JPS61129582A - Measuring method of mutual inductance - Google Patents

Abstract

PURPOSE:To measure mutual inductance easily with good accuracy without increasing the number of turns of each coil by interposing an amplifier between the free-side terminal of a secondary coil and a voltage measurement terminal, and increasing the induced voltage across the secondary coil equivalently. CONSTITUTION:Terminals 6 and 7, the secondary coil 5, a neutral point 9, an amplifier 10, etc., are provided. Then, the voltage amplification factor of the amplifier is set previously to an optional value larger than 1, so the same state with a rise in the induced voltage across the coil 5 is obtained. For the purpose, a voltage value which is detected once is regarded as the induced voltage between both terminals 6 and 7 of the coil 5 to obtain the mutual inductance value, which is divided by the voltage amplification factor to obtain the correct mutual inductance value. Consequently, the mutual inductance is measured accurately without increase the number of turns of the coils 1 and 5. The amplifier 10 is interposed between the terminal 6 of the coil 5 and the voltage terminal HP and the earth-side terminal of the amplifier 10 is connected to the neutral point 9, so noise components in the measurement result are minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for measuring mutual inductance using a four-terminal pair measurement method.

[Technical Background of the Invention] Conventionally, when measuring self-inductance using a high frequency, a four-terminal pair measurement method has been used to prevent noise and mutual interference.

Using this four-terminal pair measurement method, it is possible to determine not only the self-inductance but also the mutual inductance between the primary and secondary coils. The mutual inductance had to be calculated by switching the connections between the two and measuring it twice, and calculating the mutual inductance from the results of the two measurements. Furthermore, it was necessary to apply current to the secondary coil in addition to the primary coil. Therefore, there is a problem that not only is it impossible to directly monitor the mutual inductance value with a measuring device, but also the amount of time and effort required for measurement increases.

In order to solve these problems, the inventor invented a mutual inductance measurement method that can determine the mutual inductance in a single measurement operation (Japanese Patent Application Laid-Open No. 1986-1988).
69>. That is, as shown in FIG.
The terminals 2 and 3 of the secondary coil 5 are connected to the current terminals Hc and Lc via the core wire 4 of the coaxial cable, respectively, and the terminals 6゜7 of the secondary coil 5 are connected to the voltage terminals Hp and Lp via the core wire 4 of the coaxial cable, respectively. It is connected to the. One terminal 3 of the primary coil 1 and one terminal 7 of the secondary coil 5 are connected. The shield wires 8 of each coaxial cable 4 are connected at a neutral point 9.

In such a circuit configuration, the current terminal Ha.

When an alternating current 11 with a frequency f is supplied to Lc, a current 11 flows through the primary coil 1, the secondary coil 5 is in an open state, and an induced voltage E2 shown by equation (1) is induced between both terminals 6 and 7. do. However, in the formula 1), M is the mutual inductance between the primary coil 1 and the secondary coil 5.

E2=2πfM 11 (1
) Then, the mutual inductance M to be obtained is expressed by the formula ('2J).

Mouth M=E2/2yr f It-(2
1. Therefore, by measuring the induced voltage E2, the mutual inductance M can be measured in one measurement operation. Normally, the induced voltage -E2 is measured not by measuring the voltage between the terminals 6 and 7 of the secondary coil 5, but by measuring the voltage between the voltage terminal Hp and the neutral point 9 to which the shield wire 8 is connected, in consideration of noise etc. It is determined by measuring the potential difference within a measuring device.

[Problems with Background Art] However, even with the method for measuring mutual inductance as described above, the following problems still need to be solved. That is, when the value of the induced voltage E2 induced in the secondary coil 5 shown by equation (1) is extremely small, the mutual inductance IM determined by equation (2) also becomes small. Therefore, the resolution of the measured value of mutual inductance M decreases, and the number of effective digits of the measured value decreases.As a result, it may become difficult to detect minute changes in mutual inductance.

In order to solve this problem, the number of turns of the primary coil 1 and the secondary coil 5 is increased to increase the self-inductance value L1 of each of the primary coil 1 and the secondary coil 5. One possible method is to increase L2.

However, the primary coil 1 and the secondary coil 5 are
When used as a type detector, etc., there is a limit to increasing the number of turns of each coil 1, 5 due to constraints such as the size of the detector.

[Object of the Invention] The present invention has been made based on the above circumstances, and its purpose is to increase the induced voltage of the secondary coil equivalently by inserting an amplifier, and to increase the voltage induced in each secondary coil by inserting an amplifier. It is an object of the present invention to provide a method for measuring mutual inductance that can accurately and easily determine mutual inductance without increasing the number of turns of a coil.

[Summary of the Invention] The present invention provides an electromotive force induced in the secondary coil when one terminal of a primary coil and one terminal of a secondary coil are connected and an alternating current is supplied to the primary coil, and the alternating current is A mutual inductance measurement method in which the mutual inductance is measured using the four-terminal pair measurement method and the mutual inductance is directly determined from these measured values, and an amplifier is inserted between the other terminal of the secondary coil and the induced voltage measurement terminal. It is.

[Embodiments of the Invention] An embodiment of the present invention will be explained below with reference to the drawings. Fig. 1 is a circuit diagram for implementing the mutual inductance measuring method of the embodiment, and is the same as the circuit diagram of Fig. 2. The same reference numerals are given to the parts, and the explanation of the overlapping parts is omitted.

In this embodiment, one terminal 3 of the primary coil 1 connected between the current terminals Hc and Lc via the core 14 of the coaxial cable is connected to the voltage terminal Lp via the new line 4 of the coaxial cable. It is connected to one terminal 7 of the secondary coil 5. The other terminal 6 of the secondary coil 5 is connected to an input terminal of an amplifier 10, and an output terminal of this amplifier 10 is connected to a voltage terminal Hp via a core wire 4 of a coaxial cable.

Note that the ground terminal of the amplifier 10 is connected to a neutral point 9 to which the shield wire 8 of each coaxial cable is connected.

In such a circuit configuration, when an alternating current 11 of frequency f is supplied to the current terminals Hc and Lc, the current 11 flows through the primary coil 1 and the secondary coil 5 is in an open state, and induces an induced voltage E2 between both terminals 6 and 7, which is shown in equation (3), which is the same as equation (1). However, in equation 3, M is the voltage between primary coil 1 and secondary coil 5. is the mutual inductance between

E2−2πfMIr ・・・・・・(
3 Here, if the voltage amplification factor of the amplifier 10 is Av, the voltage value E3 detected by measuring the potential between the voltage terminal Hp and the neutral point 9 to which the shield wire 8 is connected is E3 - Av.
It becomes E2. Therefore, the required mutual inductance M
(becomes 4 equations.

M= (E3/AV)/2πfI!・・・・・・
(4) Since the voltage amplification factor Av of the amplifier 10 can be set in advance to any value greater than or equal to 1, the state is the same as if the induced voltage E2 of the secondary coil 5 had increased. Therefore, once the detected voltage value E3 is used as the induced voltage at both terminals 6.7 of the secondary coil 5, the mutual inductance value is obtained, and the obtained value is divided by the voltage amplification factor Av to obtain the correct mutual inductance M. good. For example, by appropriately setting the value of the voltage amplification factor Av, the correct value may be obtained by simply moving the decimal point of the measured value.

As a result, each measuring device such as a voltmeter that measures the voltage between the voltage terminal Hp and the neutral point 9 can be operated under the best measurement conditions, so it is necessary to ensure a sufficient number of effective digits in the measurement result. is possible. Therefore, the mutual inductance M can be determined with high accuracy without increasing the number of turns of each coil 1, 5.

Further, the amplifier 10 is connected to a voltage terminal Hp connected to a terminal 6 on the free end side of the secondary coil 5 via the core wire 4 of the coaxial cable.
Since the ground terminal of this amplifier 10 is connected to the neutral point 9 to which the shield wire 8 of each coaxial cable is connected, the noise components included in the measurement results are suppressed to a minimum. It is possible to do so.

Moreover, in practice, the secondary coil 5 is often divided into two coils connected in series, and these are operatively connected. By connecting in this way, it is possible to directly measure the difference in mutual inductance. In this case, since the value of each mutual inductance is particularly small, by using the amplifier 10 as described above, the above-mentioned effect can be greatly improved.

[Effects of the Invention] As explained above, according to the present invention, an amplifier is inserted between the free side terminal of the secondary coil and the voltage measurement terminal.

Therefore, the induced voltage in the secondary coil can be increased equidynamically, and the mutual inductance can be easily and accurately determined without increasing the number of turns of each coil.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for implementing a mutual inductance measuring method according to an embodiment of the present invention, and FIG. 2 is a circuit diagram for implementing a conventional mutual inductance measuring method. 1...Primary coil, 2.3.6.7...Terminal, 4.
・Coaxial cable core wire, 5... Secondary coil, 8...
- Shield wire, 9... Neutral point, 10... Amplifier, Ha. Lc...Current terminal, Hp, Lv...Voltage terminal.

Claims (1)

[Claims] One terminal of the primary coil and one terminal of the secondary coil are connected, an alternating current is supplied to the primary coil, and the induced voltage and the alternating current induced in the secondary coil are measured using the four-terminal pair measurement method. In the method of measuring mutual inductance, the mutual inductance between the primary coil and the secondary coil is directly obtained from these measured values, and this A mutual inductance measurement method characterized by inserting an amplifier that amplifies the induced voltage.