JPS62237362A - Resonance measuring instrument - Google Patents

Abstract

PURPOSE:To remotely find the resonance frequency of a resonance circuit with high accuracy by exciting a bridge circuit by an RF signal source frequency is variable and coupling it with the resonance circuit to the measured. CONSTITUTION:The bridge circuit 10 is coupled with the circuit 28 to be measured in such an unbalanced state that an inductor 16 is closer than an inductor 14. Consequently, the circuit 28 absorbs energy from the inductor 16 and the energy loss from the inductor 16 to the circuit 28 is modeled as effective loss resistance serial to the inductor. This effective loss resistance makes the bridge 10 unbalanced to cause some output from a detector 22 connected to an output port 24 to be read. The energy absorption by the circuit 28 becomes maximum when the frequency of the RF signal source 20 tunes to the resonance frequency of the circuit 28. The unbalance of the bridge 10 becomes maximum at this point of time. The resonance frequency of the circuit 28 is therefore determined at the point where the signal amplitude of the output port 24 is maximum by varying the frequency of the signal source 20 which is excited.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a resonance measuring device, and particularly to a device for non-contactly measuring the resonant frequency of a resonant circuit.

[Prior Art and its Problems] There have been cases where it is desired to remotely determine the resonant frequency of a radio frequency (RF) circuit. Since the 1930's there have been grid dip oscillators (GDOs) for that purpose. This G.D.O.
(or its solid-state version, a gated-dip oscillator) is a simple variable frequency oscillator with a meter attached to it to read the oscillator's grid (or gate) current. The inductor (coil) of the GDO is electromagnetically coupled to the resonant circuit under test. When the GDO tunes to the resonant frequency of the resonant circuit, it absorbs oscillation energy from the inductor, reducing the oscillation level and causing the GDO's grid current meter reading to decrease (dip). In order to further clarify this dip in the grid current, the oscillator is operated at the boundary oscillation point. In this case, the change in grid current is greatest when the oscillator is tuned to the resonance point of the coupled circuit. GDO has various drawbacks. That is, since the inductor that couples the GDO to the resonant circuit also determines the frequency of the GDO, when this inductor couples to the resonant circuit under test, this inductance changes, changing the oscillation frequency. This causes inaccuracies in the frequency calibration that is previously printed on the surface of the oscillator.

GDO also has the disadvantage of low frequency resolution.

The frequency scale printed on the GDO is generally 2-3%.
It is impossible to have more precision than that.

GDO also has usage restrictions. For example, it is difficult to apply to a resonant circuit including a toroidal inductor. The reason is that the magnetic field of the toroidal inductor is mostly confined within the toroidal core, and good coupling with the GDO inductor is not achieved.

Finally, the oscillation level of the GDO changes as the frequency changes, resulting in small changes in the meter reading. This phenomenon is particularly noticeable 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, allowing detailed determination of circuit parameters. However, NA is very expensive and impractical to apply in many cases. Since it is connected directly to the circuit, its applications are limited.

Therefore, there is a need for a new measuring device that can remotely, ie, non-contactly determine the resonant frequency of a circuit.

OBJECTIVES It is therefore an object of the present invention to provide an improved measurement device in which the resonant frequency of a circuit can be determined remotely.

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

Still another object of the present invention is to provide an apparatus capable of measuring the resonant frequency of a resonant circuit including a toroidal inductor.

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

[Summary of the Invention] The present invention is a resonance measuring device for remotely measuring the resonant frequency of a resonant circuit under test, which stimulates a bridge circuit with a variable frequency RF signal source and couples it to the resonant circuit under test. . When the stimulation frequency passes through the circuit's resonant frequency, the energy absorbed by the circuit from the bridge is maximized. This absorption disturbs the voltage and current within the bridge. By measuring this point of maximum disturbance (unbalance) using a detector, the resonant frequency of the circuit under test can be determined.

[Embodiment] FIG. 1 shows a circuit diagram of an embodiment of the resonance measuring device of the present invention. This resonance measuring device consists of a transformer network 12
and a bridge circuit 10 having two equal inductors 14 and 16.

This bridge 10 is stimulated by a variable frequency RF signal source 20 from an RF input port 18. A detector 22, such as an oscilloscope or RF voltmeter, is connected to the detector output port 24.
Connect to. From this output port 24, an output with an amplitude corresponding to the degree of unbalance of the bridge is obtained.

The bridge 1o in FIG. 1 is normally balanced. That is, the bridge is balanced with respect to the midpoint between output port 24 and transformer 12. Since the outputs of both secondary windings of the transformer 12 are of equal amplitude and opposite polarity, the outputs of the output port 24 cancel out and become approximately O volts.

To explain the operation, the bridge circuit 10 connects the circuit under test 28
It is reactively and unbalancedly coupled to.

In FIG. 1, this is shown as a coupling between inductor 16 and circuit 28. This coupling is made asymmetric by placing the inductor 16 closer to the circuit under test 28 than the inductor 14. By coupling in this way, the 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 unbalances bridge 10 and produces some output reading from detector 22. Energy absorption by circuit 28 is greatest when the frequency of RF signal source 20 is tuned to the resonant frequency of circuit 28. At this point, the unbalance of the bridge 10 is also at its maximum. Therefore, the resonant frequency of circuit 28 can be determined by varying the frequency of stimulation RF signal source 2o at the point where the signal amplitude at detector output port 24 is maximum.

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

Detector output port 24 in FIG. 1 is typically the zero point of the bridge circuit, but may be at other points. For example, the input of a detector driving an RF voltmeter with a high frequency summing operational amplifier (not shown) may be connected between the secondary windings of transformer 12. When the bridge is balanced, voltages of equal amplitude and opposite polarity are input to the input of the operational amplifier, so the output becomes zero.

However, when the bridge becomes unbalanced, the plane input voltages of the operational amplifier are no longer of equal amplitude, so some output appears. It will be appreciated that the bridge 100 can take and output power from various points.

The bridge 10 of FIG. 1 can also take other forms. In the example shown in FIG.
The transformer 32 includes a trifilar-wound transformer 32. Inductors 14 and 16 are spaced apart coils for asymmetric coupling to circuit under test 28. To minimize coupling between inductors 14 and 16, the axes may be arranged orthogonal to each other. The resonance measuring device shown in FIG. 2 is handheld and suitable for use as a probe for measuring the resonant frequency of a circuit under test.

An example of another form is shown in FIG. In this example, inductor 1
4 and 16 are etched at axially symmetrical positions on the printed board 34.

FIG. 4 shows a circuit diagram of another embodiment of the resonance measuring device according to the invention. The bridge 40 is a current transformer network (C], ) 42
and a zero point adjustment resistor 44.

CT 42 causes currents of equal amplitude and opposite polarity to flow at circuit points 46 and 48. Due to this symmetry, the voltage at circuit point 50 is approximately O. This voltage allows adjustment of the zero 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 the embodiment of FIG. 1, and details thereof will be omitted.

FIG. 5 shows yet another embodiment of the resonance measuring device according to the invention, which is the same as the embodiment of FIG. 4 except that the bridge 60 uses two coaxial cables 62, 64 instead of the CT42. Similar. The cables 62, 64 are loaded with a number of ferrite beads or small toroids arranged along their length, although not shown. RF energy source 7
0 to the center conductor 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 connects to the bridge's first inductor 78 and the shield conductor is grounded. The center conductor of the second end 80 of cable 64 connects to a second inductor 82 of the bridge, and the shield conductor is grounded.

With this cable configuration, circuit points 66 and 68 carry currents of equal amplitude and opposite polarity. The operation of the bridge 60 as a resonant indicating probe is otherwise the same as in the example of FIG. 1 and will not be described in detail here. The embodiment of FIG. 5 is suitable for microwave applications.

FIG. 6 shows yet another embodiment of a resonance measuring device according to the invention having a bridge 90 capacitively coupled to the resonant circuit 108 under test. Buri Tsuji 90 includes a transformer 92,
A balanced signal is applied to current limiting resistors 94 and 96. Each leg 98 and 100 connects a resistor 94 and 96 to a detector output port 102 and forms a capacitive coupling plate 104 and 106.

When bridge 90 is not coupled to resonant circuit under test 108, the voltage at detector output port 102 is approximately O. However, when circuit 108 is moved closer to plate 104 or 106,
Energy is transferred from the corresponding leg 98 or 100 to the circuit 10.
8 , creating an imbalance in the bridge 90 . This coupling also connects circuit 108 to one plate 104 (or 106).
) can be made asymmetric by bringing them closer together than the other. In the device described above, when the indication of the detector 110 at the detection output 102 is at a maximum, the resonant frequency of the circuit 108 and the frequency of the stimulation signal source 112 will coincide.

Another embodiment of the invention is shown in FIG. 7, in which a return loss bridge 150 is used.

This bridge 150 includes an unknown port 152 to which an unknown impedance is coupled. Other bridge elements 15
4.156 and 158 are selected so that when a predetermined impedance is connected to unknown port 152, bridge 150 is balanced. For example, when bridge resistors 154-158 are equal, equilibrium occurs when the impedance between ports 152 is equal to 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
causing a large imbalance. Therefore, the indication of detector 164 is large. The inductor 162 is connected to the resonant circuit 16 under test.
6, an effective loss resistance occurs in the inductor 162, which is very small, but results in less unbalance than if the circuit 166 were not coupled.

This will reduce the detector 164 reading.

When the frequency of the RF signal source is tuned to that of circuit 166,
Probe 160 causes the maximum resistance across ports 152. At this point, bridge 150 is at a minimum imbalance and the detected output of detector 164 is at a minimum. This minimum point determines the resonant frequency of the resonant circuit 166 and the signal source 16
This shows that the frequency of 8 has been tuned.

FIG. 8 shows a probe 16 that can couple the bridge 150 of FIG. 7 to a circuit 170 that includes a toroidal inductor 172.
An example of 0 is shown. Probe 160 includes a current loop through the center of the toroidal core, thereby electromagnetically coupling circuit 170 to bridge 150. This method made it possible to measure the resonant frequency of a resonant circuit containing a toroidal inductor, which was previously impossible or difficult.

Although various embodiments of the resonance measuring device according to the present invention have been shown above, these are merely illustrative, and it goes without saying that the present invention should not be limited to these embodiments. Those skilled in the art will readily understand that various modifications and changes can be made without departing from the spirit of the invention.

[Effects] According to the resonance measurement device of the present invention, unbalance can be caused in the bridge by connecting a variable frequency signal source to the bridge and reactively coupling the resonant circuit under test to one of the two legs constituting the bridge. The resonant frequency is determined by the signal source frequency at which the detector output is maximum (or minimum). Therefore, the circuit configuration is relatively simple, and the resonant frequency can be measured easily, reliably, and with high precision using existing measuring instruments. Incidentally, since a part of the oscillation circuit is not used for coupling with the resonant circuit to be measured, it has various remarkable effects such as obtaining substantially constant and highly accurate measurement results regardless of the degree of coupling.

[Brief explanation of drawings]

1 and 4 to 7 are circuit diagrams of different embodiments of the resonance measuring device of the present invention, and FIGS. 2 and 3 are examples of coupled inductors of the embodiments of FIGS. 1, 4, and 5. , Figure 8 is the 7th
An example of a binding probe used in the illustrated example 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 patent applicant
Sony Tektronix Corporation Figure 2
Figure 3

Claims (2)

[Claims] (1) A variable frequency signal of equal amplitude and opposite polarity is generated at two points of the bridge circuit, and the resonant circuit under test is tightly coupled reactively to one of the two legs of the bridge between the two points than the other. , a resonance measuring device configured to detect the balanced state of the bridge using a detector. (2) The resonance measuring device according to claim 1, wherein an inductive coupling attached to or etched on an insulating substrate is used as the reactive coupling.