Control arrangement for a switch such as a circuit breaker

Abstract

A control arrangement 10 for a switch arrangement (100, figure 2), the control arrangement having an ON push button switch 12, an OFF push button switch 14, and a control logic circuit 16. The logic c

Description

Field This relates to a control arrangement for a switch such as a circuit breaker. Background Switching devices, such a circuit-breakers, are used to connect and disconnect power supplies to loads. Such electrical switching devices may be controlled to move an electric contact between an ON state and an OFF state based on a mechanical input from a user or using electronic signals that control a drive system. A conventional electromechanical circuit breaker is controlled through operation of a rotary knob. A user rotates the knob in one direction to cause the circuit breaker to move from a closed state to an open state, and rotates the knob in the opposite direction to cause the circuit breaker to move from the closed state to the open state. Such devices have been well known for some time. Summary of Invention The invention provides a control arrangement for a switch arrangement, the control arrangement comprising: an ON push button switch; an OFF push button switch; and a control logic circuit having a first input electrically connected to the ON push button switch, a second input electrically connected to the OFF push button switch, and an output for connection to a switch, the control logic circuit including a state machine that is configured to exist in one of a first state and a second state at any given moment in time, and a control signal generator configured to provide on the output that is electrically connected to the switch a signal that is dependent on a current state of the state machine and / or is dependent on a change in state of the state machine, such as to cause the switch to be respectively closed or open depending on the state existing in the state machine, wherein the state machine is configured to: switch to or remain in the first state in response to detecting operation of the ON push button switch, and switch to or remain in the second state in response to detecting operation of the OFF push button switch. The control logic circuit may have a third input electrically connected to a position detection device, wherein the state machine is configured to switch to or remain in the second state in response to determining that a signal received at the third input indicates that the position detection device has determined a locking member to be in a locked position, and wherein the state machine is configured to remain in the second state as long as the signal received at the third input indicates that the position detection device has determined the locking member to be in the locked position. The position detection device may be an optical detector arrangement or a microswitch. The control logic circuit may have a fourth input electrically connected to a communications interface, wherein the state machine is configured to: switch to or remain in the first state in response to detecting an ON command at the fourth input, and switch to or remain in the second state in response to detecting an OFF command at the fourth input. The control signal generator may be electrically connected to the switch via a switch driver, which is configured to drive the switch based on signals received from the control signal generator. The invention also provides a switching arrangement comprising: a control arrangement as above, and a switch coupled to the output of the control arrangement. The switch may be a galvanic separation relay. Brief Description of the Figures The detailed description makes reference to the following figures. Figure 1 is a schematic diagram of a control arrangement according to embodiments of the invention; Figure 2 is a view of a switching device 100 in accordance with embodiments of the invention and including the Figure 1 control arrangement; Figures 3a and 3b provide a cross-sectional view of a switching device in accordance with examples of the disclosure in an unlocked state and a locked state; and Figure 4 provides a cross-sectional view of a switching device in accordance with examples of the disclosure in a state in which the actuation connector is in the ON position. Detailed Description of Embodiments A control arrangement 10 for a circuit breaker is shown in Figure 1. The control arrangement comprises an ON push button switch 12, an OFF push button switch 14 and a control logic circuit 16. All the components of the control arrangement 10 are included within a housing 11. The ON push button switch 12, the OFF push button switch 14 and the control logic circuit 16 may be mounted on a PCB 15 or other suitable substrate or mounted on a panel for instance. The ON push button switch 12 and the OFF push button 14 here include electronic components that allow their connection directly to the control logic circuit 16, but alternatively there may be separate analogue circuits that interface between the switches 12, 14 and the control logic circuit 16. The control logic circuit 16 has a first input 18 electrically connected to the ON push button switch 12, a second input 20 electrically connected to the OFF push button switch 14, and an output 22 for connection to a relay 30. The control logic circuit 16 may also have a third input 24 electrically connected to a position detection device 26. The position detecting switch 26 is coupled to detect the position of a locking member (not shown), which is operable by a user to lock the relay 30 in an OFF (open) state. The control logic circuit 16 may also have a fourth input 28 electrically coupled to a communications interface 29. The communications interface 29 may be mounted on the same PCB 15 or other suitable substrate as the other components. Control signals for controlling the relay 30 may be received from one or more remote locations using the communications interface 29. The communications interface 29 may for instance be a communications interface that communicates using a common industrial communication protocol, for instance the Modbus protocol. The communications interface 29 may alternatively communicate using a different protocol. A key function of the communications interface 29 is to allow control from remotely. The control logic circuit 16 is connected to a relay 30, or generically a switch 30, via a relay driver 32, or generically a switch driver 32. The relay driver 32 is configured to drive the relay 30 based on signals received from the control logic circuit 16. The relay 30 is for example a galvanic separation relay, or a hybrid semiconductor circuit breaker, or a solid state circuit breaker, or any other type of switchgear. The relay 30 may be a three-phase device, including three separate relays - one for each phase. In these embodiments, the relay 30 is a bistable relay, which remains in the state to which it was switched with the last driving signal. The relay driver 32 is mounted on the PCB 15 but it may alternatively be on a separate substrate or external to the housing 11. The relay 30 is external to the housing, but it may alternatively be internal. The control logic circuit 16 includes a state machine 16a that is configured to exist in either a first state or a second state at any given moment in time. The control logic circuit 16 includes a control signal generator 16b that provides on the output 22 a signal having that is based on the current state of the control logic circuit 16. The signal provided on the output 22 by the control signal generator 16b is also based on changes in state of the state machine 16a. There are 3 possible signals that can be provided on the output 22 by the control signal generator 16b: Idle, Drive-Open, and Drive-Close (reverse polarity). The relay 30 is bistable and the relay driver 32 is active only consequent to state transitions. The provision on the output 22 by the control signal generator 16b of a signal being one of an Idle, Drive-Open, and Drive-Close causes the relay 30 to be closed or open depending on the state existing in state machine that is the control logic circuit 16. The control logic circuit 16 includes logic circuits (not shown) that are configured to implement the state machine 16a with specific operation. Specifically, the control logic circuit 16 is configured to cause the following operation. First, the state machine 16a of the control logic circuit 16 switches to or remains in the first state in response to detecting operation of the ON push button switch. That is to say, if the control logic circuit 16 is already in the first state when operation of the ON push button switch 12 is detected, it remains in the first state. However, if the control logic circuit 16 is in the second state when operation of the ON push button switch 12 is detected, it switches to the first state. Secondly, the state machine 16a of the control logic circuit 16 switches to or remains in the second state in response to detecting operation of the OFF push button switch. That is to say, if the control logic circuit 16 is already in the second state when operation of the OFF push button switch 14 is detected, it remains in the second state. However, if the control logic circuit 16 is in the first state when operation of the OFF push button switch 14 is detected, it switches to the second state. Thirdly, the state machine 16a of the control logic circuit 16 is configured to switch to or remain in the second state in response to determining that a signal received at the third input 24 indicates that the position detection device 26 has determined an override input device [...] to be in a locked position. The control logic circuit 16 is configured to remain in the second state as long as the signal received at the third input 24 indicates that the position detection device has determined the override input device to be in the locked position. That is to say that detecting operation of the ON push button switch 12 does not cause the control logic circuit 16 to switch to the first state if the signal received at the third input 24 indicates that the position detection device 26 has determined an override input device [...] to be in a locked position. Put another way, receiving a signal at the third input 24 indicating that the position detection device 26 has determined an override input device be in a locked position overrides any change in state of the control logic circuit 16 that would otherwise result from detecting operation of the ON push button switch 12. Fourthly, the state machine 16a of the control logic circuit 16 is configured to switch to or remain in the first state in response to detecting an ON command at the fourth input 28, and switch to or remain in the second state in response to detecting an OFF command at the fourth input 28. That is to say, if the control logic circuit 16 is already in the first state when an ON command is received at the fourth input 28, it remains in the first state. However, if the control logic circuit 16 is in the second state when an ON command is received at the fourth input 28, it switches to the first state. Also, if the control logic circuit 16 is already in the second state when an OFF command is received at the fourth input 28, it remains in the second state. However, if the control logic circuit 16 is in the first state when an OFF command is received at the fourth input 28, it switches to the second state. Any change in state of the control logic circuit 16 that would result from the detection of commands at the fourth input 28 is overridden by any signal at the third input 24 indicating that the position detection device 26 has determined an override input device be in a locked position. The control signal generator 16b control logic circuit 16 provides on the output 22 a signal being one of an Idle, Drive-Open, and Drive-Close depending on changes in state of the state machine. Specifically, when the state of the state machine changes from the first state to the second state, the control signal generator 16b of the control logic circuit 16 provides on the output 22 a Drive-Close signal. The Drive-Close signal is provided for a period of time that is sufficient to cause the relay driver 32 to close the switch that is constituted by the relay 30. When the state of the state machine changes from the second state to the first state, the control signal generator 16b of the control logic circuit 16 provides on the output 22 a Drive-Open signal. The Drive-Open signal is provided for a period of time that is sufficient to cause the relay driver 32 to open the switch that is constituted by the relay 30. In either case, after the period of time, the control signal generator 16b of the control logic circuit 16 provides on the output 22 an Idle signal unless in the meantime another change in state of the state machine occurs. Any change in state of the state machine results in the control signal generator 16b of the control logic circuit 16 providing on the output a Drive-Closed or Drive-Open signal depending on whether the state machine changed from being in the first state to being in the second state or changed from being in the second state to being in the first state respectively. In some embodiments, the position detection device 26 is an optical detector arrangement, or put another way an optical sensor arrangement. For instance, the position detection device 26 may take the form of an optical emitter and optical sensor that are arranged such that the amount of light incident on the optical sensor changes when the override input device moves to being in a locked position from an unlocked position. Such an optical detector arrangement may take one of a number of different forms. For instance, there may be multiple optical sensors in different detection configurations. In other embodiments, the position detection device 26 is a microswitch, which may also be called a miniature snap-action switch. In these embodiments, the position detection device 26 a very sensitive electric switch that can be operated rapidly by a small movement. It can be actuated by physical force, through the use of a tippingpoint mechanism, sometimes called an "over-centre" mechanism. Such a microswitch may take one of a number of different forms. In other embodiments, the position detection device 26 is a magnetic sensor arrangement, e.g. a reed switch, in conjunction with a magnet. It may alternatively take another form. The reference numerals used for the inputs 18, 20, 22 and 28 and the output 22 of the control logic circuit 16 are also used for the outputs of the switches 12, 14, the position detector 26, the communications interface 29 and the relay driver 32 respectively. Although in Figure 1 the position detector 26 is shown as mounted on the PCB 15, it may alternatively be external to the housing 11 and coupled to the PCB 15. The ON push button switch 12 and the OFF push button switch 14 will now be discussed. In this discussion the switches 12, 14 are the same in construction and operation, although they may instead be different types. The switches 12, 14 are operable by a user pressing a button. The ON push button switch 12 includes a button 102a and the OFF push button switch 14 includes a button 102b. A button switch, push button or push-button (also spelled pushbutton) switch 12, 14 is a simple switch mechanism. Such switches are well known for controlling an aspect of a machine or a process. The buttons 102a, 102b may be made out of hard material, for instance plastic or metal. The surface of the buttons 102a, 102b may be flat. It may alternatively be shaped to accommodate the human finger or hand, so as to be easily depressed or pushed. The switches 12, 14 are biased switches, including a spring to return the switches to their un-pushed state when the user removes the depression force from the button. The ON push button switch 12 and the OFF push button switch 14 may be marked or otherwise visibly different so that a user can identify which switch is the ON push button switch 12 and which switch is the OFF push button switch 14. They may be marked by having the words 'ON' and 'OFF' on the buttons 102a, 102b, or on a surface of the housing 11. Alternatively or additionally the ON push button switch 12 and the OFF push button switch 14 may have different appearances. For instance, the ON push button switch 12 and the OFF push button switch 14 may be coloured differently. The ON push button switch 12 may be coloured green and the OFF push button switch 14 may be coloured red, for instance. The buttons 102a, 102b may alternatively be differently shaped. For instance, the ON button 102a may have a round shape and the OFF button 102b may have a square shape. The switches 12, 14 may be push to make switches, by which the switches close when pressed. They may alternatively be push to break switches, by which the switches are usually closed but open when pressed. The control logic circuit 16 is configured to respond to the change in signal level at the input 18, 20 that is caused by the pressing of the respective switch 12, 14. This means that any change between the first and second states of the state machine 16a of the control logic circuit 16 is caused by the pressing of the button 12, 14. The control logic circuit 16 is configured not to respond to the change in signal level at the input 18, 20 that is caused by the release of the respective switch 12, 14. This means that no change between the first and second states of the state machine 16a of the control logic circuit 16 is caused by the release of the button 12, 14. The arrangement of the ON push button switch 12, the OFF push button switch 14 and the control logic circuit 16 described above provides for convenient control of the relay by a user. Operation of the relay by a user is extremely simple: the user simply presses the an ON push button switch 12 to have the relay 30 be in a closed state and presses the OFF push button switch 14 to have the relay be in an open state. The user does not need to note or even know the current state of the relay 30 when controlling. The existing state of the relay 30 is not relevant; instead the user can cause the relay 30 to be in the desired state simply by pressing one of the buttons 12, 14. This is contrary to the situation that exists with rotary switches, where the initial position of the switch is different depending on the open or closed state of the relay and the user then needs to make a determination as to the current state of the relay and then make a decision as to whether the state of the relay needs to be changed before determining whether or not to operate the rotary switch. None of this is necessary with the arrangement described above. The simpler operation provided by the above arrangement thus reduces the chances of an incorrect input by a user, and thereby improves safety in that the chances of the relay 30 being unintentionally in a closed state are reduced. This also improves operation of an electrical system incorporating the relay 30, in that the simpler operation reduces the chances of the relay being unintentionally in an open state are reduced. All of this is achieved while facilitating an override function, described above in relation to the signal at the third input 24 indicating that the position detection device 26 has determined an override input device be in a locked position. It is achieved also while allowing the state of the relay 30 to be changed by signals received by the communications interface 29. The state of the control logic circuit 16, and thus the state of the relay 30, may be changed either by operation by a user of one of the switches 12, 14 or by the receipt of a control signal from a remote location via the communications interface 29. For instance, the control logic circuit 16 may be switched in the first state, in which the relay 30 is closed, in response to the user pressing the ON push button switch 12, and the control logic circuit 16 may be switched into the second state, in which the relay 30 is open, in response to receiving an OFF command via the communications interface 29. In the above-described embodiments the relay 30 is a bistable relay, but it may alternatively be monostable. In the case of a monostable relay 30, the state machine of the control logic circuit 16 is the same as described above, but the control logic circuit 16 is adapted such that the relay driver 32 is caused to provide an energising signal to the relay 30 to hold the relay 30 in the unstable state to reflect the corresponding state of the state machine. Specifically, with a relay that is stable in the open state, then the control logic circuit 16 provides on the output 22 a Drive-Closed signal whenever the state machine is in the first state and not just when the state machine transitions to the second state from the first state. Fig. 2 illustrates a switching device 100 in accordance with embodiments of the invention, and Figs. 3a, 3b and 4 illustrate a cross-sectional view of the switching device 100 in different states of operation. When in use, the switching device 100 is arranged between a power supply and one or more loads such that an electrical current passes through the switching device 100 when power is provided to the one or more loads from the power supply. The switching device 100 comprises the relay 30, which constitutes an electrical switch. As mentioned above, the relay 30 may be a galvanic separation relay. The switching device 100 comprises the control arrangement 10 (not shown) coupled to the ON button 12 and the OFF button 14 for controlling the relay driver 32 in the form of an electromagnetic drive unit that moves the electric switch 30 between ON and OFF states. The ON state may also be termed a closed switch state, and the OFF state may also be termed an open switch state. The switching device 100 further comprises a connection member 103 that is coupled to the electrical switch 101 and a locking member 104 configured to engage the connection member 103 when an engagement portion of the locking member 104 is inserted into a recess of the connection member 103. Insertion of the engagement portion of the locking member 104 into the recess of the connection member 103 causes the locking member 104 to mechanically block movement of the connection member 103. The connection member 103 is coupled, either directly or indirectly, to electrical contacts of the electrical switch such that, when the locking member 104 blocks movement of the connection member 103, the electrical switch 101 cannot be switched from an OFF state to an ON state. In other words, the electromechanical drive unit is unable to move the electrical switch 101 from the OFF state to the ON state when movement of the connection member 103 is blocked by the locking member 104. The switching device 100 comprises a housing 105. The housing 105 may include one or more recesses, channels or surfaces defining paths along which the connection member 103 and / or the locking member 104 are constrained to move. The electrical switch 101 comprises one or more movable electrical contacts that are controllable to be moved between an ON state and an OFF state. When the electrical switch 101 is in the ON state, the one or more movable electric contacts are in electrical contact with fixed electrical contacts of the electrical switch 101 and form part of a complete conductive path between the power supply and the load, thus allowing current to pass through the switching device. When the electrical switch 101 is in the OFF state, the one or more movable electric contacts are separated from the fixed electrical contacts, and the conductive path between the load and the power supply is interrupted. The electrical switch 101 may be a galvanic separation relay. The switching device 100 further comprises an actuation connector 106 that is connected to the one or more movable electric contacts of the electrical switch 101, as shown in the cross-sectional views of the switching device 100 in Figs. 2a, 2b and 3. Preferably, the actuation connector 106 is rigidly connected to the one or more movable contacts of the electrical switch 101 such that the movable electric contacts and the actuation connector 106 co-move. In some embodiments, the actuation connector 106 may be integrally formed with the movable electric contacts. The actuation connector 106 and / or the movable electric contacts are rigidly coupled to the electromagnetic drive unit. The electromagnetic drive unit is configured to provide driving forces to the actuation connector 106 and / or the movable electric contacts to move the movable electric contacts and the actuation connector 106 between an ON state and an OFF state. When moving between the ON state and the OFF state, the movable electric contacts and the actuation connector 106 move in a substantially linear path along a first direction DI. In the OFF state of the electrical switch 101 (shown in Figs. 2a and 2b), the actuation connector 106 is in an ON position, and in the OFF state of the electrical switch 101 (shown in Fig. 4), the actuation connector is in an ON position. The actuation connector 106 is coupled to a connection member 103. The connection member 103 is configured to move within the housing 105 in a substantially linear path along the first direction between a first position and a second position. The path along which the connection member 103 is configured to move may be defined by a first cavity in the housing 105 within which the connection member 103 is disposed. In embodiments in which the actuation connector 106 and the connection member 103 are rigidly coupled to each other, the first position of the connection member 103 corresponds to the ON position of the actuation connector 106 and the second position of the connection member 103 corresponds to the OFF position of the actuation connector 106. In these embodiments, the actuation connector 106 and the connection member 103 may be formed as a single element. In the embodiments described in detail in the disclosure, the connection member 103 and the actuation connector 106 are able to move relative to each other within a limited range. In particular, the actuation connector 106 and the connection member 103 are configured to move relative to each other such that when the connection member 103 is in the first position, the actuation connector 106 must be in the OFF position. As shown in Figs. 3a, 3b and 4, the actuation connector 106 may comprise a head portion 106 that is configured to move within a hollow portion of the connection member 103 in order to allow the connection member 106 to move relative to the actuation connector 106. In other embodiments, alternative means may be used to allow a limited range of relative motion between the connection member 103 and the actuation connector 106. In the state shown in Figs. 3a and 3b, the actuation connector 106 is in the OFF position and the connection member 103 is in the first position. The relative positions of the actuation connector 106 and the connection member 103 are at one end of the allowed range of motion. In this state, movement of the actuation connector 106 to the ON position requires that the connection member 103 co-moves with actuation connector 106. A first resilient member 108 biases the connection member 103 towards the first position. The first resilient member 108 may be a coil spring, a leaf spring or any other suitable means biasing for biasing the connection member towards the first position. In the state shown in Fig. 4, the actuation connector 106 is in the ON position and the connection member 103 is in the second position. Movement from the state shown in Figs. 2a to the state shown in Fig. 4 is caused by a force generated by the electromagnetic drive unit acting in on the actuation connector 106 and / or the movable electric contacts of the electrical switch 101. As the actuation connector 106 moves from the OFF position to the ON position, the actuation connector 106 pulls the connection member 103 downwards from the first position to the second position. The downwards movement of the connection member 103 from the first position to the second position causes loading of the first resilient member 108. In embodiments in which the actuation connector 106 and the connection member 103 are rigidly coupled, the switching device 100 may not include the first resilient member 108. The switching device 100 further comprises a locking member 104 comprising an engagement portion 104a. The locking member 104 is configured to move within the housing 105 along a second direction D2 between an unlocked position (shown in Fig. 3a) and a locked position (shown in Fig. 3b). Preferably, the second direction D2 is substantially perpendicular to the first direction DI. The path along which the locking member 104 is configured to move may be defined by a second cavity in the housing 105 within which the locking member 104 is at least partially disposed. Fig. 3b illustrates a state of the switching device 100 in which the locking member 104 is in a locked position. In the locked position, the engagement portion 104a of the locking member 104 is inserted into a recess 103 of the connection member 103. The engagement portion 104a may comprise a protrusion from a main body of the locking member 104 or may comprise an end portion of a main body of the locking member 104. The recess 103a may have a shape corresponding to the shape of the engagement portion 104a of the locking member 104. For example, the engagement portion 104a may comprise a flat protrusion and the recess 103a may comprise a slot shaped to receive the flat protrusion. In other example, the recess 103a may have a different shape to the engagement portion 104a. For example, the recess 103a may define a shoulder portion or lip configured to engage an upper surface of the engagement portion 104a in the locked position. When locking member 104 is in the locked position, the insertion of the engagement portion 104a into the recess 103a blocks movement of the connection member 103 from the first position towards the second position. As described above, movement of the actuation connector 106 from the OFF state to the ON state requires the connection member 103 to move from the first position to the second position. Therefore, insertion of the engagement portion 104a into the recess 103a in the locked position provides a mechanical constraint blocking movement of the electrical switch 101 from the OFF state to the ON state. The mechanical blocking of the electrical switch 101 from the OFF state to the ON state prevents turning on of the electrical switch 101, even when the electromagnetic drive unit provides a force on the movable electric contacts or the actuation connector 106 to turn the switch on. As such, turning ON of the electrical switch 101 is mechanically prevented when the locking member 104 is in the locked position, regardless of whether or not any actuation means is engaged to attempt to move elements of the electrical switch 101 into the ON state. For example, when the electrical switching device 100 is remotely controllable, a user maintaining the switching device 100 can be certain that remote actuation of the electromagnetic drive unit will not result in the electrical switch being turned ON. In the unlocked position, shown in Fig. 3a and Fig. 4, the engagement portion 104a of the locking member 104 is not inserted into the recess 103a. As such, the connection member 103 is free to move between the first position and the second position, and the electrical switch 101 can be turned ON or OFF. In some examples, a second resilient member 109 biases the locking member 104 towards to unlocked position. Preferably, the connection member 103 comprises a side wall 103b disposed above the recess 103a. When the connection member 103 is in the second position (shown in Fig. 4), the side wall 103b blocks insertion of the engagement portion 104a. Because the connection member 103 must be in the second position when the electrical switch 101 is in the ON state, the locking member 104 cannot be moved into the locked position when the switch is in the ON state. In some examples, the recess 103a comprises a slot that is only aligned with the engagement portion 104a when the connection member 103 is in the first position (and the electrical switch 101 is in the OFF state). By preventing the locking member 104 from being moved into the locked position when the electrical switch 101 is in the ON state, a user can be provided with certainty that the locked position of the locking member 104 corresponds to a state in which the electrical switch is turned OFF. In the ON state of the electrical switch 101, shown in Fig. 4, the locking member 104 must be in unlocked position. A force applied to the locking member 104 towards the locked position causes the engagement portion 104a of the locking member 103a to press into the side wall 103b of the connection member 103. Such a force would occur, for example, if a user attempted to move the locking member 104 into the locked position while the electrical switch 101 is turned on. In these circumstances, a frictional force between the locking member 104 and the connection member 103 may prevent the connection member 103 from moving from the second position to the first position while the force is applied to the locking member 104. The actuation member 106 is capable of moving relative to the connection member 103 such that the actuation member 106 is able to move to the OFF state while the connection member 103 is held in the second position. In particular, while the connection member 103 is in the second position, the head portion 106a of the actuation member 106 may move within the hollow portion of the connection member 103 to allow the actuation member 106 to move to the OFF position. As such, the electrical switch 101 cannot be held in the ON state by applying a force to the locking member 104 when the electrical switch 101 is in the ON state. This prevents manual blocking of circuit-breaking or remote disconnection capabilities of the switching device 100 using the locking member 104. A portion of the housing 105 in which the locking member 104 is disposed comprises at least one first opening 110a passing therethrough. The portion of the housing 105 in which the locking member 105 is disposed comprises at least one channel wall 105a that defines a path along which the locking member 104 moves. The locking member 104 comprises a second opening 110b passing therethrough. The at least one first opening 110a and the second opening 110b may have the same shape and size as each other. The at least one first opening 110a and the second opening 110b are positioned such that, when the locking member 104 is in the locked position, the at least one first opening 110a and the second opening 110b are aligned. The at least one first opening 110a and the second opening 110b are positioned such that, when the locking member 104 is in the unlocked position, the at least one first opening 110a and the second opening 110b misaligned. When the at least one first opening 110a and the second opening 110b are aligned, a shackle of a padlock can be inserted by a user through the at least one first opening 110a and the second opening 110b to hold the locking member in the locked position. When the at least one first opening 110a and the second opening 110b are misaligned, a shackle of a padlock cannot be inserted by a user through the at least one first opening 110a and the second opening 110b. The at least one first opening 110a and the second opening 110b allow the use of a padlock to ensure that the locking member 104 remains in the locked position until the padlock is removed. This allows the locking of the switching device 101 to be securely maintained while a user requires the electric switch to be held in an OFF state. The use of a padlock that can only be attached in the OFF state of the electrical switch 101 provides simple and reliable means to indicate that the electrical switch 101 is locked in the OFF state by visual inspection. In the examples shown in the detailed description, two first openings 110a are provided on channel walls 105a on opposite sides of the channel in which the locking member 104 moves. However, in other examples, a single channel wall 105a having a single first opening 105a may be disposed on one side of the locking member 104. The portion of the housing 105 in which the locking member 104 is disposed may be configured to at least partially surround the locking member 104. The locking member 104 may comprise an actuation part 104b that extends outside of the housing 105 at least when the locking member 104 is in the unlocked position 104. The actuation part 104b is accessible by a user to allow the user to apply a force on locking member 104b in the direction of the locked position. By pressing the actuation part 104b when the switching device 100 is in the OFF state, a user may move the locking member 104 into the locked position. In some examples, the switching device 100 further comprises the sensor 26 configured to sense the position of the locking member 104. The control circuit 102 of the switching device 100 is configured not to provide a control signal to the electromagnetic drive unit to turn the electrical switch ON when the sensor 26 determines that locking member 104 is in the locked position. This electronic locking mechanism provides a further electronic safety mechanism to prevent turning ON of the electric switch in the locked position. The electronic locking mechanism prevents undue stresses on the locking member 104, connection member 104 and electromagnetic drive unit due to actuation of the electromagnetic drive unit when the locking member 104 is in the locked state. Key to the figures: control arrangement 10 housing 11 PCB 15 ON push button switch 12 button 13 OFF push button switch 14 control logic circuit 16 state machine 16a control signal generator 16b first input 18 second input 20 output 22 third input 24 position detection device 26 fourth input 28 communications interface 29 relay 30 relay driver 32 switching device 100 10 housing 105 103 Connection member 103a Recess of the connection member 103b Side wall of the connection member 104 Locking member 104a Engagement portion of the locking member 104b Actuation part of the locking member 105 Housing 106 Actuation connector 106a Head portion of the actuation connector 108 First resilient member 110a First opening 110b Second opening

Claims

1. A control arrangement (10) for a switch arrangement (100), the control arrangement comprising:an ON push button switch (12);an OFF push button switch (14); anda control logic circuit (16) having a first input electrically connected to the ON push button switch, a second input electrically connected to the OFF push button switch, and an output for connection to a switch (30),the control logic circuit (16) including a state machine (16a) that is configured to exist in one of a first state and a second state at any given moment in time, and a control signal generator (16b) configured to provide on the output that is electrically connected to the switch (30) a signal that is dependent on a current state of the state machine (16a) and / or is dependent on a change in state of the state machine (16a), such as to cause the switch (30) to be respectively closed or open depending on the state existing in the state machine (16a),wherein the state machine (16a) is configured to:switch to or remain in the first state in response to detecting operation of the ON push button switch (12), andswitch to or remain in the second state in response to detecting operation of the OFF push button switch (14).

2. A control arrangement as claimed in claim 1, wherein the control logic circuit has a third input electrically connected to a position detection device (26), wherein the state machine (16a) is configured to switch to or remain in the second state in response to determining that a signal received at the third input indicates that the position detection device (26) has determined a locking member (104) to be in a locked position, and wherein the state machine (16a) is configured to remain in the second state as long as the signal received at the third input indicates that the position detection device has determined the locking member (104) to be in the locked position.

3. A control arrangement as claimed in claim 2, wherein the position detection device (26) is an optical detector arrangement.

4. A control arrangement as claimed in claim 2, wherein the position detection device (26) is a microswitch.

5. A control arrangement as claimed in any preceding claim, wherein the control logic circuit (16) has a fourth input electrically connected to a communications interface (29), wherein the state machine (16a) is configured to:switch to or remain in the first state in response to detecting an ON command at the fourth input, andswitch to or remain in the second state in response to detecting an OFF command at the fourth input.

6. A control arrangement as claimed in any preceding claim, wherein the control signal generator (16b) is electrically connected to the switch (30) via a switch driver (32), which is configured to drive the switch based on signals received from the control signal generator (16b).

7. A switching arrangement (100) comprising:a control arrangement (10) as claimed in any preceding claim, and a switch (30) coupled to the output of the control arrangement (10).

8. A switching arrangement (100) as claimed in claim 7, wherein the switch (30) is a galvanic separation relay.

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