Abstract:
A digital voltage detector system that is compatible with existing Armament Circuits Preload Test Sets is described. Adjustment of under and over voltage trip points is accommodated in accordance with conventional means. The digital voltage detector is compatible with all conventional Voltage Detector interface cables and adapters. Unlike the conventional voltage detector of existing Armament Circuits Preload Test Sets, over-voltage trips do not blow a fuse, eliminating the need to have replacement fuses or redundant conventional voltage detectors in an Armament Circuits Preload Test Set. Additionally, the digital voltage detector provides a digital voltage readout allowing the user to view the input voltage during a Presence of Voltage test. The digital voltage detector system facilitates timely and efficient execution of the Armament Circuits Preload Test series.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 12/136,656 filed on Jun. 10, 2008, the contents of which are hereby incorporated by reference in its entirety, and to which priority is claimed herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to voltage detectors and more particularly to a voltage detector suitable for use in an Armament Circuits Preload Test Set. 
         [0003]    Armament Circuits Preload Test Sets, are used, for example, with air to air missiles, launchers, gravity and guided bombs, multi-ejector racks, and other munitions release systems on combat aircraft. Aircraft on which Armament Circuits Preload Test Sets are used include the F-15 fighter, models A, B, C, D, and E. Armament Circuits Preload Test Sets comprise a voltage detector and interface adapters. The interface adapters provide electrical connection between the voltage detector and various connector types located on the aircraft. The conventional voltage detector performs at least four key test functions when used in an Armament Circuits Preload Test series. The voltage detector assesses Presence of Voltage, continuity in an Electroexplosive Device (EED), and Stray Voltage. The voltage detector also performs an Adapter Test. 
         [0004]    An EED conventionally consists of a conductor and a primary combustible material. A variety of propulsion systems and ordnance use an electrical signal to initiate combustion. This signal can be a dc current. Ohmic heating due to dc current flowing in the conductor can raise conductor temperature rapidly. Once a minimum ignition temperature of the primary combustible material is reached, the primary material ignites, which in turn initiates combustion of a secondary material. Part of the Armament Circuits Preload Tests may include a continuity check in an FED. The same conventional voltage detector performs an ohmic Adapter Test and two voltage tests. 
         [0005]    The Stray Voltage Test determines whether a circuit that is in an unenergized state is actually free of any voltage that could cause a malfunction in the tested circuit. For example, an FED must normally be tested to ensure that the circuit is free of any stray voltages that could cause an improper triggering of the primary combustible material. 
         [0006]    For the conventional voltage detector, an input voltage greater than 0.120 VDC or less than −0.120 VDC causes the voltage detector to turn on the indicator light. The conventional voltage detector comprises the attachment of a 3 ohm load resistance to the measurement circuit for the Stray Voltage Test. 
         [0007]    The Presence of Voltage test determines whether an input voltage between 22.0 VDC and 47.0 VDC is present. In the conventional voltage detector, if an input voltage of less than 22.0 VDC is detected, then a test light turns off. Alternatively, however, if the measured input voltage is greater than 47.0 VDC, then a protection circuitry within the conventional voltage detector trips a protection fuse. Before the conventional voltage detector can make subsequent measurements, the fuse must be replaced. And the fuse is not readily accessible, requiring the removal of screws for removal and replacement. Therefore, a technician using the conventional voltage detector would need to have spare fuses at hand and deal with the additional duties of repairing the voltage detector before proceeding with an Armament Circuits Preload Test. Another alternative is to have multiple voltage detectors in each Armament Circuits Preload Test Set. 
         [0008]    The conventional voltage detector can also trip the indicator light for a voltage level less than 22.0 VDC and can also invoke the protection circuit for voltages greater than 47.0 VDC. That is, adjustments can be made for measured-input voltage as low as 3.5 VDC to turn off the indicator light. Likewise, an over-voltage as high as 300 VDC can be measured before blowing the protective fuse. 
         [0009]    External resistors are used to adjust the level for which the indicator light will turn off or for which the fuse will blow, under voltage and over voltage, respectively. The conventional analog voltage detector  100  and internal resistors circuit  110  is shown in  FIG. 1   a . The over voltage protection circuit of the conventional voltage detector is not shown. 
         [0010]    External resistors are used to vary the input voltage level which trips under voltage or over voltage. For an under voltage trip point greater than 22.0 VDC, an external resistor  126  is connected in series with TEST_IN+  120  to create a voltage divider between the external resistor and the internal 300 ohm load  112 , as shown in  FIG. 1   b . Connection for TEST_IN+ measurement is moved to  121 , in this configuration. 
         [0011]    For an under voltage trip point of 3.5 VDC, the TRIP_ADJ pin  130  is connected to TEST_IN+  120  via connector  122 , as shown in  FIG. 1   c . This configuration raises the input voltage at sense input  142 . For under voltage trips between 3.5 and 22 VDC, the TRIP_ADJ pin  130  is connected via connector  122  to TEST_IN+  120  and an external resistor  126  is connected in series with TEST_IN+, moving the TEST_IN+ measuring point to position  121 , as shown in  FIG. 1   d . Adjustments to raise the over voltage trip point above 47.0 volts before triggering the over protection circuit are not shown. 
         [0012]    It would be desirable to have a voltage detector which is compatible with the Armament Circuits Preload Test Sets, which does not require fuse replacement upon sensing of over-voltage. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention addresses the issues presented above by providing a digital voltage detector system and method that are compatible with existing Armament Circuits Preload Test Sets and that provide an accurate digital voltage display. A digital voltage detector system and method, in accordance with the present invention can perform the four respective conventional Armament Circuits Preload Tests of Presence of Voltage. Continuity in an EED, Stray Voltage, and Ohmic Adapter Test. 
         [0014]    Another aspect of the present invention is to provide adjustment for the trip point for the Presence of Voltage test using external resistors to lower the trip voltage. 
         [0015]    Another aspect of the present invention is to provide adjustment for the trip point for the Presence of Voltage test using external resistors to raise the Presence of Voltage trip voltage. 
         [0016]    Another aspect of the present invention is a Digital Voltage Detector which provides a digital readout allowing the user to view the input voltage during a Presence of Voltage test. 
         [0017]    Another aspect of the present invention is to provide a fail indicator light in addition to a pass indicator light. 
         [0018]    Another aspect of the present invention is to allow accurate measurement of high and low input voltages with a Digital Voltage Detector. 
         [0019]    Another aspect of the present invention is to provide a Digital Voltage Detector which is compatible with all conventional Voltage Detector interface cables and adapters. 
         [0020]    Another aspect of the present invention is to provide the technician user with input voltage measurement digital display, facilitating problem identification and troubleshooting. 
         [0021]    Yet another aspect of the present invention is to enable reduced man-hours for completion of the Armament Circuits Preload Test series. 
         [0022]    Yet another aspect of the present invention is to enable more timely turn around of aircraft due at least in part to efficient execution of the Armament Circuits Preload Test series. 
         [0023]    Yet another aspect of the present invention is to reduce equipment redundancy in the conventional Armament Circuits Preload Test set. 
         [0024]    Yet another aspect of the present invention is to reduce the need for disposable fuses in an Armament Circuits Preload Test set. 
         [0025]    Those skilled in the art will further appreciate the above-noted features and advantages of the invention together with other important aspects thereof upon reading the detailed description that follows in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0026]    For more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures, wherein: 
           [0027]      FIGS. 1   a - 1   d  show a schematic representation of a conventional voltage detector for an Armament Circuits Preload Test Sets with external adjustments to alter a trip point voltage; 
           [0028]      FIG. 2  shows a digital voltage detector comprising an analog-to-digital converter and a microcontroller, replacing the analog comparator of the conventional voltage detector; 
           [0029]      FIGS. 3   a - 3   b  illustrate a schematic representation of an exemplary embodiment of a digital voltage detector in accordance with the present invention; 
           [0030]      FIG. 4  illustrates a timing diagram in accordance with an exemplary embodiment of the present invention; and 
           [0031]      FIG. 5  illustrates a schematic representation of an exemplary embodiment of a digital voltage detector in accordance with the present invention for stray voltage measurements. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The invention, as defined by the claims, may be better understood by reference to the following detailed description. The description is meant to be read with reference to the figures contained herein. This detailed description relates to examples of the claimed subject matter for illustrative purposes, and is in no way meant to limit the scope of the invention. The specific aspects and embodiments discussed herein are merely illustrative of ways to make and use the invention, and do not limit the scope of the invention. 
         [0033]    While an analog-to-digital converter and a microcontroller can be substituted for the comparator  140  of the conventional voltage detector,  100 , an accurate digital voltage reading is not displayed for the user.  FIG. 2  shows a digital voltage detector  200  comprising an analog-to-digital converter  240  and a microcontroller  245 , replacing the analog comparator  140  of the conventional voltage detector  100 . As in the conventional voltage detector, the digital voltage detector  200  uses the internal resistor circuit  110 . The Digital Voltage Detector  200  includes a digital display readout  270  in addition to PASS  250  and FAIL  255  tights. A voltage between 22.0 and 47.0 VDC causes the Digital Voltage Detector  200  to turn on the green PASS light  250 . A voltage greater than 47.0 VDC causes the Digital Voltage Detector  200  to turn on the red FAIL light  255 . A voltage less than 22.0 VDC causes the Digital Voltage Detector  200  to turn both the PASS and FAIL lights  250 ,  255  off. 
         [0034]    And, as in the conventional voltage detector  100 , the trip point for the Presence of Voltage test can be adjusted using respective external resistors in the presence or absence of a connector between the TRIP_ADJ pin and TEST_IN+ as described in relation to  FIGS. 1   a - d . These external resistor and connector configurations yield accurate pass and fail indicator light results. The pass indicator light  250  turns on for a TEST_IN+ that is within the desired voltage range, the fail indicator light  255 , turns on for a TEST_IN+ that is above the desired voltage range, and both lights turn off for a TEST_IN+ voltage which is below the range, under voltage. However, when an external resistor  226  is used, as the conventional user is accustomed, the display voltage  270  in the digital voltage detector  200  is erroneous. The erroneous digital display is summarized in TABLE 1 with respect to values of the external resistor  226  value in conjunction with the presence or absence of connector  222  between TRIP_ADJ pin  230  to TEST_IN+  220 , as shown in  FIG. 2 . 
         [0035]    Referring to TABLE 1 and  FIG. 2 , the Display Reading  270  is off of the true TEST_IN+  221 , input voltage, by the Error, in VDC. Use of an external resistor  226  and a connector  222 , or the use of the connector  222  alone, causes positive errors when displaying the input, TEST_IN+ voltage. As in the conventional voltage detector, for an under voltage trip point greater than 22.0 VDC, an external resistor  226  in the absence of connector  222  is used. In the specific example of 381 ohm external resistor added in series with TEST_IN+ on the Digital Voltage Detector  200 , the input under voltage trip point would change from 22.0 VDC to 50.0 VDC. An applied voltage, Presence of Voltage of 50 VDC will cause the Digital Voltage Detector to turn on the PASS light  250  correctly; however, the display  270  will show 22.0 VDC rather than the actual 50.0 VDC present at TEST_IN+  121 , Presence of Voltage. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 TEST_IN 
                 External 
                 TRIP_ADJ 
                 Display 
                   
               
               
                 Input Range 
                 Resistor 
                 connected? 
                 Reading 
                 Error 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3.5 
                 VDC 
                 s.c. 
                 Yes 
                 22.0 VDC 
                 +18.5 
                 VDC 
               
             
          
           
               
                 5.0 
                 VDC 
                 128 
                 ohms 
                 Yes 
                 22.0 VDC 
                 +17.0 
                 VDC 
               
               
                 10.0 
                 VDC 
                 557 
                 ohms 
                 Yes 
                 22.0 VDC 
                 +12.0 
                 VDC 
               
               
                 15.0 
                 VDC 
                 986 
                 ohms 
                 Yes 
                 22.0 VDC 
                 +7.0 
                 VDC 
               
             
          
           
               
                 22.0 
                 VDC 
                 s.c. 
                 No 
                 22.0 VDC 
                 O 
                 VDC 
               
             
          
           
               
                 25.0 
                 VDC 
                 41 
                 ohms 
                 No 
                 22.0 VDC 
                 −3.0 
                 VDC 
               
               
                 35.0 
                 VDC 
                 177 
                 ohms 
                 No 
                 22.0 VDC 
                 −10.0 
                 VDC 
               
               
                 50.0 
                 VDC 
                 381 
                 ohms 
                 No 
                 22.0 VDC 
                 −28.0 
                 VDC 
               
               
                 100 
                 VDC 
                 1063 
                 ohms 
                 No 
                 22.0 VDC 
                 −78.0 
                 VDC 
               
               
                 150 
                 VDC 
                 1745 
                 ohms 
                 No 
                 22.0 VDC 
                 −128 
                 VDC 
               
               
                 200 
                 VDC 
                 2427 
                 ohms 
                 No 
                 22.0 VDC 
                 −178 
                 VDC 
               
               
                   
               
             
          
         
       
     
         [0036]    Similarly, in the absence of connector  222 , addition of an external resistor  226 , effectively lowers the under voltage trip voltage, however, the measured and displayed voltage  270  is constant at 22.0 VDC, proportionately less than the actual Presence of Voltage, TRIP_IN+. The pass and fail tights still read correctly, however, the replacement of the voltage comparator  140  with the analog-to-digital converter  240  in combination with the conventional input resistor circuit, voltage divider, yields 22.0 VDC at the display rather than the actual 3.5 VDC at TEST_IN+  221 . 
         [0037]    Just substituting an ADC and microcontroller for the comparator is insufficient as the conventional input voltage divider will consistently yield a 22 VDC display as measure of TEST_IN+ regardless of the actual TEST_IN+ range. This problem is solved and an accurate voltage measurement display for use by the technician is obtained in accordance with the present invention as described below. 
         [0038]      FIGS. 3   a - 3   b  illustrate schematic representations of an exemplary embodiments of a digital voltage detector in accordance with the present invention. Turning to  FIG. 3   a , the case in which the low voltage trip point is lowered to 3.5 VDC by using a connector  322  from the TRIP_ADJ pin  330  to TEST_IN+  320  is shown. Rather than having the TRIP_ADJ pin  330  change the input impedance to the voltage comparator  140 , as shown in  FIG. 1   c , an additional analog-to-digital converter  342  separately measures the voltage on the TRIP_ADJ pin  330 . As shown in  FIG. 3   a , the voltage at TRIP_ADJ is measured using an analog-to-digital converter  342 , which is separate from the analog-to-digital converter  340  used to measure the input voltage, TEST_IN+  320 . In this case, either a 3.5 VDC input at TRIP_ADJ  330  or a 22 VDC input at TEST_IN+  320  will cause the PASS light  355  to turn on, as dictated by microcontrollers  346  and  345 , respectively. Microcontrollers are applicable in accordance with an exemplary embodiment, and any custom digital logic circuit which analyzes the output from the analog-to-digital converter can be used. The digital display  370 , however, only shows the voltage input at TEST_IN+  320 . 
         [0039]      FIG. 3   b  shows the additional elements utilized for the case of a raised Presence of Voltage under voltage trip point, wherein, an external resistor  326  is placed in series with TEST_IN+. In addition, to accurately report input voltage, an electronic switch  392  is placed in series with the 300 ohm load resistor  381  on the TEST_IN+ signal  321 . Switch  392  maybe a photoMOS relay, but it may also be a MOSFET or other type of switch. Switch  392  is controlled by a Timing Control module  390  in the software of the digital voltage detector in accordance with an exemplary embodiment of the present invention. The Timing Control  390  module closes switch  392 , engaging the 300 ohm resistor  382  to determine if the input voltage (TEST_IN+) is greater than the 22 VDC threshold or greater than the 3.5 VDC threshold when connector  322  is in place connecting TRIP_ADJ pin  330 . Periodically, the Timing Control Module  390  briefly turns off the 300 ohm resistor  382 , opens switch  392  and measures the input voltage at TEST_IN+  321  when an external resistor  326  and connector  322  are present. The measured and displayed voltage at TEST_IN+ is then the full input voltage without the 300 ohm load impedance  382 . The Timing Control  390  directly measures the TEST_IN+ voltage four times per second, measuring the input voltage for 4 ms  410 , every 250 ms  420 , as shown in the timing diagram in  FIG. 4 . 
         [0040]    In the absence of an external resistor  326  or of a jumper  322 , the circuit has a threshold voltage of the nominal 22.0 VDC and the digital display gives a direct reading of the input voltage. When the external resistor  326  is replaced by a wire or short circuit, the periodic opening and closing of the 300 ohm switch  392  will have minimal effect on the voltage measured at the analog-to-digital converter  440 , affording a desired accurate display. 
         [0041]    The conventional internal resistor circuit  110  includes a load resistor  112  connected from TEST_IN+  120  to TEST_IN−  125 , a resistor  111  in series with TRIP_ADJ  330 , a two resistor voltage divider  113 ,  114  off of TEST_IN+  120 , wherein resistor  111  is in parallel with resistor  113 , as shown in  FIG. 1 . 
         [0042]    In contrast, the internal resistor circuit  380 , according to an exemplary embodiment of the present invention, includes a load resistor  382  connected from TEST_IN+  320  to via a switch  392  to TEST_IN−  325 . A resistor  381  is in series with TRIP_ADJ  330 , while a two resistor voltage divider  383 ,  384  is off of TEST_IN+  320 , and wherein resistor  381  is in parallel with resistor  383 , as shown in  FIGS. 3   a  and  3   b . Internal resistor circuit  380  also includes a putt down resistor  387 . 
         [0043]    The internal resistor circuit of the conventional voltage detector is designed to keep the analog-to-digital converter in the useable range for expected input voltages. In the conventional voltage detector, an input impedance of approximately 3.385 Mega-ohms  113 , 114  is used for the input sensing circuit  110 , as shown in  FIG. 1   a . The specific resistor values chosen cause the voltage at the negative input  142  of the analog comparator  140  to equal a reference voltage of 2.5 VDC, when 22 VDC is applied to the input circuit. When an external connector  122  is placed between the TEST_IN+  120  and TRIP_ADJ  130  terminals, a tower impedance  111  of 162 kilo-ohms is added in parallel to the circuit. This causes the voltage at the negative input  142  to reach 2.5 VDC when an input voltage of only 3.5 VDC is applied. 
         [0044]    In accordance with an exemplary embodiment of the present invention, the conventional input circuit  110  is replaced by an internal resistance circuit  380  that includes two sets of measurement inputs and two independent analog to digital converters  340 ,  342 . These differences provide improved consistency of input impedance at 2.1 Mega-ohms regardless of the use of the input jumper  322 . 
         [0045]    Referring to  FIG. 5 , for the stray voltage test, in accordance with the present invention, another resistor circuit is applied between TEST_IN+ and the analog-to-digital converter. In the stray voltage test configuration, a separate three ohm load resistance  501  is electrically connected to the TEST_IN+ connection, in the absence of the 300 ohm load resistance employed in the presence of voltage tests. The control logic for the stray voltage test includes a voltage threshold criteria  502  that is set for voltages greater than 0.120 VDC or less than −0.120 VDC. The control logic also includes an overvoltage detector  503  that removes the three ohm load resistor  501  from the input circuit via an electronic switch  500 . The switch may be a MOSFET relay or an electromechanical relay. Quickly removing the three ohm resistor  501  prevents damage to the resistor and prevents fuses from being blown in the digital voltage detector, in accordance with the present invention. 
         [0046]    While specific alternatives to steps of the invention have been described herein, additional alternatives not specifically disclosed but known in the art are intended to fall within the scope of the invention. Thus, it is understood that other applications of the present invention will be apparent to those skilled in the art upon reading the described embodiment and after consideration of the appended claims and drawing.