JPH0650328B2 - Resonance measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resonance measuring device, and more particularly to a device for contactlessly measuring the resonance frequency of a resonance circuit.

[Prior Art and its Problems] There have been cases where it is desired to remotely determine the resonance frequency of a radio frequency (RF) circuit. From the 1930s there has been a Grid Dip Oscillator (GDO) for that purpose. This GDO
(Or its solid-state version, the Gate Dip Oscillator) is a simple variable frequency oscillator with a meter added to it to keep the grit (or gate) current of the oscillator. The inductor (coil) of the GOD is electromagnetically coupled to the resonant circuit to be measured. When the GOD tunes the resonant frequency of the resonant circuit, it absorbs the oscillating energy from the inductor, which lowers the oscillation level and reduces (dips) the GOD grid current meter reading. In order to make this grid current dip clearer, the oscillator is operated at the boundary oscillation point. In this case, tuning the resonance of the circuit to which the oscillator is coupled maximizes the change in grid current. GOD has various drawbacks. That is, since the inductor that couples the GOD to the resonant circuit also determines the frequency of the GOD, if this inductor couples to the measured resonant circuit,
This inductor changes and the oscillation frequency changes. This causes inaccuracies in the frequency calibration that is pre-printed on the surface of the oscillator.

GOD has the further drawback of poor frequency resolution.
Generally, the frequency scale printed on the GOD is 2-3%.
It cannot have the above precision.

There are also restrictions on the use of GOD. For example, it is difficult to apply to a resonance circuit including a toroidal inductor. The reason is that the magnetic field of the toroidal inductor is almost limited to the inside of the toroidal core, and the good coupling with the inductor of the GOD is not performed.

Finally, the oscillation level of the GOD changes as the frequency changes, causing a slight change in the meter reading. This phenomenon is remarkable especially when the oscillator is operated at the boundary oscillation point.

Another device commonly used to determine the resonant frequency of a circuit is a network analyzer (NA).
The NA is directly connected to the circuit under test, and the parameters of the circuit can be obtained in detail. However, NA is very expensive and is often impractical to apply. Its direct connection to the circuit limits its application.

Therefore, there has been a need for a new measuring device for remotely measuring the resonance frequency of a circuit, that is, without contact.

[Purpose] Accordingly, it is an object of the present invention to provide an improved measuring device in which the resonant frequency of a circuit is remotely required.

Another object of the present invention is to provide a highly accurate resonance frequency measuring device.

Still another object of the present invention is to provide a device capable of measuring the resonance frequency of a resonance circuit including a toroidal inductor.

Another object of the present invention is to provide a resonance indicating circuit which does not use a frequency affecting element in a coupling circuit.

SUMMARY OF THE INVENTION The present invention is a resonance measuring device for remotely measuring the resonance frequency of a measured resonance circuit, wherein a bridge circuit is stimulated with a variable frequency RF signal source and coupled to the measured resonance circuit. . When the stimulation frequency passes through the resonant frequency of this circuit, the energy absorbed by this circuit from the bridge is maximized.
This absorption disturbs the voltage and current in the bridge. When this maximum disturbance (unbalance) point is measured by using a detector, the resonance frequency of the circuit under test can be obtained.

[Embodiment] FIG. 1 shows a circuit diagram of an embodiment of the resonance measuring apparatus of the present invention. This resonance measuring device has a transformer network 12
And a bridge circuit 10 having two identical inductors 14 and 16. The bridge 10 is stimulated by a variable frequency RF signal source 20 from an RF input port 18. Detector 22 such as an oscilloscope or RF voltmeter
To the output port 24 of the detector. An output having an amplitude corresponding to the degree of unbalance of the bridge is obtained from the output port 24.

The bridge 10 in FIG. 1 is in a normal state in a balanced state. That is, the bridge is in equilibrium with the output port 24 and the midpoint of the transformer 12. Since the outputs of both secondary windings of the transformer 12 have the same amplitude and opposite polarities, the output of the output port 24 is canceled and becomes about 0 volt.

To explain the operation, the bridge circuit 10 has a circuit under test 28.
It is reactive and unbalanced. In FIG. 1, this is shown as the coupling between inductor 16 and circuit 28. This coupling becomes asymmetric by bringing the inductor 16 closer to the circuit under test 28 than the inductor 14.
With this coupling, circuit 28 absorbs energy from inductor 16. Energy loss from inductor 16 to circuit 28 can be modeled as an effective loss resistance in series with the inductor. This effective loss resistance causes the bridge 10 to be compromised, resulting in some output reading from the detector 22. Energy absorption by circuit 28 is maximized when the frequency of RF signal source 20 is tuned to the resonant frequency of circuit 28. In this respect, the imbalance of the bridge 10 is also the maximum. Therefore, the resonant frequency of the circuit 28 can be determined at the point where the frequency of the stimulating RF signal source 20 is changed to maximize the signal amplitude at the detector output port 24.

When the maximum value is detected, the frequency of the RF signal source 20 becomes equal to the resonance frequency of the circuit under test 28. Signal source 2
A frequency of 0 can be accurately measured with a conventional frequency counter.

The detector output port 24 in FIG. 1 is normally the zero point of the bridge circuit, but it may be another point. For example, the input of the detector driving the RF voltmeter with a high frequency summing operational amplifier (not shown) may be connected between the secondary windings of the transformer 12. When the bridge is in equilibrium, a voltage of equal amplitude and opposite polarity is input to the input of the operational amplifier, so this output is 0
Becomes However, when the bridge becomes unbalanced, both inputs of the operational amplifier are no longer of equal amplitude and some output appears. It will be appreciated that the output can be taken from various points on the bridge 10.

The bridge 10 of FIG. 1 can have other configurations. In the example shown in FIG. 2, the bridge 10 is a support member 30.
It comprises a transformer 32 wound in a trifilar configuration as above. The inductors 14 and 16 are coils separated from each other, and are designed to be asymmetrically coupled to the circuit under test 28. In order to minimize the coupling between inductors 14 and 16,
The axes may be arranged so as to be orthogonal to each other. The resonance measuring device shown in FIG. 2 is suitable for use as a handheld probe for measuring the resonance frequency of a circuit under measurement.

An example of another form is shown in FIG. In this example inductor 1
4 and 16 are formed by etching on the axially symmetrical position of the printed board 34.

FIG. 4 shows a circuit diagram of another embodiment of the resonance measuring apparatus according to the present invention. The bridge 40 has a current transformer network (CT) 42 and a zero adjustment resistor 44. CT42 is circuit point 46
Currents of equal amplitude and opposite polarities are made to flow to and 48.
Due to this symmetry, the voltage at the circuit point 50 becomes substantially zero. This voltage enables adjustment of the zero point adjustment potentiometer 44 to compensate for any imbalance that may exist in the circuit. The operation of the bridge 40 is otherwise the same as that of the embodiment shown in FIG.

FIG. 5 shows still another embodiment of the resonance measuring apparatus according to the present invention, which is the same as the embodiment of FIG. 4 except that the bridge 60 uses two coaxial cables 62 and 64 instead of CT42. Similar. Although not shown, the cables 62 and 64 have a large number of ferrite beads or small toroids arranged and loaded along their entire lengths. The RF energy source 70 is connected to the center conductors of the first ends 72,74 of both cables. The shield conductors at the first ends of both cables are grounded.
The center conductor of the second end 76 of the cable 62 is the first of the bridges.
It is connected to the inductor 78 and the shield conductor is grounded. The center conductor of the second end 80 of the cable 64 is connected to the second inductor 82 of the bridge and the shield conductor is grounded. With this cable configuration, currents of equal amplitude and opposite polarities flow through the circuit points 66 and 68. The operation of the bridge 60 as the resonance indicating probe is otherwise the same as that of the example of FIG. 1, and therefore the details thereof will be omitted here. The embodiment of FIG. 5 is suitable for microwave applications.

FIG. 6 shows another embodiment of the resonance measuring apparatus according to the present invention, which has the bridge 90 capacitively coupled to the resonance circuit 108 to be measured. Bridge 90 includes a transformer 92 for applying a balanced signal to current limiting resistors 94 and 96. Each leg 98 and 100 connects a resistor 94 and 96 to the detector output port 1
02 to form capacitive coupling plates 104 and 106. If the bridge 90 is not coupled to the resonant circuit under test 108, the voltage at the detector output port 102 will be approximately zero. However, as the circuit 108 is brought closer to the plate 104 or 106, energy is transferred from the corresponding leg 98 or 100 to the circuit 108.
Capacitively coupled to the bridge 90 causing an imbalance.
This coupling also connects the circuit 108 to one plate 104 (or 106).
Can be made asymmetrical by bringing one closer to the other. In the above device, the detector 1 at the detection output end 102
When the instruction 10 is maximum, the resonance frequency of the circuit 108 and the frequency of the stimulation signal source 112 match.

Another embodiment of the present invention is shown in FIG. 7, where a return loss bridge 150 is used. This bridge 1
50 includes an unknown port 152, to which an unknown impedance is coupled. The other bridge elements 154, 156 and 158 have been selected to cause the bridge 150 to strike when a predetermined impedance is connected to the unknown port 152. For example, bridge resistors 154 through 15
When eight are equal, the impedance across port 152 equals the resistance of these resistors.

In this example, probe 160 is connected to unknown port 152, which creates a significant inductive impedance between ports 152. This impedance is bridge 150
Cause a great deal of disagreement. Therefore, the instruction of the detector 164 is large. The inductor 162 is connected to the measured resonance circuit 16
Approaching 6 results in an effective loss resistance in inductor 162, which is much smaller, but less unbalanced than if circuit 166 were not coupled. This will reduce the detector 164 readings. When the frequency of the RF source is tuned to that of circuit 166, probe 1
60 maximizes the resistance created between ports 152.
At this point, the bridge 150 is in a minimum imbalance condition and the detection output of the detector 164 is a minimum. This minimum point indicates that the resonance frequency of the resonance circuit 166 and the frequency of the signal source 168 are tuned.

FIG. 8 shows a probe 16 capable of coupling the bridge 150 of FIG. 7 to a circuit 170 including a toroidal inductor 172.
An example of 0 is shown. Probe 160 includes a current loop through the center of the toroidal core, which electromagnetically couples circuit 170 with bridge 150. With this method, it has become possible to measure the resonance frequency of a resonance circuit that includes a toroidal inductor, which has been impossible or difficult.

Although various embodiments of the resonance measuring apparatus according to the present invention have been described above, it goes without saying that these are merely examples and the present invention should not be limited to these embodiments. Those skilled in the art can easily understand that various modifications and changes can be made without departing from the gist of the present invention.

[Effect] According to the resonance measuring apparatus of the present invention, the variable frequency signal source is connected to the bridge, and the resonance circuit to be measured is reactively coupled to one of the two legs forming the bridge, thereby causing an imbalance in the bridge. The resonance frequency is determined by the signal source frequency that causes the maximum (or minimum) detector output. Therefore, the circuit configuration is relatively simple, and the resonance frequency can be measured easily, reliably, and highly accurately by using the existing measuring instrument. Since a part of the oscillation circuit is not used for coupling with the resonance circuit to be measured, there are various remarkable effects such that a substantially constant and highly accurate measurement result can be obtained regardless of the coupling degree.

[Brief description of drawings]

FIGS. 1 and 4 to 7 are circuit diagrams of different embodiments of the resonance measuring apparatus of the present invention, FIGS. 2 and 3 are embodiments of the coupled inductors of the embodiments of FIGS. 1, 4 and 5. , Fig. 8 shows 7
An example of a binding probe used in the example of the figure is shown. 20, 70, 112 ... Variable frequency signal source 10, 40, 60, 90, 150 ... Bridge circuit 22, 110, 164 ... Detector 14, 16, 78, 82 ... Inductor

Claims (2)

[Claims] Claim: What is claimed is: 1. A variable frequency signal of equal amplitude and opposite polarity is generated at two points of a bridge circuit, and one of the two legs of the bridge between the two points has a resonant circuit under test reactively packed from the other. A resonance measuring device which is coupled to detect the equilibrium state of the bridge circuit by using a detector. 2. The resonance measuring apparatus according to claim 1, wherein as the reactive coupling, an inductive coupling attached to or etched on an insulating substrate is used.