Patent Publication Number: US-2021165943-A1

Title: Secure control device, contactor comprising such a device and method for secure processing of a control signal

Description:
TECHNICAL FIELD 
     The present invention relates to a safety control device intended in particular to control a contactor. The invention also relates to a method for safely processing a control signal for closing or opening a contactor and to a contactor having a safety control device. 
     PRIOR ART 
     Many devices have one or more contactors for controlling the powering on or powering off of electrical units, such as production machines, motors, welding devices, etc. Some devices whose operation is hazardous require increased safety in order to control them, and in particular have to have an emergency stop means in order to interrupt operation in the event of danger. In order to bolster the safety of goods and people, a command to start operation of an electric motor may be subject to validation in order to avoid any unwanted command caused for example by electromagnetic interference. In this case, when a command is invalid, the device has to be put into a safe state, generally corresponding to the device being stopped. 
     Document EP 1 538 651 A2 is known and relates to an emergency stop circuit having two lines operating in parallel, each line having contacts, the actuation of which is controlled by central units. The supply of power for the commands for the contacts is disconnected when an emergency stop is requested. 
     Patent application US 2004/0199 837 A describes a method and a device for the safe transmission of information between input and output units of a safety system.  
     Patent application US 2011/0169345 A1 describes a control system that prevents starting of a load when the command for or the supply of power to the load exhibits an anomaly. 
     DESCRIPTION OF THE INVENTION 
     The present invention relates to a safety control device intended to process a control signal and generate a first safety control order, said safety control device comprising:
         a control input having at least a first connection point and a second connection point, said control input being designed to receive the control signal,   a first protection circuit,   a first coupler having:
           a first emitter circuit connected in series with the first protection circuit, the assembly formed by the first emitter circuit and the first protection circuit being connected between the first connection point and the second connection point, said first emitter circuit being designed to emit a second signal when the control signal is present on the control input, and   a first receiver circuit designed to receive the second signal and to provide a third signal formed of at least one pulse,   
           a first switch connected in parallel across the first emitter circuit,   a pulse generator connected to the first switch and designed to cyclically control opening and closure of the first switch, and   a first processing circuit connected to the first receiver circuit in order to receive the third signal, said first processing circuit being designed to process the third signal and provide the first safety control order, said first safety control order being able to adopt at least two states:   a first start safety control order, or   a first stop safety control order.       

     Advantageously, the first emitter circuit and the first receiver circuit are galvanically isolated from one another.  
     Advantageously, the first coupler has at least one optocoupler, the first emitter circuit having an emitting diode and the first receiver circuit having a phototransistor, the emitting diode emitting radiation that forms a medium for transmitting the second signal to the phototransistor through an electrically insulating wall transparent to the radiation. 
     Advantageously, the pulse generator generates pulses having a predefined duty cycle less than or equal to 50%. 
     Preferably, the pulse generator generates pulses at a frequency of between 100 Hz and 10 kHz. 
     Advantageously, the first protection circuit has a current-limiting circuit for limiting the current flowing through said protection circuit. 
     Advantageously, the first protection circuit has a current threshold detection circuit connected to the current-limiting circuit in order to limit the current flowing through said protection circuit to a predefined maximum intensity when the amplitude of the control signal is greater than a predefined maximum voltage threshold. 
     In one particular embodiment, a voltage threshold detection circuit is connected in series with the first protection circuit and the first emitter circuit in order to limit the current flowing through said emitter circuit to a predefined minimum intensity when the amplitude of the control signal is less than a predefined minimum voltage threshold. 
     In one particular embodiment, the first switch is connected in series with the first protection circuit and the first emitter circuit. 
     According to one variant, the safety control device furthermore has:
         a validation input having a third connection point, said validation input being designed to receive a validation signal,   a second protection circuit,    a second coupler having:
           a second emitter circuit connected in series with the second protection circuit, the assembly formed by the second emitter circuit and the second protection circuit being connected between the third connection point and the second connection point of the safety control device, said second emitter circuit being designed to emit a fourth signal when the validation signal is present on the validation input, and   a second receiver circuit designed to receive the fourth signal and to provide a fifth signal,   
           a second switch connected firstly in parallel across the second emitter circuit and connected secondly to the pulse generator so that said pulse generator cyclically controls opening and closure of said second switch,   a second processing circuit connected to the second receiver circuit in order to receive the fifth signal, said second processing circuit being designed to process the fifth signal and provide a second safety control order, said second safety control order being able to adopt at least two states:
           a second start safety control order and   a second stop safety control order   
           a logic circuit having:
           a first binary input connected to the first processing circuit in order to receive the first safety control order,   a second binary input connected to the second processing circuit in order to receive the second safety control order, and   a second binary output for providing a third safety control order.   
               

     Advantageously, the third safety control order adopts at least two states:
         a third start safety control order when a first safety control order provided by the safety control device is a first start safety control order and when the second safety control order is a second start safety control order, or   a third stop safety control order when a first safety control order provided by the safety control device is a first stop safety control order or when the second safety control order is a second stop safety control order.       

     The present invention also relates to a contactor having: 
         at least one electrical contact connected to an upstream current line and a downstream current line, said electrical contact being designed to allow the flow of an electric current between the upstream current line and the downstream current line to be permitted or blocked,   an actuator designed to actuate the at least one electrical contact,   a safety control device, as described above, connected to the actuator in order to provide a first safety control order to said actuator in order to control the actuation of the at least one electrical contact,   a first connection terminal connected to a first connection point of said safety control device, and   a second connection terminal connected to a second connection point of said safety control device,       

     said contactor being such that the safety control device controls the actuator:
         so as to execute closure of the at least one electrical contact when the first safety control order is a first start safety control order, or   so as to execute opening of the at least one electrical contact when the first safety control order is a first stop safety control order.       

     Advantageously, the contactor furthermore has a third connection terminal connected to a third connection point of the safety control device. The safety control device is connected to the actuator via a second binary output in order to provide a third safety control order to the actuator, said third safety control order being able to adopt at least two states:
         a third start safety control order, or   a third stop safety control order.       

     The safety control device, by providing a third safety control order to the actuator, controls said actuator:
         so as to execute closure of the at least one electrical contact when the third safety control order is a third start safety control order, or   so as to execute opening of the at least one electrical contact when the third safety control order is a third stop safety control order.        

     The present invention also relates to a method for safely processing a third signal formed of at least one pulse provided by at least a first receiver circuit of a safety control device as described above, said method comprising iteratively counting a number of pulses provided by the first receiver circuit during a time interval of a predefined duration. 
     Advantageously, a first counter is incremented when the number of pulses counted during a time interval is between a predefined minimum number of pulses and a predefined maximum number of pulses. 
     Preferably, a first start safety control order is generated when the first counter is equal to or greater than a predefined validation threshold. 
     Preferably, a second counter is incremented when the number of pulses counted during the time interval is not between the minimum number of pulses and the maximum number of pulses. 
     Preferably, a first stop safety control order is generated when the second counter is equal to or greater than a predefined invalidation threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and features will become more clearly apparent from the following description and from particular embodiments of the invention, given by way of non-limiting example and shown in the appended drawings, in which: 
         FIG. 1  shows, in the form of a block diagram, a safety control device according to the invention, 
         FIGS. 2 a  and 2 b    show variant embodiments of a protection circuit forming part of the safety control device, and  FIG. 2 c    shows a combination of a voltage threshold detection circuit and a first coupler circuit, 
         FIG. 2 d    shows a variation curve of a current flowing in the protection circuit, and  FIG. 2 e    shows a variation curve of a current flowing in a first emitter circuit,  
         FIG. 3  shows, in the form of a block diagram, a connection variant for a first switch in a safety control device, 
         FIG. 4  shows, in the form of a block diagram, a safety control device having a validation input, 
         FIG. 5 a    shows, in the form of a block diagram, a contactor having a safety control device, and  FIG. 5 b    shows a contactor having a safety control device having a validation input, 
         FIGS. 6 a  to 6 d    are timing diagrams of a signal received by a processing circuit forming part of a safety control device, 
         FIG. 7 a    shows a flowchart of a method for safely processing a signal performed by the processing circuit, and 
         FIG. 7 b    shows a flowchart of a preferred variant of the safety processing method performed by the processing circuit. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows, in the form of a block diagram, a safety control device  1  intended to process a control signal Sig 1  and generate a first safety control order. Said safety control device  1  comprises at least:
         a control input E,   a first protection circuit  10 ,   a first coupler  20 ,   a first switch  30 ,   a pulse generator  40 ,   a first processing circuit  50 , and   a first binary output S 1 .       

     The control input E has at least a first connection point E 1  and a second connection point E 2 . The control signal Sig 1  is applied between the first point E 1  and the second point E 2 . The control signal Sig 1  is preferably a continuous voltage level or stage with an amplitude Vsig 1  of between 1 volt and 30 volts, preferably with a duration of between 5 ms and 100 ms.  
     The first protection circuit  10  is designed to clip the control signal Sig 1  if it has an abnormally high amplitude Vsig 1  and/or to limit a current i flowing in the safety control device  1 , when a control signal Sig 1  is applied. A first embodiment of the first protection circuit  10  is shown in  FIG. 2 a    and has a current limiter  11  consisting for example of at least one resistor R. The resistor R is preferably dimensioned so as to limit the current i to a predefined maximum intensity IMax of between 1 mA and 100 mA. 
     As a variant, the first protection circuit  10  has a current limiter  11  connected to a current threshold detection circuit  12 , as shown in  FIG. 2 b   .  FIG. 2 d    shows a variation curve of the current i flowing in the first protection circuit  10  as a function of the amplitude Vsig 1  of the control signal Sig 1 . When the intensity of the current i is less than the maximum current intensity IMax, the current threshold detection circuit  12  does not act, and the current i is set by the ratio between the amplitude Vsig 1  of the control signal Sig 1  and the value of the resistance R in accordance with Ohm&#39;s law. For example, for an amplitude Vsig 1  of the control signal Sig 1  equal to 24 volts and for a resistance R equal to 2000 ohms, the amplitude of the current i will be equal to 12 mA. When the amplitude Vsig 1  of the control signal Sig 1  exceeds a predefined maximum voltage threshold Umax, the current threshold detection circuit  12  acts on the current limiter  11  so as to increase the value of the resistance R in order to keep the intensity of the current i at the predefined maximum current intensity IMax. Thus, with the current i being constant, the power dissipated and therefore the heating in the current limiter  11  vary only in accordance with a linear law as a function of the amplitude Vsig 1  of the control signal Sig 1 . 
     Optionally, a voltage threshold detection circuit  13  is connected in series with the first protection circuit  10  and with the first coupler  20 , as shown in  FIG. 2 c   . In this configuration, the voltage threshold detection circuit  13  detects a predefined minimum voltage threshold Umin. For as long as the amplitude Vsig 1  of the control signal Sig 1  is less than said minimum voltage threshold Umin, the voltage threshold detection circuit  13  limits the current i flowing in a first emitter circuit  21  of the first coupler  20  to a predefined minimum intensity Imin. When the amplitude Vsig 1  of the  control signal Sig 1  is greater than the minimum voltage threshold Umin, the voltage threshold detection circuit  13  is inactive, and the current i is limited only by the current limiter  11 . A curve representative of the variation in the current i flowing in the first protection circuit  10  as a function of the amplitude Vsig 1  of the control signal Sig 1  in such an operating mode is shown in  FIG. 2 e   . Such a voltage threshold detection circuit  13  is used so that the first coupler  20  receives the control signal Sig 1  only if said control signal Sig 1  has an amplitude greater than the minimum voltage Umin, in order for example to eliminate stray signals. The threshold detection circuit  13  may consist of at least one Zener diode. 
     Optionally, for example in order to comply with the recommendations in the IEC60947-1 Standard, Appendix S, which deals with digital inputs for low-voltage appliances, a bypass resistor Rd is connected in parallel across the threshold detection circuit  13  and the first coupler  20 , as shown in  FIG. 2 c   , so that a current i is always present even when the first switch  30  is open and when the amplitude Vsig 1  of the control signal Sig 1  is less than the minimum voltage Umin. The bypass resistor Rd may also be connected in parallel across the first switch  30 . 
     In one preferred embodiment, the current limiter  11  limits the amplitude of the current i to a predefined maximum current intensity IMax of between 8 mA and 20 mA, the predefined minimum intensity of the current Imin is between 0 and 8 mA, the predefined maximum voltage threshold UMax is between 12 volts and 30 volts, and the predefined minimum voltage threshold Umin is between 0 and 12 volts. 
     The first coupler  20  has the first emitter circuit  21  connected in series with the first protection circuit  10 , the assembly formed by the first emitter circuit  21  and the first protection circuit  10  being connected between the first connection point E 1  and the second connection point E 2 , as shown in  FIG. 1 . The first emitter circuit  21  is designed to emit a second signal Sig 2  when the control signal Sig 1  is present on the control input E and when the current i is flowing in said first emitter circuit  21 . The first coupler  20  also has a first receiver circuit  22  designed to receive the second signal Sig 2  and to provide a third signal Sig 3 . Said third signal Sig 3  is formed of at  least one pulse, as will be described later on. The first emitter circuit  21  and the first receiver circuit  22  of said first coupler  20  are galvanically isolated from one another. 
     Preferably, the first coupler  20  has at least one optocoupler: the first emitter circuit  21  has an emitting diode D, the first receiver circuit  22  has a phototransistor Tr, the emitting diode D emitting radiation to the phototransistor Tr through a wall Sc transparent to the radiation, said wall being arranged between the emitting diode D and the phototransistor Tr, said radiation forming a medium for transmitting the second signal Sig 2 . The phototransistor Tr provides the third signal Sig 3  in the same way as the second signal Sig 2 . The wall Sc also has an electrically insulating property, that is to say that it does not conduct electric current, so as to provide galvanic isolation between the first emitter circuit  21  and the first receiver circuit  22 . 
     The first switch  30  is connected in parallel across the first emitter circuit  21  in order to short-circuit the first emitter circuit  21  when said first switch  30  is closed. The first emitter circuit  21  is thus able to emit only when the first switch  30  is in an open state. The first switch  30  is preferably a bipolar transistor or field-effect transistor. This configuration has the advantage of guaranteeing a constant flow of a current i as soon as a control signal Sig 1  is present on the control input E, regardless of the open or closed state of the first switch  30 . The first switch  30  is controlled by the pulse generator  40 . 
     The pulse generator  40  is connected to the first switch  30  and generates pulses in order to cyclically control opening and closure of the first switch  30 . Preferably, a pulse controls closure of the first switch  30 , the first switch  30  being open during the time interval between two consecutive pulses. The control signal Sig 1  is therefore modulated by the pulses delivered by the pulse generator  40 . 
     The pulse generator  40  generates pulses preferably having a rectangular form, having a predefined duty cycle less than or equal to 50% at a frequency preferably of between 100 Hz and 10 kHz. The pulse generator  40  is preferably a free oscillator that is not synchronized with any other signal present in the safety control device  1 .  
     In the presence of a control signal Sig 1 , the emitting diode D of the first emitter circuit  21  emits radiation to the phototransistor Tr of the first receiver circuit  22  when the first switch  30  is open. Said phototransistor Tr then provides a pulse forming the third signal Sig 3 , as shown in  FIG. 6 a   . When the first switch  30  is closed, the first emitter circuit  21  no longer emits radiation to the phototransistor Tr, and the third signal Sig 3  becomes zero. The third signal Sig 3  thus contains at least one pulse P when the control signal Sig 1  is present and when the pulse generator  40  is generating pulses. 
     The first processing circuit  50  is connected to the first receiver circuit  22  in order to receive the third signal Sig 3 . Said first processing circuit  50  is designed to execute a safety processing method  500  described later on in order to process the third signal Sig 3  and provide a first safety control order Sig 4 . Said first safety control order Sig 4  may adopt at least two states:
         a first start safety control order Sig 4 _ON, or   a first stop safety control order Sig 4 _OFF.       

     The first start safety control order Sig 4 _ON corresponds to a start safety command, and the first stop safety control order Sig 4 _OFF corresponds to a stop safety command, which is particularly suitable for a safe emergency stop order. 
     According to one connection variant for the first switch  30 , said first switch  30  is connected in series with the first protection circuit  10  and the first emitter circuit  21 , as shown in  FIG. 3 . In this case, the third signal Sig 3  is formed of pulses P when the control signal Sig 1  is present on the input E and when the first switch  30  is closed. The processing performed by the first processing circuit  50  on the third signal Sig 3  is unchanged. 
     It is often necessary to implement a double safety command in a safety installation. Such a double command contains a first safety command whose role is to control starting and a second safety command whose role is to validate or authorize, and the absence of which generally corresponds to an emergency stop command. In order to meet this need, the invention also relates to a safety control device  1 , shown in  FIG. 4 , having a safety control device  1  as described above, and furthermore having: 
         a validation input V having a third connection point E 3 , said validation input V being designed to receive a validation signal Sig 10  applied between the second connection point E 2  and said third connection point E 3 ,   a second protection circuit  110 ,   a second coupler  120  having:
           a second emitter circuit  121  connected in series with the second protection circuit  110 , the assembly formed by the second emitter circuit  121  and the second protection circuit  110  being connected between the third connection point E 3  and the second connection point E 2 , said second emitter circuit  121  being designed to emit a fourth signal Sig 20  when the validation signal Sig 10  is present on the validation input V, and   a second receiver circuit  122  designed to receive the fourth signal Sig 20  and to provide a fifth signal Sig 30 ,   
           a second switch  130  connected firstly in parallel across the second emitter circuit  121  in order to short-circuit said second emitter  121  when it is closed, and connected secondly to the pulse generator  40  so that said pulse generator  40  cyclically controls opening and closure of said second switch  130 ,   a second processing circuit  150  connected to the second receiver circuit  122  in order to receive the fifth signal Sig 30 , said second processing circuit  150  being designed to process the fifth signal Sig 30  and provide a second safety control order able to adopt at least two states:
           a second start safety control order Sig 40 _ON, and   a second stop safety control order Sig 40 _OFF, and   
           a logic circuit  160  having:
           a first binary input L 1  connected to the first processing circuit  50  in order to receive the first safety control order Sig 4 ,   a second binary input L 2  connected to the second processing circuit  150  in order to receive the second safety control order Sig 40 , and   a second binary output S 2  for providing a third safety control order Sig 50 .   
               

     The third safety control order Sig 50  may adopt at least two states:
         a third start safety control order Sig 50 _ON when the first safety control order Sig 4  provided by the safety control device  1  is a first start safety control order Sig 4 _ON  and when the second safety control order Sig 40  is a second start safety control order Sig 40 _ON, or else   a third stop safety control order Sig 50 _OFF when the first safety control order Sig 4  provided by the safety control device  1  is a first stop safety control order Sig 4 _OFF or when the second safety control order Sig 40  is a second stop safety control order Sig 40 _OFF.       

     The third start safety control order Sig 50 _ON is given when the first start safety control order Sig 4 _ON and the second safety control order Sig 40  are provided by the first and second processing circuits  50 ,  150 , respectively. The third stop safety control order Sig 50 _OFF is provided:
         when the first stop safety control order Sig 4 _OFF is provided by the first processing circuit  50 , or   when the second stop safety control order Sig 40 _OFF is provided by the second processing circuit  150 .       

     The second protection circuit  110  is similar to the first protection circuit  10 , 
     the second coupler  120  is similar to the first coupler  20 , 
     the second switch  130  is similar to the first switch  30 , and 
     the second processing circuit  150  is similar to the first processing circuit  50 . 
     The invention also relates to a contactor  100  shown in the form of a block diagram in  FIG. 5 a   . Said contactor  100  has:
         at least one electrical contact  310  connected to at least one upstream current line  320  and one downstream current line  330 , said electrical contact  310  being designed to allow the flow of an electric current between the upstream current line  320  and the downstream current line  330  to be permitted or blocked,   an actuator  2  designed to actuate the at least one electrical contact  310 ,   a safety control device  1  as described above,   a first connection terminal C 1  connected to the first connection point E 1  of said safety control device  1 , and   a second connection terminal C 2  connected to the second connection point E 2  of said safety control device  1 , the control signal Sig 1  being applied between the first  connection terminal C 1  and the second connection terminal C 2 . The safety control device  1  thus receives the control signal Sig 1  on its safety control input E.       

     The safety control device is connected, via the first binary output S 1 , to the actuator  2  in order to provide a first safety control order Sig 4  to said actuator  2  in order to control the actuation of the at least one electrical contact  310  when the control signal Sig 1  is received on its safety control input E. The safety control device  1  controls the actuator  2 :
         so as to execute closure of the at least one electrical contact  310  when the first safety control order Sig 4  is a first start safety control order Sig 4 _ON, or   so as to execute opening of the at least one electrical contact  310  when the first safety control order Sig 4  is a first stop safety control order Sig 4 _OFF.       

     According to one preferred embodiment, the contactor  100 , shown in the form of a block diagram in  FIG. 5 b   , furthermore has a third connection terminal C 3  connected to the third connection point E 3  of the safety control device  1 . The validation signal Sig 10  is applied between the second connection terminal C 2  and said third connection terminal C 3 . 
     Such a contactor  100  has two safety control inputs: a control signal Sig 1 , applied between the first and the second connection terminal, respectively C 1  and C 2 , received on the control input E of the safety control device  1 , corresponds to a start command. A validation signal Sig 10 , applied between the second connection terminal C 2  and the third connection terminal C 3 , received on the validation input V of the safety control device  1 , corresponds to validation or authorization of a command conveyed by the control signal Sig 1 . The absence of said validation signal Sig 10  corresponds to an emergency stop request. The validation signal Sig 10  is preferably a continuous voltage interval or stage with an amplitude of between 1 volt and 30 volts. 
     The safety control device  1  is connected to the actuator via a second binary output S 2  in order to provide a third safety control order Sig 50  to the actuator  2 , said third safety control order Sig 50  being able to adopt two states, as described above:
         a third start safety control order Sig 50 _ON, or   a third stop safety control order Sig 50 _OFF.        

     Said contactor  100  is designed such that:
         the safety control device  1  provides a third start safety control order Sig 50 _ON to the actuator  2  in order to control the actuator  2  so as to execute closure of at least one electrical contact  310  when the first safety control order Sig 4  is a first start safety control order Sig 4 _ON and when the second safety control order Sig 40  is a second start safety control order Sig 40 _ON, or   the safety control device  1  provides a third stop safety control order Sig 50 _OFF to the actuator  2  in order to control the actuator  2  so as to execute opening of at least one electrical contact  310  when the first safety control order Sig 4  is a first stop safety control order Sig 4 _OFF or when the second safety control order Sig 40  is a second stop safety control order Sig 40 _OFF.       

     The control signal Sig 1  is thus validated when the first processing circuit  50  has validated the compliance of the control signal Sig 1  and when the second processing circuit  150  has validated the compliance of the validation signal Sig 10 . If either the control signal Sig 1  or the validation signal Sig 10  does not comply, then the contactor  100  will be put into a safe state, corresponding to opening at least one electrical contact  310 , in order to protect personnel and prevent or limit damage to hardware. 
     Other operating modes of the contactor  100  are possible, in particular a mode in which the control signal Sig 1  is a pulsed signal of limited duration and the validation signal Sig 10  has a role of authorizing/validating said command to close the actuator  2 . The validation signal Sig 10  is applied first of all or at the same time as the control signal Sig 1 , following which the actuator  2  is actuated and at least one electrical contact  310  is closed. Said actuator  2  then remains actuated even though the control signal Sig 1  has disappeared. By contrast, as soon as the validation signal Sig 10  disappears, the actuator  2  is deactivated, and at least one electrical contact  310  is opened. Such operation may easily be implemented by the logic circuit  160 . 
     A contactor  100  may have a single electrical contact  310  connected between an upstream current line  320  and a downstream current line  330 , or else two electrical contacts  310  connected between two upstream current lines  320  and two downstream current lines  330 , the two electrical contacts  310  being isolated from one another, the upstream current lines  320  and the downstream current lines  330  also  being isolated from one another, as shown in  FIGS. 5 a  and 5 b   . A contactor  100  may also be designed to operate on a three-phase network and have three electrical contacts  310 , three upstream current lines  320  and three downstream current lines  330 . 
     The first processing circuit  50  executes the safety processing method  500  in order to process the third signal Sig 3  and generate the first safety control order Sig 4 . The second processing circuit  150  also similarly executes the safety processing method  500  in order to process the fifth signal Sig 30  and generate the second safety control order Sig 40 . Therefore, only the safety processing method  500  performed by the first processing circuit  50  is described below. 
     The safety processing method  500  comprises iteratively counting a number Q of pulses P forming the third signal Sig 3 , said pulses P being provided by the first receiver circuit  22  during a time interval of predefined duration T, as shown by  FIG. 6   a.    
     A first embodiment of the safety processing method  500  is shown in  FIG. 7 a   . In an initialization step  510 , a first stop safety control order Sig 4 _OFF is emitted in order to initialize the first safety control order Sig 4 . A first counter Q 1  and a second counter Q 2  are also initialized. Next, in a counting step  520 , the method counts Q the number of pulses P received over a predefined time interval T. At the end of counting step  520 , there is a step  530  of comparing the number Q of pulses counted with a predefined minimum number of pulses Qmin and a predefined maximum number of pulses Qmax. When the number Q of pulses counted is outside the interval between the minimum number of pulses Qmin and the maximum number of pulses Qmax, then the method continues with a step  540  of incrementing the second counter Q 2 . The second counter Q 2  is then compared with a predefined invalidation threshold Qinv in a step  550 . When the second counter Q 2  is equal to or greater than the invalidation threshold Qinv, the method considers that the number Q of pulses counted is not compliant, and the method returns to initialization step  510 , corresponding to a safe state, and in particular the first stop safety control order Sig 4 _OFF is generated. By contrast, when the number Q of pulses counted is within  the interval between the minimum number of pulses Qmin and the maximum number of pulses Qmax, then the method continues with a step  560  of incrementing the first counter Q 1 . Next, in a step  570 , the first counter Q 1  is compared with a predefined validation threshold Qval. When the first counter Q 1  is less than said validation threshold Qval, then the method returns to counting step  520  to execute an additional iteration. When the first counter Q 1  is greater than or equal to the validation threshold Qval, the method continues with a step  580  comprising generating the first start safety control order Sig 4 _ON and reinitializing the first and second counters Q 1  and Q 2 . The method then returns to counting step  520  to execute a new iteration. 
     A second embodiment of the safety processing method  500  is shown in  FIG. 7 b   . The initialization step  510 , counting step  520 , comparison step  530 , step of incrementing the second counter Q 2  in step  540 , step of comparison with the invalidation threshold in step  550  and step of incrementing the first counter Q 1  in step  560  are identical. By contrast, after said step  560  of incrementing the first counter Q 1 , a second counting step  561  is performed, followed by a step  562  of comparing the number Q of pulses counted with the minimum number of pulses Qmin and with the maximum number of pulses Qmax. When the number Q of pulses counted is less than the minimum number of pulses Qmin or greater than the maximum number of pulses Qmax, then the method continues with a step  563  of incrementing the second counter Q 2 , said second counter Q 2  then being compared with the invalidation threshold Qinv in a step  564 . When the second counter Q 2  is equal to or greater than the invalidation threshold Qinv, the method considers that the number Q of pulses counted is not compliant, and the method returns to initialization step  510 , corresponding to a safe state. When the second counter Q 2  is less than the invalidation threshold Qinv, the method returns to the second counting step  561 . When the number Q of pulses counted in step  562  is between the minimum number of pulses Qmin and the maximum number of pulses Qmax, then the method continues with a step  565  of incrementing the first counter Q 1  and a new monitoring loop for monitoring the number Q of pulses P received during a time interval T in the comparison step  566 , incrementation step  567  and comparison step  568 . In particular, in comparison step  568 , when the second counter Q 2  is less than the invalidation threshold Qinv, the method returns to the second counting step  561 . The  second embodiment of the safety processing method  500  thus described requires the number Q of pulses P counted in two successive time intervals T to be within the interval between the minimum number of pulses Qmin and the maximum number of pulses Qmax. Said second embodiment is therefore more exacting than the first embodiment of the method shown in  FIG. 7 a   , and it is better suited to implementation in industrial environments subject to significant electromagnetic interference. Other method variants for counting the number of pulses Q and decision criteria for generating the first safety control order may be constructed on the basis of the methods described above in order to adapt the method to particular environments. 
     Preferably, the minimum number of pulses Qmin is between 2 and 5, the maximum number of pulses Qmax is between 3 and 50, the validation threshold Qval is between 2 and 10, the invalidation threshold Qinv is between 2 and 5, and the duration of the time interval T is between 1 ms and 10 ms.  FIG. 6 b    illustrates, by way of a timing diagram, an example of counting a number Q of pulses P forming the third signal Sig 3  and the evolution of the first and second counters Q 1  and Q 2  over time. In this example, Qmin=2, Qmax=3, Qval=3, Qinv=3. At the initial time, the first and second counters Q 1  and Q 2  are initialized at zero. In a first time interval T, corresponding to a first iteration STEP 1 , two pulses P are counted, therefore Q=2, and the first counter Q 1  is incremented, Q 1 =1, since Q is between Qmin and Qmax. In the following period T corresponding to the iteration STEP 2 , three pulses P are counted, and therefore the first counter Q 1  is incremented once more, Q 1 =2. In the following period T corresponding to the iteration STEP 3 , a single pulse P is counted, therefore Q=1. The first counter Q 1  is not incremented since the number Q of pulses counted is outside the interval between the minimum number of pulses Qmin and the maximum number of pulses Qmax, as verified in comparison step  530 . By contrast, the second counter Q 2  is incremented. In the following period T corresponding to the iteration STEP 4 , four pulses P are counted, and the first counter Q 1  is not incremented whereas the second counter Q 2  is incremented, since the number Q of pulses counted is outside the interval between the minimum number of pulses Qmin and the maximum number of pulses Qmax. In the following period T corresponding to the iteration STEP 5 , two pulses are counted, and the first counter  Q 1  is incremented and adopts the value 2. In the following period T corresponding to the iteration STEP 6 , the first counter Q 1  is incremented since two pulses P are counted in the period T. The first counter Q 1  reaches the value 3 corresponding to the validation threshold Qval chosen in this example, and the command is therefore safe, a first start safety control order Sig 4 _ON is emitted, the first and second counters Q 1  and Q 2  are reinitialized at zero and the method returns to counting step  520  to execute a new iteration. 
       FIG. 6 c    illustrates a second example of counting a number Q of pulses P forming the third signal Sig 3  and the evolution of the first and second counters Q 1  and Q 2  over time. At the initial time, the first and second counters Q 1  and Q 2  are at zero. In a first time interval T, corresponding to a first iteration STEP 1 , two pulses P are counted, and therefore the first counter Q 1  is incremented. In the following period T corresponding to the iteration STEP 2 , a single pulse P is counted. The first counter Q 1  is not incremented but the second counter Q 2  is incremented, since the number Q of pulses counted is outside the interval between the minimum number of pulses Qmin and the maximum number of pulses Qmax. The same applies in the following period T corresponding to the iteration STEP 3  since a single pulse P is counted, and the second counter Q 2  is equal to 2. In the following period T corresponding to the iteration STEP 4 , two pulses P are counted, and the first counter Q 1  is incremented, and therefore Q 1 =2. In the following period T corresponding to the iteration STEP 5 , there is no pulse P, and the second counter Q 2  is incremented and reaches the value 3 equal to the invalidation threshold Qinv chosen in this example. The safety command is therefore invalidated, and the method returns to initialization step  510  corresponding to a safe state. The first stop safety control order Sig 4 _OFF is generated, the first and second counters Q 1  and Q 2  are reinitialized at zero and the method continues with counting step  520  to execute a new iteration. 
       FIG. 6 d    illustrates a third example in which the number of pulses Q counted in 3 iterations STEP 2 , STEP 3  and STEP 4  is equal to 0. The second counter Q 2  then reaches the value 3 at the end of the iteration STEP 4  and the first stop safety control order Sig 4 _OFF is generated. This example illustrates operation of a safe emergency stop command.  
     The first counter Q 1  thus counts the number of iterations STEP 1 , STEP 2 , STEP 3 , etc. in which the number Q of pulses P is within the interval of expected values, and the second counter Q 2  counts the number of iterations STEP 1 , STEP 2 , STEP 3 , etc. in which the number Q of pulses P is outside the interval of expected values. The response time of such a method makes it possible to validate a safety control order within a period greater than or equal to (Qval×T) after the onset of the occurrence of the third signal Sig 3 . For example, when Qval=3 and T=3 ms, the response time is greater than or equal to 9 ms, whether for a first start safety control order or a first stop safety control order. 
     The safety control device  1  and the safety processing method on which the invention is based contribute to monitoring and validating a start or stop command for a contactor so as firstly to avoid any unwanted command initialized for example by electromagnetic interference and secondly to reliably execute an emergency stop request. Galvanic isolation between inputs and outputs is additionally provided by the first and the second coupler. Lastly, implementing at least one first switch  30  in combination with a pulse generator  40  allows self-control of the circuits forming the safety control device  1  or of the safety control device  1 . Such safety control circuits and the safety processing method that they comprise may also be implemented in order to remotely control a circuit breaker or any other safety element. They are particularly suitable for installations requiring SIL 1  certification.