JPH0227849A - Immunity test circuit - Google Patents

Abstract

PURPOSE:To measure the device duration force of only a communication equipment to be tested accurately by connecting an impedance element to another coil wound on the same core with a coil with a tap of a voltage injection transformer inserted between communication equipments. CONSTITUTION:A resistor 37 as an impedance element is connected across other coil 35 wound on the same core with the coil 31 with a tap of a voltage injection transformer 30. A voltage for immunity test is applied to the communication equipment 11 to be tested via two conductors of the communication line 15 and the coil 31 with tap from a voltage generator 25 and the voltage application to an opposite communication equipment 13 is reduced by a common mode choke coil 17. Then the resonance of the tapped coil 31 is prevented by the circuit comprising the impedance element 37 connected to the other coil 35. Thus, the device immunity of the communication equipment to be tested only is measured accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to immunity test circuits that communicate with each other and operate with a common potential point (for example, earth) as a reference. For a pair of communication devices, one of the communication devices to be tested for noise tolerance, etc. is called the communication device under test.

With the other communication device as the opposing communication device, voltage is applied between the communication line connected to the communication device under test and a common potential point (for example, the ground) to check the transmission quality, such as code errors in digital transmission that occur in the communication device. This invention relates to an immunity test circuit for testing deterioration, malfunction, etc.

[Conventional technology]

Conventionally, before the operation of communication equipment (for example, during the development stage 2 of the equipment, before the equipment is installed, etc.), for example, a certain pattern is transmitted from one equipment that is the communication equipment under test to the other equipment that is the opposing equipment. However, code errors in digital transmission during that time are verified, and tests for transmission quality deterioration, malfunction, etc. in the communication line of the communication device 9 are sometimes performed. In such an operation test, an immunity test was conducted to determine the extent to which the communication device can withstand noise.

When performing such an immunity test, the circuit that applies the immunity test voltage (pseudo noise source) between the communication line connected to the communication device under test and the ground is as follows:
There was a circuit as shown in Figure 7. Here, the communication device under test 11 and the opposing communication device 1 that communicates with it
3 is a two-conductor communication line 15, a center-tapped coil 20 is inserted between these communication devices, and a center-tapped coil 20 is connected from the center point 23 of the coil 21 forming the center-tapped coil 20. This circuit applies a voltage for immunity testing using a voltage generator 25. Voltages for this test include sinusoidal alternating current voltage, amplitude modulated or frequency modulated signal voltage, surge voltage, and the like.

Between the coil 21 of this circuit and the communication line 15, there is a capacitor 27 that blocks the DC voltage (for example, -48 volts) of the communication line 15 and prevents it from flowing into the coil 21.
A resistor 2 for preventing series resonance between the capacitor 27 and the coil 21 and determining impedance when voltage is applied.
9 is inserted.

[Problem to be solved by the invention]

However, in the conventional circuit described above, the voltage generated between the two communication lines 15 (for example, the signal voltage transmitted from the communication device under test 11 to the opposing communication device 13) when voltage is applied during the immunity test. It is necessary to ensure that this does not affect the immunity test. Therefore, it is necessary that the difference between the resistance values of the two resistors 29 be small.

Along with this, when performing an immunity test, resistor 2
The current flowing into resistor 9 increases, and the power consumption in resistor 29 increases. Therefore, the resistor 29 is required to be used for high power, and the resistance values of both resistors 29 are required to be well balanced, and there is a problem in that it is technically difficult to realize this. Ta.

The present invention was created in consideration of these points, and it suppresses the voltage applied to the opposite communication device to a level that does not cause code errors or malfunctions, and accurately measures the equipment strength of only the communication device under test. The purpose is to provide an immunity test circuit that can perform measurements.

(Means for Solving the Problem) (1) Issuance according to claim 1 In order to achieve such an object, the invention according to claim 1 provides communication between at least one pair. For each device, one of the communication devices on which the desired test should be performed is called the communication device under test.

The other communication device is set as the opposite communication device, a common mode choke coil is inserted into each of the two conductors of the communication line interposed between the communication devices, and the communication line connecting the common mode choke coil and the communication device under test is connected. A coil with a midpoint tap of the transformer is inserted between the two conductors, and an impedance element is connected to another coil wound on the same core as the coil with a midpoint tap, so that the midpoint of the midpoint tapped coil of the transformer It is configured so that a test voltage is applied between it and a common potential point.

Further, in the invention set forth in claim 2, in addition to the structure of the invention set forth in claim 1, a third conductor is further provided between the two conductors of the communication line connecting the common mode choke coil and the opposing communication device. The middle point of the second center-tapped coil is interposed, the middle point of the second center-tapped coil is connected to a common potential point, and the second center-tapped coil is connected to another coil wound around the same core as the second center-tapped coil. It has a configuration in which a second impedance element is connected.

(Function) (i) Invention according to Claim 1 In the present invention, a voltage for immunity testing is applied by the voltage supply means from the center point of the coil with the center point tapped of the transformer.This voltage is applied inside the transformer. It is applied to the communication device under test via the coil with a point tap and the two conductors of the communication line.The application of this test voltage to the opposing communication device is reduced by the common mode choke coil, so it is not applied to the opposing communication device. will be unaffected by the exam.

Resonance caused by the center-tapped coil of the transformer is prevented by a circuit of impedance elements connected to another coil wound around the same core as the center-tapped coil.

Therefore, in the immunity test, it becomes possible to accurately measure the device strength of only the communication device under test, and a high-power, high-precision resistor is not required.

(ii) In the present invention according to claim 2, a second
The test voltage supplied from the center-tapped coil of the transformer is further reduced by the center-tapped coil, so that there is no effect on the opposing communication device.

Since the second impedance element is connected to another coil wound around the same core as the second center-tapped coil, resonance due to the second center-tapped coil is prevented.

Therefore, in the immunity test, it becomes possible to more accurately measure the equipment strength of only the communication device under test.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing the configuration of an immunity test path in an embodiment of the present invention, in which the same symbols as in FIG. 7 indicate the same elements, etc., and detailed explanations thereof are omitted here. do.

In FIG. 1, a voltage injection transformer 30 is provided, and a resistor 37 as an impedance element is connected to both ends of another coil 35 wound around the same core as the center-tapped coil 31 of the voltage injection transformer 30. There is. Midpoint 33 (0 point) of coil 31 with midpoint tap and voltage generator 2
A resistor 39 is inserted between the terminal 5 and the terminal 5.

The operation of the first embodiment constructed in this manner will be described below.

In FIG. 1, the communication device under test 11 and the opposing communication device 1
3, the voltage for immunity testing generated from the voltage generator 25 is applied to ff1ll made by the communication under test via the center-tapped coil 31. Further, the capacitor 27 between the center-tapped coil 31 and the communication line 15 prevents DC voltage from flowing into the center-tapped coil 31 due to the power supply voltage of the communication line 15.

On the other hand, a resistor 37 is connected to the coil 35 of the voltage injection transformer 30, thereby preventing series resonance between the center-tapped coil 31 and the capacitor 27. Furthermore, the impedance due to the midpoint clubbed coil 31 at the connection point of the capacitor 27 in the communication line 15 is determined by the number of windings between the resistor 37 and the coil, and by making this sufficiently large, the impedance from the communication device under test 11 can be reduced. This prevents the transmission signal from flowing into the voltage injection transformer 30 side, and prevents the deterioration of the transmission signal from affecting the test.

Here, if the number of windings of the coil 31 with mid-point dop is Na, the number of windings of the coil 35 is Nb, and the inductance of the coil is sufficiently large, the resistance value of the resistor 37 is R (Ω), then the communication The impedance 2□ between the common connection point A and B of the capacitor 27 on the line 15 is expressed as: Zam=R(2Na)''/Nb''.

Furthermore, by improving the balance of the windings of the center-tapped coil 31, the voltage generated between the two communication lines 15 when voltage is applied by the voltage injection transformer 30 can be adjusted between the communication device under test 11 and the voltage generated between the two communication lines 15. This can be suppressed to a level that does not affect the transmission signal with the opposing communication device 13.

Here, the resistor 39 is the impedance when applying a voltage to the communication device under test 11 in this test circuit (assuming that the common connection point A and the common connection point B are short-circuited, and the connection between that point and the ground) This determines the impedance (as seen in the figure).

This impedance is determined by the vertical circuit of the communication line 15 (communication 81
5-Earth return circuit) is simulated, and the impedance is made equal to the impedance when an induced voltage actually occurs when voltage is applied to the communication device under test 11.

FIG. 2 shows the measured values of the impedance ZAI mentioned above for the circuit in FIG. Here, FIG. 2(a) shows a case where the coil 35 is not provided, and resonance occurs at approximately 1.5 (kHz), and the impedance Z becomes extremely small. Therefore, the transmission signal is short-circuited at the voltage injection transformer 30, increasing transmission loss.

In Fig. 2(b), there is a coil 35, which is connected to 400.
Impedance Z□ when terminated with resistor 37 (Ω)
shows. From this, the impedance ZAl is 1 (k
llz) to 3 (MHz), and has a minimum of 700 (Ω) or more, and a general parallel cable has almost no effect on the transmission signal.

FIG. 3 shows the measured value of impedance ZAI-0 between common connection points A, B and point 0 in FIG. This impedance ZAI-0 is the impedance seen between the common connection point A and the common connection point B, assuming that they are short-circuited and the 0 point, and is 10 (kHz) to 3
(MHz), which is a very small value.

Therefore, it can be seen that the voltage drop at the voltage injection transformer 30 portion when voltage is applied becomes extremely small, and voltage can be efficiently applied to the communication line 15.

FIG. 4 shows the applied voltage characteristics in the first embodiment shown in FIG. 1. Here, in the circuit shown in FIG. Measured values of the voltage V applied to the device 11 (X mark) and the voltage V applied to the opposing communication device 13 (Δ mark) are shown. As can be seen from this characteristic, the voltage Vt applied to the opposing communication device 13 is reduced, especially at high frequencies.

It, 211N FIG. 5 shows a second embodiment of the present invention. This second embodiment further includes a common mode circuit coil 17 and an opposite communication device 13 in addition to the circuit shown in FIG. In between, two capacitors 41 having the same capacitance value as the capacitor 27,
A coil 45 with a center point of the transformer 40 connected to these capacitors 41 and having a center point 43 is provided, and this center point 43 is grounded. Further, a resistor 49 is connected to another coil 47 wound around the same core as the center-tapped coil 45 in order to prevent resonance caused by the capacitor 41. This transformer 40 reduces the impedance between the communication line 15 and the ground and increases the effect of the common mode choke coil 17. Especially, in the low frequency range where the effect of the common mode choke coil 17 is small, the effect of the common mode choke coil 17 is small. It has a large effect of reducing the voltage applied to the device 13.

FIG. 6 shows the applied voltage characteristics in the second embodiment shown in FIG.

In the circuit shown in FIG. 5, when a voltage V. (0 mark) is applied, a voltage V, (
X mark) and the voltage V applied to the opposing communication device 13, (
Δmark) indicates the measured value.

By the way, as shown in FIG. 4, the circuit of the first embodiment can be tested by applying a voltage at a high frequency. On the other hand, as shown in FIG. 6, in the circuit of the second embodiment,
It can be seen that the voltage v2 applied to the opposing communication device 13 is reduced from low frequency to high frequency. Therefore, when the circuit of the second embodiment is used especially at low frequencies, the voltage applied to the opposing communication device 13 can be effectively reduced, making it possible to perform an accurate immunity test.

(2) Summary of Examples As mentioned above, the voltage injection transformer 30 is installed between each pair of signal lines (communication lines 15) between the communication device under test 11 and the opposing communication device 13 that communicates with it. Insert this voltage injection transformer 30 (coil 31 with center tap)
In a test circuit that applies voltage from the midpoint 33, a coil (resonance prevention coil) 35 is wound around the same core as the midpoint tapped coil 31, and an impedance element (resistor 37) is connected to this. The most significant feature is that it prevents resonance between the coil 31 with point taps and the capacitor 27 for preventing inflow of direct current.

Further, a transformer 40 is further provided on the side where the common mode choke coil 17 and the opposite communication device 13 are connected,
The coil 47 of the transformer 40 and the resistor 49 terminating it reduce the voltage applied to the opposing communication device 13 at low frequencies.

In the conventional technology, a resistor 29 is inserted between the center-tapped coil 20 and the communication line 15 in order to prevent resonance of the coil 21, but it is possible to suppress the voltage generated between the communication line 15 and Moreover, in order to increase the voltage applied to the test device in the immunity test, a highly accurate high-power resistor was required.

In contrast, in the embodiment of the present invention, the voltage injection transformer 3
By keeping the windings of the center-tapped coil 31 of 0 well balanced, the voltage generated between the communication lines 15 can be suppressed to a low level. Also, resonance between the center-tapped coil 31 and the capacitor 27 can be prevented. The resistor 37 for this purpose is connected to a coil 35 wound around the same core as the center-tapped coil 31, and the power consumption of this resistor 37 can be small.

Furthermore, the coil 47 of the transformer 40 and the terminating resistor 49 allow the communication device under test 11 to be effectively tested even at low frequencies.

■0 Modifications of the invention It should be noted that the present invention is not limited to the above-mentioned embodiments (,
Those skilled in the art will easily guess that there are various modifications.

〔Effect of the invention〕

As mentioned above, according to the present invention, code errors.

Voltage can be efficiently applied to the communication device under test at a level that does not cause malfunctions, and the voltage applied to the opposing communication device can be suppressed, allowing accurate measurement of the device strength of only the communication device under test. . Also, high power precision resistors are not required.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an immunity test circuit according to an embodiment of the present invention, and FIG. 2 shows the impedance ZA in the circuit shown in FIG.
, FIG. 3 is a common connection point A in the circuit shown in FIG. FIG. 4 is a characteristic diagram showing the impedance ZAI-0 between point B and 0. FIG. 4 is a characteristic diagram of applied voltage in the circuit shown in FIG. 1. FIG. 5 is a configuration of an immunity test circuit according to another embodiment of the present invention. A block diagram, FIG. 6 is a characteristic diagram of applied voltage in the circuit shown in FIG. 5, and FIG. 7 is an explanatory diagram showing a conventional example. In the figure, 11 is the communication device under test, 13 is the opposing communication device, 15 is the communication line, 17 is the common moat coil, 20 is the coil with center point tap, is the voltage generator, is the voltage injection transformer, is the center point is the tapped coil, is the resistor, is the transformer, is the center-tapped coil, and is the resistor. Ini♂−′1″ Varnish υ Goi direct (hΩ) E♂−′l*varnish #l!Light direct (hΩ) Figure frequency 5 skin range (kHz) Figure voltage (c+s,,,) Procedure correction (Own ship Figure 7 1, Indication of the case Patent Application No. 178378 of 1988 2, Name of the invention Immunity test circuit 3, Relationship with the person making the amendment case) Applicant address 1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Number 6 Name (422) Nippon Telegraph and Telephone Corporation 4, Agent 〒1
51 e (03) 375-1631 Address 2-11-2 Yoyogi, Shibuya-ku, Tokyo Specification Φ "Claims column" and "Details of the invention 6, Contents of amendment (1) Scope of claims Make the corrections as shown in the attached sheet. (2) ``In relation to...
...Communication devices" should be corrected to "at least one pair of communication devices in a relationship." (3) "Communication line and...
...Apply" should be corrected to "Apply voltage (vertical voltage) to the communication line." (4) “Voltage (e.g.
...Correct ``Immunity test'' to ``Immunity test for voltage.'' (5) Delete ``Each of'' on page 6, line 9 of the specification. (6) In the 4th line directly below No. 6 of the specification, ``voltage for testing between the midpoint and...'' is corrected to ``voltage for testing with respect to the midpoint.'' (7) On page 7, lines 4 to 6 of the specification, "the midpoint of the coil is placed in a separate coil" is corrected to "in a separate coil wound around the same core as the coil". (8) "In addition,..." in lines 6 to 8 of page 17 of the specification
``It would be...'' is corrected as follows. "In addition, in the embodiment described above, the communication device under test 1
1. Although the opposing communication device 13 is shown connected to the ground, the present invention is not limited to this. For example, it may be connected to the ground of a building. Further, it is not necessary to connect directly to the ground, etc., and in that case, it will be connected to the ground via a so-called stray capacitance. Furthermore, those skilled in the art can easily imagine that there are various modifications to the present invention.'' For a pair of communication devices, in an immunity test circuit in which one communication device to be subjected to a desired test is the communication device under test and the other communication device is the opposite communication device, the communication line interposed between the pair of communication devices is a common mode choke coil that has been subjected to a 21st grade test; a coil with a center point tapped inserted between two conductors of the communication line connecting the common mode choke coil and the communication device under test; A transformer having a tapped coil and another coil wound around the same core, an impedance element connected to the other coil of the transformer, and applying a voltage for testing the midpoint member of the midpoint tapped coil of the transformer. An immunity test circuit characterized in that it is configured to include a voltage supply means for supplying a voltage. (2) A second midpoint tapped coil is interposed between the two conductors of the communication line connecting the common mode choke coil and the opposing communication device, and the second midpoint tapped coil is interposed between the two conductors of the communication line connecting the common mode choke coil and the opposing communication device.
2. The immunity test circuit according to claim 1, wherein the second impedance element is connected to a separate coil wound on the coil.

Claims (2)

[Claims] (1) For at least a pair of communication devices that communicate with each other and operate with a common potential point as a reference, one communication device to be tested is the communication device under test, and the other communication device is the opposite communication device. In an immunity test circuit used as a communication device, a common mode choke coil inserted into each of two conductors of a communication line interposed between the pair of communication devices, and connecting the common mode choke coil and the communication device under test. a transformer having a center-tapped coil interposed between two conductors of the communication line, and another coil wound around the same core as the center-tapped coil; and a transformer connected to the other coil of the transformer. An immunity test characterized by comprising: an impedance element; and a voltage supply means for applying a test voltage between the midpoint of the coil with a midpoint tap of the transformer and the common potential point. circuit. (2) A second midpoint tapped coil is interposed between the two conductors of the communication line connecting the common mode choke coil and the opposing communication device, and the midpoint of the second midpoint tapped coil is is connected to the common potential point, and a second center-tapped coil is connected to another coil wound on the same core as the second center-tapped coil.
2. The immunity test circuit according to claim 1, wherein the immunity test circuit is constructed by connecting impedance elements.