIG. 6 shows the rear plate  64  of the elongate housing  24  that contains the display  66  that is viewed by the operator  20  when ultrasonic data measurements are being taken. The display  66  is mounted in the rear plate  64  and provides visual ultrasonic data indicators and operational information to the operator  20  of the ultrasonic monitoring system  10 . The display  66  is preferably a 2×12 character matrix liquid crystal display. A down arrow user input key  68 , an up arrow user input key  70  and a mode user input key  72  are located below the display  66 . The grip  56 , the headphone jack  62  and the internal rechargeable power supply  58  are also shown in FIG.  6 . 
     The functioning of the electrical components inside the elongate housing  24  can better be understood by examining a block diagram of the components. The embodiment shown in FIG. 7 a  has a ultrasonic sensor  22  with an integral temperature sensor  74  installed in the sensor socket  36 . In a preferred embodiment, the temperature sensor  74  is coaxially mounted inside the cavity of the ultrasonic sensor  22 . The ultrasonic sensor  22  with the integral temperature sensor  74  provides ultrasonic electrical signals to the electrical contacts  42  in the sensor socket  36 . The sensor socket  36  provides the ultrasonic electrical signal that is related to the strength of the ultrasonic sound waves  12  received by the ultrasonic sensor  22  to a first voltage controlled amplifier  76 . The amount of amplification provided by the first voltage controlled amplifier  76  is controlled by a microprocessor  78 . After being amplified, the amplified ultrasonic electrical signal is sent to a mixer  80 . The mixer  80  mixes the amplified ultrasonic electrical signal with an oscillation signal provided by a microprocessor controlled variable frequency sine wave oscillator  82  to produce a signal that is related to the original ultrasonic electrical signal produced by the ultrasonic sensor  22 . This signal consists of at least: (1) the amplified ultrasonic electrical signal; (2) the oscillator signal; (3) the frequency sum of the ultrasonic electrical signal and the oscillator signal; and (4) the frequency difference of the ultrasonic electrical signal and the oscillator signal. The signal output from the mixer  80  is passed through a low pass filter  84  to remove any high frequency components above the audible frequency range of a human being. This filtered signal is then sent to a second voltage controlled amplifier  86  that is controlled by the microprocessor  78 . Finally, the amplified and filtered signal is sent to the headphones  26  where it is broadcast to the operator  20 . The point is to create a signal that can be heard by humans and is related to the ultrasonic electrical signals in a manner that allows the operator  20  to distinguish between different ultrasonic electrical signals by distinguishing between the different mixed signals. The second voltage controlled amplifier  86  is essentially a volume control for the head phones  26 . 
     An advantage of the ultrasonic monitoring system  10  of the present invention is that there are two signal paths for the ultrasonic electric signals produced by the ultrasonic sensor  22 . As discussed above, one signal path provides an audio output that can be listened to by the operator of the ultrasonic monitoring system  10 . However, the ultrasonic electrical signal received from the ultrasonic sensor  22  is also sent to a received signal strength indicator  90 . The received signal strength indicator  90  is a functional part of a Philips Semiconductor RF Communications Products Model SA637 low-voltage IF receiver. This received signal strength indicator produces an envelope waveform of the ultrasonic electrical signal consisting of instantaneous points on the waveform having a DC value related to the signal strength in decibels of the ultrasonic electrical signal at that point. 
     Referring now to FIG. 7 b , an embodiment of the received signal strength indicator  90  is depicted. The signal from the sensor is received by an envelope detector  93 . A capacitor  94  and a resistor  95  provide the envelope detector  93  with a rapid rise and slow decay output. In an especially preferred embodiment, the envelope detector  93  is provided with a response time constant of approximately 60 microseconds. The time constant is selected to substantially eliminate the intrinsic ultrasonic frequency signals while allowing any dynamic amplitude variations in those signals to be sent to microprocessor  78 . The same signal is also provided to output jack  50 . Sampling of this envelope waveform allows the microprocessor  78  to calculate a referenced decibel level of the ultrasonic sound waves at substantially any point in time. The referenced decibel level is determined by comparing the measured signal amplitude against a stored look up table of calibration values, a zero decibel value being referenced to an acoustic sound pressure level of 20 microPascals (0.0002 microBars) in an especially preferred embodiment. 
     The aforementioned envelope detection process could be referred to as a peak follower technique or, when used in conjunction with a filtering time constant, as a form of demodulation. In addition, the envelope detection process may be combined with an analog sample and hold circuit, or, in an especially preferred embodiment, with an analog to digital converter. The technique provides an energy waveform of periodic bursts or rings that represents the bursts or rings of acoustic vibrations. Depending upon the type of machinery faults generating them, these bursts may have a duration of a few milliseconds or less. The intrinsic frequency of the bursts is relatively high, usually several kHz or higher. In the case of the present invention, 40 kHz is the preferred frequency of operation. The idea is to measure the peak amplitude of the burst or ring frequencies during sample time windows. In general, the intrinsic frequency or frequencies of the bursts are not of interest. It is the signal amplitudes and signal periodicity that are of the greatest interest for analysis. Nevertheless, the technique is still of value with ultrasonic sound waves of constant amplitude and constant duration, as may be the case with a steady leak from a pipe. In the case of a constant amplitude ultrasonic sound wave, the envelope waveform would be a DC value representative of the decibel level of the ultrasonic sound wave. 
     While we use envelope detection as shown in FIG. 7B, it is expressly understood that the Peak Vue techniques disclosed in U.S. application Ser. No. 08/840,844 filed Apr. 17, 1997 which is a continuation of U.S. application Ser. No. 08/555,296 filed Nov. 8, 1995 and now abandoned may be used in accordance with an embodiment of the present invention. Both techniques perform a peak follower function and are able to capture peak amplitude values of short duration signal bursts or rings. Thus, it would be possible to incorporate the Peak Vue method into the present invention. 
     Determining a referenced decibel output is a substantial improvement over the prior art method of using an analog instrument to provide a relative indication of the amplitude of the ultrasonic sound produced in one location compared to the ultrasonic sound produced at another location. Because there is no absolute reference for the prior art ultrasonic measurements, it is difficult to compare a current reading to a prior reading taken at some earlier time. Furthermore, the unreferenced readings taken by one particular instrument are difficult to compare to the readings taken by another instrument. However, because the referenced decibel outputs of an instrument constructed in accordance with the present invention are referenced to a known value, the referenced outputs of the present invention may be stored and accurately compared to later readings obtained by other instruments. Thus, providing a referenced output allows measurements taken over an extended period of time to be analyzed to determine if the amount of ultrasonic sound produced by a particular machine is increasing or decreasing. 
     The output from the integral temperature sensor  74  is provided to the temperature sense circuit  92 . In a preferred embodiment, the temperature sense circuit  92  supplies a constant current to the temperature sensor  74 . The resistance of the temperature sensor  74  is dependent upon its temperature. Thus, the voltage produced by the constant current flowing through the temperature sensor  74  is representative of the temperature sensed by the temperature sensor  74 . This voltage is provided to the microprocessor  78  which interprets the voltage as a temperature and sends a temperature reading to the display  66 . 
     The microprocessor  78  uses the signal indicative of the strength of the received ultrasonic sound waves to calculate a number of values. The value calculated by the microprocessor  78  depends upon the mode in which the ultrasonic monitoring system  10  is operating. The operator  20  can select from different operating modes by selecting the operating mode menu with the mode key user input  72  and then scrolling through the mode menu with the up  70  and down  68  arrow input keys. Once an operating mode has been selected by the operator  20 , a symbol appears on the display  66  indicating the mode in which the ultrasonic monitoring system  10  is operating. 
     For example, if the user  20  selects the peak hold mode, the highest input signal level received by the microprocessor  78  from the received signal strength indicator  90  is retained and displayed as long as the trigger  54  remains depressed. When the trigger  54  is released, the peak value of the signal received by the microprocessor  40  is frozen on the display  66 . The display  66  and the retained peak value are reset to zero when the trigger  54  is pressed again. Another mode which can be selected is the instantaneous averaging mode. This is the preferred operating mode of the present invention. In this mode, the microprocessor  78  receives the signal indicative of the received ultrasonic electrical signals strength and determines the strength of the ultrasonic sound waves. In a similar fashion to that of the peak hold operating mode, the microprocessor  78  retains and displays the strongest signal received. However, in the instantaneous mode of operation, this value is rapidly reset. Preferably, the display  66  is updated at least three times a second. This allows an almost instantaneous indication of the strength of the ultrasonic sound waves being received by the ultrasonic sensor  22 . Yet another mode of operation is the averaged mode. In this mode, the microprocessor  78  calculates and sends to the display  66  an average referenced decibel level of the ultrasonic sound waves received between the time the trigger  54  was pressed and the current time. When the trigger  54  is released, the output is frozen. The decibel level is referenced to an accepted standard, such as zero decibels at an acoustical sound pressure level of 20 micropascals or zero decibels at 50×10 −12  inches peak to peak of mechanical displacement. Still another mode of operation is the peak factor mode of operation. In accordance with this mode, the difference between the peak value of the signal and the average value of the signal is displayed. It is readily appreciated that a number of other values representing various characteristics of the sensed ultrasonic sound waves could be calculated by the microprocessor  78 . In fact, one of the primary advantages of using a microprocessor based system is that the manner in which the digital data is analyzed and manipulated can easily be altered without requiring complex design changes. The particular values discussed are simply those of an especially preferred embodiment of the present invention. 
     The microprocessor  78  also allows an operator of the ultrasonic monitoring system  10  to enter various information concerning the results of the ultrasonic tests for later reference. For example, after the operator has performed a test, the microprocessor  78  can prompt the operator to input information concerning characteristics of the sound produced in the headphones  26  by displaying a message such as “Sounds Like?” on the display  66 . The user would then use the up arrow input key  70  and the down arrow input key  68  to scroll through a list of choices such as “buzz”, “hiss”, “crackle”, “pop”, “impacting”, etc. Once the user has located the proper description, the microprocessor  78  can be instructed to save the description in memory by pressing the mode input key  72 . It should be readily understood that a variety of other information could be stored using the above described method. 
     The ultrasonic sensor  22  and the temperature sensor  74  contain identification information that is read by the microprocessor  78  located in the elongate housing  24 . The identification information is sent by an identification circuit  23  in the sensors  22  and  74  to the microprocessor  78 . The microprocessor  78  uses the identification information to configure the ultrasonic monitoring system  10  to operate using the type of sensor  22  installed in the sensor socket  36 . The identification circuit  23  preferably consist of a memory with a serial output. Preferably, the identification information not only identifies the type and nature of the sensors  22  and  74 , but also includes calibration data used by the device  10  to accurately interpret the sensors  22  and  74  signals. 
     In an especially preferred embodiment, the identification circuit  23  is a DS2502 1 KBIT Add-Only Memory manufactured by Dallas Semiconductor. Alternatively, the identification circuit  23  is a resistor having a resistance value that corresponds to a particular sensor  22  and  74 . The microprocessor  78  determines the type of sensor  22  and  74  by determining the value of the resistor. In yet another embodiment, the identification circuit  23  is a bar graph containing visually encoded information that is read by an optical sensor located in the sensor socket  36 . 
     The sensor socket  36  is preferably designed to allow the ultrasonic monitoring system  10  to interchangeably use different types of sensors  22 . As shown in FIGS. 8 a  and  8   b , the sensor socket  36  preferably consists of a cylindrical chamber  96  for receiving the sensors  22  with a set of electrical contact pins  42  in the bottom of the cylindrical chamber  96  that are in electrical contact with corresponding contact pads  108  on a sensor  22  that has been installed in the sensor socket  36 . In an especially preferred embodiment, six pins  42  in the sensor socket  36  electrically connect the sensor  22  to the ultrasonic monitoring device  10 . Two of the pins  42  are used to send the received ultrasonic electric signals to the voltage controlled amplifier  76  of the heterodyning audio circuit and the received signal strength indicator  90 . Two pins  42  are used to provide a power supply voltage and a power supply ground to the installed sensor  22 . One of the pins  42  is used to provide a temperature reading to the temperature sense circuit  92  and, the last pin  42  is used to provide a communication line between the identification circuit  23  on the sensor and the microprocessor control circuit  78  in the elongate housing  24 . It is understood that more electrical connections could be provided if necessary. Each of the pins  42  are spring biased and move axially to yieldably engage the contact pads  108 . 
     The sensors  22  are held in the sensor socket  36  by a pair of protruding members  100  that are designed to be received by corresponding channels  98  in the walls of the cylindrical sensor socket  36 . In an especially preferred embodiment, the channels  98  are L-shaped so that the sensor  22  is installed in the sensor socket  36  by inserting the protruding members  100  into the top of the L-shaped channels  98  and pushing the protruding members  100  down into the channels  98 . The sensor is then twisted so that the protruding members  100  are securely contained in the leg of the L-shaped channels  98  and prevent the sensor  22  from being removed from the sensor socket  36 . The process is remotely similar to placing a bayonet on the end of a rifle. 
     The sensor  22  can only be inserted into the sensor socket  36  with the protrusions  100  on the sensor  22  aligned with the grooves  98  in the socket  36 . Because it is important that the contact pins  42  in the sensor socket  36  be aligned with the proper contact pads  108  of the sensor  22 , the protruding members  100  are preferably positioned so that it is mechanically impossible to install the sensors  22  oriented in the wrong fashion. For example, if the protruding members  100  are placed directly across from each other, there are two possible ways to insert the sensor  22  into the socket  36 . Therefore, the protruding members  100  are preferably positioned so that they are not directly across from one another. This insures that the contact pins  42  in the socket  36  are properly aligned with the contact pads  108  of the sensor  22 . It is understood that a number of other mechanical means could be used to key the sensors  22  to help insure proper insertion, however, the aforementioned approach is easy to implement and quite effective. 
     A wide variety of ultrasonic sensors  22  can be installed in the sensor socket  36  depending upon the particular needs of the operator  20 . While it is appreciated that there are numerous applications for an ultrasonic monitoring system  10 , machinery monitoring and leak detection are the primary uses for the ultrasonic monitoring system  10  of the present invention. The frequency range of interest for these applications is approximately 20 to 100 kHz. Conventionally, 40 KHz has been used by several manufacturers of ultrasonic instruments as the primary frequency of interest. This is probably the best general purpose frequency range, as it is high enough to be above most loud low frequency machine vibrations yet not so high as to be severely attenuated at reasonable distances. It should be understood that the ultrasonic sound waves produced by machinery defects or leaks typically do not consist of a single tone or pitch. These sounds are broadband signals that consist of many different frequencies. It is the complex nature of the signals that allows a trained operator to distinguish between the heterodyned ultrasonic sounds produced by different conditions. For example, leaks in pressurized containers generally create a rushing sound while arcing and electrical corona typically produce a cracking or buzzing sound. In addition to differences in the sounds that can be audibly detected by listening to the heterodyned signal, a machine analyzer can analyze the frequency spectrums of the waveforms to detect signal spiking caused by bearing defects or other impact producing conditions. Because of the wide range of applications, it is understood that a variety of different sensors  22  designed to detect a range of different frequencies could be utilized in accordance with the present invention and the particular types of sensors  22  discussed are for illustration purposes only. 
     Two preferred types of ultrasonic sensors  22  that are utilized with the bayonet style locking system of the present invention are the airborne ultrasonic sensor  102 , shown in FIGS. 9 a ,  9   b , and  9   c , and the contact ultrasonic sensor  104 , shown in FIGS. 10 a ,  10   b ,  10   c , and  10   d . The preferred embodiments of both sensors  102  and  104  utilize piezoelectric transducers  25  to produce ultrasonic electrical signals that correspond to the ultrasonic sound waves reaching the sensors  102  and  104 . The airborne sensor  102  preferably consist of a cylindrical housing  106  with a cylindrical PC board containing six contact pads  108  at one end that serves to establish electrical connections between the sensor  102  and the sensor socket  36 . In addition, an identification circuit  23  and a piezoelectric transducer  25  are preferably located in the main body of the cylindrical housing  106 . The piezoelectric transducer  25  is located behind a protective housing  110  in the end of the cylindrical housing  106  opposite the PC board containing the contact pads  108 . The piezoelectric transducer  25  generates ultrasonic electrical signals in response to ultrasonic sound waves. The ultrasonic electrical signals are then split between two inputs on the cylindrical PC board containing the contact pads  108 . The ultrasonic electrical signals are then sent from two of the contact pads on the cylindrical PC board  108  to the input of the received signal strength indicator  90  and the voltage controlled amplifier  76 . 
     To allow the operator  20  to determine the precise location of small leaks or ultrasonic noise sources, a rubber cone  112  with a hole in the tip can be placed over the sensor  102  as shown in FIG.  11 . The rubber cone diminishes the ability of the sensor  22  to detect ultrasonic sounds from anywhere but the open tip of the cone. Thus, the rubber cone  112  permits the operator  20  to more precisely locate a small leak. Materials other than rubber could be used to construct the cone  112 , however, the rubber cone  112  does a particularly good job of isolating the ultrasonic sound waves and its flexibility makes it easy to use. 
     Because each sensor  22  contains identification information, variations in the airborne ultrasonic sensors  102  are easily accommodated by the ultrasonic monitoring system  10 . New software can be installed in the ultrasonic monitoring system  10  that provides the system with the configuration information needed to accommodate the newly developed sensors  22 . 
     The base of the contact sensor  104  is similar to the base of the airborne sensor  102 . However, the receiving end of the contact sensor  104  consists of a long substantially hollow shaft  114 . Ultrasonic vibrations are received by placing the tip hollow shaft  114  of the contact sensor  104  on the object that is suspected of radiating ultrasonic sound waves. To reinforce and stabilize the shaft  114  of the contact sensor  104 , an adjustable washer  113 , that is received by threads located on the cylindrical housing  106  at the base of the shaft  114 , is tightened until the contact sensor  104  is firmly held in the sensor socket  36 . A piezoelectric transducer  25  is located in the base of the shaft  114 . Placing the tip of the shaft  114  against an object producing ultrasonic sound waves causes the piezoelectric transducer  25  of the contact sensor  104  to produce ultrasonic electrical signals. While the airborne ultrasonic sensor  102  is mechanically self-resonant, the contact sensor  104  is not. Therefore, the contact sensor  104  preferably contains an inductive and capacitive band pass resonant filter  27  that is preferably tuned to a frequency of 40 KHz. In a fashion similar to that of the airborne sensor  102 , the ultrasonic electrical signal is then split and sent to the cylindrical shaped PC board containing the contact pads  108  that provide electrical contacts to the sensor socket contact pins  42 . 
     The ultrasonic contact sensor  104  preferably contains a temperature sensor  116  coaxially mounted within the ultrasonic sensing shaft  114 . The tip  117  of the temperature sensor  116  is constructed out of a material, such as copper, that rapidly conducts heat. A resistance type temperature detection circuit as shown in FIG. 10 d  is the preferred approach to determining the surface temperature of the object being monitored. A section of resistance temperature dependent (RTD) material  115  is in close contact with the heat conductive tip  117  of the temperature sensor  116 . Thus, the heat conductive tip  117  acts as a conductor of heat between the surface of the object whose temperature is being measured and the RTD material  115 . The resistance of an RTD material  115  varies relatively rapidly with a change in temperature. Thus, by measuring the resistance of the RTD material  115 , a temperature measurement can be obtained. When the temperature sensor  116  is placed in contact with the surface for which a temperature reading is desired, the temperature of the tip  117  changes almost immediately to the temperature of the surface it is in contact with. The section of RTD material  115  is in close contact with the tip  117  and, thus, also rapidly changes temperature. In a preferred embodiment using copper for the heat conducting tip  117  and platinum as the RTD material  115 , the temperature sensor  116  has a time constant response of less than 500 milliseconds. 
     A constant current is supplied to the RTD section of material  115  by the temperature sense circuit  92 . As the temperature of the RTD section  115  of the temperature sensor  116  varies, so does the resistance of the RTD section  115 . By supplying a constant current to the RTD material  115 , a voltage potential is created across the material  115  that is proportional to the temperature of the sensor tip  117 . As the temperature varies so does the resistance of the section of RTD  115  and, thus, the corresponding voltage potential also varies. By measuring the voltage potential across the section of RTD material  115  in the temperature sensor  116 , the microprocessor  78  can determine the temperature of the tip  117  of the temperature sensor  116  and, thus, the surface temperature of the area in question. 
     Knowing the surface temperature of an enclosure containing bearings, gears, steam traps, valves, or other machinery provides an indication of the condition of the machinery. Temperature information is particularly useful when measurements are taken over time and compared. Many mechanical failures result in friction which, in turn, generates heat. Thus, a sudden increase in the surface temperature of a machine tends to indicate a new machinery defect is creating more friction and consequently more heat. A slow increase in surface temperature may indicate slowly progressing wear and tear in the machinery. As a further example of how surface temperature might be used to diagnose equipment failure, consider steam traps that are used to remove condensate from a steam line. Steam traps usually fail in one of two ways. First, they can fail open, meaning that they remove the condensate but allow steam to escape from the system. Second, they can fail closed, meaning that the pipes become blocked so that no condensate is removed. The temperature of the exhaust line of a steam trap which has failed open will be very high. Conversely, if the steam trap is blocked, the temperature of the downstream pipes will be much lower. Therefore, comparing the known temperature of a steam trap or machine when it is functioning properly to its present temperature can provide clues to the device&#39;s current condition. 
     The ultrasonic monitoring system  10  further includes an ultrasonic sound wave transmitter  34  that permits the ultrasonic monitoring system  10  to locate holes in containers that are not producing ultrasonic sound waves. The ultrasonic sound wave transmitter  34  is turned on and placed inside a pipe, tank, or other sealed environment that it is desired to check for leaks. For example, as shown in FIG. 12, the ultrasonic sound wave transmitter  34  can be placed in a sealed environment  118 . Once the ultrasonic sound wave transmitter  34  is activated, the operator  20  of the ultrasonic monitoring system  10  can use the ultrasonic sensor  22  in the elongate housing  24  to detect any ultrasonic sound waves  12  being emitted from the ultrasonic sound wave transmitter  34  that are escaping the sealed environment  118 . 
     One of the primary benefits of using a digitally based ultrasonic monitoring system  10  that produces referenced decibel signal strength readings is the ability to store previously acquired data for later recall and analysis. Trending this digitally stored information allows the ultrasonic monitoring system  10  to detect changes in a machine&#39;s performance over time. For example, if the level of ultrasonic noise emitted by a particular machine dramatically increases from one week to another, it is highly likely that a machine defect has appeared or worsened in the previous week. In a similar vein, if a machine has consistently produced a large amount of ultrasonic noise over an extended period of time without malfunctioning, it is unlikely that another reading indicating the machine is producing a large amount of ultrasonic noise is indicative of a problem. Thus, much of the ultrasonic data acquired by the ultrasonic monitoring system  10  is primarily useful when compared to prior data collected under similar circumstances. 
     Temperature readings are also much more informative when trended over a period of time. For example, a surface temperature reading of 180 degrees Fahrenheit may not be particularly revealing in and of itself. However, a series of 120 degree Fahrenheit readings followed by a 180 degree reading is much more likely to be indicative of a problem. Thus, trending the data acquired by the ultrasonic monitoring system  10  dramatically improves the likelihood of detecting machinery defects. 
     As briefly mentioned before, the ultrasonic analysis system  10  preferably includes a microprocessor based portable personal computer. FIG. 13 is a flow chart showing the steps of a route based method of monitoring a series of machines with the ultrasonic monitoring system  10  of the present invention. The route based method uses a central processing and storage computer, a portable computer, and a hand held ultrasonic monitoring device. To set up a trendable ultrasonic monitoring system  10 , a brief description of, and the location of, every machine that is to be monitored with the ultrasonic monitoring system  10  is entered into a central processing and storage computer. This step is shown in block  122  of FIG. 13. A monitoring schedule detailing the times at which each machine should be tested and the tests that should be performed on each machine is also programmed into the central processing computer. In a preferred embodiment, a ten character identification code is used to represent each machine and a three character identification code is used to represent each machine&#39;s location. When the time for testing the machines arrives, the central computer prompts the operator to download the testing information from the central computer to the portable computer, as shown in block  124 . The portable computer examines the testing information and prompts the operator to proceed to the first testing location in block  126 . The method then proceeds to block  128  wherein the portable computer loads the testing information needed for the first test into the hand held ultrasonic monitoring device. This testing information includes any configuration data needed for the particular tests to be performed on the machine. Furthermore, the alarm levels for the particular machine being tested are automatically sent from the portable computer to the hand held ultrasonic monitoring device. Thus, the portable computer prompts the operator to go to a particular location and perform a particular test on a particular machine and configures the microprocessor control unit in the hand held ultrasonic monitoring device to correctly perform the test. Furthermore, as shown in block  130 , the portable computer provides a detailed description of how to perform the tests to the operator. It is important that the tests be performed in the same manner each time so that the results of the current test can be accurately compared to the results of previous tests. Once the ultrasonic sound wave and temperature measurements have been taken by the operator in block  132 , the test results are downloaded from the hand held ultrasonic device to the portable computer in block  134 . In decisional block  136 , the portable computer must determine whether another test needs to be performed. If another test needs to be performed, the portable computer prompts the operator to proceed to the next test location and the method returns to block  128 . The software running on the portable computer is preferably flexible enough to auto increment through a predetermined monitoring route or receive external inputs, such as bar code information, which dictate the location in the manufacturing setting to be monitored. However, when all the required tests have been performed, the portable computer prompts the operator to download the test results from the portable computer to the central computer. In the final step of the method depicted in block  142 , the central computer compares the test data from the most recent test to the data from previous tests to determine the condition of the machines being monitored. 
     The test results from previous measurements may be used to generate alarm levels for the next series of measurements For example, an alarm level can be set so that if the ultrasonic noise level measurement from a particular machine is three decibels higher than the previous the ultrasonic noise level measurement an alarm is triggered. The increase in ultrasonic noise from one measurement to the next that is necessary to trigger an alarm may be varied by the operator depending upon the particular type of machine being monitored and the circumstances surrounding its monitoring. Similarly, the current test results may be automatically compared to predetermined criteria stored in memory to determine if an alarm situation exists. The predetermined criteria may be based upon historical or baseline data corresponding to past measurements taken from a particular type machine. In addition, even more complex criteria such as the expected ultrasonic sound wave production of a particular machine as a function of the amount of time the machine has been operating are easily accommodated by the route based system of the present invention. 
     Depending upon the memory requirements imposed by the number of devices being monitored and the number of tests being performed, the data contained in the portable computer may not need to be downloaded to a permanent base station. If the storage and processing capacity of a central computer is not required, the test data may be stored and analyzed by the portable computer. Furthermore, if sufficient memory exists in the hand held ultrasonic monitoring device, the hand held ultrasonic monitoring device can perform the steps necessary for a route based monitoring system. 
     Storing the ultrasonic electrical signals received from particular machines also improves the likelihood of detecting a machinery defect by listening to the heterodyned audio signals produced by the ultrasonic monitoring system  10 . Before the operator of the ultrasonic monitoring system  10  listens to the current audio signals produced in response to the ultrasonic sound waves received from a particular machine, the operator can prompt the portable computer to playback the audio signals previously recorded from the particular machine. This makes it much easier for the operator of the ultrasonic monitoring system  10  to detect the small changes in the audio signals which are often indicative of a developing machinery defect. 
     The ultrasonic monitoring system  10  allows a user to input a number of conditions that will result in an alarm being generated. These alarms may be audible or visual depending on the user&#39;s preference. These alarms preferably include an alarm for exceeding a user-defined decibel level, an alarm for exceeding a user-defined temperature level, and an alarm to alert the user that the incoming signal is beginning to be clipped by the internal electronic circuitry in the elongate housing  24 . 
     The decibel alarm is defined by accessing the alarm function with the mode input key  72  on the elongate housing  24  and using the up  70  and down  68  arrow input keys to set an alarm limit. Preferably, when the alarm level is reached, an audible alarm is heard in the headphones  26  and the referenced decibel readout on the display  66  flashes. The alarm limit may be triggered differently depending on which operating mode is selected. For example, in the instantaneous, peak hold and peak factor modes, the decibel alarm is preferably activated the first time the incoming signal reaches the user defined limit. However, when in the average mode, the decibel alarm is activated the first time the average reading reaches the user-defined limit. 
     The temperature alarm is also defined by accessing the temperature alarm function with the mode input key  72  and using the up  70  and down  68  and arrow keys to set the alarm limit. When the limit is reached, an audible alert is heard in the headphones  26  and the temperature readout on the display  66  flashes. The signal clipping alarm indicates the incoming signal is being clipped and that the user should decrease the volume. The signal clipping alarm can be either an audible alarm in the headphones  26  or a visual alarm on the display  66 . 
     While the invention has been described in detail, it is to be expressly understood that it will be apparent to persons skilled in the relevant art that the invention may be modified without departing from the spirit of the invention. Various changes of form, design or arrangement may be made to the invention without departing from the spirit and scope of the invention. Therefore, the above mentioned description is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined in the following claims.