CN212749063U

CN212749063U - Instrument interface device

Info

Publication number: CN212749063U
Application number: CN202020381456.8U
Authority: CN
Inventors: 吴伟; 吴跃佳
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-03-24
Filing date: 2020-03-24
Publication date: 2021-03-19
Anticipated expiration: 2030-03-24

Abstract

An instrument interface device. One end of the other capacitor is the device input end and is connected with an output neutral line of the artificial power supply network, and the other end of the other capacitor is the device output end and is connected with the other test channel of the oscilloscope; the LISN design does not need to be changed, so that the existing LISN product can be matched with an oscilloscope to carry out conducted interference test. Both capacitors had a capacitance <0.09 μ F. The requirement for A/D conversion digit of the oscilloscope is reduced, so that the oscilloscope with low price can be used for EMI test.

Description

Instrument interface device

Technical Field

The invention relates to an instrument interface device, in particular to an interface device between an artificial power supply network and an oscilloscope.

Background

Electronic product designs are designed to meet not only functional requirements but also electromagnetic compatibility (EMC) standard requirements, and therefore, electromagnetic interference (EMI) of products needs to be tested. EMI measurements on products are generally divided into conducted interference measurements and radiated interference tests; the conducted interference test needs to use an artificial power supply network (LISN) to isolate a power supply and a tested device (EUT), and the power supply input end of the LISN is connected with a power supply live wire L and a power supply neutral wire N; the power supply live wire L 'and the power supply neutral wire N' of the power supply output end of the LISN are connected with the EUT, EMI generated by the EUT is conducted to the LISN through the power supply live wire L 'and the power supply neutral wire N', and is output to the testing instrument through the signal output end RF of the LISN.

A commonly used measuring instrument for conducted interference measurements is a spectrometer. The conducted interference test needs to measure the interference voltage of L 'or N' to ground or a protected ground (PE), and since the spectrometer has only one measurement port, usually, the RF port of the LISN is connected to the input port of the spectrometer through a measurement line, and the measurement of L 'to PE and N' to PE is accomplished by toggling a selection switch on the LISN panel, which can be selectively connected to L 'or N'.

Oscilloscope-based time domain EMI measurements have advanced from research into industrial applications in recent years. The EMI measurement by using the oscilloscope instead of the spectrometer can generally shorten the measurement time, can simultaneously measure the EMI of L 'to PE and N' to PE of the EUT by using two test channels of the oscilloscope, and calculates the common mode interference and the differential mode interference of the EUT according to the EMI, and is particularly suitable for the electromagnetic compatibility pre-compatibility test of products. However, the single RF output port of the conventional LISN product and the operating mode of the toggle switch cannot meet the requirement of multi-channel measurement of the oscilloscope, and a method and a device for meeting the requirement of multi-channel measurement of the oscilloscope need to be designed.

Disclosure of Invention

The technical problem that this application actually solved is to design a method and device that satisfies the multichannel measurement requirement of oscilloscope, adopt following technical scheme to realize, include:

an interface method for an artificial power network and an oscilloscope, comprising:

connecting an output end power supply of the artificial power supply network with one end of a capacitor, and connecting the other end of the capacitor with an oscilloscope test port; the capacitance of said capacitor is <0.09 muF.

The interface method is characterized in that the output power supply of the artificial power supply network comprises a live wire or a neutral wire.

The interface method is characterized in that the other end of the capacitor is connected with an oscilloscope test port, and the oscilloscope test port is connected after the capacitor is connected with a resistor in series.

The interface method is characterized in that the other end of the capacitor is connected with an oscilloscope test port, and the method comprises the step of directly connecting with the oscilloscope test port.

The interface method is characterized in that the other end of the capacitor is connected with one end of a resistor, and the other end of the resistor is connected with the ground or a protective ground; the resistance is an option.

An interface device for an artificial power network and an oscilloscope, comprising:

one end of the other capacitor is the device input end and is connected with an output neutral line of the artificial power supply network, and the other end of the other capacitor is the device output end and is connected with the other test channel of the oscilloscope; the capacity of the two capacitors is less than 0.09 muF.

The interface device is characterized in that one end of the capacitor connected with the output end of the device is connected with a resistor in series and then is connected with the ground or a protective ground; the resistance value of the resistor is greater than 200 ohms.

The interface device is characterized in that a resistor is not connected in series between one end of the capacitor connected with the output end of the device and the ground or the protective ground.

The interface device is characterized in that the device is integrated and connected with an artificial power supply network and an oscilloscope.

The self-integrated interface device can be carried about, and can conveniently connect the existing artificial power network product to the oscilloscope without transforming the artificial power network product.

The interface device is characterized in that the device is integrated with an artificial power supply network to form the artificial power supply network with the function of being connected with the oscilloscope.

The technical scheme for integrating the interface device with the artificial power supply network ensures that the integrated artificial power supply network can be connected with an oscilloscope and a traditional frequency spectrograph, and the application range of the artificial power supply network is expanded.

IEC publication CISPR16-1-2 and corresponding Chinese standard GB/T6113.102-2008/CISPR 16-1-2: 2006 make standard regulations on the isolation and output impedance curves of the LISN, and provide an LISN electrical schematic diagram capable of meeting the standard indexes, wherein element parameters determine the output impedance curves of the LISN. The LISN manufacturers are all following these electrical schematic diagrams and their parameters to produce LISNs that meet the standards.

The capacitance of the capacitor should be greater than or equal to 0.1 muf, by the stated standard. However, the inventor misuses a capacitor of 0.01 μ F when manufacturing the interface, but unexpectedly finds that 1, an oscilloscope which originally requires an a/D converter with more than 12 bits can meet the measurement requirement of a low-cost oscilloscope which uses an a/D converter with 8 bits, and 2, the impedance is increased due to the reduction of the capacitor capacity, the overshoot signal amplitude of the input oscilloscope is compressed, and the risk of the oscilloscope being damaged due to overload of the input signal is reduced. Through simulation calculations and experimental verification, the inventors have determined that controlling the capacitance of the capacitor to <0.09 μ F achieves both of the above unexpected benefits. The principle is as follows:

the capacitance of the existing LISN product is greater than or equal to 0.1 muf. Because the voltage of the measured signal is higher when the measured signal reaches the test port of the oscilloscope after being reduced by the capacitor, for the oscilloscope with 8 grids of vertical scales, the vertical scales are required to be set in the measuring range of at least 1V of each grid, otherwise, the signal is intercepted and the interference signal is lost. At this time, since the 8 th power of 2 is equal to 256, the oscilloscope of an 8-bit a/D converter has a vertical resolution of 1VX8/256=31.25mV at a scale of 1V/grid, that is, it is impossible to recognize a disturbance having an amplitude of <31.25 mV. Generally, the minimum amplitude of electromagnetic interference generated by a device to be tested is less than 10mV, so that an oscilloscope with a/D conversion bit number >8, for example, an oscilloscope with a 12-bit a/D converter, is required, and since the 12 th power of 2 is 4096, under the same condition, the vertical resolution of the oscilloscope with the 12-bit a/D converter is 1VX8/4096=1.95mV, that is, the interference with the amplitude >1.95mV can be recognized. However, oscilloscopes that employ 12-bit A/D converters are typically quite expensive.

If we reduce the capacitance of the capacitor, so that the maximum voltage (usually occurring at 50 Hz) reaching the testing port of the oscilloscope through the capacitor is reduced, the oscilloscope will not generate clipping in the range with the vertical scale below 1V/grid, or will not influence the EMI test even if the clipping is slight. For example, an oscilloscope using an 8-bit a/D converter and setting the vertical scale to 0.2V/grid, would recognize a minimum signal amplitude of 0.2VX8/256=6.25 mV. And because the amplitude of the signal reaching the test port of the oscilloscope is reduced to 1/5, the risk of damage of the oscilloscope caused by overload of the input signal is reduced. Based on the principle, the vertical resolution of the oscilloscope can be improved by reducing the capacity of the capacitor so as to meet different EMI test requirements.

Through simulation calculation and test verification, the capacitance of the capacitor is controlled to be less than 0.09 mu F, and the oscilloscope with the 8-bit A/D converter can meet the requirement of conducted interference test. The interface method and device for the LISN to the oscilloscope customized according to the technical scheme not only realize the connection of the LISN to the oscilloscope, but also enable the oscilloscope with low price to be applied, and reduce the cost of a test system.

Advantageous effects

The method and the device disclosed by the application have the beneficial effects that:

1. the LISN design does not need to be changed, so that the existing LISN product can be matched with an oscilloscope to carry out conducted interference test.

2. A portable device can be made for connection of the LISN to the oscilloscope.

3. The LISN can be integrated with the LISN into a whole, so that the LISN can be used for testing a traditional frequency spectrograph and can also be used for testing an oscilloscope.

4. The requirement of A/D conversion digit of the oscilloscope is reduced, so that the low-price oscilloscope can be used for EMI test.

5. The signal amplitude of the input oscilloscope is reduced, and the risk of the oscilloscope damage caused by signal overload is reduced.

Drawings

FIG. 1 is a schematic diagram of a method disclosed herein;

FIG. 2 is a schematic diagram of the disclosed apparatus.

Detailed Description

The present application will be described in further detail with reference to the following drawings and examples.

Fig. 1 is a schematic diagram of an interface method disclosed herein. The interface method for the artificial power supply network and the oscilloscope disclosed by the application specifically comprises the following steps:

connecting a live wire or a neutral wire of an output end power supply of the artificial power supply network with one end of a capacitor C, namely a port 1 in the figure 1, and connecting the other end of the capacitor C, namely a port 3 in the figure 1, with a test port of an oscilloscope; the test circuit can be directly connected with an oscilloscope test port or connected with the oscilloscope test port through a resistor; the capacitance of said capacitor C is <0.09 μ F. The resistor R between the port 3 and the port 2 (4) in fig. 1 is a leakage resistor for discharging the charge on the capacitor C, and the resistance value is greater than 200 ohms to avoid causing too large influence on the input impedance of the oscilloscope; the resistor R may be disconnected.

Ports

2 and 4 are connected to ground or Protective Earth (PE), and

ports

2 and 4 may be eliminated if resistor R is eliminated.

The working principle of the method and apparatus disclosed in the present application is further explained below with reference to fig. 2 and the examples.

Example 1

As shown in fig. 2, the capacitor C is connected in series with the resistor R and then connected with the

terminals

2 and 3 and 1 and 3, and the

terminals

3 and 6 are connected; the connection points of the two capacitors C and the resistor R are respectively connected with

terminals

4 and 5, thus forming an interface device of the LISN to the oscilloscope, wherein the capacitor C has the capacity of less than 0.09 muf, and the resistor is an option and can be eliminated. In this embodiment, the capacitance C is 0.082 μ F, and the resistance R is 1000 ohm. The connection of the input end of the device to the LISN output power supply is completed by respectively connecting the

ports

1, 2 and 3 to the L, N and PE connectors of a three-pin power plug (not shown in the figure), inserting the power plug into the socket connected with the LISN output power supply, and inserting the input power plug of the EUT into the same socket. And, the

output ports

5 and 6 of the device are connected to a BNC socket (not shown in the figure), wherein the port 5 is connected to the inner core of the BNC, and the port 6 is connected to the outer shell of the BNC; connecting the

output ports

4 and 6 to another BNC socket (not shown), wherein the port 4 is connected to the inner core of the BNC and the port 6 is connected to the outer shell of the BNC; the 2 BNC sockets are respectively connected with the 2 test channels of the oscilloscope through cables, thereby completing the connection of the device to the oscilloscope.

In the embodiment, conducted interference in a frequency range of 150kHz-30MHz is measured, a capacitor C adopted by an interface device has non-negligible impedance at a low frequency end, so that a measured value is low, and the smaller the capacitance of the capacitor C is, the wider the frequency range of influence is, so that subsequent processing needs to be carried out on a measurement result of an oscillograph, and corresponding compensation is calculated; the calculation of this compensation is known to those skilled in the art and is not given here.

In the implementation process of this embodiment, the following comparative tests are also performed to verify the effects of the present invention:

test 1, the capacitance C of the capacitor is 0.1 μ F, the vertical scale of the oscilloscope needs to be set to 1V/grid under the condition of the noise level of the common office environment, and the electromagnetic interference amplitude measured by using the oscilloscope with the 8-bit a/D converter is obviously lower; normal amplitude emi was obtained using another oscilloscope measurement with a 12-bit a/D converter. And storing the test result.

In experiment 2, the capacitance C was 0.082 μ F, and in the same test site, an oscilloscope with an 8-bit a/D converter was used, since the maximum amplitude of the output signal of the device was reduced after changing the capacitance, the vertical scale of the oscilloscope was set to 0.2V/cell, and the measurement result was similar to that of experiment 1 using the oscilloscope with the 12-bit a/D converter.

Comparing test 1 and test 2, we find that both realize the connection between the oscilloscope and the LISN, and solve the technical problem to be solved by the present invention, but test 2 can use the low-cost oscilloscope with 8-bit a/D converter to complete the required test because the capacity of the capacitor C is reduced; in addition, the amplitude of the signal input into the testing port of the oscilloscope is reduced due to the reduction of the capacity of the capacitor C, so that the risk of the oscilloscope damage caused by signal overload is reduced; the unexpected technical effect is obtained.

Example 2

This example is the same as example 1, but with the resistor R eliminated.

Example 3

This embodiment is the same as embodiment 1, but the device is mounted inside or on the LISN, integrated with the LISN, and the capacitance C capacity is further reduced to 0.068 μ F. The test method is used for the electromagnetic compatibility pre-compatibility test of products, and the test result is similar to that of a standard laboratory.

Example 4

This embodiment is the same as embodiment 1, but the

device output ports

4 and 5 are connected to the input of the oscilloscope through resistors. Also, the capacitance of the capacitor C is <0.09 μ F, and the resistance is an option.

The foregoing is directed to embodiments of the present invention, and not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims

1. An instrument interface device, comprising:

2. The instrument interface device of claim 1 wherein said device output is connected in series with a resistor to ground or a protective earth; the resistance value of the resistor is greater than 200 ohms.

3. The instrument interface device of claim 1 wherein said device output is not connected in series with ground or a protective earth.

4. The instrument interface device of claim 1 wherein said device is connected to an artificial power network and an oscilloscope.

5. The instrument interface device of claim 1, wherein said device is installed in or on an artificial power network, integrated with the artificial power network, to form an artificial power network with oscilloscope interface function.