Active grounding system with look-ahead monitoring

Abstract

The present invention relates to a grounding system (100), in particular a grounding system with active grounding monitoring, wherein the grounding system (100) comprises: a control device (102); a first contactor (108, 206) for electrically connecting the control device (102) to the container; a second contactor (110, 208) for grounding the container (112, 212), wherein the control device (102) is configured to perform the following steps: determining a contact resistance between the first and second contactors while they are connected to the container (112, 212); determining whether insufficient grounding of the container (112, 212) is to be expected, based on the contact resistance; and generating a status signal when insufficient grounding of the container (112, 212) is to be expected.

Description

[0001] The present invention relates to a grounding system for the controlled electrostatic discharge of containers, in particular containers in which electrostatic charging can occur through handling liquids, granules, or powders. In particular, the invention relates to a grounding system with active grounding monitoring. According to a further aspect, the invention relates to a method for controlling a grounding system for the active discharge of containers.

[0002] When transferring, emptying, pumping, mixing, spraying, measuring, sampling, or cleaning liquids, granules, or powders, the containers or the substances themselves can become electrically charged. The degree of charge depends on several factors, such as the work processes, the properties and flow rates of the materials being processed, and the size, geometry, and material of the containers.

[0003] The charging of containers and / or filling materials described above can lead to unwanted, uncontrolled discharges during transfer and filling, which can cause a variety of problems. On the one hand, the discharge can hinder the transfer or filling process. However, there are also more serious consequences: electrical devices connected to the containers (e.g., electronic scales) can be damaged. Finally, uncontrolled discharge can also cause fires, especially when handling highly flammable materials.

[0004] To counteract such problems, it is known to use grounding systems that ensure safe grounding and a controlled discharge of the containers. Generally, a distinction is made between active and passive grounding systems.

[0005] Passive grounding systems are devices designed to establish the best possible connection (i.e., low resistance) between the container and the earth. However, the earth connection via the passive grounding system is generally not monitored. Active grounding systems were developed for this purpose. These actively monitor the connection of the container to the equipotential bonding system (e.g., earth) and the contact of the grounding clamps. If a sufficient earth connection is detected, the active grounding system allows the transfer and filling process to proceed. However, if a reliable earth connection is not detected, some active grounding systems can directly interrupt the transfer or filling process, thus preventing damage.

[0006] While existing grounding systems ensure that electrostatic charges are reliably and effectively dissipated, thus regularly preventing damage, active grounding systems, in particular, frequently interrupt the filling or transfer process, resulting in a loss of valuable time. The transfer or transfer process is often interrupted as soon as the active grounding system detects a lack of reliable grounding of the container. The process remains interrupted until a user rectifies the fault, for example, by checking the grounding clamps. To make matters worse, not every transfer or transfer process is monitored by users at all times, so correcting the grounding connection often takes some time and can therefore lead to extended downtime.

[0007] Based on the above-mentioned problem, the present invention aims to provide an earthing system that reduces downtime due to unreliable earthing to a minimum.

[0008] Accordingly, the present invention relates to a grounding system for containers, wherein the grounding system comprises a control device, a first contactor for electrically connecting the control device to the container, and a second contactor for grounding the container. The control device is configured to perform the following steps: Determining a contact resistance between the first and second contactors while they are connected to the container; determining whether insufficient grounding of the container is to be expected based on the contact resistance; generating a status signal if insufficient grounding of the container is to be expected.

[0009] The active grounding system of the present invention enables predictive monitoring of the grounding connection. In particular, the grounding system of the present invention can detect an insufficient ground connection based on the contact resistance before it leads to an emergency shutdown. Thus, the grounding system can warn the user early by means of a corresponding status signal, so that the user can either prevent an emergency shutdown or react more quickly if an emergency shutdown has already occurred. Accordingly, the present invention can prevent downtime or reduce it to a minimum.

[0010] According to the invention, the grounding system is designed to determine an increased probability of a future, anticipated inadequate grounding, for example, an expected emergency shutdown. The grounding system can determine such an increased probability in various ways. For example, the determination by the grounding system can consist, in particular, of the grounding system detecting an increase in the probability (without defining a specific percentage) and outputting a corresponding status signal (e.g., a warning signal).

[0011] According to one embodiment of the present invention, the control device is configured to determine an impending, insufficient grounding based on a comparison of the contact resistance with at least one warning resistance threshold. In this embodiment, the grounding system can determine such an increased probability of an emergency shutdown particularly quickly and easily by comparison with a resistance threshold. The warning resistance threshold can either be predefined by the manufacturer or adjustable by the user. The warning resistance threshold can be adapted to the specific application. Alternatively, the warning resistance threshold can be actively determined by the grounding system, as will be explained in more detail later.

[0012] According to another embodiment, the at least one warning resistance threshold lies between a normal resistance value with proper grounding and an emergency resistance threshold with inadequate grounding. Accordingly, the grounding system does not have to classify every deviation of the contact resistance from the normal resistance value as an increase in probability. Rather, the warning resistance threshold can allow a certain deviation from the normal value. The "normal resistance value" is, in particular, an expected resistance value with good grounding of the container. For example, the normal resistance value could be an average value of an expected resistance range.

[0013] According to a further embodiment, the control device is designed to interrupt or prevent filling of the container if the contact resistance reaches the emergency threshold. Accordingly, the aforementioned warning resistance threshold is positioned between the expected resistance and a resistance value for emergency shutdown.

[0014] According to another embodiment, the control device is designed to detect an impending grounding failure by comparing the contact resistance with a resistance range that lies between a first and a second warning resistance threshold. In some applications, the aforementioned normal resistance value is as low as possible, with only an increase in the resistance value triggering an emergency shutdown. However, this is not always the case. A decrease in contact resistance can also indicate insufficient grounding. The grounding system according to this embodiment can compare the contact resistance with a resistance range that lies between a first (upper) warning resistance threshold and a second (lower) warning resistance threshold.In other words, the first, upper threshold is above a normal resistance value, while the second, lower threshold is below a normal resistance value. Accordingly, the grounding system can also interpret a drop in resistance as an increased probability of inadequate grounding. This occurs, for example, when an unintentional short circuit in the contacts prevents electrostatic charges from the container from dissipating.

[0015] According to another embodiment, the control device is designed to perform the following steps: Receiving container data that is representative of the container to be filled; determining at least one warning resistance threshold based on the container data.

[0016] According to this embodiment, the grounding system is automatically able to adapt the warning resistance threshold(s) to the specific application. The determination of the container data can be performed automatically or by a user.

[0017] According to another embodiment, the container data includes one or more of the following data: Container type; Container manufacturer; Container model; Container size; Container position.

[0018] The container type influences the expected resistance values. For example, a big bag is expected to have a higher contact resistance than a metal drum. The control device can therefore adjust the resistance threshold to the container type. The container model and manufacturer also play a role. The control device can access a database containing information on various container manufacturers and models along with their expected resistance values. Based on automatic detection of the container model or manufacturer, or user input, the control device can then determine the expected contact resistance from the database.

[0019] The container size and position can also influence the expected resistance. The control device can, for example, be designed to increase or decrease the warning resistance threshold linearly with the container size.

[0020] The position of the container can also be taken into account by the control device when determining the warning resistance threshold. The container's position is typically communicated to the control device by the user. For this purpose, the grounding system can have a user interface, such as a touchscreen. The user interface can offer suggestions for common container positions. Depending on the selected container position, the control device can then adjust the warning resistance threshold. For example, the control device can access a database containing percentage-based threshold adjustments based on different container positions (e.g., directly on the ground or on pallets).

[0021] According to another embodiment, the control device is designed to perform the following steps: Receiving contactor data that is representative of the contactors used; determining at least one warning resistance threshold based on the contactor data.

[0022] The contactor data can include the type of contactor, the contactor manufacturer, and / or the contactor model. Naturally, the contactors themselves influence the expected contact resistance between them. For example, contact clamps or grounding clamps for grounding systems are specifically designed to keep the resistance as low as possible. Other contactors, such as contact points, often achieve different resistance values. The control device according to this embodiment can adjust the warning resistance threshold accordingly to the contactors used. For this purpose, the grounding system can have a user interface that allows the user to select the contactors in use.

[0023] In another embodiment, the control device is designed to detect an impending, inadequate grounding based on changes in contact resistance over time. According to this embodiment, the control device stores the detected contact resistances over a certain period and compares them. The control device can thus calculate the derivative of the contact resistance over time. Should there be an unexpectedly high increase or decrease in contact resistance, the control device can determine that the probability of inadequate grounding is high and issue a corresponding warning signal.

[0024] As will be explained in more detail later, the control device can simultaneously determine an impending grounding failure based on several factors, such as comparison with a threshold value and the change in contact resistance over time. Thus, the control device can issue a warning signal as soon as the contact resistance rises or falls too rapidly, even before reaching the threshold value. This gives the user the opportunity to react before the threshold is reached, which, especially in the case of a very rapid rise or fall in contact resistance, provides the user with additional time to prevent an impending emergency shutdown.

[0025] According to a further aspect, the present invention relates to a method for controlling an earthing system for unloading containers, in particular an earthing system with active earthing monitoring, wherein the method comprises the following: Determining the contact resistance between the contacts of the grounding system while they are connected to the container; determining whether inadequate grounding of the container is to be expected based on the contact resistance; providing a status signal if inadequate grounding of the container is to be expected.

[0026] The invention is described in more detail below with reference to the drawings.

[0027] This shows: FIG. 1 a schematic representation of an active grounding system according to one embodiment of the present invention; FIG. 2 a schematic representation of an active grounding system according to a further embodiment of the present invention; FIG. 3 an exemplary graph of the change in contact resistance over time; FIG. 4 an exemplary graph of the change in contact resistance over time; FIG. 5 an exemplary graph of the change in contact resistance over time.

[0028] FIG. 1 Figure 1 shows a schematic representation of an embodiment of the grounding system according to the present invention. The grounding system 100 has a control device 102 which is electrically connected to a container 112 via a contact terminal 106. The container 112 is shown as a metal drum, for example for holding chemicals.

[0029] The contact terminal 106 has a first contact element 108 and a second contact element 110. The first and second contact elements 108 and 110 are arms of the contact terminal 106. The first and second contact elements 108 and 110 are attached to the container, which is designed as a metal barrel 112, via the teeth of the contact terminal 106 and are thus electrically connected to each other via the wall of the container 112.

[0030] The first contactor 108 is connected to the control device 102 via a first line 122. In particular, the first contactor 108 is connected to a resistance measuring unit 104 via the first line 122.

[0031] The second contact transmitter 110 is connected via a second electrical line 124 to a potential equalization, here a first earth connection 114. In the FIG. 1 In the illustration shown, the second contactor 110 is connected to the first earth terminal 114, in particular via the control device 102. However, this is not strictly necessary. The second electrical conductor 124 can also be connected directly to the first earth terminal 114.

[0032] The resistance measuring device 104 is connected to a second earth connection 116. The measuring device 104, together with the two contactors 108 and 110 and the earth connections 114 and 116, forms an intrinsically safe earthing circuit. The control device is designed to supply an intrinsically safe measuring current to the intrinsically safe earthing circuit 120 via the first line 122. The intrinsically safe current flows via the first contactor 108 and the container 112 to the second contactor 110 and to the first earth connection 114 via the second line 124. The current flow returns to the measuring unit 104 via the second earth connection 116.

[0033] The measuring unit 104 is designed to measure the total resistance of the grounding circuit 120 based on the measured current and voltage. This total resistance is determined primarily from the contact resistance between the contactors 108 and 110, and any resistance that may occur between the ground terminals 114 and 116. The measured total resistance is unique to each application. The resistance between the ground terminals 114 and 116 is generally constant. Only the resistance between the contactors 108 and 110, i.e., the contact resistance, varies, for example, due to corrosion. The control device can, through a one-time calibration, fix the resistance between the ground terminals 114 and 116 and thus determine the contact resistance based on the total resistance. In other words, a change in the total resistance is a measure of the change in the contact resistance.

[0034] At the in Figur 1 In the illustrated embodiment, the contact resistance should not exceed, for example, 100 kΩ. The control device 102 can therefore set an emergency resistance threshold, above which an emergency shutdown occurs, at 50 kΩ.

[0035] The control device 102 includes a processor 105, which is configured to determine the probability of an impending insufficient grounding based on the contact resistance determined by the measuring unit 104. Examples for determining an impending insufficient grounding are given in the Figuren 3 bis 5 This is explained in more detail below. In the event of an increased probability, the processor 105 can generate a status signal which can be output to the user by the control device 102. For this purpose, the processor of the control device 102 can be connected to, or connectable to, a warning device 130. The warning device 130 can be, for example, a loudspeaker or a monitor through which acoustic or visual warning messages can be transmitted. Alternatively, the warning device 130 can be one or more lights that can, for example, change between different colors to indicate the status of the grounding. An increased probability of an impending, inadequate grounding can then be indicated by one of the colors, for example, orange. The user can react to the warning message and check the grounding before an emergency occurs.

[0036] A second embodiment of an earthing system 200 according to the invention is described in the FIG. 2 The earthing system 200 includes a control device 202 with a resistance measuring unit 204 and a processor 205. The control device is connected to a warning detector 230 on the output side.

[0037] The control device 202 is essentially identical to the control device 102 of the FIG. 1 trained. In the FIG. 2 The control device is connected to a big bag container 212 for bulk material via two contact elements designed as contact clamps (also called grounding clamps) 206, 208. The big bag container 212 has several tabs 222, 224, 226, 228 through which the contact clamps 206, 208 can be connected to the container 212. The tabs 222, 224, 226, 228 can also be used to lift the container 212.

[0038] A first contact terminal 206 is connected to a first tab 222 of the big bag container 212. A second contact terminal 208 is connected to a second tab 224 of the big bag container 212. The two tabs 222, 224 can be arranged, in particular, at opposite ends of the big bag container.

[0039] The first contact terminal 206 is connected to the measuring unit 204 of the control device 202 via a first line. The second contact terminal 208 is connected to a first earth connection 214 via a second line 234. The measuring unit 204 is connected to a second earth connection 216. This arrangement forms an intrinsically safe circuit between the measuring unit 204, the first contact terminal 206, the big bag, the second contact terminal 208, the first earth connection 214, and the second earth connection 216. The measuring device 204 can therefore be used to measure the total resistance of the intrinsically safe circuit via an intrinsically safe measuring current. In comparison to the one in FIG. 1 In the intrinsically safe circuit 120 shown, it can be expected, under otherwise identical conditions, that the total resistance of the intrinsically safe circuit after FIG. 2 assumes a higher value because the current has to flow from one end of the big bag container 212 to the other, and thus the contact resistance between the contact terminals 206, 208 is typically higher.

[0040] At the in Figur 2 In the illustrated embodiment, the contact resistance should not exceed, for example, 100 MΩ. The control device 102 can therefore set an emergency resistance threshold, above which an emergency shutdown occurs, at 50 MΩ.

[0041] The FIG. 3 An example of the contact resistance over time is shown. Diagram 300 shows an emergency resistance threshold 302. The control device can be configured to initiate an emergency shutdown if the contact resistance exceeds the emergency resistance threshold 302. The emergency resistance threshold 302 can be determined by the manufacturer or the user.

[0042] A warning resistance threshold of 304 is used to detect an impending, insufficient grounding of the container connected to the contactors. The warning resistance threshold of 304 can be set either by the manufacturer or the user, or it can be determined directly by the processor.

[0043] The course of the measured contact resistance, i.e., the resistance between the contactors according to this example, is shown as function 306. In a first region 308, the measured contact resistance is essentially constant. In the embodiment according to FIG. 1 This could be, for example, approximately 1 kΩ. This value can also be set as the standard resistance value in the control device.

[0044] At time t1, the measured contact resistance begins to increase. The second section 310 of graph 306 shows examples of increases in contact resistance with varying slopes. Such an increase in resistance can be caused, for example, by corrosion on the contact elements. On the other hand, a slow slippage of one of the contact elements from the container can lead to a slowly increasing contact resistance.

[0045] At time t2, the contact resistance has reached the warning resistance threshold of 304. At this point, the control device, which continuously or at regular intervals compares the contact resistance with the warning resistance threshold, recognizes that the threshold has been exceeded. However, at time t2, the contact resistance has not yet reached the emergency resistance threshold of 302, so the grounding is still sufficient. An emergency shutdown is not necessary.

[0046] In a third section 312 of graph 306, the contact resistance initially remains above the warning resistance threshold 304 and continues to increase. However, even in this third section 312, the contact resistance is below the emergency resistance threshold 302, so the filling or transfer process can continue safely. No emergency shutdown is required. As long as the contact resistance, as shown in section 312, is above the warning resistance threshold 304, the control device determines that there is an increased probability of an imminent failure of the container's grounding. In this case, the control device will change a status signal from normal to a warning status and warn the user accordingly. This warning status (i.e., a warning signal) is output from time t2, as in this example.

[0047] At time t3, the user has recognized the warning signal and checked the grounding. For example, the user can realign the contactors or replace them in case of corrosion before an emergency shutdown occurs. Accordingly, the contact resistance in area 314 is again below the warning resistance threshold of 304. The contact resistance in area 314 may differ from the contact resistance in area 308, as minor fluctuations can be caused by small differences in the mounting of the contactors.

[0048] A second example of a resistance curve is the FIG. 4 to be seen. Also the diagram 400 according to FIG. 4 The diagram shows an emergency resistance threshold of 402 and a warning resistance threshold of 404. The emergency resistance threshold of 402 and the warning resistance threshold of 404 can essentially be interpreted as the thresholds according to... FIG. 3 These are determined, for example, by the manufacturer or the user, or by the control device.

[0049] Also according to diagram 400, FIG. 4 Various sections 406, 408, and 410 can be identified. In the first section 406, the contact resistance is essentially constant and below the warning threshold 404. The control device is therefore designed to output a status signal corresponding to a normal state, i.e., a low probability of an impending, inadequate grounding. At time t1, there is a relatively sharp increase in the contact resistance over time. This increase is indicated by a second section 408 in FIG. 4 characterized. According to one embodiment, the control device can be configured to determine the change (here, the increase) in contact resistance over time. For this purpose, the control device can, in particular, be configured to store the contact resistance values ​​over time and compare them with each other. Should there be a sharp increase (or decrease) in contact resistance, such as in region 408, the control device can determine that there is a high probability of an imminent failure of the container's grounding.

[0050] In the example according to FIG. 4 At time t2, the control device determines that the change in contact resistance over time (for example, the derivative of the contact resistance function in region 408) exceeds a predefined slope limit. The control device can then output a status signal corresponding to a warning status / signal. This warning signal can be generated as early as time t2, i.e., while the absolute value of the contact resistance is still below the warning resistance threshold 404. Thus, according to this embodiment, the control device can inform the user of a potential grounding problem even before the warning resistance threshold 404 is reached.

[0051] Only at time t3 does the contact resistance exceed the warning resistance threshold of 404. In some embodiments, the control device is designed not to change the status signal, as it was already switched to a warning signal at time t2. However, it is also conceivable that the control device is designed in such a way that a further warning signal is generated to warn the user even more emphatically. For example, color coding could be used to distinguish between the first warning signal generated at time t2 and the second warning signal generated at time t3.

[0052] At time t4, the user recognized the warning signal and checked the grounding. Accordingly, the contact resistance at time t4 was back within the normal range and thus below the resistance threshold of 404. In this example as well, the grounding was corrected before an emergency shutdown became necessary, effectively reducing downtime.

[0053] Another example of a contact resistance curve is in the FIG. 5 shown. Diagram 500 according to FIG. 5 The diagram shows the emergency resistance threshold 502 mentioned above and a first warning resistance threshold 504. A second warning resistance threshold 506 is also shown. FIG. 5 shown. This is located below the first warning resistance threshold. The first warning resistance threshold, 504, is therefore an upper warning resistance threshold, while the second warning resistance threshold, 506, is a lower threshold. The two warning resistance thresholds, 504 and 506, form a resistance range between them in which the probability of insufficient grounding is low.

[0054] The use of the second, lower warning resistance threshold 506 is based on the idea that the contact resistance in some applications (e.g. in the embodiment according to FIG. 2 ) always exhibits a certain resistance. If this resistance is reduced to 0, an unintentional short circuit can be inferred, for example.

[0055] The graph 500 according to FIG. 5 The system has a first range 508 in which the contact resistance is within a normal range, where there is no risk of insufficient grounding. In other words, in the first range, the contact resistance lies between the first and second warning resistance thresholds. At time t1, the contact resistance decreases. It now falls below the second warning resistance threshold 506 set by the manufacturer, the user, or the control device. The control device detects this by comparing the contact resistance with the second warning resistance threshold 506 and determines that the probability of insufficient grounding has increased. The control device can therefore issue a warning signal informing the user that an emergency shutdown may occur shortly.However, it should be noted that the contact resistance in the 510 range is still above an emergency resistance threshold. This can be found in... Fig. 5 For example, it could be set to 1 Ω. In other words, even in the 510 range, the grounding is still sufficient and filling or transferring can continue. The warning signal is therefore merely an advance warning to the user.

[0056] At time t3, the user recognized the warning signal and checked the grounding. The contact resistance in area 512 is therefore back within the normal range, so the control device's warning signal can be deactivated and the normal state can be indicated.

[0057] The present invention is not limited to the embodiments shown in the figures, but results from a combination of the features disclosed herein. In particular, it should be mentioned again that exceeding the warning resistance thresholds or an excessively rapid change in contact resistance does not directly lead to an emergency shutdown. Rather, the examples given here illustrate ways in which the control device can assess the probability of an impending, inadequate grounding based on the contact resistance. Accordingly, the filling or transfer process can still be safely continued even in the warning range, i.e., as soon as the control device determines that there is an increased probability that the grounding will no longer be sufficient in the future.In other words, the control device of the grounding system described here uses a warning signal before an emergency shutdown is necessary. This warning signal can therefore be ignored by the user without risking damage from uncontrolled discharges.

[0058] The invention is not limited to the number of threshold values ​​described herein. In particular, further differentiation of the warning signals can be achieved by using additional threshold values. Thus, different threshold values ​​can trigger different warning levels.

Claims

1. Earthing system (100), in particular an earthing system with active earthing monitoring, wherein the earthing system (100) comprises: - a control device (102); - a first contactor (108, 206) for electrically connecting the control device (102) to the container; - a second contactor (110, 208) for earthing the container (112, 212), wherein the control device (102) is configured to perform the following steps: - determine a contact resistance between the first and second contactors while they are connected to the container (112, 212); - determine whether insufficient earthing of the container (112, 212) is to be expected, based on the contact resistance; - generate a status signal when insufficient earthing of the container (112, 212) is to be expected.

2. Earthing system (100) according to claim 1, wherein the control device (102) is configured to determine an impending, insufficient earthing based on a comparison of the contact resistance with at least one warning resistance threshold (304, 404, 504, 506).

3. Earthing system (100) according to claim 2, wherein the at least one warning resistance threshold (304, 404, 504, 506) lies between a normal resistance value for normal earthing and an emergency resistance threshold (302, 402, 502) for insufficient earthing.

4. Earthing system (100) according to 3, wherein the control device (102) is configured to interrupt or prevent filling of the container if the contact resistance reaches the emergency resistance threshold (302, 402, 502).

5. Earthing system (100) according to one of claims 2 to 4, wherein the control device (102) is configured to determine an impending, insufficient earthing based on a comparison of the contact resistance with a resistance range which is located between a first and a second warning resistance threshold (304, 404, 504, 506).

6. Earthing system (100) according to one of claims 2 to 5, wherein the control device (102) is configured to perform the following steps: - Receiving container data that is representative of the container (112, 212) to be filled; - Determining the at least one warning resistance threshold value based on the container data.

7. Earthing system (100) according to claim 6, wherein the container data includes one or more of the following data: - Container type - Container manufacturer - Container model - Container size - Container position 8. Earthing system (100) according to one of claims 2 to 7, wherein the control device (102) is configured to perform the following steps: - Receiving contactor data that is representative of the contactors (108, 110, 206, 208) used; - Determining the at least one warning resistance threshold (304, 404, 504, 506) based on the contactor data.

9. Earthing system (100) according to claim 8, wherein the contact element data includes one or more of the following: - type of contactor - contactor manufacturer - contactor model 10. Earthing system (100) according to one of claims 1 to 7, wherein the control device (102) is configured to determine an impending, insufficient earthing based on a change in contact resistance over time.

11. Method for controlling an earthing system (100) for controlled electrostatic discharge of containers, the method comprising: - determining a contact resistance between contactors of the earthing system while they are connected to the container; - determining whether insufficient earthing of the container is to be expected, based on the contact resistance; - providing a status signal when insufficient earthing of the container is to be expected.