Abstract:
An electrostatic monitoring system for detecting a risk of electrostatic discharge is used to detect conditions under which electrostatic discharge is likely, at distances sufficient to provide the time needed to take corrective action and mitigate any harmful effects. The system monitors electrostatic discharge conditions in the order of a few meters away, and preferably determines the direction of maximum hazard. By the invention, personnel can be screened upon entering a vulnerable area, sensitive equipment can be protected by placing sensors on the equipment to detect the risk of electrostatic discharge due to the local static potential and to preemptively turn off the equipment, and wearable sensors can be installed in clothing of personnel working in environments with high electrostatic hazard to protect both personnel and equipment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/678,196 entitled “Large Standoff, Direction Finding, Wearable Electrostatic Discharge Detection System” filed on May 6, 2005. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract Nos. NNK04OA22C and NNK05OA05C, awarded by NASA under two SBIR programs, Phase I and Phase II. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention generally pertains to the art of measuring the buildup and discharge of electrostatic charges. More particularly, the invention relates to using free-space electric field sensors to detect a buildup of electrostatic charge in various types of situations. 
         [0004]    Spontaneous electrostatic discharge has been a problem in numerous different fields for many years. Essentially a human body will tend to generate a static electric charge when parts of the body come in frictional contact with other surfaces. Triboelectric charging, as the phenomenon is known, results in a gradual buildup of electric charge that is notoriously hard to detect in a timely manner. 
         [0005]    For example, the buildup of electrostatic charge can be particularly troublesome in the field of flammable fluid distribution. The reduction of sources of electrostatic potential is important in order to reduce the chance of explosion or fire. The amount of electrostatic charge needed to ignite vaporized gasoline is extremely small. To overcome this problem, gasoline fueling systems, such as filling trucks and filling pumps, are typically grounded. If such a system detects an improper ground then the gasoline will not flow. Furthermore, when motorists refuel automobiles they are admonished to not use cell phones or other electronic devices that could potentially cause an electric discharge. 
         [0006]    Electrostatic discharge is also a problem in the production of electronic devices such as computer memory, semiconductor wafers or a personal computer motherboard. Indeed a small discharge, too small for a person to detect, may still be large enough to damage an electronic device. One way to address the electrostatic discharge problem is to use conducting floor tiles, humidity control, and other means of inducing a slow discharge of the offending high potential source. These alternatives are widely used, but are not 100% successful in addressing the problem. 
         [0007]    Currently, when a computer is being manufactured or repaired technicians will routinely ground themselves before working on various electronic components of the computer. Simply touching a ground on a power supply or using special clothing will help to avoid a sudden discharge of electrostatic potential that will damage the various components of the computer, such as random access memory which can be particularly sensitive to such currents. Grounding straps, which are typically worn on a person&#39;s wrist, are also common in such manufacturing environments. However, simply grounding equipment and personnel has not proven sufficient. People sometimes forget to wear grounding straps or will enter a sensitive area, such as an area where semiconductor wafers are being made, and produce destructive electrostatic discharge events before putting on a grounding strap. 
         [0008]    Any situation in which an electrostatic charge can build up and discharge in the vicinity of flammable liquid or vapor is a hazardous situation. Any type of facility with machinery whose motion can build up a charge in the presence of any flammable substance can benefit from electrostatic monitoring. Some industries with a history of electrostatic discharge related accidents include: Gasoline Vending, Transporting and Storage; Oil Refining; Shipping; Paper Processing; Chemical Manufacturing; and Fiberglass-related manufacturing (boats). 
         [0009]    The combination of shrinking product geometries and increasing sensitivity has left many products and manufacturing processes vulnerable to even modest levels of electrostatic charge. Product and process contamination through electrostatic attraction has been and remains a critical issue in numerous industries. Pulse EMI (E-field and H-field components) generated by electrostatic discharges has probably caused more mysterious problems for more processes and products than any other single source. High electric fields lead to electrostatic discharge that can injure personnel or damage or destroy sensitive apparatus such as semiconductor wafers and chips during the fabrication stages. Effective control requires monitoring and intervention prior to charge imbalances reaching critical thresholds. Industries for which this is applicable include, among others: Semiconductor Manufacturing; Flat Panel Display Manufacturing; Disk Drive Manufacturing; Medical Manufacturing; Pharmaceutical Processes; Military Contractors; MEMS Technology and Nanotechnology. 
         [0010]    Based on the above, certain solutions have been proposed. For instance, some manufacturers have produced handheld devices that can detect a 1000V source at a distance of 1 cm. However such devices are woefully inadequate in giving enough warning to workers in a production line to stop an electromagnetic discharge or in screening personnel as they enter sensitive areas. 
         [0011]    U.S. Pat. No. 6,150,945 discloses a wearable device for measuring static charge buildup on a user. People working around sensitive electronic equipment use the device. However, the device detects static buildup on the wearer and does not identify a static potential difference to other objects. 
         [0012]    U.S. Pat. No. 5,218,306 is a wearable static charge warning device that detects charge flow to or from a needle point worn on a wrist or elsewhere on a body. The charge flow can be indicative of a possible electrostatic discharge hazard. The warning device does not detect hazardous voltages, but rather it only detects charge flow. 
         [0013]    U.S. Pat. No. 5,461,369 relates to a wearable device for detecting electrostatic discharge events. The device does not warn of dangerous potentials prior to an actual discharge. 
         [0014]    U.S. Pat. No. 4,007,418 describes an electrostatic safety monitor that can be carried or worn. This device generates a signal when detecting the transfer of energy from a human body to its surrounding. While such detection is useful, it does not provide advanced warning of electrostatic discharge, but instead relies on the discharge itself to generate the signal. In this respect it fails to supply advanced warning of electrostatic hazards and only provides a warning after discharge has occurred and damage possibly done. Another consequence of detecting energy transfer is that essentially no standoff detection is provided. 
         [0015]    As can be seen from the above discussion, there exists a need in the art for a compact electric potential sensor for monitoring ambient electric fields in different modalities. The sensor should be able to detect conditions under which electrostatic discharge is likely, at distances sufficient to provide the time needed to take corrective action and mitigate any harmful effects. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention is directed to an electrostatic monitoring system for detecting a risk of electrostatic discharge and for monitoring ambient electric fields in different modalities. The system is compact and extremely sensitive compared to existing systems. The system is used to detect conditions under which electrostatic discharge is likely, at distances sufficient to allow coverage of a section of a process area, and with enough precision to provide warning in time to take corrective action and mitigate any harmful effects. The system monitors electrostatic discharge conditions a few meters away, and also provides a means to determine the direction of maximum hazard. 
         [0017]    The system may be used for at least the following three modes of operation: personnel are screened upon entering a vulnerable area by having sensors placed on doorways to screen them for high electrostatic charge on their bodies when they enter a sensitive facility; equipment is protected by placing sensors on sensitive equipment to detect the risk of electrostatic discharge due to the local static potential in order to turn off the equipment or otherwise warn a worker away from the equipment; and wearable sensors are installed in clothing of personnel working in environments with high electrostatic hazard to protect both personnel and equipment. 
         [0018]    More specifically, the invention concerns an electrostatic monitoring system for detecting a risk of electrostatic discharge by measuring a static electric field potential of an electric field produced by a source and alerting appropriate personnel when the electrical field potential exceeds a preset limit. The system includes a sensor having an electrode, located near, but not in direct contact with, the source, for producing a sensed signal voltage based on the static electric field potential. A pre-amplifier has an input electrically connected to the electrode by an electrical path. The pre-amplifier produces an amplified voltage signal based on the sensed signal. A controller receives the amplified voltage signal and determines if the amplified voltage signal is above a predetermined threshold. If the amplified voltage signal is above the threshold, then a user is notified of the risk of electrostatic discharge. 
         [0019]    In one preferred embodiment, the system includes a ground electrode and a resistor having an input shunt resistance of 1 Teraohm that is located between the electrical path and the ground electrode. The sensor further includes processing circuitry that preferably includes a capacitor located between the electrical path and ground. Such a capacitor adds a shunt capacitance of approximately 1 picofarad. For even better results, the sensor further includes a feedback circuit having a feedback amplifier, such as an op-amp with two inputs and an output, with the output of the pre-amplifier being connected to one input of the feedback amplifier and the output of the feedback amplifier being connected to the input of the pre-amplifier. A resistor having a resistance value of at least 10 Mega-ohms is provided in the feedback path. Optionally, a second sensor may be added. The second sensor also includes a second electrode located near, but not in direct contact with, the source for producing a second sensed signal voltage based on the static electric field potential, a second pre-amplifier having an input electrically connected to the second electrode by an electrical path and an output. The second pre-amplifier produces a second amplified voltage signal at the output based on the sensed signal, wherein the controller receives the second amplified voltage signal. The first and second sensors are mounted in an array and the controller is adapted to use the first amplified voltage signal and the second amplified voltage signal to determine a direction to the source. Optionally additional sensors may be added for enhanced accuracy and/or verification purposes. 
         [0020]    In one preferred embodiment, the system includes the first and second sensors mounted on a doorway, with the system being adapted to detect the electrostatic potential of people passing through the doorway. Since doorways can cause field distortion, the system preferably uses an AC source used to compensate for the distortion. 
         [0021]    In yet another preferred embodiment the first and second sensors are mounted close to a machine that is sensitive to electrostatic discharge. The system employs a mounting fixture for supporting the sensors. In this configuration, the first sensor is mounted at least 2 cm away from the machine, while the second sensor is mounted at least 2 cm away from the first sensor and at least 4 cm away from the machine. The machine is preferably a gasoline pump or a semiconductor wafer production line. 
         [0022]    In yet another preferred embodiment, the system is wearable on a human body and a ground electrode is adapted to be in electrical contact with the body. For example the sensor may be mounted on a hat such that, when the hat is worn, the sensor will be positioned away from the body. Preferably the hat has a visor, with the sensor being mounted on the visor and the ground electrode being mounted on a brim of the hat near the wearer&#39;s forehead. The brim is made of conductive fabric so that the ground electrode can make electrical contact with the body through the fabric. Alternatively the sensor can be mounted on a sleeve of a garment, such as a chemical safety suit, or on a pair of safety glasses. In a still further embodiment, the system may be mounted on a badge. 
         [0023]    In use the system is employed to detect a risk of electrostatic discharge by first measuring a static electric field potential of an electric field produced by a distant source and then producing a signal representative of the field potential. Distortion is then removed from the signal and an alert is produced when the electric field potential exceeds a preset limit so that the electric field potential can be reduced in a harmless manner before an electrostatic discharge occurs. Also the direction to the source of the electric field may be determined. 
         [0024]    Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of a preferred embodiment when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  shows a perspective view of an electrostatic monitoring system with sensors mounted on a door to a vulnerable area in accordance with a first preferred embodiment of the invention; 
           [0026]      FIG. 2  is a circuit diagram of the electrostatic monitoring system of  FIG. 1  including a feedback loop; 
           [0027]      FIG. 3  is a circuit diagram of the electrostatic monitoring system of  FIG. 1  including an analog switch; 
           [0028]      FIG. 4  shows perspective view of the electrostatic monitoring system with sensors mounted on a handle of a gasoline pump according to a second preferred embodiment of the invention; 
           [0029]      FIG. 5  shows a schematic side view of the electrostatic monitoring system with a sensor mounted in a semiconductor wafer production line according to a third embodiment of the invention; 
           [0030]      FIG. 6  shows side view of an electrostatic monitoring system with sensors mounted on equipment according to a fourth preferred embodiment of the invention and sensors mounted on clothing according to a fifth preferred embodiment of the invention; 
           [0031]      FIG. 7  shows a model used to simulate the electrostatic monitoring system of  FIG. 6  when the sensors are mounted in different positions on clothing; and 
           [0032]      FIG. 8  is graph developed with the model shown in  FIG. 7 , showing an electrical potential distribution from a 1 kV voltage source with and without a human body present. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    In general, an electrostatic discharge occurs when static electricity has accumulated a charge on a surface to a point where an electric potential of the charge is sufficient to have the charge jump across a gap from the surface to an object with a lower electric potential, sometimes called a ground. As mentioned above, a human body can generate such a charge when rubbing against a surface of high friction. Typically, people experience so called “triboelectric charging” when they rub their feet on a carpet. They then experience an electrostatic discharge or spark when they touch a doorknob. When such a discharge passes through a sensitive electronic component, the component may be damaged. When the discharge passes through vaporized flammable gas, ignition results, along with a number of particularly unpleasant results. 
         [0034]    When a built-up static charge cannot find an easy path to ground, the charge creates an electric field that emanates away from the charge surface. As the charge gets larger, so does the field&#39;s strength. It is this electric field that can be sensed to determine when the built-up static electric charge is getting dangerously large and therefore a discharge may be presumed to be imminent. The present invention provides an electric field sensing device that senses, from a distance, the level of static charge and provides a warning before the field strength reaches a potentially dangerous level. 
         [0035]    As will become fully evident below, the present invention can take various forms, depending on the particular application. With initial reference to  FIG. 1 , an electrostatic monitoring system constructed in accordance with one embodiment of the invention is generally indicated at  10 . Monitoring system  10  is designed so that an object  11 , such as a person  12 , is screened upon entering a vulnerable area  15 . In this case, person  12  includes a source  25  having an electrostatic voltage charge potential  26 . For instance, person  12  may have rubbed his feet  30  on a carpet  32  or may have created electrostatic voltage charge potential  26  some other way. Regardless, how charge potential  26  is generated is not important. Instead, detecting electrostatic voltage charge potential  26  on person  12  before person  12  enters vulnerable area  15  with sensitive equipment  35  is important. 
         [0036]    As depicted in  FIG. 1 , source  25  creates electrostatic voltage charge potential  26  which, in turn, creates an electric field  37  that emanates from person  12 . In this case, electric field  37  is shown schematically as a unidirectional vector E, but it should be understood that field  37  actually emanates in all directions. In accordance with the embodiment shown, monitoring system  10  includes sensors  46 - 49  placed on a doorway or gateway  50 . Each of sensors  46 - 49  is about the size of a coin, such as a penny or dime, and is preferably connected via respective wiring  52  to a central control unit  55 . Each sensor  46 - 49  has its own internal circuitry, as detailed further below, that can be tailored to a particular mounting arrangement. In operation, each sensor  46 - 49  sends a signal to control unit  55  which may then provide warnings directly to person  12  or other personnel, such as through a visual and/or audible alarm  57 , that there is a danger of an electrostatic discharge event. To rectify the situation, precautionary measures, such as having person  12  touch a grounding unit (not shown), can be performed, thereby making it safe for person  12  to enter vulnerable area  15 . In a preferred embodiment, control unit  55  is provided with a memory unit  60  to record an event time, along with the corresponding level of static charge detected, for later data downloading and analysis. 
         [0037]    Sensitive equipment  35  provided in vulnerable area  15  may take many forms. For instance, sensors  46 - 49  on doorway  50  could monitor electrostatic voltage charge potential  26  of person  12  entering an electrostatic discharge vulnerable area  15  of a wafer process room, a gas handling facility or a NASA vehicle assembly facility. While one or more sensors  46 - 49  in doorway  50  may be used to detect electrostatic voltage charge potential  26  of object  11  passing through doorway  50 , preferably four sensors  46 - 49  are used to achieve a high level of detection. At this point, it should be realized that various objects could be monitored and the particular monitoring arrangement would be accordingly designed. For instance, a conveyor arrangement (not shown) could be utilized in combination with sensors  46 - 49  to scan objects entering vulnerable area  15 . In any case, in the embodiment shown, control unit  55  uses an algorithm preferably implemented on a microprocessor to detect electrostatic voltage charge potential  26  of person  12  walking through doorway  50 . The potential varies as 1/r 2  (where r is the distance of the person  12  from the particular sensor  46 - 49 ). Based on this measurement result, the electrostatic voltage charge potential  26  represented by the variable Va as detected by one or more of sensors  46 - 49  is represented by: 
         [0000]    
       
         
           
             
               
                 
                   Va 
                   = 
                   
                     a 
                     * 
                     
                       V 
                       
                         r 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where r is a distance between person  12  and a sensor, for example, sensor  46 , a is a calibration coefficient, and V is the potential of person  12 . In the case of doorway  50 , considering top two sensors  48  and  47 , the potential detected by sensors  47  and  48  when person  12  is at a distance r from sensor  48  is given by the equations (1) and (2) respectively, 
         [0000]    
       
         
           
             
               
                 
                   Vb 
                   = 
                   
                     a 
                     * 
                     
                       V 
                       
                         
                           ( 
                           
                             L 
                             - 
                             b 
                             - 
                             r 
                           
                           ) 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where L is the width of doorway  50  and b is the width of person  12 . Solving equations (1) and (2), we can calculate the absolute potential V on person  12  for a known value of L, b and a. Considering absolute values of Va and Vb and solving equations (1) and (2), we have 
         [0000]    
       
         
           
             
               
                 
                   V 
                   = 
                   
                     
                       
                         
                           ( 
                           
                             L 
                             - 
                             b 
                           
                           ) 
                         
                         2 
                       
                       * 
                       Va 
                       * 
                       Vb 
                     
                     
                       a 
                       ( 
                       
                         Va 
                         + 
                         Vb 
                         + 
                         
                           2 
                            
                           
                             Va 
                           
                            
                           
                             Vb 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0038]    The potential V on person  12  is then calculated using equation (3). By knowing the potential of person  12 , system  10  is able to provide a warning signal if the potential is above a threshold, which can be set for different applications. Again, if the detected electrostatic voltage charge potential  26  is greater than a predetermined limit, alarm  57  is activated or some other measure is taken to prevent person  12  from entering vulnerable area  15  for safety reasons. It should be recognized that, if doorway  50  is made of metal, a distortion to electric or E-field  37  will be created near doorway  50  where sensors  46 - 49  are mounted. However, this distortion is effectively calibrated out in accordance with the invention by providing an AC source  65 , which is connected to control unit  55 , in doorway  50 . 
         [0039]    A circuit  100  preferably employed in connection with each of sensors  46 - 49  of the present invention is shown in  FIG. 2 . In general circuit  100  includes a preamplifier  110  having an output  115  connected to a feedback path  120 . Circuit  100  functions to measure a voltage signal  130  representative of the size of electrical field  37  that is created by the electrostatic voltage charge potential  26  on measured object  11 , amplifies voltage signal  130  and sends an amplified signal  140  to control unit  55 . More specifically, circuit  100  includes a capacitive sensing electrode  150  that senses voltage signal  130 . Electrode  150  has an associated capacitance Cs, such as about 0.043 Pico farads. Voltage signal  130  travels from electrode  150  to a non-inverting input  160  of preamplifier  110 . An input shunt resistor  165 , preferably in the order of 1 Terra Ohm, is provided at amplifier input  160 . Additionally, a shunt capacitance  167  to ground  168 , preferably 1 or 5 pf, is added at input  160  to preamplifier  110 . In general, a 5 pf shunt capacitance is considered preferable in that it provides a flatter frequency response and thus less signal distortion. 
         [0040]    Preamplifier  110  is preferably an operational amplifier and is shown to have an input capacitance  169 , such as in the order of 1 pf. Various standard operational amplifiers of a correct size could be used, such as ultra low bias current operational amplifier model OPA 129 produced by Burr-Brown products of Texas Instruments. As shown, output  115  of preamplifier  110  is also connected back to inverting input  180  of preamplifier  110 . Additionally output  115  from preamplifier  110  is sent to feedback path  120 . 
         [0041]    Feedback path  120  includes a feedback amplifier  170  that is also an operational amplifier. Feedback path  120  is used to reduce a DC offset at input  160  of preamplifier  110 . In particular, output  115  from pre-amplifier  110  is sent to an inverting input  171  of feedback amplifier  170  through a resistor  175 . In the preferred embodiment, resistor  175  has a value of 10 M ohm. The placement of resistor  175  reduces both overshoot and an idle period. Another resistor  176 , also in the order of 10 M ohm, is provided between a non-inverting input  177  of feedback amplifier  170  and ground  168 . An output  178  of feedback amplifier  170  travels through shunt resistor  165  and then returns to non-inverting input  160  of pre-amplifier  110 . Output  178  from feedback amplifier  170  is also connected back to inverting input  171  of feedback amplifier  170 . Once again, while most standard operational amplifiers of a correct size could be used, a preferred amplifier is micro-power single supply operational amplifier model OPA2244 produced by Burr-Brown products of Texas Instruments. 
         [0042]    Referring now to  FIG. 3 , there is shown a schematic of another circuit  200  which can be employed with one or more of sensors  46 - 49 , wherein circuit  200  includes a preamplifier  210  having an output  215  connected to a feedback path  220  and an additional analog switch  225  added to reduce recovery time of sensors  46 - 49 . Circuit  200  measures a voltage signal  230  representative of the size of electric field  37  that is created by electrostatic voltage charge potential  26  of measured object  11 , amplifies voltage signal  230  and sends an amplified signal  240  to control unit  55 . More specifically, circuit  200  includes a sensing electrode  250  that senses voltage signal  230 . Electrode  250  has an associated capacitance Cs, preferably about 0.043 Pico farads. Voltage signal  230  travels from electrode  250  to preamplifier  210 . An input shunt capacitor  264  and an input shunt resistor  265 , preferably in the order of 1 Terra Ohm, is provided in parallel between at amplifier input  280 . Additionally, a shunt capacitor  267 , having a capacitance of preferably 1 pf or 5 pf, is added at input  280  to preamplifier  210 . For the reasons set forth above in connection with the embodiment of  FIG. 2 , a 5 pf shunt capacitance is considered preferable. 
         [0043]    Similarly, preamplifier  210  is preferably an operational amplifier with a 1 pf input capacitance  269 , such as ultra low bias current operational amplifier model OPA 129 produced by Burr-Brown products from Texas Instruments. In any case, amplifier  210  sends an output voltage signal  240  through wires  52  to control unit  55 . Output  285  of preamplifier  210  is connected back to inverting input  260  of preamplifier  210 . Additionally output  215  from preamplifier  210  is sent to feedback path  220 . 
         [0044]    In a manner corresponding to the previously described embodiment, feedback path  220  includes a feedback amplifier  270  that is also an operational amplifier. In particular, output  215  from preamplifier  210  is sent to an inverting input  277  of feedback amplifier  270  through a resistor  275 . In a preferred embodiment, resistor  275  has a value of 10 M ohm. A non-inverting input  271  of feedback amplifier  270  is connected to ground  268 . Output  278  of feedback amplifier  270  travels through a shunt resistor  265 , preferably having a value of 1 Terra ohm, and then returns to non-inverting input  280  of preamplifier  210 . Once again, while most standard operational amplifiers of a correct size could be used, a preferred amplifier is a micro-power single supply operational amplifier model OPA2244 produced by Burr-Brown products from Texas Instruments. 
         [0045]    Of particular distinction in connection with the  FIG. 3  embodiment is the presence of analog switch  225  between output  215  of preamplifier amplifier  210  and non-inverting input  280  of preamplifier  210 . As shown, analog switch  225  is in series with parallel arranged resistor  292  and capacitor  294 . Capacitor  294  has a preferred value of 10 microfarads, while resistor  292  has a preferred value of 50 mega ohms or larger. While most standard analog switches could be employed, a preferred switch is a quad analog switch produced by Maxim products from Dallas Semiconductor. Switch  255  is controlled by a digital output from module  55 . When output voltage signal  240  is larger than a specified high threshold level, module  55  opens switch  255  until output voltage signal  240  falls below a set low threshold level. 
         [0046]    As indicated above, the electrostatic monitoring system of the invention can take various forms and be used in a wide range of applications. Turning now to  FIG. 4 , there is shown an electrostatic monitoring system  300  constructed in accordance with another embodiment of the invention. As shown, monitoring system  300  is mounted on a piece of equipment that is sensitive to electrostatic discharge. More particularly monitoring system  300  is shown mounted on a gasoline pump  310 . System  300  may be mounted in numerous different places, but preferably includes a sensor  314  mounted on a dispensing handle  315 . More specifically, a single sensor  314  or multiple sensors may be mounted on handle  315  having an associated hose  318 , while a wire  322  travels along dispensing hose  318  and to a controller  325  and an alarm  326 . 
         [0047]    Alternatively, a mounting fixture  330  may hold one or more capacitive sensors  336  and  337 . Mounting fixture  330  preferably keeps one sensor  336  at least 2 cm away from pump  310  and keeps a second sensor  337  at least 2 cm away from first sensor  336  and 4 cm away from pump  310 . Sensors  336  and  337  are connected to a controller  338  by wiring  339 . In either embodiment, if a person approaches pump  310 , a visual and/or audible warning will be given by alarm  326  if the person/object has accumulated a dangerously large static electric charge. In one preferred form of the invention, controller  325  of system  300  actually disables pump  310  until the high static potential has been safely discharged. 
         [0048]    Turning now to  FIG. 5 , there is shown an electrostatic monitoring system  350  constructed in accordance with another preferred embodiment of the invention. As shown, monitoring system  350  includes a control module  355  analogous to control module  55  discussed above. In addition, a sensor  356  is connected to control module  355  via a communication line  359 . In this embodiment, monitoring system  350  is shown in a semi-conductor wafer production line  360 . Production line  360  includes a robotic arm assembly  365  which carries a semiconductor wafer  370  along a robotic process pathway  375 . Sensor  356  is mounted so as to face semiconductor wafer  370  and measure an electric field E emanating therefrom. Sensor  356  is particularly sensitive so as to allow for remote measurement and monitoring of electrostatic charges on semiconductor wafer  370 . In addition, the sensitivity of sensor  356  allows for discrimination between electrostatic charges on wafer  370  verses electrostatic charges produced from other field voltage sources generally indicated at  380 . Such general voltage field sources  380  create electric fields E S  as best shown in  FIG. 5 . Electric field source  380  here represents numerous other voltage field sources which are typically found in automated handling systems, such as wafer production line  360 . With this arrangement, sensor system  350  can be installed outside robotic process pathway  375  and provide real time monitoring of electrostatic charges on the semiconductor wafer  370 . For example, monitoring system  350  is able to detect a 100 volt charged wafer  370  at a distance of 0.5 to 1 meter above pathway  375 . Of course, once a relatively large electrostatic charge is sensed on semiconductor wafer  370 , or for that matter reticles and carriers typically found in wafer production lines, corrected action can be taken to avoid unwanted electrostatic discharge. 
         [0049]    Various other forms of the invention are represented in  FIG. 6 . More specifically, there is shown an embodiment wherein a monitoring system  400  can be provided on sensitive equipment  401  or as a wearable arrangement. In particular, on one hand, system  400  can be incorporated into a hat  402 , a badge  403  or on one or more sleeves  404  of protective clothing, such as a chemical suit, worn by a person  412 . On the other hand, monitoring system  400  can be placed on equipment  401 . At this point, it is important to note that these embodiments convey, in addition to variations in the articles that the sensor can be incorporated, that the electrostatic charge of interest could emanate from an object and be sensed with sensors on an individual, or emanate from the individual and be sensed with sensors on the object. In either case, the invention provides for sensing the charge at a considerable distance, as discussed further below, which enables corrective action to be taken. 
         [0050]    In the embodiment where the individual carries the electrostatic charge, this is similar to the arrangement of  FIG. 1 , but with the monitoring system being carried by the object, rather than in a gateway or the like leading to the object. In the particular case shown, sensors  446  and  447  are mounted on a fixture  448  that keeps sensor  446  away from equipment  401 , preferably at least 2 cm, keeps second sensor  447  away from first sensor  446 , again preferably at least 2 cm, and further maintains second sensor away from equipment  401 , preferably at least 4 cm. Sensors  446  and  447  are connected to a controller  455 . If person  412  approaches equipment  401 , a warning will be given if person  412  has accumulated a dangerously large static electric charge. A detection range of at least 2 to 3 meters is established with system  400  so that an advanced warning through a suitable unit  457  can be given, thereby allowing plenty of time to take corrective action. As indicated above, equipment  401  could take various forms such as, for example, an object in a clean room. 
         [0051]    In other situations, a certain object  401  may produce an electric field E. As the body of a person  412  is a good conducting object, it can be subjected to and distort the local electric potential. In various situations, it would be desirable to sense the local electric potential at body  412 . To this end, various arrangements are disclosed wherein monitoring system  400  is worn by person  412 . In deploying a wearable sensor on person  412 , the mounting position is important. In accordance with one embodiment shown, a baseball hat  402  provided with a visor  460  has be employed for the effective mounting of wearable capacitive sensors  462  and  463 . Preferably, sensing electrodes  150 ,  250 , referenced above, would preferably face outward in order to effectively sense the potential in free space. As shown in  FIG. 6 , sensors  462  and  463  located on visor  460 , are mounted with one sensor  462  being closer to person  412  than the other sensor  462 . Wiring (not separately labeled) is provided to transport sensed signals to a controller  464 . A connection is also made to a conductive object, such as a fabric patch  465 , on hat  402  near person  412  to provide a ground. 
         [0052]    In another depicted form, system  400  may have sensors  472  and  473  located on badge  403 . Once again, a controller  474  is provided with an electrical connection  475 . Controller  474  is preferably incorporated into badge  403 , but may also be located elsewhere. Finally, in another shown form of the invention, a sensor  482  is located on the sleeve(s)  404  of a garment, such as a chemical suit, worn by person  412 . Once again, a controller  484  is provided with an electrical connection  485 . Controllers  464 ,  474 ,  484  may each be connected to an alarm  490 . Regardless of the particular form taken for these embodiments, the person carries the requisite monitoring system which will alert the person when they are subjected to an electrostatic potential above a predetermined level. 
         [0053]    Turning now to  FIG. 7 , a human body model, used in the assistance of designing a wearable system, is shown at  500 . As depicted, a person  figure 512  is modeled on a grounding mat  532  at a certain distance from a high voltage source  535 . In one tested arrangement, the potential distribution around high-voltage source  535  was modeled with an ElecNet electrostatic and electrodynamic modeling package. During a conducted simulation represented by  FIG. 7 ,  figure 512  was standing on and in electrical contact with grounding mat  532 . Two sensor positions were simulated: one on a hat  540 , 6 cm in front of  figure 512  and 1.75 m above mat  532 ; and the other outside of a shirt  545 , 1 cm in front of  figure 512  and 1.10 m above mat  532 . Voltage source  535  was modeled as a charge uniformly distributed on a metal can of 20 cm in diameter and 20 cm in height. The center of source  535  was positioned 1.1 m above mat  532 . 
         [0054]    The simulation results are shown in  FIG. 8  as a graph.  Figure 512  is 60 cm and 100 cm from the edge of high-voltage source  535 . The graph also shows simulated results without the effect of  figure 512 . Several points were noted. When a sensor is placed very close to  figure 512 , the potential is zero. The further away a sensor is from  figure 512 , the higher the potential. The potential is higher 6 cm in front of  figure 512  on hat  540 , than 1 cm in front of  figure 512  on shirt  545 . The potential is inversely proportional to the distance from source  535 . Whether shoes  546  are conducting or insulating, the results are very similar, owing to capacitive coupling from  figure 512  to mat  532 . At a 1 m distance from a 1 kV source, the DC potential is 40 V near hat  540 , and 4 V near shirt  545 . With  figure 512  walking at an average speed of 1 m/s, the signal has an effective frequency of at least 1 Hz, putting it well inside the measurement bandwidth of system  10 . 
         [0055]    Although described with reference to preferred embodiments of the invention, it should be readily understood that various changes and/or modifications could be made to the invention without departing from the spirit thereof. For example, the sensors could be mounted on many other objects, such as additional items worn by a person, for example, safety glasses or other types of clothing. In general, the invention is concerning with sensing a potentially hazardous electrostatic voltage charge potential, providing a suitable warning and enabling corrective measures to be taken at a significant distance from any location that damage can be inflicted by the potential. In any case, the invention is only intended to be limited by the scope of the following claims.