Abstract:
A method and apparatus for testing components is disclosed. The method involves a system operating to collect data in a certain frequency range, and utilizing signals outside that frequency range to test the system during operation. Such testing may be conducted on a not-to-interfere basis, thereby allowing for testing during operation of systems in continuous use.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally relates to in-system testing of components and more specifically relates to testing of components while those components are functioning, or testing components in an operating range the components do not operate in during normal system operation. 
     2. Description of the Related Art 
     Over the years, several systems have been employed for land seismic exploration. A common system that is currently in use employs vibroseis trucks to impart seismic energy in the form of acoustic waves into the ground. The frequency of these acoustic waves are typically in the range of 10-100 Hz. 
     Seismic energy reflected from acoustic impedance discontinuities is detected by geophones and the output of the geophones is connected to an instrument box. In the instrument box are signal conditioning devices, A/D converters, a means of recording the data or sending it via telemetry to a recorder at the Recording truck, power supply and a processor. 
     Because the geophones are often connected together and to the instrument box with cables having connectors, the system is susceptible to a variety of problems. Among other things, rodents and cows can chew on the cables or trample them. Naturally, other forces of nature and other defects in the system can also cause problems. Animals, rainwater, and other forces can lead to degradation in performance of the system. This degradation can be manifested by increased cable resistance, short or open circuits, cross-talk between sensors or chains of sensors, leakage of signals to ground, and other similar manifestations. 
     As a result of these problems, a variety of tests need to be performed to determine if there is any degradation in the system. In some cases, such as leakage of signals to ground or increased resistance, a compensation factor can be determined. In other cases, such as short or open circuits, data cannot be collected until the problem is repaired, and previously collected data may need to be ignored. Determining when these measures are necessary requires testing connectivity of the sensors to the instrument box, leakage of the sensors and/or their cables, and cross-talk between the cables and their associated cables. 
     One example of a leakage test would involve sending a test signal to a sensor and observing what signal was received back from the sensor. The changes in characteristics from the test signal to the received return signal would give an indication of how the signal is distorted when it passes along the connection between the sensor and the instrument box or other receiving system. An example of a cross-talk test would involve sending a test signal to a first sensor and observing the signal received from a second sensor with no direct connection to the first sensor. If no signal from the second sensor appeared to be related to the test signal, no cross-talk would be occurring, whereas if a strong signal from the second sensor appeared to be related to the test signal, cross-talk would be occurring. With regard to connectivity, or an open and short circuits test, again a test signal could be sent to a sensor or string of sensors and the response of that sensor or string of sensors observed. Whatever signal or response was received (or not received) would give an indication of whether the sensor in question was not functioning properly. Those skilled in the art will appreciate that other methods of implementing these tests exist. 
     However, these tests are typically performed during the downtime of the operation, when no information signals are being recorded. Normally, such systems have used modes of operation that always had intervals of dead time, i.e. time when no receive signal activity occurred, during which instruments could be tested to determine their quality. With the introduction of the slip-sweep vibroseis operation there is no interval of dead time during actual operation of the system in which the components can be tested to verify that they are working correctly while the system operates. The slip-sweep vibroseis operation involves sweeping a signal generator through a range of frequencies on a repeated basis, such that each successive sweep overlaps the previous sweep, resulting in not only a constant generation of some signal, but some intervals during which two or more signals are generated simultaneously. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention is a method of testing a component including operating the component; sending an out-of-band test signal to the component; and observing a response of the component to the out-of-band test signal. Alternatively, the invention may be an apparatus for testing a set of one or more components comprising a signal generator, the signal generator coupled to one or more of the components, the signal generator for generating test signals outside of an operating frequency band of interest; and a receiver, the receiver coupled to one or more of the components, the receiver for receiving signals outside of the operating frequency band of interest. 
     Likewise, the invention may be an apparatus for testing a set of one or more components including generating means for generating a test signal, the generating means coupled to at least one of the components, the generating means configured to generate a test signal at a frequency outside an operating frequency band of interest of the components; and receiving means configured to receive a response to a test signal, the receiving means coupled to at least one of the components. 
     Another alternative embodiment of the present invention is a method of testing a component including operating the component, triggering a test signal, the component sending an out-of-band test signal while the component operates, and observing the out-of-band test signal while the component operates. 
     Additionally, an alternative embodiment of the present invention is a method of testing including operating the component using signals appropriate to the intended purpose of the component, sending a test signal different from the appropriate signals to the component while operating the component, and observing a response of the component to the test signal while operating the component. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example and not limitation in the accompanying figures. 
     FIG. 1 illustrates one embodiment of a system suitable for out-of-band testing. 
     FIG. 2 illustrates an exemplary frequency response of both the sensor and a test unit suitable for out-of-band testing in accordance with the teachings of the present invention. 
     FIG. 3 illustrates an alternative embodiment of a system suitable for out-of-band testing in accordance with the teachings of the present invention. 
     FIG. 4 illustrates an alternative embodiment of a system suitable for out-of-band testing in accordance with the teachings of the present invention. 
     FIG. 5 further illustrates an alternative embodiment of a system suitable for out-of-band testing in accordance with the teachings of the present invention. 
     FIG. 6 also illustrates an alternative embodiment of a system suitable for out-of-band testing in accordance with the teachings of the present invention. 
     FIG. 7 illustrates the process employed in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION 
     A method and apparatus for testing components is described. A method of testing components in the system is needed that allows the system components to be tested while normally operating, e.g. actually receiving data. Furthermore, the system avoids problems of disturbing data collection or otherwise distorting the data collected by the system while it is tested. In addition, the system avoids damaging system components or otherwise rendering them inoperable. The system tests components that are operating in one frequency range (a sense frequency or operating frequency range or signals appropriate to the operation of the component) with signals in a separate frequency range (a test frequency range). The components respond to the signals in the test frequency range, without interference to the operations in the sense frequency or operating frequency range. As such, this testing can be characterized as out-of-band testing on a not-to-interfere basis. 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the invention. Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
     FIG. 1 illustrates an embodiment of an apparatus suitable for out-of-band testing that operates in accordance with the teachings of the present invention. In the embodiments described, the signals are typically electrical signals. However, the system may be configured to operate on a variety of signals, including optical signals. Instrument  120  is connected to external sensor  110 . Instrument  120  includes sensor apparatus  130  and testing apparatus  140 . An exemplary frequency response for a sensor apparatus and a testing apparatus is shown in FIG. 2 where the overlap between the sensor response and the test response is an area with a relatively low response for either component. It has been determined that instrument  120  can function more efficiently when it can determine whether sensor  110  is functioning properly during gathering of data. In order to test sensor  110  while sensor  110  is receiving data, test apparatus  140  sends signals to and examines signals from sensor  110 . 
     To achieve testing of sensor  110  during gathering of data, the data signals and the test signals must be such that they will not interfere. One way to do this is to use signals out of the sense range. The sense range referred to herein is the frequency range of signals utilized in the collection of data. However, these test signals must be at a frequency which will allow sensor  110  to respond. The test signals must also be at a frequency and amplitude such that sensor  110  is not damaged. Additionally, the test signals should not cause the sensor apparatus  130  to receive any incorrect data. 
     An exemplary response curve for the sensor is illustrated by curve  210  in FIG.  2 . In the present example, sensor apparatus  130  examines signals from sensor  110  in the frequency range of 10 to 100 Hz as shown by curve  220 . However, sensor  110  responds to signals in a much broader frequency range as shown by curve  210 . Thus, a test range out of the 10-100 Hz range may be used for testing. For example, test signals in the 250 to 350 Hz range (as illustrated by curve  230 ) are sufficiently removed from the 10 to 100 Hz range of sensor apparatus  130  yet an acceptable frequency response from sensor  110  is exhibited. As a result, instrument  120  may test whether sensor  110  is functioning properly while instrument  120  is receiving data from sensor  110  in sensor apparatus  130 . 
     It will be appreciated that the illustration in FIG. 2 is exemplary. A test signal may be any signal not appropriate to the operation of the sensor at the time of operation of the sensor. The test signal need not produce a response in the sensor of the same magnitude as the responses produced by signals that are appropriate to the operation of the signal, so long as the response may be measured and used to verify some aspect of the operation or connectivity of the sensor. Thus, the test signals of FIG. 2 would still be useful if the response of the sensor was 5 dB or 10 dB less in the test signal range than in the range of signals appropriate to operation of the sensor during the test for example. 
     Additionally, a desirable relationship between the test signal and signals appropriate to operation of the sensor may be described as two signals which are orthogonal or nearly so, such that the test signal does not unduly interfere with the operation of the sensor with respect to signals appropriate to operation of the sensor. Orthogonality of functions may be expressed mathematically as: 
     
       
         ∫ h ( n ) y ( n ) dn =0 
       
     
     Where h(n) and y(n) are functions representing the test signal and a signal appropriate to operation of the sensor respectively. It will be appreciated that such orthogonality need not be as absolute as defined by the equation, that for purposes of this description, orthogonality is satisfied where the two signals do not cause interference while they operate simultaneously, so two signals may be considered orthogonal when they satisfy the relationship: 
     
       
         ∫ h ( n ) y ( n ) dn ≅0 
       
     
     or such that the two signals cause at most a small amount of interference. It will be appreciated that orthogonality may be achieved by using non-interfering frequencies for the signal appropriate for the operation of the sensor and the test signal as illustrated in FIG.  2 . However, it will be appreciated that orthogonality may also be achieved by exploiting other relationships between a test signal and a signal appropriate to the operation of the sensor. As an example, if a sensor may record motion in both an x and a y direction which are perpendicular to each other, and the signal appropriate to the operation of the sensor causes the sensor to move only in the y direction, then a test signal which causes the sensor to move in the x direction would be orthogonal to the signal appropriate to the operation of the sensor because two directions are orthogonal if they are perpendicular to each other in Euclidean space. As will be appreciated, orthogonality may be achieved in innumerable manners, such as spatial orthogonality, orthogonality in the time domain (orthogonality in time), or orthogonality in the frequency domain, for example. All of these manners of achieving orthogonality fit the criteria just described. 
     Note that the signals appropriate to the operation of the sensor will depend on the intended use of the sensor, such that, for example, if a geophone were used to sense signals in the 10 to 300 Hz range, the 250 to 350 Hz would no longer include only signals not appropriate to the operation of the geophone. However, the 450-550 Hz range, for example, would then be a more useful range of frequencies in which to send a test signal. 
     Ultimately, the sensitivity of the sensor must be considered when choosing signals not appropriate to the operation of the sensor for testing purposes, but most sensors have transfer functions which are understood well enough such that a response to a test signal may be measured and utilized effectively merely be adjusting to the transfer function or response curve of the sensor for the test signal in question. Thus, as long as some form of truth table or response curve exists for the signals, both appropriate and not appropriate to the operation of the sensor, the sensor may be tested by using the signals not appropriate to operation of the sensor and compensating for the sensor&#39;s response thereto. 
     In the present embodiment, instrument  120 , includes both sensor apparatus  130  and testing apparatus  140 . It should be noted that this configuration is exemplary and it is contemplated that the sensor apparatus  130  and testing apparatus  140  may be embodied in one or more separate devices or instruments. 
     In one embodiment, sensor apparatus  130  and test apparatus  140  include filters such that the apparatus  130  and  140  process the proper signals as specified by the frequency range of operation. Thus in the example discussed herein, sensor apparatus  130  may include a filter that filters out-of-band signals, e.g. filters out signals not within or near the 10-100 Hz range of operation. Testing apparatus  140  may include a filter that filters out signals within the 10-100 Hz range. 
     The filters used may be analog or digital filters or embodied in digital signal processors. Furthermore, the filter functions may be combined with other functions of the device. For example, sensor apparatus  130  may also include recording or transmission functionality to record the sensed data or transmit the data to a central processing or recording facility. The sensor apparatus may alternately include processing capability to perform processing on the received sensed signal. Similarly, testing apparatus  140  may also include the necessary components to initiate and/or process received test signals. 
     Turning to FIG. 3, another embodiment of an apparatus suitable for out-of-band testing is illustrated. Instrument box  300  is connected to a network of sensors  310 . Each sensor  310  in this embodiment is identical and each is connected to instrument box  300  through a two-wire connection. Other types of sensors and other types of connections may be used. Instrument box  300  is also connected to power  320  and data storage  330  or data telemetry  340 . Sensors  310  are deployed such that they are laid out over a wide area of ground. In the present embodiment, instrument box  300  is configured to sense and record signals generated during operation. In addition, instrument box  300  includes the filters and functionality to test the sensors and line connections. Thus, in one embodiment, instrument box  300  is able to determine whether sensors  310  are functioning at any given time and whether unacceptable cross-talk or leakage is occurring. In addition, instrument box  300  sends test signals out to sensors  310  to determine whether they are functioning properly. Additionally, in accordance with typical instrument operation, instrument box  300  receives data from sensors  310  and can control sensors  310 . 
     FIG. 4 illustrates an alternative embodiment of a system that operates in accordance with the teachings of the present invention. Controller  410  is coupled to instrument  430  and signal generator  420 . Instrument  430  may be coupled to components  450  in two different ways. For instance, instrument  430  can be coupled to two components  450  through two-wire connections, possibly with intermediate devices interposed, and connected to a third component  450  via a radio link that may or may not require intermediary devices. Likewise, signal generator  420  is shown coupled to each of three components  450  through a different way. For instance, signal generator  420  may be coupled to a first component  450  through a cable or two-wire connection, to a second component  450  through a radio connection, and to a third component  450  through an optical or line-of-sight connection. Other methods of connecting components, such as but not limited to buses, carrier waves in general, and physical connection, may be suitable as well. 
     In the embodiment of FIG. 4, the controller  410  controls and coordinates the operation of signal generator  420  and instrument  430  such that data collection by instrument  430  will be useful. Likewise, controller  410  controls and coordinates such that test signals generated by signal generator  420  can be utilized by instrument  430  to test components  450  or connections to components  450 . Note that controller  410 , signal generator  420  and instrument  430  may be integrated together, may be discrete objects, and may each be collections of components. 
     Turning to FIG. 5, another embodiment is illustrated. Instrument box  570  is coupled to sensor  510 . Instrument box  570  includes sense apparatus  530 , test apparatus  540 , and signal generator  550 . It also includes controller  560 , which controls and coordinates the actions of sense apparatus  530 , test apparatus  540  and signal generator  550 . Note that controller  560  need not be separate from any of the other components of instrument box  570 , it may be integrated into or distributed among the components. Sensor  510  operates to receive signals from outside signal source  520 , which may be a controlled signal source such as a vibroseis truck, an uncontrolled signal source such as a dynamite chirp, or simply the ambient environment. Sense apparatus  530  receives data from sensor  510 . Signal generator  550  may send signals to sensor  510 , and test apparatus  540  may receive signals or data from sensor  510 . 
     In the out-of-band case, signal generator  550  produces signals out of the band most suitable for use by sense apparatus  530 , but within a band suitable for use by test apparatus  540 . In that case, test apparatus  540  detects the signals generated by signal generator  550  as reflected back or processed by sensor  510 . In the process, information on the performance of sensor  510  and connectivity to sensor  510  is gained. Since the signals generated are out of the band utilized by sense apparatus  530 , the performance of sensor  510  and sense apparatus  530  are not affected. Note that the block diagram illustrates a simple coupling between the various components. In one embodiment, the coupling may be such that the same signal sent from signal generator  550  to sensor  510  is also sent to sense apparatus  530  and test apparatus  540  directly. In an alternative embodiment the coupling might be such that sense apparatus  530  and test apparatus  540  do not receive the signal sent to sensor  510  by signal generator  550 . 
     Turning to FIG. 6, a detailed illustration of an alternative embodiment is displayed. Instrument box  670  includes communications channel  1  ( 645 ) and channel  2  ( 655 ), sense apparatus  650 , test apparatus  660  and signal generator  680 . Sense apparatus  650  has, in one embodiment, a lowpass filter with a cutoff (3 db) at 150 Hz. Test apparatus  660  is, in one embodiment, a digital signal processor (DSP) programmed to have a bandpass filter with a range of 250-350 Hz. Signal generator  680  is, in one embodiment, a component capable of generating signals, preferably in the 250-350 Hz range. 
     Communications channel  1  ( 645 ) is coupled to modulator  635 , which is designed to work optimally for frequencies below 1 kHz. Modulator  635  is coupled to signal conditioner  630 , which is also designed to work optimally for frequencies below 1 kHz. Signal conditioner  630  is coupled to sensors  610 , which are connected together in a series-parallel arrangement. Resistance  605  is, for example, a 1 Mega-ohm parasitic resistance to ground associated with the coupling of sensors  610  to signal conditioner  630 . Communications channel  2  ( 655 ) is coupled to modulator  640 , which is coupled to signal conditioner  625 . Both modulator  640  and signal conditioner  625  may be designed to work optimally for frequencies below 1 kHz. Signal conditioner  625  is coupled to sensors  620 , and resistance  615  is, for example, a 100 kilo-ohm parasitic resistance to ground associated with this coupling. Signal Generator  680  is coupled to Signal conditioner  625  and Signal conditioner  630 . 
     In one embodiment, Signal conditioners  625  and  630  are two-way filters designed to protect Instrument box  670  and its components from unintended electrical signals. Such unintended electrical signals may include lightning strikes, and may also include other over-voltage or under-voltage signals such as those associated with static electricity for example. Furthermore, in one embodiment, Modulators  640  and  635  are sigma-delta modulators used for conversion of signals from analog to digital form. In such an embodiment, a corresponding digital-to-analog converter may also be included in Signal Generator  680  for purposes of converting digital signals to analog signals to which Sensors  610  may respond. 
     Instrument box  670  coordinates the actions of sense apparatus  650 , test apparatus  660 , and signal generator  680 . During a slip-sweep operation, sense data is received in sense apparatus  650  continuously. However, signal generator  680  sends signals in the 250-350 Hz band to sensors  610  or sensors  620  through Signal conditioner  625  or Signal conditioner  630  respectively. Test apparatus  660  then receives returning test signals from sensors  610  and sensors  620 , and may also receive signals from signal generator  680  directly back through signal conditioners  625  and  630  and modulators  635  and  640 , thereby allowing for out-of-band testing on a not-to-interfere basis while the system operates. A leakage test of communications channel  1  ( 645 ) would likely give an indication of the presence of resistance  605 , and allow instrument box  670  to flag or compensate for the resulting degradation in signals. A similar leakage test on communications channel  2  ( 655 ) would likely give an indication of the presence of resistance  615 . Likewise, such a leakage test might give an indication of open or short circuits within the connections, such as a break in the connections between sensors  610  and signal conditioning  630  due to a rodent attack. A cross-talk test in which a signal is injected by signal generator  680  into communications channel  1  ( 645 ) and the return signal was observed by test apparatus  660  on communications channel  2  ( 655 ) would give an indication of how much cross-talk occurred between the channels. 
     It should be noted again that signal generator  680  and test apparatus  660  do not need to be located in receiver box  670 . Signal generator  680  may be attached to Modulators  635  and  640  and just as easily inject signals into the network of communications channels  1  ( 645 ) and  2  ( 655 ). Likewise, test apparatus  660  may be housed separately and coupled to both channel  1  ( 645 ) and channel  2  ( 655 ), or coupled to only one of the two channels. Furthermore, both signal generator  680  and test apparatus  660  may be coupled to the system at virtually any point in the system and still provide some ability to test the system. Also, multiple signal generators and testing apparatuses may be utilized as appropriate. In particular, signal generators may be coupled to each geophone, allowing for individualized testing of the connection between each geophone and a instrument box. 
     The present invention can be configured to operate in different frequency ranges than those discussed herein. Alternate ranges of operation and testing may be used to meet system or environmental requirements. In addition, the 250-350 Hz frequency range of test apparatus  660  may be adjusted. Within the confines of the system, it appears that the restrictions on useful signals are imposed by the modulators ( 635 ,  640 ) and the signal conditioning components ( 625 ,  630 ). As a result, any frequency below 1 kHz may be appropriate for testing the system. Likewise, different components may be tested, such that a signal generator connected to the coupling of signal conditioning  630  and sensors  610 , in conjunction with a test apparatus connected to the coupling of signal conditioning  630  and modulator  635  could be used to test the functioning of signal conditioning  630  during operation of the system. Additionally, signal generators and test apparatus may be used to test connections to power or data storage such as those illustrated in FIG.  3 . 
     As further illustration of the method of the present invention, FIG. 7 illustrates a flow diagram of the method. The method begins with initialization step Start  710 . Following that, the method branches into two paths. Along the first path, the method flows to operation  720 , where the components operate normally. In one embodiment, operation  720  is exemplified by sensors receiving data, disk drives recording data, or power supplies supplying power. Along the second path, the method flows to signaling  730  and then to observing  740 . In one embodiment, signaling  730  is exemplified by a signal generator sending a test signal at an out-of-band frequency to a component. Likewise, in one embodiment, observing  740  is exemplified by a receiver receiving the reflected or returned test signal, or the response signal, from a component to be tested. From each of the two paths, the method then flows either back to repeat one or both paths again, or to termination step  750 . 
     While this method of testing was developed for vibroseis slip-sweep operation, one skilled in the art will readily see the applicability of this method to other forms of sensor and receiver apparatuses and other systems using a two-wire or multi-wire systems for connection. Any system in which a signal can be sent and received over the same wires or through the same connection is suitable for such testing as open and shorts testing, cross coupling between channels, and leakage testing. Furthermore, when an out-of-band signal generator is connected to a component to be tested, the system need only receive the test signals through the connection, so a one-way connection may be sufficient. Alternatively, the system may transmit a signal to induce or trigger a test signal, and then receive the test signal. Therefore, using out-of-band signals to test on a not-to-interfere basis while signals are being received in the signal band may be applied to a wide range of applications. A system may be any collection of components operating cooperatively, it may be integrated tightly or distributed across multiple locations or pieces of equipment, and components need not be housed in a single piece of equipment or location, either. Likewise, sensors are not the only types of components that may be tested in the manner described above. 
     In the foregoing detailed description, the method and apparatus of the present invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present invention. The present specification and figures are accordingly to be regarded as illustrative rather than restrictive.