CA2695640A1 - Safe resistance indicating static bonding module - Google Patents

Abstract

The invention makes use of resistance measuring and monitoring circuitry along with one or two indicators and a variety of clamps to provide a go-no-go indication. The circuitry is of multi-configuration design and along with a battery is housed in an encapsulated encasement. The design of the electronics module allows for the use of different styled spring tensioned clamps where the clamps have a pair of physically opposed, electrically conductive, gripping contact points with one point being electrically isolated from the clamp body. The clamp/s and or grounding connections are connected to the electronics module via multi-conductor cabling and circular multi-pin twist lock connectors. The twist lock connectors allow for quick changing of the different clamp styles, attachments, and battery charging. The electronics module, clamp/s, ground point, cabling and grasped material form a conductive static bonding loop and where the total resistance in the loop is monitored.

Description

SAFE RESISTANCE INDICATING STATIC BONDING MODULE
BACKGROUND OF THE INVENTION

1. Field of the Invention The invention pertains to static bonding protection equipment, which can be found in places such as;
protecting electronics during handling and the manufacturing process, during the transfer of combustible materials such as petroleum products, coal, and even wheat grain.
Generally the main purpose of the static bonding clamps is to equalize the static electrical charge between a source vessel and a receiving vessel that are involved in the transfer of combustible materials. Static bonding can also be between an object such as a conveyor belt or a oil drum and earth ground.
In this configuration the main purpose is to bleed off the static charge to earth ground. The equalizing of the static electric charge is used to prevent a static electrical discharge whenever the means to transfer the combustible material is connected or disconnected from the receiving or source vessel.

Almost all static bonding clamps are simple clamping devices that are made out of metal, are spring tensioned, and have pincher points to help break through rust and paint. To achieve static bonding on metal, an electrical connection capable of carrying current must exist between the source and receiving vessels or between a source vessel and an earth ground. Industry standards call for ideally 10 ohms of resistance or less, and herein lies the problem with conventional clamps. With conventional clamps, to ensure that the connection between the source and receiving vessel is less than 10 ohms a person needs to use an ohm meter to read the resistance between the source and receiving vessels. This measuring of the resistance alone can be a daunting task if there is quite some distance between the vessels. Also required is a means to ensure that during the transfer of materials the resistance is monitored. The present standard design of static bonding clamps does not indicate to the user if an electrically conductive bond with a resistance below 10 ohms has been established, also there is no monitoring of the resistance.

The current designs of resistance measuring and monitoring systems for static bonding falls into one of two categories, portable and non-portable. The portable designs use a rather large and bulky clamp that houses all the electronic circuitry and battery. Because these portables are battery powered and are of an older electronic design they require frequent battery changes and can be expensive to purchase and maintain. The large clamp size of portables makes them cumbersome to use and in some cases it makes them impractical to use. The non-portable designs are usually wall mounted, have indicator lights that may not be visible to the user in a convenient manor, they use modified standard clamps, they use 120 - 240 volt AC for power, and for static bonding they are usually connected only between a receiving object and earth ground. It should be mentioned that almost all designs that measure the resistance, use the same technology as a digital ohm meter in that, a DC current flows through a resistance that in turn produces a voltage drop across the resistance. The measuring and monitoring devices use the measured voltage drop and a comparator circuit to compare the voltage drop (resistance) against a preset voltage trigger level. Once voltage trigger level has been reached the device indicates to the user a hazardous condition exists. One design found, uses a transformer coupled AC circuit for resistance measurement and to remove the static electricity. With today's safety standards it is important to ensure that users are not just protected by the equipment but, from the equipment and the use of the equipment. The invention incorporates safety features such as being intrinsically safe and electro-static discharge safe to the not just it self but, to the use as well.

The invention has improvements over prior art designs in that the invention uses the latest designs in integrated circuits that have low power consumption and consolidated features.
The new ICs (integrated circuits) not only use less power than older designs but, the new ICs can measure resistance more accurately and reject more noise at the same time. The new ICs have a smaller footprint on the circuit board and yet have more features. The main IC of the invention is a sampling window comparator. It (the window comparator) has a self cycling sleep mode and as does the flasher IC which greatly reduces power consumption so that a single "D" cell battery can last up to 5 years. The invention uses a modular design so that different clamps or attachments can be used with the same module and it does not need to be removed from the hazard area to accomplish this. The circuit board design allows for easy pairing and mating with other circuitry such as pump control circuitry when used in stationary wall mounted units. The invention uses such little power that the amount of energy used to measure the resistance is incapable of creating a spark that could ignite any type of fuel, so it is intrinsically safe. The invention is ROHS compliant, is ESD protected, uses either a non-rechargeable Lithium Thionyl Chloride battery or a rechargeable Lithium-Ion Polymer battery, is fully encapsulated, uses simple go-no-go LED indicators, and circular multi-pin connectors that allow for quick changing of attachments and the connectors also provide a simple means for turning the power on and off. The voltage regulator used provides full circuit protection from current over flow, shorted output, thermal overheat, and reversed input polarity. The use of a flashing red LED also has the benefit of letting the user know when the clamp is opened if the battery is getting weak or if the module is defective.

2. Description Of Prior Art US 5,909,181 issued to Golzmane US 5,113,303 issued to Herres US 5,159,523 issued to Claassen US 6,924,740 applicant Newson Gale Limited also found under WIPO
PCT/GB2001/003324, WO/2002/010781, and British patent GB2369447 Four relevant prior arts were found, and all but one, U.S. patent 5,159,523 -Claassen used indicators to indicate a safe and/or unsafe condition, this prior art connects to existing second party hardware to control fuel transfer. All four prior arts used some type of clamp to make a static bonding connection but, only the U.S. patent 5,909,181 - Golzmane design showed that it could go between a source vessel and a receiving vessel while the others were between the clamp and earth ground. The invention and all four prior arts use a current loop to monitor resistance between their end points. U.S. patent 5,113,303 - Herres is the only design that is AC current powered. U.S. patent 6,924,740 -Newson Gale design is for a homogenous clamp containing all the major components such as a circuit board, indicator, and a 9 volt battery within the clamp body. The invention has three major differences or advantages over these prior arts. The first being that the standard version of the invention uses only one red flashing LED to indicate a problem, this is a major conservation of battery power. The second difference or advantage is that the invention uses a hermetically sealed and loosely attached electronics module that allows the multiple connection configurations. The third difference or advantage is the use of a voltage window comparator which uses fewer parts.

US patent 6,924,740 has been issued to Newson Gale for an "Electrical resistance monitoring device".
The Newson Gale homogenous design makes for a large and bulky clamp body that can make it ergonomically and situational difficult to use. The Newson Gale design has a single external green indicator LED that will be pulsed when the measured resistance is below a predetermined level. The predetermined level is accomplished by forming a DC current loop consisting of the clamp pincher points, electronic circuitry, and a two wire cable. The cable goes from the electronic circuit board, out the rear of the clamp through a connector to a common ground point. To measure resistance in the current loop an op-amp is used to amplify the voltage which, in turn has it's output tied to the inverting input of an op-amp that is configured as a voltage comparator. Another op-amp is used to provide a pulsed reference voltage to the non-inverting input of the comparator. The voltage comparator is used to compare the amplified voltage drops within the loop and a predetermined voltage level. When the amplified voltage drop is below the reference voltage the output of the comparator is tied to another op-amp that is used to activate the external LED. The invention uses a purpose built Window comparator to perform all these functions. The resistance trigger point of the Newson Gale design can be set from 1 to 100 ohms. This prior art uses a 555 timer to flash the LED by switching the non-inverting inputs from high to low on two of the op-amps, this is not an efficient form of energy conservation. The invention uses a purpose built flasher that goes into low power consumption mode between flashes.
This prior art also uses a ZTX751 medium power transistor as a voltage regulator, this setup does not provide for any protection against circuitry faults and therefore requires the use a high wattage current limiting resistor, this also is not very energy conserving. The invention uses a low dropout voltage regulator that is fully protected against circuitry faults. This prior art device has a stainless steel body with tungsten carbide pincher points, an internal monitoring system, and the LED remains flashing while bonded to a conductive material. The invention only flashes a red LED to indicate an error or unsafe condition.

US patent 5,909,181 has been issued to Golzmane; Michael J. for a method and apparatus for indicating electrical connection. This prior art is portable, uses battery power, LEDs for indicators, and uses a START/TEST button, only prior art to have this feature. This apparatus also uses a voltage comparator and associated circuitry to sense conductivity by measuring a voltage drop in a current loop and comparing this voltage to a reference value, resistance trip point is 100 ohms. The indicator LEDs are used to indicate OK, BAD, LOOSE, and BAT. The circuitry used is quite complicated using latches, filters, a voltage comparator, flasher circuits, current driver circuit and the device must be turned on before it can be used. This prior an also has a continuous flashing LED whenever it is on so battery consumption is high. All though this prior art states that the flashing of the LEDs conserves power, this alone does not provide robust energy conservation. This prior art uses an electronic latch to indicate that a temporary high resistance was sensed. The documentation found does not elaborate on how some of the circuitry accomplishes certain tasks. The invention has advantages over this prior art in energy conservation, simplicity of use, and sensitivity. The invention does not require a switch to turn it on or off, simply connecting the circular connectors turns on the invention. The invention uses only one red LED to indicate an error, good battery, and high resistance. The invention uses a window comparator that can sense a change of 0.1 ohms resistance and is adjustable from 0.1 ohms to 50 ohms resistance.

US 5,159,523 issued to Claassen, et al. for a grounding system and detection circuit for fueling aircraft, vessel, or a vehicle. This prior art uses two separate cables to form a current loop that is used to check for continuity. The grounding system and detection circuit of this invention comprises a dual grounding configuration having a first or primary grounding means and a second or default grounding means, and a detection circuit connected to both the first and second grounding means. To achieve this type of grounding requires two clamps and two cables that go back to the detection circuit which is mounted in a non-portable housing. This prior art relies mainly on sufficient current flow through the current loop and enough circuit voltage to bias on a N-channel FET. The amount of current and voltage required is quite low, and the current flow does indicate continuity. Once the FET is turned on, current flowing through the gate or drain is used to turn on a relay. The detection circuit may be coupled to an indicator to identify a properly grounded configuration to the operator, and to an interrupt or control means which prevents operation of a fuel dispensing system unless a proper grounding configuration is observed. The main disadvantage to this design lies with the coil of the relay being in the current loop;
if the ground point is lost then the energy stored in the coil could rupture through the FET or an arc could jump back to the ground point and cause a hazardous situation. This prior art lacks the ability to precisely measure the resistance in the current loop. Industrial users insist that the resistance between a source and receiving vessel or a receiving vessel and ground be less than 10 ohms, this prior art can not ensure this level of measurement and indication.

US patent 5,113,303 issued to Herres for Grounding detection circuit. This prior art uses 120 volt AC
that is stepped down, then half-wave rectified to 15 volts and therefore is not portable. This prior art does not state if the clamp used has electrically isolated pincher tips in it's clamp but, it does use a current loop that is grounded. This prior art indicates continuity, so long as there is sufficient current and voltage available to turn on the opto-isolator. Turning on the opto-isolator will in turn power on a relay, the relay will then switch the lights from indicating red to indicating green, and the relay can also turn on ancillary equipment. This prior art is similar to the invention only in that it can indicate continuity in the current loop. This prior art is similar to the Claassen art in that it can not ensure an industry standard level of measurement and indication of 10 ohms or less.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig.1 is an external top or bottom view of the invention.
Fig.2 is an external side view of the invention.
Fig.3 is an external end view of the invention showing the LEDs and connector 2A.
Fig. 4 is an external end view of the invention showing connector 2B.
Fig. 5 is a drawing of typical layout and modification of a standard pincher clamp.
Fig. 6 is a drawing of typical layout and modification of a standard gripper clamp.
Fig. 7 shows a cut away view of the isolated gripping point on the clamp in figure 6.
Fig. 8 shows a matrix of possible accessories and how they can be interconnected.
Fig. 9 depicts a typical current loop such as the one the invention uses.
Fig. 10 is an electronic schematic of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention makes use of the electronics module (Fig.1 through Fig.4), cabling (Fig.8), clamp/clamps (Fig.5, 6 and 7), and or central grounding point (item 24 -Fig.8) to form a current loop (Fig.9). The electronics module contains a circuit board (Fig.10), battery (B
1 Fig.10), LED indicator/s (LED 1 and LED2 Fig.10), and circular cable connectors items 2A and 2B Fig.1.
The electronics module converts the rate of current flow within the current loop (Fig.9) into a voltage that represents the resistance in the said current loop (Fig.9). The electronics module that the invention uses represents a major change from prior art in that a multitude of combinations exist with the use of different styled clamps and ground points. The cable from the clamp to the electronics module is short, approximately 8 inches or 20cm, so that the LED on the module can be easily seen. With reference to Fig.8, the use of circular quick connectors on both ends of the electronics module allows the module to be easily adapted from connecting between a receiving vessel and a fixed ground, to between a receiving vessel and a source vessel with two clamps. The portability of the invention allows it to be used on a fuel truck and then taken to a stationary drum filling station and back again to the truck. Fig.5, 6, and 7 show how standard bonding clamps can be modified to work with the invention greatly reducing costs.
Normally only a red flashing LED is used to indicate a problem and this alone greatly conserves battery power.

The invention uses an electronics module consisting of an aluminum enclosure (item 1 Fig. I and Fig.2). The aluminum enclosure has multi-pin circular connectors (items 2A and 2B Fig.1 through Fig.4) that are mounted to the end plates (items 3 & 4 - Figs.3 & 4) using fasteners (item 8 - Fig.3 &4).
The circular connectors have sealing o-rings on their mating face with the end plates to form a liquid tight seal. End plate (item 4) also has a metal LED holder (item 5 & 5A) which protects LED (item 6 &
6A). Both end plates use screws (item 7) to secure the end plates to the enclosure body, the screws also provide for a secure seal. If the customer orders a rechargeable or stationary wall mount unit then metal LED holder (item 5A) and a green LED (item 6A) are installed. The enclosure on final assembly is hermetically sealed by filling the enclosure with epoxy resin.

The typical clamps (Fig.5 and Fig.6) used by the invention are mostly spring tensioned (item 18) standard bonding and grounding clamps that have been modified to provide electrical isolation (Fig.7) of one of the pincher or gripper points on one jaw half. The clamp body (item 9) and the opposing non-isolated pincher or gripper points (item 12 & item 19) provides for a current path through bolt (item 14), wire (item 16), connector (item 17), through the electronics module, and then to either a second clamp or to a grounding point (item 24 Fig.8). To modify a standard pincher style clamp a hole (item 15 Fig. 5&6) can be drilled to allow one of the two wires in cable (iteml6) to be protected by the clamp body. Next an insulating material (items 10 and 11) such as nylon can be used to isolate the carbide pincher (item 12) and it's fastening nuts to be electrically isolated from the clamp body. Wire (item 13) provides for a current path from the isolated pincher point, (item 12) through the cable, (item 16) and connector (item 17) and then back to the electronics module. Figure 6 and 7 show how the gripping point (item 19) which is held in place by a pin (item 21) can be isolated by using nylon inserts (item 20). Wire (item 22) is fastened to gripper (item 19) by a screw (item 23), the wire (item 22) goes back through the clamp body and out cable (item 16) and connector (item 17) to the electronics module.
Figure 8 shows a compilation of the possible combinations of connections the electronics module allows.

The battery type used for the invention depends on the end user and their particular need. The battery can be either a non-rechargeable 3.6 volt Lithium Thionyl Chloride battery or a rechargeable 12 volt Lithium Ion Polymer battery. Only two components are changed to accommodate the battery type, the battery and the voltage regulator U4. Power for the circuitry in the invention is regulated by one of two regulators depending on the battery used, either a Micrel MIC5219-2.8xxx or MIC5319-2.8xxx. These LDO (low drop out) regulators, other than their input voltage limits, have the same characteristics including reversed battery protection, current limiting, over temperature shutdown, and 2.8 volt output.
Overall Short circuit protection for the circuitry is provided by fuse (FI
Fig.10). Voltage regulator output filtration is provided by bypass capacitors (Cl, C2, and C3 Fig.10).

The main sensing circuitry in the electronics module makes use of a Linear Technology LTC 1042 window comparator (U1 Fig.10). UI is set to sample the voltage that is present across the current loop every 0.5 seconds. The voltage sensed is the voltage drop across the current loop (Fig.9) and (R3 Fig.10). U1 compares this voltage to a preset voltage window. The voltage window has its centre voltage set by voltage divider (R2 & R4 Fig. 10) and the window width is set by (R7 & R5 Fig.10). (R6 & C4 Fig. 10) set the sampling frequency of U 1. The window comparator takes approximately 80 micro-seconds to complete the sampling and then goes into low power sleep mode until the next sampling cycle. The sampled voltage is compared to the voltage window and is either within or higher than the window. Whenever the input voltage, Vin (pin 3 - U1), is inside the window the within window output (pin 1 U 1) is high. The above window output (pin 6 - U 1) is high whenever Vin (pin3 -Ul) is above the voltage window. Both outputs (pin 1 and pin 6 - U1) are internally latched until the next sample. RI and R3 form a voltage divider that sets the current limit for the current loop (Fig.9), sensitivity of the voltage Vin, also R3 helps to convert the current flow in the current loop. If the voltage Vin is higher than the voltage window then this would indicate that the resistance within the current loop (Fig.9) is to high and the output (>window) pin 6 will go high.
This output from (pin 6 U1) is feed to the chip select/reset pin (pin 3, U2, Fig.10) of a Micrel MIC
1557 oscillator.

When the chip select/reset (pin 3 - U2) goes high it brings U2 out of low power shutdown mode and U2 begins to oscillate at a frequency defined by (R9 & C5 - U2) at a duty cycle of 50%. The output of U2 is used to turn (Ql - Fig.10) a 2N7002 FET on and off and Q1 is used to turn (LED1- Fig.10) on and off. The use of U2 and Q1 allows for very low leakage current and a more abrupt turning on and off of LED 1. The brightness of LED1 can be factory set for indoor or outdoor use by setting jumper (JP 1 - Fig.10). Current flow through LED 1 is limited by R8 to a safe level.
The LED/s used are of the high brightness design which provides for better visibility when the invention is used outdoors.

If the voltage Vin is within the voltage window then this would indicate that the resistance within the current loop (Fig.9) is 10 ohms or less and the output pin (IN-WIND) (pin 1 -U2) will go high. This output from (pin 1) is feed to the chip select/reset pin (pin 3, U3, Fig.10) of a Micrel MIC 1557 oscillator. U3 when enabled oscillates at a frequency defined by (R10 & C6 -U2) at a duty cycle of 50%. The output of U3 is used to turn (Q2 - Fig.10) a 2N7002 FET on and off and Q2 is used to turn (LED2- Fig. 10) on and off. The brightness of LED2 can be factory set for indoor or outdoor use by setting jumper (JP2 - Fig.10), current flow through LED2 is limited by R12.

TVS I and TVS2 provide for ESD (electro static discharge) protection of the circuitry and the user of the invention. To recharge the battery on the rechargeable battery version an after-market off the shelf charger is used and so is not shown or discussed here.

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Claims (11)

1. A portable, battery powered device that measures and monitors resistance in a static bonding current loop consisting of an electronic module, cabling, a clamp or clamps, and/or earth grounding points, and the tactile connection on supply and receiving vessels and when said resistance is above or within a preset range will notify the user of the device through the use of go-no-go indicating lights.

2. With respect to the combination defined in claim 1, the said electronic module is separate from clamp body but, closely coupled to the clamp via a multi-conductor cable and connector.

3. With respect to the combination defined in claim 1, when a non-rechargeable battery is used a single red flashing LED is used to indicate an unsafe 'no-go' condition.

4. With respect to the combination defined in claim 1, when a rechargeable battery is used the purchaser can order the module with a green flashing LED indicator to indicate a 'go' safe condition along with the red flashing LED to indicate an unsafe 'no-go' condition.

5. With respect to the combination defined in claim 1, the resistance measuring and monitoring is achieved through the use of a dedicated single window comparator.

6. With respect to the combination defined in claim 1, the use of modified industry standard static bonding and grounding clamps to provide a plurality of choices.

7. With respect to the clamps defined in claim 6, the invention uses circular screw connection multi-pin cable connectors on the said electronic module and said cabling to permit a combination of clamp styles and or grounding options.

8. With respect to the combination defined in claim 1, the said electronic module is epoxy encapsulated and henceforth the said electronic module is hermetically sealed.

9. With respect to said electronic module in claim 8, the said electronic module uses non-replaceable batteries.

10. With respect to the combination defined in claim 1, the said electronic module can be powered by an optionally customer ordered rechargeable battery.

11. With respect to the combination defined in claim 1, the invention uses electro static discharge protection devices to protect the electronic module and the user of the invention.