JPH0374499B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a three-terminal standard capacitor used for precision measurement of various electrical quantities, and in particular, in order to eliminate measurement differences caused by its loss coefficient, etc. This article relates to a three-terminal standard capacitor with an additional circuit to compensate for the loss factor.

[Conventional technology]

Some three-terminal air capacitors for standard equipment with special consideration for construction have a loss coefficient of 10 ^-5 or less, but such air capacitors have a small dielectric constant of 1000 pF or less. It is used only within its capacity. Therefore, small-sized dielectric capacitors (using dielectrics other than air) with a loss factor of about 10 ^-4 to 10 ^-3 are currently widely used as standard capacitors.

However, as mentioned above, dielectric capacitors cannot be said to have an extremely small loss coefficient, so when measuring various electrical quantities using this as a standard, the more complex the measurement circuit, the lower the loss coefficient of the capacitor. This becomes a problem as an error factor.

In order to eliminate measurement errors due to such loss coefficients, conventional electronic capacitor measuring instruments use an operational amplifier to reverse the polarity of the voltage drop at the resistor terminal and obtain a negative equivalent resistance. The method used is to obtain

[Problem to be solved by the invention]

In such conventional compensation methods, compensation for the loss coefficient of the dielectric capacitor is limited to about 10 ^-4 due to constraints due to the characteristics of the operational amplifier itself, such as noise, gain, and stability. However, in order to provide a standard capacitor suitable for high-precision measurements, it is necessary to compensate its loss factor to 10 ^-5 or less.

[Structure and operation of the invention]

Therefore, the present invention provides a three-terminal standard capacitor in which a first capacitor is housed in a shield case that also serves as a ground terminal, and a Y-connected compensation circuit that includes second and third capacitors and a resistor. A three-terminal standard capacitor with a loss coefficient close to zero is realized by connecting the first capacitor and applying a negative equivalent resistance obtained from this compensation circuit between both terminals of the first capacitor.

〔Example〕

Examples of the present invention will be described below.

FIG. 1 shows an embodiment of a three-terminal standard capacitor according to the present invention.

In the figure, capacitor C ₀ is a dielectric capacitor used as the defined capacitance of this standard capacitor. This dielectric capacitor C ₀ is
When mounted, it is housed in an electrostatic shield case S that also serves as a ground terminal G, as shown in FIG. 2a.
If these are expressed as an equivalent circuit, it will be as shown in FIG. 2b, and this equivalent circuit element is also used in FIG. Incidentally, the configuration shown in FIG. 2 is that of a conventional general three-terminal standard capacitor.

Further, in this embodiment, small capacitance capacitors C _{1 and} C ₂ are connected in series between both terminals H and L of the dielectric capacitor C _{0 .}
interconnection point and shield case S (ground terminal G)
A variable resistor R is connected between the two. As described later, these two small capacity capacitors C ₁ and C ₂
The loss coefficient of the dielectric capacitor C ₀ can be compensated by the Y-connection circuit consisting of the variable resistor R and the variable resistor R. In addition, this compensation circuit is a shield case S.
is located outside.

Hereinafter, the operation of this embodiment configured as described above will be explained.

First, the loss coefficient of a conventional standard capacitor before adding a compensation circuit will be explained with reference to FIG. 2b.

In the figure, capacitors C _g1 and C _g2 are ground capacitances of this standard capacitor due to the stray capacitance between the dielectric capacitor C ₀ and the shield case S. Also, the resistor R ₀ in parallel with the dielectric capacitor C ₀
is the equivalent loss resistance corresponding to the dielectric loss of this dielectric capacitor C ₀ . In the following description, the reference numerals of each circuit element are also used as the electrical values of each element.

One terminal H of the dielectric capacitor C ₀ is connected to the power supply, and the other terminal L is used at the same ground potential as the shield case S. For this reason, ground capacity
C _g1 is added in parallel to the power supply, and the ground capacitance C _g2 essentially no longer functions as a capacitor. the result,
The ground capacitances C _g1 and C _g2 of this standard capacitor are separated from the measurement target, and only the inductive capacitor C ₀ (including loss resistance R ₀ ) is used as the defined capacitance of this standard capacitor.

Therefore, the equivalent loss coefficient D ₀ of this conventional standard capacitor at the angular frequency ω is expressed as D ₀ =1/ωC ₀ R ₀ .

Next, the operation of the compensation circuit consisting of the small capacitors C ₁ and C ₂ and the variable resistor R will be explained.

FIG. 3a shows only this compensation circuit. Converting this to an equivalent circuit with a △ connection as shown in figure b, the parallel impedance Z _HL added between both terminals H and L of the dielectric capacitor C ₀ is Z _HL = -j1/ωC ₁ - j1 /ωC ₂ +(
-j1/ωC ₁ )(-j1/ωC ₁ )/R =-j1/ω(1/C ₁ -j1/C ₂
It is expressed as -1/ω ² C ₁ C ₂ R [Ω]...(1). Here, if the circuit constants are selected so that 1/ωC ₁ , 1/ωC ₂ >>R, then Z _HL ≒-1/ω ² C ₁ C ₂ R [Ω] ...(2), and parallel Impedance Z _HL is equivalent to a negative resistance component.

Next, based on the above consideration, the operation of this embodiment will be explained with reference to FIG. 4, which is a rewrite of FIG. 1 using the equivalent circuit of FIG. 3b.

In FIG. 4, the impedances Z _Hg and Z _Lg newly generated by the compensation circuit between the terminals H and L and the ground terminal G become ground impedances, so
Ground capacity of conventional three-terminal standard capacitors
Similar to C _g1 and C _g2 , it is a circuit constant that does not cause any inconvenience to the defined capacitance C ₀ . Therefore, only the parallel impedance Z _HL acts on the defined capacitance C ₀ . As described above, the parallel impedance Z _HL is a negative resistance component, and its value is determined by the angular frequency ω and the circuit constants C ₁ , C ₂ , and R of the compensation circuit. Therefore, it is clear that the loss coefficient regarding the defined capacitance C ₀ can be compensated to zero by appropriately adjusting the variable resistor R so that |Z _HL |=R ₀ . To explain in more detail, the loss coefficient D _HL regarding the defined capacitance C ₀ in this example is D _HL = 1/ωC ₀ R ₀ −1/ωC ₀ Z _HL ≒1/ωC ₀ R ₀ −ωRC ₁ C ₂ / It is expressed as C ₀ =D ₀ −ωRC ₁ C ₂ /C ₀ (3). Note that the first term D ₀ in equation (3) is the loss coefficient of the dielectric capacitor C ₀ itself, and the second term is the loss coefficient
This is a term that compensates for D ₀ .

Based on this equation (3), the variable resistor R is adjusted according to the angular frequency ω so that ωRC ₁ C ₂ /C ₀ =D ₀ .
By adjusting , the loss coefficient _DHL can be compensated to zero.

As described above, according to this embodiment, the loss coefficient is
10 ^-4 ~ 10 ^-3 standard three-terminal capacitor, 2
By simply connecting an extremely simple circuit consisting of a fixed capacitor and a variable resistor, it is possible to compensate for the loss factor of this standard capacitor for a specific frequency. This amount of compensation can be adjusted using a variable resistor, so the compensation circuit capacitor C ₁ ,
A component capacitor with a tolerance of a few percent is sufficient for _C2 . Furthermore, since no electronic circuits such as operational amplifiers are used, the loss coefficient can be compensated to a value extremely close to zero, making it possible to reliably use standard capacitors for high-precision measurements that require a loss coefficient of 10 ^-5 or less. Can be provided. Additionally, changes in frequency can be freely handled by adjusting variable resistor R for small changes, and by changing the selection of capacitors C ₁ and C ₂ and variable resistor R for large changes. can do.

〔Effect of the invention〕

As explained above, according to the present invention, a negative parallel equivalent resistance obtained from two capacitors and a resistor is added to a three-terminal standard capacitor to compensate for the loss resistance of this standard capacitor. Therefore, the amount of compensation can be easily adjusted by adjusting the circuit constants of the compensation circuit, and since no electronic circuits such as operational amplifiers are used, highly accurate adjustment is possible, and therefore the loss coefficient is extremely low. This makes it possible to provide high-quality standard capacitors close to .

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure shows the actual circuit and equivalent circuit of the part in Figure 1 that is common to the conventional configuration, Figure 3 shows the actual circuit and equivalent circuit of the compensation circuit part of Figure 1, and Figure 4 shows the actual circuit and equivalent circuit of the part of the compensation circuit in Figure 1. This is an equivalent circuit of FIG. 1. C ₀ ……Dielectric capacitor (defined capacitance), R ₀ ……
Equivalent loss resistance of C ₀ of dielectric capacitor, H, L
... Both terminals of dielectric capacitor C ₀ , S ... Electrostatic shielding case, G ... Ground terminal, C _g1 , C _g2 ...
Ground capacitance of C ₀ of dielectric capacitor, C ₁ , C ₂ ...
Small capacity capacitor, R...variable resistor, Z _HL ...
Parallel impedance.

Claims (1)

[Claims] 1. A first capacitor housed in a shield case that also serves as a ground terminal, in which a second and third capacitor are connected in series between both terminals of the first capacitor, and the second and third capacitors are connected in series between both terminals of the first capacitor. Third
A resistor is connected between the interconnection point of the capacitors and the shield case, and the second and third capacitors and the resistor compensate for the loss coefficient of the first capacitor. A three-terminal standard capacitor characterized by providing a negative parallel equivalent resistance.