Measuring range expanding device of direct current sensor

Abstract

The utility model discloses a measuring range expanding device of a direct current sensor, which comprises a floating power supply system, a compensating coil, a direct current sensor, a commutation circuit and a current generator, the floating power supply system comprises a direct current power supply and a load, and a line connecting the direct current power supply and the load penetrates into the direct current sensor. A compensating coil is arranged on the direct current sensor, one end of the commutation circuit is electrically connected with the current generator, and the other end of the commutation circuit is electrically connected with the compensating coil. According to the invention, the measuring range of the direct current sensor can be expanded, so that the direct current sensor can work normally under a large current value, and a grounding fault can be rapidly positioned.

Description

Technical Field

[0001] The utility model belongs to the technical field of electronic circuits, and in particular relates to a range expansion device for a direct current sensor. Background Art

[0002] In the control loop of the automatic control field, 24V low-voltage DC power supply is widely used. In recent years, in order to improve its reliability, DC systems generally use floating ground power supply mode in which the negative pole of the power supply is not grounded. In view of the single-end grounding incident of power supply that is more likely to occur on site, this power supply mode greatly reduces the probability of serious accidents such as power supply short circuit, and can effectively improve the continuity and reliability of power supply.

[0003] When a floating power supply system is grounded, it should be discovered and handled in a timely manner. Otherwise, the fault will be delayed from single-point grounding to multiple-point grounding of the positive and negative poles, resulting in errors in the acquisition of switch quantity / analog quantity, affecting the safe operation of the system and the accuracy of measurement. In more serious cases, it will cause malfunction of the switch quantity / analog quantity output, thus causing production accidents.

[0004] In order to quickly locate the ground fault, an electronic switch can be used to generate a weak test pulse current. Figure 1 It can be seen that because only the grounding loop has a current path to the ground, only the grounding loop can detect the test pulse, thereby realizing the location of the grounding fault. The detection uses a high-sensitivity DC current sensor, which uses the fluxgate or magnetic modulation principle, with high resolution but narrow range. Therefore, when using the above method to detect the pulse current signal, it is usually required that the positive and negative lines are inserted into the sensor at the same time to offset the large load current, and the remaining weak unbalanced current (including the test pulse current) can be detected.

[0005] But problems arise. When the above ground fault location method is used in a low-voltage 24V DC system, an extremely difficult problem arises: the load power supply circuit rarely has positive and negative poles wired in pairs, but there are a large number of positive or negative common terminals, such as Figure 2 This means that the DC current sensor can only detect the positive or negative power supply circuit of a single line, and a very large load current cannot be offset, and the DC current sensor cannot work because it exceeds the measurement range.

[0006] Therefore, how to expand the measuring range of the DC current sensor so that the DC current sensor can work normally under a large current value and quickly locate the ground fault is a technical problem that needs to be solved. Utility Model Content

[0007] The utility model aims to provide a range extension device for a DC current sensor, so as to solve the technical problem in the prior art that the range of the DC current sensor cannot be extended and the DC current sensor cannot work normally under a current with a large value.

[0008] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0009] A range extension device for a DC current sensor, comprising:

[0010] A compensation coil, a DC current sensor, a commutation circuit and a current generator. The DC current sensor is provided with a compensation coil, one end of the commutation circuit is electrically connected to the current generator, and the other end of the commutation circuit is electrically connected to the compensation coil.

[0011] Optionally, the current generator includes a voltage setting circuit and a constant current source circuit, the constant current source circuit includes a transistor, an operational amplifier and a fixed resistor, the voltage setting circuit is electrically connected to the positive input terminal of the operational amplifier, the output terminal of the operational amplifier is electrically connected to the base of the transistor, the common connection point of the reverse input terminal of the operational amplifier and the emitter of the transistor is connected to the fixed resistor, the collector of the transistor is electrically connected to the compensation coil, and the voltage setting circuit is used to provide voltage.

[0012] Optionally, the voltage setting circuit is a manually adjustable potentiometer, and the manually adjustable potentiometer is electrically connected to the constant current source circuit.

[0013] Optionally, the voltage setting circuit includes a digital-to-analog converter and a processor, the processor is electrically connected to the input end of the digital-to-analog converter, and the output end of the digital-to-analog converter is electrically connected to the constant current source circuit.

[0014] Optionally, the commutation circuit includes a double-pole double-throw relay, and the direction of the current flowing through the compensation coil is changed by changing the power-on state or the power-off state of the double-pole double-throw relay.

[0015] Optionally, the number of turns of the compensation coil is 10 to 1000.

[0016] Optionally, the DC current sensor is a caliper-type DC current sensor.

[0017] Beneficial effects:

[0018] 1. This application adds a compensation coil to the DC current sensor. By adding a very small compensation current to the coil, the DC current sensor with high sensitivity but very narrow range can work normally under a large background current. When the ground fault location method is used in a low-voltage 24V DC system, it can be accurately located without any fault.

[0019] 2. The compensation current is generated by the current generator and its direction is controlled by the commutation circuit. Adaptive compensation can be achieved through software control. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A circuit diagram of a DC floating power supply system provided by the prior art;

[0021] Figure 2 A circuit diagram of a DC floating power supply system provided by the prior art;

[0022] Figure 3 A schematic diagram of the structure of a range extension device for a DC current sensor provided in an embodiment of the present application;

[0023] Figure 4 A schematic diagram of a circuit for generating a compensation current provided in an embodiment of the present application;

[0024] Figure 5 A circuit diagram for manually adjusting a compensation current provided in an embodiment of the present application;

[0025] Figure 6 A circuit diagram for automatically adjusting a compensation current provided in an embodiment of the present application;

[0026] Figure 7 A circuit diagram of a commutation circuit provided in an embodiment of the present application;

[0027] Description of Figure Numbers:

[0028] 1. Compensation coil; 2. Manual adjustment potentiometer; 11. Constant current source circuit; 3. Operational amplifier; 22. Commutation circuit. DETAILED DESCRIPTION

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the utility model or the prior art, the utility model will be briefly introduced below in combination with the drawings and the description of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. It should be noted that the description of these embodiments is used to help understand the utility model, but does not constitute a limitation of the utility model.

[0030] Example:

[0031] like Figure 3 As shown, this embodiment provides a range extension device for a DC current sensor, comprising:

[0032] A compensation coil 1, a DC current sensor, a commutation circuit 22 and a current generator. The DC current sensor is provided with a compensation coil 1, one end of the commutation circuit 22 is electrically connected to the current generator, and the other end of the commutation circuit 22 is electrically connected to the compensation coil 1.

[0033] As an embodiment of the present application, a range extension device of a DC current sensor is applied in a floating power supply system, which is a prior art. The floating power supply system includes a DC power supply and a load, and a line connecting the DC power supply and the load passes through the DC current sensor. The floating power supply system also includes a first balancing resistor and a second balancing resistor. The positive electrode of the DC power supply and the common point of the first balancing resistor are connected to one end of the load, and the negative electrode of the DC power supply and the common point of the second balancing resistor are connected to the other end of the load, and the common point of the first balancing resistor and the second balancing resistor are grounded.

[0034] It should be noted that the range extension device of the DC current sensor of the present application is not only suitable for floating power supply systems, but any application scenario that can enable a highly sensitive but very narrow range DC current sensor to work normally under a large background current falls within the scope of protection of the present application.

[0035] It should be noted that the DC current sensor itself is manufactured in a caliper type. When a ground fault occurs, the caliper-type DC current sensor is used to clamp on different lines or different positions of the same line, and the ground fault is located by detecting the test pulse sent by the front end of the signal. The DC current sensor is clamped on the line under test during the test. The DC current sensor itself is a ring-shaped iron core with a set of coils wound on the iron core, which is the measuring coil. This technology is based on this and adds another set of coils, namely the compensation coil 1, which is independent of the original measuring coil.

[0036] An auxiliary coil (or compensation coil 1) is added to the DC current sensor, with a certain number of turns (e.g. 100 turns, usually 100 turns and above). If the circuit to be detected contains a large load current (e.g. 1000mA), a smaller compensation current (e.g. 10mA) can be input into the auxiliary coil to offset the larger load current. For example: Regarding the number of turns of the compensation coil, when the number of turns is 10, a compensation current of 1 / 10 of the background current can be used to offset it.

[0037] It should be noted that in order to use the smallest possible compensation current to offset the larger background current, the more turns the better, but in practical applications, 100 turns or 200 turns are selected as the best after experimental testing. The number of turns of the compensation coil of the present application is 10-1000 turns. As an embodiment of the present application, the number of turns of the compensation coil is not limited. Any number of turns of the compensation coil that can offset the larger background current with a small compensation current belongs to the protection scope of the present application.

[0038] Since the loads are all some kind of DC powered devices, they usually have power filter circuits inside, so at the time of testing, the load current is a relatively constant value relative to the changing test pulse current. Based on this, as long as the current of the appropriate value is input into the auxiliary coil, the sensor can work within the measurement range.

[0039] refer to Figure 4 The compensation current input into the auxiliary coil is generated by a current generator. The current generator is composed of a voltage setting circuit and a constant current source circuit 11. The voltage setting circuit is electrically connected to the constant current source circuit 11, and the voltage setting circuit is used to provide voltage. Figure 5 It is a circuit diagram for manually adjusting the compensation current. The constant current source circuit 11 includes a transistor Q, an operational amplifier 3 and a fixed resistor R, the voltage setting circuit is a manually adjustable potentiometer 2, the manually adjustable potentiometer 2 is electrically connected to the positive input terminal of the operational amplifier 3, the output terminal of the operational amplifier 3 is electrically connected to the base of the transistor Q, the common point of the reverse input terminal of the operational amplifier 3 and the emitter of the transistor Q is connected to the fixed resistor R, and the collector of the transistor Q is electrically connected to the compensation coil. By manually adjusting the potentiometer 2, the compensation current can be adjusted.

[0040] Figure 6It is a circuit diagram for automatically adjusting the compensation current. One automatic compensation scheme is: the voltage setting circuit includes a digital potentiometer and a processor, the processor is electrically connected to the input end of the digital potentiometer, the output end of the digital potentiometer is electrically connected to the positive input end of the operational amplifier 3, the output end of the operational amplifier 3 is electrically connected to the base of the transistor Q, the common connection point between the reverse input end of the operational amplifier 3 and the emitter of the transistor Q is connected to the fixed resistor R, and the collector of the transistor Q is electrically connected to the compensation coil. Another automatic compensation scheme is: the voltage setting circuit includes a digital-to-analog converter and a processor, the processor is electrically connected to the input end of the digital-to-analog converter, the output end of the digital-to-analog converter is electrically connected to the positive input end of the operational amplifier 3, the output end of the operational amplifier 3 is electrically connected to the base of the transistor Q, the common connection point between the reverse input end of the operational amplifier 3 and the emitter of the transistor Q is connected to the fixed resistor R, and the collector of the transistor Q is electrically connected to the compensation coil. The processors of the two schemes control the digital potentiometer or the digital-to-analog converter to make the latter output voltage, thereby generating a compensation current.

[0041] It should be noted that whether to use manual adjustment or program-controlled adjustment is selected according to specific application requirements, and either adjustment scheme falls within the protection scope of this application.

[0042] In one embodiment of the application, in actual application, the load current has positive and negative directions, and correspondingly, the compensation current input to the compensation coil 1 should also have a direction. For this purpose, a commutation circuit 22 is added, and the commutation circuit 22 includes a double-pole double-throw relay. The core of the commutation circuit 22 is a double-pole double-throw relay. By changing the relay state (power on / off), the current commutation (changing the direction of the current flowing through the compensation coil 1) is achieved through the contact group conversion. Figure 7 The relay is controlled by the processor software and can complete the compensation current commutation operation as needed. When the sensor output exceeds the positive range, a negative compensation current is input to the compensation coil 1. When the sensor output exceeds the negative range, a positive compensation current is input to the compensation coil 1.

[0043] The adaptive compensation method is:

[0044] 1. At the beginning of the test, the processor reads the sensor output. If the value is small (for example, within 20% of the maximum range), no compensation is required.

[0045] 2. If the value is large but does not exceed the maximum range (no overflow), the compensation amount is calculated based on the sensor output, the compensation current is output, and the compensation is completed.

[0046] 3. If the value exceeds the maximum range (overflow), it is necessary to output 50% of the compensation amount, re-read the sensor output, and re-judge.

[0047] 4. If the value is small (for example, within 20% of the maximum range), the compensation is complete.

[0048] 5. If the value is large but does not exceed the maximum range (no overflow), the deviation is calculated based on the sensor output, the compensation current is adjusted, and the compensation is completed.

[0049] 6. If the value exceeds the maximum range (overflow), it is necessary to increase or decrease the compensation amount by 25%, re-read the sensor output, and re-judge.

[0050] 7. According to the above logic, after one or several rounds of adjustment, the compensation current will be adjusted from coarse adjustment to fine adjustment, and finally will be adjusted to a suitable value.

[0051] The DC current sensor of the present application uses a caliper-type DC current sensor with a range of ±100mA and a resolution of 0.1mA. This design can be more convenient for on-site operation. The compensation coil 1 is set to 200 turns, and the programmable current generator (including the commutation circuit 22) outputs ±10mA, which is controlled by a digital potentiometer with a resolution of 1 / 100. According to actual measurements, the range can be expanded to ±2000mA, which greatly improves the sensor characteristics.

[0052] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A range extension device for a DC current sensor, characterized in that: include: A compensation coil, a DC current sensor, a commutation circuit and a current generator. The DC current sensor is provided with a compensation coil, one end of the commutation circuit is electrically connected to the current generator, and the other end of the commutation circuit is electrically connected to the compensation coil.

2. The range extension device of a DC current sensor according to claim 1, characterized in that: The current generator includes a voltage setting circuit and a constant current source circuit. The constant current source circuit includes a transistor, an operational amplifier and a fixed resistor. The voltage setting circuit is electrically connected to the positive input terminal of the operational amplifier, the output terminal of the operational amplifier is electrically connected to the base of the transistor, the common connection point of the reverse input terminal of the operational amplifier and the emitter of the transistor is connected to the fixed resistor, the collector of the transistor is electrically connected to the compensation coil, and the voltage setting circuit is used to provide voltage.

3. The range extension device of a DC current sensor according to claim 2, characterized in that: The voltage setting circuit is a manual adjustment potentiometer, and the manual adjustment potentiometer is electrically connected to the constant current source circuit.

4. The range extension device of a DC current sensor according to claim 2, characterized in that: The voltage setting circuit includes a digital potentiometer and a processor, the processor is electrically connected to the input end of the digital potentiometer, and the output end of the digital potentiometer is electrically connected to the constant current source circuit.

5. The range extension device of a DC current sensor according to claim 2, characterized in that: The voltage setting circuit includes a digital-to-analog converter and a processor, the processor is electrically connected to the input end of the digital-to-analog converter, and the output end of the digital-to-analog converter is electrically connected to the constant current source circuit.

6. The range extension device of a DC current sensor according to claim 1, characterized in that: The commutation circuit includes a double-pole double-throw relay, and the direction of the current flowing through the compensation coil is changed by changing the power-on state or the power-off state of the double-pole double-throw relay.

7. The range extension device of a DC current sensor according to claim 1, characterized in that: The number of turns of the compensation coil is 10 to 1000.

8. The range extension device of a DC current sensor according to claim 1, characterized in that: The DC current sensor is a caliper type DC current sensor.

Images