JPH0113065B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a voltage dividing circuit for high voltage measurement, which comprises a voltage dividing main circuit, a coaxial cable, and an output circuit, and reduces and guides high voltage from a measuring point to a measuring device such as a cathode ray tube oscillography device. It is related to.

Because it is necessary to measure high voltage, the voltage divider circuit for high voltage measurement is placed in a separate location from the main voltage divider circuit to which high voltage is applied and the output circuit connected to the measuring instrument, and the two are connected by a coaxial cable. It is.

For this reason, impedance matching between the voltage dividing main circuit and output circuit and the coaxial cable is required.
The characteristic impedance of coaxial cable is 50Ω to 75Ω
Therefore, impedance matching is easy for voltage divider main circuits and output circuits with low resistance up to several kilohms, but impedance matching is difficult for capacitive voltage divider main circuits with high resistance or high impedance. .

A conventional voltage divider circuit for high voltage measurement equipped with a capacitive voltage divider type main voltage divider circuit has a capacitance as shown in Figure 1.
First and second capacitors 1 and 2 for C ₀ and C ₁
and a capacitive voltage dividing main circuit 4 equipped with a first matching resistor 3 whose resistance value is selected to have a resistance value R equal to the characteristic impedance Z ₀ of the coaxial cable, which will be described later; ₀ coaxial cable 5, an output circuit 8 comprising a matching resistor 6 with a resistance value of R and a second capacitor 7 with a capacitance of _C2 , and performs impedance matching only on high frequency components. was.

Therefore, in the conventional voltage divider circuit for high voltage measurement, impedance matching of low frequency components is not performed, the overall frequency response characteristic is not flat, and the measurement range is limited.

Furthermore, because impedance matching has not been performed well in the past, there has been no voltage divider circuit for measuring high voltages with excellent frequency characteristics from direct current to high frequencies.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wideband, high impedance voltage dividing circuit for high voltage measurement.

Hereinafter, a specific example of the present invention will be explained in detail with reference to FIG. In this embodiment, the voltage dividing main circuit 4 and coaxial cable 5 are the same as before. The voltage dividing main circuit 4 is
First and second capacitors 1 and 2 are connected in series with capacitances C ₀ and C ₁ and one end is grounded, and the resistance value R is selected to be equal to the characteristic pedance Z ₀ of the coaxial cable 5. and a first resistor 3 whose one end is connected to the voltage dividing point of both capacitors 1 and 2. The other end of the resistor 3 is connected to one end of the center conductor 5a of the coaxial cable 5.
The outer conductor 5b of the coaxial cable 5 is grounded similarly to the capacitor 2.

The output circuit 8 includes a second resistor 9 having a resistance value of (1-r)R, a third resistor 10 having a resistance value rR,
A second capacitor 7 having a capacitance of _C2 is connected in series, and the end of this series circuit on the second resistor 9 side is connected to the other end of the center conductor 5a of the coaxial cable 5.
The end on the second capacitor 7 side is grounded, and the second capacitor 7 side is grounded.
The voltage dividing point Q of the third resistors 9 and 10 is the output terminal 11
The ground terminal of the second capacitor 7 is connected to the output terminal 12. Here, r=2C ₁ /C ₂ .

Next, it will be explained that such a voltage dividing circuit for high voltage measurement has a wide band response characteristic and impedance matching with the coaxial cable 5 is achieved.

In Fig. 2, if a step voltage of voltage "1" is applied to capacitor 2 at t=0, the output voltage v is expressed in Laplace notation as follows: v=r(S+2/ra ₂ )/2a ₁ a _2∞ 〓 〓 ^k=0 [a ₁ a ₂ / (S+a ₁ ) (S+a ₂ )] ^k+1 e ^-2kST ………(1
) is given by Here, a ₁ = 1/2Z ₀ C ₁ , a ₂ = 1/2Z ₀ C ₂ , and S = plus operator. Now, if we choose r so that 2/r=a ₁ /a ₂ , equation (1) becomes v _c = S + a ₁ / a ₁ ² _∞ 〓 〓 ^k=0 [a ₁ a ₂ / (S + a ₁ ) (S+a ₂ )] ^k+1 e ^-2kST ………(2
) becomes. Here, if C ₁ ≪C ₂ , that is, a ₂ ≪a ₁ , then equation (2) becomes a step function. The voltage of this step function is t=0. and at t=∞ becomes. Here, C ₃ is the capacitance of the coaxial cable 5.

The above equation means that a step function response of C ₁ /C ₂ times the input step function can be obtained. This means that an output with the same voltage division ratio can be obtained for all frequencies, and means that the impedance matching of the coaxial cable 5 is achieved.

Experimental example In the circuit shown in Figure 2, C ₀ = 6.4pF, C ₁ = 1nF,
C ₂ = 64 nF, R = 50 Ω, and a 10 m coaxial cable 5 with a characteristic impedance Z ₀ of 50 Ω was used.
A 200KV shielded voltage divider circuit was created by setting r=2C ₁ /C ₂ =1/32 and connecting a 500MΩ resistor in parallel to capacitor 1 and a 50KΩ resistor in parallel to capacitor 2. The input rise of this voltage divider circuit
When a step voltage of 1 nS was applied and the divided output waveform was observed, a step voltage with a rising edge of 5 nS was obtained. The partial pressure ratio was 1: ¹⁰⁴ .

We also measured voltages at frequencies of DC, 50Hz, 1KHz, 10MHz, and 100MHz, and confirmed that the voltage division ratio was 1: ¹⁰⁴ .

As explained above, according to the present invention, it is possible to provide a voltage dividing circuit for high voltage measurement that has substantially uniform frequency response characteristics over a wide band from direct current to high frequencies and has high impedance.

[Brief explanation of drawings]

FIG. 1 is a wiring diagram of a conventional voltage dividing circuit, and FIG. 2 is a wiring diagram showing an embodiment of the voltage dividing circuit according to the present invention. 1, 2...First and second capacitors, 3...First resistor, 4...Voltage dividing main circuit, 5...Coaxial cable, 5a...Center conductor, 5b...Outer conductor, 7
...Third capacitor, 8...Output circuit, 9,1
0... Second and third resistors, 11, 12... Output terminals.

Claims (1)

[Claims] 1 The main voltage dividing circuit to which high voltage is applied and the output circuit connected to the measuring instrument are connected by a coaxial cable,
The voltage dividing main circuit includes a first capacitor having a capacitance of C ₀ , a second capacitor having a capacitance of C ₁ , and a first resistor having a resistance value R equal to the characteristic impedance of the coaxial cable; 1. An input terminal is provided on the first capacitor side of a series circuit formed by connecting second capacitors in series, the second capacitor side of this series circuit is grounded, and the input terminal is connected to the first and second capacitors. One end of the first resistor is connected to a voltage dividing point, the other end of the first resistor is connected to the center conductor of the coaxial cable, and the outer conductor of the coaxial cable is grounded. In the voltage divider circuit for high voltage measurement, the output circuit has a resistance value of (1-r)R(t), where r=
2C ₁ /C ₂ ) and a third resistor with resistance rR.
and a third capacitor having a capacitance of _C2 , the second and third resistors and the third capacitor are connected in series in this order to form a series circuit, and this series The second resistor side in the circuit is connected to the center conductor of the coaxial cable, the third capacitor side in this series circuit is grounded, and voltage dividing points of the second and third resistors are connected to an output terminal. A voltage divider circuit for high voltage measurement, characterized by comprising: