GB2043358A

GB2043358A - Measuring instrument containing a printed-circuit assembly

Info

Publication number: GB2043358A
Application number: GB7939221A
Authority: GB
Original assignee: Yokogawa Electric Works Ltd
Current assignee: Yokogawa Electric Corp
Priority date: 1979-02-22
Filing date: 1979-11-13
Publication date: 1980-10-01
Also published as: BR7906292A; JPS55112517A; NL7909260A; GB2043358B; JPS6351252B2; DE2940515A1; DE2940515C2

Abstract

To facilitate the testing and assembly of a measuring instrument necessary electronic and electrical components including meter 300 are mounted on printed-circuit board 400 so that the overall operation test of the instrument can be performed solely by testing this assembly mounted between cases 100, 200, upper case 100 having spring claws 108 engaging the meter. Line and earth probes 600, 700 are held by case 200 immovably in notches 110, 111. Optical guide 304 is shaped to transmit and spread light from lamp 405 across a meter scale plate. Compartment 201 contains a battery. <IMAGE>

Description

SPECIFICATION Measuring instrument containing a printed-circuit assembly The present invention relates to a measuring instrument containing a printed-circuit assembly.

Such a measuring instrument needs electrical components such as measuring terminals, a battery case, a meter and measuring switches in addition to transistors, capacitors, resistors and so forth. Of these components, the transistors and capacitors and so forth are normally mounted on a printedcircuit board to constitute a unit, and it is usual to connect the printed-circuit board with other electric components by means of leadwires. However, such connection by the leadwires generally requires a considerable number of production steps and is liable to cause electrical troubles. Moreover, with respect to manufacture, there is a disadvantage that an overall operation test is impossible until completion of wiring among the components including the printed-circuit board.And furthermore, when the indicating meter is mounted generally on the case of a a printed-circuit board by means of screws and nuts, which is disadvantageous in view of the number of components used and the amount of work involved.

It is a principle object of the present invention to provide an improved measuring instrument wherein all the required electric and electronic components including transistors and resistors are mounted on a single printed-circuit board to eliminate wiring and to reduce the number of production steps necessitated by wiring, and wherein an overall operation test can be performed solely by means of the printed-circuit assembly thus constituted.

And another object of the invention resides in providing a measuring instrument which is capable of being constructed so that the components themselves are equipped with integral attachment devices so as to decrease the number of screws and nuts used, hence attaining a reduction in the number of production steps.

According to the invention, there is provided a measuring instrument with a meter for indicating a measured value, wherein necessary electric components including said meter are mounted on a single printed-circuit board to constitute an assembly, and the overall operation test of the instrument can be performed solely by testing said printed-circuit assembly.

The present invention is adapted particularly for use in a small-sized portable measuring instrument with a battery power source such as insulation resistance meter or tester.

In order that the invention may be clearly understood and readily carried into effect, a measuring instrument in accordance therewith will now be described, by way of example, with reference to the accompanying drawings, in which :- Figure 1 is an exploded perspective view of the measuring instrument; Figure 2(A) is a top view of the measuring instrument; Figure 2(B) is a sectional view taken along a line X-X' in Figure 2(A); Figure 2(C) is a sectional view taken along a line Y-Y' in Figure 2(A); Figure 3 is a perspective view of a lamp assembly; Figure 4 is a side view of an indicating meter; Figure 5(A) and Figure 5(B) are side and front elevations of an optical guide forthe light of a lamp; Figure 6(A) and Figure 6(B) are a front and sectional side elevation of a structure for mounting a probe on a case; and Figure 7 is an elevation showing a connection between a battery terminal and a printed-circuit board.

Hereinafter the present invention will be described with reference to the accompanying drawings. In Figures 1, 2(A), 2(B) and 2(C) labelled as 100 is an upper case; 200 is a lower case; 300 is an indicating meter; 400 is a printed-circuit board; 500 is a bottom coverforthe lower case; 600 is a line-side probe; 700 is an earth-side probe; 800 is a push-button head; and 900 is a knob.

The printed-circuit board 400 mounts thereon all electronic components (not shown) such as transistors, resistors, capacitors and diodes required for constituting a circuit, and is further equipped with a push switch 401, a rotary switch 402, and connectors 403 and 404 which are to be coupled with connectors 601 and 701 connected to the line-side probe 600 and the earth-side probe 700 respectively. The printedcircuit board 400 also mounts thereon a lamp 405 and a meter 300.

As shown in detail in Figure 3, the lamp 405 is rotated after being inserted into a hole 406 from the reverse side of the printed-circuit board 400, so that the lamp is set thereon by the action of projections 407 and 408. On the reverse side of the printedcircuit board 400, there is formed a pattern which communicates with the push switch 401 of Figure 1 and is connected to a battery (which will be described below). When the lamp 405 is mounted on the printed-circuit board 400, leadwires 410 and 41 1A attached to a socket 409 are connected electrically to the pattern. And the lamp 405 is turned on by pressing the push switch 401.

The meter 300 comprises, as shown in its side view of Figure 4, a nontransparent case 301, a transparent acrylic cover 302, a scale plate 303, and an optical guide 304 composed of a transparent resin and serving to guide the light from the lamp 405 to the scale plate 303, wherein the two ends 305 and 306, Figure 5(A) of the optical guide 304 are inclined to form light reflecting surfaces. In front elevation, Figure 5(B), the optical guide 304 is predominantly frusto-triangular so as to spread the light from the lamp. The optical guide 304 has an arm 307 which serves also as a holding memberforthe scale plate 303. And a notch 308 is formed on one inclined surface 305.The terminals of the meter 300 with the optical guide 304 are inserted into through holes 407A and 408A formed on the printed-circuit board 400 of Figure 1 via spacers 309 and 310, and subsequentlythe terminals are clamped by tightening nuts 416 and 417 from the reverse side of the board 400 so that the meter is set thereon, with the terminals being connected electrically to the pattern formed on the reverse side of the board 400. As a result of mounting the meter 300 on the board 400, the lamp 405 is positioned in the notch 308 formed on one inclined surface 306 of the optical guide 304 in the meter300. When the lamp 405 is turned on, its light passes through the optical guide 304 while being guided by the reflecting surfaces 306,311 and 305 of the optical guide as shown by arrows in Figures 5(A) and (B), and comes to illuminate the scale plate 303.

In this manner, the entire electric components including the meter 300 are mounted on the printed-circuit board 400 and are interconnected by the pattern formed on the reverse side of the board 400, so that the overall operation test can be performed by means of the printed-circuit assembly thus constituted.

The upper case 100 has a hole 101 formed at a position opposed to the transparent cover 302 of the meter 300, a hole 102 for insertion fo the shaft 415 of the rotary switch 402 mounted on the printed-circuit board 400, a hole 103 for insertion of the push switch 401 on the board 400, bosses 104-107, and resilient claws 108, 109 located at the two sides of the hole 101. The bosses 104-107 and the claws 108, 109 are formed integrally with the uppercase 100 by mould- ing. These claws have elasticity, and each of the bosses has a screw hole extending in its axial direction.

When the meter 300 is pressed into the upper case 100 from below in the manner that the cover 302 is opposed to the hole 101, the lateral portions 311 and 312 of the cover 302 are held by the claws 108 and 109 so that the printed-circuit board 400 is set in the upper case 100 together with the meter 300. Labelled as 110 and 111 are square notches formed on the upper case 100, and the probes 600 and 700 are attached thereto by engaging these notches and the lower case 200. The probe 600 is equipped with a columnar mounting part 603 having a groove 602 and formed integrally with the probe body, and is attached to the cases 100 and 200 by fitting the groove 602 into the notch 110 on the upper case 100 as shown in Figure 6(A) and (B) and then supporting the mounting part 603 by the notch 110 and the lower case 200.Similarly, the probe 700 is also equipped with a mounting part 703 having a groove 702, and is attached to the cases by utilizing the groove 702 in the same manner as the probe 600.

Since the notches 110 and 111 are square, the probes 600 and 700 attached to the cases are prevented from rotating without additional provision of any particular lock means.

In the lower case 200, labelled as 201 is a battery case for housing a power supply battery therein.

After a battery is housed, a bottom cover 500 is fitted to the bottom of the battery case 201. Mounting posts 202-205 are formed atfourcorners of the bat- tery case 201 by moulding integrally with the lower case 200 and have through holes 202-209 respectively in the axial direction thereof; Labelled as 210, 211 are holes formed in the battery case 201; 212, 213 are battery connecting terminals made by bending L-shaped metal plates at right angles and having legs 214,215 which are to be inserted into the holes 210,211. These legs have claws 217-220 which serve to prevent separation after insertion of the legs 214, 215 into the holes 210,211. Holes 221,222 are formed in the terminals 212,213 to lie opposite the through holes 206,207 of the posts 202,203 when the terminals 212,213 are set in the holes 210,211 of the lower case 200.Four set screws, e.g. 223, 225 and 226 unite the lower case 200, the printed-circuit board 400 and the upper case 100 fixedly with one another. When the screw 223 is tightened the battery connecting terminal 212 is brought into direct contact with the pattern 418 formed on the reverse side of the printed circuit board 400 as shown in Figure 7, thereby achieving connection between the battery (power source) and the electric circuit. Similarly, tightening the screw 224 as in Figure 7 brings the battery connecting terminal 213 into direct contact with the pattern on the printed-circuit board 400. In this manner, the battery connecting terminals 212 and 213 are clamped by the screws 223 and 224 which are used for coupling the cases 100 and 200 and the printed-circuit board 400 with one another.

The measuring instrument having the abovedescribed structure is assembled according to the following procedure. The push switch 401, the rotary switch 402 and the connectors 403,404 are mounted on the printed-circuit board 400 together with the electronic circuit elements such as transistors, capacitors and so forth. The lamp 405 is set in the hole 406 and the indicating meter300 is mounted with its terminals clamped by the nuts 416 and 417.

Thus, the entire electric components are disposed on the printed-circuit board 400 to constitute an assembly. The components thus mounted are connected with one another to attain electric continuity by the pattern formed on the printed-circuit board 400.

Consequently, the overall operation test of the measuring instrument including a lighting test for the lamp 405 can be performed merely by the printed-circuit assembly equipped with the entire electric components. After completion of testing the printed-circuit assembly, the meter 300 is pressed into the upper case 100 from below so as to be positioned in the hole 101, and then the lateral por tons 31 1 and 312 of the cover 302 are held by the claws 108 and 109, so that the printed-circuit assem bly 400 including the meter 300 is secured to the upper case 100. In this procedure, the push-button head 800 is disposed previously in the hole 103 of the upper case 100, and the push switch 401 mounted on the printed-circuit board 400 is pressed thereto from below. Then the tip of the push-button head 800 is exposed from the upper case 100 when the printed-circuit assembly is secured to the upper case 100. After setting of the printed-circuit board 400 with the meter 300 in the upper case 100, the connectors 601,701 of the probes 600,700 are coupled with the connectors 403,404 on the printedcircuit board, and the grooves 602,702 of the mounting parts 603,703 are fitted respectively into the notches 110, 111 formed on the upper case 100.

Subsequently, the top of the lower case 200 is butted against the bottom of the upper case 100 from the reverse side of the printed-circuit board 400. With the bottom cover 500 removed, the screws 223-226 are inserted into the through holes 206-209 formed in the posts 202-205, so that the tips of the screws pierce through four holes, e.g., 411,412, 413 on the printed circuit board 400 and are screwed into the holes formed in the bosses 104-107 of the upper case 100. In this procedure, the mounting parts 603, 703 of the probes 600,700 are held between the lower case 200 and the square notches 110,111 on the upper case 100 so as not to slip off from the case.

The terminals 212 and 213 forthe battery are connected to the pattern on the printed-circuit board 400 by tightening the screws 223 and 224 respectively.

When the printed-circuit assembly is secured to the upper case 100, the shaft 415 of the rotary switch 402 passes through the hole 102 on the upper case 100, and a knob 900 is attached to the shaft 415. After the battery 223 is housed in the battery case 201, its positive and negative terminals are connected to the terminals 212 and 213, and the bottom cover 500 is set in position to complete the whole assembly procedure. Although an analog meter is employed in the foregoing embodiment for indicating a measured value, the meter may be of digital display type as well.

The measuring instrument of the above-described structure offers the following advantageous effects: (A) Since the entire electric components are mounted on a single printed-circuit board, there is no necessity of wiring among the components to bring about a reduction in the wiring work, with a further merit of eliminating electric troubles that may otherwise occur due to wiring.

(B) The overall operation test is executable by means of a single printed-circuit assembly to attain a great operational convenience.

In addition to the above, the upper case itself is equipped with ia function of securing the meter, and the battery terminals are clamped together with the case, so that it becomes possible to decrease the number of the required screws, hence minimizing the total number of assembly operations as a result and reducing the screw tightening steps. Moreover, as the probes are disposed on the upper case alone and are supported through cooperation of the square notches and the lower case, another advantage is achieved in the point that no fastening devices are needed particularly to prevent rotation of the probes, and therefore a mold for the lower case is easily manufactured.

Claims

1. A measuring instrument with a meterforindi- cating a measured value, wherein necessary electric components including said meter are mounted on a single printed-circuit board to constitute an assembly, and the overall operation test of the instrument can be performed solely by testing said printedcircuit assembly.

2. A measuring instrument as defined in Claim 1, in which the printed-circuit board with the meter mounted thereon is covered by a molded case having resilient claws molded integrally therewith which engage the meter to hold the meter in the case.

3. A measuring instrument as defined in Claim 1 or Claim 2, in which the printed-circuit board with the meter mounted thereon is contained in a case consisting of two interengaging parts and in which a probe is provided for introducing to the printedcircuit board an electrical quantity to be measured, the probe being supported between the two parts and formed so as to mate with a rectangular notch in one of the parts.

4. A measuring instrument as defined in any one of the preceding claims, in which the meter is an analog indicator.

5. A measuring instrument as defined in any one of Claim 1 to 3, in which the meter provides a digital display.

6. A measuring instrument as defined in Claim 4, in which a lamp is mounted on said printed-circuit board and the light emitted from said lamp is guided to a scale plate of said analog indicator through an optical guide having reflecting surfaces and shaped so as to spread the light across the scale plate.

7. A measuring instrument substantially as hereinbefore described with reference to the accompanying drawings.