WO1999004277A1

WO1999004277A1 - Zero voltage wrist strap monitor

Info

Publication number: WO1999004277A1
Application number: PCT/US1998/014878
Authority: WO
Inventors: Michael Albert Sanchez
Original assignee: Semtronics Corporation
Priority date: 1997-07-17
Filing date: 1998-07-17
Publication date: 1999-01-28
Also published as: AU8411798A; EP1019739A1; WO1999004277A9

Abstract

A dual conductor wrist strap monitoring circuit that allows the operator to remain at approximately zero volts. The monitor couples the operator, through resistors, to two voltage potentials equal in value with respect to earth ground, but opposite in polarity. Because typically there is symmetry in the resistance in each side of a dual conductor wrist strap, the operator is at zero potential with respect to earth ground. There is still a conductive path for the operator to discharge any charge potential they build up with no negative affect on decay times.

Description

ZERO VOLTAGE WRIST STRAP MONITOR

Cross-Reference to Related Applications

This application claims priority to United States Provisional Application Serial

No. 60/052,944, filed July 17, 1997 by Michael A. Sanchez entitled "Zero Voltage Wrist Strap Monitor".

Background of the Invention The discharge of static electricity creates problems in the electronics and other industries. Many microelectronic components such as integrated circuits and some diodes may be disabled or destroyed by over-voltages or power density stresses. Some semiconductor junctions can be destroyed by the application often or fifteen volts. Static electricity discharges can produce sufficient power densities to alter dopant distributions and even vaporize metallization layers and the silicon chip material. Similarly, magneto-resistive circuits, such as those used in hard disk drives, can be damaged or destroyed by very small potentials. For example, hard drive manufacturing processes may require workers to be maintained at potentials of less than plus or minus five volts. Yet a person walking on carpet on a dry day can accumulate as much as 30,000 volts of potential, and he or she can triboelectrically generate thousands of volts by simply changing his or her position in a chair or handling a styrofoam cup. Similar charges may accumulate through conduction or induction.

Such a person can inadvertently discharge such static potential into a circuit or component by touching it and causing over- voltage or excessive power density. Additionally, the potential in such a person's body can induce a charge in a circuit that can later cause over- voltage or excessive power density when the circuit is subsequently grounded. Likewise, manufacturing equipment and other objects that come in contact with the circuits may accumulate charges capable of discharging through and damaging the circuits. Those in industries in which integrated circuits and other microelectronic components are handled or assembled may take measures to limit the failure rate of those circuits and components by attempting to keep them as well as their environment at zero electrical potential. Such measures include providing operators and work stations with electro-static discharge (ESD) protective devices which act to dissipate electrostatic discharge or to provide shielding from electrostatic discharge or electrostatic fields. Examples of ESD protective devices include antistatic carpet, conductive or dissipative grounded desk top work surfaces, hot air ion generators which emit ions to neutralize static charges, grounding wrist straps, heel grounders, static suits and other devices that allow operators to remain at zero potential by providing a discharge path to ground. One of the most common methods for protecting against ESD damage is to provide a discharge path from the operator handling or equipment in contact with sensitive devices to ground. For example, an operator may wear a grounded wrist strap or equipment may be connected via a wire to ground. (Hereinafter, for convenience, the discussion will be directed to ESD devices worn by operators, although it is to be understood that the same problems and principals apply to ESD devices applied to manufacturing equipment and other objects.) Grounding the operator provides a discharge path for any accumulated charge. The resistance of that path as well as the operator's capacitance dictate the speed and magnitude of charge/discharge events. Increased resistance allows for a larger potential and faster charge rate and a slower discharge rate. Increased capacitance allows for a slower charge rate and a slower discharge rate.

Even when a discharge path is provided, however, it is necessary to provide a means for verifying that the ESD protective device is functioning properly. There are several products on the market to continuously monitor the integrity of the operator's grounded wrist strap. One common method is to use a single conductor wrist band and monitor the capacitance of the operator and wristband. This technique has been shown to be unreliable because the monitor may indicate that the operators are properly grounded even though they are isolated from ground, for instance, by wearing the wrist strap over insulative clothing like a smock or glove. Thus, there is no way of ensuring that they are properly grounded. One approach used to overcome the limitations of the single conductor wrist band is to use a dual conductor wrist strap such as that described in U.S. Patent Nos. 4,639,825, entitled "Stretchable Grounding Strap Having Redundant Conductive Sections," dated January 27, 1987; 4,745,519, entitled "Grounding Strap Which Can Be Monitored," dated May 17, 1988; and 4,813,459, entitled "Stretchable Material Having Redundant Conductive Sections," dated March 21, 1989, all of which are incorporated herein in their entirety by this reference. Also bodysuits, heel straps and other devices using two conductive paths may be used. One of the two conductors is connected through a one megohm safety resistor directly to earth ground. The other conductor is connected to a one megohm safety resistor that is connected to a selected voltage potential, typically between about +7v to +30v. The operator acts as a resistor between the two conductors. This arrangement creates a resistor divider circuit in which the operator's resistance can be determined by the voltage measured at the junction of the two resistances, i.e., the resistor and the operator. Dual conductor wrist straps with one end connected directly to earth ground are effective because they let the operator discharge any charge potential that builds up on the operator. The resistance and capacitance of the wrist strap and operator dictate the rate at which the charge decays. However, because one end of the wrist strap is coupled to earth ground and the other end coupled to a given or selected potential, the operator will be at a potential greater than earth ground. This condition is undesirable in ESD sensitive manufacturing processes. This is because electronics are becoming more and more sensitive to voltages applied to the operators handling the electronics. In fact, some electronics may be sensitive to voltages as low as plus or minus five volts. Nonetheless, the current dual conductor approach allows anywhere from one to thirty volts to be applied to the operator, depending on the operator's resistance. Thus, it would be desirable to provide a wrist strap monitoring system that applies little or no net voltage to the operator with respect to earth ground.

Summary of the Invention The present invention provides a dual conductor wrist strap monitoring circuit that allows the operator to remain at approximately zero volts. The improved monitor of the present invention couples the operator, through resistors, to two voltage potentials equal in value with respect to earth ground, but opposite in polarity. Because typically there is symmetry in the resistance in each side of a dual conductor wrist strap, the operator is at zero potential with respect to earth ground. There is still a conductive path for the operator to discharge any charge potential they build up with no negative affect on decay times.

The improved monitor may use low voltages, e.g., less than ten volts. Because wrist band-to-skin resistance is non-linear at low voltages, measuring with lower voltages may result in a higher skin resistance reading. Therefore, using lower voltages to measure the resistance guarantees that the operator will remain within a safe resistive range for all voltages. The improved monitor also may be used to monitor dissipative mats, bodysuits, heel straps and any other types of dual conductor ESD protective devices.

Accordingly, it is an object of the present invention to provide a circuit for monitoring an ESD protective device that typically applies little or no net voltage with respect to earth ground to the object to which the protective device is applied.

Other objects, features, and advantages of the present invention will become apparent with reference to the remainder of the written portion and the drawings of this application. Brief Description of the Drawings

FIG. 1 is a functional diagram of a dual conductor wrist strap and monitoring circuit in accordance with the present invention.

FIG. 2 is a schematic diagram of a first embodiment of the monitoring circuit of FIG. 1. FIGS. 3 A-3F are schematic diagrams of a second embodiment of the monitoring circuit of FIG. 1.

FIG. 4 is a flow diagram for controlling the monitoring circuit of FIGS. 3A-3F.

FIG. 5 is a flow diagram for controlling the monitoring circuit of FIGS. 3A-3F.

FIG. 6 is a flow diagram for controlling the monitoring circuit of FIGS. 3A-3F. FIG. 7 is a flow diagram for controlling the monitoring circuit of FIGS. 3A-3F. Detailed Description

ESD monitors in accordance with the present invention couple the operator through resistors to electrical potential equal in value or magnitude with respect to earth ground, but opposite in polarity. The voltages may be direct current (dc) or pulsed. FIG. 1 shows the basic configuration of one possible dc circuit 10. Other circuits which provide the desired results will be apparent to one skilled in the art.

Circuit 10 comprises positive voltage supply 12, negative voltage supply 14, ground circuit 16, and resistive devices 18 and 20. Voltage supplies 12 and 14 are complimentary, i.e., they provide voltages of equal magnitude, but opposite polarity. For example, voltage supplies 12 and 14 may supply positive and negative one and one quarter volts, respectively. Of course, other voltages may be supplied as desired or appropriate. Also, if a voltage with respect to earth ground other than zero volts is allowed, the potentials need not be of equal magnitude. Complimentary current supplies may be used in lieu of voltage supplies. Voltage supplies 12 and 14 are connected to ground circuit 16 at their negative and positive terminals, respectively.

Resistive devices 18 and 20 may be resistors, thermistors or any devices with a non-zero resistance or that otherwise may be used to calculate the resistance of the operator 26 or object 26 to which the ESD protective device is affixed. In the illustrative embodiments, resistive devices 18 and 20 are one megohm resistors and are connected to voltage supplies 12 and 14, respectively.

Resistor symbols 22 and 24 represent the resistance in each of the conductors of the dual conductor ESD protective device. For example, if the ESD protective device is a dual-conductor wrist strap, the resistance in each side includes the resistance of the cord leading to the conductor segment (which includes a one megohm resistor to protect the operator from electrocution), conductor/skin interface and operator's body, combined. The sum of these resistances 22 and 24 comprise the loop or series resistance of operator 26. Typically there is symmetry in the resistances 22 and 24 and thus the operator is at zero potential with respect to earth ground when no external charge is introduced. In other words, the monitor allows the operator or object to be at zero potential by providing a discharge path to ground and applying equal, but opposite (and therefore canceling) voltages for monitoring purposes. Variations in skin contact resistance, imprecision of the voltage source and other variations may result in a small potential existing on the operator. For example, in the illustrative embodiments described below, these factors may result in maximum charges of plus or minus 1.17 volts on the operator at any time. Also, if one of the conductors becomes detached or otherwise loses its connection to the operator, the operator will go to plus or minus 1.25 volts (the polarity will depend on which of the two conductors becomes detached). This voltage is, however, substantially below the twelve volts which may be allowed by conventional dual conductor monitoring systems. Moreover, increased precision in voltage control, use of lotions to improve skin contact resistance values and other means of reducing system variations may further reduce maximum potential on the operator.

By measuring the voltages at points 28 and 30 of circuit 10, the operator's 26 status may be determined. For instance, if the voltages at points 28 and 30 move closer to zero volts, the operator's 26 resistance is decreasing. Conversely, if the voltages 28 and 30 move closer to their respective supplies (+/- 1.25 volts in the illustrative embodiment), the operator's resistance is increasing. If the voltages 28 and 30 both shift towards the positive supply 12, then operator 26 is discharging a positive charge through circuit 10. If the voltages 28 and 30 shift towards the negative supply 14, then operator 26 is discharging a negative charge through circuit 10. Threshold levels and logic can be used to determine pass and fail conditions for both high and low operator resistance levels as well as positive and negative charge build up. This may be implemented with hardware and/or firmware.

FIG. 2 is a schematic diagram of a first illustrative embodiment of circuit 100 in accordance with the present invention. One skilled in the art will understand that circuit 100 is but one possible embodiment of the circuit 10 shown in FIG. 1. Circuit 100 provides the status of the operator and/or external equipment which may be displayed at the unit visually and/or audibly. The status also may be transmitted from the unit to a data acquisition system.

Circuit 100 comprises connections 102 for an AC adapter (not shown), positive voltage regulators 104, voltage inverter 106, negative voltage regulators 108, positive monitoring circuit 110, negative monitoring circuit 112, logic circuit 114, op amp power supply 116, optional mat ground monitor 118, operator presence circuit 161 and operator interface 120. Connections 102 connects circuit 100 to a conventional AC to DC power source to provide DC power to circuit 100. Connections 102 also provides an earth ground to circuit 100, thereby providing a dissipation path for operator 26 (through interface 120). AC adapter 102 provides power to positive voltage regulators 104 via line 122. AC adapter 102 provides power to negative voltage regulators 108 (through inverter 106) via line 124.

Positive voltage regulators 104 may be any conventional regulated power supply capable of providing the desired voltage level. In the illustrative embodiment, regulators 104 provide two and one-half volts positive at line 126 and five volts positive at line 125. Other voltage levels may be selected as appropriate.

Inverter 106 receives power via line 124, inverts the charge and delivers the power to negative voltage regulators 108 via line 128. Inverter 106 may be any conventional inverter circuit. Negative voltage regulators 108 may be any conventional regulated power supply capable of providing the desired voltage level. Regulators 108 should match regulators 104 so as to provide the same voltage as lines 126 and 130, but of opposite polarity. Thus, in the illustrative embodiment, regulators 108 provides two and one-half volts negative at line 130 and six and four tenths volts negative at line 131. (The voltages provided at lines 125 and 131 are used to power op amps as shown in segment 116. Consequently, the voltages at lines 125 and 131 need not match.)

Positive monitoring circuit 110 receives power from regulators 104 via line 126. Circuit 110 monitors input from line 134, which is ultimately connected to one side of the operator's wrist strap. The input signal is processed through a low-pass filter 138 and diodes 140 (which protect the op amps in circuit 110 from over- voltages). The signal is then passed through a voltage follower 142 which acts as a buffer to prevent signal processing that occurs downstream of follower 142 to affect the characteristics of the signal upstream of follower 142. The signal is then processed through two amplifiers 144 and 146. Each amplifier 144 and 146 provides an analog output which reflects the measured voltage. Amplifier 144 is optimized to provide signals reflecting a low resistance condition and thus uses a gain of about three. Amplifier 146, which provides a differential function, is optimized to provide signals reflecting a high resistance condition and thus uses a gain of about twenty.

Negative monitoring circuit 112 monitors line 136 and is essentially the same as circuit 110, with the following exceptions. Amplifiers 148 and 150 are arranged in an inverter configuration so that the output has a reverse polarity from the input signal. This is necessary because the input signal is negative and logic circuit 114 requires input signals in the range from 0 to +5 volts. Of course, if a processor which accepts negatively charge input signals is used, an inverter configuration is not necessary. Also, because amplifier 150 does not act as a differential amplifier and invert the signal simultaneously, amplifier 152 is provided to perform the differential function, thereby creating the desired signal, which is then inverted by amplifier 150. Thus, amplifiers 148 and 150 each provide an analog output signal reflecting low and high resistance conditions, respectively.

The output signals from amplifiers 144, 146, 148 and 150 provide input to logic circuit 114. The output signals are in analog form; however, one of skill in the art could modify circuits 110 and 112 to provide a digital output reflecting the pass or fail status of the wrist strap. In the illustrative embodiment, the analog signals from amplifiers 144, 146, 148 and 150 are converted into digital form by processor 154. The digital data is then analyzed, through hardware, firmware or software logic in processor 154 to determine the status of the wrist strap. The processor then controls light emitting diodes 156 and buzzer 158 to provide the appropriate status signal. For instance, if the system is in use and operational, only a green LED is illuminated. If the wrist strap is in use and is failing high, a red LED marked "FAIL/HIGH" is illuminated and the buzzers sounds, and so forth. Moreover, the status data may be directed to a data acquisition, storage and processing system via output interface 160. Operator interface 120 allows the operator to connect his or her wrist strap to the monitoring circuit. For instance, a dual conductor wrist strap (not shown) or other dual conductor grounding device is connected to pins 12 and 14 of interface 120. An "operator present" circuit 161 may also be provided. Circuit 161 senses an operator by detecting the voltage drop resulting from the short that occurs between pins 11 and 12 of interface 120 when the operator plugs his or her ESD device into interface 120.

Because the voltage drop is predictable, circuit 161 may be set to detect a voltage level below a certain threshold and thus, provide an "operator present" signal to circuit 114. Circuit 161 provides a signal via line 162 to circuit 114 indicating the presence or absence of the operator. This allows logic circuit 114 to avoid illuminating LED's 156 and sounding buzzer 158 when a failure signal is detected where that failure signal is merely the result of an absent operator. (A wrist strap that is not in use creates a signal that is similar to a wrist strap in use that has failed.)

Logic circuit 114 can determine the following conditions about the operator from signals 144, 146, 148, and 150. If signals 146 and 150 are below their thresholds, then the operator's resistance is too high. If signals 144 and 148 are below their thresholds then the operator's resistance is too low. If signal 146 is well below the threshold and signal 150 is above the threshold then the operator is positively charged. If signal 150 is well below the threshold and signal 146 is above the threshold then the operator is negatively charged.

Monitoring circuit 100 may also be used to monitor the status of other ESD devices, such as a dissipative mat 166. For example, circuit 118 may be provided which provides an output signal 164 to logic circuit 114. Mat 166 is connected to ground 168 on one end and to circuit 118 via line 170. Resistor 172 generates a voltage divider which is monitored by logic circuit 174 to provide the digital input to processor 154. LED 175 provides an indication of a fault condition (e.g., mat resistance above a predetermined threshold value).

Alternatively, circuit 174 could produce an analog signal (as do circuits 110 and 112). In such a configuration, processor 154 could be programmed with the mat levels, through hardware, firmware or software, in order to provide the desired status indications. In the illustrative embodiment, processor 154 does not have sufficient analog-to-digital (A/D) converters to allow this function; however, one skilled in the art may readily select alternative processors 154 which provide the desired processing capabilities and features and the desired number of A/D converters. Also, additional circuits similar to circuits 110 and 112 may be added to circuit 100 to provide additional monitoring capability. FIGS. 3 A-F are schematic diagrams of a second illustrative embodiment of circuit 200 in accordance with the present invention. One skilled in the art will understand that circuit 200 is but one possible embodiment of the circuit 10 shown in FIG. 1. Circuit 200 provides the status of 2 operators and/or 2 pieces of external equipment which may be displayed at the unit visually and/or audibly. The status' also may be transmitted from the unit to a data acquisition system. Circuit 200 comprises connections 202 for an AC/DC adapter (not shown), positive voltage regulators 204 A&B, voltage inverter 206, negative voltage regulators 208, positive monitoring circuit 210, negative monitoring circuit 212, logic circuit 214, op amp and comparator power supply 216, optional mat ground monitor 218, operator presence circuit 261 and operator interface 220. Connections 202 connects circuit 200 to a conventional AC/DC power source to provide dc power to circuit 200.

Connections 202 also provides an earth ground 201 to circuit 200, thereby providing a dissipation path for operator 26 (through interface 220). AC/DC adapter 202 provides power to positive voltage regulators 204 via line 222. AC/DC adapter 202 provides power to negative voltage regulators 204 (through inverter 206) via line 224. Positive voltage regulators 204 A & B may be any conventional regulated power supply capable of providing the desired voltage level. In the illustrative embodiment, regulators 204 provide one and one-quarter volts positive at line 226 and five volts positive at line 225. Other voltage levels may be selected as appropriate. 2 Inverter 206 receives power via line 224, inverts the charge and delivers the power to negative voltage regulators 208 via line 228. Inverter 206 may be any conventional inverter circuit. Negative voltage regulators 208 may be any conventional regulated power supply capable of providing the desired voltage level. Regulators 208 should be selected so as to provide the same voltage on lines 226 and 230, but of opposite polarity. Thus, in the illustrative embodiment, regulators 208 provides one and one-quarter volts negative at line 230 and six and four tenths volts negative at line 231. (The voltages provided at lines 225 and 231 are used to power op amps as shown in segment 216. Consequently, the voltages at lines 225 and 231 need not match.)

Positive monitoring circuit 210 receives power from regulators 204 via line 226. Circuit 210 monitors input from line 234, which is ultimately connected to one side of the operator's wrist strap. The input signal is processed through a low-pass filter 238 and diodes and resistor 240 (which protect the op amps in circuit 210 from over voltage). The signal is then passed through a voltage follower 242 which acts as a buffer to prevent signal processing that occurs downstream of follower 242 to affect the characteristics of the signal upstream of follower 242. The signal is then processed through two amplifiers 244 and 246. Each amplifier 244 and 246 provides an analog output which reflects the measured voltage. Amplifier 244 is optimized to provide signals reflecting a low resistance condition and thus uses a gain of about six point six. Amplifier 246, which provides a differential function, is optimized to provide signals reflecting a high resistance condition and thus uses a gain of about twenty six.

Negative monitoring circuit 212 monitors line 236 and is essentially the same as circuit 210, with the following exceptions. Amplifiers 248 and 250 are arranged in an inverter configuration so that the output has a reverse polarity from the input signal. This is necessary because the input signal is negative and logic circuit 214 requires input signals in the range from 0 to +5 volts. Of course, if a logic circuit which accepts negatively charge input signals is used, an inverter configuration is not necessary. Also, because amplifier 250 does not act as a differential amplifier and invert the signal simultaneously, amplifier 252 is provided to perform the differential function, thereby creating the desired signal, which is then inverted by amplifier 250. Thus, amplifiers 248 and 250 each provide an analog output signal reflecting low and high resistance conditions, respectively. The output signals from amplifiers 244, 246, 248 and 250 provide input to logic circuit 214. The output signals are in analog form; however, one of skill in the art could modify circuits 210 and 212 to provide a digital output reflecting the pass or fail status of the wrist strap. In the illustrative embodiment, the analog signals from amplifiers 244, 246, 248 and 250 are converted into digital form by processor 254. The digital data is then analyzed, through hardware, firmware or software logic (as described below) in processor 254 to determine the status of the wrist strap. The processor then controls light emitting diodes 256 through latches 290 and buzzer 258 to provide the appropriate status signal. For instance, if the system is in use and operational, only a green LED is illuminated. If the wrist strap is in use and is failing high, a red LED marked "FAIL/HIGH" is illuminated and the buzzers sounds, and so forth. Moreover, the status data may be directed to a data acquisition, storage and processing system through latches 290 to output interface 260.

Operator interface 220 allows the operator to connect his or her wrist strap to the monitoring circuit. For instance, a dual conductor wrist strap (not shown) or other dual conductor grounding device is connected to pins 12 and 14 of interface 220. An "operator present" circuit 261 may also be provided. Circuit 261 senses an operator by detecting the voltage drop resulting from the short that occurs between pins 11 and 12 of interface 220 when the operator plugs his or her ESD device into interface 220. Because the voltage drop is predictable, circuit 261 may be set to detect a voltage level below a certain threshold and thus, provide an "operator present" signal to circuit 214. Circuit 261 provides a signal via line 262 to circuit 214 indicating the presence or absence of the operator. This allows logic circuit 214 to avoid illuminating LED's 256 and sounding buzzer 258 when a failure signal is detected where that failure signal is merely the result of an absent operator. (A wrist strap that is not in use creates a signal that is similar to a wrist strap in use that has failed.)

Logic circuit 214 can determine the following conditions about the operator from signals 244, 246, 248, and 250. If signals 246 and 250 are below their thresholds, then the operator's resistance is too high. If signals 244 and 248 are below their thresholds then the operator's resistance is too low. If signal 246 is well below the threshold and signal 250 is above the threshold then the operator is positively charged. If signal 250 is well below the threshold and signal 246 is above the threshold then the operator is negatively charged.

Alternatively, referring to FIG. 1 , a conventional logic circuit could be used in conjunction with circuit 10. For example, a conventional monitor could be connected to circuit 10 at either point 28 or 30. While this approach might diminish the accuracy of the monitoring system and eliminate the ability to distinguish between charges on the operator and increases in resistance, it would allow an operator to remain at zero potential, due to the application of equal, but opposite voltages. Thus, this approach might be used to minimize the cost and complexity of the monitoring system while still providing a means for allowing an operator to remain at a very low potential. Mat monitoring may be performed as described above in connection with the first embodiment or in the same manner as monitoring an operator.

Alternatively, circuit 274 could produce an analog signal (as do circuits 210 and 212). In such a configuration, processor 254 could be programmed with the mat levels, through hardware, firmware or software, in order to provide the desired status indications. In the illustrative embodiment, processor 254 does not have sufficient analog-to-digital (A/D) converter inputs to allow this function; however, one skilled in the art may readily select alternative components 254 which provide the desired processing capabilities and features and the desired number of A/D converter inputs. FIGS. 4-7 show the logic flow for programming processor 254 in accordance with the present invention. Similar programming may be used in processor 154 of the first illustrative embodiment.

Referring to FIG. 4, the power up procedure includes the following steps:

- Power on 300, initialize all variables and A/D 302 - Set calibration bit and look for echo back 304. If echo back, call CALIBRATION routine 306, else continue

- Read alarm levels from eeprom and subtract 6 bits to calculate actual alarm levels 308 (note: this gives 6 bits of hysteresis)

Referring to FIG. 5, the processor then determines the presence of each operator or mat connected thereto. The code listed below is performed first for operatorl , replace # with a 1 and then for operator2, replace # with a 2.

LOOP:

- check charge data out and charge display bits and set flags appropriately 310 - read operator# A/D inputs 312

- check operator# present bit 314, if bit indicates operator not present goto OP#_CHKl 316

- check for new status# delay, if in delay, update delay counter and skip to MAT#_CHECK 318, else goto OP#_CHKl 316 (Note: when a new operator status is qualified, condition is held for ~ls)

Referring to FIG. 6, the processor again determines the presence of each operator or mat connected thereto and, if so, determines the status of each. OP#_CHKl 316:

- check last qualified operator status:

- if operator was present and bit indicates he still is goto OP#_HERE 320

- if operator was not present , require operator to be present for l/4s before qualifying operator is here. We know operator is present if operator# bit is low or the WS- voltage is > limit, goto MAT#_CHECK 318

- if operator was present , but bit indicates he is not, require operator to be gone for l/4s before qualifying operator is not present, goto MAT#_CHECK 318

OP#_HERE 320 :

- check if ws#_high+ voltage is <= upper limit 322, if so goto CHECK#LOW 326

- check if ws#_high- voltage is <= upper limit 322, if so goto CHECK#LOW 326

- if code falls through to here, operator fails high, set high resistance status# and new status# flags 324 and goto MAT#_CHECK 318

CHECK#LOW 326:

- check if ws#_low+ voltage is >= lower limit, if so goto CHECK#SAFE 328

- check if ws#_low- voltage is >= lower limit, if so goto CHEC SAFE 328

- if code falls through to here, operator fails low, set low resistance status# and new status# flags 324 and goto MAT#_CHECK 318

CHECK#SAFE 328:

- check charge data out and charge display flags, if neither option set, goto SKLPCHARGE# 330 - check if new status# flag set, if it is, skip to MAT#_CHECK 318

- check if ws#_high+ voltage < 8 bits, if so then operator at >=+l .25 v, goto POSITIVE_CHARGE# 332 check if ws#_high- voltage < 8 bits, if so then operator at <=-l .25 v, goto

NEGATΓVE_CHARGE# 334 - else fall through to SKLPCHARGE# 330

SKIPCHARGE# 330: clear charge flags check if ws#_high+ voltage < safe limit, in hysteresis band, goto HYSTERESIS#_HIGH 336

- check if ws#_high- voltage < safe limit, in hysteresis band, goto HYSTERESIS#_HIGH 336

- check if ws#_low+ voltage < safe limit, in hysteresis band, goto HYSTERESIS#_LOW 338 - check if ws#_ low- voltage < safe limit, in hysteresis band, goto HYSTERESIS#_LOW 338

- else operator is safe, if new status flag set, goto MAT#_CHECK 318 else set new status# and safe status# flags and goto MAT#_CHECK 318 HYSTERESIS#_HIGH 336:

- check if operator# resistance high flag and new status# flags are set, if so goto MAT#_CHECK 318

- set current status to last status and goto MAT#_CHECK 318

HYSTERESIS#_LOW 338:

- check if operator# resistance low flag and new status# flags are set, if so goto MAT#_CHECK 318

- set current status to last status and goto MAT#_CHECK 318

POSITIVE_CHARGE# 332: check if operator* resistance high flag and new status# flags are set, if so goto MAT#_CHECK 318 else set new status* and charge status# flags and goto MAT#_CHECK 318

NEGATIVE_CHARGE# 334: check if operator* resistance high flag and new status* flags are set, if so goto MAT#_CHECK 318 else set new status* and charge status* flags and goto MAT#_CHECK 318

Referring to FIG. 7, the processor checks the mat, displays the status of the operator(s) and mat (sounding an alarm if necessary) and provides data as desired.

MAT#_CHECK 318: - check if new mat* status flag is set, if so skip mat check, if in operator 1, repeat all steps for operator 2, if in operator 2, got DISPLAY

- check mat* bit, if bit set, set mat# resistance high and new mat* status flags

DISPLAY 340: - check operator 1 status flags and turn on appropriate leds

- check operator2 status flags and turn on appropriate leds

BUZZER 342:

- check operator 1 status flags and turn on buzzer 1 flag for all status' except safe and standby

- check operator 2 status flags and turn on buzzer2 flag for all status' except safe and standby

- check if both operators buzzer flags set, if so buzzer on continuously, if not, toggle buzzer on and off at a slow rate for operator 1 and a fast rate for operator 2 to distinguish between the two.

DATA:

- check operators' status and set appropriate data out bits

- goto LOOP: CALIBRATE 306:

- turn on operator high leds and wait for calibrator signal bit to go low to indicate start of high resistance calibration

- take the average of 255 A/D reading for wsl_high+, wsl_high-, ws2_high+, and ws2_high-

- if the averages are not within 245 bits and 30 bits, turn on buzzer and go into an endless loop

- else beep once, turn off operator high leds and turn on operator low leds

- wait for calibrator signal bit to go low to indicate start of low resistance calibration - take the average of 255 A/D reading for wsl_low+, wsl_low-, ws2_low+, and ws2_low-

- else beep once, turn off operator low leds, store all averages in eeprom as resistance limits and return from subroutine

The foregoing is provided for purposes of illustration, explanation, and description of an illustrative embodiment of monitoring systems in accordance with the present invention. Modifications and adaptations to this embodiment will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention.

Claims

Claims: 1. A system for providing and monitoring a discharge path comprising: a) a positive power source connected to a first conductive path and a first ground path; b) a negative power source connected to a second conductive path and a second ground path.

2. The system of claim 1 further comprising a first resistive device connected to the first conductive path.

3. The system of claim 2 further comprising a second resistive device connected to the second conductive path.

4. The system of claim 3 further comprising a monitoring circuit connected to the first and second resistors at a point on a path between the resistors and an electro-static discharge (ESD) protective device affixed to an object to be discharged.

5. The system of claim 3 further comprising a monitoring circuit connected to one of the first and second resistors at a point on a path between the resistors and an electro-static discharge (ESD) protective device affixed to an object to be discharged.

6. The system of claim 4 further comprising a visual display connected to the monitoring circuit.

7. The system of claim 4 further comprising an audible alarm connected to the monitoring circuit.

8. The system of claim 4 in which the ESD protective device is a grounded body suit.

9. The system of claim 4 in which the ESD protective device is a dual conductor wrist strap.

10. The system of claim 4 in which the ESD protective device is footwear.

11. The system of claim 4 in which the ESD protective device is a dissipative mat.

12. The system of claim 4 in which the ESD protective device conductive path between and object to be discharged and ground.

13. A system for providing and monitoring a discharge path from an object comprising: a) an electrostatic discharge protective device connected to the object with first and second conductive paths; b) a positive power source connected to the first conductive path; c) a negative power source connected to the second conductive path; d) a ground connected to the positive and second power sources; and e) a monitoring circuit connected to the first and second conductive paths.

14. The system of claim 13 further comprising a first resistive device connected to the positive power source.

15. The system of claim 13 further comprising a second resistive device connected to the negative power source.

16. The system of claim 13 further comprising a visual display connected to the monitoring circuit.

17. The system of claim 13 further comprising an audible alarm connected to the monitoring circuit.

18. The system of claim 13 in which the ESD protective device is a grounded body suit.

19. The system of claim 13 in which the ESD protective device is a dual conductor wrist strap.

20. The system of claim 13 in which the ESD protective device is footwear.

21. The system of claim 13 in which the ESD protective device is a dissipative mat.

22. The system of claim 13 in which the ESD protective device conductive path between and object to be discharged and ground.

23. A method of providing and monitoring a discharge path from an object comprising the steps of: a) affixing a first conductive path to the object; b) affixing a second conductive path to the object; c) applying a first voltage to the first conductive path; d) applying a second voltage equal in magnitude but opposite in polarity to the first voltage to the second conductive path; and e) measuring the voltages of the first and second conductive paths.

24. The method of claim 23 further comprising the step of providing a visual alarm when measured voltages fall outside of a predetermined range.

25. The method of claim 23 further comprising the step of providing an audible alarm when measured voltages fall outside of a predetermined range.

26. A method of providing and monitoring a discharge path from an object comprising the steps of: a) affixing a first conductive path to the object; b) affixing a second conductive path to the object; c) applying a first current to the first conductive path; d) applying a second current equal in magnitude but opposite in polarity to the first current to the second conductive path; and e) measuring the currents of the first and second conductive paths.

27. The method of claim 26 further comprising the step of providing a visual alarm when measured currents fall outside of a predetermined range.

28. The method of claim 26 further comprising the step of providing an audible alarm when measured currents fall outside of a predetermined range.