JP6786331B2 - Electrical equipment - Google Patents

Description

The present invention relates to various electric devices, and more particularly to an electric device provided with means for reducing the influence of fluctuations in the load in the electric device on a predetermined function.

Currently, various electric devices are used in various fields. In general, in electrical equipment, factors that hinder normal operation, such as external or internally generated noise, may cause malfunctions and transmission errors in signal transmission between electrical equipment. Various attempts have been made to suppress noise and the like in order to obtain normal operation of electrical equipment. For example, Patent Document 1 describes that a slew rate control circuit that blunts a communication waveform is inserted into a communication line of a communication device to suppress harmonic components in a communication waveform that is a source of electromagnetic noise. There is.

International Publication No. 2012/132215

In an electric device, generally, an electric circuit that fulfills a function of each electric device is formed on a circuit board in the electric device. In addition, there are many electric devices having not only one function but also a plurality of functions. In that case, resistance to factors that impede normal operation, such as noise, may differ for each functional block that performs its individual function. That is, in order to prevent malfunction, for example, there may be a functional block that requires the addition of a noise suppression circuit such as the slew rate control circuit of Patent Document 1, and there may be one that does not particularly need it. For example, an electric device having a predetermined function (hereinafter referred to as function A) as a main function may also have a function other than function A (for example, a communication function with another electric device, hereinafter referred to as function B). If it has, the functional block responsible for the function A does not require a noise suppression circuit or the like, but a noise suppression circuit or the like may be required to normally perform the function B or the like.

In such a case, the user who uses the function B is provided with an electric device provided with a noise suppression circuit together with the function block responsible for the function B, and the user who does not use the function B is provided with the block and the noise suppression circuit which are responsible for the function B. It is preferable to provide an electric device that is not provided in terms of cost reduction and miniaturization. However, if all the functional blocks are formed on one circuit board, when the same circuit board is used for common components, simply removing the block responsible for the function B and the noise suppression circuit is sufficient. There are problems that cost reduction cannot be sufficiently obtained and miniaturization cannot be achieved. Further, when the function B is added to an electric device that performs a function different from the function A (hereinafter referred to as the function C), the circuit board of the electric device having the function C, which is different from the electric device having the function A. Remodeling is required. That is, it is necessary to modify the circuit board for each electric device having a different function. Therefore, there is a problem that it is not possible to efficiently upgrade existing plurality of types of electric devices.

For example, even in an electric device having a communication function by a transmission method having a relatively large noise tolerance, a communication function by a transmission method capable of transmitting and receiving a large number of signals as various signals are required to be transmitted for functional improvement is available. May be added. Then, a noise suppression circuit or the like may be required for the normal operation of the functional block carrying the communication function having such a high transmission capacity. For example, in the HART protocol mainly used for communication between instrumentation devices, the current amplitude of digital signals transmitted and received by frequency shift keying (FSK) is as small as about 0.8 mA _PP , so fluctuations in ground potential, etc. Is superimposed on the digital signal as noise, it is considered that a transmission error is likely to occur. Therefore, when adding a communication function using the HART protocol to an electric device having a communication function that does not use the HART protocol, it is necessary to add a circuit that suppresses fluctuations in the ground potential in addition to the communication function using the HART protocol. There is. In that case, if the circuit board is modified for each electric device having a different function, there is a problem that the function of each electric device cannot be efficiently improved as described above.

Further, for example, when adding a communication function by the HART protocol together with a ground potential fluctuation suppression circuit to an existing electric device, if such an additional part is formed on the existing circuit board, it is necessary to increase the circuit board size. There is. However, some electrical equipment, such as gas detectors into which flammable gas flows, are required to comply with safety standards that require an explosion-proof structure, etc., and electrical equipment that has already been certified to comply with the standards It may be difficult to change the structure of the housing in which the circuit board described above is housed.

The present invention has been made in view of such a problem, and a means having a specific function that can be affected by a factor that hinders normal operation such as load fluctuation of an internal circuit operates normally, and moreover, this means. It is an object of the present invention to provide an electric device which can easily add or remove such a function and has a high degree of freedom in layout of an electric circuit housed in a housing.

The electric device of the present invention includes a first circuit board including an electric circuit including a load portion whose load fluctuates with time, and a second circuit board detachably connected to the first circuit board. The second circuit board includes a signal processing means having a predetermined function, and a current control means configured to reduce the influence of fluctuations in the load of the load unit on the predetermined function.

The electric circuit further includes a power supply unit that supplies a first voltage, and the current control means is configured to operate by receiving electric power from the power supply unit and supply a current to the load unit at a second voltage. You may.

The signal processing unit may be configured to transmit and receive a signal with reference to a ground that shares the same line as the ground of the power supply unit with an external device according to a predetermined protocol.

Further, it has a housing for accommodating the first and second circuit boards, and the first circuit board and the second circuit board are fixed to the housing by a predetermined fixing means so as to overlap each other. One of the first circuit board and the second circuit board is fixed to the housing via a fixing plate, and the first circuit board and the other of the second circuit board of the fixing plate are fixed to each other. It is preferable that a notch is provided at a position corresponding to the fixing means for fixing.

A connection portion with an external electric circuit is provided on the other side of the first circuit board and the second circuit board, and a notch is provided at a position corresponding to the connection portion of the fixing plate. Is preferable.

The second circuit board is fixed to the housing via the fixing plate, and the component of the current control means and the fixing plate are in direct or indirect contact with each other so as to be heat conductive. Is preferable.

Further, it includes a detection means for detecting the state of the surrounding environment, and may be configured so that the load of the load unit fluctuates according to the state of the detection means.

According to the present invention, the second circuit board includes, for example, a signal processing means having a predetermined function such as a communication function, and a current control means for reducing the influence of fluctuations in the load portion on the predetermined function. Therefore, it is possible to obtain an appropriate predetermined function without malfunction. Moreover, the addition or removal of a predetermined function to the electric device can be easily realized by adding or removing the second circuit board. Further, even in other electric devices having different functions, by combining the second circuit board, a predetermined function provided in the second board can be easily added, and the function can be efficiently improved for a plurality of electric devices. It may also be possible to do so. Furthermore, since the relative position and angle between the first circuit board and the second circuit board can be changed, the degree of freedom in the layout of the electric circuit in the housing is increased, and the shape and size of the housing can be changed. While avoiding it, it may be possible to add a predetermined function provided in the second circuit board.

It is a figure which shows typically an example of the structure of the electric device of one Embodiment of this invention. It is a block diagram which shows typically an example of the electric connection form in the electric device of one Embodiment of this invention. It is a figure which shows the appearance of the gas detector which is an example of the electric device of one Embodiment of this invention. It is a figure which shows the appearance of the gas detector which is an example of the electric device of one Embodiment of this invention. It is a figure which shows the cross section by the IIIC-IIIC line of FIG. 3A. It is a figure which shows the gas detector of FIG. 3A and FIG. 3B in a state where the main body side housing and the lid side housing are separated. It is a figure which shows the fixing plate used for the gas detector of FIG. 3A and FIG. 3B. It is a figure which shows the cross section by the VI-VI line of FIG. It is a figure which shows the 1st circuit board in the state which the fixing plate shown in FIG. 4 is not attached to a lid side housing. It is a figure which shows the 2nd circuit board fixed to the fixing plate shown in FIG. It is a circuit diagram which shows an example of the electric circuit which comprises the current control means of FIG. It is a figure which shows the measurement result of the inflow current to the load part in one Example and comparative example of this invention which has the current control means of FIG. It is a figure which shows the measurement result of the current flowing through the ground line of one Example and comparative example of this invention under the fluctuation of the current shown in FIG. 10A. It is a figure which shows the result of having measured the current shown in FIG. 10A by enlarging the time axis. It is a figure which shows the result of having measured the current shown in FIG. 10B by enlarging the time axis.

Hereinafter, the electric device according to the embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 schematically shows an example of an electric device 100 according to an embodiment of the present invention. Further, FIG. 2 shows a block diagram showing an electrical connection within the electrical device 100 of one embodiment.

As shown in FIG. 1, the electric device 100 of the present embodiment has a first circuit board 31 and a second circuit board 32. The first circuit board 31 includes an electric circuit 6, and the electric circuit 6 includes a load unit 3 whose load fluctuates with time. The second circuit board 32 is configured to reduce the influence on the first function due to the load fluctuation of the signal processing means 4 having a predetermined function (hereinafter referred to as the first function) and the load unit 3. The current control means 1 is provided. The signal processing means 4 is configured to carry out a part or all of the first function. The second circuit board 32 is detachably connected to the first circuit board 31 by connecting means such as connectors 43a and 43b. The positional relationship between the first circuit board 31 and the second circuit board 32 shown in FIG. 1 is only an example, and both can be arranged in an arbitrary positional relationship. For example, the first circuit board 31 and the second circuit board 32 may be juxtaposed. Further, FIG. 1 accurately shows the size of the region where the current control means 1, the load unit 3, the signal processing means 4, and the electric circuit 6 are formed, and the position in the first circuit board 31 or the second circuit board 32. That is not intended. Further, in FIG. 1, the current control means 1 and the like are drawn so as to have an integral outer shape individually, but these are only schematically drawn. The current control means 1 and the like are actually composed of electrical components such as semiconductor devices and resistors, and wiring connecting them, as will be described later. Further, the current control means 1 and the like may include software written in the storage element in the semiconductor device.

Here, "(load fluctuates with time)" means that the current flowing through the load unit 3 changes by a change amount of a certain magnitude or more per unit time due to the fluctuation of the load. Specifically, this "fluctuation" means that the current of the load unit 3 changes so rapidly that the first function is hindered, for example, when the current control means 1 of the present embodiment is not provided. It means that. For example, when the current control means 1 of the present embodiment is not provided, the current flowing through the ground line in the electric device 100 changes due to a change in the current flowing through the load unit 3, and when the change is rapid, the ground potential fluctuates. May cause. Then, the level of the signal in the signal processing means 4 also fluctuates with the fluctuation of the ground potential, which may cause a trouble in the first function. In addition, "change with time" includes both regular change and irregular change.

In the present embodiment, the signal processing means 4 having the first function of being affected by the load fluctuation of the load unit 3 when the current control means 1 of the present embodiment is not provided, and the influence of the load unit 3 are reduced. The current control means 1 (the operation of the current control means 1 will be described later) is collectively formed on the second circuit board 32. Then, the second circuit board 32 is detachably connected to the first circuit board 31 including an electric circuit 6 including an electric element other than the current control means 1 and the signal processing means 4. With such a configuration, it is possible to reduce malfunctions in the first function due to load fluctuations of the load unit 3, and when a function-reduced electric device having no first function is preferred, the first function is used. By adopting a configuration in which the two circuit boards 32 are not connected, it is possible to significantly and easily reduce the cost and size, including the reduction effect of the second circuit board 32.

Further, when the first function is added to a plurality of types of electric devices having different functions, the first function can be added to each of the electric devices having different functions without major modification. That is, the circuit board of each electric device is modified on a small scale (for example, a portion for connecting the second circuit board 32 is added) to form the first circuit board 31, and the second circuit board 32 common to each electric device is connected. The first function can be added to a plurality of types of electric devices having different functions. Therefore, it is possible to efficiently upgrade existing plurality of types of electric devices. For example, when adding a communication function using the above-mentioned HART protocol (hereinafter, simply referred to as HART communication) to a plurality of types of electric devices having a communication function by a transmission method that is relatively insensitive to noise, a means (hereinafter, simply referred to as HART communication) that bears the HART communication function. A signal processing means 4) and a circuit (current control means 1) that suppresses fluctuations in the ground potential are formed on one circuit board (second circuit board 32). By using this second circuit board 32 in common among a plurality of types of electric devices and connecting it to a different circuit board (first circuit board 31) for each type of electric device, it is possible to efficiently connect to a plurality of types of electric devices. Moreover, it is possible to add a HART communication function that is less likely to malfunction due to fluctuations in the ground potential.

Further, in the present embodiment, the signal processing means 4 that bears the first function and the current control means 1 that reduces the influence of the load fluctuation of the load unit on the first function are the second separate from the first circuit board 31. It is provided on the circuit board 32. When the electric device has a housing and the electric circuit of the electric device is arranged in the space secured inside the housing, the first circuit board 31 and the second circuit board 31 and the second circuit board are arranged according to the shape and size of the internal space. The relative position with respect to the circuit board 32 can be selected. For example, when adding the first function to an electric device in which a circuit board (first circuit board) is arranged in the internal space of the housing, the position of the second circuit board is selected according to the empty area of the internal space. be able to. For example, if there is not much free space in the internal space in the direction parallel to the first circuit board, but there is free space in the direction orthogonal to the first circuit board, the second circuit board is placed above the first circuit board. That is, a part or all of the second circuit board can be arranged so as to overlap the first circuit board in a plan view. According to the present embodiment, as compared with the case where the signal processing means 4 and the current control means 1 are formed on the first circuit board 31, the degree of freedom in the layout of the signal processing means 4 and the current control means 1 is increased. Since it is expensive, it may be possible to add a predetermined function to the electric device 100 while avoiding a change in the shape and size of the existing housing. Even if it is difficult to change the housing structure due to the safety standards mentioned above, it may be possible to add functions to electrical equipment.

As shown in FIGS. 1 and 2, the electric circuit 6 formed on the first circuit board 31 further includes a power supply unit 2, and the power supply unit 2 has an electric device 100 at a first voltage V1. Power the components inside. Power is supplied to the current control means 1 formed on the second circuit board 32 from the power supply unit 2 on the first circuit board 31 at the first voltage V1. The current control means 1 is configured to operate by receiving electric power from the power supply unit 2 and supply a current to the load unit 3 at a second voltage V2. That is, the load unit 3 formed on the first circuit board 31 does not receive power directly from the power supply unit 2 formed on the first circuit board 31 at the first voltage V1, but the second circuit. Power is supplied at the second voltage V2 via the current control means 1 provided on the substrate 32. In other words, the current flowing from the power supply unit 2 toward the load unit 3 flows out from the first circuit board 31, once crosses the second circuit board 32 side, passes through the current control means 1, and then again passes through the first circuit board. It returns to the 31 side and flows into the load unit 3. Here, "formed", "configured", "provided", "mounted" or "provided" on the first circuit board 31 or the second circuit board 32 are electricity constituting the current control means 1 and the like. It does not mean that a component or the like is placed by physically contacting the main body portion with each substrate. These also include that the input / output terminals of electric components arranged at positions away from each circuit board are electrically connected to the conductor portion on each circuit board by wiring or the like.

The magnitude of the internal load of the load unit 3 changes with time according to the operating state of the electric device 100, and the magnitude of the current flowing into the load unit 3 changes according to the change. Of the components of the electrical device 100, any element whose internal load magnitude changes in this way can be regarded as the load unit 3. The load unit 3 may be a part that performs a main function of the electric device 100, or may be a part that performs a secondary function, for example, an interface function with a user such as a display unit or an operation unit. The load unit 3 includes a central processing device of the electric device 100, a storage device such as a ROM or RAM, a modem when the electric device 100 has a communication function, various sensors, a display device such as a display, a lighting device such as an LED, or a lighting device such as an LED. , Input devices such as keyboards and touch panels, and peripheral circuits thereof are exemplified.

The power supply unit 2 supplies the first voltage V1 based on the electric power from a commercial power source, a battery, or the like. For example, as the power supply unit 2, an electric circuit constituting a linear regulator or a switching regulator that outputs a stable voltage, an integrated circuit device configured as such a regulator, and peripheral circuits thereof are exemplified. Further, when the electric device 100 does not need the function of generating or stabilizing the first voltage V1, such as when a stable voltage is applied from the external power supply B at the first voltage V1, it is connected to the external electric circuit. The connection unit 101 (see FIG. 2) corresponds to the power supply unit 2. Further, when the electric device 100 is operated by the electric power of the battery (not shown) set in the electric device 100, the power supply unit 2 holds the battery and sets the battery voltage in the electric device 100 as the battery is set. It may be a battery holding unit that supplies the components of the above. The connection portion 101 shown in FIG. 2 is a connector or coupler for connecting the external power supply B and the electric device 100, or a terminal for connecting an external wire rod connected to the external power supply B to the electric device 100. It may be a pad or the like.

The current control means 1 is configured to reduce the influence of the load fluctuation of the load unit 3 on the first function by reducing the fluctuation of the ground potential of the electric device 100. Specifically, the current control means 1 divides the current supplied from the power supply unit 2 into the current i1 flowing into the load unit 3 and the current i2 having a current value corresponding to the fluctuation of the current i1. It is configured. In the example of FIG. 2, the current control means 1 includes a constant current generation unit 11 and a constant voltage generation unit 12. The constant current generation unit 11 is configured to cause the constant current Ic to flow out from the constant current generation unit 11. The constant voltage generation unit 12 supplies a second voltage V2, which is a constant voltage, to the load unit 3. The constant voltage generation unit 12 is configured such that a current i2 having a magnitude corresponding to the fluctuation of the current i1 flowing into the load unit 3 flows in from the constant current generation unit 11. Since the constant current Ic flows out from the constant current generation unit 11, the constant voltage generation unit 12 is configured to decrease (increase) the current i2 by substantially the same amount as the increase (decrease amount) of the current i1. .. Due to the action of the current control means 1, the fluctuation of the current flowing out from the power supply unit 2 and the current returning to the power supply unit 2 via the ground line becomes smaller than the fluctuation of the current i1 flowing in the load unit 3, and the ground Fluctuations in potential are suppressed. As a result, the influence of the load fluctuation of the load unit 3 on the first function is suppressed. A specific circuit example of the current control means 1 will be described later.

The signal processing means 4 fulfills a part or all of a predetermined function (first function) by processing an arbitrary electric signal generated in the electric device 100 or received from the outside by the electric device 100. The signal processing means 4 is composed of hardware such as an integrated circuit device, individual semiconductor elements, and an electric circuit composed of passive components such as resistors, which are configured to enable signal processing carried out by the signal processing means 4. .. Further, the signal processing means 4 may include software such as a program in which an instruction for causing the integrated circuit device to perform a predetermined process is written.

The first function in which the signal processing means 4 bears a part or all of the signal processing means 4 may be any function among the functions possessed by the electric device 100. For example, the first function is a control function of a specific part of the electric device 100, a recording function of various information, an interface function between the electric device 100 and the user of the electric device 100, and the electric device 100 and an external device. It may be a communication function between. The example shown in FIG. 2 is an example in which the signal processing means 4 plays a part of a communication function between the electric device 100 and the external device E. When the first function is a communication function, the signal processing means 4 determines, for example, a signal inside the communication control IC and the electric device 100 programmed to perform signal processing necessary for signal transmission with an external device. It may consist of a modem IC that modulates the format transmission / reception signal and demodulates the transmission / reception signal, and peripheral circuits of these ICs. Further, the first function may be, among the functions related to communication, particularly responsible for the above-mentioned HART communication. In that case, the signal processing means 4 may include a communication control IC for processing a control signal used for HART communication, a modem for HART communication, and the like. In the present embodiment, the first function is a part of the functions of the electric device 100 in that the first function can be easily added to the electric device 100 and the first function can be easily removed from the electric device 100. Is preferable. In other words, it is preferable that the first function is not all the functions of the electric device 100 at most.

In the example of FIG. 2, the signal processing means 4 is connected to the external device E via the second line L2. The electric device 100 is connected to the external device E by the first line L1, the second line L2, and the third line L3 with respect to signal transmission. That is, the signal processing means 4 is configured to play a part of a communication function for transmitting and receiving signals by a so-called three-wire communication protocol. Here, the first line L1 is a power supply line in which power is supplied from either one of the electric device 100 or the external device E to the other, and the second line L2 is a signal through which a signal including desired information is transmitted. It is a transmission line, and the third line L3 is a ground line that serves as a reference for the potential of the transmitted signal. In FIG. 2, the signal processing means 4 and the external device E are directly connected via the second line L2, but the signal processing means 4 uses the external device E via means for actually transmitting and receiving a transmission signal. It may be connected to.

The third line L3 is connected to the ground of the power supply unit 2, and the power supply unit 2 and the signal processing means 4 share one third line L3 with respect to power supply and signal transmission between the external device E and the external device E. There is. The signal processing means 4 is configured to have a communication function of transmitting and receiving a signal with reference to the ground sharing the same line as the ground of the power supply unit 2 with the external device E according to a predetermined protocol. When the electric device 100 of the present embodiment does not have the current control means 1, the current flowing into the ground G fluctuates according to the fluctuation of the current i1 flowing into the load unit 3. When the change of the current i1 is steep, the potential of the ground G fluctuates with the change of the current flowing into the ground G, and the potential of the third line L3 connected to the ground G also fluctuates. Therefore, the potential of the signal transmitted via the second line L2 fluctuates with respect to the potential (ground potential) of the third line L3, and normal signal transmission between the electric device 100 and the external device E is hindered. Sometimes. That is, when the current control means 1 is not provided, the first function in which the signal processing means 4 plays a part thereof may be affected by the load fluctuation of the load unit 3.

In particular, in the above-mentioned HART communication, since the current amplitude of the transmitted digital signal is very small, it is considered that transmission errors and malfunctions due to fluctuations in the ground potential are likely to occur. In HART communication, in order to prevent malfunctions caused by such sharing of the ground line, so-called 4-wire communication is also performed in which the ground of the power supply line and the ground of the signal transmission line are separated. However, since the 4-wire system requires two ground lines, it may be disadvantageous in terms of cost reduction and miniaturization.

In the present embodiment, as described above, the current control means 1 suppresses fluctuations in the ground potential due to fluctuations in the current flowing into the load unit 3, so that even in so-called three-wire HART communication, transmission errors and malfunctions occur. A signal can be appropriately transmitted between the electric device 100 and the external device E without causing the occurrence. The protocol of the communication function that the signal processing means 4 of the present embodiment can carry is not limited to the 3-wire HART communication, and may be a 2-wire or 4-wire HART communication. In addition, Modbus Protocol, FOUNDATION Fieldbus, Profibus, Ethernet (registered trademark), and the like are exemplified as communication protocols by the signal processing means 4. However, in the embodiment having the current control means 1, the signal processing means 4 is responsible for the three-wire HART communication function in that the signal can be appropriately transmitted and received with a small number of lines even if the signal has a minute amplitude. It is more beneficial if it is configured to.

The electric device 100 is a device that receives power from a commercial power source, a battery, or the like and performs a predetermined function, and may be an electric device for any purpose of industrial use or consumer use, and the use thereof is not particularly limited. .. For example, the electric device 100 is a household electric appliance such as a control device for an automobile, a communication device, and a control device incorporated in various control systems constructed in a plant, so-called white goods, which are required to prevent malfunction due to noise. It may be any of various electric devices such as products. Therefore, the electric device 100 has one or more load portions in which the current from the power supply portion 2 flows in, which is a portion that fulfills a specific function according to the application, in addition to the load portion 3. You may be.

Further, the electric device 100 may be a detector or an alarm that monitors the surrounding environment and detects that the surrounding environment is in a specific state. Such detectors and alarms include gas detectors that detect the presence of a specific type of gas at a predetermined concentration or higher, smoke detectors, fire alarms, and crime prevention that detects the intrusion of people. An alarm device for use is exemplified. When the electric device 100 is a detector or the like, the electric device 100 may have detection means (not shown) such as various sensors according to the detection target. Examples of such a sensor include a gas sensor that detects carbon monoxide (CO) gas, methane gas (CH ₄ ), a temperature sensor composed of a thermistor, a humidity sensor, a smoke sensor, and the like (however, the sensors include these). Not limited to). When a current is supplied to the detecting means from, for example, the power supply unit 2, the magnitude of the current flowing into the detecting means may vary depending on the detection state. Therefore, such a detection means may be included in the load unit 3. Further, the detection means may be connected to the power supply unit 2 or the current control means 1 separately from the load unit 3.

When the electric device 100 is a detector as described above, the detection means detects not only the inflow current to the detection means but also the current flowing through the display device displaying the detection result according to the detection state of the detection means (not shown). It can vary depending on the condition. As described above, the load unit 3 may be such a display device. For example, when the load unit 3 is a digital display 29 (see FIG. 3A) described later, the number of lit segments changes according to the detection state of the detection means, and the inflow current to the load unit 3 fluctuates. Further, in this case, even if the change in the surrounding physical environment detected by the detection means is gradual, the display state of the digital display 29 changes in an extremely short time, for example, a transition time of 2 milliseconds (one). Or multiple segments can change from on to off and vice versa). Therefore, the inflow current to the load unit 3 may change so rapidly that the ground potential fluctuates according to the detection state of the detection means. However, in the present embodiment, since the current control means 1 is provided, the fluctuation of the ground potential is reduced. Therefore, it is possible to prevent malfunction of the electric device 100.

Next, taking the case where the electric device 100 is a gas detector for detecting flammable gas or toxic gas, which has a 3-wire HART communication function, as an example, the structure of the electric device according to the embodiment of the present invention. An example will be described.

3A and 3B show the appearance of the gas detector 200, which is an example of the electric device of the present invention. FIG. 3A is a front view seen from the side opposite to the surface to be the installation surface side when the gas detector 200 is installed, and FIG. 3B is a bottom view seen from the upper and lower sides of FIG. 3A. As shown in FIGS. 3A and 3B, the gas detector 200 has a housing 20 composed of a main body side housing 21 and a lid side housing 22. The main body side housing 21 constitutes a portion of the housing 20 on the installation surface side. The main body side housing 21 and the lid side housing 22 are engaged by the hinge portion 23 and are connected by four housing fixing screws 24. The gas detector 200 includes a detection unit 25 including a gas sensor that detects the gas to be detected, and the gas detector 200 and an external power source (not shown) are electrically mounted on the side surface of the main body side housing 21. A cable insertion portion 26 for inserting a connecting cable (not shown) is provided.

On the front surface 22a of the gas detector 200, four switches 27 for adjusting the gas detector 200 that can be operated from the outside with a stick-shaped operation tool, and three displays such as the operating state of the gas detector 200 are displayed. A lamp unit 28 is provided. Further, the gas detector 200 is provided with a lighting element having 8 segments per digit, including a dot display indicating a decimal point, which is provided so as to be visible from the front surface 22a side through the opening 22b of the lid side housing 22. It is equipped with a 4-digit digital display 29 for displaying. The digital display 29 displays the detection status of the gas detector 200 and the like.

FIG. 3C shows a cross-sectional view taken along the line IIIC-IIIC of FIG. 3A (unlike FIG. 3B, the main body side housing 21 is located on the upper side of FIG. 3C). Further, FIG. 4 shows the inside of the gas detector 200 in a state where the main body side housing 21 and the lid side housing 22 are separated (the main body side housing 21 is shown on the right side in FIG. 4). Is shown, and the lid-side housing 22 is shown on the left side). In FIG. 4, the hinge portion 23, the detection portion 25, and the cable insertion portion 26 shown in FIGS. 3A to 3C are omitted.

As shown in FIGS. 3C and 4, the main body side housing 21 and the lid side housing 22 have recesses 21c and recesses 22c, respectively. A space is secured in the housing 20 by the recess 21c of the main body side housing 21 and the recess 22c of the lid side housing 22, and the first circuit board 31 and the second circuit board 32 are accommodated in this space. Further, a third circuit board 33 is arranged in the recess 21c of the main body side housing 21, and the first circuit board 31 and the third circuit board 33 are electrically connected by a plurality of internal cables 30a. The internal cable 30a and the first circuit board 31 are connected via the connector 35a, and the internal cable 30a and the third circuit board 33 are connected via the connector 35b (in FIG. 4, the connector 35a is coupled). The main body side housing 21 and the lid side housing 22 are shown in the unreachable state).

The first circuit board 31 and the second circuit board 32 are fixed to the lid-side housing 22 so as to be substantially parallel to each other, separated from each other in the thickness direction, and overlap each other. With such an arrangement, it is possible to obtain a small gas detector 200 with respect to the occupied area on the installation surface where the gas detector 200 is installed. The first circuit board 31 is fixed to the lid side housing 22 with two first circuit board fixing screws 39. The second circuit board 32 is fixed to the lid-side housing 22 via the fixing plate 34 of the second circuit board 32. By using the fixing plate 34, the second circuit board 32 can be stably arranged at a predetermined relative position with respect to the first circuit board 31. The first circuit board 31 is covered with a fixing plate 34, except for a part. The four corners of the fixing plate 34 are fixed to the lid-side housing 22 by four plate fixing screws 41. The second circuit board 32 is fixed to the fixing plate 34 with two second circuit board fixing screws 44. In addition, unlike the example shown in FIG. 3C, the second circuit board 32 may be arranged closer to the lid side housing 22 than to the first circuit board 31. In that case, the first circuit board 31 may be fixed to the lid-side housing 22 via the fixing plate. The arrangement positions of the first circuit board 31 and the second circuit board 32 can be arbitrarily selected according to the electric components mounted on each board and the like.

The digital display 29 is mounted on the bottom surface of the recess 22c of the first circuit board 31 (upper and lower surfaces in FIG. 3C, hereinafter simply referred to as the back surface). The digital display 29 is mounted at a position corresponding to the opening 22b of the lid-side housing 22 so that the display can be visually recognized from the outside of the gas detector 200. As described above, the electrical load of the digital display 29 changes according to the detection state of the gas detector 200, that is, with time. Therefore, the digital display 29 can be regarded as the load unit 3 of the electric device of the present embodiment, which is the gas detector 200. Although not shown, a lighting device such as an LED is mounted on the first circuit board 31, and a light guide member 28a that guides the light of the lighting device (not shown) to the lamp portion 28 is inside the recess 22c of the lid side housing 22. It is located in. The fixing means of the first circuit board 31, the fixing plate 34, and the second circuit board 32 is not limited to the screws as indicated by reference numerals 39, 41, or 44. For example, the fixing means of the first circuit board 31, the fixing plate 34, and the second circuit board 32 may be a rivet or an adhesive, and the protrusion of the lid-side housing 22 designed to be tightened. It may be a simple fit between the portion and the through hole of the first circuit board 31 or the like.

The third circuit board 33 is arranged near the bottom of the recess 21c of the main body side housing 21 substantially parallel to the first circuit board 31 and the second circuit board 32. Although not shown, the third circuit board 33 is fixed to the main body side housing 21 by an arbitrary fixing means such as a screw. An external cable connector 36 is mounted on the third circuit board 33. A plurality of external cables 30b for connecting to an external power source or the like are introduced into the main body side housing 21 through the cable insertion portion 26 and connected to the external cable connector 36. The external cable connector 36 is a type of connector in which the external cable 30b is diagonally inserted and fixed to the mounting surface (the surface facing the third circuit board 33) of the external cable connector 36. Therefore, the external cable 30b is not in the vertical direction or the parallel direction with respect to the third circuit board 33 and the first and second circuit boards 31 and 32, but is obliquely from the cable insertion portion 26 side to the external cable connector 36. It is inserted. With such an insertion direction, the external cable 30b can be easily inserted into the external cable connector 36. Moreover, even when the flexibility of the external cable 30b is relatively low, the external cable 30b can be accommodated between the fixing plate 34 and the third circuit board 33 without giving excessive stress to both boards and the external cable 30b. Can be done. Although not shown, the third circuit board 33 may be provided with a protection circuit for protecting the electric circuit in the gas detector 200 from an external surge voltage or the like, in addition to the external cable connector 36. An O-ring 37 is provided around the recess 21c of the main body side housing 21.

The fixing plate 34 is formed of a rectangular plate as a whole, as shown in FIGS. 5 (a) and 5 (b), respectively, in a plan view and a front view thereof, and is formed of a main body portion 341 and facing each other on the outer circumference. It has a side end portion 342 composed of a portion in the vicinity of each of the two sides. The main body portion 341 and the side end portion 342 are connected so as to form a step between them, and the fixing plate 34 is shown in FIG. 5 (b) when viewed from the edge side without the side end portion 342. As shown in, it has a convex shape as a whole. The main body 341 is provided with two through holes 34d for the second circuit board fixing screw, and the side end 342 is provided with four through holes 34e for the plate fixing screw. Further, the fixing plate 34 is provided with three notches 34a, 34b and 34c.

Referring to FIGS. 3C and 4 again, the first circuit board 31 has a terminal portion 38 electrically connected to a predetermined node of the electric circuit configured in the first circuit board 31 in addition to the connector 35. Is provided. Although the terminal portion 38 is formed by a connector in the examples of FIGS. 3C and 4, a conductor pad formed on the conductor layer of the first circuit board 31 may be used. The terminal portion 38 is provided, for example, for inspecting an electric circuit configured on the first circuit board 31 and writing information to a storage element (not shown) mounted on the first circuit board 31. In the example of FIG. 4, a notch 34a is provided at a position corresponding to the connector 35a on the fixing plate 34, and the connector 35a is exposed in the notch 34a. Further, a notch 34b is provided at a position corresponding to the terminal portion 38, and the terminal portion 38 is exposed in the notch 34b. Therefore, the connector 35a can be easily inserted and removed while the fixing plate 34 is fixed to the lid-side housing 22, and writing to the storage element can be performed via the terminal portion 38.

FIG. 6 shows a cross-sectional view taken along the line VI-VI of FIG. 4 of the lid-side housing 22 on which the first circuit board 31 and the like are arranged (FIG. 6 is a cross-sectional view of the cross-sectional view shown in FIG. 3C. It is a cross-sectional view seen from the side opposite to the viewpoint. The light guide member 28a is omitted). As shown in FIG. 6, a counterbore surface 22e is provided on the outer peripheral portion of the recess 22c of the lid-side housing 22 at a position recessed from the bonding surface 22d with the main body-side housing 21 (see FIG. 3C). The first circuit board 31 is placed on the counterbore surface 22e and fixed to the lid side housing 22 with the first circuit board fixing screw 39. Further, the fixing plate 34 is fixed to the counterbore surface 22e with the plate fixing screw 41 via the spacer 40. The second circuit board 32 is fixed to the fixing plate 34 via the spacer 42.

A board-to-board type connector 43a is mounted on the first circuit board 31, and a board-to-board type connector 43b that fits into the connector 43a is mounted on the second circuit board 32. When the first circuit board 31 is attached to the lid-side housing 22, and then the second circuit board 32 is fixed to the lid-side housing 22 via the fixing plate 34, the connector 43a and the connector 43b are coupled. Will be done. At this time, if the first circuit board 31 is not fixed at an accurate position with respect to the lid-side housing 22, the connector 43a and the connector 43b cannot be properly coupled. However, referring to FIG. 4 again, the first circuit board fixing screw 39, which is the fixing means of the first circuit board 31, is exposed in the notches 34a and 34c. That is, the fixing plate 34 is provided with notches 34a and 34c at positions corresponding to the first circuit board fixing screw 39. Therefore, the first circuit board fixing screw 39 can be turned even when most of the first circuit board 31 is covered with the fixing plate 34 on which the second circuit board 32 is attached. That is, the first circuit board 31 may not be fixed to the lid-side housing 22 at the time when the fixing plate 34 is attached to the lid-side housing 22. For example, the first circuit board 31 and the fixing plate 34 can be fixed to the lid-side housing 22 after the connector 43a and the connector 43b are connected in advance. Alternatively, for example, the connector 43a and the connector 43b are coupled while being aligned with each other in a state where the first circuit board 31 is temporarily fixed to the lid side housing 22, that is, in a state where the first circuit board 31 can be slightly moved. Can be done. After that, the first circuit board 31 can be completely fixed by tightening the first circuit board fixing screw 39, and the fixing plate 34 can be further fixed to the lid side housing 22.

FIG. 7 shows the first circuit board 31 in the recess 22c of the lid-side housing without the fixing plate 34 shown in FIG. 4 attached. The first circuit board 31 is provided with a connector 35, a connector 43a, and a terminal portion 38, and is formed with a predetermined electric circuit 6 constituting the gas detector 200. The electric circuit 6 includes the power supply unit 2 described above. Although not shown, the electric circuit 6 is also formed on the back surface of the first circuit board 31 (the surface opposite to the surface shown in FIG. 7), and the back surface of the first circuit board 31 is described above. A digital display 29 (see FIG. 3C) that can serve as the load unit 3 is mounted as described above.

On the other hand, in the gas detector 200, as shown in FIG. 8, the current control means 1 is formed on the second circuit board 32 (in FIG. 8, the fixing plate 34 shown in FIG. 4 is shown in FIG. 4). The second circuit board 32 attached to the fixing plate 34 in a state of being inverted in the left-right direction is shown). For example, the components of the current control means 1 such as the shunt regulator U1, the reference voltage generator U2, the operational amplifier U3, the transistor Q1, and the resistors R1 to R9 (all of which are referred to in FIG. Will be implemented. Further, on the second circuit board 32, a signal processing means 4 composed of an electric circuit for controlling three-wire HART communication and modulating and demodulating the HART signal is formed in the gas detector 200.

As shown in FIGS. 7 and 8, in the gas detector 200, the power supply unit 2 is formed on the first circuit board 31, and the current control means 1 provided on the second circuit board 32 receives a current from the power supply unit 2. Is supplied. The current flowing out from the current control means 1 returns to the first circuit board 31 side and flows into the load unit 3 (see FIG. 6) including the digital display 29. As described above, the current control means 1 suppresses fluctuations in the ground potential due to fluctuations in the current to the load unit 3. The signal processing means 4 having a 3-wire HART communication function (first function) that is easily affected by fluctuations in the ground potential is formed on the second circuit board 32 together with the current control means 1. That is, the portion responsible for the HART communication function and the portion responsible for suppressing the fluctuation of the ground potential so that the 3-wire HART communication can be normally performed form other components of the electric circuit of the gas detector 200. The substrate (first circuit board 31) and another substrate (second circuit board 32) are collectively formed. Therefore, a low-priced gas detector having no HART communication function can be easily obtained simply by omitting the connection of the second circuit board 32. On the contrary, by simply connecting the second circuit board 32 to a plurality of types of gas detectors that do not have the HART communication function, a plurality of types that have the HART communication function can be easily obtained without major modification of the existing part. A gas detector 200 can be obtained. Moreover, an HART communication function that is not easily affected by fluctuations in the current of the load unit 3 and has few malfunctions and transmission errors can be added to the existing gas detector. When the second circuit board 32 is not used, a jumper member or the like is mounted on a connection pad provided in advance on the first circuit board 31 so that power is directly supplied from the power supply unit 2 to the load unit 3. Then, the power supply unit 2 and the load unit 3 may be electrically connected.

The power supply unit 2 shown in FIGS. 7 and 8, and the current control means 1 and the signal processing means 4 simply indicate that they are formed on the first circuit board 31 or the second circuit board 32. It is only shown and is not intended to indicate its size or its exact location on each circuit board. The power supply unit 2, the current control means 1, and the like may be formed on a surface opposite to the surface shown in FIGS. 7 and 8, and may be formed on both surfaces of the first and second circuit boards 31 and 32. May be good. For example, a part or all of the current control means 1 may be formed on a surface opposite to the surface shown in FIG. 8 (a surface facing the fixing plate 34). Further, in that case, the component of the current control means 1 and the fixing plate 34 may be in direct contact with each other or indirectly in a heat conductive manner. Since a current corresponding to the inflow current to the load unit 3 flows into the current control means 1, the components of the current control means 1, such as an integrated circuit device, an individual semiconductor element, or an electric resistance, generate heat during operation. There is. By arranging such components in direct or thermally conductive contact with the fixing plate 34, which may be formed of, for example, a metal material such as aluminum or stainless steel, they are prevented from becoming overheated. can do. Here, "indirectly (contacting) with thermal conductivity" means contacting the fixing plate 34 at least through a material having a higher thermal conductivity than air.

In the second circuit board 32 shown in FIG. 8, the inspection of the electric circuit configured in the second circuit board 32, the writing of information to the storage element (not shown) mounted on the second circuit board 32, and the like are performed. A connector 45 provided for this purpose is mounted on the edge of the second circuit board 32. The mating surface of the connector 45 with the connector on the other side is directed to the side of the second circuit board 32. Therefore, even when the fixing plate 34 is fixed to the lid side housing 22 (see FIG. 4), the connector on the other side of the connector 45 is inserted into the connector 45 from the side of the second circuit board 32 to store the storage element. You can write to.

FIG. 9 shows an example of a specific electric circuit constituting the constant current generation unit 11 and the constant voltage generation unit 12 of the current control means 1. In the example of FIG. 9, the constant current generator 11 is composed of an operational amplifier U3, a reference voltage generator U2, a P-channel field effect transistor (hereinafter, simply referred to as a “transistor”) Q1, and resistors R1 to R6. A shunt regulator that outputs a constant reference voltage Vr2 to the reference voltage output terminal U2r with respect to the anode terminal is used as the reference voltage generator U2, and the reference voltage output terminal U2r and the cathode terminal are connected to each other. The current Ic1 flows into the source terminal of the transistor Q1 from the power supply unit 2 (see FIG. 1), and the constant current Ic flows out from one end R6a of the resistor R6 opposite to the drain side of the transistor Q1. A commercially available operational amplifier can be used as the operational amplifier U3. The transistor Q1 is also not particularly limited as long as it has a rated drain current exceeding the constant current Ic1. The resistance values of the resistors R1 to R3 and R6 are appropriately selected according to the desired constant current Ic and the magnitude of the reference voltage Vr2 of the reference voltage generator U2.

In the example of FIG. 9, the constant voltage generation unit 12 is composed of a shunt regulator U1 and resistors R7 to R9. The shunt regulator U1 has an accuracy of a reference voltage Vr1 capable of generating a second voltage V2 with a desired accuracy, and has a sufficient current capacity with respect to the flowing current i2 according to the fluctuation of the current i1. There is no particular limitation. Two resistors R7 and R8 connected in series are used, but if the desired resistance value and tolerance can be satisfied, one resistor is the cathode terminal of the shunt regulator U1 and the reference voltage output terminal U1r. It may be connected in between.

The operation of the constant current generation unit 11 and the constant voltage generation unit 12 shown in FIG. 9 will be described. A reference voltage Vr2 of the reference voltage generator U2 is applied to both ends of the series circuit of the resistor R1 and the resistor R2, and a potential difference is generated at a constant voltage between one end R1a and the other end R1b of the resistor R1. Further, the voltage Vin of the other end R1b of the resistor R1 is input to the non-inverting input terminal of the operational amplifier U3, and the voltage of one end R6a of the resistor R6 connected to the inverting input terminal of the operational amplifier U3 is a negative feedback circuit. Is controlled by the operational amplifier U3 in which the voltage is formed so as to be substantially the same as the voltage Vin. As a result, a potential difference of the same constant voltage as between both ends of the resistor R1 is generated across the resistor R6, and a constant current Ic flows through the resistor R6 which is a fixed resistor. This constant current Ic is supplied to the load unit 3 and the constant voltage generation unit 12. On the other hand, in the constant voltage generation unit 12, the shunt regulator U1 generates a second voltage V2 based on the reference voltage Vr1 and the resistance values of the resistors R7 to R9.

As described above, the constant current Ic is supplied from the constant current generation unit 11, while the current i1 flowing through the load unit 3 fluctuates with time. In the example of FIG. 9, the cathode current is adjusted by the shunt regulator U1 so that a constant voltage second voltage V2 is generated. Therefore, the current i2, which is the difference between the constant current Ic and the current i1 to the load unit 3, is shunted to the shunt regulator U1 side as a cathode current so that the second voltage V2 is kept constant, and passes through the ground G. Is returned to the power supply unit 2. Even if the current i1 to the load unit 3 fluctuates, the current i2 corresponding to the fluctuation is shunted by the shunt regulator U1. As a result, the constant current generation unit 11 can continue to flow the constant current Ic without being affected by the fluctuation of the load of the load unit 3. Further, since the constant voltage generation unit 12 generates a constant voltage second voltage V2, the voltage at one end R1a of the resistor R1 and the cathode terminal of the reference voltage generator U2 become substantially constant. Therefore, the current flowing through the reference voltage generator U2 and the resistor R1 is also substantially constant, and the current Ic1 flowing from the power supply unit 2 into the constant current generation unit 11 is also substantially constant. As a result, fluctuations in the current flowing out of the power supply unit 2 and the current returning to the power supply unit 2 via the ground line are suppressed, the ground potential of the power supply unit 2 is stabilized, and malfunction of the electric device 100 is prevented. Can be done.

In this way, the current i2 flows into the shunt regulator U1 according to the change in the current i1 to the load unit 3. Therefore, the shunt regulator U1 may generate heat in its operation. Therefore, the shunt regulator U1 is preferably arranged on the surface of the second circuit board 32 on the fixing plate 34 side, and is arranged so as to be in direct contact with the fixing plate 34 or indirectly so as to be thermally conductive. ..

Example 1
A current control means 1 including a constant current generation unit 11 and a constant voltage generation unit 12 shown in FIG. 9 is added to a gas detector (manufactured by New Cosmos Electric Co., Ltd .: KD-12B) to reduce fluctuations in the ground potential. I investigated the effect. The gas detector had a digital display 29 as shown in FIG. 3A and a lamp unit 28 that radiates light from an LED (however, it does not have a HART communication function). The state of the LED that emits light from the digital display 29 and the lamp unit 28 is changed over time, and gas detection is performed for fluctuations in the current i1 flowing through the load unit 3 (see FIG. 2) including the digital display 29 and the LED. The fluctuation of the current flowing through the ground line of the vessel was investigated.

In this survey, the power supply unit of the gas detector KD-12B was disconnected, and the evaluation board of Texas Instruments' switching regulator IC: LM2501 was connected as the power supply unit 2, and 24V from an external power supply was connected to this power supply unit 2. The voltage was supplied. The power supply unit 2 was set to a switching frequency of 500 kHz and an output voltage of 3.6 V. That is, in this embodiment, the first voltage V1 (see FIG. 2) was 3.6V. Renesas Electronics' μPC1093 was used as the shunt regulator U1, and resistors R7 to R9 were selected so that the second voltage V2 was 3.18V. A Texas Instruments shunt regulator TLV431A was used as the reference voltage generator U2, and the reference voltage generator U2 had a reference voltage Vr2 of 1.24 V as a TYPE value. OPA170 from Texas Instruments and RQ5E035AT from ROHM were used as the operational amplifier U3 and the transistor Q1, and resistors R1 to R3 and R6 were selected so that the constant current Ic was 57.4 mA.

For each current measurement, only the most significant digit of the digital display 29 with 8 segments x 4 digits is turned on every 8 milliseconds, and the three LEDs that emit light to the lamp unit 28 are cycled for 1 second. , While blinking at a duty ratio of 50%. The current i1 to the load unit 3 was measured by inserting a 0.5 Ω resistor between the current control means 1 and the load unit 3 and measuring the voltage drop due to this resistor. Similarly, the current flowing through the ground line was measured by inserting a 20Ω resistor into the ground line between the external power supply and the power supply unit 2 and measuring the voltage drop thereof. Each current was measured using an oscilloscope.

10A and 11A are measurement results of the current i1 flowing through the load unit 3, and FIGS. 10B and 11B are measurement results of the current of the ground line. Here, FIGS. 10A and 10B observe the oscilloscope time axis setting as 5 seconds per division, and FIGS. 11A and 11B expand the time axis setting to 0.1 seconds per division. It was observed. Further, in FIGS. 10B and 11B, the reference numeral ig indicates the current of the ground line measured in this embodiment, and the reference numeral ix is a comparative example in which the current control means 1 is not added, which is measured for comparison. It shows the current of the ground line. Since there is no difference in the current to the load unit 3 between this embodiment and the comparative example, only one current waveform (current i1) is shown in FIGS. 10A and 11A.

As shown in FIG. 10A, the magnitude of the current i1 to the load unit 3 changes in a cycle P1 of about 1 second in accordance with the blinking cycle (1 second) of the LED. Further, as shown in FIG. 11A, which is the result of measurement by enlarging the time axis, the current i1 has a period P2 of about 8 milliseconds in accordance with the change in the display state of the digital display 29 having a period of 8 milliseconds. The size of is fluctuating. That is, although the current i1 is painted black in FIG. 10A and drawn in a band shape, it finely fluctuates in a cycle of about 8 milliseconds according to the amount of current flowing through the digital display 29, and emits light from the lamp unit 28. It fluctuates in a cycle of about 1 second according to the amount of current flowing through the emitted LED. 11A and 11B show the measurement results for 0.2 seconds (time from t1 second to (t1 + 0.2) seconds) in which the LED is lit. Further, in FIG. 10A, since the LED indicator lamp 28 is always lit after the time T1, the current i1 does not fluctuate in a 1-second cycle. Further, since the current i1 also flows to the components of the gas detector other than the digital display 29 and the LED, it continues to flow without dropping to the zero level in FIGS. 10A and 11A.

In a situation where the current i1 to the load unit 3 fluctuates as shown in FIGS. 10A and 11A, in the comparative example, the ground line current ix corresponds to the fluctuation of the current i1 as shown in FIG. 10B. It fluctuates in a 1-second cycle, and further fluctuates in an 8-msec cycle as shown in FIG. 11B. On the other hand, in this embodiment, as shown by the reference numerals ig in FIGS. 10B and 11B, the current ig of the ground line flows at a substantially constant current value without being affected by the fluctuation of the current i1. I understand. Therefore, the potential of the signal line in the gas detector does not fluctuate due to the fluctuation of the current flowing through the digital display 29 or the like, and the normal operation of the gas detector can be obtained. Further, in the above-mentioned HART communication, a standard for ground level fluctuation of 2.2 mVrms or less is defined in the frequency band of 500 Hz to 10 kHz when the load resistance is 500 Ω, but in this embodiment, the ground level fluctuation is defined. Is approximately 0 mVrms, and the HART communication standard can be satisfied by using the current control means 1 of the embodiment illustrated in FIG.

1 Current control means 2 Power supply unit 3 Load unit 4 Signal processing means 6 Electric circuit 11 Constant current generation unit 12 Constant voltage generation unit 21 Main unit side housing 22 Lid side housing 29 Digital display 31 First circuit board 32 Second circuit Board 33 Third circuit board 34 Fixing plates 34a, 34b, 34c Notches 39 First circuit board fixing screw 41 Plate fixing screw 43a Connector on the first circuit board 43b Connector on the second circuit board 100 Electrical equipment 200 Gas detector B External power supply E External device G Ground i1 Current flowing into the load unit i2 Current flowing through the current control means Ic Constant current flowing out from the constant current generator ig Ground line current ix of the embodiment of the present invention Ground line current L1 1st line L2 2nd line L3 3rd line U1 Shunt regulator U2 Reference voltage generator U3 Computational amplifier V1 1st voltage V2 2nd voltage

Claims (8)

A first circuit board including an electric circuit including a load portion whose load fluctuates with time, and
It has a second circuit board that is detachably connected to the first circuit board.
The second circuit board
Signal processing means having a predetermined function, and wherein the current supplied from the first circuit board side to be supplied to the load unit, it little impact on the predetermined function due to variations in the load of the load unit An electrical device equipped with a current control means for controlling such as. The electric circuit further includes a power supply unit that supplies the current at the first voltage.
The electric device according to claim 1, wherein the current control means operates by receiving electric power from the power supply unit and supplies a current to the load unit at a second voltage. The electrical circuit further includes a power supply that supplies the current and powers the components of the electrical device.
The electrical device according to claim 1, wherein the signal processing means is configured to transmit and receive a signal with reference to a ground that shares the same line as the ground of the power supply unit with an external device according to a predetermined protocol. .. Further, it has a housing for accommodating the first and second circuit boards.
The first circuit board and the second circuit board are fixed to the housing by a predetermined fixing means so as to overlap each other.
One of the first circuit board and the second circuit board is fixed to the housing via a fixing plate.
The invention according to any one of claims 1 to 3, wherein a notch is provided at a position corresponding to the fixing means for fixing the first circuit board and the other of the second circuit board of the fixing plate. Electrical equipment. The other of the first circuit board and the second circuit board is provided with a terminal portion and / or a connector electrically connected to the electric circuit formed by the other, and the terminal in the fixing plate . The electrical device according to claim 4, wherein a notch is provided at a position corresponding to the portion or a position corresponding to the connector . The second circuit board is fixed to the housing via the fixing plate, and the components of the current control means and the fixing plate are in direct or indirect contact with each other so as to be heat conductive. The electrical device according to claim 4 or 5. Further, according to any one of claims 1 to 6, the detection means for detecting the state of the surrounding environment is included, and the load of the load unit is configured to fluctuate according to the state of the detection means. Electrical equipment. The present invention according to any one of claims 1 to 7, wherein the current control means divides a part of the current supplied from the first circuit board side at a current value corresponding to a fluctuation of the load of the load unit. Electrical equipment.

Images