JP2012026952A - Noise measurement cable and noise measurement apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise measurement cable, which is used for a WBFC approach, capable of suppressing deterioration of measurement sensitivity by suppressing mismatching of a characteristic impedance even in the case where a distance between a measurement target and a housing bottom surface is changed.SOLUTION: A noise measurement cable 1 includes a line 10 connecting a measurement target 120 and connectors 60, 61 mounted at a position in which a height from a bottom surface 111 of a housing 110 is lower than the measurement target 120, and a dielectric body 20 disposed between the line 10 and the housing bottom surface 111. The dielectric body 20 is formed to become thicker as the dielectric body 20 gets closer from the connectors 60, 61 to the measurement target 120, namely, as the distance between the line 10 and the housing bottom surface 111 becomes longer. End portions of the line 10 are connected with the connectors 60, 61 via five chip resistors 40 which are connected in parallel with one another.

Description

  The present invention relates to a noise measurement cable and a noise measurement device, and in particular, for measuring a common mode voltage generated between a casing and a measurement object by arranging the measurement object inside a conductive casing. The present invention relates to a noise measurement connection cable and a noise measurement apparatus using the noise measurement connection cable.

  In IEC (International Electrotechnical Commission), a work bench Faraday cage method (hereinafter referred to as “WBFC method”) that enables easy measurement of common mode noise without using a large-scale measurement field such as an anechoic chamber. (For example, see Patent Document 1). Here, in the WBFC method, a measurement object (EUT: Equipment Under Test) is placed in a conductive housing (WBFC), and the measurement object is operated with respect to the absolute reference potential of the housing. In this method, a common mode voltage (electromagnetic wave noise) generated at a reference potential of an object is measured by a measuring instrument provided outside the casing. The specification is defined in “IEC 62132-5”.

  In the WBFC method, an object to be measured is connected to a noise measurement connection cable that is a 150Ω transmission system, and is connected to a 50Ω measurement device via a 100Ω resistor for impedance conversion. At that time, in order to keep the characteristic impedance at a specified value (150Ω), IEC62132-5 specifies that the measurement object and the noise measurement cable are arranged at a height of 30 mm from the bottom of the housing.

JP 2003-307535 A

  By the way, when the size of the measurement object is increased, the capacitance formed between the measurement object and the bottom surface of the housing may increase, and the characteristic impedance may be lower than a specified value (150Ω). On the other hand, the distance between the measurement object and the bottom surface of the housing is increased so that the characteristic impedance becomes a specified value (150Ω), that is, the height of the measurement object is increased, and the measurement object and the bottom surface of the housing are increased. It is conceivable to reduce the capacitance formed between the two. However, when the height of the measurement object is increased, the end of the noise measurement cable that connects the measurement object and the connector attached to the housing is also lifted. Here, as described above, the noise measurement cable is designed so that the characteristic impedance becomes a specified value (150Ω) when the height from the bottom surface of the housing is 30 mm. For this reason, when one end of the noise measurement cable is lifted, the characteristic impedance of the noise measurement cable increases beyond 150Ω. As a result, characteristic impedance mismatch between the measurement object and the measurement sensitivity may be deteriorated.

  The present invention has been made to solve the above-described problems. A measurement object is arranged inside a conductive casing, and a common mode voltage generated between the casing and the measurement object is measured. This is a noise measurement cable that is used for this purpose, and even if the distance between the object to be measured and the bottom of the housing changes, the mismatch of characteristic impedance is suppressed and the deterioration of measurement sensitivity is suppressed. It is an object of the present invention to provide a noise measurement cable that can be used, and a noise measurement device using the noise measurement cable.

  The noise measurement cable according to the present invention is a noise measurement cable that is used to place a measurement object inside a conductive casing and measure a common mode voltage generated between the casing and the measurement object. A cable having a distance between the bottom surface of the housing and the measurement target and a conductive thin plate-like line connecting the connector attached to the housing, and between the track and the housing The thickness in the direction perpendicular to the bottom surface of the housing is changed according to the distance between the line and the housing so that the characteristic impedance becomes a specified value. A dielectric is formed.

  As described above, when the distance from the bottom surface of the measurement object is changed in order to suppress the change in the capacitance between the measurement object and the bottom surface of the housing, the noise measurement cable One end is lifted. Here, according to the cable for noise measurement according to the present invention, the thickness of the dielectric disposed between the line and the casing can be changed according to the distance between the line and the casing. Therefore, the mismatch of the characteristic impedance of the noise measurement cable can be eliminated, and the characteristic impedance can be adjusted to the specified value (150Ω). As a result, even when the distance between the measurement object and the bottom surface of the housing changes, it is possible to suppress the deterioration of measurement sensitivity. In addition, since the electromagnetic noise of a specific frequency radiated from the measurement object is absorbed by the dielectric, the measurement accuracy can be improved.

  In the noise measurement cable according to the present invention, the line connects the measurement object and a connector installed at a position closer to the bottom surface of the housing than the measurement object, and the dielectric is It is preferably disposed between the track and the bottom surface of the housing, and formed so that the thickness gradually increases as the measurement object is approached from the connector.

  For example, as described above, when the distance between the bottom surface of the housing and the measurement object is increased in order to adjust the characteristic impedance of the measurement object having a large size to a specified value (150Ω) (that is, the measurement object When the height is increased), the characteristic impedance of the noise measurement cable increases from the specified value. Here, according to the cable for noise measurement according to the present invention, the thickness of the dielectric disposed between the track and the bottom surface of the housing gradually increases as the measurement object placed at a higher position is approached. It is formed to be thick. Therefore, the characteristic impedance can be adjusted to the specified value (150Ω) at any position of the noise measurement cable. As a result, it is possible to eliminate the degree of mismatch of characteristic impedance even for a measurement object having a large size, and to suppress deterioration in measurement sensitivity.

  The noise measurement cable according to the present invention is a noise measurement cable that is used to place a measurement object inside a conductive casing and measure a common mode voltage generated between the casing and the measurement object. A cable having a distance between the bottom surface of the housing and the measurement target and a conductive thin plate-like line connecting the connector attached to the housing, and between the track and the housing The dielectric is formed by changing the dielectric constant according to the distance between the line and the housing so that the characteristic impedance becomes a specified value. And

  According to the noise measurement cable according to the present invention, the dielectric constant of the dielectric disposed between the line and the housing can be changed according to the distance between the line and the housing. Therefore, the mismatch of the characteristic impedance of the noise measurement cable can be eliminated and the characteristic impedance can be adjusted to a specified value. As a result, even when the distance between the measurement object and the bottom surface of the housing changes, it is possible to suppress the deterioration of measurement sensitivity. In addition, since the electromagnetic noise of a specific frequency radiated from the measurement object is absorbed by the dielectric, the measurement accuracy can be improved.

  In the noise measurement cable according to the present invention, the line connects the measurement object and a connector installed at a position closer to the bottom surface of the housing than the measurement object, and the dielectric is It is preferable that the dielectric constant is disposed between the track and the bottom surface of the housing, and the dielectric constant increases as the measurement object approaches from the connector.

  According to the noise measurement cable according to the present invention, the dielectric constant of the dielectric disposed between the line and the bottom surface of the housing increases as the measurement object placed at a higher position is approached. Is formed. Therefore, the characteristic impedance can be adjusted to the specified value (150Ω) at any position of the noise measurement cable. As a result, it is possible to eliminate the degree of mismatch of characteristic impedance even for a measurement object having a large size, and to suppress deterioration in measurement sensitivity.

  The end of the line is preferably connected to the connector via a plurality of chip resistors connected in parallel to each other.

  In this way, the characteristic impedance of the cable body can be specified. Further, since the chip resistor is small and leadless, the influence of the inductance on the characteristic impedance of the noise measurement cable can be reduced as compared with the insertion mounting type resistor having leads.

  In the noise measurement cable according to the present invention, it is preferable that the line forms a microstrip line having a specified characteristic impedance by the bottom surface of the housing and the dielectric.

  In this way, by applying the microstrip line design method, it is possible to easily set the thickness of the dielectric or the dielectric constant, that is, the characteristic impedance of the line.

  The noise measurement cable according to the present invention preferably further includes a second dielectric disposed so as to face the dielectric across the line.

  In this case, electromagnetic noise of a specific frequency radiated from a measurement object or the like is absorbed by two dielectrics arranged opposite to each other across the line, so that electromagnetic noise can be prevented from entering the line. Measurement accuracy can be improved.

  A noise measuring device according to the present invention includes a conductive housing in which a measurement object is disposed, a connector attached to the housing, and any one of the noise measurement cables that connects the measurement object and the connector. It is characterized by providing.

  According to the noise measurement device of the present invention, since any one of the above noise measurement cables is provided, the noise measurement cable can be used even when the distance between the measurement object and the bottom surface of the housing changes. And the characteristic impedance of the measurement object can be adjusted to a specified value (150Ω). Therefore, it is possible to eliminate the degree of mismatch of characteristic impedance, and to suppress deterioration of measurement sensitivity.

  According to the present invention, in a noise measurement cable used for measuring a common mode voltage generated between a casing and a measuring object, the measuring object is placed inside a conductive casing. Even when the distance between the object and the bottom surface of the housing changes, it is possible to suppress mismatch in characteristic impedance and suppress deterioration in measurement sensitivity.

It is a longitudinal section showing typically the composition of the noise measuring device using the cable for noise measurement concerning a 1st embodiment. It is a top view which shows the structure of the cable for noise measurement which concerns on 1st Embodiment. It is a perspective view which shows typically the evaluation model using the cable for noise measurement concerning 1st Embodiment used for the measurement of reflection amount. It is a perspective view which shows typically the evaluation model which concerns on the comparative example 1 used for the measurement of reflection amount. It is a perspective view which shows typically the evaluation model which concerns on the comparative example 2 used for the measurement of reflection amount. It is a graph which shows the measurement result of the reflection amount of the evaluation model which concerns on 1st Embodiment, and the evaluation model which concerns on the comparative example 1 and the comparative example 2. FIG. It is a side view which shows typically the structure of the cable for noise measurement which concerns on 2nd Embodiment. It is a side view which shows typically the structure of the cable for noise measurement which concerns on 3rd Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted.

(First embodiment)
First, the configuration of the noise measurement cable 1 according to the first embodiment and the configuration of the noise measurement device 100 using the noise measurement cable 1 will be described with reference to FIGS. 1 and 2 together. FIG. 1 is a longitudinal sectional view schematically showing a configuration of a noise measuring device 100 in which a noise measuring cable 1 is used. FIG. 2 is a plan view showing the configuration of the noise measurement cable 1.

  The noise measuring apparatus 100 includes two noise measuring cables 1 and 1 and a housing 110 that houses a measurement object 120 therein. Details of the noise measuring cable 1 will be described later. The housing 110 is a conductive housing formed of a metal material such as iron or copper, and a known WBFC can be used. The housing 110 is grounded, and the bottom surface 111 of the housing 110 is set to the system ground (reference potential).

  A measurement object 120 such as an electronic device or a circuit board is accommodated inside the housing 110 so as to be parallel to the bottom surface 111 of the housing 110. In IEC62132-5, the distance from the bottom surface 111 of the housing 110 to the measurement object 120, that is, the height from the bottom surface 111 on which the measurement object 120 is arranged is used to maintain the characteristic impedance at a specified value (150Ω). 30 mm. However, when the size of the measurement object 120 is large, the capacitance formed between the measurement object 120 and the bottom surface 111 of the housing 110 increases, and the characteristic impedance falls below a specified value (150Ω). As a result, a mismatch occurs between the connected 150Ω noise measurement cable. Therefore, as shown in FIG. 1, in the present embodiment, the height at which the measurement object 120 is arranged is increased (for example, 50 mm) so that the characteristic impedance is 150Ω, and the measurement object 120 and the bottom surface of the casing 110 are increased. The electrostatic capacitance formed between the two is lowered.

  One end of the line 10 constituting the first noise measurement cable 1 is connected to one reference potential portion (common mode point) 121 of the measurement object 120 by, for example, soldering or copper foil tape. The other end of the line 10 is connected to a connector 60 attached to the side surface of the housing 110 via five chip resistors 40 connected in parallel to each other. Here, the connector 60 is attached to a position where the height from the bottom surface 111 of the housing 110 is 30 mm. Therefore, the line 10 connecting the measurement object 120 and the connector 60 is arranged so that the height from the bottom surface 111 of the housing 110 increases as the measurement object 120 side approaches from the connector 60 side. Note that a 50 ohm termination resistor 130 is attached to the connector 60 outside the housing 110.

  One end of the line 10 constituting the second noise measurement cable 1 is connected to the other reference potential portion (common mode point) 122 of the measurement object 120 by, for example, soldering or copper foil tape. The other end of the line 10 is connected to a connector 61 attached to the side surface of the housing 110 via five chip resistors 40 connected in parallel to each other. Here, the connector 61 is attached at a position where the height from the bottom surface 111 of the housing 110 is 30 mm. Therefore, the line 10 connecting the measurement object 120 and the connector 61 is arranged so that the height from the bottom surface 111 of the housing 110 increases as the measurement object 120 side approaches from the connector 61 side. Note that a measuring instrument (not shown) such as a network analyzer disposed outside the housing 110 is connected to the coaxial connector 61 through a coaxial cable 140.

  As described above, a loop is formed between the measurement object 120 and the housing 110 via the two noise measurement cables 1 and 1, and common mode noise (common mode voltage) flowing through the loop is measured. To the vessel. Note that a power cable, a signal cable, and the like are connected to the measurement object 120 as necessary so that the measurement object 120 can be operated in the housing 110.

  Next, the configuration of the noise measurement cable 1 will be described in detail. As described above, the noise measurement cable 1 is a noise measurement connection cable used in WBFC. More specifically, in the noise measurement cable 1, the measurement object 120 is disposed inside the conductive casing 110, and the measurement object 120 is operated with the measurement object 120 being operated. This is a connection cable used to connect the reference potential portions 121 and 122 of the measurement object 120 and the external termination resistor 130 or a measuring instrument when measuring a common mode voltage (noise) generated therebetween.

  The noise measuring cable 1 includes a thin plate-like line 10 having a rectangular cross section made of, for example, a metal material mainly composed of copper. As shown in FIG. 2, the line 10 is formed in a strip shape having a constant line width when viewed in plan. More specifically, the line width of the line 10 is formed such that the characteristic impedance becomes a specified value (150Ω) when the distance from the bottom surface 111 of the housing 100 is set to 30 mm, for example. One end of the line 10 is electrically connected to the measurement object 120 by, for example, soldering or copper foil tape, and the other end is connected to the casing 110 via five chip resistors 40 connected in parallel to each other. Are connected to connectors 60 and 61 attached to the side surfaces of

A dielectric 20 is disposed between the line 10 and the bottom surface 111 of the housing 110 so as to be in contact with the lower surface of the line 10. The dielectric 20 is made of a dielectric material such as rubber, plastic, or ceramic. The material of the dielectric 20 is not particularly limited. In the present embodiment, rubber having a dielectric constant ε _r of 3 is used.

  As shown in FIG. 2, the dielectric 20 has a rectangular shape in which the lateral width is the same as one side of the measurement object 120 and the longitudinal length is the same as the longitudinal length of the line 10 when viewed in plan. Is formed. On the other hand, as shown in FIG. 1, the dielectric 20 has a direction (height) perpendicular to the bottom surface 111 of the housing 110 as it approaches the measurement object 120 from the connector 60, 61 side when viewed from the side. (Direction) is gradually increased. Here, as described above, the track 10 is arranged so that the height from the bottom surface 111 of the housing 110 increases as the distance from the connector 60, 61 side approaches the measurement object 120 side. Therefore, the dielectric 20 is formed so that the thickness increases as the distance between the line 10 and the bottom surface 111 of the housing 110 increases (that is, the height from the bottom surface 111 of the line 10 increases). .

Here, the method for setting the thickness of the dielectric 20 will be described more specifically. The line 10 forms a microstrip line whose characteristic impedance is a specified value (150Ω) by the bottom surface 111 of the housing 110 and the dielectric 20. The characteristic impedance Z ₀ of the microstrip line is obtained by the following formula (1) (2) or (3) (4), where W is the line width and h is the thickness of the dielectric 20. Therefore, from the following formulas (1), (2), (3), and (4), the thickness h of the dielectric 20 at which the characteristic impedance becomes the specified value (150Ω) can be calculated backward.

ただし、ε_ｒｅは実効比誘電率、ε_ｒは比誘電率である

However, ε _re effective dielectric constant, is ε _r is the relative dielectric constant

  Thus, by setting the thickness h and the line width W of the dielectric 20 based on the microstrip line theory, the characteristic impedance matches the specified value (150Ω) at any position of the noise measurement cable 1. Adjusted to

  Five chip resistors 40 connected in parallel to each other are connected to the other end of the line 10, and the line 10 is attached to the side surface of the housing 110 via these chip resistors 40. Connected to connectors 60 and 61. These chip resistors 40 are for specifying the characteristic impedance of the cable body, and the resistance value of each chip resistor 40 is set to 510Ω (and thus the combined resistance value is about 100Ω). Note that the noise measurement cable 1 (dielectric 20) is preferably supported by, for example, polystyrene foam.

  When used in the WBFC, as described above, one end of the line 10 constituting the noise measurement cable 1 is soldered to the reference potential portions 121 and 122 of the measurement object 120 arranged inside the housing 110. It is connected with adhesive copper foil tape. On the other hand, the other end of the line 10 is connected to the connectors 60 and 61 attached to the side surface of the housing 110 via the chip resistor 40, and the termination resistor 130 outside the housing is connected via the connectors 60 and 61. Alternatively, it is connected to a measuring instrument (not shown) such as a network analyzer.

  In the WBFC method, common mode noise (common mode voltage) generated in the reference potential of the measurement target 120 with respect to the absolute reference potential of the casing 110 in a state where the measurement target 120 is operated in the sealed casing 110. ) Is measured by a measuring instrument provided outside the housing 110.

  Here, in order to evaluate the consistency of the characteristic impedance of the noise measurement cable 1 according to the present embodiment, the WBFC method is simulated, the presence / absence of a dielectric material, and the size and height of the measurement object are changed. The reflection amount (S11) indicating impedance matching was measured. Subsequently, referring to FIGS. 3 to 6 together, the characteristic impedance matching (reflection amount) of the noise measurement cable 1 according to the present embodiment and the noise measurement cables according to Comparative Example 1 and Comparative Example 2 are compared. The measurement results will be shown and described.

  An evaluation noise measurement device (evaluation model) used for the measurement of the reflection amount (S11) is shown in FIGS. 3 to 5, the side surface and the upper surface (lid portion) of the housing are omitted in order to make the internal configuration easy to see. FIG. 3 is a perspective view schematically showing an evaluation model in which the noise measurement cable 1 according to the embodiment is used. FIG. 4 is a perspective view schematically showing an evaluation model according to Comparative Example 1 in which a noise measurement cable having no dielectric is connected to a large measurement object. FIG. 5 is a perspective view schematically showing an evaluation model according to Comparative Example 2 in which a noise measurement cable having no dielectric is connected to a measurement object having an appropriate size.

  As shown in FIG. 3, in the evaluation model according to the embodiment, a rectangular measuring object 120 having a relatively large size and having a horizontal width of 31.3 mm and a vertical length of 30 mm was used. The measurement object 120 was placed at a height of 50 mm from the bottom surface 111 so that the theoretical value of the characteristic impedance was 150Ω. On the other hand, the connectors 60 and 61 were attached to a height of 20 mm from the bottom surface 111. Then, one end of the line 10 constituting the noise measurement cable 1 formed of a copper plate is connected to the measurement object 120, and the other end is connected in parallel to each other so that the combined resistance value is about 100Ω. The connectors 60 and 61 were connected via two chip resistors 40. That is, the line 10 constituting the noise measuring cable 1 is disposed so as to be inclined so that the height from the bottom surface 111 is 20 mm (connector end) to 50 mm (measurement object end). Further, the line 10 is formed in a belt shape having a constant line width of 11.6 mm and a length of 50 mm.

A dielectric 20 is disposed between the line 10 and the housing bottom surface 111 so as to be in contact with the lower surface of the line 10. Here, the dielectric 20 was made of rubber having a dielectric constant ε _r of 3. The dielectric 20 has a triangular prism shape having a width of 31.3 mm, a length of 50 mm, and a thickness of 0 mm (connector end) to 35.5 mm (measurement object end), and the theory of characteristic impedance of the noise measurement cable 1. It formed so that a value might be set to 150Ω. Further, a 50Ω termination resistor 130 was connected to one connector 60, and a network analyzer (not shown) was connected to the other connector 61.

  As shown in FIG. 4, in the evaluation model according to Comparative Example 1, a rectangular measurement object 120 having a relatively large size and having a horizontal width of 31.3 mm and a vertical length of 30 mm was used. The measurement object 120 was placed at a height of 50 mm from the bottom surface 111 so that the theoretical value of the characteristic impedance was 150Ω. On the other hand, the connectors 60 and 61 were attached to a height of 20 mm from the bottom surface 111. Then, one end of a noise measurement cable (line) formed from a copper plate is connected to the measurement object 120, and the other end is connected to each other in parallel so that the combined resistance value is about 100Ω. The connectors 60 and 61 were connected via the container 40. That is, the noise measurement cable (line) is disposed so as to be inclined so that the height from the bottom surface 111 is 20 mm (connector end) to 50 mm (measurement object end). The noise measurement cable (line) was formed in a strip shape (the theoretical value of the characteristic impedance was 150Ω to 209Ω) with a constant line width of 11.6 mm and a length of 50 mm. Further, a 50Ω termination resistor 130 was connected to one connector 60, and a network analyzer (not shown) was connected to the other connector 61. Note that no dielectric is disposed between the noise measurement cable (line) and the bottom surface 111 of the housing.

  As shown in FIG. 5, in the evaluation model according to Comparative Example 2, a rectangular measuring object 120 </ b> D having an appropriate size of 11.6 mm in width and 30 mm in length formed from a copper plate is measured from the bottom surface 111 to 20 mm. Arranged at a height (theoretical value of characteristic impedance is 150Ω). Further, the connectors 60 and 61 were attached to a height of 20 mm from the bottom surface 111. Then, one end of a noise measurement cable (line) formed from a copper plate is connected to the measurement object 120D, and the other end is connected to each other in parallel so that the combined resistance value is about 100Ω. The connectors 60 and 61 were connected via the container 40. The noise measurement cable (line) was formed in a strip shape (the theoretical value of the characteristic impedance was 150Ω) having a constant line width of 11.6 mm and a length of 50 mm. Further, a 50Ω termination resistor 130 was connected to one connector 60, and a network analyzer (not shown) was connected to the other connector 61.

  In the state of being connected as described above, S11 (reflection amount) of the S parameter was measured by a network analyzer, and the consistency of the characteristic impedance and the estimated measurement sensitivity were evaluated. S11 indicates a signal reflected to port 1 when a signal is input from port 1 (connector 61 on the network analyzer side), that is, a reflection coefficient of port 1.

  FIG. 6 shows the measurement results of the reflection amount (S11) of the evaluation model according to the embodiment described above and the evaluation models according to Comparative Example 1 and Comparative Example 2. The horizontal axis of the graph shown in FIG. 6 is the frequency (MHz), and the vertical axis is the reflection amount (S11). In the graph of FIG. 6, the measurement result (S11) of the evaluation model according to the embodiment is a solid line, the measurement result (S11) of the evaluation model according to Comparative Example 1 is a broken line, and the evaluation model measurement according to Comparative Example 2 is measured. The results (S11) are indicated by alternate long and short dash lines.

  As shown by the one-dot chain line in FIG. 6, in the comparative example 2 (see FIG. 5) in the matching state, the reflection amount is about −3.4 dB up to about 500 MHz (in terms of impedance (from the network analyzer side), about 250Ω). ), A substantially flat characteristic was obtained. That is, in Comparative Example 2, it is considered that the characteristic impedance is matched in the region up to about 500 MHz, and the measurement sensitivity is hardly deteriorated.

  On the other hand, as shown by a broken line in FIG. 6, in Comparative Example 1 (see FIG. 4) in which the size and height of the measurement target 120 </ b> D are changed with respect to Comparative Example 2, as a result of the mismatch in characteristic impedance, The amount of reflection started to increase from around 50 MHz, and the amount of reflection increased greatly in the region of 100 to 500 MHz than the result of Comparative Example 2 described above. Therefore, in Comparative Example 1, there is a possibility that the measurement sensitivity deteriorates in the high frequency region.

  As shown by a solid line in FIG. 6, in this embodiment (see FIG. 3), the amount of reflection in the vicinity of 100 to 500 MHz increased in Comparative Example 1 is suppressed, and although some resonance is seen, Comparative Example 2 Near flat characteristics were obtained. This is considered because the characteristic impedance mismatch was eliminated and the amount of reflection could be reduced by inserting the dielectric 20 formed so that the thickness increased as the distance between the line 10 and the bottom surface 111 increased. It is done.

  From the above results, the noise measurement cable 1 according to the present embodiment has a measurement sensitivity even when the size and height of the measurement object are changed as compared with the noise measurement cable having no dielectric. It was confirmed that the degradation of the can be suppressed.

  According to the present embodiment, as the distance between the track 10 and the bottom surface 111 of the housing 110 increases, that is, as the height of the track 10 from the housing bottom surface 111 increases, the relationship between the track 10 and the housing bottom surface 111 increases. The dielectric 20 disposed therebetween is formed so as to have a large thickness. Therefore, the mismatch of the characteristic impedance of the noise measuring cable 1 can be eliminated, and the characteristic impedance can be adjusted to the specified value (150Ω). As a result, even if the distance between the measurement object 120 and the housing bottom surface 111 is changed, it is possible to suppress deterioration in measurement sensitivity. Further, according to the present embodiment, the electromagnetic noise of a specific frequency radiated from the measurement object 120 or the like is absorbed by the dielectric 20, so that the measurement accuracy can be improved.

  As described above, when the distance between the housing bottom surface 111 and the measurement object 120 is increased in order to adjust the characteristic impedance of the large measurement object 120 to the specified value (150Ω) (that is, the measurement object). When the height of 120 is increased), the characteristic impedance of the noise measurement cable 1 increases from a specified value. Here, according to the present embodiment, the thickness of the dielectric 20 is gradually increased as the measurement object 120 is approached. Therefore, the characteristic impedance can be adjusted to the specified value (150Ω) at any position of the noise measurement cable 1. As a result, it is possible to eliminate the degree of mismatch of characteristic impedance even for the measurement object 120 having a large size, and to suppress deterioration in measurement sensitivity.

  According to this embodiment, since the five chip resistors 40 connected in parallel are connected to the other end of the line 10, the characteristic impedance of the cable body can be specified. Further, since the chip resistor 40 is small and leadless, it is possible to reduce the influence of the inductance on the characteristic impedance of the noise measurement cable as compared with the insertion-mounted resistor having leads. .

  According to the present embodiment, the line 10 forms a microstrip line whose characteristic impedance is a specified value (150Ω) by the bottom surface 111 of the housing 110 and the dielectric 20. Therefore, it is possible to easily set the dielectric thickness, that is, the characteristic impedance of the line 10 by applying the microstrip line design method.

  According to the noise measurement apparatus 100 according to the present embodiment, since the noise measurement cable 1 described above is provided, even if the distance between the measurement target 120 and the housing bottom surface 111 is changed, the noise is measured. The characteristic impedance of the measurement cable 1 and the measurement object 120 can be adjusted to a specified value (150Ω). Therefore, it is possible to eliminate the degree of mismatch of characteristic impedance, and to suppress deterioration of measurement sensitivity.

(Second Embodiment)
In the first embodiment described above, the thickness of the dielectric 20 is changed according to the height of the line 10 from the housing bottom surface 111. However, the thickness of the dielectric is constant and the dielectric constant of the dielectric is changed. It is good also as a structure. Next, the noise measurement cable 2 according to the second embodiment will be described with reference to FIG. FIG. 7 is a side view schematically showing the configuration of the noise measurement cable 2. In FIG. 7, the same or similar components as those in the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 7, the noise measurement cable 2 has a constant thickness in the height direction of the housing 110 and the distance between the line 10 and the bottom surface 111 of the housing 110 increases, that is, The dielectric 21 is formed between the line 10 and the bottom surface 111 of the housing 110 so that the dielectric constant becomes higher as the measurement object 120 approaches the connector 60 (61). This is different from the noise measuring cable 1 described above. Since other configurations are the same as or similar to the noise measurement cable 1 described above, detailed description thereof is omitted here.

  The dielectric 21 is integrally formed so that the dielectric constant gradually increases as the measurement object 120 is approached from the connector 60 (61). The dielectric 21 may be formed by stacking a plurality of dielectrics having different dielectric constants so that the dielectric constant increases as the measurement object 120 approaches the connector 60 (61). Note that the dielectric constant of the dielectric 21 is that the noise measurement cable 2 is regarded as a microstrip line, and the above-described formula (1) (2) or (3) (4) ) Can be set.

  According to the present embodiment, as the distance between the track 10 and the bottom surface 111 of the housing 110 increases, that is, as the height of the track 10 from the housing bottom surface 111 increases, the relationship between the track 10 and the housing bottom surface 111 increases. The dielectric 21 disposed therebetween is formed so as to have a high dielectric constant. Therefore, the mismatch of the characteristic impedance of the noise measuring cable 2 can be eliminated, and the characteristic impedance can be adjusted to the specified value (150Ω). As a result, even if the distance between the measurement object 120 and the housing bottom surface 111 is changed, it is possible to suppress deterioration in measurement sensitivity. Further, according to the present embodiment, the electromagnetic noise of a specific frequency radiated from the measurement object 120 or the like is absorbed by the dielectric 21, so that the measurement accuracy can be improved.

  As described above, when the distance between the housing bottom surface 111 and the measurement object 120 is increased in order to adjust the characteristic impedance of the measurement object 120 having a large size to the specified value (150Ω), the noise measurement cable is used. The characteristic impedance of 2 increases from the specified value. Here, according to the present embodiment, the dielectric 21 is formed such that the dielectric constant of the dielectric 21 increases as the measurement object 120 is approached. Therefore, the characteristic impedance can be adjusted to the specified value (150Ω) at any position of the noise measurement cable 1. As a result, it is possible to eliminate the degree of mismatch of characteristic impedance even for the measurement object 120 having a large size, and to suppress deterioration in measurement sensitivity.

(Third embodiment)
Next, the noise measurement cable 3 according to the third embodiment will be described with reference to FIG. FIG. 8 is a side view schematically showing the configuration of the noise measurement cable 3. In FIG. 8, the same or equivalent components as those in the first embodiment are denoted by the same reference numerals.

  The noise measurement cable 3 is further provided with a second dielectric 22 disposed on the upper surface of the line 10 so as to face the dielectric 20 with the line 10 interposed therebetween. Different from cable 1. Since other configurations are the same as or similar to the noise measurement cable 1 described above, detailed description thereof is omitted here. Instead of the noise measurement cable 1, a configuration in which the second dielectric 22 is added to the noise measurement cable 2 described above may be used.

  The width of the line 10 constituting the noise measuring cable 3 and the thicknesses and dielectric constants of the dielectric 20 and the dielectric 22 are determined in accordance with the known strip line theory by regarding the noise measuring cable 3 as a strip line. The characteristic impedance can be set to a specified value (150Ω).

  According to this embodiment, even when the distance between the measurement object 120 and the housing bottom surface 111 is changed, the degree of mismatch of characteristic impedance can be eliminated, and deterioration of measurement sensitivity is suppressed. It becomes possible. In addition, electromagnetic noise of a specific frequency radiated from the measurement object 120 or the like is absorbed by the two dielectrics 20 and 22 arranged opposite to each other with the line 10 interposed therebetween, so that electromagnetic noise enters the line 10. Can be prevented and the measurement accuracy can be further improved.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made. For example, the shapes, dimensions, materials, arrangements, and the like of the dielectrics 20 and 21 and the measurement object 120 are not limited to the above embodiment. Further, the number of chip resistors 40 is not limited to five. In particular, the widths of the dielectrics 20 and 21 do not have to be the same as the width of the measurement object 120 and are preferably wider.

  In the above embodiment, the dielectrics 20 and 21 are disposed between the line 10 and the bottom surface 111 of the housing. However, the dielectric is disposed between the line 10 and the top surface (lid portion) of the housing 110. Also good. In the above embodiment, the measurement object 120 having a large size has been described as an example, but conversely, the measurement object 120 having a smaller size can also be applied.

1, 2, 3 Noise measurement cable 10 Line 20, 21 Dielectric 22 Second dielectric 40 Chip resistor 60, 61 Connector 100 Noise measurement device 110 Case 111 Bottom surface 120, 120D Measurement object

Claims (8)

A noise measurement cable used to place a measurement object inside a conductive housing and measure a common mode voltage generated between the housing and the measurement object,
A distance between the bottom surface of the housing is different from each other, and a thin plate-like line having conductivity connecting the measurement object and a connector attached to the housing;
A dielectric disposed between the line and the housing;
The dielectric is formed by changing the thickness in the direction perpendicular to the bottom surface of the housing in accordance with the distance between the line and the housing so that the characteristic impedance becomes a specified value. Cable for noise measurement, characterized by The track connects the measurement object and the connector installed at a position closer to the bottom surface of the housing than the measurement object,
The dielectric is disposed between the line and a bottom surface of the housing, and is formed so that the thickness gradually increases as the measurement object is approached from the connector. The noise measurement cable according to claim 1. A noise measurement cable used to place a measurement object inside a conductive housing and measure a common mode voltage generated between the housing and the measurement object,
A distance between the bottom surface of the housing is different from each other, and a thin plate-like line having conductivity connecting the measurement object and a connector attached to the housing;
A dielectric disposed between the line and the housing;
The noise measurement cable, wherein the dielectric is formed with a dielectric constant changed according to a distance between the line and the housing so that a characteristic impedance becomes a specified value. The track connects the measurement object and the connector installed at a position closer to the bottom surface of the housing than the measurement object,
The dielectric is disposed between the line and a bottom surface of the housing, and has a dielectric constant that increases as the measurement object is approached from the connector. The cable for noise measurement according to 3.   5. The noise measuring cable according to claim 1, wherein an end of the line is connected to the connector via a plurality of chip resistors connected in parallel to each other. .   The noise measurement according to any one of claims 1 to 5, wherein the line forms a microstrip line whose characteristic impedance is a specified value by a bottom surface of the casing and the dielectric. Cable.   The noise measurement cable according to claim 1, further comprising a second dielectric disposed so as to face the dielectric with the line interposed therebetween. A conductive housing that places the measurement object inside;
A connector attached to the housing;
A noise measurement device comprising: the noise measurement cable according to claim 1, which connects the measurement object and the connector.

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