Abstract:
An electromagnetic door lock system, allowing emergency exiting of a building, including an armature mount allowing considerable outward movement of the door with respect to the door frame on which the electromagnet is mounted, whereby outward movement of the door initiates a time delay door release, and gives an increased reassurance that the door will open in an emergency, and allows for improved tamper resistance and reduced false alarms, as the distance the door opens out of the door frame in response to actuation of a panic bar from within is greater than that of conventional systems. A tamper resistant door position sensor includes redundant magnetic reed switches for sensing the position of the door and can include an additional reed switch for detecting when an external magnet is placed near the sensor in an attempt to tamper with the system.

Description:
RELATED APPLICATIONS 
     This application is a continuation in part of U.S. patent application Ser. No. 08/831,069 filed Apr. 1, 1997, now abandoned which is a continuation in part of U.S. patent application Ser. No. 08/603,649 filed Feb. 20, 1996 now U.S. Pat. No. 5,758,913. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of the present invention relates to electromagnetic emergency exit door lock systems. More particularly, the present invention relates to tamper-resistant time delay emergency exit electromagnetic door lock systems. 
     2. Description of the Related Art 
     Electromagnetic locks are commonly used in “delayed exit” systems. The purpose of a delayed exit system is to allow people to exit a building immediately in the event of an emergency, or after a 15 to 30 second delay in a non emergency situation while at the same time providing an acceptable measure of security against unauthorized entry or exit. Typically, a person who wishes to exit in an emergency activates the door by pressing down on a spring biased push bar sometimes called a “panic bar” mounted on the door. Alternately a lever or door knob may be turned. This initiates an audible alarm. If the person maintains the initiate signal by holding the panic bar down for the duration of a “nuisance delay” period which is typically 1 to 3 seconds, the system will then begin a delay known as an irrevocable release or egress delay. At the end of the egress time delay the door will open. The egress time is typically 15 or 30 seconds under most building codes. 
     The purpose of the nuisance delay is to cope with accidental striking of the door or push bar. When someone inadvertently presses against the push bar, an audible alarm warns the person away from the door. If the initiate signal is maintained for less than the duration of the nuisance delay period, the door will “reset” when the initiate signal stops and will therefore not release at the end of the 15 or 30 seconds. This maintains security and also saves building staff from the necessity of going to the door and re-locking it if it had released. The nuisance delay concept was intended to not only deal with accidental striking of the door, but with casual vandalism as might be expected from young persons who would push the door, hear the alarm, and then run away. On the other hand, if the initiate signal is maintained for longer than the nuisance delay period, release after 15 or 30 seconds becomes irrevocable. Such systems are in broad use, particularly in retail establishments where they greatly reduce theft loss while complying with building codes that require a minimum number of emergency exits. 
     One of the earliest electromechanical delayed exit systems is disclosed in U.S. Pat. No. 4,257,631 issued to Logan. Logan discloses a switch located within a push bar mounted on the door to sense when somebody attempts to exit the building. There are two significant drawbacks to this design. First, on existing doors a push bar is already present so it must be replaced at relatively high cost with a push bar equipped with a switch. Second, the wires to the switch within the push bar must be routed from the door to the frame which carries the electromagnetic lock. This requires either an electric hinge which is costly to purchase and install, or a “door cord” which is looped between the door and frame. Such door cords invite vandalism as the wiring is exposed. 
     U.S. Pat. No. 4,609,910 issued to Geringer discloses a delayed exit system in which two bolts which mount the armature plate to the door are allowed slack in their holes. When the door is pushed, the door can move slightly, thereby taking up this slack. The door remains securely held by the electromagnetic lock but the slight motion can be detected by a plunger type switch. The switch initiates the delay without the need to supply a switch equipped push bar or to route wires into the door. 
     One problem with this system is that it is prone to false initiation. To avoid having to precisely align the door and the door frame, the push bar-activated latch is often allowed a significant amount of slack within its securing recess. Wind or vandals rattling the door can take up the slack provided in the bolts of Geringer, thereby activating the switch and initiating the delay even though a person had not intended to exit. This constitutes a type of “false alarm”. 
     A further drawback of this design is that it is vulnerable to tampering. The plunger switch can be taped down such that the switch is incapable of recognizing when the door has been pushed away from its fully closed position in an effort to exit the building. This type of tampering may be performed by building guards for example who desire to increase security at the expense of egress safety, or who do not wish to have to check on the door when it is activated, either by someone who has exited or by a false initiation. This creates a hazardous and potentially fatal situation. 
     A similar design is disclosed in U.S. Pat. No. 4,652,028 issued to Logan et al. As in the Geringer design, slack is created by the use of bolts whose heads fit loosely within the armature plate. This design is prone to similar false initiations. Since the Logan et al. design uses a Hall effect sensor to detect the slight movement of the door provided by the slack in the bolts, the mechanism cannot be overridden by the use of tape. However, the system may still be tampered with by the application of an external magnet, which can disrupt the operation of the Hall effect sensor. 
     A further design is illustrated in U.S. Pat. No. 4,915,431 issued to Bailey. As in Geringer, Bailey employs a mechanical plunger switch, but the switch is positioned in the center of the armature which makes it relatively immune to tampering. As in Geringer, the slack that allows door movement is created by allowing mounting bolt heads to move slightly within the armature. This design is also vulnerable to false initiation by rattling of the door caused by wind or vandals. 
     A still further design is illustrated in U.S. Pat. No. 5,065,136 issued to Frolov et al. In this design, the electromagnet body is permitted to pivot slightly in response to pressure on the door. The rotational action of the top of the electromagnet creates a small gap between the electromagnet top and the door header which permits a spring biased switch to change state by its trigger moving into the gap. This design is also prone to tampering. Someone working within the facility can temporarily pivot the electromagnet body down and insert a piece of tape to prevent the switch from moving into the gap. This would prevent the switch from being triggered by movement of the door. 
     An armature mount assembly is disclosed in U.S. Pat. No. 5,184,856, issued Feb. 9, 1993 to Waltz. The disclosure teaches a mount that allows the armature to be pulled outward from the door a small distance to contact an electromagnet mounted to the door frame. However, there is no teaching of an armature mount that allows the door to be opened outwardly a considerable distance while the armature is held against the electromagnet. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general object of this invention to provide a delayed exit door control system that can be economically implemented for retrofit applications. 
     It is a further object of the invention to provide a delayed exit door control system that is resistant to false initiations by rattling caused by wind or vandals. 
     It is a further object of the invention to provide a delayed exit door control system that is resistant to tampering, either from casual vandals or by personnel within the facility. 
     It is also an object of the invention to overcome disadvantages of the prior art. 
     To achieve these and other objects, the present invention includes an electromagnet mounted to a door frame, an electromagnet armature mounted to a door facing the electromagnet, and an armature mount allowing considerable outward movement of the door with respect to the frame while the armature is held against the electromagnet. One way of doing this is by providing an armature mounting bolt (sometimes referred to as a “sex bolt” within the industry) that includes a novel internal spring biased plunger to which the armature is mounted. The spring biased plunger extends out the back of the armature mounting bolt, and is threaded so that the armature may be mounted directly to the back of the plunger. The spring allows the armature to be pulled away from the armature mounting bolt as for example by someone pushing on the door to initiate a delayed exit sequence, and return towards the bolt once the external force is removed. 
     The spring provides a bias force to assist in the return of the door to its fully closed position in the event that someone intentionally or unintentionally pushes the panic bar on the door, causing the door to open to its activation position momentarily and hence initiating the nuisance delay. Provided that the vandal or other person releases the door before the end of the nuisance delay period, the door will be assisted in returning to its fully closed position, and the door will remain locked. This provides a significant advantage over prior art systems that lack a mechanism for positively returning the door to its fully closed position, as for example systems that employ slack in mounting bolts. 
     The spring biased plunger of the present invention moves within the space of the armature mounting bolt, which is mounted through a hole in the door. The plunger therefore can move through the volume defined by the door, as much as the entire thickness of the door and even more if the armature bolt hollow interior is allowed to be longer than the thickness of the door. This provides a much greater travel distance than was possible with prior art systems that relied on slack movement of mounting bolts within the volume of the armatures themselves. Since conventional armatures are typically steel plates on the order of one-half inch (1.27 cm) thick, the prior art systems were limited to significantly less than that amount of movement (on the order of ⅛″ or 3 mm). With the present invention, the door movement distance required for activation can be set at a sufficient distance that mere rattling of the door within the panic bar latch cannot initiate the system. Rather, the panic bar latch must be released and the door pushed by an individual a sufficient distance to activate the system. For example, on a 1 ¾″ (44.45 mm) door, the most common commercial door thickness, the present invention permits door movement of up to 1.1″ (28 mm). This amount of movement is well beyond the distance a door could be moved by rattling but is less than the thickness of the door which precludes the insertion of a crowbar so it represents an ideal choice. 
     Note that although the preferred embodiment of the present invention employs a spring within the armature mounting bolt to bias the moving plunger within the armature bolt towards assisting reclosure of the door, the utility of this aspect of the invention is not dependent on the presence of the spring but rather on the ability of the plunger to move a substantial distance within the armature bolt. In an alternate embodiment, the spring could be deleted because commercial doors of the type that receive delayed exit locking systems almost invariably include a door closer which externally replicates the functions of the spring. 
     The present invention also includes a novel sensor system for detecting movement of the door to its activation position. The sensor system includes a permanent magnet mounted to the door, and a triad of magnetically activated reed switches mounted to the door frame. When the door is in its fully closed position, the permanent magnet activates (“energizes”) the first two reed switches, which are redundantly connected in case either switch fails. Movement of the door to the delay initiating position de-activates the two reed switches. This signals a system controller that someone is attempting to exit. The first two reed switches by themselves could be tampered with by placing a large permanent magnet into proximity with these switches, which would fool the reed switches into sensing a magnetic field even though the door had been moved to its activation position. To prevent this, a third tamper detection reed switch is added to the system. This tamper detection reed switch is not activated (not “energized”) by the permanent magnet mounted to the door, but will be activated by the presence of a second permanent magnet introduced for tampering purposes. Thus, the system automatically detects when someone brings a second permanent magnet into proximity with the sensor in an attempt to tamper with it. In the present invention, such tampering immediately initiates delayed exit which preserves the safety function of the door as well as sounding an alarm. 
     It should be understood that the part of the present invention which prevents tampering can be separated from the previously described part which permits extensive door movement prior to initiating the exit delay sequence. In certain applications, tampering is not an important concern and the removal of the anti-tampering parts from the invention results in a much lower cost and less physically obtrusive system to be mounted on the door. 
     In one aspect, the present invention includes a door equipped with an armature for locking engagement with an electromagnet mounted to a door frame; an armature mounting bolt mounted within a hole in the door; a spring mounted within the armature mounting bolt for providing a bias that draws the armature to the door and urges the door to its fully closed position; a detent within the armature mounting bolt for allowing a predetermined limited movement of the door in a direction against the spring bias; a sensor mounted to the door frame for sensing when the door has been urged by an external force away from its fully closed position to an activation position; a controller for determining when the door has been urged to the activation position for at least a nuisance delay period and providing an alarm signal in response thereto, and thereafter counting an egress time period, and de-energizing the electromagnet at the end of the egress time period; at which point the person who has initiated the process may exit the door. 
     In another aspect, the armature mounting bolt of the present invention includes: a hollow shaft having a flanged end or head abutting the outside surface of the door, and having an opposite open end; a plunger within the shaft that is capable of moving in a direction coaxial with the shaft, the plunger head being positioned adjacent the shaft flanged end; a spring within the shaft, the spring engaging a lip within the shaft and further engaging the plunger head such that the plunger is biased away from the open shaft end and toward the flanged first end, the lip defining a detent; and a fastener for fastening the armature to the plunger back end. The plunger back end is threaded for engaging the fastener. The shaft is positioned within a hole in the door, and the plunger therefore defines a member that engages the armature and is movable within the volume defined by the door thickness. A threaded cap engages corresponding threads on the back of the shaft, thus retaining the spring and plunger within the shaft. The cap has a hole in it, such that the plunger can move forward and backward while being retained within the shaft. 
     The above-described objects of the present invention and other features and benefits of the present invention will become clear to those skilled in the art when read in conjunction with the following detailed description of a preferred illustrative embodiment and viewed in conjunction with the attached drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of a delayed exit door equipped with a first preferred embodiment of the present invention. 
     FIG. 2 is an exploded view showing major components of the first preferred embodiment of the present invention shown in FIG.  1 . 
     FIG. 3 is an exploded view of the spring biased armature mounting bolt of the present invention. 
     FIG. 4 is a side elevation view of a door equipped with the system of the present invention when the door is in its fully closed position. 
     FIG. 5 is a top sectional view of the system of the present invention when the door is in its fully closed position. 
     FIG. 5A is a sectional view showing additional details of the armature mounting bolt of FIG.  5 . 
     FIG. 6 is a top sectional view of the system of the present invention when the door has been moved to its activation position. 
     FIG. 6A is a sectional view showing additional details of the armature mounting bolt of FIG.  6 . 
     FIG. 7 is a schematic representation of the reed switches within the sensor assembly  24  of FIG.  1 . 
     FIG. 8 is a perspective view of the sensor assembly  24  of FIG. 1 shown mounted on an adjustable frame. 
     FIG. 9 illustrates a delayed exit door equipped with a second preferred embodiment of the present invention. 
     FIG. 10 is an exploded view showing major components of the second preferred embodiment of the present invention shown in FIG.  9 . 
     FIG. 11 is a perspective view of an armature mount in an embodiment of the invention; 
     FIG. 12 is an exploded top view of an armature mount similar to that shown in FIG. 11, but could also be a side view in another embodiment; 
     FIG. 13 is a top view, partially in section, of an armature mount in an embodiment of the invention, but could also be a side view in another embodiment; 
     FIG. 14 is a sectional view of an armature mount in an embodiment of the invention; 
     FIG. 15 is an exploded perspective view of the armature mount of FIG. 14; 
     FIG. 16 is a sectional view of an armature mount in an embodiment of the invention, and could be a top view in one embodiment or a side view in another embodiment; 
     FIG. 17 is a sectional view of an armature mount in an embodiment of the invention, and could be a top view in one embodiment or a side view in another embodiment; 
     FIG. 18 is a top view of an armature mount in an embodiment of the invention; 
     FIG. 19 is a side view of the armature mount of FIG. 18, however, in another embodiment FIG. 18 can be a side view and FIG. 19 a top view; 
     FIG. 20 is a top view of an armature mount in an embodiment of the invention; and 
     FIG. 21 is a side view of the armature mount of FIG. 20, however in another embodiment FIG. 20 is a side view and FIG. 21 is a top view. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with a preferred embodiment of the present invention, FIG. 1 shows a typical emergency delayed exit door system. Door  10  is equipped with a panic bar  12  that operates a latch (not shown), the latch engaging a corresponding recess in door frame  14 . Note that the latch could also be operated by a door knob or door lever set. Mounted to door frame  14  is an electromagnet assembly  16  including electromagnet  18 . Door  10  is provided with an armature plate  20  for electromagnetically locking to electromagnet  18 . To exit, a person presses on panic bar  12  and pushes the door outward for at least the nuisance delay period. The door will then be available for egress following the expiration of the typically 15 or 30 second egress delay period. 
     FIG. 2 shows major components of the system in greater detail. Electromagnet assembly  16  includes electromagnet  18  typically containing “E” shaped electromagnet elements, and sensor assembly  24  containing a triad of magnetic reed switches. Electrical wires  25  serving sensor assembly  24  and electromagnet  18  feed up through the door frame header, and are not exposed. Assembly  16  includes a cover  26 . Electromagnet armature  28  having two alignment pins  30  is fastened via fastener  32  to armature mounting bolt  34 . The shaft of armature mounting bolt  34  is fitted through a corresponding hole in door  10  (FIG.  1 ), and is secured thereto by a post-installation cap  36  which forms part of armature mounting bolt  34 . Typically, two or more flexible washers  38  allow armature  28  to pivot slightly relative to door  10  such that armature  28  can abut electromagnet  18  in full contact with it for maximum locking hold force. Permanent magnet  40  is also mounted to door  10  such that when door  10  is in its fully closed position, permanent magnet  40  is brought into sufficient proximity with sensor assembly  24  (FIG. 4) so that sensor assembly  24  detects that the door is fully closed. Controller  80  is connected to sensor assembly  24  and electromagnet  18  by electrical wires  25 , and is also connected to alarm  82 . 
     FIG. 3 is an exploded view of armature mounting bolt  34 . A hollow shaft  42  threadably engages head  44  which abuts the outer surface  11  of door  10  (FIG. 5) when installed. Head  44  is typically made of hardened steel to repel hacksaw or similar attacks on the security of door  10  from outside. A plunger  46  within shaft  42  includes a plunger rod  47 , a head  48  at one end of rod  47  relatively positioned adjacent the armature mounting bolt head  44 , and threaded end  50  opposite plunger head  48 . Threaded end  50  engages fastener  32  (FIG. 2) to hold armature  28  to plunger  46 . Plunger rod  47  fits within spring  52 . A seal cap  54  having lip  56  threadably engages shaft  42  to retain spring  52  and plunger  46  within shaft  42 . This method of construction of armature bolt  34  permits changing the spring in applications where use is so heavy that failure of the spring could be a concern. Alternately seal cap  54  can be made a permanent part of shaft  42  which reduces the cost of armature bolt  34  but does not permit changing the spring. In either case, lip  56  acts as a detent to limit outward movement of plunger  46 . Hole  58  in seal cap  54  has a large enough diameter to allow plunger rod  47  to pass therethrough. One end of spring  52  engages plunger head  48 , while the other end of spring  52  engages lip  56 . 
     FIG. 5 shows the electromagnetic lock installed in a door and door frame, with the door in its fully closed position. Armature  28  abuts electromagnet  18 , and is electromagnetically locked to it. As shown in detail in FIG. 5A, spring  52  defines a resilient member that biases plunger  46  into shaft  42 . This draws armature  28  against door  10 , thus providing a bias means mounted within a volume defined by door  10  for providing a bias that urges the door toward its fully closed position. Permanent magnet  40  is sufficiently proximate to sensor assembly  24  to activate two of the three reed switches therein, thus signaling to system controller  80  (FIG. 2) that the door is in its fully closed position. 
     FIG. 6 shows the components of FIG. 5 when someone is attempting to exit the building. The person first pushes panic bar  12  (FIG. 1) or similar door activating device to release the latch. The person is then able to push the door away from its fully closed position to the activation position shown in FIG.  6 . To do so, the person must supply sufficient external force to overcome the bias provided by spring  52 . Spring  52  must therefore be chosen to provide a small enough force so that even a small or frail person can push the door to the activation position. At the same time, the spring should provide enough bias so that when the door is pushed momentarily and then released, as for example by a vandal, the door will tend to overcome the resistance of the latch mechanism and return the door to its fully closed position. Accordingly, spring  52  is chosen to provide a bias force in the range of approximately 1 to 50 pounds, and preferably approximately 15 pounds. The spring can be pre-biased to provide a more constant bias force over the travel distance of plunger  46 . Of course, the preferred force may be affected by development of building codes, as those codes develop with respect to systems such as that disclosed herein by themselves or in combination with other mechanisms attached to the door which may provide additional bias force. For example, the door may be equipped with a conventional door closer, and building codes may be passed that specify the maximum total force necessary to overcome the combination of mechanisms and open the door. In such a case, the spring must be chosen so as not to exceed such a maximum when combined with the door closer. 
     As shown in FIG. 6, the external force applied to the door by a person wishing to exit causes plunger  46  to be drawn outward from shaft  42 , thus compressing spring  52 . Since shaft  42  is positioned within the hole in door  10 , as the door is moved plunger  46  moves within the volume defined by door  10  in a direction corresponding to the thickness of the door. As used herein, the phrase “within” the door will be understood to mean “at least partially within” the door. Plunger  46  is free to move a distance at least half the thickness of the door. If maximum possible travel distance is desired, armature mounting bolt head  44  could be formed such that plunger  46  extends into head  44  when the system is in its unforced state. In theory, this would allow plunger  46  to move a distance as much as or even more than the width of door  10 . By allowing the plunger to move within the volume defined by the door thickness, the present invention achieves a much greater movement distance than could be achieved with prior art systems. These prior art systems provided only limited movement of the door, since slack was provided only within the armature plate. Since typical armature plates are on the order of one-half inch (1.27 cm), allowed lineal movement was small. In contrast, a typical security door is on the order of 1 ¾ inch (3.4 cm) thick. The present system therefore allows travel distances of at least 1, 2, or even 3 or more cm. There are several advantages to this greater travel distance. The first is that the activation distance can be set far enough such that rattling within the space of the usual slack in the latch will not cause a false initiation of the system. 
     A second advantage is that it provides greater tactile and visual feedback to the person attempting to make an emergency exit. This provides greater assurance to a possibly panic-stricken individual that the door is functioning properly and will release shortly. A third advantage is that with a greater travel distance, the sensors that sense when someone is attempting to exit need not be as precise in their ability to measure that the door has been moved a specified amount. This allows sensors to be more economical, more tamper-resistant, and/or easier to install and maintain. 
     For example, the present system includes a sensor assembly  24  comprising a triad of magnetic reed switches as shown in FIG. 7 to sense when the door has been moved in an attempt to exit the building. Two reed switches  62  and  64  designated “delay initiating reed switches” sense the presence of permanent magnet  40  in the fully closed door position. When door  10  is moved from the fully closed position, switches  62  and  64  change state by becoming deenergized. This defines the door “activation position” (FIG.  6 ). In the embodiment shown in FIG. 7, the delay initiating reed switches are of the normally open configuration. The presence of permanent magnet  40  causes the switch contacts to close. First and second delay initiating reed switches  62  and  64  are electrically connected in a redundant manner so that even if one fails to properly signal that permanent magnet  40  has been moved away, a delay initiating signal will be generated nevertheless. In the configuration shown, even if one delay initiating switch fails such that its contacts become stuck in the closed position, the other switch will open up such that the controller sees an open circuit across terminals  68  and  70 . If the open circuit condition (the “delay initiating signal”) persists for more than the nuisance delay, the system controller begins an egress delay countdown, at the end of which the controller issues a door unlock signal that causes electromagnet  18  to be de-energized. It will be noted that the magnetic field created by electromagnet  18  is sufficiently confined and directed such that the field does not affect the operation of the sensors within sensor assembly  24 . 
     Without an aspect of the present invention, it would be possible to tamper with the system by bringing a large permanent magnet  72  such as shown in FIG. 6 into proximity with sensor assembly  24 . While a casual vandal would be unlikely to know that magnetic sensors are positioned underneath cover  26  and how to defeat them, a security guard or someone else familiar with security systems is likely to have such knowledge. Magnet  72  introduced by such a person would cause the contacts of delay initiating reed switches  62  and  64  to close and stay closed, even after someone attempting to exit had pushed the door to its activation position. This would prevent the door from ever opening, which could result in a person being trapped. To prevent this situation, a third reed switch  66  is provided. This reed switch detects the presence of tampering. Tamper-detect reed switch  66  is of the normally closed configuration. Permanent magnet  40  mounted to door  10  is insufficient to cause the contacts of switch  66  to open. Thus, when the door is in its fully closed position, all the contacts of switches  62 ,  64 , and  66  are closed. However, if someone attempts to tamper with the system by introducing magnet  72 , the contacts of reed switch  66  will open, thus sending an initiate signal to the controller. The activation gauss levels of the switches, and the position of the switches, are chosen such that an external magnet  72  will cause the contacts of tamper-detection reed switch  66  to open before the contacts of delay initiating reed switches  62  and  64  close. Thus, an attempt to tamper with the system will cause alarm  82  to sound, and the egress delay to be initiated. The sensor assembly is therefore highly immune to tampering of the type that plagues systems currently in use. It will be observed that although the embodiment shown uses two normally open activation switches and one normally closed tamper detection switch all connected in series, one could substitute instead two normally closed activation switches and one normally open tamper detection switch all connected in parallel. The embodiment shown is preferred, because cutting of either of the two wires that exit sensor assembly  24  by someone attempting to defeat the system will create an open circuit or activation condition, thus immediately sounding the alarm. 
     In a preferred embodiment shown in FIG. 8, reed switches  62 ,  64 , and  66  are potted and mounted on a frame  74 , the frame being secured to base  76  of electromagnet assembly  16  by securing screws  78 . By loosening securing screws  78 , the system installer can easily slide sensor assembly  24  back and forth, then secure the assembly in its new position. This allows the installer to easily adjust the amount of movement permitted to the door prior to the delay initiating. This permits, for example, accommodation to differing amounts of free movement in the door latching hardware. 
     FIGS. 9 and 10 show an alternate embodiment of the present invention for applications where the threat of tampering is not significant and where low cost is important. By relaxing the anti-tampering requirement, many components can be eliminated from the preferred embodiment. 
     FIGS. 9 and 10 are variations on FIGS. 1 and 2, and are presented to make the reduction of components in the alternate embodiment clear. In the alternate embodiment, the costly and relatively complex sensor assembly  24  and permanent magnet  40  are respectively replaced by small and inexpensive cylindrical permanent magnet  84  and reed switch  86 . The permanent magnet  84  is fitted into a hole drilled in the top of the door as shown and the reed switch  86  is fitted into a hole drilled into the door header  88 . The combination of permanent magnet  84  and reed switch  86  are widely sold as pairs called “door switches” or “magnetic contacts” from companies such as Sentrol, C&amp;K and Ademco. The use of this separately mounted door position sensor eliminates as well the requirement for cover  26  whose function was to protect sensor assembly  24  from tampering. Without cover  26 , there is no need for an electromagnet assembly plate. Instead, the electromagnet  18  mounts directly onto door header  88 . The reduction in number of components in the alternate embodiment not only reduces system cost but presents a much less obtrusive appearance on the door which is important to certain customers. The function of the system is the same as in the preferred embodiment except that it is relatively easy for a building guard to defeat the egress initiating signal from the reed switch  86  by affixing a permanent magnet adjacent to it so that reed switch  86  will not change state as the door begins to open. 
     It will be observed that a distinct advantage of the present invention over certain prior art systems is that it allows existing doors equipped with panic bars to be retrofitted to allow for delayed exit, without the need to replace the existing push bar or other latching hardware. With prior art systems that employed a switch located within the push bar, replacing the existing push bar with one that included a switch was necessary. It will also be observed that various types of positive feedback can be provided to inform the person attempting to exit of the time remaining before release, such as a visual countdown indicator or a voice synthesizer as disclosed in U.S. Pat. No. 5,429,399 issued to Geringer et al. It will further be appreciated that the controller function can be provided by a variety of mechanisms including a mechanical controller, hardwired electronic logic, a microprocessor or microcontroller, or some intermediate type of electronic controller such as a sequential circuit programmable logic device (PLD). 
     With reference to FIGS. 11 and 12, in another embodiment the mounting of the armature  100  is effected by a bracket  102  which contains the armature but allows movement toward and away from the door  104 . As can be appreciated, the bracket is generally U-shaped and fits over an electromagnet  106  mounted to a door frame (not shown). As the door closes the armature and the electromagnet make contact and the bracket continues past the electromagnet so that the electromagnet is received at least partially within the bracket. As the door is opened, the armature, which is held against the electromagnet, prevents the bracket from moving past, catching on inwardly extending flanges  108 ,  110 ,  112  at the front of the bracket  102 . 
     The bracket  102  is attached to the door  104  by fasteners  114 . In one embodiment elongated attaching fasteners  116  are provided having a long shank  118  which extends through the bracket  102 , and cooperates with a slot  120  or hole (not shown) in the armature to stabilize the armature within the bracket. It will be understood that if the bracket and armature are sized relative to one another so that the armature cannot turn excessively within the bracket that no stabilization is needed. However, if the bracket is made quite deep, allowing considerable opening movement of the door while the electromagnet  106  holds the armature  100 , some provision for stabilizing the armature within the bracket will be required. In another example of such a stabilization arrangement, in FIG. 12 the armature is shown having a bar  122  extending into a hole  124  formed in the door or a sleeve  126  fitted in the door. 
     With reference to FIG. 13, in another embodiment the armature  100  rides on headed pins  128 ,  130  extending from the door  104 . Holes  132 ,  134  in the armature receive the headed pins, which are attached to the door by a threaded connection or by welding or another secure means. When the door closes the pins extend inwardly on either side of the electromagnet  106 , the distance between the pins being great enough to allow them to swing past the electromagnet along an arc, but close enough that the armature is not subject to large bending forces if the door is opened with considerable force, for example by kicking the door. In one embodiment a headed pin closest to the hinge side of the door can be slightly shorter than the other headed pin, so that as the door is opened along an arcing path, the two headed bolts  128 ,  130  contact the armature  100  at the same time. 
     With reference now to FIGS. 14 and 15, in another embodiment the mounting of the armature  100  is by means of two armature mounting bolts  136 ,  138  and a mounting plate  140 . The mounting plate is attached to a door  104  by fasteners  114 , and recesses  142  are provided in the door to accommodate the length of the armature mounting bolts. The mounting plate, armature mounting bolts and recesses cooperate to provide considerable movement of the armature relative to the door. This allows opening the door  104  by this same amount while the armature  100  is still held against the electromagnet ( 106  in FIG.  12 ). Optionally, a spring  144  and washers  146  can also be provided. The washers can be replaced by threaded locking nuts (not shown) which cooperate with the armature mounting bolts  136 ,  138  and armature to prevent loosening of the armature mounting bolts. The optional spring acts to pull the door and the armature together. 
     Turning now to FIG. 16, in another embodiment mounting of the armature  100  is accomplished by a slightly different structure wherein a flanged sleeve  148  supports a armature mounting bolt  150 , and thereby the armature. The flanged sleeve is attached to the door by fasteners  114  over a recess  142  in the door  104  accommodating the length of the armature mounting bolt within the door. A pin  152  cooperates with a hole  154  in the door to keep the armature from rotating. Alternatively two armature mounting bolts can be provided in a manner similar to that illustrated in FIG.  15 . With reference again to FIG. 16, an optional spring  144  can be provided, but is not necessary. 
     With reference to FIG. 17, in another embodiment a similar structure in appearance is provided on the inside of the door  104 , but instead of providing a recess in the door for the armature mounting bolt  150 , a covered enclosure  156  is provided on the outside of the door to accommodate movement of the armature mounting bolt with respect to the door. Plates  158 ,  160  are provided on each side of the door. A cover  162  is attached to the outer plate  160  by a tamper-resistant means such as pinning or welding to protect the armature mounting bolt. A spring  144  for biasing the armature  100  toward the door  104  can be provided if desired, but is not necessary. The armature is prevented from rotating around the armature mounting bolt by providing a pin arrangement such as that shown in FIG. 16, or by using two armature mounting bolts as previously described. 
     With reference now to FIGS. 18 and 19, in another embodiment mounting of the armature  100  to the door  104  is accomplished by another means allowing relative movement therebetween. A stationary bracket  164  is attached to the door by fasteners (not shown), welding, or another known secure means. The stationary bracket is attached to a moving bracket  166  by swing arms  168  and pins  170 . The moving bracket carries the armature. The pins are held in slots  172  formed in the stationary bracket. As the armature moves towards and away from the door, the pins move in the slots in a transverse direction toward and away from each other. The amount of relative movement is governed by the lengths of the swing arms and of the slots. In one embodiment an optional spring  174 , or multiple springs, can be provided to bias the pins apart, and thereby bias the armature toward the door. 
     A variation of this arrangement is shown in FIGS. 20 and 21. A stationary bracket  176  is attached to a door  104  in a secure fashion, for example by fasteners  114 . A moving bracket  178  carries the armature  100  and is attached to the stationary bracket by accordion-folding swing arms  180  connected by pins  182 . As will be appreciated, by lengthening the swing arms considerable travel of the armature with respect to the door is enabled. In a further variation, an optional armature mounting bolt  184  can be provided. While FIG. 20 is a top view and FIG. 21 a side view, these views can be reversed if the armature mounting bolt is included to stabilize the armature. Furthermore, a recess  186  is provided in the door to accommodate the armature mounting bolt, if one is used. An optional spring  144  can be provided to bias the armature toward the door. 
     As can be appreciated, numerous ways to attach the armature  100  to the door  104  can be used, the common feature being that the armature is free to move away from the door. It will be apparent that some of the mounting means described above allow movement greater than the thickness of the door if that is desired. Further, a spring may be used to bias the armature towards the door, but a spring is not required in most cases for functionality of the mounting. For example a coil spring could be disposed over the shank  118  in the embodiment of FIG. 11, or over the headed pins  128  and  130  in the embodiment of FIG. 13, to bias the armature toward the door, but such springs are not needed for the mounting arrangement to function otherwise as intended. 
     Commonly owned copending U.S. patent application Ser. No. 08/831,069, of which this application is a continuation in part, is hereby incorporated by reference. 
     Although the present invention has thus been described in detail with regard to the preferred embodiments and drawings thereof, it should be apparent to those skilled in the art that various adaptations and modifications of the present invention may be accomplished without departing from the spirit and the scope of the invention. For example, although a spring is preferred for simplicity, a gas cylinder or other bias member could be mounted within the armature mounting bolt to perform the biasing function. Or, as has been stated earlier, the spring may be eliminated and the door closer which is invariably present on commercial doors will solely perform the function of closing the door. Additionally, the armature mounting bolt described herein can also be employed in systems which rely on door position sensors of other types than the magnetic reed switch arrangement disclosed herein. Accordingly, it is to be understood that the detailed description and the accompanying drawings as set forth hereinabove are not intended to limit the breadth of the present invention, which should be inferred only from the following claims and their appropriately construed legal equivalents.