Pincer-shaped grounding resistance measuring equipment

Abstract

The utility model belongs to the technical field of ground resistance measurement, and particularly relates to pincer-like ground resistance measuring equipment, which comprises an excitation voltage output device and an induced current measuring device, the excitation voltage output device comprises a square wave generation module, a band-pass filtering module, a power amplification module and a voltage excitation coil; the induced current measuring device comprises a current induction coil, a primary signal amplification filtering module, a secondary signal amplification filtering module, a full-wave rectification module, a multi-stage low-pass filtering module, an ADC sampling module and a data processing module. According to the ground resistance measuring method and measuring equipment, the value of the ground resistance can be measured by fitting the curve mapping relation and the value of the induced current, so that the sampling circuit structure is simplified, the hardware cost is reduced, and meanwhile, the accuracy of the measured value of the ground resistance can be improved.

Description

Technical Field

[0001] The present application relates to the field of grounding resistance, and in particular to a clamp-type grounding resistance measuring device. Background Art

[0002] At present, grounding technology is widely used in power systems to prevent power equipment from being struck by lightning. It is also an effective means to protect personal safety. Grounding resistance is an important device used to measure whether the grounding state is good. It is an electrical characteristic that must be focused on during the inspection and maintenance of power systems. Usually, a clamp grounding resistance meter is used to measure the grounding resistance. Among them, the grounding resistance is measured by two-wire method, three-wire method, four-wire method, single clamp measurement method, and double clamp method.

[0003] The basic principle of measuring ground resistance with a clamp-on ground resistance meter is to measure loop resistance. The jaws of the clamp meter generally include a voltage coil and a current coil. The voltage coil provides an excitation signal and generates an electric potential E on the measured loop. Under the action of the electric potential, a current I is generated in the measured loop. The current coil measures the current I and obtains the ground resistance R based on the formula R=E / I. This method requires the use of two ADCs to simultaneously sample the electric potential E and current I in order to calculate the value of the ground resistance R. In this way, the signal transmission and processing requirements are very high, and it is difficult to meet the linearity and accuracy requirements of the instrument, and the hardware cost is also relatively high.

[0004] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Utility Model Content

[0005] In view of at least one of the above technical problems, the present application provides a clamp-type ground resistance measuring device.

[0006] The embodiment of the present application provides a clamp-type ground resistance measuring device, including: an excitation voltage output device and an induced current measuring device;

[0007] The excitation voltage output device is used to output the excitation voltage to the circuit to be tested;

[0008] The induced current measuring device includes a current sensing coil, a primary signal amplifying and filtering module, a secondary signal amplifying and filtering module, a full-wave rectifier module, a multi-stage low-pass filtering module, an ADC sampling module and a data processing module. The current sensing coil is used to sense the induced current in the circuit to be measured and convert it into a voltage signal corresponding to the induced current. The primary signal amplifying and filtering module is used to amplify and filter the output voltage of the current sensing coil. The secondary signal amplifying and filtering module is used to amplify and filter the output voltage of the primary signal amplifying and filtering module. The full-wave rectifier module is used to shape the output voltage of the secondary signal amplifying and filtering module. The multi-stage low-pass filtering module is used to convert the output voltage of the full-wave rectifier module into a DC signal. The ADC sampling module is used to collect the DC signal output by the multi-stage low-pass filtering module. The data processing module is used to generate a ground resistance measurement value based on the DC signal sampled by the ADC sampling module and the fitting curve mapping relationship.

[0009] Compared with the existing technology, the clamp-type grounding resistance measuring device can measure the value of the grounding resistance by fitting the curve mapping relationship and the value of the induced current, which simplifies the sampling circuit structure, reduces the hardware cost, and can also improve the accuracy of the measured value of the grounding resistance.

[0010] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 A schematic diagram of a clamp-type ground resistance measuring device shown in an embodiment of the present application;

[0013] Figure 2 for Figure 1 Schematic diagram of the module of the induction current measurement device;

[0014] Figure 3 for Figure 2 Circuit diagram of the medium current sensing coil and primary signal amplification and filtering module;

[0015] Figure 4 for Figure 2 Circuit diagram of the secondary signal amplification and filtering module;

[0016] Figure 5 for Figure 2 Circuit diagram of full-wave rectifier module and multi-stage low-pass filter module;

[0017] Figure 6 for Figure 1 Circuit diagram of the excitation voltage output device; DETAILED DESCRIPTION

[0018] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0019] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0020] In the description of the present application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present application, "plurality" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0021] In the embodiments of the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0022] Figure 1 A schematic diagram of a clamp-type ground resistance measuring device shown in an embodiment of the present application; Figure 2 for Figure 1 Schematic diagram of the module of the induction current measurement device; Figure 5 for Figure 2 The circuit diagram of the full-wave rectifier module and the multi-stage low-pass filter module; Figure 1 , Figure 2 , Figure 5 As shown, in a second aspect of the embodiment of the present application, a clamp-type ground resistance measuring device is provided, comprising: an excitation voltage output device 100 and an induced current measuring device 200;

[0023] The excitation voltage output device 100 is used to output an excitation voltage to the circuit to be tested;

[0024] The induced current measuring device 200 includes a current sensing coil 210, a primary signal amplifying and filtering module 220, a secondary signal amplifying and filtering module 230, a full-wave rectifier module 240, a multi-stage low-pass filter module 250, an ADC sampling module 260 and a data processing module 270. The current sensing coil 210 is used to sense the induced current in the circuit to be measured and convert it into a voltage signal corresponding to the induced current. The primary signal amplifying and filtering module 220 is used to amplify and filter the output voltage of the current sensing coil 210. The secondary signal amplifying and filtering module 230 is used to amplify and filter the output voltage of the primary signal amplifying and filtering module 220. The full-wave rectifier module 240 is used to shape the output voltage of the secondary signal amplifying and filtering module 230. The multi-stage low-pass filter module 250 is used to convert the output voltage of the full-wave rectifier module 240 into a DC signal. The ADC sampling module 260 is used to collect the DC signal output by the multi-stage low-pass filter module 250. The data processing module 270 is used to generate a ground resistance measurement value based on the DC signal sampled by the ADC sampling module 260 and the fitting curve mapping relationship.

[0025] When the current sensing coil 210 senses the induced current in the circuit to be tested and converts it into a voltage signal corresponding to the induced current, the signal is very weak and is easily affected by the alternating electromagnetic field in the environment and mixed with interference signals. Therefore, a stable induced signal needs to be obtained after being processed by the primary signal amplification and filtering module 220 and the secondary signal filtering module.

[0026] Figure 3 for Figure 2 The circuit diagram of the current sensing coil 210 and the primary signal amplification and filtering module 220; Figure 3 As shown, in some embodiments, the primary signal amplification and filtering module 220 includes a primary signal amplification circuit 221 and a primary bandpass filtering circuit 222;

[0027] The primary signal amplifying circuit 221 includes a first operational amplifier IC3A, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a third switch D3S3, a first node and a second node. The first end of the first operational amplifier IC3A is coupled to the current sensing coil 210 and the first node. The third end of the first operational amplifier IC3A is coupled to the primary band-pass filter circuit 222 and the second node. The eighth resistor R8 and the ninth resistor R9 are coupled between the first node and the second node. The tenth resistor R10, the eleventh resistor R11 and the third switch D3S3 are coupled between the first node and the second node and are connected in parallel with the eighth resistor R8 and the ninth resistor R9. When the third switch D3S3 is disconnected, the eighth resistor R8 and the ninth resistor R9 are connected in series to form a first-stage feedback resistor unit with a gain of 13.6 times. When the third switch D3S3 is closed, the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 and the eleventh resistor R11 are connected in parallel to form a second-stage feedback resistor unit with a gain of 10 times. The passband center frequency of the primary bandpass filter circuit 222 is 1.58 kHz. In addition, the primary signal amplifier circuit 221 of the present embodiment may be configured by omitting or changing some of these elements, or by adding other elements.

[0028] The original induction signal output by the current induction coil 210 is first amplified (two-stage amplification factor) by the primary signal amplifier circuit 221, and then filtered by the primary bandpass filter circuit 222 to filter out interference signals other than the 1.58 kHz characteristic frequency.

[0029] In some embodiments, the primary bandpass filter circuit 222 may include a fourteenth capacitor and a fifteenth resistor. The RC high-pass filter circuit composed of the fourteenth capacitor and the fifteenth resistor has a cut-off frequency of about 1kHz and can block direct current to eliminate the influence of the direct current bias signal that the operational amplifier may output. In addition, the primary bandpass filter circuit 222 of this embodiment may also be configured to omit or change part of these elements, or to add other elements.

[0030] Figure 4 for Figure 2 The circuit diagram of the secondary signal amplification and filtering module 230; Figure 4 As shown, in some embodiments, the secondary signal amplification and filtering module 230 includes a secondary signal amplification circuit 231 and a secondary bandpass filtering circuit 232;

[0031] The secondary signal amplifying circuit 231 includes a second operational amplifier IC4A, a first switch D1S1, a second switch D2S2, a fourth switch D4S4, a sixteenth resistor R16, a seventeenth resistor R17, an eighteenth resistor R18, a nineteenth resistor R19, a twentieth resistor R20, a third node, a fourth node, a fifth node and a sixth node. The first end of the second operational amplifier IC4A is coupled to the primary signal amplifying and filtering module 220. The third end of the second operational amplifier IC4A is coupled to the third node and the secondary band-pass filtering circuit 232. The sixteenth resistor R16, the seventeenth resistor R17, the eighteenth resistor R18, the nineteenth resistor R19 and the twentieth resistor R20 are connected in series. The sixteenth resistor R16 is coupled to the third node. The fourth node is located between the sixteenth resistor R16 and the seventeenth resistor R17. The second node is located between the eighteenth resistor R18 and the nineteenth resistor R19. The first node is located between the nineteenth resistor R19 and the twentieth resistor R20. The fourth switch D4S4 S4 is coupled between the second end of the second operational amplifier IC4A and the fourth node, the second switch D2S2 is coupled between the second end of the second operational amplifier IC4A and the second node, and the first switch D1S1 is coupled between the second end of the second operational amplifier IC4A and the first node; when only the fourth switch D4S4 is closed, the sixteen switches and the seventeenth resistor R17, the eighteenth resistor R18, the nineteenth resistor R19, and the twentieth resistor R20 are connected in parallel to form a third-stage feedback resistor unit with a gain of 1 times; when only the second switch D2S2 is closed, the sixteen switches, the seventeenth resistor R17, the eighteenth resistor R18, the nineteenth resistor R19, and the twentieth resistor R20 are connected in parallel to form a fourth-stage feedback resistor unit with a gain of 1.175 times; when only the first switch D1S1 is closed, the sixteen switches, the seventeenth resistor R17, the eighteenth resistor R18, the nineteenth resistor R19, and the twentieth resistor R20 are connected in parallel to form a fifth-stage feedback resistor unit with a gain of 1.182 times. The passband center frequency of the secondary bandpass filter circuit 232 is 1.58 kHz. In addition, the secondary signal amplifier circuit 231 of the present embodiment may be configured by omitting or changing some of these elements, or by adding other elements.

[0032] The current sensing signal processed by the primary signal amplification and filtering module 220 enters the secondary signal amplification and filtering module 230 for further amplification processing. In the secondary signal amplification circuit 231, the first switch D1S1, the second switch D2S2 and the fourth switch D4S4 can switch the three-level amplification factor. Combined with the two-level amplification factor of the primary amplification circuit, a total of 4 resistance measurement positions of Range0~3 can be formed to measure the grounding resistance of different resistance ranges respectively, which can cover the full range of 0.001Ω~1200Ω. Among them, the resistance measurement range and switch switching relationship corresponding to the 4 resistance measurement positions are as follows:

[0033]

[0034]

[0035] In some embodiments, the secondary bandpass filter circuit may include a nineteenth capacitor, which can block direct current to eliminate the influence of a direct current bias signal that may be output by the operational amplifier. In addition, the secondary bandpass filter circuit of this embodiment may also be configured to omit or change some of these elements, or to add other elements.

[0036] The specific circuit structures of the full-wave rectifier module 240 and the multi-stage low-pass filter module 250 are not limited. Figure 5 for Figure 2 The circuit diagram of the full-wave rectifier module 240 and the multi-stage low-pass filter module 250; Figure 5 As shown, the full-wave rectifier module 240 performs full-wave rectification on the output voltage of the secondary signal amplification and filtering module 230, and flips its negative periodic signal into a positive periodic signal; the cutoff frequency of the multi-stage low-pass filter module 250 is 72 Hz, which is used to filter the positive fluctuation signal in the output voltage of the full-wave rectifier module 240 into a DC signal, and then output it to the ADC sampling module 260.

[0037] Figure 6 for Figure 1 The circuit diagram of the excitation voltage output device 100; Figure 6 As shown, in some embodiments, the excitation voltage output device 100 includes a square wave generating module 110, a bandpass filtering module 120, a power amplifying module 130 and a voltage excitation coil 140; the square wave generating module 110 is used to output a square wave signal with a frequency of 1.58kHz, the bandpass filtering module 120 is used to filter the square wave signal, the power amplifying module 130 is used to power amplify the output voltage of the bandpass filtering module 120, and the voltage excitation coil 140 is used to output an excitation voltage to the circuit to be tested.

[0038] like Figure 6 As shown, in some embodiments, the power amplifier module 130 includes a push-pull output circuit, which is used to power amplify the output voltage of the bandpass filter module 120 so that the output voltage of the bandpass filter module 120 has the ability to drive the load. The push-pull output circuit includes a third operational amplifier IC7B, a first power MOS transistor, a second power MOS transistor and a seventh node. The first end of the third operational amplifier IC7B is coupled to the bandpass filter module 120, the second end of the third operational amplifier IC7B is coupled to the seventh node, the first power MOS transistor and the second power MOS transistor are respectively coupled to the seventh node, and the seventh node is coupled to the voltage excitation coil 140. In addition, the push-pull output circuit of this embodiment can also be configured to omit or change part of these elements, or add other elements.

[0039] The clamp-type grounding resistance measuring device implements a grounding resistance measuring method, including:

[0040] Get the induced current value;

[0041] In this step, an induction current measuring device is used to obtain the induction current value in the circuit to be measured.

[0042] According to the induced current value and based on the fitting curve mapping relationship, a ground resistance measurement value is generated;

[0043] The mapping relationship of the fitting curve is:

[0044]

[0045] Wherein, y is the ground resistance measurement value, x is the induced current value, and a, b, and c are the pre-configured first calibration parameter, second calibration parameter, and third calibration parameter.

[0046] In some embodiments, before the step of obtaining the induced current value, the following steps are included:

[0047] Select the first loop resistor, the second loop resistor and the third loop resistor;

[0048] Under the same measurement gear, respectively measure the induced current of the first loop resistance, the second loop resistance and the third loop resistance, and generate a first measurement value, a second measurement value and a third measurement value;

[0049] Generate a first calibration parameter, a second calibration parameter, and a third calibration parameter according to the first loop resistance, the second loop resistance, the third loop resistance, the first measurement value, the second measurement value, and the third measurement value, and based on a fitting curve mapping relationship;

[0050] A fitting curve mapping relationship is configured according to the first calibration parameter, the second calibration parameter, and the third calibration parameter.

[0051] Among them, by selecting the first loop resistance, the second loop resistance and the third loop resistance, and measuring the corresponding first measurement value, the second measurement value and the third measurement value, the fitting curve mapping relationship is calibrated, and the first calibration parameter, the second calibration parameter and the third calibration parameter are generated. In this way, the measurement accuracy can be improved, and both the high end and the low end of the range can be taken into account. In addition, the calculation process of the fitting curve mapping relationship is simple, which is conducive to realizing the calculation on a low-cost MCU with low computing speed.

[0052] The above is only a preferred embodiment of the present application and does not constitute any formal limitation to the present application. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present application by using the above disclosed methods and technical contents without departing from the scope of the technical solution of the present application, or modify it into an equivalent embodiment of equivalent changes. Therefore, all equivalent changes made according to the shape, structure and principle of the present application without departing from the content of the technical solution of the present application should be included in the protection scope of the present application.

Claims

1. A clamp-type ground resistance measuring device, characterized in that: include: Excitation voltage output device and induced current measuring device; The excitation voltage output device is used to output an excitation voltage to the circuit to be tested; The induced current measuring device includes a current induction coil, a primary signal amplification and filtering module, a secondary signal amplification and filtering module, a full-wave rectifier module, a multi-stage low-pass filter module, an ADC sampling module and a data processing module. The current induction coil is used to sense the induced current in the circuit to be measured and convert it into a voltage signal corresponding to the induced current. The primary signal amplification and filtering module is used to amplify and filter the output voltage of the current induction coil. The secondary signal amplification and filtering module is used to amplify and filter the output voltage of the primary signal amplification and filtering module. The full-wave rectifier module is used to shape the output voltage of the secondary signal amplification and filtering module. The multi-stage low-pass filter module is used to convert the output voltage of the full-wave rectifier module into a DC signal. The ADC sampling module is used to collect the DC signal output by the multi-stage low-pass filter module. The data processing module is used to generate a ground resistance measurement value based on the DC signal sampled by the ADC sampling module and the fitting curve mapping relationship.

2. The clamp-type ground resistance measuring device according to claim 1, characterized in that: The primary signal amplification and filtering module includes a primary signal amplification circuit and a primary bandpass filtering circuit; The primary signal amplifier circuit includes a first operational amplifier, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a third switch, a first node and a second node, the first end of the first operational amplifier is coupled to the current sensing coil and the first node, the third end of the first operational amplifier is coupled to the primary band-pass filter circuit and the second node, the eighth resistor and the ninth resistor are coupled between the first node and the second node, the tenth resistor, the eleventh resistor and the third switch are coupled between the first node and the second node, and are connected in parallel with the eighth resistor and the ninth resistor; When the third switch is disconnected, the eighth resistor and the ninth resistor are connected in series to form a first-stage feedback resistor unit with a gain of 13.6 times; When the third switch is closed, the eighth resistor, the ninth resistor, the tenth resistor and the eleventh resistor are connected in parallel to form a second-stage feedback resistor unit with a gain of 10 times.

3. The clamp-type ground resistance measuring device according to claim 2, characterized in that: The passband center frequency of the primary bandpass filter circuit is 1.58 kHz.

4. The clamp-type ground resistance measuring device according to claim 2, characterized in that: The secondary signal amplification and filtering module includes a secondary signal amplification circuit and a secondary bandpass filtering circuit; The secondary signal amplification circuit includes a second operational amplifier, a first switch, a second switch, a fourth switch, a sixteenth resistor, a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a twentieth resistor, a third node, a fourth node, a fifth node and a sixth node, the first end of the second operational amplifier is coupled to the primary signal amplification and filtering module, the third end of the second operational amplifier is coupled to the third node and the secondary band-pass filtering circuit, the sixteenth resistor, the seventeenth resistor, the eighteenth resistor, the nineteenth resistor and the twentieth resistor are connected in series, the sixteenth resistor is coupled to the third node, the fourth node is located between the sixteenth resistor and the seventeenth resistor, the second node is located between the eighteenth resistor and the nineteenth resistor, the first node is located between the nineteenth resistor and the twentieth resistor, the fourth switch is coupled between the second end of the second operational amplifier and the fourth node, the second switch is coupled between the second end of the second operational amplifier and the second node, and the first switch is coupled between the second end of the second operational amplifier and the first node; When only the fourth switch is closed, the sixteenth resistor and the seventeenth resistor, the eighteenth resistor, the nineteenth resistor, and the twentieth resistor are connected in parallel to form a third-stage feedback resistor unit with a gain of 1; When only the second switch is closed, the sixteenth resistor, the seventeenth resistor, the eighteenth resistor, the nineteenth resistor, and the twentieth resistor are connected in parallel to form a fourth-stage feedback resistor unit with a gain of 1.175 times; When only the first switch is closed, the sixteenth resistor, the seventeenth resistor, the eighteenth resistor, the nineteenth resistor and the twentieth resistor are connected in parallel to form a fifth-stage feedback resistor unit with a gain of 1.182 times.

5. The clamp-type ground resistance measuring device according to claim 4, characterized in that: The passband center frequency of the secondary bandpass filter circuit is 1.58 kHz.

6. The clamp-type ground resistance measuring device according to claim 1, characterized in that: The excitation voltage output device includes a square wave generating module, a bandpass filtering module, a power amplifying module and a voltage excitation coil; the square wave generating module is used to output a square wave signal with a frequency of 1.58kHz, the bandpass filtering module is used to filter the square wave signal, the power amplifying module is used to amplify the output voltage of the bandpass filtering module, and the voltage excitation coil is used to output the excitation voltage to the circuit to be tested.

7. The clamp-type ground resistance measuring device according to claim 6, characterized in that: The power amplification module includes a push-pull output circuit, and the push-pull output circuit is used to power amplify the output voltage of the band-pass filtering module so that the output voltage of the band-pass filtering module has the ability to drive a load.

8. The clamp-type ground resistance measuring device according to claim 7, characterized in that: The push-pull output circuit includes a third operational amplifier, a first power MOS tube, a second power MOS tube and a seventh node. The first end of the third operational amplifier is coupled to the bandpass filter module, the second end of the third operational amplifier is coupled to the seventh node, the first power MOS tube and the second power MOS tube are coupled to the seventh node respectively, and the seventh node is coupled to the voltage excitation coil.

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