You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a lock with a bolt arranged in a lock housing, wherein the bolt can be shifted between an opened position and a closed position by a closing element, in the closing position the closing element can be blocked by a blocking element, and the blocking element is coupled with an armature of an electromagnet and can be actuated by the armature.  
         [0003]     2. Discussion of Related Art  
         [0004]     A lock is known from U.S. Pat. No. 1,721,730. The electromagnet is coupled to a lever mechanism by an armature. The lever mechanism supports the blocking element. A push bar lock can be released or blocked by the blocking element. A danger of unauthorized manipulation exists with such locks. It is thus possible to shift the armature of the electromagnet from the outside of the locked door by a strong permanent magnet. This is possible particularly with rare earth magnets, which build up a strong magnetic field. If the armature is brought out of engagement with the locking element in this way, it is then possible to open the door.  
       SUMMARY OF THE INVENTION  
       [0005]     It is one object of this invention to provide a lock of the above mentioned type but which offers increased protection against unauthorized manipulation.  
         [0006]     This object is attained if an armature and/or the electromagnet are covered, at least over portions, by at least one shielding element made of a low-retentive magnetic material arranged on or in the housing.  
         [0007]     The shielding element made of a low-retentive magnetic material, for example iron, bundles the magnetic field emanating from the magnet used for the manipulation. Thus, the armature and/or the electromagnet are protected in a simple manner. Because the shielding element is directly associated with the housing, no additional installation cost outlay for shielding is created when assembling the lock.  
         [0008]     In accordance with one embodiment of this invention, the housing has a connecting side on which lock operating elements, such as a keypad or grille, are arranged, and the shielding element is arranged in the area of or near the housing facing the connecting side. With its connecting side the lock can be installed on the inside of a door of a locker, for example. This connecting side is protected against the interfering action.  
         [0009]     A structurally simple lock design results if the housing is closed by a cover, and the cover supports the shielding element on its side facing the housing interior.  
         [0010]     In order to achieve effective shielding even against very strong magnets, the shielding element can be formed by a sheet metal plate with a wall thickness of at least 0.8 mm. The shielding element can also be directly installed on the electromagnet for achieving effective protection.  
         [0011]     An additional function is assigned to the armature, if the armature or the blocking element supports a switching element which actuates a contactless switch. The contactless switch can monitor the blocking state of the blocking element. Because of the use of a contactless switch, no or only slight switching forces for the performance of the switching process are created. Accordingly, the electromagnet need not have any additional switching power, so that it can be operated with a low output of energy. This has a positive effect, particularly if a battery-generated current supply is used for the lock.  
         [0012]     Thus, the armature or the blocking element has a permanent magnet as the switching element, by which a change of the switching state of the contactless switch, which is embodied as a reed contact, can be performed. To prevent unauthorized influencing of the reed contact, the reed contact can be arranged in the area of or near the shielding element.  
         [0013]     In one possible lock variation, a permanent magnet which maintains the armature in its opening state is assigned to the armature. A magnetic force which acts counter to the force of the permanent magnet can be applied to the armature by the electromagnet, and a spring is assigned to the armature which, in the open state, applies a spring force acting on the armature in the closing direction. With this lock layout it is possible to employ an electromagnet acting in one direction, which makes possible a low energy requirement. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     This invention is explained in greater detail in view of an exemplary embodiment represented in the drawings, wherein:  
         [0015]      FIG. 1  shows a lock in a lateral view, along a section line shown in  FIG. 2 ;  
         [0016]      FIG. 2  shows the lock in accordance with  FIG. 1 , in a top view;  
         [0017]     FIGS.  3  to  6  show flow diagrams representing the procedure for operating the lock. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]     A lock with a housing  10  is shown in  FIG. 1 . The housing  10  has a bottom  11 , from which lateral walls  11  arise all around. At the top as shown in  FIG. 1 , the housing  10  forms a connecting side. There, the housing  10  is closed off by a screwed on cover  20 . As revealed in  FIG. 2 , the housing  10  has two fastening flanges  13  with fastening receivers  13 . 1  on the sides of the cover  20 . With these the lock can be screwed on the inside of a door, flap or the like, for example.  
         [0019]     The cover  20  has a ring-shaped rose holder  24 , which surrounds a keypad field. A keypad  26 , for example a silicon switching plate, is fastened to the rear of the cover  20  and protrudes with its keys through openings in the cover  20 . Also, at least one LED  26 . 2 , which indicates the operational states of the lock, is assigned to the keypad  26 . Furthermore, a line jack  26 . 1  is integrated into the keypad  26 . With this, the presently battery-powered lock can have electrical current if the battery fails. The line jack  26 . 1  is advantageously integrated into the silicon switching plate as a predetermined breaking point. If needed, a plug can be pushed through the predetermined breaking point and electrical current can be supplied externally. Following the removal of the plug, the hole seals itself because of the inherent elasticity of the created hole. A removable compartment cover  16  is provided on a side of the lock facing away from the connecting side and covers a battery compartment  14 , in which the batteries that provide the lock with electrical current are maintained. A rose  25  is pushed onto the rose holder  24  shown in  FIG. 1 . The rose holder  24  protrudes into an opening of the connected door. The rose  25  is inserted from the front of the door and covers an edge of the opening with a radially protruding flange.  
         [0020]     A support section  23 , which extends annularly and surrounds a bearing receiver  21  of the cover  20 , is formed on the cover  20 . A rose  22  can be pushed on a handle  30 . Then the rose  22  is arranged above the support section  23 . The rose  22  is used for covering an edge of a circle-shaped opening in the door, through which the handle  30  has passed. The rose  22  is continuously adjustable with respect to the handle  30  in an assigned bore receptacle of a door, and the rose  25  on the rose holder  24 , for matching different door thicknesses.  
         [0021]     The handle  30  is connected with a locking element  40 . The handle  30  is inserted with a plug-in shoulder  32  into a plug-in receptacle  45  of the locking element  40 . The locking element  40  has a screw receptacle  42  aligned with a threaded receiver  31  of the handle  30 . A screw can be passed through the screw receptacle  42  and screwed into the threaded receiver  31 .  
         [0022]     The locking element  40  is rotatably maintained with a first bearing shoulder  43  on a bearing  15  of the housing  10 , and with a second bearing shoulder  44  in the bearing receiver  21  of the cover  20 . The locking element  40  can be rotated around the bearing axis, which extends vertically in  FIG. 1 .  
         [0023]     The locking element  40  engages with a bolt  46  that can be moved between an opened and a closed position in a slide guide of the housing  10  by the locking element  40 .  FIG. 1  shows the opened position with the bolt  46  retracted. In  FIG. 2  the bolt  46  is extended from the housing  10 .  
         [0024]     As  FIG. 1  shows, the locking element  40  has an arresting receptacle  41 , which is arranged in the form of a radially accessible recess in the area of or near the bearing shoulder  43 . A blocking element, which is a part of an armature  51  of an electromagnet  50 , is assigned to the arresting receptacle  41 . The electromagnet  50  is maintained in the housing  10  and can be activated by the battery. The electromagnet  50  pushes the armature  51  out and, from the opened position shown in  FIG. 1 , reaches the blocking position, in which the blocking element  52  engages the arresting receptacle  41 . The electromagnet  50  has a permanent magnet  53 . In the currentless state of the electromagnet  50 , it maintains the armature  51  in the initial position illustrated in  FIG. 1 . When the electromagnet  50  is activated, the armature  51  is pushed away from the permanent magnet  53 . For saving electrical current, the electromagnet  50  is only briefly provided with electrical current. This is already sufficient for lifting it slightly off the permanent magnet  53 . Then a spring  55 , which prestresses the armature  51  in the closing position, pushes the armature  51  into the arresting receptacle  41 .  
         [0025]     The electromagnet  50  is surrounded by a hoop-shaped shielding element  54  made of a low-retentive magnetic material that provides shielding against magnetic radiation acting from the outside.  
         [0026]      FIG. 1  further discloses that the armature  51  supports a permanent magnet  56  which, in the form of a ring, is pushed onto the armature  51 , which is round in cross section. A reed contact as a contactless switch  57 , which is fastened on a plate  60 , is assigned to the permanent magnet  56 . Together with the armature  51 , the permanent magnet  56  is moved between two positions. It then also moves the reed contact into different switching positions.  
         [0027]     A further shielding element  58  is provided on the inside of the cover  20  and is made in the form of a 1 mm thick plate of a low-retentive magnetic material. The shielding element  58  shields the armature  51  in the transition area to the electromagnet  50  and prevents the effects of magnetic radiation from the direction of the connecting side. The plate  60  receives the electric switching devices of the lock and receives the reed contact, a micro-controller and the switches which can be actuated by the keys of the keypad  26 .  
         [0028]     An operation and functioning of the lock is explained in greater detail in view of FIGS.  3  to  6 .  
         [0029]     The procedure for closing the lock is explained in greater detail in  FIG. 3 . First, the handle  30  and the locking element  40  is rotated. During this, the arresting receptacle  41  is assigned to the blocking element  52 . Subsequently it is possible to input a code, limited to a specified number, for example with four digits, which is freely selected by the user and can be acknowledged by a locking key of the keypad  26 .  
         [0030]     The control circuit arranged on the plate  60  is triggered via the locking key, so that it activates the electromagnet  50  by a short electrical current pulse that pushes the armature  51  away from the permanent magnet  53 . Then the spring  55  pushes the armature  51 , together with its blocking element  52 , into the arresting receptacle  41 . As shown in  FIG. 3 , two control stages, small diamond-shaped boxes, are programmed and check whether the locking key is actuated within a pre-specified time window, and whether the code is admissible. In addition, the reed switch checks whether the armature  51  is switched into the closed position. Only then is the code dependably stored.  FIG. 4  describes the process for opening the lock. Accordingly, the code pre-specified in accordance with  FIG. 3  is entered and an opening key is then pushed. If the opening key is actuated within a pre-specified time window and the correct code has been entered, the memory of the control circuit is released for the renewed entry of a code after an acknowledgement signal is issued. The opening key simultaneously activates an electrical circuit in the control circuit, which activates the electromagnet  50  so that the armature  51  is moved out of the arresting receptacle  41 . In the process, the armature  51  is moved counter to the force of the spring  55  against the permanent magnet  53  and is then held by it. This position is represented in  FIG. 1 . If the armature  51  does not move back correctly, for example, because the lock is jammed, the user can again operate the opening key. During this an extended electrical current pulse is applied to the electromagnet  50 . The reed contact or contactless switch  57  signals that the mechanism is unlocked. Then the lock can be unlocked by the handle  30 . Thus, the handle is rotated so that the bolt  46  enters the housing  10 .  
         [0031]      FIG. 5  shows the procedure for opening the lock by a master code. As the representation shows, the sequence is selected analogous to the routine shown in  FIG. 4 . A flow diagram is shown in  FIG. 6 , which shows the procedure for re-programming the master code. Changing the master code is possible in the opened, as well as in the locked state of the lock.  
         [0032]     So that the lock can also be opened if the master code is lost, the control circuit can be set as a freely definable handling code.  
         [0033]     For making optimum use of the life of the batteries, the lock has an energy circuit which is activated if the lock is not operated within a pre-specified time window. Switching from the economy mode into the operating mode occurs as soon as a key of the keypad  26  is actuated.

Summary:
A lock with a bolt, arranged in a lock housing. The bolt may be adjusted between an open and a closed position, by a closing element, and the closing element may be locked in a closed position, by a locking element. The locking element is coupled to an armature of an electromagnet and may be operated by the same. For better protection against manipulation for such a lock, the armature and/or the electromagnet are at least partly covered by at least one screening element, arranged in, or on the housing, which can be made from a soft magnetic material.