Abstract:
Provided is a relay unit that can sufficiently suppress defects that are caused by an insulation failure of insulating member that insulates and separates a load power supply from a device power supply, and a method for controlling a relay circuit. A control unit includes an insulating member diagnosis unit that performs diagnosis of an insulation failure of the capacitor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2015-018895 filed Feb. 2, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates to a relay unit including an insulating member for insulating and separating a load power supply for operating a load from a device power supply, which is different from the load power supply, and to a method for controlling a relay circuit. 
       BACKGROUND 
       [0003]    The following configuration is known as a relay unit (relay circuit) that has the function of switching between current flow and no current flow of a load using relays. 
         [0004]    That is, the relay unit includes an insulating member for insulating and separating a load power supply for operating a load from a device power supply, which is different from this load power supply. Note that the device power supply functions as a power supply for operating mainly a microcomputer (microcontroller) of the relay unit and the like. Examples of the relay unit including the insulating member are disclosed in JP H5-55435U and EP 1202313A. 
         [0005]    The specifications of JP 5-55435U (Jul. 23, 1993) and EP 1202313B (May 2, 2002) are examples of background art. 
         [0006]    When an insulation failure (such as a short circuit) of the insulating member occurs, there is the risk that the following defects occur: A high voltage may be applied to the relay unit from the load power supply, causing a fault of the relay unit, a voltage may be applied to the load from the device power supply, causing a malfunction of the load, and the like. 
         [0007]    Note that as means for preventing various defects that are caused by the insulation failure, it is conceivable to increase the number of insulating members. However, even when the number of insulating members is increased, insulation failures may occur in, for example, all the insulating members due to a common reason. Accordingly, even by increasing the number of the insulating members, it is difficult to sufficiently suppress various defects that are caused by the insulation failures. 
         [0008]    The present invention was made in view of the above-described problem, and an objective thereof is to provide a relay unit that can sufficiently suppress defects that are caused by insulation failures of insulating members for insulating and separating a load power supply from a device power supply, and a method for controlling a relay circuit. 
       SUMMARY 
       [0009]    In order to solve the above-described problems, an inventive relay unit includes a switching circuit that includes a relay configured to be connected to a first power supply for operating a load; 
         [0010]    a control unit that is operated by a second power supply, which is different from the first power supply; and 
         [0011]    an insulating member that insulates and separates the first power supply from the second power supply; 
         [0012]    wherein the control unit includes an insulating member diagnosis unit that is configured to perform diagnosis of an insulation failure of the insulating member. 
         [0013]    Furthermore, in order to solve the above-described problems, an inventive method for controlling a relay circuit is provided, the relay circuit including a switching circuit that includes a relay configured to be connected to a first power supply for operating a load; and an insulating member that insulates and separates the first power supply from a second power supply, which is different from the first power supply, the method including: 
         [0014]    an insulating member diagnosis step of performing diagnosis of an insulation failure of the insulating member. 
         [0015]    According to the above-described configuration, the diagnosis of an insulation failure of the insulating member is performed. Therefore, by performing appropriate processing (such as stopping the relay unit upon detection of an insulation failure) based on a result of this insulation failure diagnosis, it is possible to sufficiently suppress various defects that are caused by an insulation failure of the insulating member. 
         [0016]    Furthermore, in the relay unit of the present invention, it is preferable that the control unit includes a first diagnosis-signal output unit that is configured to output a first diagnosis signal, and the insulating member diagnosis unit is configured to perform the diagnosis of an insulation failure of the insulating member based on a first diagnosis-result signal that is obtained by the first diagnosis signal passing through the insulating member. 
         [0017]    According to the above-described configuration, the diagnosis of an insulation failure of the insulating member is possible based on a first diagnosis-result signal that is obtained by the first diagnosis signal passing through the insulating member. 
         [0018]    Furthermore, in the relay unit of the present invention, it is preferable that the control unit include a second diagnosis-signal output unit that is configured to output a second diagnosis signal; and a switching circuit diagnosis unit that is configured to perform fault diagnosis of the switching circuit based on a second diagnosis-result signal that is obtained by the second diagnosis signal passing through the switching circuit. Furthermore, in the relay unit of the present invention, it is preferable that the control unit include a switching circuit diagnosis unit that is configured to perform the fault diagnosis of the switching circuit based on the first diagnosis-result signal. 
         [0019]    According to the above-described configuration, it is possible to further perform the fault diagnosis of the switching circuit. Note that the fault diagnosis of the switching circuit may be performed using the same signal as that of the diagnosis of an insulation failure of the insulating member, or a different signal from that of the diagnosis of an insulation failure of the insulating member. 
         [0020]    Furthermore, in the relay unit of the present invention, it is preferable that the insulating member diagnosis unit perform the diagnosis of an insulation failure of the insulating member while current flows through the load. Furthermore, in the relay unit of the present invention, it is preferable that the insulating member diagnosis unit perform the diagnosis of an insulation failure of the insulating member while no current flows through the load. 
         [0021]    According to the above-described configuration, it is possible to perform the diagnosis of an insulation failure of the insulating member both while current flows through the load and while no current flows through the load. 
         [0022]    Furthermore, in the relay unit of the present invention, it is preferable that the insulating member be a capacitor, the first diagnosis signal be a pulse, and the insulating member diagnosis unit determine that the capacitor has an insulation failure if a digital signal obtained by subjecting the first diagnosis-result signal, which is obtained based on the pulse, to analog-digital conversion has a predetermined pulse width or greater. 
         [0023]    If the first diagnosis signal is a pulse, the waveform of the first diagnosis-result signal is a triangular wave due to charge and discharge of the capacitors. If the capacitors are subject to an insulation failure, the greater the degree of the failure is, the closer the waveform of this first diagnosis-result signal to a rectangular wave is. Also, the closer the waveform of the first diagnosis-result signal to a rectangular wave is, the greater the pulse width of a digital signal that is obtained by subjecting this first diagnosis-result signal to analog-digital conversion is. Therefore, it is possible to determine that the capacitors are subject to an insulation failure if this digital signal has a predetermined pulse width or greater. Accordingly, it is possible to detect insulation failures of the capacitors accurately. 
         [0024]    Furthermore, in the relay unit of the present invention, it is preferable that the insulating member be a capacitor, an insulating transformer, or a photocoupler. 
         [0025]    According to the present invention, it is possible to provide a relay unit that can sufficiently suppress defects that are caused by an insulation failure of an insulating member for insulating and separating a load power supply from a device power supply, and a method for controlling a relay circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a circuit block diagram illustrating a schematic configuration of a load controlling system provided with a relay unit according to the present invention, in which mechanical switches are in the open state. 
           [0027]      FIG. 2  is a circuit block diagram illustrating a schematic configuration of the load controlling system provided with the relay unit according to the present invention, in which the mechanical switches are in the closed state. 
           [0028]      FIG. 3  shows waveform charts illustrating the principles of diagnosis of insulation failures of insulating members, the diagnosis being performed by an insulating member diagnosis unit and a first diagnosis-signal output unit. 
           [0029]      FIG. 4  is a flowchart illustrating the flow of processing that is performed by a control unit using the insulating member diagnosis unit, the first diagnosis-signal output unit, and a switching circuit diagnosis unit. 
           [0030]      FIG. 5  is a flowchart illustrating the flow of processing that is performed by the control unit using the insulating member diagnosis unit, the first diagnosis-signal output unit, a second diagnosis-signal output unit, and the switching circuit diagnosis unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Embodiments for implementing the present invention will be described with reference to  FIGS. 1 and 2 . 
         [0032]      FIGS. 1 and 2  are circuit block diagrams illustrating schematic configurations of a load controlling system  10  provided with a relay unit  24 .  FIG. 1  shows the state in which mechanical switches  22  and  23  are in the open state, and  FIG. 2  shows the state in which the mechanical switches  22  and  23  are in the closed state. 
         [0033]    The load controlling system  10  is a system for switching between current flow and no current flow through a load  21  using the relay unit  24 . Note that a load power supply (first power supply)  9  is an AC power supply that serves as a power supply for the load  21 . 
         [0034]    The relay unit  24  includes a control unit  2  and a switching circuit (relay circuit)  3 . 
         [0035]    The switching circuit  3  includes two contact relays, namely, a first contact relay circuit (relay)  5  and a second contact relay circuit (relay)  6 . 
         [0036]    The first contact relay circuit  5  includes a mechanical switch  22  and a relay coil  7 . The first contact relay circuit  5  generates an electromagnetic force using excitation of the relay coil  7  and uses this electromagnetic force to switch the mechanical switch  22  between the open state and the closed state. Note that the first contact relay circuit  5  includes, as contacts of the mechanical switch  22 , an a1 contact, which is a so-called “a” contact, and a b1 contact, which is a so-called “b” contact. In the specification of the present application, “the closed state of the mechanical switch  22 ” refers to the state in which the mechanical switch  22  is in contact with the a1 contact. On the other hand, in the specification of the present application, “the open state of the mechanical switch  22 ” refers to the state in which the mechanical switch  22  is in contact with the b1 contact. 
         [0037]    The second contact relay circuit  6  includes a mechanical switch  23  and a relay coil  8 . The second contact relay circuit  6  generates an electromagnetic force using excitation of the relay coil  8 , and uses this electromagnetic force to switch the mechanical switch  23  between the open state and the closed state. Note that the second contact relay circuit  6  includes, as contacts of the mechanical switch  23 , an a2 contact, which is a so-called “a” contact, and a b2 contact, which is a so-called “b” contact. In the specification of the present application, “the closed state of the mechanical switch  23 ” refers to the state in which the mechanical switch  23  is in contact with the a2 contact. On the other hand, in the specification of the present application, “the open state of the mechanical switch  23 ” refers to the state in which the mechanical switch  23  is in contact with the b2 contact. 
         [0038]    Furthermore, the mechanical switches  22  and  23  are connected in series to each other to constitute a series circuit, and this series circuit is connected in series to the load  21  and the load power supply  9 . Accordingly, when all the mechanical switches  22  and  23  are put in the closed state, current starts to flow through the load  21 . On the other hand, when at least one of the mechanical switches  22  and  23  is put in the open state, the current flow through the load  21  is interrupted. 
         [0039]    Furthermore, the switching circuit  3  includes two capacitors (insulating members) C 1  and C 2 . These capacitors C 1  and C 2  are provided to insulate and separate the load power supply  9  from an external power supply (second power supply)  11 . The capacitor C 1  is connected between a b1 contact of a first contact relay circuit  5  and the control unit  2 , and the capacitor C 2  is connected between a b2 contact of a second contact relay circuit  6  and the control unit  2 . The capacitor C 1  may be provided outside the switching circuit  3 , and also the capacitor C 2  may be provided outside the switching circuit  3 . Instead of the capacitor C 1 , an insulating transformer or a photocoupler may be used, and also instead of the capacitor C 2 , an insulating transformer or a photocoupler may be used. The reason is that an insulating transformer and a photocoupler can also function as an insulating member. 
         [0040]    The control unit  2  includes one or more microcomputers (microcontrollers), and is configured to perform overall control of the relay unit  24 . Particularly, the control unit  2  controls switching of the mechanical switches  22  and  23  by controlling whether or not to excite each of the relay coils  7  and  8 . Note that the external power supply  11  is a DC power supply serving as a power supply for the relay unit  24 , and supplies power to the control unit  2  via a power supply circuit  25  included in the relay unit  24 . If the control unit  2  includes a plurality of microcomputers, which perform the same processing, the processing is made redundant and more accurate control is possible, making the load controlling system  10  safer. 
         [0041]    Furthermore, the relay unit  24  includes a first input circuit  14 , a second input circuit  15 , a reset circuit  17 , an auxiliary output circuit  18 , an indicator light circuit (notification unit)  19 , and a load cooperative circuit  20 . Furthermore, in the load controlling system  10 , a first input switch  12 , a second input switch  13 , and a reset switch  16  are connected to the relay unit  24 . 
         [0042]    The first input switch  12  and the second input switch  13  may respectively be, for example, an emergency stop switch and a safety sensor, and are provided in order to reliably operate the load controlling system  10 . The first input circuit  14  converts a signal generated by on/off switching of the first input switch  12  into a signal of a format that can be processed appropriately by the control unit  2  and supplies the converted signal to the control unit  2 . The second input circuit  15  converts a signal generated by on/off switching of the second input switch  13  into a signal of a format that can be processed appropriately by the control unit  2  and supplies the converted signal to the control unit  2 . 
         [0043]    The reset switch  16  is a manual switch that is provided in order to operate reliably, together with the first input switch  12  and the second input switch  13 , the load controlling system  10 . The reset circuit  17  converts a signal generated by pressing of the reset switch  16  into a signal of a format that can be processed appropriately by the control unit  2 , and supplies the converted signal to the control unit  2 . 
         [0044]    The auxiliary output circuit  18  is a circuit for use in, for example, controlling of the load controlling system  10  by an external device (not shown), and outputs a result of detecting whether current flows or does not flow through the load  21  to the outside of the load controlling system  10 . 
         [0045]    The indicator light circuit  19  emits light or blinks depending on the state of the load controlling system  10 , and performs notification so that the state of the load controlling system  10  can be viewed. 
         [0046]    The load cooperative circuit  20  is associated with the state and/or operation of the load  21 , and is configured to convert a signal that is generated depending on, for example, various types of states and/or operations of the load  21  into a signal of a format that can be processed appropriately by the control unit  2 , and supplies the converted signal to the control unit  2 . 
         [0047]    Meanwhile, when all the mechanical switches  22  and  23  are in the open state, a signal output from the control unit  2  can pass through the capacitor C 1 , the mechanical switch  22 , the mechanical switch  23 , and the capacitor C 2  in the stated order, and can return to the control unit  2 . 
         [0048]    The control unit  2  includes an insulating member diagnosis unit  26 , a first diagnosis-signal output unit  27 , a second diagnosis-signal output unit  28 , and a switching circuit diagnosis unit  29 . 
         [0049]    The insulating member diagnosis unit  26  performs diagnosis of insulation failures (such as short circuits) of the capacitors C 1  and C 2 . 
         [0050]    The first diagnosis-signal output unit  27  outputs a first diagnosis signal  30 . This first diagnosis signal  30  passes through the capacitor C 1 , the mechanical switch  22 , the mechanical switch  23 , and the capacitor C 2  in the stated order, and is supplied as a first diagnosis-result signal  31  to the insulating member diagnosis unit  26 . The insulating member diagnosis unit  26  performs the diagnosis of insulation failures of the capacitors C 1  and C 2  based on this first diagnosis-result signal  31 . 
         [0051]    The second diagnosis-signal output unit  28  outputs a second diagnosis signal  32 . This second diagnosis signal  32  passes through the capacitor C 1 , the mechanical switch  22 , the mechanical switch  23 , and the capacitor C 2  in the stated order, and is supplied as a second diagnosis-result signal  33  to the switching circuit diagnosis unit  29 . 
         [0052]    The switching circuit diagnosis unit  29  performs fault diagnosis of the switching circuit  3  based on the second diagnosis-result signal  33 . 
         [0053]    Examples of the principles of the fault diagnosis of the switching circuit  3  include the followings. That is, a plurality of second diagnosis signals  32  are output from the second diagnosis-signal output unit  28 . If second diagnosis-result signals  33  have appropriately been obtained from all the second diagnosis signals  32 , the switching circuit diagnosis unit  29  determines that the switching circuit  3  does not have a fault. Conversely, if no second diagnosis-result signal  33  has appropriately been obtained from at least one of the second diagnosis signal  32 , the switching circuit diagnosis unit  29  determines that the switching circuit  3  has a fault. Note that according to the same principles, the switching circuit diagnosis unit  29  may perform the fault diagnosis of the switching circuit  3  based on the first diagnosis-result signals  31 . 
         [0054]      FIG. 3  shows waveform charts illustrating the principles of the diagnosis of insulation failures of the capacitors C 1  and C 2  by the insulating member diagnosis unit  26  and the first diagnosis-signal output unit  27 . 
         [0055]    Plot (a) in  FIG. 3  shows the waveform of the first diagnosis signal  30  immediately after having been output from the first diagnosis-signal output unit  27 . As shown in Plot (a) in  FIG. 3 , the first diagnosis signal  30  is a pulse. 
         [0056]    Plot (b) in  FIG. 3  shows the waveform of the first diagnosis-result signal  31  immediately before being input to the insulating member diagnosis unit  26  when the capacitors C 1  and C 2  do not have an insulation failure. When the first diagnosis signal  30  is a pulse, the waveform of the first diagnosis-result signal  31  is a triangular wave as shown in Plot (b) in  FIG. 3  due to charge and discharge of the capacitors C 1  and C 2 . 
         [0057]    The insulating member diagnosis unit  26  compares the signal level of the first diagnosis-result signal  31  shown in Plot (b) in  FIG. 3  with an analog-digital conversion threshold  34 . If the signal level of the first diagnosis-result signal  31  is the analog-digital conversion threshold  34  or greater, a high-level signal will be output, and if the signal level of the first diagnosis-result signal  31  is smaller than the analog-digital conversion threshold  34 , a low-level signal will be output. Accordingly, the insulating member diagnosis unit  26  subjects the first diagnosis-result signal  31  to analog-digital conversion so as to convert the first diagnosis-result signal  31  into a digital signal  35  shown in Plot (c) in  FIG. 3 . The pulse width of the digital signal  35  is taken as a pulse width W 1 . 
         [0058]    On the other hand, if the capacitors C 1  and C 2  have an insulation failure, the greater the degree of the failure is, the closer the waveform of the first diagnosis-result signal  31  that is immediately before being input to the insulating member diagnosis unit  26  is to a rectangular wave. That is, as shown in Plot (d) in  FIG. 3 , the waveform of a first diagnosis-result signal  31 ′, which is the first diagnosis-result signal  31  when this insulation failure is present, is closer to a rectangular wave than the waveform of the first diagnosis-result signal  31  shown in Plot (b) in  FIG. 3 . This is because when this insulation failure is present, the capacity of the circuit increases and the discharge time is extended. 
         [0059]    The insulating member diagnosis unit  26  compares the signal level of the first diagnosis-result signal  31 ′ shown in Plot (d) in  FIG. 3  with the analog-digital conversion threshold  34 . The insulating member diagnosis unit  26  then subjects the first diagnosis-result signal  31 ′ to analog-digital conversion so as to convert the first diagnosis-result signal  31 ′ into a digital signal  35 ′ (the digital signal  35  when the capacitors C 1  and C 2  have an insulation failure) shown in Plot (c) in  FIG. 3 . A pulse width W 1 ′ is longer than the pulse width W 1 , where the pulse width W 1 ′ is the pulse width of the digital signal  35 ′. 
         [0060]    As described above, the insulating member diagnosis unit  26  can determine that the capacitors C 1  and C 2  have an insulation failure when the digital signal  35  has a predetermined pulse width or greater. At that time, the “predetermined (pulse width)” may be, for example, any width exceeding the pulse width W 1 . Accordingly, it is possible to accurately detect insulation failures of the capacitors C 1  and C 2 . 
         [0061]    Note that the insulating member diagnosis unit  26  may perform the diagnosis of insulation failures of the capacitors C 1  and C 2  while current flows through the load  21 , or may perform the diagnosis of insulation failures of the capacitors C 1  and C 2  while no current flows through the load  21 . 
         [0062]      FIG. 4  is a flowchart illustrating the flow of the processing of the control unit  2  using the insulating member diagnosis unit  26 , the first diagnosis-signal output unit  27 , and the switching circuit diagnosis unit  29 . 
         [0063]    First, the first diagnosis-signal output unit  27  outputs the first diagnosis signal  30 . Accordingly, the first diagnosis-result signal  31  is supplied to the insulating member diagnosis unit  26  and the switching circuit diagnosis unit  29  (step S 11 ). 
         [0064]    The switching circuit diagnosis unit  29  performs fault diagnosis of the switching circuit  3  based on the first diagnosis-result signal  31  (step S 12 ). 
         [0065]    If, as a result of the diagnosis, a fault of the switching circuit  3  has been detected (the result of step S 12  shows NG), processing associated with a malfunction of the switching circuit  3  (malfunction processing  1 ) is performed (step S 15 ). 
         [0066]    If, as a result of the diagnosis, no fault of the switching circuit  3  has been detected (the result of step S 12  shows OK), the insulating member diagnosis unit  26  performs diagnosis of insulation failures of the capacitors C 1  and C 2  based on the first diagnosis-result signal  31  (step S 13 ). That is, the insulating member diagnosis unit  26  detects whether or not the digital signal  35  has a predetermined pulse width or greater according to the principles that have been described above with reference to  FIG. 3 . 
         [0067]    If, as a result of the diagnosis, insulation failures of the capacitors C 1  and C 2  have been detected (the result of step S 13  shows NG), processing associated with the malfunctions of the capacitors C 1  and C 2  (malfunction processing  2 ) is performed (step S 16 ). 
         [0068]    If, as a result of the diagnosis, no insulation failures of the capacitors C 1  and C 2  have been detected (the result of step S 13  shows OK), the relay unit  24  performs normal operation (normal control processing) (step S 14 ). 
         [0069]    Note that examples of the malfunction processing  1  and  2  include various types of processing for ensuring the safety of the load control system  10  such as shut-down of the relay unit  24 . 
         [0070]    According to the flow of the operation shown in the flowchart of  FIG. 4 , the number of processing steps can be reduced, and thus there is the advantage that the processing time is reduced. 
         [0071]      FIG. 5  is a flowchart showing the flow of the processing of the control unit  2  using the insulating member diagnosis unit  26 , the first diagnosis-signal output unit  27 , the second diagnosis-signal output unit  28 , and the switching circuit diagnosis unit  29 . 
         [0072]    First, the second diagnosis-signal output unit  28  outputs the second diagnosis signal  32 . Accordingly, the second diagnosis-result signal  33  is supplied to the switching circuit diagnosis unit  29  (step S 21 ). 
         [0073]    The switching circuit diagnosis unit  29  performs fault diagnosis of the switching circuit  3  based on the second diagnosis-result signal  33  (step S 22 ). 
         [0074]    If, as a result of the diagnosis, a fault of the switching circuit  3  has been detected (the result of step S 22  shows NG), processing associated with a malfunction of the switching circuit  3  (malfunction processing  1 ) is performed (step S 26 ). 
         [0075]    If, as a result of the diagnosis, no fault of the switching circuit  3  has been detected (the result of step S 22  shows OK), the first diagnosis-signal output unit  27  outputs the first diagnosis signal  30 . Accordingly, the first diagnosis-result signal  31  is supplied to the insulating member diagnosis unit  26  (step S 23 ). 
         [0076]    The insulating member diagnosis unit  26  performs diagnosis of insulation failures of the capacitors C 1  and C 2  based on the first diagnosis-result signal  31  (step S 24 ). That is, the insulating member diagnosis unit  26  detects whether or not the digital signal  35  has a predetermined pulse width or greater, according to the principles that have been described above with reference to  FIG. 3 . 
         [0077]    If, as a result of the diagnosis, insulation failures of the capacitors C 1  and C 2  have been detected (the result of step S 24  shows NG), processing associated with malfunctions of the capacitors C 1  and C 2  (malfunction processing  2 ) is performed (step S 27 ). 
         [0078]    If, as a result of the diagnosis, no insulation failures of the capacitors C 1  and C 2  have been detected (the result of step S 24  shows OK), the relay unit  24  performs normal operation (normal control processing) (step S 25 ). 
         [0079]    According to the flow of the operation shown in the flowchart of  FIG. 5 , it is possible to perform the fault diagnosis of the switching circuit  3  and the diagnosis of insulation failures of the capacitors C 1  and C 2  separately, and thus there is the advantage that the diagnosis accuracy can easily be improved. 
         [0080]    Hereinafter, the flow of the operation of the load controlling system  10  will be described briefly with reference to the following items ( 1 ) to ( 8 ). Note that in the initial state of the load controlling system  10 , the external power supply  11 , the first input switch  12 , the second input switch  13 , and the reset switch  16  are in the OFF state, and the load cooperative circuit  20  is in the ON state. Furthermore, in the same initial state, both the mechanical switches  22  and  23  are in the open state. 
         [0081]    (1) The external power supply  11  is turned on and thereby the control unit  2  is started. 
         [0082]    (2) The first input switch  12  and the second input switch  13  are turned on. Thereby, the load controlling system  10  is put in a safe state. 
         [0083]    (3) The reset switch  16  is pressed and then the pressing is released. 
         [0084]    (4) The control unit  2  recognizes that the item (2) has been performed based on signals supplied from the first input circuit  14  and the second input circuit  15 . Furthermore, the control unit  2  recognizes that the item (3) has been performed based on a signal supplied form the reset circuit  17 . 
         [0085]    (5) Fault diagnosis of the switching circuit  3  and diagnosis of insulation failures of the capacitors C 1  and C 2  are performed. 
         [0086]    (6) The control unit  2  excites the relay coil  7  and  8 . This makes it possible for the mechanical switches  22  and  23  to be put in the closed state. 
         [0087]    (7) When both the mechanical switches  22  and  23  are switched to the closed state, current flow through the load  21  is started. 
         [0088]    (8) When at least one of the first input switch  12  and the second input switch  13  is turned off, both the mechanical switches  22  and  23  are put in the open state and the current flow through the load  21  is interrupted. 
         [0089]    In relay unit  24 , the insulating member diagnosis unit  26 , the first diagnosis-signal output unit  27 , the second diagnosis-signal output unit  28 , and the switching circuit diagnosis unit  29  are realized by the control unit  2 . However, various circuits (hardware) for realizing the same functions as those of the insulating member diagnosis unit  26 , the first diagnosis-signal output unit  27 , the second diagnosis-signal output unit  28 , and the switching circuit diagnosis unit  29  may be used. 
         [0090]    The description above is given taking a case in which two contact relays, namely, the first contact relay circuit  5  and the second contact relay circuit  6  are used as an example, but three contact relays or more may be used. Furthermore, instead of contact relay, non-contact relay may be used. 
         [0091]    The above description will apply similarly to the case where the switching circuit  3  is controlled to realize the same function as that of the relay unit  24 . That is, the present invention encompasses a method for controlling the switching circuit  3 , and in this case, it can be construed that the control unit  2  of the load controlling system  10  executes the insulation member diagnosis step. 
         [0092]    The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope indicated in the Claims. The technical scope of the present invention also encompasses embodiments obtained by suitably combining technical means disclosed in different embodiments. 
       INDUSTRIAL APPLICABILITY 
       [0093]    The present invention is applicable to a relay unit including an insulating member for insulating and separating a load power supply for operating a load from a device power supply, which is different from the load power supply, and to a method for controlling a relay circuit.