JPH044226Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a clamp-type ammeter, and more specifically, to an improvement of a clamp arm as a current detection section.

[Technical background of the invention] Clamp-type ammeters are extremely convenient in that they can measure the current flowing through the wires as they are without cutting them, but they also have a pair of split cores that can be opened and closed. The quality of the abutting surfaces has a direct impact on measurement accuracy. FIG. 5 and FIG. 6, which is a cross-sectional view taken along the line 5, show one side of the clamp arm used in a conventional clamp-type ammeter. The clamp arm 1 has, for example, a semicircular core 2 made of a magnetically conductive material, and a coil bobbin 4 having a coil 3 is fitted into the core 2. That is, the core 2 and the coil 3 constitute the current detection section 7. This current detection section 7
is placed in a shield case 5 to avoid the influence of external magnetic fields. In this case, conventionally, for example, epoxy resin 6 is potted inside the shield case 5 to prevent mechanical stress from being applied to the core 2. The current detecting section 7 is fixed by using the same. Note that reference numeral 8 is a core cover.

The end face of the core 2 is polished to a mirror finish using a polishing means such as a grindstone to prevent an air gap from forming between it and the other end face of the core. Since the resin 6 is held in a floating state within the shield case 5, when the epoxy resin 6 expands or contracts due to temperature changes, an air gap or the like occurs between the abutting end surfaces of the core 2, and as a result, measurement The drawback was that accuracy deteriorated.

[Purpose of the invention] This invention was devised in view of the above-mentioned drawbacks of the conventional technology.The purpose of this invention is to accurately position the current detection unit including the core against the shield case so as to prevent air gaps from occurring between the end faces of the core. An object of the present invention is to provide a clamp-type ammeter having a clamp arm having a structure that allows it to be held.

[Examples] Hereinafter, this invention will be described in detail with reference to embodiments shown in the accompanying drawings.

This clamp type ammeter is equipped with a clamp arm 10 shown in FIG. This clamp arm 10 is used as a left and right pair, but since their configurations are the same, only one of them is shown in the figure. Referring also to the exploded perspective view of FIG. 2, this clamp arm 10 has a magnetically conductive core 11 formed, for example, in a semicircular shape. The core 11 is made of a predetermined number of semicircular punched magnetic plates stacked one on top of the other, and the stacked bodies are fixed together with pins 12. A coil bobbin 14 having a coil 13 is fitted around the core 11, and as a result, a current detection section 15 is detected as in the conventional case.
is formed. In order to avoid the influence of an external magnetic field, the current detection unit 15 has a shield case made of a metal material, preferably a non-magnetic metal material (such as brass), which is formed by forming a semicircular frame body with a U-shaped cross section, for example. However, according to this invention, retaining plates 17,
17 is attached, and the current detection section 15 is disposed inside the shield case 16 via the holding plates 17, 17. This retainer plate 17 is made of a non-magnetic metal material having almost the same coefficient of thermal expansion as the shield case 16, and has a mounting hole 17a that fits into the end face of the core 11 and a hole for preventing the shot ring from forming on the core 11. A slit 17 is cut from one predetermined side to the mounting hole 17a to
b is provided. The holding plate 17 is made of a non-magnetic metal material having a coefficient of thermal expansion that is almost the same as that of the shield case 16 as described above, but it is more preferable that the holding plate 17 has a coefficient of thermal expansion similar to that of the core 11. As illustrated in FIG. 3, each holding plate 17 is attached to the end surface 11a of the core 11 so as to be substantially flush with it, and is soldered to the core 11 and the shield case 16. Alternatively, it may be brazed. The shaded area in FIG. 1 indicates the soldering position. In that case, in order to facilitate soldering, a notch may be provided in a portion corresponding to the shaded portion in FIG. 1. Further, as shown in FIG. 3, a solder drip prevention plate 18 is provided on the back side of the holding plate 17 to prevent excess solder from spilling into the shield case 16.
It is also possible to provide In addition, as shown in FIG. 4, in order to improve the accuracy of attachment of the retaining plate 17 to the core end surface 11a, a pin 12 is attached to the retaining plate 17.
A leg piece 19 having an engagement groove 19a that engages with the core end 11a may be provided in a row, and the leg piece 19 may be used to guide the attachment position of the retaining plate 17 to the core end 11a.

As described above, the current detection unit 15 is housed in the shield case 16 via the holding plate 17 attached to the core 11, but in this invention, the joint by soldering or brazing is In order to remove the unevenness, the core 11a and the holding plate 17 are polished by a polishing means such as a grindstone (not shown) so that the end surface to be joined to the mating member is finished in a mirror-like finish. The other clamp arm is assembled and polished in the same manner, and the pair is opened and closed by a known hinge mechanism or the like. Further, a core cover 20 is attached to the inner surface of the shield case 16. This core cover 20 is made of an electrically insulating material such as synthetic resin, and although not shown, is also combined with the core cover 20 on the outer surface of the shield case 16, and also includes a protective core that covers the entire shield case 16. The cover is attached.

[Effect] As is clear from the above description of the embodiment, according to this invention, retaining plates 17, 17 made of a non-magnetic metal material having almost the same coefficient of thermal expansion as the shield case 16 are provided at both ends of the core 11. The current detection unit 15 is fitted into the shield case 16 via the holding plates 17, 17, and the end face of the core 11 and the holding plate 17 are polished to a mirror finish using a polishing means such as a grindstone. By finishing it, the end face that butts against the other clamp arm can be stabilized over a long period of time without being affected by temperature changes, etc., and the reliability of measurement accuracy is further increased. . Furthermore, since a filling solidifying material such as an epoxy resin is not required, production costs can also be reduced.

[Brief explanation of the drawing]

Fig. 1 is a front view of the clamp arm according to this invention, Fig. 2 is an exploded perspective view of the same clamp arm, Fig. 3 is a sectional view taken along the line - - of Fig. 1, and Fig. 4 shows another embodiment of the holding plate. 5 is a front view showing a conventional example, and FIG. 6 is a sectional view taken along the line -- in FIG. 5. In the figure, 10 is a clamp arm, 11 is a core, 1
3 is a coil, 15 is a current detection section, 16 is a shield case, and 17 is a holding plate.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A pair of clamp arms each comprising a current detection unit with a coil wound around a magnetically conductive core mounted in a shield case made of metal material, each of the clamp arms In a clamp-type ammeter that can be opened and closed, holding plates made of a non-magnetic metal material having almost the same coefficient of thermal expansion as the shield case are fitted to both ends of the core, and the same is inserted through the holding plates. A clamp-type ammeter characterized in that a core is housed in the shield case, and the end face of the core and the holding plate are polished to a mirror finish using a polishing means such as a grindstone. (2) The clamp-type ammeter according to claim (1), characterized in that the holding plate is provided with a notch for preventing shortening of magnetic flux. (3) In claim (1) or (2) of utility model registration, the clamp-type ammeter is characterized in that the holding plate is fixed to the core and shield case by soldering or brazing. .