CN116265963A - Precision current sensor circuit based on sampling resistor - Google Patents
Precision current sensor circuit based on sampling resistor Download PDFInfo
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- CN116265963A CN116265963A CN202111548966.5A CN202111548966A CN116265963A CN 116265963 A CN116265963 A CN 116265963A CN 202111548966 A CN202111548966 A CN 202111548966A CN 116265963 A CN116265963 A CN 116265963A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
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Abstract
The invention provides a precision current sensor circuit based on sampling resistor, comprising: the device comprises an instrument amplifier U1, an anode detection lead, a cathode detection lead, n four-terminal sampling resistors and n synchronous switching devices; the n four-terminal sampling resistors are arranged between the positive electrode detection lead and the negative electrode detection lead in parallel; the positive electrode 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 electrode detection lead is connected with the other terminal of one end of each four-terminal sampling resistor through one contact in each synchronous switching device; the negative electrode input port of the instrument amplifier is connected with one terminal of the other end of each four-terminal sampling resistor through one contact in each synchronous switching device; the negative electrode 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 equal-ratio increasing or decreasing.
Description
Technical Field
The invention 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
When the resistance value of the resistor is far smaller than the loop impedance to be measured, 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 loop current I to be measured:
I＝Vs/Rs…………………………(1)
in order to reduce the influence of the introduction of Rs on the tested loop, rs should be far smaller than the impedance of the loop to be tested, and the Vs value 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 ensured. In order to fully develop the performance of the a/D converter and ensure the measurement accuracy, it is necessary to amplify Vs by a voltage amplifier to a level suitable for the input range of the a/D converter 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 the conversion from current to voltage to be measured is realized. In order to adapt to the different measured currents, the measuring range or range of the current sensor should have certain adjustment capability. There are two methods for adjusting the measuring range or range of a current sensor based on a sampling resistor: 1. 1 non-inductive resistor with fixed resistance value is used, the amplification factor A of the amplifier is designed to be adjustable in a stepping way, and proper gear is selected according to the requirement; 2. preparing a plurality of noninductive resistors with different resistance values, fixing the amplification factor A of the amplifier, and selecting a resistor with proper resistance value according to the requirement, 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 approach is that when the amplification factor a of the subsequent amplifier is changed, the bandwidth of the amplifier generally decreases with increasing amplification factor, which is undesirable. The second method needs to use a switch or a relay to realize the switching of sampling resistors, but the switch or the relay inevitably has contact resistors, the measured loop current will generate voltage drops when flowing through the contact resistors, so that sampling errors are caused, the problem is more prominent in a large range, and larger loop current generates larger voltage drops on the contact resistors.
Disclosure of Invention
The present invention proposes a precision current sensor circuit based on a sampling resistor for overcoming or at least partially solving or alleviating the above-mentioned problems.
A precision current sensor circuit based on a sampling resistor, comprising: the instrument amplifier U1, the positive electrode detection lead L1, the negative electrode detection lead L2, n four-terminal sampling resistors Rn and n synchronous switching devices Sn, wherein each switching device comprises three synchronous switch contacts; the n four-terminal sampling resistors Rn are arranged between the positive electrode detection lead L1 and the negative electrode detection lead L2 in parallel; the positive electrode 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 switching device; the positive electrode detection lead L1 is connected with the other terminal of one end of each four-end sampling resistor Rn through one contact in each synchronous switching device; the negative electrode input port of the instrument 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 electrode detection lead L2 is directly connected with the other terminal of the other end of each four-end sampling resistor Rn; the resistance values of the four-terminal sampling resistors Rn are equal-ratio increasing or decreasing. At any given moment, only one of the n synchronous switching devices Sn is in an on state, and the rest are all required to be turned off.
The precision current sensor circuit based on sampling resistor of the present invention also has the following optional features.
Optionally, the synchronous switching device Sn is a triple pole single throw switch or 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 precision current sensor circuit based on the sampling resistor only flows through the first contact in a certain synchronous switching device, the sampling signal is sent to the post-stage amplifier through the second contact and the third contact, and the sampling signal does not contain the voltage drop of the measured current on the switch, the resistor lead and the welding point resistor. Since instrumentation amplifiers typically have very high input impedance, very little input current, and very little voltage drop due to the amplifier input current, and thus measurement errors, is very small. The scheme effectively eliminates sampling errors caused by voltage drop generated on the sampling resistance change-over switch or the relay contact, the resistor lead and the welding spot resistor, and is particularly important for larger current measurement.
Drawings
Fig. 1 is a schematic diagram of a precision current sensor circuit 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, which is characterized by comprising: the device comprises an instrument amplifier U1, an anode detection lead L1, a cathode detection lead L2, n four-terminal sampling resistors Rn and n synchronous switching devices Sn (in the example, the switching devices are three-pole single-throw switches); the n four-terminal sampling resistors Rn are arranged between the positive electrode detection lead L1 and the negative electrode detection lead L2 in parallel; after the measuring range is selected, the positive input port of the instrument amplifier U1 is connected with one terminal of one end of one four-end sampling resistor Rn through one contact in one synchronous switching device; the positive electrode detection lead L1 is connected with the other terminal of one end of one four-end sampling resistor Rn through one contact in each synchronous switching device; the negative electrode input port of the instrument amplifier U1 is connected with one terminal of the other end of the four-end sampling resistor Rn through one contact in a synchronous switching device; the negative electrode detection lead L2 is directly connected with the other terminal of the other end of the four-end sampling resistor Rn; the resistance values of the four-terminal sampling resistors Rn are equal-ratio increasing or decreasing. At any given moment, only one of the n synchronous switching devices Sn is in an on state, and the rest are all required to be turned off.
In FIG. 1, the model of the instrumentation amplifier U1 is AD8421ARZ, and the anode input end of the instrumentation amplifier U1The port +IN is connected with the positive electrode detection lead L1 through a safety resistor R5, the negative electrode detection port-IN of the instrument amplifier U1 is connected with the negative electrode detection lead L2 through a safety resistor R6, the +Vs port of the instrument amplifier U1 is connected with +15V positive power supply VDD, -Vs port is connected with-15V negative power supply VDD, the REF port is grounded, and the resistance values of R5 and R6 are 100 omega. Two R of the instrumentation amplifier U1 G A resistor R9 is connected between the ends and is used for setting the amplification factor of the amplifier, in this example r9=100Ω, and the amplification factor a=100 of the instrumentation amplifier. In FIG. 1, the circuit example of the precision current sensor based on the sampling resistor has four gears, the sensitivities of the circuit are respectively 1V/A, 10V/A, 100V/A and 1000V/A, the measuring ranges are respectively 10A, 1A, 0.1A and 10mA, and the corresponding measuring ranges are respectively-10A, -1A, -0.1A and-10 mA. Four sampling resistors Rn are respectively four sampling resistors R1, R2, R3 and R4, and the resistance values are respectively 0.01Ω, 0.1Ω, 1Ω and 10Ω, and synchronous switching devices S1, S2, S3 and S4 are respectively arranged between the sampling resistors R1, R2, R3 and R4 and the positive electrode detection lead L1 and between the positive electrode input port connection and the negative electrode input port connection of the instrumentation amplifier U1.
When detecting current, a measurement gear is set according to the estimated value of the current to be detected, for example, 1A, a four-terminal sampling resistor R2 is adopted, a terminal I+ of a positive detection lead L1 and a terminal I-of a negative detection lead L2 are connected into a detected loop, the current I to be detected flows through a contact S2_1 of a synchronous switching device S2 and the four-terminal sampling resistor R2 at the welding end of the negative detection lead L2 and the corresponding four-terminal sampling resistor R2, although voltage drops are generated at the two ends of the sampling resistor R2, the contacts S2_2 and S2_3 of the synchronous switching device S2 avoid the contact S2_1 of the synchronous switching device S2 and the welding end of the four-terminal sampling resistor R2 at the negative detection lead L2, only the voltage of the sampling resistor R2 is collected and sent to a post-amplifier, and the post-amplifier amplifies by a certain multiple to form the sensor output voltage Vo.
Obviously, the voltage drop generated by the measured current at the welding end of the negative electrode detection lead L2 by the contact S2_1 of the synchronous parallel switch device S2 and the four-terminal sampling resistor R2 is effectively subtracted. Since the instrumentation amplifier input current is small, the voltage drops generated at contacts s2_2 and s2_3 are also small and can be ignored when the sampling accuracy requirements are not particularly high. The same effect as described above is also achieved when selecting other gear positions. Because the amplification factor of the amplifier is fixed, the bandwidth of the amplifier cannot be changed along with the change of the measurement gear.
Similarly, when the estimated value of the measured current is 10A, the four-terminal sampling resistor R1 is used to detect the current, the measured current I flows through the contact s1_1 of the synchronous switching device S1 and the four-terminal sampling resistor R1 at the welding end of the negative electrode detection wire L2 and the corresponding four-terminal sampling resistor R1, although a voltage drop is generated at both ends of the sampling resistor R1, the contacts s1_2 and s1_3 of the synchronous switching device S1 can avoid the contact s1_1 and the welding end of the four-terminal sampling resistor R1 at the negative electrode detection wire 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 four-terminal sampling resistor R3 is used to detect the current, the measured current I flows through the contact s3_1 of the synchronous switching device S3 and the four-terminal sampling resistor R3 at the welding end of the negative electrode detection wire L2 and the corresponding four-terminal sampling resistor R3, although a voltage drop occurs at both ends of the sampling resistor R3, the contacts s3_2 and s3_3 of the synchronous switching device S3 can avoid the contact s3_1 and the welding end of the four-terminal sampling resistor R3 at the negative electrode detection wire L2, and only the voltage of the sampling resistor R3 is collected and sent to the subsequent 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 switching device S4 and the four-terminal sampling resistor R4 at the welding end of the negative electrode detection wire L2 and the corresponding four-terminal sampling resistor R4, although a voltage drop is generated at both ends of the sampling resistor R4, the contacts s4_2 and s4_3 of the synchronous switching device S4 can avoid the contact s4_1 and the welding end of the four-terminal sampling resistor R4 at the negative electrode detection wire L2, and only the voltage of the sampling resistor R4 is collected and sent to the post-stage amplifier.
Example 2
The synchronous switching device Sn is a three pole single throw switch or relay on the basis of embodiment 1.
The relay is adopted as a synchronous switching device Sn, eight pins are arranged in the relay, two pins are connected with a 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 corresponding contacts on the positive detection lead L1, a positive input port connecting wire of the instrument amplifier U1 and a negative input port connecting wire of the instrument amplifier U1.
Example 3
Referring to fig. 1, on the basis of 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 R7 connected with +15V voltage VDD and R8 connected with-15V voltage VEE, wherein a diode D1 and a diode D2 which are mutually connected in series, a diode D3 and a diode D4 which are mutually connected in series and a diode D5 and a diode D6 which are mutually connected in series are connected in parallel between the R7 and the R8, the conduction directions of the diode D1 and the diode D2 are from R7 to R8, the conduction directions of the diode D3 and the diode D4 are from R8 to R7, and the conduction directions of the diode D5 and the diode D6 are from R8 to R7; the positive input port of the instrument amplifier U1 is connected between the diode D3 and the diode D4, the negative input port of the instrument amplifier U1 is connected between the diode D5 and the diode D6, and the connection part between the diode D1 and the diode D2 is grounded.
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims. The components and structures not specifically described in this embodiment are well known in the art and are not described in detail herein.
Claims (4)
1. A precision current sensor circuit based on a sampling resistor, comprising: the device comprises an instrument amplifier U1, an anode detection lead L1, a cathode detection lead L2, n four-terminal sampling resistors Rn and n synchronous switching devices Sn; the n four-terminal sampling resistors Rn are arranged between the positive electrode detection lead L1 and the negative electrode detection lead L2 in parallel; the positive 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 switching device; the positive electrode detection lead L1 is connected with the other terminal of one end of each four-end sampling resistor Rn through one contact in each synchronous switching device; the negative electrode input port of the instrument 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 electrode detection lead L2 is directly connected with the other terminal of the other end of each four-end sampling resistor Rn; the resistance values of the four-terminal sampling resistors Rn are equal-ratio increasing or decreasing.
2. The precision current sensor circuit based on sampling resistor according to claim 1, wherein the synchronous switching device Sn is a triple pole single throw switch or relay.
3. The precision current sensor circuit based on the sampling resistor according to claim 1, wherein an amplifier input protection circuit C1 is further connected between the positive input port and the negative input port of the instrumentation amplifier U1.
4. The precision current sensor circuit based on sampling resistor according to claim 1, wherein the four-terminal sampling resistor Rn is a single fixed value four-terminal resistor.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111548966.5A CN116265963A (en) | 2021-12-17 | 2021-12-17 | Precision current sensor circuit based on sampling resistor |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111548966.5A CN116265963A (en) | 2021-12-17 | 2021-12-17 | Precision current sensor circuit based on sampling resistor |
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| Publication Number | Publication Date |
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| CN116265963A true CN116265963A (en) | 2023-06-20 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202111548966.5A Pending CN116265963A (en) | 2021-12-17 | 2021-12-17 | Precision current sensor circuit based on sampling resistor |
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| CN (1) | CN116265963A (en) |
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- 2021-12-17 CN CN202111548966.5A patent/CN116265963A/en active Pending
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