Abstract:
Pressure sensors and techniques are presented in which one or more piezoelectric discs are housed in a holder structure with a hole allowing exposure of the piezoelectric disc(s) to ambient pressure within a borehole, with wiring leads passing through the holder structure for conveying an electrical signal from the piezoelectric device to an external interface circuit or for conveying an electrical signal from an internal interface circuit to an external data acquisition system.

Description:
[0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61/597,238 that was filed on Feb. 10, 2012 and is entitled METHOD AND APPARATUS TO MEASURE BOREHOLE PRESSURE DURING BLASTING, the entirety of which is incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure involves blasting instrumentation technology in general, and particularly relates to techniques and apparatus for measuring borehole pressure during blasting. 
       BACKGROUND 
       [0003]    In blasting and seismic measurement operations, detonators and explosives are buried in the ground, for example, in holes (often referred to as “bore holes”) drilled into rock formations, etc., and the detonators are wired for external access to blasting machines that provide electrical signaling to initiate detonation of explosives. A tremendous amount of pressure is developed in the boreholes during blasting, and excessive pressure from the firing of one detonator may impair detonators, whether non-electric, electric, or electronic. This situation can be particularly problematic where a plurality of detonators are in a single borehole, and an earlier-firing detonator can produce a pressure wave that disables a later firing detonator in the same borehole. Dynamic pressures during blasting, especially sympathetic pressures from adjacent holes or underlying decks, have been suspected to cause misfires in electronic and non-electronic detonators. Measuring borehole pressures during detonation can facilitate understanding the magnitude of the pressure developed as a function of blasting conditions on the resulting fragmentation, and will help advance the blasting technology. Further, steps may be taken to alleviate such excess pressures based on borehole pressure measurements. 
         [0004]    Thusfar, borehole pressure measurement is primarily done using carbon resistor sensors and strain gauges, which exhibit changes in electrical resistance upon external pressure conditions. However, carbon resistors and strain gauges are piezo-resistive i.e. the resistance changes with external pressure. These sensors, moreover, typically require elaborate mounting and must be supplied with a constant current or a voltage divider as well as thermal compensation and autozeroing via a bridge circuit for proper electrical biasing and feedback. Moreover, conventional borehole pressure measurement techniques are generally costly and complex. Manganin foil gauges have been used for high detonation pressures, and are attractive because of their extremely low thermal coefficient of resistivity and high sensitivity towards hydrostatic pressure. Conventional piezoelectric pressure sensors tend to be expensive and bulky, and often require bulky extraneous charge amplifiers and noise filtering electronics to acquire the signals. Thus, a need remains for improved techniques and apparatus for measuring borehole pressure during blasting operations. 
       SUMMARY 
       [0005]    Various aspects of the present disclosure are now summarized to facilitate a basic understanding of the disclosure, wherein this summary is not an extensive overview of the disclosure, and is intended neither to identify certain elements of the disclosure nor to delineate the scope thereof. Instead, the primary purpose of this summary is to present some concepts of the disclosure in a simplified form prior to the more detailed description that is presented hereinafter. 
         [0006]    The disclosure relates to use of piezoelectric devices to measure the peak borehole pressure during blasting, supported by an internal or external circuit interface with a simple charge integrator and appropriate storage capacitor(s) to provide an output signal indicative of peak borehole pressure associated with a blasting operation. 
         [0007]    A pressure sensor apparatus as well as pressure sensor-equipped detonators and blasters are disclosed along with techniques for measuring borehole pressure during blasting operations. The pressure sensor apparatus comprises a housing with one or more holes or apertures, and one or more piezoelectric devices disposed within the interior of the housing, along with a pair of wire leads that are coupled with the piezoelectric device and which extend outside the sensor housing. 
         [0008]    In certain embodiments, the piezoelectric device or devices at least partially face the aperture of the housing, and all or a portion of the housing interior may be provided with a filler material such as silicone grease to protect against moisture penetration and/or to provide mechanical coupling for transfer of a pressure wave to the piezoelectric device. 
         [0009]    In certain embodiments, moreover, two or more piezoelectric devices are provided within the housing interior, and these can be coupled with one another into a single circuit, such as parallel connection, for improved signal to noise performance. 
         [0010]    An interface circuit may be provided within the housing in certain embodiments, which includes a rectifier coupled with the piezoelectric device and one or more output capacitors to provide a signal to the wire leads, where the piezoelectric device&#39;s longitudinal charge coefficient and the interface circuit capacitance are selected to advantageously provide an output signal with a maximum voltage of about 3-5 V. In some embodiments, the longitudinal charge coefficient of the piezoelectric device is about 300 pC/N or more, such as about 500 pC/N or more, and the piezoelectric device may be made of a ceramic perovskite material, such as lead zirconate titanate (PZT). 
         [0011]    In certain embodiments, the piezoelectric device(s) is at least partially covered with a heat shrink material. In various embodiments, moreover, the sensor apparatus further includes a metal shell. 
         [0012]    In accordance with further aspects of the present disclosure, a pressure sensing apparatus is provided for measuring borehole pressure during blasting operations, which includes one or more piezoelectric devices encapsulated inside a molded structure, as well as a pair of wire leads electrically coupled with the piezoelectric device and protruding from the molded structure. In various implementations, the apparatus may further include metal shell at least partially surrounding the molded structure. 
         [0013]    In accordance with further aspects of the present disclosure, the above described piezoelectric-based pressure sensor apparatus may be incorporated into a blasting detonator, such as within a detonator housing, and/or the sensor apparatus may be mounted to a booster assembly housing. 
         [0014]    A method is provided for sensing pressure in a borehole during a blasting or seismic measurement operation in accordance with further aspects of the disclosure. The method includes locating a piezoelectric-type pressure sensor apparatus within the borehole, initiating a blasting operation, measuring an electrical signal on the pair of wire leads contemporaneously with the blasting operation, and determining a borehole pressure value at least partially according to the measured electrical signal. In certain embodiments, the method further includes connecting the pair of wire leads to an interface circuit, measuring an electrical signal at the output of the interface circuit, and determining the borehole pressure value based at least partially on the output of the interface circuit. In some embodiments, the pressure sensor apparatus is located proximate a detonator or a booster within the borehole. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the various principles of the disclosure may be carried out. The illustrated examples, however, are not exhaustive of the many possible embodiments of the disclosure. Other objects, advantages and novel features of the disclosure will be set forth in the following detailed description of the disclosure when considered in conjunction with the drawings, in which: 
           [0016]      FIG. 1  is a side elevation view in section illustrating an exemplary pressure sensor apparatus with a piezoelectric sensor inside a housing having a pressure interface apparatus for measuring borehole pressure in a blasting operation in accordance with one or more aspects of the present disclosure; 
           [0017]      FIG. 2  is a top plan view illustrating the pressure sensor apparatus of  FIG. 1 ; 
           [0018]      FIG. 3  is a side elevation view in section illustrating another exemplary pressure sensor apparatus with a plurality of piezoelectric sensors proximate corresponding apertures in a common housing in accordance with further aspects of the disclosure; 
           [0019]      FIG. 4  is a simplified side elevation view illustrating an exemplary booster equipped with a detonator and a piezoelectric-based pressure sensor apparatus according to further aspects of the disclosure; 
           [0020]      FIG. 5  is a simplified side elevation view illustrating an exemplary detonator equipped with an internal piezoelectric-based pressure sensor apparatus in accordance with further aspects of the disclosure; 
           [0021]      FIG. 6  is a partial side elevation view illustrating use of the piezoelectric-based pressure sensor apparatus in boreholes formed in the ground as part of a blasting operation, and connection thereof with external interface circuitry and a data acquisition system; 
           [0022]      FIG. 7  is a schematic diagram illustrating an exemplary interface circuit with a rectifier input coupled to a piezoelectric disc and one or more capacitors coupled with the rectifier output for providing a signal to a data acquisition system; 
           [0023]      FIG. 8  is a partial side elevation view in section illustrating another exemplary pressure sensor apparatus with piezoelectric sensor and an interface circuit inside the housing in accordance with further aspects of the present disclosure; 
           [0024]      FIG. 9  is a perspective view showing an exemplary piezoelectric disc and corresponding lead wires for pressure sensing during blasting operations; 
           [0025]      FIG. 10  is a graph showing an exemplary voltage output curve illustrating an output signal from an interface circuit coupled with a piezoelectric sensor apparatus during a blasting operation; 
           [0026]      FIG. 11  is a graph illustrating comparative pressure measurements using a piezoelectric sensor apparatus and a commercial sensor; 
           [0027]      FIGS. 12-14  are perspective views illustrating an exemplary piezoelectric sensor apparatus and incorporation thereof into a booster for sensing borehole pressure during blasting operations; 
           [0028]      FIG. 15  is a graph illustrating piezoelectric-based sensor apparatus output data obtained during electronic detonator blast; 
           [0029]      FIG. 16  is a partial schematic diagram illustrating an exemplary piezoelectric pressure measurement test setup with a piezoelectric sensor set a fixed distance from a donor detonator, along with a conventional PCB sensor and corresponding charge amplifier for comparative testing; 
           [0030]      FIG. 17  is a graph illustrating a voltage output from the interface circuit in response to a pressure wave from a donor detonator spaced 60 mm away from the piezoelectric sensor in the setup of  FIG. 16 ; 
           [0031]      FIG. 18  is a graph illustrating an interface circuit output voltage waveform resulting from multiple pressure pulses in the test setup of  FIG. 16 ; 
           [0032]      FIG. 19  is a graph illustrating the pressures as a function of spacing distance using the conventional PCB sensor and the new piezoelectric sensor; 
           [0033]      FIG. 20  is a blast diagram illustrating a first test site in which the piezoelectric sensors were tested; 
           [0034]      FIG. 21  is a partial side elevation view illustrating deck position of the piezoelectric sensor in the test setup of  FIG. 20 ; 
           [0035]      FIG. 22  is a graph illustrating sensor output voltages for two piezoelectric sensors in the first test site of  FIG. 20 ; 
           [0036]      FIG. 23  is a graph illustrating output voltages of two piezoelectric sensors in a second test site; 
           [0037]      FIG. 24  is a sectional side elevation view illustrating another exemplary pressure sensor apparatus with a piezoelectric sensor inside a housing, where the piezoelectric sensor element is at least partially covered with a heat shrink material; 
           [0038]      FIGS. 25 and 26  are perspective and top plan views illustrating another exemplary pressure sensor apparatus with a piezoelectric element encapsulated in a molded structure; and 
           [0039]      FIG. 27  is a perspective view illustrating another embodiment of the pressure sensor apparatus including a metal shell at least partially surrounding the molded structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    Referring now to the figures, several embodiments or implementations of the present disclosure are hereinafter described in conjunction with the drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the various features and plots are not necessarily drawn to scale. 
         [0041]      FIGS. 1 and 2  illustrate sectional side and top plan views of an exemplary piezoelectric pressure sensor apparatus  100  in accordance with one or more aspects of the disclosure. The sensor  100  includes a housing  102 , such as wood, metal, plastic, or other sturdy rigid material that provides an interior cavity, and includes at least one hole or aperture  104  providing a passageway between the interior cavity and the exterior of the housing  102 . As seen in  FIG. 2 , the housing  102  is generally rectangular shaped, but any suitable shape, aspect ratio and/or form factor may be used. 
         [0042]    Within the interior of the housing  102  is a piezoelectric device  110  for sensing borehole pressures during blasting operations. In certain embodiments, the piezoelectric device is a disc-shaped (e.g., cylindrical) structure, but a piezoelectric device  110  of any suitable size, shape, aspect ratio and/or form factor may be used. In one embodiment, the piezoelectric device  110  is made from a material having a high d 33  longitudinal piezoelectric charge coefficient material property in order to generate high values of piezoelectric charge upon pressure pulses and thus afford a high signal-to-noise ratio during measurement operations. For instance, a ceramic perovskite material such as lead zirconate titanate (PZT) may be used, having a longitudinal charge coefficient of about 300 pC/N or more, more preferably about 500 pC/N or more, such as a NAVY Type 6 device  110  having a d 33  coefficient of about 650 pC/N, a disc diameter about 6.35 mm and a thickness of about 2 mm. 
         [0043]    In general, the piezoelectric sensor device  110  develops a voltage (or potential difference) across two opposite faces when compressed in a direction orthogonal to the faces, and therefore at least one of the sensing faces of the piezoelectric device  110  preferably faces the pressure interface aperture  104  at least partially, as seen in  FIG. 1 . The device  110  can be made of any suitable piezoelectric material or materials, including without limitation piezoelectric ceramics and single crystal materials (gallium phosphate, quartz, tourmaline, lead magnesium niobate-lead titanate (PMN-PT), etc.), where piezoelectric ceramic materials (e.g., PZT) advantageously have high piezoelectric constants to provide better sensitivity and signal-to-noise ratio than is commonly obtainable using single crystal piezoelectric materials. Without being tied to any particular theory, PZT type materials exhibit electric dipole moments in solids, which can be induced for ions on crystal lattice sites with asymmetric charge surroundings (as in barium titanate (BaTiO 3 ) and PZT). 
         [0044]    As seen in  FIGS. 1 and 2 , the piezoelectric device  110  is disposed within the interior cavity of the housing  102 , and may be mounted or supported therein in any suitable manner. The apparatus  100  further includes a pair of wire leads  120  electrically coupled with the piezoelectric device  110  and extending from the interior cavity outside the housing  102 . In one possible implementation, the top and bottom sensing faces of the disc-shaped piezoelectric device  110  are suitably provided with conductive electrode material  112  (top) and  114  (bottom) so that conductive portions  122  of the wires  120  can be soldered to the conductive faces  112 ,  114  using solder  116  as shown. The opposing faces of the piezoelectric discs in one example are metallized to form the electrodes  112 ,  114 , preferably silver or Au—Pd to ensure solderability to subsequent exposed portions  122  of the wires  120 . In certain embodiments, the piezoelectric disc  110  is preferably less than 0.5 inches in diameter and most preferably about 0.25 inches, wherein larger diameter discs may crack during the pressure pulses while very small discs  110  may be difficult to handle and to solder wires to. In other embodiments, any suitable form of electrical connection can be used to connect the conductive portions  122  of the lead wires  120  to the piezoelectric device  110 . Other portions of the lead wires  120  may include insulation  124  as shown, which preferably extends to the external portions of the lead wires  120 . 
         [0045]      FIG. 9  is a photograph showing an exemplary piezoelectric disc  110  and corresponding soldered lead wires  120  for pressure sensing during blasting operations. 
         [0046]    Returning to  FIG. 1 , with the leads  120  connected, the piezoelectric device  110  is then located within the interior cavity of the housing  102 , and may be mounted in any suitable fashion using any suitable mechanical mounting apparatus (not shown), although not a requirement of the present disclosure. The enclosure housing  102  is preferably a sturdy structure that operates to inhibit ingress of moisture, water, fluid, dust, dirt, etc. so as to preserve the sensing capabilities of the device  110 . In this regard, certain embodiments of the sensor apparatus include a filler material  130  provided within all or at least a portion of the interior cavity of the housing  102  in order to protect against moisture penetration and/or to provide mechanical coupling to transfer a pressure wave to the at least one piezoelectric device  110 . In certain embodiments, for instance, the filler material  130  can be silicone grease. In addition, the piezoelectric device  110  is preferably located within the housing interior such that all or a portion of one of the sensing faces  112 ,  114  at least partially faces the aperture  104 , wherein any included filler material  130  may, but need not, overlie the sensing face of the piezoelectric device  110 . 
         [0047]    As seen in  FIG. 3 , the apparatus  100  in certain embodiments may include two or more piezoelectric devices  110  within the interior cavity of the housing  102 . In some implementations, moreover, multiple aperture holes  104  may be provided, preferably located so as to at least partially face a sensing surface or face of the piezoelectric devices  110 . In order to improve sensing capability and to provide a higher signal-to-noise ratio of the apparatus, moreover, the piezoelectric devices  110  in certain embodiments are advantageously coupled with one another into a single circuit. For instance, multiple piezoelectric discs  110  can be arranged with their opposite faces electrically connected to one electrical path, such as by using a single top lead wire  120  as shown in  FIG. 3  with multiple exposed conductive portions  122  soldered to the top faces of the piezoelectric devices  110 , with a similar lower lead wire  120  having conductive portions  122  soldered to the bottom faces of the devices  110 . Also, multilayer piezoelectric ceramics can be used in certain embodiments, wherein higher numbers of piezo discs or layers in the multilayer ceramics advantageously provide higher piezoelectric generated charge during impulse, and thus the better signal-to-noise ratio. 
         [0048]    Referring also to  FIGS. 4-6 ,  FIG. 4  illustrates an exemplary booster  210  equipped with a detonator  204  and a piezoelectric-based pressure sensor apparatus  100  attached to the booster  210 . The booster assembly  210  thus includes a booster housing to which the sensor housing is mounted using any suitable means, such as tape in one example. In the example of  FIG. 4 , the pressure sensor housing  102  is mounted to the bottom of the booster housing, although alternative embodiments are possible in which the pressure sensor housing  102  can be mounted using any suitable technique and structure to other sides or surfaces of the booster  210 . For instance, the pressure sensor apparatus  100  may be advantageously located as close as possible to the detonator  204  that is operatively associated with the booster  210  such that the pressure measurements obtained by the sensor apparatus  100  can closely reflect the actual pressure seen in the borehole  202  by the detonator  204  to facilitate analysis of detonator performance in withstanding actual pressures seen in boreholes  202  prior to detonation of that detonator  204 . 
         [0049]    As seen in  FIG. 5 , the piezoelectric-based pressure sensor apparatus  100  may alternatively be provided as part of a detonator  204  for use in initiating a blasting operation. In this respect, the sensor  100  may be affixed to or otherwise mounted to the detonator apparatus  204  by any suitable means. As seen in the example of  FIG. 5 , for instance, the sensor apparatus  100  can be located inside a detonator shell, and may be crimped with the two piezo electrode wires  120  coming out from the shell, and the detonator/sensor assembly  204 / 100  may be lowered into a borehole by the detonator wires  206  and/or by the pressure sensor signal wires  120 . 
         [0050]      FIG. 6  illustrates use of the piezoelectric-based pressure sensor apparatus  100  in boreholes  202  formed in the ground  200  as part of a blasting operation. The simplified figure illustrates two such boreholes  202   a  and  202   b  packed with main explosives  220 , with the first borehole  202   a  including a single detonator  204  installed within a single booster  210 , and a pressure sensor apparatus  100   a  installed at the bottom of the booster housing  210 . The detonator wires  206  are connected to a blasting machine  230 , and the lead wires  120  of the sensor apparatus  100   a  are coupled to an external interface circuit  140 , which in turn provides an interface output signal to a data acquisition system  150 . In the second borehole  202   b  in  FIG. 6 , two detonator/booster assemblies  204 / 210  are positioned one above the other. The upper detonator/booster assembly  204 / 210  in borehole  202   b  includes a pressure sensor  100   b  mounted to the bottom of the booster  210 . The upper detonator lead wires  206  of both detonators  204  are connected to the blasting machine  230 , and the lead wires  120  of the sensor apparatus  100   b  are connected to another interface circuit  140 , which in turn is connected to the data acquisition system  150 . 
         [0051]    In this example setup, both the sensors  100   a  and  100   b  can be used via the associated interface circuits  140  to obtain pressure measurements corresponding to the borehole pressures experienced by the associated boosters  210  and/or detonators  204  upon activation of the lower detonator  204  in the second borehole  202   b . Thereafter, the sensor apparatus  100   b  can be used to detect borehole pressure in the second borehole  202   b  upon activation of the detonator  204 , booster  210 , and main explosive  220  in the first borehole  202   a . This latter blasting operation will typically lead to destruction of the first sensor apparatus  100   a , and subsequent activation of the upper detonator  204  in the second borehole  202   b  will similarly result in destruction of the corresponding sensor apparatus  100   b . It is noted that this set-up can also be used to measure acceleration inside the borehole  202  and/or to measure vibration/acceleration and thus peak particle velocity on the surface of the ground  200  near the blasting array. The same set up can be used for associated borehole pressure measurements when the firing sequence involves initial detonation of the lower detonator  204  of borehole  202   b , followed by activation of the upper detonator  204  of borehole  202   b  and then activation of the detonator  204  in the first borehole  202   a.    
         [0052]    Referring also to  FIG. 7 , the interface circuit  140  in certain embodiments can be external (e.g., as shown in  FIG. 6 ) and/or may be internal to the sensor apparatus housing  102  (e.g., as shown in  FIG. 8  discussed below). The exemplary interface circuit  140  in  FIG. 7  includes a rectifier formed by diodes D 1 -D 4  for full bridge rectification and subsequent capacitive integration of the voltage signal provided by the piezoelectric disc  110 . Other embodiments are possible in which half bridge rectification can be used with either a single diode or a pair of diodes, or any suitable rectifier circuitry may be provided at the input of the interface circuit  130  for connection to the piezoelectric device or devices  110 . 
         [0053]    The output of the rectifier D 1 -D 4  provides a rectified signal to one or more capacitances C 1 -C 3 , where three such capacitors are shown connected in parallel in the illustrated example of  FIG. 7 . Any suitable single capacitor or multiple-capacitor configuration can be used, including any suitable series and/or parallel connection of capacitor components in the interface circuit  140 . In other embodiments, any suitable integrator circuit can be provided at the output of the rectifier. The signal provided by the rectifier output is thus connected across the capacitance and provided as an input signal to the data acquisition system  150 . In certain embodiments, the longitudinal charge coefficient of the piezoelectric device  110  and the capacitance value are selected such that an output signal of the interface circuit  140  for a rated pressure provides a maximum voltage output of about 3-5V or any other desired voltage level to properly interface with analog-to-digital conversion (ADC) circuitry of the data acquisition system  150 . For example, small values of capacitance of the interface circuit  140  (e.g., 1-20 nF) can lead to high voltage output (e.g., 100-200V) whereas large capacitance values (e.g. 1 or 2 uF) can results in maximum voltage output of 3 or 5V for pressures up to 20 kpsi in certain implementations using the above-mentioned PZT type piezoelectric device  110 . 
         [0054]    In operation, pressure pulses presented to the piezoelectric device  110  via the aperture  104  will generate electrical piezoelectric charges, which are channeled through the rectifier to the charge integrator which is a simple capacitor(s) in the illustrated embodiment. The capacitance is advantageously sized to limit the maximum voltage that can be sensed by the acquisition circuit  150  ( FIG. 6 ). For example, using an I/O ADC pin on a microcontroller employed to sense and record the voltage output, a 1 uF capacitor will max out at 3V at a pressure peak of about 10 kpsi using a piezo exhibiting a d 33  coefficient of approximately 650 pC/N. This is important because the I/O pins on the microcontroller typically have a maximum rating, usually 3.3 or 5V input, beyond which the excessive voltage may damage the internal microcontroller circuitries. 
         [0055]    Another embodiment of the pressure sensor apparatus  100  is illustrated in  FIG. 8 , in which an interface circuit  140  is provided within the interior cavity of the housing  102 . For instance, a circuit board is provided with the rectifier and capacitance components of the interface circuitry  140  shown in  FIG. 7 , and is electrically connected with the piezoelectric device  110  and with the pair of lead wires  120  by any suitable electrical interconnection means. Once again, the value of the capacitance of the on-board interface circuitry  140  is advantageously selected so as to provide a maximum output voltage level corresponding to the input range of a connected data acquisition system  150 . 
         [0056]    It is noted in  FIG. 6  that the interface circuitry  140  (if externally provided) and the data acquisition system  150  will typically be located near the blasting machine  230  which initiates the blast. The data acquisition system  150  preferably includes a fast microcontroller with fairly high speed ADC conversion rate (e.g., 1-10 kHz). The voltage readings are collected and stored into a USB flash-drive, SD/multimedia card or other suitable storage medium. Thereafter, a laptop can access these voltages and convert them into peak pressures form the voltage transition points. 
         [0057]    A graph  300  in  FIG. 10  illustrates an exemplary voltage output curve  302  showing an output signal from an interface circuit  140  coupled with a single PZT piezoelectric sensor apparatus  100  during a blasting operation. In this example, the curve  302  represents the voltage output from a piezo disc  110  subjected to a detonator output 60 mm away. The interface circuitry capacitance in this example was approximately 5 nF, and the voltage output reached about 375V, corresponding to 13000 psi. In one particular implementation, the data acquisition system  150  and/or another computing device which obtains signal values from the data acquisition system  150  for the curve  302  can employ a spreadsheet or other computational application to calculate peak pressure using the capacitance value of the interface circuitry  140  and the peak output voltage from the interface circuitry  140  as follows: 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 d33 
                 650 
                 pc/N 
               
               
                   
                 Cap of piezo 
                 5 
                 nF 
               
               
                   
                 Cap of Storage cap 
                 5 
                 nF 
               
               
                   
                 Peak Voltage 
                 376 
                 V 
               
               
                   
                 Peak psi 
                 13,254 
                 psi 
               
               
                   
                   
               
             
          
         
       
     
         [0058]      FIG. 11  provides a graph  310  illustrating comparative pressure measurements using a piezoelectric sensor apparatus  100  as described above as well as a commercial sensor (made by PCB). Below is another exemplary computation showing that the pressure readings form the set-up is fairly close to those obtained using a commercial sensor which is bulky and expensive. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Storage Cap 
                 Voltage output 
                 Peak Pressure 
               
               
                 (nF) 
                 (V) 
                 (psi) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 50 
                 3966 
               
               
                   
                 100 
                 7931 
               
               
                   
                 150 
                 11897 
               
               
                   
                 200 
                 15862 
               
               
                 1000 
                 1 
                 3569 
               
               
                   
                 2 
                 7138 
               
               
                   
                 3 
                 10707 
               
               
                   
                 5 
                 17845 
               
               
                   
               
             
          
         
       
     
         [0059]      FIGS. 12-14  illustrate an exemplary piezoelectric sensor apparatus  100  and incorporation thereof into a booster  210  ( FIG. 14 ) for sensing borehole pressure during blasting operations. In this example, the housing  102  was fabricated from two pieces of wood, one of which was drilled to form an aperture  104  ( FIG. 12 ). Wire leads  120  were fed out of the apparatus  100 , and silicone grease  130  was provided between the two pieces of wood  102 . Tape can be used to wrap the apparatus  100  ( FIG. 13 ) with the aperture  104  exposed, and this assembly was taped to the bottom of a blasting booster  210  ( FIG. 14 ) with the resulting booster/sensor assembly  210 / 100  having a detonator  204  installed with detonator leads  206  and pressure sensor leads  120  extending from the assembly ( FIG. 14 ). 
         [0060]      FIG. 15  is a graph  320  illustrating piezoelectric-based sensor apparatus output data curves  322  and  324  obtained during electronic detonator blasts. In these examples, sensors  100  were lowered inside boreholes in blasts using non-electric and electronic detonators  204 , and detonators were activated in neighboring boreholes. As seen in  FIG. 15 , the output voltages  322  and  324  are shown as a function of time, wherein various voltages corresponding to the different peak pressures experienced by the sensors  100  are seen from detonations in neighboring adjacent boreholes. The maximum peak pressure measured using the two sensors indicated in  FIG. 15  were calculated to be at 5100 and 9500 psi, respectively. 
         [0061]    Referring also to  FIGS. 16-23 , the piezoelectric sensor device  110  was compared with a commercial pressure sensor inside a water tank where underwater testing of standard output electronic detonators were utilized. As seen in  FIG. 16 , the test set up 400 includes an oscilloscope or other data acquisition system  150  coupled to the piezoelectric sensor  102  via the interface circuit  140  which is spaced a distance D from a donor detonator  402 , where a PCB 138A25 sensor  410  is also spaced from the donor detonator  402  and is coupled with a church amplifier  412 , where the donor detonator  402 , the piezoelectric sensor  102  and the PCB sensor  410  are underwater in the exemplary test set up 400. The comparative test results show excellent agreement between the measurements of both systems obtained in a range of 34-128 MPa, and the actual outputs also compared well with SPICE simulation results. Results were obtained on several blasts where non-electric and electronic detonators were used. Single primed and decked shots were monitored in dry holes, sympathetic pressures from neighboring boreholes or underlying decks of 34-48 MPa were measured while wet holes can exhibit almost 69 MPa of peak pressure. The system can measure a maximum pressure of 138 MPa in the boreholes. Pressure waves on the sensor  102  result in piezoelectric charge generation according to the formula Q=A*d33*P where Q=piezoelectric charge generated; A=area of sensor; d33=piezoelectric longitudinal charge voltage coefficient; and P=pressure. The charge is then sensed by the interface circuitry  140  and transformed into a voltage signal captured analog or digitally via an ADC of the scope or data logger or other data acquisition system  150 . 
         [0062]    During lab testing, the donor detonator  402  was an Austin E-star electronic detonator with aluminum shell containing 750 mg of PETN base charge, and a blasting machine (not shown) was utilized to function the donor detonator  402  when ready. This detonator  402  was inserted into a central fixture, and the piezoelectric element  102  was mounted in a fixture spaced from the donor detonator  402  at fixed distances D ranging from 80, 70, 60, 50 and 40 mm. 
         [0063]      FIG. 17  provides a graph  420  with a curve  422  showing a typical voltage output of the interface circuit  140  based on pressure wave from a donor detonator  402  60 mm away from the piezoelectric element  102 , where the output voltage in this example was monitored using a Tektronix 2024B scope  150  and an x1000 PM-6102 probe. In this case, the output has a plateau at about 600 V and is similar to that obtained through SPICE simulation. The output can reach a few hundred volts but can be judiciously scaled by using the appropriate storage capacitor values in the interface circuit  140  (see  FIG. 7  above). In one experiment, the voltage output was left intentionally high to obtain excellent signal to noise ratio in the beginning of testing. 
         [0064]    A graph  430  in  FIG. 18  illustrates the voltage output curve  432  resulting from multiple reflections of pressure waves detected inside the test water tank. These multiple waves add steps to the voltage output, as predicted by SPICE results. Below are two examples of calculations used to obtain the peak pressure in MPa from the value of the voltage peak and storage capacitance of the interface circuitry  140  using a d33 piezo element  110 : 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 d33 
                 650 
                 pc/N 
               
               
                   
                 Cap of piezo 
                 5 
                 nF 
               
               
                   
                 Cap of Storage cap 
                 5 
                 nF 
               
               
                   
                 Peak Voltage 
                 550 
                 V 
               
               
                   
                 Peak Pressure 
                 133.7 
                 MPa 
               
               
                   
                 d33 
                 683 
                 pc/N 
               
               
                   
                 Cap of piezo 
                 12.5 
                 nF 
               
               
                   
                 Cap of Storage cap 
                 1000 
                 nF 
               
               
                   
                 Peak Voltage 
                 2.8 
                 V 
               
               
                   
                 Peak Pressure 
                 65.6 
                 MPa 
               
               
                   
                   
               
             
          
         
       
     
         [0065]    A commercial pressure sensor  410  was used, made by PCB Piezotronics to calibrate and compare the pressure obtained using the novel piezoelectric elements  100 . The 138A25 (Underwater ICP Blast Pressure sensor) sensor  410  is capable of measuring up to 172 MPa of pressure, and was connected to a PCB 482A22 ICP Signal Conditioner, displayed the peak pressure underwater during detonation. 
         [0066]    Graph  440  in  FIG. 19  shows the composite data of peak pressures using the novel piezoelectric element  102  and the PCB sensor  410 , where the peak pressures follow an inverse relationship with distance D from the donor detonator  402 , and the values calculated using the novel sensor elements  110  are fairly close to those obtained using the commercial system  410  for pressures &lt;138 MPa and at donor detonator distances D of 40-80 mm. 
         [0067]    As seen in  FIGS. 6 and 21 , in field applications, the piezoelectric sensors  100  may be placed within the explosive columns  460 , and are not expected to survive (including the legwires) the detonation and will not yield the in-situ detonation pressure. Thus these piezoelectric sensors  100  can yield only the sympathetic pressures from other adjacent blasts or form the decks below. As seen in  FIGS. 20 and 21 , a first field test was conducted in boreholes containing decked shots containing shock tube detonators at a limestone quarry, in which 21 boreholes (numbered 1″ through “21” in  FIG. 20 ) were formed in two rows, where the boreholes were of a borehole diameter of 14.0 cm, borehole depth of 24.4 m, burden of 3.7 m, spacing of 4.3 m, stem depth of 2.1 m and water depth of 1.8 m, using 5 decks per borehole as seen in  FIG. 21 . The first borehole had delays of 201, 551, 576, 601 and 626 ms while the other boreholes used delays of 67, 417, 442, 467 and 492 ms. As seen in  FIG. 21 , stems  462  and interleaved ANFO explosives  464  were arranged in columns, with each explosive portion  464  including a detonator/booster (labeled as DT/B)  210 , and the uppermost explosive portion  464  also including a piezoelectric sensor  100  (labeled PZO in the drawing). In one experiment, the deck immediately below the piezoelectric sensor contained 140 lb of ANFO and each borehole had up to 550 lb of explosives, and the two piezoelectric sensors  100  were placed on the bottom of the top boosters in boreholes #8 and #10, facing downwards where the shock tube detonators were attached. 
         [0068]      FIG. 22  provides a graph  470  illustrating output voltages  472  and  474  registered on the sensing electronics based on the two piezoelectric sensors  100  in boreholes #8 and #10. In this experiment, the measured peak pressures were calculated to be 36 MPa and 42 MPa in these boreholes #8 and #10, respectively. 
         [0069]    Testing was also performed at a second test site (a limestone quarry) where Austin EStar electronic detonators  402  were used. In this experiment, there were 48 boreholes divided into three rows with borehole diameters of 16.5 cm, borehole depths of 14.5 m, burden of 4.6 m, spacing of 5.5 m and stem depth of 2.4 m. Two piezoelectric sensors were placed in the back row at the corner locations, where the blasting pressure was expected to be the highest coming from earlier detonations. Delay times of the detonators at these corner holes were 720 ms and 895 ms (last ones to fire). The borehole with the 720 ms delay was relatively dry (water depth of 2.1 m), whereas the hole with the 895 ms delay was quite wet and was dewatered prior to loading the shot, and water could be seen still trickling from the borehole walls.  FIG. 23  shows a graph  480  with output voltage curves  482  and  484  monitored during the blast. In this test, peak measured pressures were measured and calculated to be 66 MPa and 35 MPa in a wet hole and dry hole, respectively. 
         [0070]    The presently disclosed piezoelectric sensors  100  with interface circuits  140  are thus operable to sense pressure pulses in boreholes during blasting from adjacent boreholes or underlying decks. These sensors and electronics were verified and calibrated in an underwater lab environment inside a water tank and donor detonators, and the obtained results were very close compared to those obtained using a commercial sensor system. Maximum pressure that can be measured can reach 138 MPa using such piezoelectric sensors  100 . 
         [0071]    Referring now to  FIG. 24  another pressure sensor embodiment  100  is illustrated, in which the piezoelectric device  110 , the lead wires  122 ,  124 , the housing  102 , etc. are generally as described above. In addition, the piezoelectric device  110  is at least partially covered with a heat shrink material  500 , where the heat shrink material  500  can be any suitable heat shrink tubing or other material normally used for electrical connections. The heat shrink material  500  can be used in embodiments which include the aperture  104 , as well as other embodiments having no aperture, and can be used in embodiments employing filler material  130  (e.g.,  FIG. 1  above) or embodiments having no such filler material. In addition, the heat shrink material  500  can be employed in implementations using an on-board interface circuit (e.g., circuit  140  above), and the heat shrink material  500  may, but need not, also cover such interface circuitry  140 . Furthermore, such each shrink material  500  can be employed in embodiments utilizing more than one piezoelectric device  110  within the housing  102 , with the material  500  at least partially covering multiple piezoelectric devices  110 . Also, the interface circuitry itself may be adjusted or otherwise calibrated to accommodate or correct for pressure absorption or damping of the heat shrink material  500  such that the electrical output of the sensor apparatus and associated interface circuitry  140  accurately represents the measured borehole pressure during blasting operations. 
         [0072]      FIGS. 25 and 26  show another exemplary pressure sensor apparatus with a piezoelectric element  110  encapsulated in a molded structure. The molded structure in the illustrated example includes a main portion  502  and a lead wire support portion  506 , with the main portion encapsulating the piezoelectric device  110  and an optional associated circuit board  504  to which lead wires  120  are soldered or otherwise electrically coupled. In addition, the molded structure in this example includes an optional lead wire support  506 , which may, but need not, include through holes  508  exposing portions of the encapsulated lead wires  120 . Any suitable molding material can be used to construct the structure  502 ,  506 , such as molding compound including without limitation Henkel Macromelt DM635 or equivalent. In the illustrated example, moreover, the main portion  502  of the molded structure has a length  510 , such as about 1.42 inches, and an overall molded structure length  512 , such as about 2.2 inches. 
         [0073]    Other embodiments are possible including a variety of sizes and shapes for the molded structure, for example, cylindrical or tubular structures. Use of such a molded structure advantageously facilitates protection of the piezoelectric element from surrounding environmental conditions, particularly water and humidity. The lead wires  120  can be directly coupled to the piezoelectric device disk electrodes, or may be connected to an associated circuit board or other structure  504  as seen in  FIGS. 25 and 26 , and protrude from the molded structure for connection via waterproof connector for connectors to an appropriate external interface circuit  140  (or the interface circuit may be within the molded structure), wherein the lead wires  120  ultimately provide connection to the associated data acquisition system (e.g., data acquisition system  150  as described above). As with the above-mentioned use of heat shrink material  500 , the full or partial encapsulation of the piezoelectric sensing element  110  in the molded structure  502 ,  506  may affect the pressure transducer performance of the apparatus  100 , and thus the apparatus and associated interface circuit  140  may be tuned or calibrated to ascertain the degree of correction for the eventual calculation of pressure impinging on the piezoelectric device  110  through the molded material, particularly the main portion  502 . 
         [0074]    Referring also to  FIG. 27 , another embodiment is shown, in which the sensor apparatus  100  includes a metal shell structure  520 , which can be cylindrical or tubular as shown, or may be of any suitable shape. In this regard, a cylindrical shape may be used such that one or more portions of the exterior of the molded structure contacts or engages an interior surface of the metal shell  520 , although not a requirement for all embodiments of the present disclosure. Embodiments are also possible in which the sensor apparatus  100  includes a metal shell at least partially surrounding the piezoelectric device  110 , without use of a molded structure. Furthermore, embodiments are possible in which a fully or partially surrounding metal shell structure  520  is used in combination with the above described filler material  130  (e.g.,  FIG. 1 ) and/or with heat shrink material  500  (e.g.,  FIG. 24  above). Furthermore, embodiments are possible in which the trick material  500  can be employed around a molded structure  502 ,  506 , with the molded structure encapsulating (fully or at least partially) the piezoelectric sensor apparatus  110 . Other embodiments are possible, in which heat shrink material  500  is provided around all or a portion of the outside of an included metal shell structure  520 . 
         [0075]    The above examples are merely illustrative of several possible embodiments of various aspects of the present disclosure, wherein equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, systems, circuits, and the like), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component, such as hardware, processor-executed software and/or firmware, or combinations thereof, which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the illustrated implementations of the disclosure. In addition, although a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Also, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.