CN221177804U

CN221177804U - Display equipment testing device for identifying nuclear power station DCS equipment

Info

Publication number: CN221177804U
Application number: CN202322802730.0U
Authority: CN
Inventors: 时建纲; 周洋; 邹华明; 包凯
Original assignee: China Techenergy Co Ltd
Current assignee: China Techenergy Co Ltd
Priority date: 2023-10-18
Filing date: 2023-10-18
Publication date: 2024-06-18
Anticipated expiration: 2033-10-18

Abstract

The utility model discloses a display equipment testing device for identifying nuclear power station DCS equipment, which comprises a power module, a photomultiplier end flange, an optical fiber and a tested equipment end flange. Specifically, the photomultiplier is connected with the power supply module through a power supply cable; the photomultiplier is connected with an external test instrument or an automatic test device through a signal cable; the photomultiplier is fixed on one side of the photomultiplier end flange; the photomultiplier tube end flange is connected with the tested equipment end flange through an optical fiber; the tested equipment end flange is provided with a light inlet hole, and test light rays are emitted into the light inlet hole from one side of the tested equipment end flange. The display equipment testing device for identifying the DCS equipment of the nuclear power station can perform pattern test on tested equipment and acquire optical signals in a severe environment, so that the testing of the DCS display equipment can be comprehensively and accurately realized, and the safety of the DCS display equipment in operation is further ensured.

Description

Display equipment testing device for identifying nuclear power station DCS equipment

Technical Field

The utility model relates to the technical field of DCS (distributed control system) testing, in particular to a display equipment testing device for identifying nuclear power station DCS equipment.

Background

The devices in the distributed control system (Distributed Control System, DCS) need to pass test items such as product testing, device identification, and factory entry verification before being put into use. Among them, the identification type test is an important component. The test is carried out under the severe environments of high temperature, low temperature, temperature and humidity integration, electromagnetic compatibility (electromagnetic compatibility, EMC), mechanical vibration, shock resistance and the like according to the characteristics of the product. The DCS system generally comprises functional modules such as data acquisition, computer control, control output, man-machine interaction, communication and the like. In addition, the man-machine interaction also comprises relevant operation devices, such as input devices of a keyboard, a key touch screen and the like, and information display devices of a display screen, an indicator light and the like. The verification of the information display device is an important component of DCS testing. The verification content comprises: whether the display of the input information is correct (e.g., data display, indicator lights are lit or flashing, etc.), and a response time test from input to display output.

Currently, in a test under a conventional environment, an automatic test for display of a display screen or an indicator lamp can be realized by testing a light intensity or a color change of a display device using a Photomultiplier (PMT). Wherein the photomultiplier is a vacuum electronic device that converts a weak light signal into an electrical signal. As shown in fig. 1, the photosensitive element 110 of the PMT is held against the display 120 under test or at a distance from the indicator light under test during testing. Meanwhile, the outside should adopt shading measures to increase the test sensitivity. The photomultiplier tube 130 converts an optical signal of light intensity or color (wavelength) variation in a certain wavelength range into an electrical signal of 0 to 5V variation by adjusting gain. When the automatic testing device 140 injects a control signal into the DCS system to be tested, the light signal (light intensity or color) of the display 120 or the indicator lamp to be tested will change, and the output voltage of the PMT will also change accordingly, i.e. the voltage signal collected by the automatic testing device 140 will change, so that the automatic test of the DCS display device can be realized based on the change of the voltage signal and the control signal. The corresponding relation between the DCS injection electric control signal and the output optical signal can be obtained by configuring the tested DCS in advance.

However, PMTs typically operate at normal temperatures of 5-50 ℃, so in high temperature/low temperature type tests, the product being tested is placed in an incubator below 0 ℃ or above 55 ℃, and PMTs cannot be brought close to the object being tested to achieve the test. In addition, the PMT has certain mass and volume, the PMT can be tightly attached to the tested display equipment by adopting temporary measures such as adhesive tape adhesion and the like for shading treatment in the conventional test, and the PMT cannot be tested by the conventional method in the mechanical vibration test. Therefore, the PMT has a narrow normal operating temperature range and is inconvenient to fix, so that test work cannot be performed in a severe environment of type tests (such as high temperature and mechanical vibration), and only the tested product can be verified before and after test stress, thereby limiting the test scene of the DCS display device. Patent CN202189274 discloses a DCS system response time testing device, which comprises a display screen for displaying the processing procedure and result of the FPGA, an FPGA module for receiving and processing the signal, and a photoelectric conversion module for converting the image color change of the controlled device, and can obtain the response time of the current controlled device by calculating the action change time when the FPGA receives the control signal and the feedback time received by the DCS control terminal. However, the device cannot perform testing work of DCS display devices in a severe environment.

Disclosure of Invention

The present utility model aims to solve at least to some extent one of the technical problems described above.

Therefore, the utility model aims to provide the display equipment testing device for the identification of the DCS equipment of the nuclear power station, which can perform pattern test on tested equipment and optical signal acquisition in a severe environment, so that the test on the DCS display equipment can be comprehensively and accurately realized.

In order to achieve the aim, the embodiment of the utility model provides a display equipment testing device for identifying nuclear power station DCS equipment, which comprises a power module, a photomultiplier end flange, an optical fiber and a tested equipment end flange,

The photomultiplier is connected with the power supply module through a power supply cable;

The photomultiplier is connected with an external test instrument or an automatic test device through a signal cable;

the photomultiplier is fixed on one side of the photomultiplier end flange;

The photomultiplier tube end flange is connected with the tested equipment end flange through an optical fiber;

the tested equipment end flange is provided with a light inlet hole, and test light rays are emitted into the light inlet hole from one side of the tested equipment end flange.

Optionally, the apparatus further comprises a gain adjustment potentiometer,

The gain adjustment potentiometer is arranged on a power supply cable connected with the photomultiplier and the power supply module.

Optionally, the other side of the photomultiplier tube flange and the other side of the tested equipment end flange are respectively provided with a first optical fiber interface and a second optical fiber interface,

The first optical fiber interface is connected with one end of the optical fiber, and the second optical fiber interface is connected with the other end of the optical fiber.

Optionally, the optical fiber is an ST multi-film optical fiber, and the first optical fiber interface and the second optical fiber interface are ST multi-film optical fiber standard female heads.

Optionally, the length of the optical fiber is less than or equal to 30 meters, and the working environment temperature is-40-75 ℃.

Optionally, the photomultiplier tube flange and the tested equipment end flange comprise a flange base, an optical fiber connector, a mounting hole and a light inlet hole,

The optical fiber connector is connected with the flange base in a welding mode;

The photomultiplier is fixed on one side of the photomultiplier end flange through a mounting hole;

The light inlet hole is arranged at the center of the flange base and is coaxial with the optical fiber connector.

Optionally, the photomultiplier tube flange further comprises:

a light absorption unit is arranged between the flange base and the photomultiplier.

Optionally, the light absorbing unit is light absorbing flannelette.

Optionally, the thickness of the light absorbing unit does not exceed 1mm.

Optionally, the gain adjustment potentiometer uses a 10K adjustable resistor.

By applying the technical scheme in the embodiment of the utility model, the following technical effects are realized:

1. The test device can carry out pattern test and optical signal acquisition on the tested equipment in a severe environment by combining the photomultiplier, the optical fiber and the flange to connect the tested equipment at the far end, so that the test on the DCS display equipment can be comprehensively and accurately realized.

2. The gain of the photomultiplier can be adjusted by the gain adjusting potentiometer according to the light intensity and wavelength characteristics, so that the sensitivity of the photomultiplier is improved.

3. The light absorption unit is arranged on the mounting plane of the flange, so that light leakage can be effectively reduced, and the signal to noise ratio of the DCS display test process can be improved, thereby effectively improving the accuracy of the test result.

4. The testing device connects the optical fiber, the photomultiplier and the tested equipment through the flange, is easy to detach, install, carry and use, and is suitable for various working scenes.

Additional aspects and advantages of the utility model will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the utility model.

Drawings

The accompanying drawings, which are included to provide a further understanding of the utility model and are incorporated in and constitute a part of this specification, illustrate embodiments of the utility model and together with the description serve to explain the utility model. In the drawings:

FIG. 1 shows a schematic diagram of a prior art DCS test device;

FIG. 2 shows a schematic structural diagram of a display device testing apparatus for nuclear power plant DCS equipment qualification according to one embodiment;

FIG. 3 (a) shows a left side view of a photomultiplier tube end flange or device under test end flange of one embodiment;

FIG. 3 (b) shows a cross-sectional view of a photomultiplier tube end flange or device under test end flange of one embodiment;

FIG. 3 (c) shows a right side view of a photomultiplier tube end flange or device under test end flange of one embodiment;

FIG. 4 shows a schematic structural diagram of another embodiment of a display device testing apparatus for identification of nuclear power plant DCS equipment;

FIG. 5 (a) shows a cross-sectional view of a photomultiplier tube flange according to yet another embodiment;

FIG. 5 (b) shows a right side view of a photomultiplier tube flange according to yet another embodiment;

FIG. 6 (a) shows a left side view of a connection flange of one embodiment;

FIG. 6 (b) shows a front view of a connection flange of one embodiment;

FIG. 6 (c) shows a right side view of a connection flange of one embodiment;

Reference numerals: 110. a photosensitive member; 120. a display to be tested; 130. a photomultiplier tube; 140. an automatic test device; 1. a power module; 2. a power supply cable; 3. gain adjustment potentiometer; 4. a photomultiplier tube; 5. a photomultiplier tube end flange; 51. a flange base; 52. an optical fiber connector; 53. a mounting hole; 54. a light inlet hole; 6. a first fiber optic interface; 7. an optical fiber; 8. a second fiber optic interface; 9. an end flange of the tested equipment; 91. a flange base; 92. an optical fiber connector; 93. a mounting hole; 94. a light inlet hole; 10. a signal cable; 11. a light absorbing unit; 610. a flange base; 620. ST standard fiber optic connectors; 630. mounting a via hole; 640. light-absorbing flannelette; 650. light holes.

Detailed Description

It should be noted that, without conflict, the embodiments of the present utility model and features of the embodiments may be combined with each other. The utility model will be described in detail below with reference to the drawings in connection with embodiments.

The utility model is described in further detail below in connection with specific examples which are not to be construed as limiting the scope of the utility model as claimed.

In the description, unless clearly indicated and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present application will be understood in specific cases by those of ordinary skill in the art. Furthermore, in the description of the present application, unless otherwise indicated, the meaning of "a plurality" is two or more.

The display device testing apparatus for identification of a nuclear power station DCS device according to an embodiment of the present utility model is described below with reference to the accompanying drawings.

Fig. 2 is a schematic structural diagram of a display device testing apparatus for identifying DCS devices of a nuclear power plant according to an embodiment of the present utility model. As shown in fig. 2, the display device testing device for identifying the DCS device of the nuclear power plant comprises a power module 1, a photomultiplier tube 4, a photomultiplier tube end flange 5, an optical fiber 7 and a tested device end flange 9.

In the present embodiment, as shown in fig. 2, the photomultiplier tube 4 is connected to the power supply module 1 through the power supply cable 2. Thereby, the power supply in the power supply module 1 can be introduced to the photomultiplier tube 4 through the power supply cable 2, thereby realizing the power supply of the power supply module 1 to the photomultiplier tube 4. In one embodiment, the photomultiplier tube 4 has a supply voltage of + -4.5-5.5 VDC and a maximum current of 10mA. Therefore, the power module 1 can adopt a small-sized double-path output power module with an output voltage of + -5 VDC and an output current of 0.5A to meet the power supply requirement.

In the present embodiment, the photomultiplier tube 4 is connected to an external test meter or an automatic test device through a signal cable 10. Thus, the electrical signal converted from the optical signal via the photomultiplier tube 4 can be output to an external test meter or an automatic test device through the signal cable 10, so that the DCS display device can be tested based on the change of the voltage signal collected by the external test meter or the automatic test device. For example, when the tested equipment is switched between yellow/blue light and black/white light, a distinct step change signal, i.e. a voltage change of 100mV or more, can be detected in the test meter or the automatic test equipment.

In this embodiment, the photomultiplier tube 4 is fixed to one side of a photomultiplier tube flange 5. As shown in fig. 3 (a) -3 (c), the photomultiplier tube flange 5 includes a flange base 51, an optical fiber connector 52, a mounting hole 53, and an light inlet hole 54. Specifically, the photomultiplier tube 4 is fixed to one side of the photomultiplier tube flange 5 through the mounting hole 53. In one embodiment, one side of the photomultiplier tube flange 5 may be screwed into mounting threads in mounting holes 53 in the photomultiplier tube 4.

The optical fiber connector 52 is integrally connected to the flange base 51 by welding. And, an optical inlet hole 54 is provided in the center of the flange base 51 coaxially with the optical fiber connector 52 for transmitting the optical fiber 7 to the photomultiplier tube 4.

In this embodiment, as shown in fig. 2, the photomultiplier end flange 5 is connected with the tested device end flange 9 through the optical fiber 7, so that the photomultiplier end flange is easy to disassemble, install, carry and use, and can be suitable for various working scenes. Specifically, the other side of the photomultiplier tube flange 5 and the other side of the device under test end flange 9 are respectively provided with a first optical fiber interface 6 and a second optical fiber interface 8. The first optical fiber interface 6 is connected to one end of the optical fiber 7, and the second optical fiber interface 8 is connected to the other end of the optical fiber 7. Thereby, optical signals can be transmitted from the device under test end flange 9 to the photomultiplier tube end flange 5 via optical fiber conduction. In addition, the normal temperature and humidity operation range of the optical fiber and the flange far exceeds the normal temperature and humidity operation range of the photomultiplier, so that the combination of the photomultiplier, the optical fiber and the flange is used for connecting the remote tested equipment, the tested equipment can be subjected to pattern test and optical signal acquisition in a severe environment, and the test of the DCS display equipment can be comprehensively and accurately realized.

It is worth noting that in high temperature/low temperature version experiments, the device under test will be placed in a harsh environment below 0 ℃ or above 55 ℃. In a specific embodiment, the operating environment temperature of the optical fiber 7 is-40-75 ℃. Therefore, the optical signal can be conducted to the photomultiplier 4 from the tested device end flange 9 in a severe environment through the optical fiber jumper consisting of the first optical fiber interface 6, the optical fiber 7 and the second optical fiber interface 8, the photomultiplier 4 can normally operate in the environment within the temperature and humidity range required by the photomultiplier, and the limitation of the working environment required by the photomultiplier to the DCS display device testing working environment is solved, so that the DCS display device testing work can normally perform type tests in the severe environment.

In addition, since the loss of the optical fiber is low, the length of the optical fiber 7 may be set to 10 meters or less to satisfy the requirements of the type test. In a preferred embodiment, the optical fiber 7 is an ST multi-film optical fiber, and the first optical fiber interface 6 and the second optical fiber interface 8 are ST multi-film optical fiber standard female heads, which can not only be suitable for the transmission distance requirement in the DCS display device test scene, but also can carry the transmission of multiple optical signals.

In this embodiment, as shown in fig. 3 (a) -3 (c), the device under test end flange 9 has an entrance aperture 94, and test light can enter the entrance aperture 94 from one side of the device under test end flange 9. In addition, the device-side flange 9 under test further includes a flange base 91, a fiber optic connector 92, and mounting holes 93. Specifically, the optical fiber connector 92 is connected to the flange base 91 by welding. And, an optical inlet 94 is provided at the center of the flange seat 91 coaxially with the optical fiber connector 52 for transmitting the test light to the optical fiber 7.

In addition, in a specific embodiment, since the end flange 9 of the tested device is made of a light metal material, the total weight of the end flange 9 of the tested device and the second optical fiber interface 8 can be smaller than 10g, so that one side of the end flange 9 of the tested device can be bonded with the plane of the tested device by adopting double faced adhesive tape or adhesive tape, not only can the end flange be not easy to fall off or deform in an anti-vibration test and a mechanical vibration test, but also damage to the surface of the tested device and a flange joint can be avoided when the double faced adhesive tape is removed at the end of the test.

Further, in another embodiment, as shown in fig. 4, the apparatus may further comprise a gain adjustment potentiometer 3. Specifically, the gain adjustment potentiometer 3 is provided on the power supply cable 2 to which the photomultiplier tube 4 is connected to the power supply module 1. In one embodiment, the gain adjustment potentiometer 3 may employ a 10K adjustable resistor, and may adjust the gain of the photomultiplier tube according to the light intensity and wavelength characteristics. The PMT gain may be adjusted prior to the pattern test so that the output voltage difference of the PMT is between 0.1V and 5V at the time of signal switching.

Further, in still another embodiment, as shown in fig. 2 and fig. 5 (a) -5 (b), a light absorbing unit 11 is provided between the flange base 51 and the photomultiplier tube 4. In one embodiment, the light absorbing unit 11 is a light absorbing fleece. Further, the thickness of the light absorbing unit 11 does not exceed 1mm. Specifically, black flannelette with the thickness not exceeding 1mm and other light-absorbing materials can be adopted, the photomultiplier tube end flange 5 is tightly pressed against the surface of the photomultiplier tube 4, and the middle opening is transparent, so that light leakage can be effectively reduced, the signal-to-noise ratio of a DCS display test process is improved, and the accuracy of a test result is effectively improved.

The following describes in detail a display device testing apparatus for identification of a DCS device of a nuclear power plant in one embodiment.

As shown in fig. 4, in the present embodiment, the display device testing apparatus includes a power module 1, a power supply cable 2, a gain adjustment potentiometer 3, a photomultiplier tube 4, a photomultiplier tube end flange 5, a first optical fiber interface 6, an optical fiber 7, a second optical fiber interface 8, a device under test end flange 9, and a signal cable 10. The specific functions of the above components of the display device testing apparatus are as follows:

A power module 1 for supplying direct current power to the photomultiplier;

a power supply cable 2 for introducing power supply of the power supply module to the photomultiplier;

the gain adjusting potentiometer 3 is used for adjusting the sensitivity of the photomultiplier, namely the amplification factor of the photomultiplier.

A photomultiplier 4 for converting a weak optical signal into an electrical signal;

A photomultiplier tube flange 5, one end of which is fixed with the mounting screw thread on the photomultiplier tube by a screw; the other end is an ST multi-film optical fiber standard female head which is connected with an optical fiber;

The first optical fiber interface 6, the optical fiber 7 and the second optical fiber interface 8 are integrated into a whole and are used for transmitting optical signals. Wherein, the first optical fiber interface 6 and the second optical fiber interface 8 are ST optical fiber connectors, and the optical fiber 7 is ST multi-film optical fiber. In addition, the ST optical fiber jumper with the length less than or equal to 30m is adopted in the embodiment, for example, ST optical fiber jumper with the length of 2.5m, 5m, 10m, 15m or 30m can be adopted, and the normal working environment temperature is-40 ℃ to 75 ℃ and the loss is less than or equal to 0.2dB.

The flange 9 at the tested equipment end, one end of which is an ST multi-film optical fiber standard female head and is connected with an optical fiber; the other end is a flange end of the tested equipment and comprises a light inlet hole.

The signal cable 10 transmits an output electric signal of the photomultiplier as an output terminal to an automatic test device or a test meter.

Further, in order to solve the application limitation of the working temperature of the photomultiplier at 5-50 ℃, the optical signal of the tested device is conducted by adopting a multimode optical fiber jumper which is composed of a first optical fiber interface 6, an optical fiber 7 and a second optical fiber interface 8 in fig. 4. Because the loss of the optical fiber is very low and is less than 0.3dB/km, the ST optical fiber jumper used for the test in the embodiment is not more than 10m so as to meet all the field requirements of the test.

Wherein, photomultiplier and multi-film optical fiber, and the junction device between tested equipment and multi-film optical fiber: the structural design of the connection flange, i.e., the photomultiplier tube end flange 5 and the device under test end flange 9 of fig. 6 is shown in fig. 6 (a) -6 (c).

Specifically, the flange base 610 is made of light aluminum material and has a thickness of 2mm; ST standard fiber optic connector 620, which is integrally connected to flange base 610 by welding; the mounting via hole 630 can be used for drilling according to the mounting hole of the photomultiplier on the flange base, and can also be used for drilling according to the mounting requirement of the tested equipment. The thickness of the light-absorbing flannelette 640 of the circular ring is less than 1mm, and when the flange base 610 is in close contact with the photomultiplier or the tested equipment, external stray light can be effectively prevented from entering the optical fiber transmission channel; the light transmitting hole 650, from where the light signal to be measured is transmitted to the optical fiber 7 of fig. 4, or transmitted from the optical fiber 7 to the photomultiplier 4 of fig. 4.

It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises an element.

It should be noted that in the description of the present specification, descriptions of terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present utility model. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

Claims

1. A display equipment testing device for identifying nuclear power station DCS equipment is characterized by comprising a power supply module (1), a photomultiplier (4), a photomultiplier end flange (5), an optical fiber (7) and a tested equipment end flange (9),

The photomultiplier (4) is connected with the power supply module (1) through a power supply cable (2);

the photomultiplier (4) is connected with an external test instrument or an automatic test device through a signal cable (10);

The photomultiplier tube (4) is fixed on one side of the photomultiplier tube flange (5);

the photomultiplier end flange (5) is connected with the tested equipment end flange (9) through the optical fiber (7);

The tested equipment end flange (9) is provided with a light inlet hole, and test light rays are emitted into the light inlet hole from one side of the tested equipment end flange (9).

2. The display device testing apparatus for nuclear power plant DCS device qualification as claimed in claim 1, further comprising a gain adjustment potentiometer (3),

The gain adjustment potentiometer (3) is arranged on the power supply cable (2) connected with the photomultiplier (4) and the power supply module (1).

3. The display device testing apparatus for nuclear power station DCS equipment identification according to claim 1, wherein the other side of the photomultiplier tube flange (5) and the other side of the tested equipment end flange (9) are respectively provided with a first optical fiber interface (6) and a second optical fiber interface (8),

The first optical fiber interface (6) is connected with one end of the optical fiber (7), and the second optical fiber interface (8) is connected with the other end of the optical fiber (7).

4. A display device testing apparatus for identification of nuclear power plant DCS devices as claimed in claim 3, wherein the optical fiber (7) is an ST multi-film optical fiber, and the first optical fiber interface (6) and the second optical fiber interface (8) are ST multi-film optical fiber standard female heads.

5. The display device testing apparatus for nuclear power station DCS device identification of claim 1, wherein the length of the optical fiber (7) is 30m or less, and the operating environment temperature is-40 ℃ to 75 ℃.

6. The display device testing apparatus for nuclear power plant DCS device qualification as claimed in claim 1, wherein the photomultiplier tube flange (5) and the device under test end flange (9) each include a flange base, an optical fiber connector, a mounting hole and an optical inlet hole,

The photomultiplier (4) is fixed on one side of the photomultiplier end flange (5) through the mounting hole;

the light inlet hole is arranged in the center of the flange base and is coaxial with the optical fiber connector.

7. The display device testing apparatus for nuclear power plant DCS device qualification of claim 6, wherein the photomultiplier tube flange further comprises:

A light absorption unit (11) is arranged between the flange base and the photomultiplier tube (4).

8. The display device testing apparatus for nuclear power plant DCS device qualification as claimed in claim 7, wherein the light absorbing unit (11) is a light absorbing flannelette.

9. Display device testing apparatus for the identification of nuclear power plant DCS devices according to claim 7, wherein the thickness of the light absorbing unit (11) is not more than 1mm.

10. The display device testing apparatus for nuclear power plant DCS device qualification as claimed in claim 2, wherein the gain adjustment potentiometer (3) employs a 10K adjustable resistor.