JPH01162166A - Q measuring apparatus - Google Patents

Abstract

PURPOSE:To measure a Q value simply without removing a capacitance, by determining Q of a coil to be measured from a ratio during the resonance between a current passing through the coil being measured connected in parallel to a second capacitance and an output voltage of an AC power source. CONSTITUTION:An LCR meter determines a complex admittance of an element to be measured by a known vector ratio calculation from a measuring voltage V of a voltmeter 3 and a measuring current I of an ammeter 8. A coil to be measured shown equivalently with a resistance 7 (resistance value (r) thereof) and an inductance 6 (inductance value l thereof) is connected to the side of the ammeter 8 through a fixed capacitance 4 between a signal source resistance 2 and the ammeter 8. A variable capacitance 5 is connected between a connection point of the fixed capacitance 4 and the coil being measured and the ground. In measurement, a short-circuiting is caused at both ends of the coil being measured to measure a capacitance value C1. Then, an actual admittance Ytr is measured to determine Q=Ytr/(omegaC1).

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a Q measuring device for determining the Q value of a coil.

[Prior art and its problems]

In recent years, measuring instruments have come into use that apply an alternating current voltage to an element to be measured and measure the immittance of the element to be measured from the vector ratio of the alternating voltage to the current flowing through the element. Such measuring instruments include Model 4274A and Model 42 commercially available from Yokogawa Left Backard Corporation.
I have a 75A multi-frequency LCR meter. Hereinafter, a measuring device having such a function will be referred to as an LCR meter.

When measuring the Q of a coil with a conventional LCR meter, especially the Q
When the value was large, the error was large. The Q value is given by the ratio of the imaginary component and the real component of the immittance of the device under test,
The measurement accuracy of each of them is determined by the required dynamic range, which is the larger one (the value of the imaginary component), so the error becomes larger (for example, the measurement accuracy is 0.5%, the Q
Considering the case of a value of 100, Imaginary component = 1 ± 0.005° Real component = 1 /100 ± 0.005 = 0.01 ± 0
．． If the Q value measured from 005 is Qm, then Qm! = 1 / (0,01±0.005)-100
/(1±0.5), resulting in an error of 50%. Since such a large error is due to a large imaginary component, the following solution was used.

(1) Parallel resonance method Connect a low-loss variable capacitor in parallel with the coil under test, vary the low-loss variable capacitor to resonate, eliminate the imaginary component of the coil admittance under test, and accurately measure the real component. .

When measuring the imaginary component, the low-loss variable capacitor is removed (and the imaginary component is assumed to have a sufficiently larger absolute value than the real component). Q is calculated from the values measured in this manner.

(2) Series Resonance Method The series resonance method is the dual of the parallel resonance method (1), in which the coil to be measured and the low-loss variable capacitor are connected in series and measured.

The imaginary component of the impedance of the coil to be measured is determined by short-circuiting the low-loss variable capacitor, the imaginary component is eliminated to determine the real component, and then the Q value is calculated. Both of the above methods require the removal of variable capacitors and additional calculations and cannot be automated.

[Purpose of the invention]

Therefore, an object of the present invention is to solve the above-mentioned problems with a Q measuring device that can easily measure the Q value by simply generating resonance using a variable capacitor.

[Summary of the invention]

According to one embodiment of the present invention, the voltage applied by the LCR meter is divided by a capacitive voltage divider consisting of a fixed capacitor and a variable capacitor, and then applied to the coil to be measured. A variable capacitor connected in parallel with the coil to be measured is varied to find the point where the current flowing through the coil to be measured and the applied voltage are in phase (or the point at which the maximum admittance is reached).

The Q of the measuring coil is determined from the fixed capacitance value, angular frequency, and admittance value at this time.

Therefore, if the fixed capacitance value and angular wave number are selected appropriately, Q will be LC
It can be read directly from the R meter reading. Alternatively, by using the capacitance calculation function built into the LCR meter, the Q value can be directly read from the LCR meter reading simply by appropriately selecting a fixed capacitance value.

[Embodiments of the invention]

FIG. 1 shows a Q measuring device according to an embodiment of the present invention.

AC signal source 1, signal source resistance 2, voltmeter 3, and ammeter 8 are as follows:
This is a functional representation of the inside of the aforementioned LCR meter. The internal resistance of ammeter 8 is zero.

The LCR meter determines the complex interference of the device to be measured from the voltage V measured by the voltmeter 3 and the current I measured by the ammeter 8 through well-known vector ratio calculation.

In one embodiment of the present invention, a coil to be measured equivalently represented by a resistance 7 (resistance value r) and an inductance 6 (inductance value 2) has a fixed capacitance 4 between a signal source resistance 2 and an ammeter 8. Connected to the ammeter side via. The variable capacitor 5 is connected between the connection point between the fixed capacitor 4 and the coil to be measured and the ground.

Let the signal angular frequency be ω, and the admittance Y in Fig. 1
Calculating t, where C,, C, is the fixed capacitance 4. The capacitance value of the variable capacitor 5, jt = l. Vary Cz and Y.

If is a real number, then ω”(C1+Cg) jt=1 becomes.

The value Ysr of Y at this time is given by the following equation.

ytr-ωC+Q Here, Q=1-ωIl/r: When Q of the test coil and Q are sufficiently large, set 02 so that the absolute value of Y is maximum.
Similar results can be obtained by adjusting .

In the measurement, first, both ends of the coil to be measured are short-circuited and the capacitance value C1 is measured. At this time, the variable capacitor I5 does not, in principle, cause an error in the measurement of C3. Next, if Ytr is measured as described above, Q can be obtained as Q=Yt,/(ωC+).

If ωC3 is selected to be an integer power of 10, the calculation of Q becomes easy.

It is clear that the Q measuring device of the present invention can be easily implemented using any LCR meter, such as a four-terminal CR meter or a two-terminal CR meter.

If you make the internal calculation of the LCR meter the same as when measuring capacity and display the Ytr mentioned above, the CIQ will be displayed, so you can calculate the Q from the displayed value by simply knowing 01 regardless of the frequency.
A value is required.

〔Effect of the invention〕

As described in detail above, according to the embodiment of the present invention, a Q measuring instrument capable of calibrating without removing the additional capacitor 1i (4, 5) and capable of accurately measuring a Q value with a high Q is provided. L
It can be easily configured using a CR meter.

Furthermore, in an LCR meter that can display the actual admittance as a capacitance, the Q value can be directly read by selecting C1 as an integer power of 10.

[Brief explanation of the drawing]

FIG. 1 shows a Q measuring device according to an embodiment of the present invention. 1. AC signal source 2. Signal source resistance 3. Voltmeter 4. Fixed capacity 5. Variable capacity 6. Inductance of the coil to be measured 7. Resistance of the coil to be measured 8. Ammeter IG 1

Claims (1)

[Claims] It consists of an AC power source and first and second capacitors forming a voltage divider that divides the output voltage of the AC power source, and resonance between the current flowing through the coil under test connected in parallel to the second capacitor and the output voltage. A Q measuring device characterized in that the Q of the coil to be measured is determined from a ratio of times.