Abstract:
A detection circuit for detecting changes in capacitance. The detection circuit includes a tuned ratio circuit and an alternating current (AC) source AC-coupled to the tuned ratio circuit. The tuned ratio circuit includes first and second tuned circuits that are tuned to, or close, to the frequency of the AC source. Output circuitry is coupled between the two tuned circuits. During use as a transducer, an active capacitive transducer is inductively coupled to the first tuned circuit. Changes in the capacitance of the active capacitive transducer cause changes in the tuning of the first tuned circuit. The output circuitry generates an output signal that is a function of the difference between the tunings of the first and second tuned circuits.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 61/156,558, filed Mar. 2, 2009, and titled “Detection Circuit for Use in Various Types of Capacitive Transducers and a Transducer Including Such a Circuit,” that is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to the field of electrical transducers. In particular, the present invention is directed to a detection circuit for use in various types of capacitive transducers and a transducer including such a circuit. 
       BACKGROUND 
       [0003]    Transducers that translate forces, pressures, displacements, etc. into electrical signals that can be used to measure such forces, pressures, displacements, etc. are used in many applications. A currently popular type of such transducer is a Kulite Type BG-10, manufactured by Kulite Semiconductor Products, Inc. Although these semiconductor strain gauge transducers are widely used, they can suffer from a number of drawbacks, such as being easily damaged by slight overloads applied to the force beam, causing the transducer to be non-functional, or have a very large offset voltage, that may not be able to be compensated for in electronic amplifiers. 
         [0004]    As mentioned in the above paragraph the semiconductor style of strain gauge is very fragile when made for a low force/weight application, where the gauge itself is physically small. The semiconductor gauges are glued onto the force beam in an area that has a milled-out pocket in the metal beam. This gives an area that “moves” in relation to the applied forces. If the force beam is moved sharply or has more force applied to it than recommended, which can easily happen by dropping the gauge, or over tightening a screw to attach a load to the force beam, the glue holding the gauges may let go, or one or more of the glass-like semiconductor gauges may break making a very expensive device inoperative. If the semiconductor gauge is subjected to larger-than-recommended forces, a large offset voltage may appear on the output signal. This offset voltage may be 2-3 times greater than the desired force signal and may be large enough to not allow compensation by offset controls in signal conditioning equipment. 
         [0005]    Another type of transducer available is a capacitive force transducer typically used for measuring small biological force signals. These devices typically contain a free-running resistor-capacitor (RC) oscillating circuit, which generally has a practical upper frequency limit of about 3 MHz due to instability issues. While free-running RC oscillating circuits can go into the hundreds-of-MHz range, stability becomes a major problem at such high frequencies. Even at 1 MHz, the task of frequency compensation is tedious because of the need to hand-select compensation components and oven-test the devices. In addition, the low operating frequency of such a free-running circuit requires the capacitor to be physically large. This slows the response of the circuit to fast external signals and limits the upper frequency range because a small external force must overcome the “at-rest” position of the capacitor plates. A particular 1-MHz free-running RC-circuit-type capacitive transducer investigated by the present inventor was about 2 inches square and about 0.75 inch thick. This large size limits the usefulness of the transducer. 
       SUMMARY OF THE INVENTION 
       [0006]    In one implementation, the present disclosure is directed to a transducer system. The system includes: an alternating current (AC) voltage source for providing a constant frequency voltage; a tuned ratio detector AC coupled to the AC voltage source, the tuned ratio detector including first and second tuned circuits each coupled to the AC voltage source by corresponding respective first and second coupling elements; a transducer link inductively coupled to the first tuned circuit; a transducer electrically coupled to the transducer link; and signal output circuitry electrically coupled between the first and second tuned links. 
         [0007]    In another implementation, the present disclosure is directed to a transducer system. The system includes: a cantilever-beam capacitive transducer for providing a transducer signal; a detection circuit for detecting the transducer signal and outputting a measurement signal as a function of the transducer signal, the detection circuit including: an alternating current (AC) voltage source for providing a constant frequency voltage; a tuned ratio detector AC coupled to the AC voltage source, the tuned ratio detector including first and second tuned circuits each coupled to the AC voltage source by corresponding respective first and second coupling elements; a transducer link inductively coupling the cantilever-beam capacitive transducer to the first tuned circuit; and signal output circuitry electrically coupled between the first and second tuned links for outputting the measurement signal; and a housing supporting the cantilever-beam capacitive transducer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
           [0009]      FIG. 1A  is a schematic diagram of a transducer system made in accordance with concepts disclosed in the present disclosure;  FIG. 1B  is an enlarged elevational view of a sensor for sensing the magnitude of direct current in a conductor that can be used with the detection circuitry of  FIG. 1A ; 
           [0010]      FIG. 2  is a graph of voltage versus frequency of the detection circuit portion of the transducer system of  FIG. 1A  illustrating the effect of differing quality-factor values on the sensitivity of the circuit; 
           [0011]      FIG. 3  is a combination isometric view/high-level block diagram of a force measuring system made in accordance with concepts of the present disclosure; 
           [0012]      FIG. 4  is an enlarged cross-sectional view as taken along line  4 - 4  of  FIG. 3 ; and 
           [0013]      FIG. 5  is an enlarged cross-sectional view as taken along line  5 - 5  of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Some embodiments of the present disclosure are directed to unique capacitive-transducer-based transducer systems for converting physical manifestations, such as pressure, force, displacement, strain, translation, vibration, rotation, etc., into electrical signals, and detection circuits for such systems. Other embodiments of the present disclosure may be configured for non-contact measurement of direct current (DC) in DC circuits. Transducer systems and detection circuits made in accordance with the broad concepts of the present disclosure can be made very sensitive and very stable, and transducer systems thusly made can be made small in size and very rugged, if desired. 
         [0015]    At a high level, the designs of detection circuits disclosed herein are based on the principles of reactance of a tuned circuit. In one instantiation, the design utilizes a pair of parallel tuned circuits tuned at or near resonance with a oscillating-voltage source, such as a radio-frequency (RF) voltage source. A capacitive transducer is inductively coupled to one of the tuned circuits so that the influence of the pertinent physical manifestation(s) on the capacitive transducer is transformed into variation in the tuned circuit. As the tuning of this circuit is moved off of resonance, the voltage on its output changes, showing up as a positive or negative voltage signal, depending on whether the tuning at a particular instant is above or below resonance. Typically, the output, or measurement, signal is in the hundreds-of-millivolts regime and can be used as is or, in some embodiments, the measurement signal can be amplified to provide a more robust output. 
         [0016]    Referring now to the drawings,  FIG. 1A  illustrates an example transducer system  100  made in accordance with broad concepts of the present invention. Transducer system  100  includes a detection circuit  102 , a capacitive transducer  104  and a transducer link  106  connecting the capacitive transducer to the detection circuit. In this example, detection circuit  102  includes an RF voltage source  108 , a pair of parallel tuned circuits  110 ,  112 , and output circuitry  114  electrically coupled between the parallel tuned circuits. RF voltage source  108  may be any suitable source that provides a stable RF frequency voltage, such as a crystal oscillator. In one prototype built by the present inventor, RF voltage source  108  was a pre-packaged surface-mount oscillator operating from a 5-volt DC power supply (not shown) and provided a voltage frequency in the megahertz regime. 
         [0017]    In this embodiment, each parallel tuned circuit  110 ,  112  includes an inductor-capacitor pair  116 ,  118 , respectively, each of which contains an inductor  120 ,  122  and a variable capacitor  124 ,  126 . As described below, capacitors  124 ,  126  are variable so as to provide a means for tuning corresponding respective parallel tuned circuits  110 ,  112 . Each inductor  120 ,  122  and capacitor  124 ,  126  is electrically connected to a signal ground  128 . In this example, inductors  120 ,  122  are of the wound, iron-core type. However, in other instantiations, inductors  120 ,  122  may be of another type, such as the spiral type etched onto a printed circuit board. It is noted that while in this example capacitors  124 ,  126  are variable, in other instantiations inductors  120 ,  122  may additionally or alternatively be variable so as to provide the tuning adjustment needed to tune parallel tuned circuits. 
         [0018]    In an out-of-resonance state, parallel tuned circuits  110 ,  112  exhibit a low impedance to the RF voltage signal coming from RF voltage source  108  until the parallel tuned circuits are brought into resonance using corresponding respective variable capacitors  124 ,  126 . With each inductor-capacitor pair  116 ,  118  out of resonance, the RF voltage across them is low. When each parallel tuned circuits  110 ,  112  is brought to resonance, the impedance of the inductor-capacitor pair  116 ,  118  rises, as does the RF voltage. The two parallel tuned circuits  110 ,  112  are tuned, or substantially tuned, to the frequency of RF voltage source  108 . A further description of the tuning of parallel tuned circuits  110 ,  112  is provided below in connection with describing the operation of detection circuit. 
         [0019]    Parallel tuned circuits  110 ,  112  are capacitively coupled to RF voltage source  108 , for example by a coupling capacitor  130 , so as to block any DC voltage originating with the RF voltage source from reaching the parallel tuned circuits. Each parallel tuned circuit  110 ,  112  is isolated from RF voltage source  108  by a corresponding isolator, in this case a resistor  132 ,  134 , that provides isolation of the sensitive parallel tuned circuit from the RF voltage source. The resistance values of the two resistors  132 ,  134  are preferably identical to one another. The resistance value selected for resistors  132 ,  134  is generally not critical. In one example, this resistance value is in the range of about 2 kΩ to about 3.5 kΩ. Other isolators, such as RF transformers, could be used, if desired. However, resistors are typically the least expensive of the isolators that may be used and will often be entirely suitable. 
         [0020]    In this example, output circuitry  114  includes a variable resistor  136  and a pair of rectifiers, here single diodes  138 ,  140 , electrically coupled between corresponding respective ones of parallel tuned circuits  110 ,  112  and the variable resistor. Diodes  138 ,  140  rectify the RF voltage that appears across parallel tuned circuits  110 ,  112 , and the resulting DC voltage is applied across variable resistor  136 . Variable resistor  136  can be used as a zeroing control to remove slight imbalances in the parallel tuned circuits  110 ,  112 . It can also be used to remove any preloads that may be applied to capacitive transducer  104 . For example, if capacitive transducer  104  is a cantilever-beam-type transducer, variable resistor  136  can be adjusted to remove a preload from the beam of the transducer. This can be thought of as being analogous to a tare function found on electronic balances. Variable resistor  136  includes a wiper arm  142  that is capacitively coupled to signal ground  128  by a coupling capacitor  144 . This capacitive coupling provides filtering for the rectified RF voltage and also inhibits RF energy from detection circuit  102  from reaching any electronic devices (not shown), such as an amplifier, that may be electrically connected to output circuitry  114 . 
         [0021]    In the example transducer system  100  shown in  FIG. 1A , capacitive transducer  104  is of the cantilever-beam type in which the capacitive element  146  includes a fixed charge plate  148  and a movable charge plate  150  electrically isolated from the fixed charge plate. Movable charge plate  150  is fixed at one end and free at the other so as to provide the cantilever-beam characteristic of this type of capacitive transducer. Depending on the direction of an external load  152  applied to movable charge plate  150 , the movable capacitor plate moves toward or away from fixed charge plate  148 , thereby changing the capacitance of capacitive element  146 . It is this change in capacitance that is detected by detection circuit  102  and allows transducer system  100  to measure, in this example, the force applied to movable capacitor plate  150 . 
         [0022]    The shapes of fixed and movable charge plates  148 ,  150  are preferably selected so that the output of capacitive transducer  104  is linear as the movable charge plate is moved toward and away from the fixed charge plate. As those skilled in the art will appreciate, this capacitive element could also be used to measure displacement, pressure, etc. In other instantiations of transducer system  100 , capacitive element may be of another type, such as, for example, one in which one charge plate translates relative to another charge plate, one in which one charge plate moves toward and away from another without any bending, and one in which a movable dielectric moves in and out of a space between two fixed charge plates. The form of the type of capacitive element selected for capacitive element  146  is up to the designer of capacitive transducer  104 . 
         [0023]    In this example, capacitive transducer  104  also comprises an RF transformer  154  that includes a pair of primary and secondary windings  156 ,  158  and, in this example, an iron core  160 . Transducer link  106  is a low-impedance link that includes an inductor  162  and a coaxial cable  164  that electrically couple capacitive transducer  104  to detection circuit  102  and allows the capacitive transducer to be spaced from the detection circuit by the distance required for a particular design. It is noted that the length of coaxial cable  164  generally does not affect the performance of transducer system  100  and, so, could be relatively very long, if desired. 
         [0024]    Inductor  162  is connected to signal ground  128  and inductively couples the signal (not shown) carried by coaxial cable  164  to detection circuit  102 . Coaxial cable  164  includes a core conductor  166 , which caries the signal, and a grounded sheath  168  grounded to signal ground  128 . Primary winding  156  of RF transformer  154  is electrically coupled between core conductor  166  and ground sheath  168 . In this example, secondary winding  158  is electrically coupled between fixed charge plate  148  and ground sheath  168 , and movable charge plate  150  is electrically coupled to the ground sheath of coaxial cable  164 . Capacitive element  146  is across secondary winding  158  of RF transformer  154  and forms a parallel tuned circuit very similar to parallel tuned circuit  110  formed by inductor-capacitor pair  116 . 
         [0025]    Very slight changes in capacitance of capacitive element  146  caused by physical movement of movable charge plate  150  relative to fixed charge plate  148  are translated to inductor-capacitor pair  116  and affect the resonance of parallel tuned circuit  110 . With proper adjustment to parallel tuned circuits  110 ,  112 , movement of movable charge plate  150  of capacitive transducer  104  in one direction will provide a positive output voltage at output circuitry  114 , and movement in the opposite direction will provide a negative output voltage. The amount of voltage varies with the applied force on movable charge plate  150 . In a prototype built by the present inventor, the output signal from wiper arm  142  of variable resistor  136  was approximately 20 millivolts per gram of force on cantilevered movable charge plate  150 . 
         [0026]    While the example of  FIG. 1A  is directed to a device for measuring a force, pressure, displacement, etc. based on a physical movement of movable charge plate  150  relative to fixed charged plate  148 , transducer system  100  of  FIG. 1A  can be modified to sense the amount of current flowing in a wire carrying direct current. The changes to the basic circuit needed to accomplish this are minimal. For example, transducer system  100  can be modified to a DC-measuring system by making secondary winding  158  ( FIG. 1A ) into a winding  172  ( FIG. 1B ) (formed from core conductor  166  of  FIG. 1A ) on a toroidal core  176  ( FIG. 1B ) and resonating this winding with a fixed value of capacitance. A conductor  180  extending through the opening of toroidal core  176  and carrying direct current will change the permeability of the toroidal core and cause a voltage output signal on core conductor  166  that is proportional to the direct current in conductor  180 . The voltage output signal on core conductor  166  would then be detected by detection circuit  102  ( FIG. 1A ). 
         [0027]    Referring to  FIG. 2 , and also to  FIG. 1A ,  FIG. 2  is a graph  200  showing three voltage-versus-frequency curves  202 ,  204 ,  206  illustrating resonance in RF circuits having three differing quality, or “Q-factors.” The amount of voltage across an inductor-capacitor pair, such as either of inductor-capacitor pairs  116 ,  118  of parallel tuned circuits  110 ,  112  of  FIG. 1A , depends on the source voltage applied to the tuned circuit and the Q-factor of the inductor-capacitor pair. The Q-factor of a tuned circuit is primarily related to the inductor&#39;s physical properties and how good it is, such as the magnetic core losses and wire losses. The quality of capacitors  124 ,  126  in parallel tuned circuits  110 ,  112  in detection circuit  102  is generally not of significance to the Q-factor of the respective parallel tune circuits because capacitors typically have lower losses as compared to inductors, here inductors  120 ,  122 . 
         [0028]    In  FIG. 2 , curve  202  illustrates that a tuned circuit having a high Q-factor, corresponding to low losses, has a relative narrow resonance band  202 A. Consequently, the sensitivity of high-Q-factor tuned circuits is high. Curve  204  illustrates that a tuned circuit having a lower Q-factor has a wider resonance band  204 A. The sensitivity of such a circuit is somewhat lower. Curve  206  illustrates a tuned circuit having a low Q-factor, i.e., high losses. As seen, the resonance band  206 A is wide, and the circuit has low sensitivity. 
         [0029]    As mentioned above, in this example, inductors  120 ,  122  are fixed at a particular inductance, and capacitors  124 ,  126  are variable. Assuming the tuning of parallel tuned circuits  110 ,  112  is initially out of their resonance band, as the capacitances of capacitors  124 ,  126  are varied, the RF voltage across these capacitors slowly rises as resonance is approached. This can be seen from, for example, curve  202  of  FIG. 2  with the voltage increasing as the tuning approaches resonance from either side of peak  202 B. If the capacitances of capacitors  124 ,  126  are continued to be changed in the same direction, the voltage will continue to rise, until a peak, e.g., peak  202 B of curve  202  of  FIG. 2 , is reached in each parallel tuned circuit  110 ,  112 . After that, any further changes of capacitances in the same direction will go beyond peak resonance and the voltages will start to drop. 
         [0030]    With the proper tuning of parallel tuned circuits  110 ,  112 , moving movable charge plate  150  in one direction will give a positive output signal (not shown) at wiper arm  142  of variable resistor  134 , and moving it in the opposite direction will provide a negative voltage signal at the wiper arm. The exact amount of voltage per unit force is generally a function of the physical design of capacitive element  146  of transducer  104  and the sensitivity of detection circuit  102 . As mentioned, in a prototype made by the present inventor, an output signal of about 20 millivolts per gram was obtained, and the output signal was linear up to about 25 grams. The maximum load limit is a function of, for example, beam thickness, and amount of travel. 
         [0031]    The proper choice of parts is important for good operation, and all parts used in the prototypes made by the present inventor were of the surface mount type. Capacitors  124 ,  126 ,  130  were temperature-stable types and diodes  138 ,  140  were both in the same surface mount package for temperature stability. This allowed diodes  138 ,  140  to both be influenced in the same amount as temperatures changed, making the output of detection circuit  102  more stable. These design measures are good RF design options for stable operation of circuits operating in the tens-of-megahertz range. 
         [0032]    All of the prototypes made by the present inventor operated at 12 megahertz. This frequency was chosen because the sizes of inductors  120 ,  122  and primary winding  156  were good for hand assembly. However, 12 megahertz should not be considered at all to be limiting relative to the broad range of frequencies that can be used in many other embodiments. In addition, the present inventor had to manually wind the coupling links of inductor  162  and secondary winding  158 . Transducer system  100  will operate from a low-kilohertz regime to a hundreds-of-megahertz regime. The primary component values that change for wide excursions in frequency are the corresponding respective values of RF voltage source  108 , primary and secondary windings  156 ,  158  in RF transformer  154 , capacitors  124 ,  126  and inductors  120 ,  122 . While the prototype of detection circuit  102  was made from surface-mount type devices, those skilled in the art will understand that depending on the operating regime at issue, such a detection circuit may be implemented using integrated-circuit type devices and techniques. 
         [0033]    Referring now to  FIGS. 3-5 , these figures illustrate a force measuring system  300  that includes an integrated force-transducing device  302  and a power supply/measurement apparatus  304 . Integrated force-transducing device  302  integrates a transducer system  400  ( FIG. 4 ) within a suitable housing  306 . Transducer system  400  is a transducer system made in accordance with the broad concepts of the present disclosure, such as transducer system  100  of  FIG. 1A . Transducer system  400  includes a capacitive transducer  404  and a detection circuit  408  electrically coupled to the capacitive transducer via a transducer link  412 . When transducer system  400  is configured like transducer system  100  of  FIG. 1A , details of capacitive transducer  404 , detection circuit  408  and transducer link  412  can be found above relative to corresponding capacitive transducer  104 , detection circuit  102  and transducer link  106  of  FIG. 1A . Consequently, there is no need to repeat those details here. 
         [0034]    Referring to  FIGS. 3 and 4 , in this example, housing  306  is generally a two-piece housing having a cuboid shape and consisting of a first piece  308  and a second piece  312  secured to one another to form a monolithic assembly. It is noted that while housing  306  is shown as being cuboidal, in other embodiments the housing may have another shape, such as cylindrical, among many others. Moreover, any housing provided need not have two pieces, but rather may have more or fewer as needed to suit a particular design. 
         [0035]    First and second pieces  308 ,  312  may be secured to one another in any suitable manner, such as by brazing, adhesive bonding, soldering, welding, mechanical fastening, and any combination thereof. One end of housing  306  has a beam opening  316  that receives a cantilever beam  320  that forms part of capacitive transducer  404  ( FIG. 4 ) located inside the housing. The size of beam opening  316  can be selected based on the deflection requirements of cantilever beam  320 , including, as needed, stop surfaces  500 ,  504  ( FIG. 5 ) that mechanically limit the displacement of the cantilever beam so as to inhibit damage to any components of capacitive transducer  404  and/or detection circuit  408 . 
         [0036]    Cantilever beam  320  may be made of any suitable material(s), such as one or more metals, one or more metal-containing composite, one or more plastics, one or more ceramics, and any combination thereof. In one particular example, cantilever beam  320  is made of a nickel steel alloy having a very low coefficient of thermal expansion, such as INVAR® steel (INVAR is a registered trademark owned by Imphy Alloys, Puteaux, France). If cantilever beam  320  is made of a dielectric material, an electrically conductive region must be located in relation to a fixed charge plate  416  ( FIG. 4 ) so as to provide a movable charge plate that, when it moves, drives the variable capacitance that underlies the functionality of capacitive transducer  404 . Of course, when cantilever beam  320  comprises a conductive material, such as the INVAR® steel mentioned above, at least a portion of the cantilever beam itself acts as the movable charge plate. Fixed charge plate  416  may be made of any suitable conductive material, such as a metal or metal containing composite. In one example, fixed plate  416  is made of the same INVAR® steel used to make cantilever beam  420 . 
         [0037]    In this example and referring to  FIG. 4 , each of first and second pieces  308 ,  312  of housing  306  is primarily a unitary monolithic block having various recesses and openings for accommodating certain parts of integrated force-transducing device  302 . While each of first and second pieces  308 ,  312  of housing  306  may be made of any suitable material(s), in one particular example each piece is made from a block of aluminum into which the various recesses and openings are formed, for example, by molding or machining (or any other type of material removal operation) and any combination thereof. In this example, first piece  308  includes a beam recess  420  that receives a portion of cantilever beam  320  and is sized to allow the cantilever beam to deflect by a maximum desired amount. When first and second pieces  308 ,  312  confront one another as shown, in this embodiment beam recess  420  and surface  422  of the second piece together define beam opening  316  and a beam pocket  424  into which the cantilever beam is fixedly engaged. This fixed engagement may be effected in any suitable manner, such as by brazing, adhesive bonding, soldering, welding, mechanical fastening, shrink fit, and any combination thereof. 
         [0038]    Second piece  312  of housing  306  in this example includes a first recess  428  that contains fixed charge plate  416  and other components of capacitive transducer  404 , such as an RF transformer (not shown). When second piece  312  comprises an electrically conductive material, fixed charge plate  416  should be electrically insulated from the second piece by a suitable dielectric material  432 , such as a fluoropolymer, epoxy, silicon or other material, and any combination thereof. Dielectric material  432  should be suitably rigid to inhibit movement of fixed charge plate  416  relative to second piece  312  of housing  306 . Fixed charge plate  416  may also be electrically insulated from cantilever beam  420  (or movable conductive plate attached thereto) using a suitable dielectric layer  434 , which may be in addition to air in the space between the first charge plate and cantilever beam (or movable plate attached thereto). Dielectric layer  434  may be made of any suitable dielectric material(s). 
         [0039]    In this example, second piece  312  of housing  306  also includes a second recess  436  that contains detection circuit  408 . Detection circuit  408  may be secured within second recess  436  using any suitable means, such as a backfill of a dielectric material  440 , such as an epoxy, silicon or other non-electrically conductive material. In this example, second piece  312  of housing  306  also includes a first opening  444 , which extends between first and second recesses  428 ,  436  through which transducer link  412  extends from capacitive transducer  404  and detection circuit  408 , and a second opening  446  through which power and signal wires  448  extend to a point outside of integrated force-transducing device  302 , here, to power supply/measurement apparatus  304  ( FIG. 3 ). One, the other, both, or neither of first and second pieces  308 ,  312  of housing  306  may include, or have attached thereto, one or more structures for securing integrated force-transducing device  302  to a support structure (not shown). In this example, second piece  312  includes a tab  324  having a pair of apertures  328  for receiving mechanical fasteners, such as screws. 
         [0040]    In this example, power supply/measurement apparatus  304  ( FIG. 3 ) includes a power source  332  for providing power to detector circuit  408  ( FIG. 4 ), particularly the voltage oscillator (not shown, but see, e.g., RF voltage source  108  of  FIG. 1A ). Voltage oscillators suitable for use as the voltage oscillator of detector circuit  408  are well-known in the art, as are power supplies for such oscillators. Therefore, further description of such power supplies is not necessary herein for those skilled in the art to make and use force-measuring system  300  or any other force-measuring system made in accordance with the broad concepts of the present disclosure. 
         [0041]    Power supply/measurement apparatus  304  of this example also includes measurement circuitry  336  for translating a voltage signal output by integrated force-transducing device  302  into a measurement expressible, for example, in a standard unit of force, such as a newton or pound-force. Such measurement circuitry is well known in the art, such that a detailed explanation is not necessary here. In the present example, power supply/measurement apparatus  304  is configured as a standalone device, in this case meaning that it can both power integrated force-transducing device  302 , but it can also display, via a display  340 , measurements determined by measurement circuitry  336  using signals obtained from integrated force-transducing device  302 . It is noted that measurement circuitry suitable for use as measurement circuitry  336  includes not only analog circuitry, but also digital circuitry that is programmable to provide the measurement determination functionality, and a combination of analog and digital circuitry. In one example, measurement circuitry  336  includes, among other things, an analog-to-digital (A/D) converter and a microprocessor (both not shown). The A/D converter converts the signal from integrated force-transducing device  302  to a digital value that it provides to the microprocessor, which may solve a suitable equation for calculating a force value as a function of the value of the digitized signal. 
         [0042]    As those skilled in the art will readily appreciate, power supply/measurement apparatus  304  may include any one or more of a variety of useful features, such as one or more communications ports  344  (wired and/or wireless). Such communications ports  344  can be used for communicating data, such as raw analog and/or digital signals acquired from integrated force-transducing device  302  and/or calculated measurement data, to another apparatus, such as a general purpose computer, digital storage device, etc. (not shown). Another useful feature that power supply/measurement apparatus  304  may include is a hard user interface  348  for allowing a user to manually tune detection circuit  408  ( FIG. 4 ), for example, in the manner discussed above. Alternatively, or in addition, to hard user interface  348 , power supply/measurement apparatus  304  may include a soft user interface (not shown) for providing the same functionality. Such a soft user interface may be displayable on, for example, display  340  and implemented in software. It is noted that in other embodiments, a suitable power supply/measurement apparatus may be implemented in a personal computing machine, such as a desktop or laptop computer. For example, a desktop computer may be fitted with a daughterboard having appropriate circuitry, such as an analog-to-digital converter, transducer power supply, etc., for interfacing with a transducing device made in accordance with broad concepts of the present disclosure. In other embodiments, a transducing device made in accordance with broad concepts of the present disclosure may incorporate the appropriate interfacing circuitry such that all that is needed to interface with a personal computer or other computing machine is a suitable connection between the device and the machine, such as a universal serial bus connection, a FIREWIRE (IEEE 1394) connection and a BLUETOOTH (IEEE 802.15.1) connection, among others. 
         [0043]    Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.