JP6709893B2 - Magnetic sensor device for outputting instrument pointer value, instrument equipped with the same, and calibration method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor device for outputting a meter pointer value, a meter equipped with the same, and a calibration method thereof. More specifically, it can be retrofitted to an instrument equipped with a scale plate, a pointer that rotates on the scale plate, and a transparent cover plate that covers the scale plate and the pointer, and a magnet and a magnetic sensor attached to the pointer, BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instrument pointer output magnetic sensor device that outputs an indicator value of a pointer as an electric signal at a relative position of a magnet with respect to a magnetic sensor, an instrument including the same, and a calibration method thereof.

As an IC tag unit that can be used as an assisting device for confirming instrument calibration and performing regular instrument inspection by attaching it to an existing instrument, for example, an industrial instrument such as a pressure gauge, a thermometer, a flow meter, and a power meter, The one described in Patent Document 1 is known. An IC tag that has a non-contact IC tag capable of transmitting stored information by radio waves and an attaching means for attaching the IC tag to the instrument and can read and write instrument information, calibration information, inspection information, etc. It can be attached to the instrument without being affected by the parts and hindering the visibility of the instrument scale, and without being deteriorated by dust or raindrops. Further, an RFID is used in which an IC chip is driven by an electromotive force of an electromagnetic wave by transmitting and receiving an RF (Radio Frequency) radio wave and the radio wave communicates with a memory of the IC chip. However, when confirming the measured value, it was necessary to perform visual confirmation and record it by a person.

Further, a device described in Patent Document 2 is known as a device that can be retrofitted to an analog instrument and can digitize the value of the instrument without impairing the calibration state of the instrument. However, according to this invention, the transparent cover plate requires special processing, and the wiring is exposed to the scale plate side, so that the visibility is also impaired.

International Publication No. 2015/174374 Registered utility model 3161399

In view of the conventional situation as described above, the present invention provides a magnetic sensor for outputting a meter pointer value, which can be retrofitted to an analog meter and does not impair the calibration state and visibility of the meter, and which can read the value indicated by the pointer and take it out to the outside. An object of the present invention is to provide a device, an instrument equipped with the device, and a calibration method thereof.

In order to achieve the above-mentioned object, the characteristic of the magnetic sensor device for outputting an instrument pointer according to the present invention is that an instrument provided with a scale plate, a pointer rotating on the scale plate, and a transparent cover plate that covers the scale plate and the pointer is attached to a retrofit. In a configuration that can be attached and has a magnet and a magnetic sensor to be attached to the pointer, and outputs the indicated value of the pointer as an electric signal at the relative position of the magnet with respect to the magnetic sensor, the magnet is used as the center of the pointer for the pointer of the instrument. A magnetic clip is attached at a position displaced in the circumferential direction from the shaft, the magnetic sensors are provided at a plurality of locations around the central axis, and the rotational displacement of the magnet due to the rotation of the pointer is provided at a plurality of locations. Is to be obtained as an electric signal at the relative position of, and a pair of magnetic sensors at each location are provided so as to be overlapped with respect to the central axis direction, and the outputs of each pair of magnetic sensors are differentially output. Especially.

According to the magnetic sensor device having the same configuration, a pair of magnetic sensors at each location are provided so as to be overlapped with respect to the central axis direction, and the output of each pair of magnetic sensors is differentially output. It is possible to eliminate the influence of external magnetism such as geomagnetism that commonly affects. Further, since the pair of magnetic sensors are arranged in the central axis direction, there is an advantage that the displacement in the rotation angle direction due to the rotation with the magnet is small and the error is small. Moreover, the magnet can be attached only to the position displaced by the clip in the circumferential direction from the central axis of the pointer, and the magnetic sensors and the like can be concentrated near the central portion of the transparent cover plate, which also hinders the visibility of the scale. Never. Regarding the replacement of the transparent scale cover plate equipped with a sensor, for example, regarding the replacement of the transparent scale cover plate related to the aneroid type pressure gauge, repair within the scope of "minor repair" prescribed in Article 10 of the Ordinance for Enforcement of the Measurement Act of Japan. Therefore, it corresponds to the repair that does not affect the accuracy and performance of the specified measuring instrument. Anyone can do it without the need for notification of repair business and removal of certification stamps. Data can be taken out from the surface of the transparent cover plate by wireless communication.

In the above feature, each of the magnetic sensors is a barber pole type magnetoresistive element in which a magnetoresistive circuit is spirally provided on a base material, and the pair of magnetic sensors have the spiral directions in the same direction, and are substantially parallel to each other. You may arrange in proximity. According to this configuration, since each pair of barber pole type magnetic sensors are arranged in parallel in the same direction with the spiral directions being the same, the magnetic characteristics with respect to the geomagnetism are also the same, and the influence of the geomagnetism on each sensor. It can be wiped off without considering the characteristics of.

In addition, each pair of magnetic sensors at each of the locations may be provided at angular positions corresponding to the zero position of the pointer, the maximum position of the pointer, and the position of the intermediate value therebetween. By arranging each pair of magnetic sensors in this way, the differential output at each position becomes maximum, and high accuracy after calibration can be secured.

According to the gist of the present invention, in constructing an instrument, a scale plate, a pointer rotating on the scale plate, and a transparent cover plate for covering the scale plate and the pointer, a dial and a main body, and a meter pointer value output having the above-mentioned characteristics By providing the magnetic sensor device for use in the central portion of the transparent cover plate in a state where the scale of the scale plate is not concealed, an instrument whose visibility is not hindered is provided.

Further, in the instrument, the dial and the main body or the scale plate may be composed of a magnetic shield. With this configuration, the magnetic force lines passing through the magnetic sensor are blocked by the shield effect, and the influence of geomagnetism can be wiped off.

On the other hand, the characteristic of the calibration method of the magnetic sensor device for outputting the meter pointer value in the above-mentioned measuring instrument is that the sensor device has a sensor unit having the sensor and an output correcting means, and the sensor unit is provided on the transparent cover plate. After the magnet is attached and the magnet is attached to the pointer with a clip, the sensor unit is rotated together with the transparent cover plate to calibrate the output value during movement of the pointer, and store it in the output correction means. According to this feature, calibration can be performed by rotating the transparent cover plate without actually giving a physical quantity to the existing instrument and operating the pointer, and installation and maintenance are extremely easy.

Another feature of the magnetic sensor device of the present invention is that it further has a transparent cover plate, and the sensor unit having the sensor is provided at a position where the scale of the scale plate is not hidden when the transparent cover plate is attached to the instrument. It is in. According to the same feature, by attaching the center of the transparent cover plate and the center of the sensor unit in advance, the sensor alignment is completed only by replacing the transparent cover plate with the sensor unit attached, Installation will be facilitated.

According to the characteristic configuration of the present invention, a magnetic sensor device for outputting a meter pointer value, which can be retrofitted to an analog meter and does not impair the calibration state and visibility of the meter, and which can be read out by reading the value indicated by the pointer, It has become possible to provide an instrument equipped with this and a calibration method thereof.

Other objects, configurations and effects of the present invention will be apparent from the following embodiments of the invention.

It is a front view of an instrument provided with a magnetic sensor device for outputting an instrument pointer according to the present invention. It is the side view which crushed a part of FIG. It is an exploded side view of an instrument. (A) is a front view of a 1st board|substrate, (b) is a front view of a 2nd board|substrate, (c) is a front view of a 1st pair sensor, (d) is a side view of a 1st pair sensor. It is a principal part sectional drawing of FIG. It is a figure which shows the electric system of this sensor unit. It is a figure for demonstrating the calibration method of the sensor unit concerning 2nd Embodiment of this invention, (a) is a normal position of a sensor unit, (b) is calibration of the zero point of a sensor unit, (c). FIG. 4 is a diagram for explaining a calibration method for the maximum points of the sensor unit. It is 3rd Embodiment which uses a different kind of magnetic sensor, (a) is a circuit diagram which shows an element simple substance, (b) is a magnetic detection circuit which uses a different element.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the first embodiment will be described with reference to FIGS.
As shown in FIGS. 1 to 3, an instrument 50 provided with the “instrument pointer value output magnetic sensor device 1” (hereinafter, referred to as a magnetic sensor device) according to the present invention has a Bourdon tube mechanism 57 in a case body 51, as shown in FIGS. Is supported, the rotary shaft coming out of the Bourdon tube mechanism 57 is inserted into the scale plate 56, and the pointer 55 is attached, whereby the pointer 55 is rotated relative to the scale 56a of the scale plate 56 by the action of the Bourdon tube mechanism 57, Display pressure. A transparent cover plate 53 for protecting the scale plate 56 is provided on the front surface of the scale plate 56, and is supported by the case body 51 by screwing the cover 52 to the case body 51 via the dial 54. Here, the Bourdon tube pressure gauge is taken as an example, but the present invention can be applied to any kind of gauge having a pointer.

The scale 56a of the scale plate 56 is arranged in an arc around the central axis of the pointer 55. In this example, the tip of the pointer 55 is rotated by the pressure supplied from the lower portion to the Bourdon tube mechanism 57 from the scale 0 to 1.5. And display the pressure. The manufacturer name and the type of instrument, such as a pressure gauge and a flow meter, are indicated near the center of the scale plate 56, and the company emblem and the like are indicated as instrument information at the bottom.

The magnetic sensor device 1 includes the magnetic sensor unit 10 provided on the transparent cover plate 53 and the magnet unit 40 provided on the pointer 55. The magnetic sensor unit 10 is configured by sequentially providing a first substrate 11 and a second substrate 12 on a mounting sheet 14. The mounting sheet 14 includes a transparent sheet body 14a and an adhesive layer 14b for attaching the sheet body 14a to the transparent cover plate 53. Although illustration is omitted, by providing a cover seat body substantially similar to the seat body 14a and sandwiching the both substrates 11 and 12 between the seat body 14a and the cover seat body, the waterproof performance can be improved. .. In the magnet unit 40, as shown in FIGS. 1 and 5, a magnet 41 made of a permanent magnet is attached to a pointer 55 by two clips 42. The sheet body 14a is made of a deformable synthetic resin, and one or both of them may be made of glass or a hard synthetic resin sheet. In the present embodiment, the sheet body 14a is made of a transparent synthetic resin sheet so as not to obstruct the view of the scale plate 56. Similarly, the adhesive layer 14b is transparent. Although the sheet body 14a and the adhesive layer 14b are circular with the same diameter and formed smaller than the inner diameter of the cover 52, they may be formed close to the same inner diameter but slightly smaller.

The magnetic sensor unit 10 includes a first board 11 having a wireless module 20 and a battery 21 on the surface of a circuit board 11a shown in FIGS. 1, 4(a) and 5, and a circuit board shown in FIGS. The second substrate 12 having the MPU 22 on the front surface of 12a and the three pair sensors 13A to 13C on the back surface thereof is laminated and provided. Further, as shown in FIGS. 4C and 4D, the first pair sensor 13A is provided with a first near sensor 13a and a first distance sensor 13b on the front and back surfaces of the circuit board 13x, respectively. Are arranged in parallel with each other with the thickness a of the circuit board 13x in the axial direction of the pointer. Both sensors 13a and 13b use barber pole type magnetoresistive elements, and both have the same spiral direction. By arranging both sensors 13a and 13b in this way and taking the difference between them (more specifically, subtracting the value of the first distance sensor 13b from the output value of the first near sensor 13a) The effect of the detected geomagnetism can be offset. The second and third pair sensors 13B and 13C are also configured similarly to the first pair sensor 13A.

When the magnetic sensor unit 10 is attached to the instrument, the first pair sensor 13A is set to the zero point position of the scale 56a, the third pair sensor 13C is set to the maximum position of the scale 56a, and the second pair sensor 13B is set to the middle of the scale 56a. Set to the position. In the state of FIGS. 1 and 4, the first and third pair sensors 13A and C are arranged 90 degrees apart, and the second pair sensor 13B and the first and third pair sensors 13A and C are arranged 135 degrees apart. These may be arranged according to the configuration of the scale 56a. On the preceding sheet body 14a, the first mark 15a is located at the zero point position of the scale 56a corresponding to the first pair sensor 13A, the third mark 15c is located at the maximum position of the scale 56a corresponding to the third pair sensor 13C, and the second pair sensor 13B is located. The second mark 15b is displayed at the intermediate position of the corresponding scale 56a, and is used for alignment.

Next, the circuit configuration of the magnetic sensor unit 10 will be described with reference to FIG. In the first pair unit 13A, the differential output of the first near sensor 13a and the first far sensor 13b is obtained by the operational amplifier 25, converted into a digital signal by the A/D converter 26, and input to the correction unit 27. The outputs of the second and third pair units 13B and 13C are processed in the same manner and input to the correction unit 27. Taking the first pair unit 13A as an example, the digital output becomes maximum when the magnet 41 is positioned at the position of the first mark 15a, and the digital output becomes minimum when the magnet 41 is positioned at a diagonal position 180 degrees apart. At the intermediate position, the output value fluctuates trigonometrically so as to take the intermediate value of these values. The same applies to the second and third pair units 13B and C, and it is possible to obtain the indication value of the pointer 55 by combining the differential outputs of the three pair units in the correction unit 27. The storage unit 28 stores the indication value of the pointer at each time, the inspection state before sticking to the instrument or at the time of inspection, the unique ID number of the instrument 50, the model of the instrument 50, the calibration deadline of the instrument 50, the previous inspection of the instrument 50. Information such as date, scheduled next inspection date, inspection operator name, and time stamp may be stored. The communication module 20 includes a module main body 20a and an antenna 20b. For example, in response to a request from an external reader/writer 70, the data in the previous storage unit 28 is extracted, and the control unit 29 performs calibration in the correction unit 27. I do.

The reader/writer 70 includes a transmission/reception unit 71a, an antenna 71b, a control unit 72, and a touch panel 73, controls the magnetic sensor unit 10 through the communication module 20 and extracts the value of the pointer. As the driving power of the magnetic sensor unit 10, the driving power may be supplied by the electromotive force of an electromagnetic wave by transmitting and receiving an RF (Radio Frequency) radio wave through the transmitter/receiver 71a and the antenna 71b, in addition to using the battery 21.

As a material of the sheet body 14a, for example, a biaxially stretched nylon film, a biaxially stretched polypropylene (OPP) film, a biaxially stretched polyester resin film, or a single body thereof is used. A film is particularly preferably used. The thermoplastic resin layer only needs to be capable of storing RFID tags by being melted by heat and fusing the laminated body to each other, and examples thereof include low density polyethylene, medium density polyethylene, high density polyethylene, and linear ( Cotton-like) low density polyethylene, ethylene/α-olefin copolymer polymerized using metallocene catalyst (single-site catalyst), polypropylene, ethylene/vinyl acetate copolymer, ionomer resin, ethylene-ethyl acrylate copolymer , Ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-propylene copolymer, methylpentene polymer, polyolefin resin such as polyethylene or polypropylene, acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, etc. One or more selected from acid-modified polyolefin resins modified with unsaturated carboxylic acids can be used. The thickness of the thermoplastic resin layer is preferably about 10 μm to 100 μm in consideration of heat sealability and the like.

In the instrument 50, the dial 54 (or the cover 52) and the main body 51 or the scale plate 56 may be configured by a magnetic shield. With this configuration, the magnetic force lines passing through the magnetic sensor are blocked by the shield effect, and the influence of geomagnetism can be wiped off. Magnetic shields include iron, cobalt, nickel, silicon steel, supermalloy, permalloy, and amorphous magnetic materials, as well as soft magnetic electronic ceramic materials containing iron oxide as the main component, such as soft ferrite, and polyester-based silver-copper conductive materials. Paint or the like can be used.

Further, as the transparent cover plate 53, a glass plate or the like can be used in addition to the material of the above-described sheet 14 formed to be rigid, an acrylic plate, a polycarbonate plate. As the adhesive layer 15, for example, an acrylic pressure-sensitive adhesive can be used, and a layer containing a cross-linking agent together with an acrylic polymer may be used. By adhering the sheet body 14a to the transparent cover plate 53 with the attaching layer 14b, the strength of the transparent cover plate 53 is increased and cracking and scattering are prevented.

When attaching the magnetic sensor device 1, the release paper that protects the adhesive layer 14b is peeled off, the cover 52 and the transparent cover plate 53 are removed, and the center of the sheet 14 and the center of the transparent cover plate 53 are aligned as much as possible. It is attached to the back surface of the transparent cover plate 53. The magnetic sensor device 1 considers that the pressure gauge can be easily installed on the user side by anyone, but this is allowed by the Japanese Measurement Law, which is stipulated in Article 10 of the Measurement Law Enforcement Regulations. "Repairs" that do not affect the accuracy or performance of the specified measuring instrument (there is no need for notification of repair business or removal of certification stamps, anyone can do it.) ..

Calibration and initial setting when the magnetic sensor unit 10 is installed will be described. By operating the reader/writer 70 or the like in a state where no pressure is applied to the meter 50, the three values obtained by the difference in the three pair sensor units 13A to 13C are stored in the storage unit 28 as zero values. Next, pressure is applied to the instrument 50 to set the pointer 55 to the maximum value, and the reader/writer 70 or the like is operated to store the three differential outputs at this time in the storage unit 28 as the maximum values. As a result, the maximum value is calibrated, and the outputs (voltage values) of the three pair sensors 13A to 13C can be converted into pressure values together with the minimum value and the intermediate value to be measured. The value of this calibration is stored in the storage unit 28 together with the date and time of the calibration. Also, settings such as the interval for sending sensor data, clock adjustment, and pressure value for sending an alarm mail are set via the reader/writer.

Next, another embodiment of the present invention will be described. In the following description, the same members as those in the above-described embodiment are designated by the same reference numerals. Moreover, each embodiment can be implemented in combination with each other.

In the second embodiment shown in FIGS. 7A to 7C, the zero point and the highest point are calibrated without moving the pointer 55. In the present embodiment, as shown in FIG. 7A, the magnetic sensor unit 10 is formed to have a larger diameter than that of the previous embodiment, and the outer periphery thereof is close to the scale 56a of the instrument 50. The first mark 15a and the third mark 15c are provided at the zero point and the highest point of the scale 56a, respectively.

In the calibration, as shown in FIG. 7B, first, the magnetic sensor unit 10 is moved in the direction of arrow R1 together with the transparent cover plate 53 so that the first mark 15a overlaps the indicator 55a of the pointer 55. Rotate until 15a and indicator 55a overlap. In this state, the previous zero point calibration is performed. Next, as shown in FIG. 7C, the magnetic sensor unit 10 is rotated together with the transparent cover plate 53 in the direction of arrow R2 until the third mark 15c and the indicating portion 55a overlap. In this state, perform the highest point calibration. Then, the magnetic sensor unit 10 is rotated until the state of FIG. 7A is reached, and the calibration is completed. A procedure for moving the second mark 15b so as to overlap the instruction section 55a may be further included.

Unlike the barber pole type magnetic sensor shown in the previous embodiment, the third embodiment shown in FIG. 8 is a magnetic sensor 13a1 in which magnetoresistive elements are arranged in a meandering manner as shown in FIG. 8A. The difference is that they use'. The magnetic sensor 13a1' has an element in which magnetic resistances Rx and Ry are connected in series, and detects proximity of the magnet 41 (decrease in distance d) by both magnetic resistances Rx and Ry.

In the magnetic sensor of this embodiment, as shown in FIG. 8B, the X-direction magnetic resistance Rx, the Y-direction magnetic resistance Ry, the variable resistance Rv, and the fixed resistance Rf form a bridge 13a2'. The voltage E is applied to the input terminals 61a and 61b, and the variable resistor Rv is adjusted so that the voltage of the output terminals 62a and 62b, which are not close to the magnet 41, are normally zero. Since the effect of temperature acts on both the X-direction magnetic resistance Rx and the Y-direction magnetic resistance Ry, the output of the bridge is not easily affected by temperature. However, since the magnetic fields have X and Y directions, the proximity of the magnet 41 can be detected by taking the difference between the output terminals 62a and 62b. In each pair sensor, two magnetic sensors 13a1', 13b1' (not shown, the same as the above-mentioned relationship of 13a, 13b) are superposed with Rx, Ry oriented in the same direction, and the bridge 13a2' closer to the magnet. The influence of the geomagnetism is excluded by subtracting the differential output of the output terminals 62a and 62b of the bridge 13b2' (not shown, which is the same as the relationship of 13a and 13b above) farther from the magnet from the differential output of the output terminals 62a and 62b of It is better to obtain the output signal.

INDUSTRIAL APPLICABILITY The present invention can be used as an assisting device for confirming instrument calibration and performing regular instrument inspection by attaching the instrument to an existing instrument. INDUSTRIAL APPLICABILITY The present invention can be used for existing measuring instruments, for example, industrial measuring instruments such as pressure gauges, thermometers, flow meters, and power meters.

1: Magnetic sensor device for outputting meter pointer value, 10: Magnetic sensor unit, 11: First substrate, 11a: Circuit substrate, 12: Second substrate, 12a: Circuit substrate, 13: Pair sensor substrate, 13a: First proximity sensor , 13b: first distance sensor, 13c: second near sensor, 13d: second far sensor, 13e: third near sensor, 13f: third far sensor, 13x: circuit board, 13A: first pair sensor, 13B: first. Two pair sensor, 13C: Third pair sensor, 13a1': Magnetic sensor, 13a2': Bridge, 14: Mounting sheet, 15a: First mark, 15b: Second mark, 15c: Third mark, 20: Communication module, 20a: Module body, 20b: antenna, 21: battery, 22: MPU, 25: operational amplifier, 26: A/D converter, 27: correction unit, 28: storage unit, 29: control unit, 40: magnet unit, 41: magnet , 42: clip, 50: instrument, 51: case body, 52: cover, 53: transparent cover plate, 54: facing, 55: pointer, 55a: indicator, 56: scale plate, 56a: scale, 57: Bourdon tube Mechanism, 61a, 61b: Input terminal, 62a, 62b: Output terminal, 70: Reader/writer, 71a: Transmitter/receiver section, 71b: Antenna, 72: Control section, 73: Touch panel, Rx: X direction magnetic resistance, Ry: Y direction Magnetic resistance, Rv: Variable resistance, Rf: Fixed resistance

Claims (7)

It can be retrofitted to an instrument equipped with a scale plate, a pointer that rotates on the scale plate, and a transparent cover plate that covers the scale plate and the pointer. A magnetic sensor device for meter pointer output that outputs the indicated value of the pointer as an electric signal at the relative position of
The pointer of the instrument is provided with a magnet clip that attaches the magnet to a position displaced in the circumferential direction from the central axis of the pointer, and the magnetic sensors are provided at a plurality of positions around the central axis, and the magnetic sensor is provided with the rotation of the pointer. The rotational displacement of the magnet is obtained at relative positions with a plurality of magnetic sensors and is output as an electric signal. The magnetic sensors at each position are provided in a pair so as to be overlapped with respect to the central axis direction. The sensor output is a differential output, and is a magnetic sensor device for meter pointer value output. Each of the magnetic sensors is a barber pole type magnetoresistive element in which a magnetoresistive circuit is spirally provided on a base material, and the pair of magnetic sensors have the spiral directions of the same direction, and are arranged close to each other substantially in parallel. The magnetic sensor device for outputting a meter pointer value according to claim 1. The magnetic sensor for outputting a meter pointer value according to claim 1, wherein the pair of magnetic sensors at each of the locations are provided at angular positions respectively corresponding to a zero position of the pointer, a maximum position of the pointer and a position of an intermediate value therebetween. apparatus. A scale plate, a pointer that rotates on the scale plate, a transparent cover plate that covers the scale plate and the guide line, a counter and a main body, and the magnetic sensor device for outputting an instrument pointer value according to claim 1 is provided at the center of the transparent cover plate. An instrument provided so as not to cover the scale of the scale plate. The instrument according to claim 4, wherein the reward and the main body or scale plate are constituted by a magnetic shield. A calibration method of a magnetic sensor device for outputting an instrument pointer value in an instrument according to claim 4, wherein the sensor device has a sensor unit having the sensor and an output correcting means, and the sensor unit is provided on the transparent cover plate. After the magnet is attached and the magnet is attached to the pointer by a clip, the sensor unit is rotated together with the transparent cover plate to calibrate the output value when the pointer is moved and stored in the output correction means. Method for magnetic sensor device for automobile. Furthermore, it has a transparent cover plate,
The magnetic sensor device for outputting an instrument pointer value according to claim 1, wherein the sensor unit having the sensor is provided at a position where the scale of the scale plate is not hidden when the transparent cover plate is attached to the instrument.

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