JPS606761Y2 - Circuit constant measurement device - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an apparatus for measuring constants of circuit elements.

For example, as a device for measuring the circuit constant (capacitance value) of a circuit element such as a capacitor, there is a conventional example of an apparatus for measuring circuit elements such as a capacitor.

That is, an AC bridge method is adopted, in which equal alternating currents are supplied to the element under test and the standard element forming the bridge, and the circuit constants of the element under test are measured based on the voltage across the pixel element.

However, it is necessary to use a coaxial cable to connect the measurement terminal of the measurement device and the device under test, especially when the two are far apart, and the influence of parasitic components in this measurement cable arises.

In particular, the higher the frequency of the measurement alternating current, the greater this influence becomes, causing measurement errors.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and aims to provide a circuit constant measuring device that eliminates errors caused by measurement cables.

According to one embodiment of the present invention, the voltage across the standard element is detected with a delay through the same length of cable that is in a constant relationship with the measurement cable.

This cancels out errors caused by the measurement cable.

The present invention will be explained in detail below using the drawings.

The figure is a block diagram of a circuit constant measuring device according to an embodiment of the present invention.

In the figure, the measuring device 10 has a pair of current terminals H9 and L.
Four measuring terminals are provided: c and a pair of voltage terminals Hpg Lp.

Each of these measuring terminals has a measuring cable 12.1
4, 16, and 18 are connected.

One end 22 of the capacitor 20 of the device under test is common with the rain center conductor at the other end of the measuring cable 12.14, and the other end 24 of the capacitor 20 is common with the rain center conductor at the other end of the measuring cable 16.18. Connected (contacted).

The measurement cables 12-18 are all identical coaxial cables of the same length l, and their shielding outer conductors are all connected in common.

The secondary side of the transformer 32 with the AC signal source 30 on the primary side is connected to the center conductor and the outer conductor of the measuring terminal H8.

A standard resistor 34 and a secondary coil 38 of a transformer 36 are connected in series between the center conductor and the outer conductor of the measurement terminal Lc.

The center conductor of the measuring terminal is connected to the input end of a control circuit 40, and the output end of the control circuit 40 is connected to the transformer 36.
It is grounded via the primary coil 42 of.

The first input end 46 of the detection circuit 44 is connected to the center conductor of the measurement terminal H2, and the second input end 48 is connected to the coaxial cable 50 (its length 1
2) to a common connection point 52 between the standard resistor 34 and the secondary coil 38, and the output end 54 to an indicator 56, respectively.

The operation of the above configuration will be explained.

The voltage developed by the signal source 30 on the secondary side of the transformer 32 is applied to the center conductor of the cable 12, the capacitor 20, the center conductor of the cable 18, the standard resistor 34, the coil 38 and the outer conductor of the cables 18, 16, 14, 12. is supplied to the series circuit.

Here, the function of the controller 40 is to detect the potential VLP at the measurement terminal Lp and transmit it to the secondary coil 3 through the transformer 36.
8 in a direction that cancels out the potential VLP, thereby making the potential VLP zero.

This is also discussed in the above patent.

In this balanced state, the current i flowing through the capacitor 20.

are all supplied to cable 18.

Therefore, the current iR flowing through the standard resistor 34 is 1R=eC11YX@Co5hγ11
It is expressed as (1).

Here, eo is the voltage across the capacitor 20, Yx is the admittance of the capacitor 20, and γ is the propagation constant of the coaxial cable.

Therefore, the voltage eR across the resistor 34 is: eR=R@1R=R@eo@Yx@C05hγ11(2
), where R is the resistance value of resistor 34.

Coaxial cable 50 is the same cable as measurement cables 12-18.

Therefore, the voltage e4 at the second input 48 of the detector 44
8 is.

- at the first input 46 of the force detector 44; The voltage e,,6 at It is.

The capacitance value Cx of the capacitor 20 to be measured is set to both voltages e and 8.
．． When determined by the ratio of e46, the detector 44
performs the calculation and the result is displayed by display 56.

If this is calculated from both equations (3) and (4) above, becomes.

Therefore, if only the voltage ratio 648/646 is determined by the detector 44, an error will occur due to the coaxial cable.

Therefore, if the hyperbolic function on the right side of equation (5) is expanded into Macro-Lin and the third and subsequent terms are ignored, the relationship ν holds true.

Then, if 1°-='211, the right side of equation (6) = +
It becomes 1.

Therefore, measure the length of cable 50 from cables 12 to 18.
By selecting 72 times as large as , it is possible to minimize errors caused by the influence of the measurement cables 12 to 18.

Theoretically, it is necessary to do so.

The cable 50 described above is connected externally to the mounting device 10 and changed each time depending on the measurement cables 12 to 18, or the cable 50 is changed each time using a changeover switch or the like. It is practical to choose.

Note that although the above description has been made regarding the case where the device to be measured is a capacitor, it is needless to say that the device to be measured is not limited to this and may be any other circuit device.

As detailed above, according to the present invention, it is possible to realize a circuit constant measuring device in which errors caused by measurement cables are minimized, and it is extremely effective in practical use.

[Brief explanation of drawings]

The figure is a block diagram of a circuit constant measuring device according to an embodiment of the present invention, in which 10: measuring device, 12 to 18: measuring cables,
20: Capacitor to be measured, 34: Standard resistor, 40: Control circuit, 44: Detection circuit, 56: Display device.

Claims (1)

[Scope of utility model registration request] It has a pair of current terminals and a pair of voltage terminals, one of the current terminal and the voltage terminal is brought into contact with one terminal of the device to be measured via a first and second cable, and the current terminal and the voltage terminal The other terminals of the device under test are brought into contact with the other terminals of the device under test via third and fourth cables, and the same current is supplied to the series circuit including the device under test and the standard device. In the apparatus for measuring the circuit constant of the device under test by introducing the voltage between the terminals of the device and the standard device into a detection circuit, the first to fourth cables are of the same length, and the standard device and the detection circuit are connected to each other. 1st
- A circuit constant measuring device characterized in that the circuit constant measuring device is connected to the fourth cable by a fifth cable having a fixed length, and the first to fifth cables are the same coaxial cable.