CN217007520U - Precision current sensor circuit based on sampling resistor - Google Patents
Precision current sensor circuit based on sampling resistor Download PDFInfo
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- CN217007520U CN217007520U CN202123180400.XU CN202123180400U CN217007520U CN 217007520 U CN217007520 U CN 217007520U CN 202123180400 U CN202123180400 U CN 202123180400U CN 217007520 U CN217007520 U CN 217007520U
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Abstract
The utility model provides a precision current sensor circuit based on a sampling resistor, which comprises: the device comprises an instrument amplifier U1, a positive electrode detection lead, a negative electrode detection lead, n four-terminal sampling resistors and n synchronous switch devices; the n four-end sampling resistors are arranged between the positive detection lead and the negative detection lead in parallel; the positive input port of the instrument amplifier is connected with one terminal of one end of each four-end sampling resistor through one contact in each synchronous switching device; the positive detection lead is connected with the other terminal of one end of each four-end sampling resistor through a contact in each synchronous switch device; the negative input port of the instrument amplifier is connected with one terminal of the other end of each four-end sampling resistor through one contact in each synchronous switching device; the negative detection lead is directly connected with the other terminal of the other end of each four-end sampling resistor; the resistance values of the four-terminal sampling resistors are subjected to equal ratio increasing or decreasing.
Description
Technical Field
The utility model belongs to the technical field of electronics, metering and testing, and particularly relates to a precision current sensor circuit based on a sampling resistor.
Background
A non-inductive resistor Rs is connected in series in a circuit where a current to be detected is located, when the resistance value of the resistor Rs is far smaller than the impedance of a loop to be detected, the resistor can be used as a loop current sampling resistor, and the voltage Vs at two ends of the resistor reflects the magnitude of the current I of the loop to be detected:
I＝Vs/Rs…………………………(1)
in order to reduce the influence of the introduction of the Rs on the tested loop, the Rs should be much smaller than the impedance of the tested loop, and the value of Vs is generally smaller. When Vs is small, the performance of the subsequent a/D converter cannot be fully exerted, and the current measurement accuracy cannot be guaranteed. In order to fully exert the performance of the a/D converter and ensure the measurement accuracy, it is necessary to amplify Vs to a degree suitable for the input range of the a/D converter by a voltage amplifier, and then perform analog-to-digital conversion by the a/D converter.
The sampling resistor and the voltage amplifier form a precise current sensor circuit based on the sampling resistor, and conversion from current to be measured to voltage is realized. In order to adapt to the magnitude of different measured currents, the measuring range or measuring range of the current sensor should have certain adjusting capability. The measuring range or range of the current sensor based on the sampling resistor is adjusted by two methods: firstly, 1 non-inductive resistor with fixed resistance is used, the amplification factor A of the amplifier is designed to be adjustable in a stepping mode, and proper gears are selected according to requirements; secondly, preparing a plurality of non-inductive resistors with different resistance values, fixing the amplification factor A of the amplifier, and selecting a resistor with a proper resistance value according to requirements, namely changing the size of the sampling resistor Rs. The first method is convenient to implement and only needs one non-inductive resistor. The main disadvantage of this method is that when the amplification a of the subsequent amplifier is changed, the bandwidth of the amplifier is usually undesirably reduced as the amplification increases. The second method needs a switch or a relay to switch the sampling resistors, but the switch or the relay inevitably has contact resistors, and the current of the detected loop flows through the contact resistors to generate voltage drop, which causes sampling errors, and has a prominent problem in a large range, and the larger loop current generates larger voltage drop on the contact resistors.
SUMMERY OF THE UTILITY MODEL
The present invention proposes a precision current sensor circuit based on a sampling resistor to overcome the above problems or at least partially solve or alleviate them.
A precision current sensor circuit based on a sampling resistor, comprising: the device comprises an instrument amplifier U1, a positive electrode detection lead L1, a negative electrode detection lead L2, n four-terminal sampling resistors Rn and n synchronous switch devices Sn, wherein each switch device comprises three synchronous switch contacts; n four-terminal sampling resistors Rn are arranged between the positive detection lead L1 and the negative detection lead L2 in parallel; the positive detection port of the instrument amplifier U1 is connected with one terminal of one end of each four-terminal sampling resistor Rn through one contact in each synchronous switch device; the positive detection lead L1 is connected with the other terminal of one end of each four-terminal sampling resistor Rn through a contact in each synchronous switch device; the negative electrode input port of the instrumentation amplifier U1 is connected with one terminal of the other end of each four-terminal sampling resistor Rn through one contact in each synchronous switching device; the negative detection lead L2 is directly connected with the other terminal of the other end of each four-terminal sampling resistor Rn; the resistance values of the four-terminal sampling resistors Rn are subjected to equal ratio increasing or decreasing. At any time, only one of the n synchronous switching devices Sn is in an on state, and the others are all turned off.
The precision current sensor circuit based on the sampling resistor of the present invention also has the following optional features.
Optionally, the synchronous switching device Sn is a three-pole single-throw switch or a relay.
Optionally, an amplifier input protection circuit C1 is further connected between the positive input port and the negative input port of the instrumentation amplifier U1.
Optionally, the four-terminal sampling resistor Rn is a single fixed-value four-terminal resistor.
The measured current signal of the precise current sensor circuit based on the sampling resistance only flows through a first contact in a certain synchronous switch device, the sampling signal is sent to a post-stage amplifier through a second contact and a third contact, and the sampling signal does not contain the voltage drop of the measured current on a switch, a resistor lead and a welding point resistor. Because the instrumentation amplifier usually has very high input impedance, the input current is very small, and the voltage drop caused by the input current of the amplifier is very small due to the resistance of the switch, the resistor lead wire and the welding point, so that the measurement error caused by the voltage drop is very small. The scheme effectively eliminates sampling errors caused by voltage drop generated on a sampling resistance change-over switch or a relay contact, a resistor lead and a welding spot resistor, and is particularly important for large current measurement.
Drawings
Fig. 1 is a schematic diagram of a circuit of a precision current sensor based on a sampling resistor according to the present invention.
Detailed Description
Example 1
Referring to fig. 1, an embodiment of the present invention provides a precision current sensor circuit based on a sampling resistor, including: an instrumentation amplifier U1, a positive electrode detection lead L1, a negative electrode detection lead L2, n four-terminal sampling resistors Rn and n synchronous switch devices Sn (in this example, the switch devices are three-pole single-throw switches); n four-terminal sampling resistors Rn are arranged between the positive detection lead L1 and the negative detection lead L2 in parallel; after the range is selected, the positive input port of the instrument amplifier U1 is connected with one terminal of one end of a four-terminal sampling resistor Rn through one contact in a synchronous switch device; the positive detection lead L1 is connected with the other terminal of one end of a four-terminal sampling resistor Rn through a contact in each synchronous switch device; the negative pole input port of the instrument amplifier U1 is connected with one terminal of the other end of a four-terminal sampling resistor Rn through one contact in a synchronous switch device; the negative electrode detection lead L2 is directly connected with the other terminal of the other end of the four-terminal sampling resistor Rn; the resistance values of the four-terminal sampling resistors Rn are in equal ratio and are increased or decreased progressively. At any time, only one of the n synchronous switching devices Sn is in an on state, and the others are all turned off.
IN the fig. 1, the model of the instrumentation amplifier U1 is AD8421ARZ, a positive input port + IN of the instrumentation amplifier U1 is connected with a positive detection lead L1 through a safety resistor R5, a negative detection input port-IN of the instrumentation amplifier U1 is connected with a negative detection lead L2 through a safety resistor R6, a + Vs port of the instrumentation amplifier U1 is connected with a +15V positive power supply VDD, a-15V negative power supply VDD, a REF port is grounded, and the resistance values of R5 and R6 are both 100 Ω. Two R of instrumentation amplifier U1GA resistor R9 is connected between the terminals to set the amplifier amplification, in this example R9 equals 100 Ω and the instrumentation amplifier amplification a equals 100. In fig. 1, the circuit example of the precise current sensor based on the sampling resistor of the utility model has four gears, the sensitivities are respectively 1V/a, 10V/a, 100V/a and 1000V/a, the ranges are respectively 10A, 1A, 0.1A and 10mA, and the corresponding measuring ranges are respectively-10A, -1A, -0.1A and-10 mA. Four-terminal sampling resistors Rn are respectively a four-terminal sampling resistor R1, a four-terminal sampling resistor R2, a four-terminal sampling resistor R3 and a four-terminal sampling resistor R4, the resistance values of the four-terminal sampling resistors are respectively 0.01 Ω, 0.1 Ω, 1 Ω and 10 Ω, and a synchronous switch device S1, a synchronous switch device S2, a synchronous switch device S3 and a synchronous switch device S4 are respectively arranged between the four-terminal sampling resistor R1, the four-terminal sampling resistor R2, the four-terminal sampling resistor R3, the four-terminal sampling resistor R4 and the positive detection lead L1, between the positive input port connecting line of the instrumentation amplifier U1 and between the negative input port connecting lines.
When the current is detected, a measurement gear is set according to an estimated value of the detected current, for example, 1A, a four-terminal sampling resistor R2 is adopted, a terminal I + of a positive electrode detection lead L1 and a terminal I-of a negative electrode detection lead L2 are connected to a detected loop, the detected current I flows through a contact point S2_1 of a synchronous switching device S2 and a four-terminal sampling resistor R2 at a welding end of the negative electrode detection lead L2 and a corresponding four-terminal sampling resistor R2, although a voltage drop is generated at two ends of the sampling resistor R2, a contact point S2_2 and a contact point S2_3 of the synchronous switching device S2 avoid a contact point S2_1 of the synchronous switching device S2 and a welding end of a four-terminal sampling resistor R2 at the negative electrode detection lead L2, only the voltage of the sampling resistor R2 is collected and sent to a post-stage amplifier, and the post-stage amplifier is amplified by a certain multiple to form a sensor output voltage Vo.
Obviously, the voltage drop of the measured current generated at the contact point S2_1 of the synchronous parallel switching device S2 and the welding end of the four-terminal sampling resistor R2 on the negative detection lead L2 is effectively deducted. Since the instrumentation amplifier input current is small, the voltage drop across contacts S2_2 and S2_3 is also small and negligible when the sampling accuracy requirements are not particularly high. The same effect as described above can be obtained when other gears are selected. Because the amplification factor of the amplifier is fixed, the bandwidth of the amplifier cannot change along with the change of the measurement gear.
Similarly, when the estimated value of the measured current is 10A, the current is detected by using the four-terminal sampling resistor R1, the measured current I flows through the contact S1_1 of the synchronous switch device S1 and the welding end of the four-terminal sampling resistor R1 on the negative detection lead L2 and the corresponding four-terminal sampling resistor R1, although a voltage drop is generated across the sampling resistor R1, the contacts S1_2 and S1_3 of the synchronous switch device S1 can avoid the welding end of the contact S1_1 and the welding end of the four-terminal sampling resistor R1 on the negative detection lead L2, and only the voltage of the sampling resistor R1 is collected and sent to the post-stage amplifier.
Similarly, when the estimated value of the measured current is 0.1A, the current is detected by using the four-terminal sampling resistor R3, the measured current I flows through the contact S3_1 of the synchronous switch device S3 and the welding end of the four-terminal sampling resistor R3 on the negative detection lead L2 and the corresponding four-terminal sampling resistor R3, although a voltage drop is generated at two ends of the sampling resistor R3, the contacts S3_2 and S3_3 of the synchronous switch device S3 can avoid the welding end of the contact S3_1 and the welding end of the four-terminal sampling resistor R3 on the negative detection lead L2, and only the voltage of the sampling resistor R3 is collected and sent to the post-stage amplifier.
Similarly, when the estimated value of the measured current is 10mA, the four-terminal sampling resistor R4 is used to detect the current, the measured current I flows through the contact S4_1 of the synchronous switch device S4 and the welding end of the four-terminal sampling resistor R4 on the negative detection lead L2 and the corresponding four-terminal sampling resistor R4, although a voltage drop occurs across the sampling resistor R4, the contacts S4_2 and S4_3 of the synchronous switch device S4 can avoid the contact S4_1 and the welding end of the four-terminal sampling resistor R4 on the negative detection lead L2, and only the voltage of the sampling resistor R4 is collected and sent to the post-stage amplifier.
Example 2
On the basis of embodiment 1, the synchronous switch device Sn is a three-pole single-throw switch or a relay.
And a relay is adopted as the synchronous switch device Sn, the relay is provided with eight pins, two pins are connected with the control coil, one ends of the remaining three pairs of pins are respectively connected with three ports of the four-port sampling resistor Rn, and the other ends of the remaining three pairs of pins are respectively connected with a corresponding contact on the positive detection lead L1, a positive input port connecting wire of the instrumentation amplifier U1 and a negative input port connecting wire of the instrumentation amplifier U1.
Example 3
Referring to fig. 1, in addition to embodiment 1, an amplifier input protection circuit C1 is further connected between the positive input port and the negative input port of the instrumentation amplifier U1.
The amplifier protection circuit C1 comprises a R7 connected with a +15V voltage VDD and a R8 connected with a-15V voltage VEE, a diode D1 and a diode D2 which are connected with each other in series are connected between the R7 and the R8 in parallel, a diode D3 and a diode D4 which are connected with each other in series, and a diode D5 and a diode D6 which are connected with each other in series, the conduction directions of a diode D1 and a diode D2 are from R7 to R8, the conduction directions of a diode D3 and a diode D4 are from R8 to R7, and the conduction directions of a diode D5 and a diode D6 are from R8 to R7; the anode input port of the instrumentation amplifier U1 is connected between the diode D3 and the diode D4, the cathode input port of the instrumentation amplifier U1 is connected between the diode D5 and the diode D6, and the connection between the diode D1 and the diode D2 is grounded.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims. The components and structures of the present embodiments that are not described in detail are well known in the art and do not constitute essential structural elements or elements.
Claims (4)
1. A precision current sensor circuit based on a sampling resistor, comprising: the system comprises an instrumentation amplifier U1, a positive electrode detection lead L1, a negative electrode detection lead L2, n four-terminal sampling resistors Rn and n synchronous switch devices Sn; n four-terminal sampling resistors Rn are arranged between the positive detection lead L1 and the negative detection lead L2 in parallel; the positive pole input port of the instrument amplifier U1 is connected with one terminal of one end of each four-terminal sampling resistor Rn through one contact in each synchronous switch device; the positive detection lead L1 is connected with the other terminal of one end of each four-terminal sampling resistor Rn through a contact in each synchronous switch device; the negative electrode input port of the instrumentation amplifier U1 is connected with one terminal of the other end of each four-terminal sampling resistor Rn through one contact in each synchronous switching device; the negative detection lead L2 is directly connected with the other terminal of the other end of each four-terminal sampling resistor Rn; the resistance values of the four-terminal sampling resistors Rn are subjected to equal ratio increasing or decreasing.
2. The precision current sensor circuit based on the sampling resistor, as claimed in claim 1, wherein the synchronous switch device Sn is a three-pole single-throw switch or a relay.
3. The precision current sensor circuit based on the sampling resistor is characterized in that an amplifier input protection circuit C1 is further connected between a positive input port and a negative input port of the instrumentation amplifier U1.
4. A precision current sensor circuit based on sampling resistance according to claim 1, wherein the four-terminal sampling resistance Rn is a single fixed value four-terminal resistance.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202123180400.XU CN217007520U (en) | 2021-12-17 | 2021-12-17 | Precision current sensor circuit based on sampling resistor |
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| CN202123180400.XU CN217007520U (en) | 2021-12-17 | 2021-12-17 | Precision current sensor circuit based on sampling resistor |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115951291A (en) * | 2023-03-14 | 2023-04-11 | 北京森社电子有限公司 | Automatic zero setting equipment of closed-loop Hall sensor |
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2021
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115951291A (en) * | 2023-03-14 | 2023-04-11 | 北京森社电子有限公司 | Automatic zero setting equipment of closed-loop Hall sensor |
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