An AC standard resistor for reducing frequency error

Abstract

An AC standard resistor for reducing frequency error reduces the frequency error by introducing an adjustable capacitor. On this basis, small-volume device resistors with opposite temperature coefficients, opposite drift directions, and opposite deviations can be selected and connected in series to reduce the temperature coefficient and deviation of the AC resistor, improve stability, and meet the transmission requirements of the AC quantum resistor. The invention is characterized in that the left end of a first resistor is connected to a high end via a left end node, the right end of the first resistor is connected to the left end of a second resistor via an intermediate node, the right end of the second resistor is connected to a low end via a right end node, the resistance values ​​of the first resistor and the second resistor are both 1 / 2 of the AC standard resistor value, and a compensation capacitor for reducing the time constant is connected between the left end node and the right end node or between the intermediate node and the ground terminal according to the set AC standard resistance value.

Description

Technical Field

[0001] The invention relates to the technical field of AC standard resistors, in particular to an AC standard resistor capable of reducing frequency error. Background Art

[0002] Resistors are one of the most common electrical components. High-precision resistors are not only the core components of high-precision instruments, but are also widely used in many scientific research occasions. In most practical work, resistors are mostly used in AC and high-frequency circuits. Due to the parasitic inductance and capacitance in resistors, as well as the skin effect of the wires in the AC state, the proximity effect between the wires, and the surrounding dielectric loss, resistors have frequency errors, which can be decomposed into real error and imaginary error. Figure 1 It is a schematic diagram of the equivalent structure of the resistor under AC conditions in the prior art. Figure 1 As shown, under AC state, the resistance will change with the change of frequency, so that the real part of the impedance of the resistance element in the AC circuit is not equal to the resistance value under DC state.

[0003]

[0004]

[0005] Imaginary part R j =jwτR (3)

[0006] Real part R sc ≈R(1+ω 2 τ 2 ) (4)

[0007] Where Z is the impedance of the AC resistor, R ac is the real part of the AC resistance, R j is the imaginary part of the AC resistance, R is the DC resistance, j is the sign of the imaginary part, ω is the angular frequency, L is the parasitic inductance, C is the parasitic capacitance, and τ is the time constant.

[0008] Resistors with small frequency error, small deviation and good stability can be called AC standard resistors. As for frequency error, it is necessary to reduce the frequency error caused by parasitic inductance and capacitance. From formula (3) and formula (4), it can be seen that when the value of time constant τ is reduced, the imaginary error in AC resistance can be directly reduced; the real error of AC resistance is related to τ. 2 Therefore, reducing the time constant τ also reduces the real part error.

[0009] Currently, the more mature AC standard resistor products in the world include the 5685 AC / DC standard resistor from the British company Tinsly. It is characterized by good stability, small frequency error and small deviation. It is the oldest AC standard resistor in the world and one of the most stable standard resistors in the world. Its structure is wire-wound and uses a non-inductive winding method to minimize distributed inductance and distributed capacitance, but it still has large frequency errors and temperature coefficients, making it difficult to meet the transmission of high-level AC standard resistor values, especially the transmission needs of AC quantum resistors. Summary of the invention

[0010] In view of the defects or shortcomings in the prior art, the present invention provides an AC standard resistor for reducing frequency error. The frequency error of the AC resistor is reduced by introducing a compensation capacitor. On this basis, resistor devices with opposite temperature coefficients, opposite drift directions, and opposite deviations can be selected and connected in series to reduce the temperature coefficient and deviation of the AC resistor, and improve stability and power characteristics, thereby meeting the transmission requirements of the AC quantum resistor.

[0011] The technical solution of the present invention is as follows:

[0012] An AC standard resistor for reducing frequency error, characterized in that the left end of a first resistor is connected to a high end via a left end node, the right end of the first resistor is connected to the left end of a second resistor via an intermediate node, the right end of the second resistor is connected to a low end via a right end node, the resistance values ​​of the first resistor and the second resistor are both 1 / 2 of the AC standard resistance value, and a time constant compensation capacitor is connected between the left end node and the right end node or between the intermediate node and the ground terminal according to the set AC standard resistance value.

[0013] The time constant compensation capacitor includes a third capacitor or a fourth capacitor.

[0014] If the set AC standard resistance value is less than 1kΩ, a third capacitor is set, the left end of the third capacitor is connected to the left end node, and the right end of the third capacitor is connected to the right end node. The third capacitor is used to compensate for the time constant generated by the first parasitic inductance in the first resistor and the second parasitic inductance in the second resistor.

[0015] If the set AC standard resistance value is greater than 1kΩ, a fourth capacitor is set, one end of the fourth capacitor is connected to the intermediate node, and the other end of the fourth capacitor is grounded. The fourth capacitor is used as an equivalent inductor to compensate for the time constant generated by the first parasitic capacitance in the first resistor and the second parasitic capacitance in the second resistor.

[0016] Assuming that the capacitance of the fourth capacitor is C4, the resistance of the first resistor is R1, and the resistance of the second resistor is R2, the equivalent inductance of the fourth capacitor is Ls=R1*R2*C4.

[0017] The first resistor and the second resistor have opposite temperature coefficients, opposite drift directions, and opposite deviations.

[0018] The time constant expression is as follows:

[0019] τ=L / R-CR

[0020] Where L is the parasitic inductance, R is the resistance, C is the parasitic capacitance, and τ is the time constant.

[0021] The high end is connected to a high current end and a high voltage end respectively, and the low end is connected to a low current end and a low voltage end respectively.

[0022] The technical effects of the present invention are as follows: the present invention is an AC standard resistor for reducing frequency error, which uses two resistors instead of one to achieve compensation of temperature coefficient, deviation, stability and increase of power handling; for AC resistors below 1kΩ, a method of connecting small capacitors in parallel at both ends is adopted to offset the time constant caused by distributed inductance, thereby reducing the imaginary error introduced by inductance; for AC resistors above 1kΩ, a small capacitor is connected between the two resistors and the casing to offset the time constant caused by distributed capacitance, thereby reducing the imaginary error introduced by distributed capacitance.

[0023] After actual testing and assessment, it is proved that the temperature coefficient is 10 -6 / ℃, deviation is 10 -6 Magnitude, stability is 10 -6 The magnitude and time constant are of the ns order (ns is nanosecond).

[0024] Taking the 10kΩ AC standard resistor as an example, the time constant realized by the present invention is compared with the time constants of the existing 5685 type AC / DC standard resistor of the British Tinsly Company and the USR-103SF (10kΩ) type standard resistor of the Japanese Alpha Company. The result is that the time constant of the 10kΩ AC standard resistor based on the present invention is -1.6ns, while the time constant of the 5685 type 10kΩ AC standard resistor is -97ns, and the time constant of the USR-103SF (10kΩ) standard resistor is -38ns, which can prove the effectiveness of the present invention in greatly reducing the imaginary error. Since the real error of the AC resistor is related to τ 2 The decrease in the time constant τ also greatly reduces the real part error of the AC resistance, effectively reducing the frequency error of the AC standard resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1It is a schematic diagram of the equivalent structure of a resistor under AC conditions in the prior art. Figure 1 R is the real resistance in the AC resistance, L is the parasitic inductance in the AC resistance, and C is the parasitic capacitance in the AC resistance.

[0026] Figure 2 The present invention is a schematic diagram of the structure of an AC standard resistor of less than 1 kΩ in an AC standard resistor for reducing frequency error.

[0027] Figure 3a The present invention is a schematic diagram of the structure of an AC standard resistor with a capacity of more than 1 kΩ in an AC standard resistor for reducing frequency error.

[0028] Figure 3b yes Figure 3a Schematic diagram of the equivalent AC standard resistor structure.

[0029] Figure 4a The present invention is a schematic diagram of an AC standard resistor structure for reducing frequency error. Figure 4a The resistors involved are standard AC resistors below 1kΩ.

[0030] Figure 4b It is another structural schematic diagram of an AC standard resistor for reducing frequency error according to the present invention. Figure 4b The resistors involved are standard AC resistors above 1kΩ.

[0031] The reference numerals are explained as follows: R-resistance (as the resistance R under AC conditions, it includes parasitic inductance L and parasitic capacitance C. When the parasitic inductance L and parasitic capacitance C are involved, R only represents the real resistance. When the parasitic inductance L and parasitic capacitance C are not involved or when the parasitic inductance L and parasitic capacitance C are ignored or implied, R is the entire resistance); L-parasitic inductance or distributed inductance; C-parasitic capacitance or distributed capacitance; R1-first resistance (R1 has a first parasitic inductance L1 and a first parasitic =R1+R2; Ls-equivalent inductance (Ls=R1*R2*C4); Z-equivalent impedance to ground (derived from C4 grounding); C'-equivalent parasitic capacitance of R1 and R2 in series; HC-high current terminal; LC-low current terminal; HP-high voltage terminal; LP-low voltage terminal. DETAILED DESCRIPTION

[0032] Below is the attached figure ( Figure 1-Figure 4b ) and Examples illustrate the present invention.

[0033] Figure 1 It is a schematic diagram of the equivalent structure of a resistor under AC conditions in the prior art. Figure 2The present invention is a schematic diagram of the structure of an AC standard resistor of less than 1 kΩ in an AC standard resistor for reducing frequency error. Figure 3a The present invention is a schematic diagram of the structure of an AC standard resistor with a capacity of more than 1 kΩ in an AC standard resistor for reducing frequency error. Figure 3b yes Figure 3a Schematic diagram of the equivalent AC standard resistor structure. Figure 4a This is a schematic diagram of an AC standard resistor structure for reducing frequency error according to the present invention. Figures 1 to 4b As shown, an AC standard resistor for reducing frequency error includes a high end connected to the left end of a first resistor R1 through a left end node, a right end of the first resistor R1 connected to the left end of a second resistor R2 through an intermediate node, and a right end of the second resistor R2 connected to a low end through a right end node, the resistance values ​​of the first resistor R1 and the second resistor R2 are both 1 / 2 of the AC standard resistance value, and a time constant compensation capacitor (for example, a third capacitor C3 or a fourth capacitor C4) is connected between the left end node and the right end node or between the intermediate node and the ground terminal according to the set AC standard resistance value.

[0034] The time constant compensation capacitor includes a third capacitor C3 or a fourth capacitor C4.

[0035] If the set AC standard resistance value is less than 1kΩ, a third capacitor C3 is set, the left end of the third capacitor C3 is connected to the left end node, and the right end of the third capacitor C3 is connected to the right end node. The third capacitor C3 is used to compensate for the time constant caused by the first parasitic inductance L1 in the first resistor R1 and the second parasitic inductance L2 in the second resistor R2.

[0036] If the set AC standard resistance value is greater than 1kΩ, a fourth capacitor C4 is set, one end of the fourth capacitor C4 is connected to the intermediate node, and the other end of the fourth capacitor C4 is grounded (that is, connected to the outer shell of the AC standard resistor), and the fourth capacitor C4 is used as an equivalent inductance Ls to compensate for the time constant brought by the first parasitic capacitor C1 in the first resistor R1 and the second parasitic capacitor C2 in the second resistor R2.

[0037] Assuming the capacitance of the fourth capacitor is C4, the resistance of the first resistor is R1, and the resistance of the second resistor is R2, the equivalent inductance of the fourth capacitor Ls=R1*R2*C4. The first resistor R1 and the second resistor R2 have opposite temperature coefficients, opposite drift directions, and opposite deviations.

[0038] The time constant expression is as follows: τ = L / R-CR; where L is the parasitic inductance, R is the resistance, C is the parasitic capacitance, and τ is the time constant.

[0039] The high end is connected to the high current terminal HC and the high voltage terminal HP respectively, and the low end is connected to the low current terminal LC and the low voltage terminal LP respectively.

[0040] The AC standard resistor for reducing frequency error provided by the present invention can be used for calibration of an RLC measuring instrument (RLC refers to resistance, inductance and capacitance), and the measurement uncertainty can be reduced by one order of magnitude.

[0041] A high-grade AC standard resistor comprises a resistor R1, a resistor R2, an adjusting capacitor C, an inner shielding terminal, a casing, a high potential terminal HP, a low potential terminal LP, a high current terminal HC, and a low current terminal LC. The resistor has the characteristics of small frequency error, small temperature coefficient, good stability, and small deviation, and is suitable for the transmission of high-grade AC resistors.

[0042] Will Figure 1 One resistor (R) is replaced by two resistors (R1 and R2). Figure 2 and Figure 3a As shown, the two resistor devices are small-volume, high-stability resistors with opposite temperature coefficients, opposite drift directions, and opposite deviations, so as to achieve low temperature coefficient, small deviation, and higher stability.

[0043] Usually, the frequency error introduced by the distributed capacitance and distributed inductance of the resistor with 100Ω≤R<1KΩ can offset each other. Figure 1 And the calculation formula of impedance Z. However, AC resistance below 1kΩ usually presents inductance characteristics, and AC resistance above 1kΩ usually presents capacitance characteristics. Therefore, for AC resistance below 1kΩ, a small capacitor is connected in parallel at both ends to offset the frequency error introduced by distributed inductance, such as Figure 2 As shown; for AC resistances above 1kΩ, a small capacitor is connected between the two resistors and the housing, as shown in Figure 3(a). According to the T-Δ transformation, the model of Figure 3(b) can be equivalently obtained to form an equivalent inductance, which can offset the frequency error introduced by the larger resistance distributed capacitance.

[0044] In order to reduce the influence of distributed capacitance and distributed inductance, a small capacitance adjustment method is adopted. For AC resistors below 1kΩ, a small capacitor is connected in parallel at both ends to offset the frequency error introduced by the distributed inductance (see Figure 2 , Figure 4a ). For AC resistors above 1kΩ, a small capacitor is connected between the two resistors and the chassis. After T-Δ transformation, the equivalent inductance can offset the frequency error introduced by the distributed capacitance (see Figure 3a , Figure 3b , Figure 4b ). Figure 3b Where Rs is the equivalent resistance (Rs=R1+R2), Ls is the equivalent inductance (Ls=R1*R2*C4), and Z is the equivalent impedance to ground (derived from C4 grounding).

[0045] Rs+jωLs=R1+R2+jω*R1*R2*C4

[0046] According to the AC resistance model, this term and the resistor in parallel with the capacitor are offset. Therefore, by adjusting the parallel capacitor C, the time constant term is made zero.

[0047] In order to reduce the temperature coefficient and deviation of the AC standard resistor, resistors R1 and R2 are connected in series with small devices with opposite temperature coefficients, opposite drift directions, and opposite deviations (see Figure 2 , Figure 3a , Figure 4a , Figure 4b ). Figure 4b C' is the parasitic capacitance of the equivalent R1 and R2 connected in series (ie, the combination of the parasitic capacitance C1 in R1 and the parasitic capacitance C2 in R2).

[0048] In order to reduce the influence of frequency error, resistors R1 and R2 are preferably planar resistors with higher resistivity and smaller area. Their distributed inductance and distributed capacitance are smaller, and the skin effect is smaller, so the frequency error is smaller. In order to obtain AC standard resistors with better temperature characteristics and stability, the materials of the planar resistors are selected from multi-element alloy materials such as Ni, Cr, Cu, and Al.

[0049] The AC standard resistor adopts a four-terminal pair structure, and the four-terminal leads are all shielded wires. The electromagnetic field is closed and no additional error will be generated (see Figure 4a and Figure 4b ).

[0050] The stability of the AC resistance working standard developed in this project is equivalent to that of the existing DC standard resistance. After actual testing, it is proved that the temperature coefficient is 10 -6 / ℃, deviation is 10 -6 Magnitude, stability is 10 -6 The magnitude and time constant are of ns order.

[0051] Taking 10 kΩ as an example, the time constant realized by the present invention is compared with the time constant of the existing 5685 type AC standard resistor, and the result can prove the effectiveness of the present invention.

[0052] AC resistance parameters The present invention Type 5685 USR-103SF Time constant -1.6ns -97ns -38ns

[0053] The present invention adopts two resistors to replace one resistor, so as to realize the compensation of temperature coefficient, deviation and stability.

[0054] For AC resistors below 1kΩ, a small capacitor is connected in parallel at both ends to offset the frequency error introduced by the distributed inductance. For AC resistors above 1kΩ, a small capacitor is connected between the two resistors and the casing to offset the frequency error introduced by the larger distributed capacitance.

[0055] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. An AC standard resistor for reducing frequency error, characterized in that: The left end of the first resistor includes a high end connected via a left end node, the right end of the first resistor is connected to the left end of the second resistor via an intermediate node, the right end of the second resistor is connected to the low end via a right end node, the resistance values ​​of the first resistor and the second resistor are both 1 / 2 of the AC standard resistance value, and a time constant compensation capacitor is connected between the left end node and the right end node or between the intermediate node and the ground terminal according to the set AC standard resistance value; The time constant compensation capacitor includes a third capacitor or a fourth capacitor; If the set AC standard resistance value is less than 1 kΩ, a third capacitor is set, the left end of the third capacitor is connected to the left end node, the right end of the third capacitor is connected to the right end node, and the third capacitor is used to compensate for the time constant caused by the first parasitic inductance in the first resistor and the second parasitic inductance in the second resistor; If the set AC standard resistance value is greater than 1 kΩ, a fourth capacitor is set, one end of the fourth capacitor is connected to the intermediate node, the other end of the fourth capacitor is grounded, and the fourth capacitor is used as an equivalent inductance to compensate for the time constant caused by the first parasitic capacitance in the first resistor and the second parasitic capacitance in the second resistor; The AC standard resistor adopts a four-terminal pair structure, and the four-terminal leads are all shielded wires. The high end is respectively connected to the high current end and the high voltage end, and the low end is respectively connected to the low current end and the low voltage end.

2. The AC standard resistor for reducing frequency error according to claim 1, characterized in that The capacitance value of the fourth capacitor is C4, the resistance value of the first resistor is R1, and the resistance value of the second resistor is R2, then the equivalent inductance of the fourth capacitor is Ls=R1*R2*C4.

3. The AC standard resistor for reducing frequency error according to claim 1, characterized in that: The first resistor and the second resistor have opposite temperature coefficients, opposite drift directions, and opposite deviations.

4. The AC standard resistor for reducing frequency error according to claim 1, characterized in that: The first resistor and the second resistor are both planar resistors with high resistivity and small area, and their distributed inductance and distributed capacitance are small, the skin effect is small, and the frequency error is small.

Images