JPH08236977A - Housing of electric measurement device - Google Patents

Abstract

PURPOSE: To realize manufacturing without requiring masking treatment, eliminate the possibility of electric shock and provide shielding effect by isolating a conductive layer of first and second inner parts from a fitting contact part of first and second semi-housings. CONSTITUTION: A housing 40 is fit to an upper semi-housing 42 which is a first semi-housing and a lower semi-housing 44 which is a second semi-housing. An upper surface parts 46a, a lower surface part 50a and side surface parts 46a, 50b are formed of an insulation material such as plastic. Plating treatment is performed for first and second inner parts 46, 50 by an electroless plating method, that is, immersion in plating solution and a conductive layer such as nickel is applied all over a surface. A recessed part 48a of the upper semi- housing 42 and a projecting part 52a of the lower semi-housing 44 are fit and the housing 40 is assembled. In the assembly state, an exposed conductive layer, that is, an end part of a shield layer is isolated by an insulation material from a contact part wherein the first and second semi-housings 42, 44 are fit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casing of a handy type electric measuring instrument such as a digital multimeter (DMM).

[0002]

2. Description of the Related Art FIG. 4 is a plan view showing a handy type DMM 10. The DMM 10 includes an enclosure 12 formed of an insulating material such as plastic, a digital display unit 14 including a liquid crystal display, a plurality of push buttons 16 for selecting various functions related to measurement, voltage measurement, and resistance measurement. It has a dial type mode changeover switch 18 for selecting each mode of continuity test, frequency measurement, and current measurement, and input terminals 20 to 26 to which a measurement probe is selectively connected according to the measurement mode. When performing voltage measurement, resistance measurement, continuity test or frequency measurement, the mode selector switch 18 is aligned with the mark representing each measurement mode, and two measurement probes are connected to the input terminals 24 and 26, respectively.
In addition, when performing current measurement, the mode switch 18
To the mark of the current measurement mode according to the magnitude of the current to be measured, and connect the two measurement probes to the input terminals 24 and 20.
Or connect to 22. When the tip of the measurement probe is brought into contact with an appropriate portion of the object to be measured, the measurement result is displayed on the display unit 14 as a digital value.

[0003]

The DMM 10 displays the waveform of the signal under measurement on the display 14 from the meter mode in which the measurement result is displayed as a digital value on the display 14 by pressing a predetermined push button 16. You can switch to scope mode. In scope mode, you can check waveforms for abnormal phenomena such as power line spikes and frequency fluctuations. In order to display such a waveform,
The DMM 10 has a built-in waveform acquisition circuit similar to that of a digital oscilloscope, and the clock generator generates, for example, 2
The input signal is sampled using a relatively high frequency sampling clock signal of 0 MHz. However, such a sampling clock signal becomes a source of electromagnetic noise, and in addition to its fundamental wave, harmonics cause
This may cause malfunction of surrounding computer-controlled equipment. Therefore, in such a DMM 10, it is desired to form a shield layer on the inner surface of the housing 12 in order to suppress the leakage of electromagnetic noise to the outside.

FIG. 5 is a schematic sectional view showing a case where a shield layer is applied to the inner surface of the casing 12. The casing 12 includes an upper half casing 28 and a lower half casing 30. Half-case 28
The end 32 has a concave cross section, the end 34 of the half-shelf 30 has a convex cross-section, and these are engaged to join the half-shelf 28 and 30 together. In order to prevent leakage of electromagnetic wave noise, a shield layer 32 made of, for example, aluminum is attached to the inner surface of the casing 12. Since the electromagnetic wave noise of the harmonic of the clock signal from the clock generator has a short wavelength, it may leak to the outside from the engaging portions of the half casings 28 and 30. Therefore, it is necessary to apply the shield layer 32 also to this engaging portion.

The shield layer 32 is electrically connected to the common input terminal 24. In the floating measurement state of the DMM 10, a high voltage may be applied to the common terminal 24,
At that time, if the distance from the shield layer 32 to the outer surface of the housing 12 is short, the operator may be electrocuted by creeping discharge from the shield layer 32 at the engaging portion. Therefore, it is necessary to perform an effective shield effect without fear of such electric shock. Further, when the plating process is performed to apply the shield layer, it is necessary to perform masking for covering the portions of the individual enclosures to which the plating is not attached, so the work is complicated and troublesome.

Therefore, an object of the present invention is to provide a housing of an electric measuring instrument which is manufactured without requiring a masking process, has no fear of electric shock, and has an effective shield effect.

[0007]

The housing of the electric measuring instrument according to the present invention comprises a first and a second semi-housing connected to each other. First
The semi-insulative body is made of an insulating material and has a first step portion having a thin thickness formed on the inner surface of the end portion, and the first step portion is entirely covered with a conductive layer.
It has an inner portion and a first outer portion which is made of an insulating material and which covers the first step and the outer surface of the first inner portion and has a recess formed therein. The second semi-insular body is made of an insulating material, has a second step portion having a thin thickness formed on the inner surface of the end portion, and has a second inner portion entirely covered with a conductive layer, and a second semi-insular body made of an insulating material. Two
A second protrusion that covers the second step and the outer surface of the inner portion and has a convex portion formed at a position corresponding to the tip of the end portion of the second inner portion.
And an outer portion. The recesses of the first semi-insulator and the projections of the second semi-insular body are engaged to join the first and second semi-insular bodies, and the ends of the first and second inner portions overlap in the engaged state. .

[0008]

Since the conductive layers of the first and second inner portions are separated from the engaging contact portions of the first and second half-housings by a part of the outer portion, the conductive layer to the operator is provided through the engaging portions. There is no fear of electric shock. Further, since the end portions of the first and second inner portions covered with the conductive layer overlap at the engaging portion, it is possible to effectively prevent the electromagnetic noise from leaking to the outside of the housing. Further, the inner part is immersed in a plating solution by an electroless plating method to form a conductive layer on the entire surface, and a predetermined molding die is used to attach the outer part to form a half-housing. Therefore, the masking process which is troublesome before the plating process can be omitted.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An enclosure 40 of an electric measuring instrument according to the present invention is shown in FIG.
The casing 12 may have a similar outer shape, and FIG. 1 shows a sectional view thereof. The enclosure 40 is formed by connecting an upper half enclosure 42 which is a first half enclosure and a lower half enclosure 44 which is a second half enclosure. The upper half-shelf 42 consists of a first inner part 46 and a first outer part 48, and the lower half-shelf 44 consists of a second inner part 50 and a second outer part 52.

The first inner portion 46 has a planar upper surface portion 46a extending horizontally in the figure and a side surface portion 46b extending vertically downward from the peripheral edge thereof. The upper surface portion 46a may be curved. The second inner portion 50 has a planar lower surface portion 50a extending in the horizontal direction and a side surface portion 50b extending vertically upward from the peripheral edge thereof. These upper surface portions 46
a, the lower surface portion 50a and the side surface portions 46b, 50b are formed of an insulating material such as plastic. The length between the facing inner walls of the side surface portion 46b is equal to the length between the facing inner walls of the side surface portion 50b. On the other hand, the length between the facing outer walls of the side surface portion 46b is shorter than the length between the facing outer walls of the side surface portion 50b.

The inner surface of the end portion of the side surface portion 46b of the first inner portion 46 is step-processed so that the thickness becomes thin, and a thin portion 46c is formed.
Is formed. The inner surface of the end portion of the side surface portion 50b of the second inner portion 50 is also step-processed so that the thickness is thin, and the thin portion 50 is formed.
c is formed. The length between the opposing inner walls of the thin portion 50c is longer than the length between the outer walls of the side surface portion 46c.

The first and second inner portions 46 and 50 are electrolessly plated, that is, plated by immersing in a plating solution, and conductive layers 54 and 56 of nickel or the like are deposited on the entire surfaces, respectively. Has been done.

The inner wall and the entire outer surface of the thin portion 46c of the first inner portion 46 are covered with an outer portion 48 made of an insulating material such as plastic to form an upper half-shoulder 42. The conductive layer 46d on the inner surface portion of the first inner portion 46 excluding the thin portion 46c is exposed. The outer portion 48 on the outer wall of the side surface portion 46b is sufficiently thick, and the recess 48a is formed parallel to the outer wall. Thinned portion 50 of second inner portion 50
The entire inner wall and outer surface of c is covered by an outer portion 52 made of an insulating material similar to the outer portion 48 to form the lower half-housing 44. Therefore, in the second inner portion 50, the conductive layer 50d on the inner surface portion except the thin portion 50c is exposed.
The outer portion 52 at the tip of the thin portion 50c is formed thin,
The convex portion 52a is formed.

By engaging the concave portion 48a of the upper half-shelf 42 and the convex portion 52a of the lower half-shake 44, the case 40
Is assembled. In the assembled state, the ends of the exposed conductive or shield layers 54 and 56 are separated from the mating contact portions of the first and second half-shoulders 42, 44 by an insulating material, so that the case 40. The creepage distance to the outer surface can be made sufficient, and even if a high potential is applied to the shield layer, the operator who holds the enclosure 40 is not at risk of electric shock. Further, since the ends of the first inner portion 46 and the second inner portion 50 overlap each other, it is possible to effectively prevent leakage of electromagnetic wave noise generated inside the housing 40.

FIG. 2 is a cross-sectional view showing how the upper half-shoulder body 42 is manufactured by using a molding die 52, and FIG. 3 is the lower half-shoulder body 44 which is manufactured by using a molding die 60. The molding die 52 is composed of an upper die part 52a and a lower die part 52b.
Consists of an upper mold part 60a and a lower mold part 60b. To manufacture the upper half-shelf 42, the first inner part 46, which has already been plated, is placed on the lower mold part 52b. The inner surface of the side surface portion 46b of the first inner portion 46 other than the thin portion 46c contacts the lower die 52b. Next, the upper mold part 52a is placed on the lower mold part 52b. These mold parts 52a and 52
b is aligned by the engagement of the concave portion and the convex portion provided at each end. In the molding die 52, a space corresponding to the shape of the outer portion 48 is formed around the inner portion 46. The first outside 48 can be formed by injecting the melted insulating material from the injection port 52e provided in the upper mold part 52a. After the insulating material is solidified, the upper half housing 42 is taken out from the molding die 52. The lower half-housing 44 is manufactured in the same manner as the upper half-housing 42, and a description thereof will be omitted.

[0016]

In the electrical measurement enclosure of the present invention, the conductive layers of the first and second inner portions are separated from the engaging contact portions of the first and second semi-enclosures by a portion of the outer portion. Therefore, there is no fear of electric shock to the operator through the engaging portion. Further, since the end portions of the first and second inner portions covered with the conductive layer overlap at the engaging portion, it is possible to effectively prevent the electromagnetic noise from leaking to the outside of the housing. Further, the inner portion is dipped in a plating solution by electroless plating to form a conductive layer on the entire surface, and a predetermined molding die is used to attach the outer portion to form a half-housing. Therefore, the masking process which is troublesome before plating can be omitted.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of an enclosure of an electric measuring instrument of the present invention.

FIG. 2 is a cross-sectional view showing a method for manufacturing the upper half-shelf of FIG.

FIG. 3 is a cross-sectional view showing the method for manufacturing the lower half housing of FIG.

FIG. 4 is a plan view showing a DMM.

FIG. 5 is a cross-sectional view of a DMM casing.

[Explanation of reference numerals] 42 first semi-housing 44 second semi-housing 46 first inner part 48 first outer part 50 second inner part 52 second outer part

Claims (1)

[Claims] 1. An enclosure for an electric measuring instrument comprising a first and a second semi-insular body joined together, wherein the first semi-insular body is made of an insulating material and has a thin inner surface at an end. A first inner portion having a one-step portion and entirely covered with a conductive layer, and a first outer portion made of an insulating material and covering the first step portion and the outer surface of the first inner portion and having a recess formed therein. The second semi-insular body is formed of an insulating material, and a second step portion having a thin thickness is formed on the inner surface of the end portion, and a second inner portion entirely covered with a conductive layer is provided. A second outer portion which is made of an insulating material, covers the second step portion and the outer surface of the second inner portion, and has a convex portion formed at a position corresponding to the tip of the end portion of the second inner portion. Having the concave portion of the first semi-insular body and the convex portion of the second semi-insular body are engaged, and in the engaged state, the first and second The casing of the electric measuring instrument, characterized in that the ends of the inner part overlap.