Abstract:
The receiver has a casing member and a tip is removably attached to the casing member. A transmitter is connected to a battery and the transmitter produces a transmitter signal by periodically connecting a resistance to the battery. Preferably, the transmitter signal has a frequency of about 20 kHz. A sensor may be placed adjacent to, but not in contact with, an electrically conductive member to take advantage of the air capacitance. An electrical field is created between the sensor and the electrically conductive member. Due to the periodical load on the battery, the sensor may sense the transmitter, signal in the DC carrying conductive member. The transmitter signal is passed through an integrated circuit to filter out all frequencies except the desired 20 kHz and a detection signal is sent to the indicator to activate the indicator.

Description:
TECHNICAL FIELD 
     The invention relates to a direct current (DC) voltage detection stick for non-contacting detection of a direct current in a wire by using the capacitance of air. 
     BACKGROUND INFORMATION AND SUMMARY OF THE INVENTION 
     Electrical voltage sticks are known in the art for both detecting alternating current (AC) and direct current (DC). The prior art voltage sticks may require that a needle is inserted through the plastic protection cover of the cable and into the metal wire to be able to detect the DC voltage. This leaves a permanent damage of the wire cover and water and other contaminants may enter into the opening after the needle has been withdrawn. This a particular problem in automobiles and other equipment that are operated in rain and snow conditions and have an electrical system that is powered a battery such as 12 or 24 VDC. Other DC testing devices rely on a relatively unreliable electromagnetism system for detecting cables carrying a DC current. 
     The present invention is a device and a method for detecting a direct current by using the capacitance in the air. The receiver has a casing member and a tip is removably attached to the casing member. A sensor is disposed within the casing member for sensing the presence of a transmitter signal when the sensor is positioned adjacent to an electrically conductive member carrying a direct current. An indicator and an integrated circuit is disposed within the casing member. The integrated circuit that may act as a first filter and a power source are disposed within the casing member for powering the sensor, the indicator and a first integrated circuit. A transmitter is connected to a direct current generating power source and the transmitter produces a transmitter signal by periodically connecting a resistance R to the battery. Preferably, the transmitter signal has a frequency of about 20 kHz. During detection, the tip is placed adjacent to, but not in contact with, the electrically conductive member to take advantage of the capacitance in the air disposed between the sensor and the electrically conductive member. Due to the period load on the battery, the sensor may sense the electrical field created between the two opposite poles of the battery. The detected transmitter signal is passed through the integrated circuit to filter out all frequencies except the desired 20 kHz and a direct current detection signal is sent to the indicator to activate the indicator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional side view of a casing of the DC volt detection stick of the present invention; 
     FIG. 2 is a detailed cross-sectional side view of a probe tip of the DC volt detection stick of the present invention; 
     FIG. 3 is a perspective view of the transmitter end of the DC testing system of the present invention; 
     FIG. 4 is a schematical flow diagram showing the flow of signals in the DC testing system of the present invention; 
     FIG. 5 is a schematical diagram showing the signals generated by the transmitter of the present invention; and 
     FIG. 6 is a schematical illustration of the use of the capacitance between the receiver and wire to be tested. 
    
    
     DETAILED DESCRIPTION 
     With reference to FIGS. 1-3, the voltage probe or receiver  10  of the present invention comprises a casing  12 , a battery cap  14  and a probe tip  16  so that the battery cap  14  may be attached to a rear end  18  of the casing  12  and the probe tip  16  may he removably attached to an opposite front end  20  of the casing  12 . The battery cap  14  may be screwed onto the casing  12  and removed from the casing  12  by unscrewing the cap  14 . A helical spring member  13  may be disposed and attached within the cap  14 . The spring member  13  extends inwardly so that it comes into contact with a battery  21  when the cap is screwed onto the casing  12 . 
     The casing  12  is preferably an elongate hollow member having a channel  22  extending therethrough. The hollow member is preferably made of a polymeric material such as polypropylene. Polypropylene provides good electrical insulation and is durable. The channel  22  may have a length that is dimensioned to hold two AAA-sized batteries  21 . 
     A spring biased pocket clip  30  is, preferably, integrally formed with a side wall  32  of the casing  12  adjacent to the rear end  18  thereof. The clip  30  has a pocket holder  34  and a cap holder  36 . The pocket holder  34  extends in a direction that is opposite to the cap holder  36 . The cap holder  36  has an enlarged outer portion  38  including a perpendicular flat clamp surface  40 . Similarly, the pocket holder  34  has a tip  42  that bears against the outer surface of the casing  12 . 
     Preferably, the probe tip  16  has bifurcated or forklike narrow tip portions  47 ,  48  and a conical shaped mid-section  50  and a cylindrical rear portion  52 . The tip portions  47 ,  48  define a groove  54  that has a round bottom  56  to safely hold a cord or wire therein to be tested. It is to be noted that the probe tip  16  is not glued to the casing  12  but is only firmly snapped or otherwise removably attached to the front portion  20 . Preferably, the probe tip  16  is made of a polymeric material such as sicoamide- 6  or any other suitable material. It is to be understood, the probe tip  16  does not have to be bifurcated but could be a single protruding end portion. 
     A first circuit board  25  and a second circuit board  27  may be disposed in the probe tip  16  and the casing  12 . An inner end  29  of the board  25  and an inner end  31  of the board  27  may be mechanically and electrically connected to one another at a connection point  33  that is disposed outside the probe tip  16  and inside the casing  12 . An outer end  35  of the board  25  extends into the tip portion  47  while an outer end  37  of the board  27  extends into the tip portion  48  so that the boards  25 ,  27  form a V-section. As discussed below, the boards  25 ,  27  shield and prevent the sensor inside the probe tip from sensing an adjacent wire that is located outside the groove  54 . Preferably, the circuit boards  25 ,  27  may be made of a polymeric material such as a glass-fiber reinforced epoxy resin. Other suitable materials may also be used. 
     An indicator or light source  72  such as a surface mounted light emitting diode (led) or a 3 millimeter 700 mcd red led may also be electrically connected to the circuit boards  25 ,  27  and may be used to indicate that a direct current has been detected. A suitable buzzer may also be used to indicate that a direct current has been detected. For example, the led may be made by Citizen or any other suitable manufacturer. Light emitting diodes are the preferred type of light source because they provide a high intensity at a relatively low current. The light source  72  provides sufficient illumination so that the light emitted from the light source  72  may be seen through the probe tip  16 . 
     An integrated circuit  76  is attached to the circuit board  25 ,  27 . 
     As best seen in FIG. 3, the transmitter  80  has a housing  82  nay be made of ABS plastics or any other suitable material it wire  84  extends from the housing  82  and includes a first clip  86  and a second clip  88 . The first clip  86  may be connected to the plus pole  90  of a battery  92  that powers the DC system to be tested while the second clip may be connected to, for example, a chassis part  93  of a vehicle or to a minus pole  95  of the battery  92 . 
     An important feature of the present invention is the use of the capacitance of air in the communication between the transmitter  80  and the receiver  10 , as shown in FIG.  6 . In general, two objects that are separated by air has a capacitance C therebetween. The capacitance C varies with the distance A. The capacitance C only permits alternating current (AC) to pass therethrough. Because the battery  92  produces a direct current, the transmitter  80  must produce a transmitter signal that is similar to an alternating current over the battery  92  so that the receiver may detect the transmitter signal. It is also important to note that there is no contact between the wire  100  to be tested and the sensor disposed inside the bifurcated probe tip  16  of the receiver  10 . 
     In the present invention, the transmitter creates a current by periodically connecting a resistance  85  of the transmitter  80  so as to artificially create an alternating current that may pass the air capacitance C that is formed between the antennas  103   a  and  103   b  and the wire  100  that is disposed inside the bifurcated tip (see FIG.  2 ). It is important to note that there is no direct contact between the antennas  103   a  and  103   b  and the wire  100  and that there is a distance D therebetween. 
     The size of the resistance  85  used by the transmitter  80  depends upon the voltage of the battery  92 . When the antennas  103  in the receiver  10  is sufficiently close to the wire  100 , a detectable current I D  is permitted to pass through a resistance  111  that is part of the circuitry  25 ,  27  of the receiver  10 . The current I D  is then amplified and filtered, as described below. In a modified version, it may be possible to only use an internal resistor R A1  of the amplifier  106 . 
     More particularly, the transmitter  80  produces a transmitter signal  81  at a frequency of between about 5 kHz and 40 kHz. More preferred, the frequency of the signal  81  is between about 15 kHz and 25 kHz. Most preferred, the frequency is about 20 kHz in periods of about 4 Hz to avoid unnecessary interference with other electrical equipment in a vehicle such as a car stereo or an alternator. 
     The periods of short circuiting of the battery  92  may vary from about 2 Hz and 10 Hz and results in the above described alternating current I D  that may be detectable over the resistance  111 . In general, a period in the range of about 1 second produces a flashing light  72  that is too slow at the receiver  10 , as discussed below, because the operator needs to know if the wire is carrying direct current in the shortest possible time. In other words, it is too long to have to wait for one second to know if there is current in the wire to be measured. A frequency that is too high for the human eye cannot be seen by the operator as a blinking light but as a constant light. Therefore, a blinking light at 4 Hz is a suitable frequency. 
     As mentioned above, the size of the resistor  85  depends upon the voltage of the battery  92 . The transmitter signal  81  may be produced by connecting a 1.5 Ohm resistor  85  to the transmitter  80  if the transmitter  80  is connected to a 12V electrical system or to a 3 Ohm resistor  87  if the transmitter  80  is connected to a 24V electrical system. Of course, other suitable resistor values may be used. In other words, the load or short circuiting of the battery  92  is performed at about 4 Hz intervals. 
     In a 12V electrical system, the short circuiting varies the voltage to be between 11.5V and 12.5V. Preferably, the voltage variation should be about 0.4 Vrms. More particularly, the variation should not be more than about 0.5 Vrms not to influence other electronic systems in, for example, a car. By operating at a frequency of about 20 kHz the artificially generated load of the battery  92  is not interfered by the normal load from the automobile because 20 kHz is above the operation of alternators and most car stereos. By increasing the revolutions per minute (rpm) of the engine sufficiently, it may also be possible to measure the operation of the alternator. 
     The 20 kHz frequency has been selected to take advantage of the internal capacitance and resistance within most automobile batteries to increase the transmitter signal  81  both at the time of the short circuiting of the battery and when the short circuiting is terminated. FIG. 5 schematically shows the wave that results from the intermittent short circuiting of the battery wherein the transmission signal is at a frequency of 20 kHz. In general, the higher the frequency of the transmission signal, the easier it is for the signal to travel in the wire  100  to be tested. One limiting factor for the highest frequency that may effectively be used in the system is often the electronics at the receiver  10  because it is difficult, with the electronics currently available, to amplify a signal that has a frequency that is too high. Another limiting factor of using a frequency that is too high is the band width of the amplifier. A too high of a frequency may produce a radio signal may undesirably reduce the selectivity. 
     The housing  82  of the transmitter  80  has an indicator lamp  94  that may emit a red light, to indicate that the transmitter is incorrectly connected, or a blinking green light, to indicate that the transmitter  80  is operating correctly. The electronics in the transmitter  80  is supervised by a micro-controller  96  that generates all the signals required. 
     The micro-controller  96  has a sensor  98  that senses if there is any direct current flowing in the clips  86 ,  88  and if the transmitter  80  is connected to a 12V or a 24V electrical system. The transmitter  80  also has a protective circuit to protect the transmitter from damage as a result of over-loading, over-heating or polarization. 
     When the tips  47 ,  48  of the probe tip  16  are placed over a wire  100  (see FIG. 2) connected to the transmitter  80  via the battery  92 , the light  72  of the probe tip  16  may flash to indicate that the receiver  10  has detected the transmitter signal  81  at 20 KHz in the wire  100  to be tested. The fork like tip enhances the sensitivity of the receiver  10  when measuring a wire that is disposed in a harness of wires. The fork like tip also ensures that the correct wire is measured. 
     The circuit boards  25 ,  27  disposed in the receiver  10  may include a sensor  102  that is connected to the antenna  103  for sensing the transmitter signal  81  in the wire  100 . When the transmitter signal  81  is detected from the transmitter  80 , an amplification signal  104  is sent from the sensor  102  to a high impedance amplifier  106  to amplify the transmitter signal to a workable level. A selection signal  108  is sent from the amplifier  106  to two band pass filters  109 ,  110  that may be part of the integrated circuits to filter out all noise in the selection signal  108  except the desired 20 kHz frequency of the frequency signal  112 . The integrated circuits themselves may act as filters. The frequency signal  112  is sent from the filter  110  to a comparator  114  that compares the level of the signal  112  to a preset level. In the preferred embodiment, the preset level is 20 mV. The preset level could range from about 10 mV to about 400 mV. If the preset level is too high, then the resistance of the wire itself may reduce the signal too much so that the antenna  103  and thus the sensor  102  cannot detect the transmitter signal  81 . 
     If the level of the signal  112  exceeds the preset level, then a triggering signal  116  is sent to the led driver  118  that is turn sends an illumination signal  120  to the illuminator  72 , such as a LED indicator, to emit a flashing light indicating that the receiver  10  has detected the transmitter signal  81  in the wire  100  that was transmitted by the transmitter  80  and therefore the wire  100  is properly connected to the battery  92  and carries a sufficiently strong direct current. The system must be correctly connected to produce the light that indicates that everything is properly connected. 
     While the present invention has been described in accordance with preferred compositions and embodiments, it is to be understood that certain substitutions and alterations may be made thereto without departing from the spirit and scope of the following claims.