Measuring device with reed switch

Abstract

Measuring instrument for measuring and evaluating a physical quantity, comprising a measuring element for detecting the physical quantity, wherein the measuring element moves according to the physical quantity, a pointer mechanism (2) which rotates a pointer (8) in a pointer plane about a pointer axis according to the movement of the measuring element, wherein the pointer (8) is provided with a switching magnet (9), and a first and a second support component (41, 42) which are rotatably adjustable about the pointer axis, lie in a plane parallel to the pointer plane and each is provided with a bistable reed switch (511, 521) actuated by the switching magnet (9), wherein the longitudinal axes of both reed switches (511, 521) do not pass through the pointer axis, and wherein the distance from the longitudinal axis of the first reed switch (511) to the pointer axis is less than the distance from the longitudinal axis of the second reed switch (521) to the pointer axis.

Description

TECHNICAL AREA The invention relates to a measuring device for measuring and evaluating a physical quantity, such as pressure, and more precisely to a measuring device with at least one mains voltage-compatible, bistable reed switch adjustable around the axis of rotation of a pointer. STATE OF THE ART DE 33 13 925 A1 discloses a manometer with an electrical switching device that can be actuated depending on the measured pressure. The switching device has a reed contact and a pointer connected to a pressure-dependent lever. The pointer carries a magnet for actuating the reed contact. The reed contact is attached to a holder. From US 3,527,903 A, a combination of measuring device and limit switch is also known, comprising: a pair of spaced-apart supports, wherein one end of each support terminates in a pointer; at least one magnetically actuated reed switch attached to each of the supports; a pointer mounted to run over the cantilevered supports, the pointer being mounted on a shaft carrying a pinion; a sensing and translation device coupled to the line assembly for translating a pressure change in a line assembly into a rotary motion, the sensing and translation device being engaged with the pinion; and a magnet held on the pointer, whereby the rotary motion of the pinion rotates the pointer and moves the magnet near at least one of the reed switches. Reed switches essentially consist of two contact reeds made of ferromagnetic material, which are hermetically sealed in an inert atmosphere inside a glass tube or similar container. The contact reeds overlap within the glass tube, forming a gap in their contact area. Both contact reeds are typically coated with contact material in the contact zone, and when a sufficiently strong magnetic field approaches, the reeds attract each other, thus closing the contact. The main advantages of reed switches are their low cost. Advantages include the manufacturing cost, the fact that no power supply is required, the possibility of use in potentially explosive atmospheres, contactless operation, and the relatively long service life of several hundred million switching cycles. A special type of reed switch is the bistable reed switch, which retains its current switching state even when the triggering magnetic field is removed, until a magnetic field of opposite polarity acts on the switch or the switching reeds. An example of the use of a simple reed switch, i.e., a non-bistable reed switch, is shown in US 3,683,135 in a pressure gauge that includes a dial and a pointer with a permanent magnet for analog display of the pressure being measured. To define switching points, such as a minimum or maximum measuring range (end value), two mounting brackets are provided that can be rotated around the pointer's axis of rotation. Each mounting bracket is equipped with a reed switch (normally open contact) that can be actuated by the pointer's permanent magnet. The pointer, the mounting brackets, and the reed switches attached to them are arranged coaxially, with the center axes of the reed switches passing through the pointer's axis of rotation.When the permanent magnet attached to the pointer sweeps across one of the normally open reed switches, the reeds of the switch, connected to a low-current source, close, and a corresponding current signal is sent to a circuit or relay. This circuit typically controls a load circuit, for example, to operate a pump or similar electrical equipment. In the previously described US patent, small reed switches (i.e., with a short glass body) are typically used in the pressure gauge to minimize its footprint. Reed switches suitable for mains voltage and capable of switching larger currents have correspondingly large contact reeds and therefore require a relatively large installation space. If such high-current reed switches are used as shown in US 3,683,135, problems can arise such as the reed switches and their mounting devices interfering with each other, or the width of the adjustable measuring range becoming too small. SUMMARY OF THE INVENTION The present invention is therefore based on the objective of providing a measuring device that can directly switch a consumer current within a large measurement range in a simple manner. This problem is solved according to the invention by a measuring device having the features of claim 1. According to the invention, a measuring device used for measuring and evaluating a physical quantity comprises a measuring element for detecting the physical quantity, wherein the measuring element, for example a Bourdon tube or the like, moves in accordance with a change in the physical quantity, i.e., converts a change in the physical quantity into a detectable movement. Furthermore, the measuring device comprises a pointer mechanism that rotates a pointer in a pointer plane around a pointer axis in accordance with the movement of the measuring element, the pointer being equipped with a switching magnet. In addition, the measuring device includes a first and a second support component, which are rotatable independently of the measuring element, the pointer mechanism, or the pointer and can be adjusted by rotating about the pointer's axis. The support components lie in a plane parallel to the pointer plane and are each equipped with a bistable reed switch.Each reed switch can be actuated by the switching magnet, wherein the longitudinal axis of at least one of the reed switches in the measuring instrument according to the invention does not pass through the pointer rotation axis. To activate the reed switch, the solenoid must pass over the reed switch within a specific switching distance. This switching distance is the maximum distance between the solenoid and the reed switch at which the solenoid can reliably activate the reed switch through its magnetic force. Bistable reed switches typically have a permanent magnet attached to the outer casing, i.e., the glass body of the reed switch. This magnet acts on the reed switches and magnetically biases them, holding them in a specific position. This means that the on or off state of the reed switch remains stable even if the actuating solenoid is already further away from the reed switch than the switching distance. The bistable reed switches of the measuring device according to the invention are therefore preferably each provided with a bias permanent magnet for holding the corresponding switching tongue of the respective reed switch in a predetermined switching position. This means that when the switching magnet provided on the pointer passes by, the corresponding switching tongue is moved into a specific switching position, for example a closed switching position, and is held in this position by the bias permanent magnet until the bias magnet passes by the reed switch again and changes the switching position of the switching tongue accordingly. When the support components are each in their maximum possible offset position, i.e., when the support components are in their maximum open position and thus define the maximum possible measuring range between the two reed switches, one of the two reed switches is preferably arranged radially behind the other reed switch, starting from the pointer's axis of rotation. In a front view of the measuring device, the two reed switches are arranged one after the other or in series along the pointer's axis of rotation. According to the invention, the longitudinal axes of both reed switches do not pass through the pointer's axis of rotation and therefore do not intersect it. In the measuring device according to the invention, the distance from the longitudinal axis of the first reed switch to the pointer's axis of rotation is smaller than the distance from the longitudinal axis of the second reed switch to the pointer's axis of rotation. The second reed switch is preferably arranged radially behind the first reed switch, starting from the pointer's axis of rotation, when the support components are each in their maximum possible offset positions, thus spanning the maximum possible measuring range. Preferably, the magnetically sensitive area of ​​the first reed switch is located further away from the magnetically sensitive area of ​​the second reed switch than the maximum possible switching distance between the switching magnet and the magnetically sensitive area of ​​either reed switch. Furthermore, it is preferable that the support components of the measuring device according to the invention are identical in construction. When used in the measuring device, these are preferably arranged in a mirror-image fashion relative to each other and are each rotatably mounted on the pointer axis, so that the support components can be adjusted relative to each other about this axis. The measuring device according to the invention preferably has a dial on which the pointer indicates the physical quantity based on a measured value. Preferably, each support component has an adjustment element, such as a slider component with a pointer attached to it, which can be locked at various points on the outer circumference of the dial and indicates the corresponding set switching value. Furthermore, the slider components create a force-fit connection between each support component and the dial, generating the necessary friction. It is also conceivable that, in accordance with the switching hysteresis of the reed switch, fixed locking points are provided on each support component, optionally for increasing or decreasing pressure, at which the slider component can be locked.Each supporting component can also be rotatably attached to a bushing through which the pointer axis passes, relative to the dial. Preferably, a retaining plate, which is attached, for example, to the spring carrier of the Bourdon tube as a measuring element, supports the dial at two points and also mounts the aforementioned bushing. In the measuring device according to the invention, the smallest arc angle between the two reed switches is preferably at least 10°, which corresponds to a minimum adjustable switching range. Furthermore, the largest arc angle between the two reed switches is preferably at most 220°, which corresponds to a maximum adjustable switching range. The adjustable switching range can comprise 10 to 90% of the full-scale value. This means that, for a scale of 0 to 100 measuring units, the maximum adjustable switching range comprises, for example, at least 10 measuring units and at most 90 measuring units. Of course, a switching point can also be located at the end of the scale, for example, at a measuring unit of 0 or 100. Furthermore, the reed switches can function as fully functional changeover switches between two poles and can have a magnetic sensitivity of 40 to 45 or 45 to 50 ampere turns (AW), which corresponds to a low AW value and thus a high magnetic sensitivity. Therefore, the reed switch in the measuring device according to the invention can be actuated even with a relatively weak magnetic field. Further tasks, advantages and aspects arise from the dependent claims, the description of the exemplary embodiments and the drawings. The invention is described in more detail below using an exemplary embodiment with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded view of a measuring instrument according to the invention in the preferred embodiment, showing a detailed view of the arrangement of the switching magnet relative to the pointer; Fig. 2 is an enlarged view of the support components, the circuit boards and the reed switches of the measuring instrument according to the preferred embodiment; and Fig. 3A shows the support components shown in Fig. 2, including the circuit boards and the reed switches, in the assembled state in a fully pivoted end position, and Fig. 3B shows the rear side of the arrangement shown in Fig. 3A. DETAILED DESCRIPTION OF THE PREFERRED EXECUTION EXAMPLE The preferred embodiment of the measuring instrument according to the invention, shown in the exploded view in Fig. 1, includes, among other things, a measuring instrument housing 1. The main body 11 of the measuring instrument housing 1 has a pot-like shape, and a cable housing or cable box 12 is fixedly attached to one side of the main body 11, with a main cable 13 leading outwards from the cable box 12. Furthermore, a spring carrier 3 of a Bourdon tube spring (not shown), which acts as a measuring element, is shown. In the assembled state, the spring carrier 3 is arranged in the cylindrical main body 11 of the measuring instrument housing 1. The spring carrier 3 has a process connection on its underside and a pointer mechanism 2 on its upper side. A connecting element 21 of the pointer mechanism 2 is directly connected to a free end of the measuring element (not shown) in the assembled state, and a pointer 8 of the pointer mechanism 2 indicates the measured value on a dial 6.Furthermore, a retaining plate 31 is attached to the spring carrier 3, the upper end of which has a projection 32 with a continuous, circular recess in which a bushing 7 is mounted in the assembled state and secured by means of a retaining ring 33. At the lower end of the retaining plate 31, two cylindrical pins 35 protrude, to which the dial 6 is attached and which simultaneously serve as a mechanical stop for a first and a second support component 41, 42. The first support component 41 and the second support component 42, which are identical in construction and to which a bistable reed switch 511, 521, biased by a bias magnet 512, 522, is attached via a respective printed circuit board 51, 52, overlap in a rotation axis of the pointer 8. The support components 41, 42 are furthermore rotatably mounted via a spiral spring 34 acting as a compression spring and rest on a projection 32 of the spring carrier 3 via the retaining ring 33. The dial 6, the support components 41, 42 including the printed circuit boards 51, 52 and the reed switches 511, 521 are connected to each other via the socket 7 by the compression spring 34 and the axial retaining ring 33. The spring 34 generates the contact pressure required for a backlash-free mounting of the aforementioned components near the axis.The dial 6 is further secured by the pins 35, which protrude through the bores 61 in the dial 6. The first reed switch 511 can be moved into a desired position by rotating the first support component 41 about a pointer rotation axis, and the second reed switch 521 can be moved into a desired position similarly by rotating the support component 42. This means that the first reed switch 511, which is attached to the first support component 41 by means of the first circuit board 51, can be moved into a specific position about the pointer rotation axis by means of the support component 41, which is rotatably mounted on the mounting plate 31. Similarly, the second reed switch 521, which is attached to the second support component 42 by means of the second circuit board 52, can be moved into a specific position about the pointer rotation axis by means of the support component 42, which is rotatably mounted on the mounting plate 31.In a frontal view of the measuring instrument on the dial 6, the first support component 41 is arranged behind the second support component 42 with respect to the pointer rotation axis. A slider element 411, 421 with a setpoint indicator function is attached to the outer circumference of each support component 41, 42. This slider element is continuously movable along the dial 6 and along a specific portion of the outer circumference of the respective support component 41, 42. It displays the desired measuring range (end) value, set by the respective reed switch 511, 521, on the dial 6. Each slider element 411, 421 also connects the corresponding support component 41, 42 to the dial 6 by means of a force-fit connection to prevent unwanted adjustment of the support components 41, 42. Below each slider component 411, 421, a cylindrical recess 417, 427 is provided in each support component 41, 42, into which, in the assembled state of the measuring device, a rubber element, optionally as a friction brake (not shown), is inserted to prevent the respective support component 41, 42 from slipping relative to the dial 6 or 42.to prevent the support components 41, 42 from slipping relative to each other. The measuring device according to the invention also has a viewing window (not shown) made of glass or plastic, in which an adjusting lock (not shown) is axially installed. An adjusting arm (not shown) is rigidly connected to the adjusting lock, with which the slide components 411, 421 and thus also the reed switches 511, 521 can be moved from the outside by an operator in the radial direction of the axis of rotation. As can be seen in the detailed view in Fig. 1, a switching magnet 9, magnetized parallel to the dial 6, is arranged at the tip of the pointer 8 on a designated end section 82 of the pointer 8 in the assembled state of the measuring instrument for switching the reed switches 511, 521. The switching magnet 9 can, for example, be glued to the end section 82 or connected to it by another known connection method, such as clamping or the like. A precise arrangement of the support components 41, 42 and the components attached to them in the assembled state is shown in the exploded view in Fig. 2 in a top view of the rear of the measuring instrument shown in Fig. 1 as well as in Fig. 3A and Fig. 3B. As can be seen in Figs. 2, 3A, and 3B, the support components 41, 42 overlap at a round projection 412, 422, which is provided on each support component 41, 42. A hole is provided in each projection 412, 422 through which the socket 7 passes when the measuring device is assembled. This ensures that the support components 41, 42 can only be rotated about the pointer axis shown by a dashed line. Furthermore, a rectangular recess 419, 429 is provided in each support component 41, 42, in which connecting pins 5131, 5231 of terminals 513, 523 are exposed, thus enabling a connection of the circuit board 51, 52 to the main cable harness 13. The circuit board 51 is attached to the carrier component 41 in the assembled state of the measuring device, lying flat on it, with pins 414 provided on the carrier component 41 being pressed into holes 514 provided in the circuit board 51.Similarly, in the assembled state of the measuring device, the circuit board 52 is attached to the carrier component 42, with pins 424 provided on the carrier component 42 being pressed into holes 524 provided in the circuit board 52. For this type of connection, plastic pins can also be softened, for example, with ultrasound or thermally melted, resulting in a rivet-like connection. Each circuit board 51, 52 has a continuous recess 515, 525, which, by its shape, can accommodate the respective reed switch 511, 521, with the reed switch being conductively connected to the respective circuit board 51, 52. A conductor (not shown) provided in each circuit board 51, 52 electrically connects the reed switch 511, 521 to the corresponding terminal 513, 523. The electrical connection between the terminals 513, 523 and the cable socket 12 is also provided.The main cable harness 13 is connected via pre-assembled control cables, flexible circuit boards or stranded wires (not shown). As can be clearly seen in Fig. 2, the arrangement of the reed switch 511 on the carrier component 41 differs from the arrangement of the reed switch 521 on the carrier component 42, since the circuit board 52 is mounted on the carrier component 42 in such a way that the position of the reed switch 521 with respect to the pointer rotation axis differs from the position of the reed switch 511. In Fig. 3A and Fig. 3B, the components shown in Fig. 2 are depicted in their assembled state, approximately in a fully pivoted end position of the support components 41, 42. In this position, a section 416 of one of the support components 41 is partially located in a gap 426 formed by the support component 42 and the circuit board 52. In the view shown in Figs. 3A and 3B, it is clearly visible that the reed switches 511, 521 are arranged one behind the other in this position of the support components 41, 42, i.e., that the reed switches 511, 521 partially overlap at their respective ends closest to the axis of rotation. In this view, reed switch 521 is arranged radially in front of reed switch 511, starting from the axis of rotation of the support components 41, 42, with the longitudinal axes of the reed switches 511, 521 being parallel to each other and thus spanning approximately the maximum possible measuring range.The magnetically sensitive area of ​​one of the reed switches 511, 521, which can also be assumed to be located in the center of the respective reed switch, is located further away from both the magnetically sensitive area of ​​the other reed switch 511, 521 and the bias magnet 512, 522 of the other reed switch 511, 521 than the maximum possible switching distance between the switching magnet 9 and the magnetically sensitive area of ​​one of the reed switches 511, 521. This prevents mutual interference between the reed switches 511, 521. Figure 3B shows a rear view of the arrangement shown in Figure 3A. The cylindrical recesses 417, 427 in each support component 41, 42, into which a rubber element (not shown) is inserted when the measuring instrument is assembled, are located near the recesses 418, 428, in which the slide components 411, 421 are guided when the measuring instrument is assembled. The connecting pins 5131, 5231 of the terminals 513, 523 located on the respective circuit boards 51, 52, which serve to connect the circuit boards 51, 52 to the main cable harness 13, are located in the corresponding recesses 419; 429 when the instrument is assembled, in order to ensure a flat bearing surface for the support components 41, 42 on the back of the dial 6. The invention is not limited to the detailed embodiment described above. It can be modified to the extent specified in the following claims. Apart from its use in a pressure gauge, other applications for the previously described setup are conceivable. For example, the reed switch setup used in the measuring device can be used in any other conceivable measuring device with an analog display. It suffices if a pointer element can be equipped with a permanent magnet and the two reed switches are mounted on the described supports so that they can rotate around the pointer axis.

Claims

Measuring instrument for measuring and evaluating a physical quantity, comprising a measuring element for detecting the physical quantity, wherein the measuring element moves according to the physical quantity, a pointer mechanism (2) which rotates a pointer (8) in a pointer plane about a pointer axis according to the movement of the measuring element, wherein the pointer (8) is provided with a switching magnet (9), and a first and a second support component (41, 42) which are rotatably adjustable about the pointer axis, lie in a plane parallel to the pointer plane and each is provided with a bistable reed switch (511, 521) actuated by the switching magnet (9), wherein the longitudinal axes of both reed switches (511, 521) do not pass through the pointer axis, and wherein the distance from the longitudinal axis of the first reed switch (511) to the pointer axis is less than the distance from the longitudinal axis of the second reed switch (521) to the pointer axis. Measuring device according to claim 1, wherein one of the two reed switches (521) is arranged radially behind the other reed switch (511) starting from the pointer rotation axis, when the support components (41, 42) each assume a maximum pivoted end position away from each other. Measuring device according to claim 2, wherein the second reed switch (521) is arranged radially behind the first reed switch (511) starting from the pointer rotation axis, when the support components (41, 42) each assume a maximum end position pivoted away from each other. Measuring device according to claim 3, wherein the magnetically sensitive area of ​​the first reed switch (511) is further away from that of the second reed switch (521) than the maximum possible switching distance between the switching magnet (9) and the magnetically sensitive area of ​​one of the reed switches (511, 521). Measuring device according to one of the preceding claims, wherein the support components (41, 42) are identical in construction. Measuring instrument according to claim 5, wherein the support components (41, 42) are arranged in a mirror-image fashion and rotatably mounted on the pointer axis. Measuring instrument according to one of the preceding claims, wherein the measuring instrument further comprises a dial (6) for displaying a measured value indicating the physical quantity by means of the pointer (8). Measuring instrument according to claim 7, wherein an adjusting element (411, 421) is provided on each support component (41, 42) which is adjustable relative to the respective support element (41, 42) in order to display the corresponding set switching measurement value on the dial outer diameter. Measuring device according to claim 8, wherein fixed locking points are provided on each support component (41, 42) in accordance with a switching hysteresis of the reed switch, optionally for increasing or decreasing pressure. Measuring instrument according to claim 8 or 9, wherein the adjusting element (411, 421) provided on each support component (41, 42) generates a contact pressure between the respective support component (41, 42) and the dial (6). Measuring instrument according to one of claims 7 to 10, wherein each support component (41, 42) is rotatably mounted relative to the dial (6) by means of a bushing (7) through which the pointer axis passes. Measuring device according to claim 11, wherein a retaining plate (31) supports the dial (6) at two points and supports the bushing (7). Measuring device according to one of the preceding claims, wherein the smallest arc angle between the two reed switches (511, 521) is a minimum of 10°, which corresponds to a minimum adjustable switching range. Measuring device according to one of the preceding claims, wherein the largest arc angle between the two reed switches (511, 521) is a maximum of 220°, which corresponds to a maximum adjustable switching range. Measuring device according to one of the preceding claims, wherein the adjustable switching range comprises 10 to 90% of the full scale value. Measuring device according to one of the preceding claims, wherein the reed switches (511, 521) have a magnetic sensitivity of 40 to 45 or 45 to 50 ampere turns and can be switched as full-fledged changeover switches between two poles. Measuring device according to one of the preceding claims, wherein the bistable reed switches (511, 521) are each provided with a bias permanent magnet (512, 522) for holding the corresponding switching tongue of the respective reed switch (511, 521) in a predetermined switching position. Measuring device according to one of the preceding claims, wherein the reed switches (511, 521) are designed to be mains voltage capable.

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