GB2490663A

GB2490663A - A door mount having a sensor determining the force exerted on the mount

Info

Publication number: GB2490663A
Application number: GB201107485A
Authority: GB
Inventors: Phil Barsby; Roger Tipple
Original assignee: Intastop Ltd
Current assignee: Intastop Ltd
Priority date: 2011-05-05
Filing date: 2011-05-05
Publication date: 2012-11-14
Also published as: GB201107485D0

Abstract

Apparatus 101 for mounting a door 1201 within a frame 1101. The apparatus comprises a track 106 to be mounted on a doorjamb 1101, a sliding element 107 mounted on the track so that it is able to slide on the track, and a door mounting plate 103 attached to the sliding element. The door mounting plate, e,g, hinge, arranged to swing about the track 106 for the purposes of allowing a door mounted by the apparatus to swing open and closed. A support element 507 configured to resist the sliding element sliding along the track, and a sensor device, e.g. strain gauge, 511B configured to provide a changing electrical characteristic in dependence upon force applied to the support element 507 by the sliding element 107 which allows detection of a suicide attempt by a person hanging themselves on the door. Also provided is a method of installing the track on the door jamb by inserting a first screw and measuring a first force to lift the sliding element 107 upwards inserting a second screw and adjusting the second screw based on a measured second force.

Description

Apparatus For Mounting A Door Within A Frame

CROSS REFERENCE TO RELATED APPLICATIONS

This application represents the first application for a patent directed towards the invention and the subject matter

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatus for mounting a door within a frame and a method of mounting a door hinge apparatus within a frame.

2. Description of the Related Art

For a number of establishments, Ihe possibility of a pefsdnátiépfi --to commit suicide while on the premises is a major concern. In particular, it is of concern that such people would attempt to hang themselves from a door of a room, and thereby strangle, or asphyxiate, themselves until dead. Examples of establishments where this is a potential problem are mental institutions, police cells, prison cells, etc. One previously proposed solution to this problem involves locating an elongated pressure switch along the top of a door. The pressure switch is * connected to an alarm system, and so if a person attempts to position a hook * * 1:> over the top of the door for such use, the weight applied to the switch, closes the switch and sets off the alarm system. However, a problem with this arrangement is that it only operates properly when weight is applied to the top

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of the door.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided apparatus for mounting a door within a frame as claimed in claim 1.

According to a second aspect of the present invention, there is provided a method a method of mounting a door hinge apparatus within a frame as claimed in claim 21.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a perspective view of door hinge apparatus 101 for mounting a door within a doorirame; F1dré 2 shows an èitéd ieW of the end sectibrfs of the apparatus 101; Figure 3 shows the apparatus of Figure 1 in plan view; Figure 4 shows separately the door hinge plate 103, the C-shaped channel 116, the sliding element 107 and the track 106 of the apparatus 101; Figure 5 shows a perspective view of the lower section 202 of the track 106; Figure 6 shows a cross-sectional view of the lower section 202 of the S.....

* track 106; S.**S * S Figure 7 shows a diagram illustrating the electrical components present in the apparatus 101; Figuie B shows a flow chart of the process performed by the * .SSS* S * microcontroller 706 during use; Figure 9 shows a flow chart providing further detail of the process step 803 of Figure 8; Figure 10 shows a flow chart providing further detail of the re-calibration s process identified as step 805 in Figure 8; Figure 11 shows the apparatus 101 attached to a doorjamb 1101; Figure 12 shows the apparatus 101 attached to the doorjamb 1101 with a door 1201 attached to the door mounting plate 103 of the apparatus; and Figure 13 shows a cross-sectional view of the lower end of the apparatus 101 mounted to the doorjamb 1101 and with the door 1201 attached to the door mounting plate 103.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Figures 1, 2 and 3 A door hinge apparatus 101 for mounting a door within a doorframe is is shown in the perspective view of Figure 1 and the plan view of Figure 3, while an enlarged view of the end sections of the apparatus is shown in Figure 2.

The apparatus, in accordance with the present invention is configured to provide a changing electrical characteristic in dependence upon force applied to it. Thus, during use, the apparatus is able to provide an electrical indication ** * * that a person is attempting to asphyxiate themselves by hanging themselves 1:':' from a door mounted on the apparatus.

The apparatus 101 comprises a first part 102 to which a door mounting *:*::* plate 103 is attached by a hinge mechanism 104. The door mounting plate 103 * ****** * * defines a plurality (in this example sixteen) countersunk holes 105 for receiving screws to fix a door to the door mounting plate.

The first pad 102 comprises a track 106 and a sliding element 107 mounted on the track so that it is slidable along the track. As will be described further below, the track 106 is provided with countersunk holes for fixing it to a jamb of a doorframe, and the sliding element 107 is provided with holes 108 arranged to allow a screw to pass through for fixing the track to the doorjamb.

The track 106 has a front face 109 over which the sliding element extends and an opposite rear face 110 that is affixed against a doorjamb in use. A groove 111 extends along the length of the track along the rear face 110, and a bundle of insulated wires 112 extend along the groove. Adhesive --tape 113 is affixed to the rear face 110 to maintain the wires 112 within the groove. The wires 112 extend from electronic circuitry within the apparatus 101 along the groove 111 to their free ends, which extend from the upper end 114 of the apparatus 101.

As will be further described below, the front face 109 of the track defines a series of ridges 115 (in the present embodiment four ridges) extending along the length of the track to provide protection for further wires that extend along the front face 109.

As may best be seen in Figure 3, the door mounting plate 103 is attached to the sliding element 107 by the hinge mechanism 104.

Consequently, during use, when a door is attached to the door mounting plate 103 the door is able to be moved up and down (at least by a limited amount) * ** * * 0 * ** * ** 00 * * by sliding the sliding element 107 along the track 106.

In the present embodiment, the track has a substantially T-shaped cross-section, the front face 109 being wider than the rear face 110 by virtue of a lip 121 extending along each of its two side faces 122. The sliding element 107 defines a substantially T-shaped groove, extending along its length, configured receive the track 106 in a sliding manner. It will be understood that the 1-shaped cross-section of the track and the groove of the sliding element enable these two components to interlock such that the movement of the sliding element with respect to the track is substantially restricted to movement along the track.

In an alternative embodiment, the track 106 has a differently shaped cross-section to that of the present embodiment. In this alternave, the side --faces 122 of the track 106 are provided with a V-shaped groove extending along their length and inner walls of the sliding element 107 are provided with correspondingly V-shaped ridges that locate within the V-shaped grooves.

In the present embodiment, the hinge mechanism comprises a geared hinge arrangement, as is known in the art. Thus, the hinge mechanism includes a C-shaped channel 116 having a pair of cylindrically shaped edges 117 and 118. The door mounting plate 103 and the sliding element are each provided with curved edges 119 and 120 defining teeth that interlock with those of the other curved edge.

In the present embodiment the sliding element itself defines the teeth on the curved edge 119, which form part of the hinge mechanism. However, in * S. * S I * I.

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an alternative embodiment the sliding element is formed separately from, but rigidly attached to, a hinge plate defining the teeth.

In the present embodiment, the hinge mechanism allows for a mounted door to open in one direction. But, in an alternative embodiment, the hinge mechanism has features of the double swing hinge mechanism as disclosed in the Applicant's earlier patent application published as GB 2 451 276 A. Thus, the hinge of this alternative embodiment allows a door to be mounted in a doorway such that it is able to swing both ways through the doorway.

In a further alternative embodiment, the door mounting plate 103 and the sliding element 107 have edges formed substantially in the manner of conventional door hinge plates and are connected together by a hinge pin.

--In yet further alternative! odi en he door mounting plate 103 is mounted to the sliding element by a hinge mechanism of the type known in the art for providing a double swing door. "5

Figure 4 The door hinge plate 103, the C-shaped channel 116, the sliding element 107 and the track 106 are shown separated from each other in Figure 4. A central portion of these components has been omitted from Figure 4 for the purposes of clarity.

In the present embodiment, each of the door hinge plate 103, the C-i.:'> shaped channel 116 and the sliding element 107 are formed of single pieces of extruded aluminium. * ** * . * * ** S.* * *

The track 106 is also formed of extruded aluminium, but, in the present embodiment, it is formed of two pieces 201 and 202, in order to simply its manufacture. In the present embodiment the two pieces 201 and 202 are arranged end to end. The upper piece 201 (having a length of approximately 1700mm) is substantially longer than the lower piece 202 (having a length of approximately 300mm). (In an alternative embodiment, the track is formed of a single length of material.) Both pieces 201 and 202 of the track 106 are drilled to provide countersunk holes 203 for receiving screws to allow the track to be affixed to a doorjamb.

io During use, the apparatus 101 supports a door, and the weight of the door applies a moment of force to the apparatus. This moment of force tends to pull the upper end of the apparatus 101 away from the doorjamb, while other parts of the apparatus 101 are not exposed to such a large moment. In addition7 it has been found that for the optimal functioning of the apparatus the is torsion forces applied to the track should be kept to a minimum. Consequently, a large proportion of the screw holes 203 are located within a short distance of the upper end of the track, while other parts of the track are provided with relatively few screw holes. Thus, a relatively large number of screws may be used to act against the large moment applied to the upper end of the apparatus, while relatively few screws are used in lower parts of the track to maintain it in position. Generally, in preferred embodiments, at least a half of the screw holes 203 are located within 20cm of the upper end of the track. * 0. * 0 0 * 0.

*0 000 0 0 Figures 5 and 6 The lower section 202 of the track 106 is shown in the perspective view of Figure 5 and the cross-sectional view of Figure 6.

The lower section 202 is provided with a milled trough 501 towards its upper end 502. An electronic circuit board 503 is located within the trough 501 and supported in place by a potting compound. The wires 112 are connected to appropriate terminals on the electronic circuit board 503 and routed through a channel 504 in the front face 109 of the lower section 202 and through a hole 505 to the groove 111 extending up the rear face 110.

A portion of the lower section 202 adjacent to its lower end 506 is provided with a recessed surface 601 on which is mounted a support element 5. Thc!yppp rnpnc7i do Loerpiec! 202 of track 106 by a pair of screws 508 located towards the upper end of the support element.

As is shown in Figure 6, the supporting element 507 has an L-shaped cross-section and the lower end of the support element defines a protrusion 509 that extends proud of the front face 109 of the lower section 202 of the track 1,06.

During use, the support element 507 supports the sliding element 107, resisting downward movement of the sliding element. Specifically, as the weight of a door tends to slide the sliding element 107 downward along the track 106, the protrusion 509 of the support element 507 resists downward 0*.*.t.

* * movement, i.e. it supports the weight of the door.

In the present embodiment, the support element is formed of stainless steel. * S. * S S * 55

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*. p555 S 5 As seen in Figure 5, the support element 507 is machined to provide a relatively narrow necked portion 510 between the fixing screws 508 and the protrusion 509 Thus, in use, the necked portion 510 is subjected to increased stress due to its small cross section, and the resulting strain of the necked portion is increased.

A first strain gauge 51 1A is cemented to one side of the necked portion 510 while a second strain gauge 51 lB is cemented to its other side. Wires 512 connected to the first strain gauge 511A extend along the front face 109 between a first pair of the ridges 115 to the electronic circuit board 503.

Similarly, wires 513 from the second strain gauge SuB extend along the front face 109 between a second pair of the ridges 115 to the electronic circuit board50l -The electronic circuitry present on the circuit board 503 is configured to provide an electrical indication in dependence of the magnitude of strain is present in the necked portion 508.

During use, the support element 507 will generally be subjected to a force resulting from the weight of the door being supported. Consequently, the necked portion 510 will become strained and the strain gauges 51 IA and 511 B will exhibit an electrical resistance corresponding to that force. If the force is increased, for example by a person adding their weight to the door in an attempt to asphyxiate themselves, then the necked portion 510 will be further strained and the strain gauges will exhibit an increased electrical resistance. This change in electrical resistance is measured and monitored by * S. * II * * 5) 55*t5* * * the electronic circuitry of circuit board 503, as will be further described below.

In addition, it has been considered that a person intending to commit suicide by hanging themselves from a door may try to wedge the door up to prevent the apparatus from sensing the increased weight. However, the reduction in force caused by such a wedging action reduces the strain of the necked portion 510 and the electrical resistance exhibited by the strain gauges reduces accordingly. This change in electrical resistance of the strain gauges is also detected and monitored by the electronic circuitry of circuit board 503.

Figure 7 A diagram illustrating the electrical components present in the is shown Agure 7. As mentioned above, the strain gauges 51 IA and 511 B are mounted on the support element 507, but, in the present embodiment, the other electrical components are mounted on the circuit board is 503.

In the present embodiment, one terminal of the first strain gauge 51 IA is connected to a first voltage supply rail 701 while the second terminal of the first strain gauge is connected to a first terminal of a first resistor 702. The second terminal of the first resistor is connected to a second voltage supply rail 703.

Similarly, one terminal of the second strain gauge 5IIB is connected to the second voltage supply rail 703 while its second terminal is connected to a first terminal of a second resistor 704. The second terminal of the second * S. * p. * d

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S. S) C-* S resistor is connected to the first voltage supply rail 701.

The junction of the first strain gauge 51 1A and the first resistor 702 is connected to a first input of a high gain differential amplifier 705, while the junction of the second strain gauge 511 B and the second resistor 704 is s connected to a second input of the amplifier.

Thus, the strain gauges 51 IA and 511 B, along with the two resistors 702 and 704 are connected together in a strain gauge bridge circuit. In the present embodiment, the resistors 702 and 704 have resistance values that are approximately equal to the unstressed strain gauges. As the stress applied to the support element 507 increases (for example by someone applying their weight to that of a door being supported by the apparatus 101) ---the re&stance of the strafti gauges increases. Alternatively, as the stress applied to the support element 507 decreases (for example by someone wedging upwards the door being supported) the resistance of the strain gauges decreases. Consequently, as the resistance of the strain gauges varies, the imbalance of the bridge circuit varies, and the difference in voltages applied to the two inputs of the amplifier depends upon the stress applied to the support element 507. As will be understood, the output signal from the amplifier 705 also depends upon the stress applied to the support element S..... * S

In an alternative embodiment, the second strain gauge 51IB is replaced by a third resistor. This arrangement avoids the expense of the second strain gauge, but the resulting bridge circuit provides smaller signals to the amplifier * .* * $ S * ** * *.* Sd S j 705. In a further alternative embodiment, the resistors 702 and 704 are replaced by respective strain gauges to which no stress is applied. As is known in the art, this arrangement automatically compensates for variations in resistance of the active strain gauges caused by temperature variations.

Although this arrangement may be more costly than the circuit shown in Figure 7, it is particularly useful in situations where the strain gauges may be subjected to relatively large variations in temperature.

In the present embodiment the circuitry on the circuit board 503 comprises a microcontroller 706 comprising an analogue to digital converter that receives the output signal from the amplifier 705. Depending upon the amplitude and duration of voltage signals received from the amplifier, the rnicrocontroflerprovkiesan output!i!h!r. indicating an alarm condition or a non-alarm condition.

More specifically, the microcontroller 706 monitors the output signal is from the amplifier. Under normal operating conditions, the output signal will correspond to strain in the support element 507 due to the weight of the door being supported. Also, relatively moderate forces tending to pull the door downward or upward may be exerted on the door in normal use, and correspondingly small variations in the output signal from the amplifier 705 will *.... 20 be produced. When such "normal" output signals are detected by the microcontroller 706, it provides an output indicative of a non-alarm condition.

However, for amplifier output signal values above a predetermined threshold value (indicative of a downward force applied to the door above a * ** 1 * * ** * * predetermined value (for example 150 newtons), the microcontroller determines that a potential problem exists (corresponding to a possible suicide attempt). If it receives such a high signal for more than a predetermined period of time (of typically more than three seconds), it provides an output indicative S of an alarm condition.

In addition, in instances where the door is wedged upwards by more than a predetermined force (for example 100 newtons), the output signal from the amplifier falls below a second threshold value. If such a low output signal is detected for more than a predetermined period of time, the microcontroller io again provides an output indicative of an alarm condition.

In the present embodiment, the output signal provided by the -microcontrofler is supplied toa relay 707 having two output terminals, labelled 0/P 1 and 0/P 2 in Figure 7. In the present embodiment, the relay is configured (i) to provide an open circuit between its output terminals when it receives a signal from the microcontroller indicating a non-alarm condition and (ii) to provide a closed circuit between its output terminals when it receives a signal indicating an alarm condition.

As will be understood, the characteristics of the electrical output provided by the apparatus may be adjusted to suit the system into which the apparatus is incorporated. Thus, in an alternative embodiment the relay is * * configured to provide a closed circuit on receipt of a signal indicating a non-alarm condition and an open circuit on receipt of a signal indicating an alarm condition. * 0 * . * * ** *

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Other alternative embodiments will also now be apparent to a person skilled in the ad. For example, the microcontroller may be configured to provide a coded signal for transmission over a bus, or supplied to a radio transmitter for transmission to a separate pad of the system, etc. s In a further alternative embodiment, the circuitry present in the apparatus 101 merely comprises the strain gauges SI1A and SUB, resistors 702 and 704 and the amplifier 705. The processing means (such as the microcontroller 706) required to analyse the output from the amplifier is located in a separate unit that forms part of a monitoring system.

It is envisaged that the apparatus 101 will be used within a system that that monitors the relays (such as relay 707) of many apparatuses (like apparatus 101). As such, an alarm will be Ls!d by the system ata locaflon remote from the apparatus 101 where the situation may be brought to the attention of relevant people who are then able to go to the source of the alarm.

However, alternatively, the relay may form part of a simple audio and/or light system such that the operation of the relay causes the emission of an audio and/or visible alarm.

In the above-described embodiments, strain gauges are used to detect strain produced in a support element 507 that is placed in tension by the weight of the door being supported. However, in an alternative embodiment, the sliding element 107 is supported by an upstanding support element that is put in compression such that the support element tends to be deformed in a bending manner by the weight of the door. In this embodiment, strain gauges * *. * S * S.

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are arranged on opposite sides of the support element such that one strain gauge is configured to be compressed when the support element bends, while the second strain gauge is configured to be simultaneously stretched. In this embodiment, the bridge circuit is reconfigured such that the two strain gauges appear in series across the supply voltage, in parallel with the two resistors.

Thus the amplifier has one input connected to the junction of the two strain gauges and the other input connected to the junction of the resistors.

Figure 8 The process performed by the microcontroller 706 during use is illustrated by the flow chart shown in Figure 8. Firstly, at step 800 the microcontroller output is set to a value indicating anon-alarm condition.

During operation, the microcontroller must monitor the input signal received from the amplifier 705 to determine if there has been a sudden change in the load applied to the apparatus 101. To do this the microcontroller first determines a base value (labelled BASE VALUE in Figure 8) that is typical of the received signal when the apparatus is in a normal state, e.g. merely supporting the weight of a door. Thus, initially a calibration procedure is performed at step 801 to produce a base value. In the present embodiment this is achieved by taking a sample of input signal values (in the present example 60 input signal values) to find a total, referred to herein as a "CALIBRATION TOTAL", and then dividing the CALIBRATION TOTAL by the SAMPLE SIZE (in this case 60). * .. * . I * I.

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During operation, the apparatus is typically subjected to varying conditions such as humidity and temperature, and the condition of the apparatus itself may alter slowly over time. Consequently, the microcontroller 706 is configured to perform a re-calibration process periodically (for example every ten seconds) during use. Consequently, at step 802 a calibration timer is reset and started.

The microcontroller 706 then performs step 803 in which it provides an output value (in the present embodiment to the relay 707) in dependence of the input signal from the amplifier. This step will be further described below with reference to Figure 9.

At step 804 it is determined if the calibration timer has reached a -predetemrnned value and if not then steps 803 and 804 are repeate If the calibration timer has reached the predetermined value then a re-calibration process is performed at step 805. This step will be further described below with reference to Figure 10. On completion of step 805 the process then returns to step 802 where the calibration timer is reset before monitoring of the input signal from the amplifier is repeated at step 803.

Figure 9 The process step 803 of Figure 8 is shown in further detail in the flow * * chart of Figure 9.

Firstly an alarm timer is reset and restarted at step 901, before a value (herein labelled "DIFFERENCE") is calculated at step 902 by subtracting the * ** * * * * ** * **.*.e * S BASE VALUE from the current input signal value received from the amplifier.

The DIFFERENCE is then compared to a predetermined upper threshold value at step 903. If the DIFFERENCE is the larger then this would indicate that a new adcBtonal load has been applied to the apparatus 101 and a s potential problem exists. If DIFFERENCE is found to be larger than the upper threshold value, the alarm timer is compared to a predetermined time threshold (e.g. three seconds) at step 905. If the alarm timer has passed the predetermined time threshold then the microcontroller provides an output value indicating an alarm condition at step 906.

If the alarm timer has not yet reached the time threshold at step 905, the process returns to step 902 where a new value of DIFFERENCE is cakuiated from the new present hiput signal vahie. Thu whHe ever the question at step 903 is answered in the affirmative, the process repeats steps 902, 903 and 905 until the alarm timer reaches the timer threshold value at step 905 resulting in an alarm output value being provided at step 906.

If the value of DIFFERENCE is not found to be larger than the upper threshold value at step 903 then at step 904 it is determined whether DIFFERENCE is less than a predetermined lower threshold value at step 904.

If it were, this would indicate that a load has been removed from the apparatus 101 such as by the door being wedged upwards. If DIFFERENCE is found to be less than the predetermined lower threshold value, the alarm timer is compared to the time threshold value at step 905. lf the alarm timer has passed the predetermined time threshold then the microcontroller provides an * ** * * I * ** * * ***** * S output value indicating an alarm condition at step 906.

If the alarm timer has not yet reached the time threshold value, then the process returns to step 902, where a new value of DIFFERENCE is calculated from the new present input signal value. Thus, while ever the question at step s 904 is answered in the affirmative, the process repeats steps 902, 903, 904 and 905 until the alarm timer reaches the timer threshold value at step 905 resulting in an alarm output value being provided at step 906.

If the DIFFERENCE is found to be less than the upper threshold value at step 903 and then found not to be less than the lower threshold value at step 904, then step 903 is complete and the process returns to step 804.

Thus, the microcontroller continues to provide an output indicating a non-alarm condition. PJso, it may be noted that under normal operafing condffions when no unusual toads are applied to the apparatus 101, the microcontroller only performs steps 901 to 904 during step 803.

Figure 10 The re-calibration process identified as step 805 in Figure 8 is shown in further detail in Figure 10. During the re-calibration process the existing BASE VALUE is effectively adjusted in dependence upon the present input signal :: 20 value received from the amplifier. Generally, a new BASE VALUE is generated I.....

* S with a value between the old BASE VALUE and the present input signal value, so that if the input signal value drifts slowly upwards or downwards over time, then the BASE VALUE will follow that change. * S. * . S * Se

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In the present embodiment, firstly within step 805, at step 1001, the existing BASE VALUE is subtracted from the stored CALIBRATION TOTAL and the new input signal value is added to generate a new value for CALIBRATION TOTAL. A new value for BASE VALUE is then calculated at step 1002 by dividing CALIBRATION TOTAL by the (predetermined) SAMPLE SIZE (in the present example sixty).

Figure 11 A method of mounting the apparatus 101 within a doorirame will now be described with reference to Figure 11, in which the apparatus 101 is attached to a doorjamb 1101. The apparatus 101 is first attached to the doorjamb 1101 by locating a screw through one of the holes 108 nearest to one!nd of the apparatus 101 and screwing it into the doorjamb. It will be understood that this screw passes through a corresponding one of the holes 203 in the track 201, and so fastens the track to the doorjamb. (The sliding element 107 is still free to slide along the track.) In the present embodiment, one of the holes 108 closest to the upper end of the apparatus is used for this purpose. Typically, all six holes 108 nearest the upper end of the door will receive a screw to rigidly fix the track to the doorjamb in the initial step in the procedure.

With one end of the track fixed to the doorjamb in this way, a force measuring device 1102 is used to lift the sliding element upwards along the track. The force measured by the device 1102 partly depends upon the weights of the sliding element 107 and door mounting plate 103 but also * ** ** S * S.

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depends upon the friction between the sliding element and the track 106.

The force measuring device may be a spring balance or an electronic equivalent of a spring balance of the type available for measuring luggage weight.

The track is then further fixed to the doorjamb 1101 using at least one additional screw. Each screw is located within the next available one of the holes 108 working from the end of the apparatus that is already fixed to the jamb 1101.

The force measuring device 1102 is then used to lift the sliding element io upward along the track again, and the required force is re-measured. The difference between this second measurement and the first measurement is atct.ilated and if the difference than a predetermined value the newly added additional screws are adjusted. (The calculated difference between the two forces results from an increased frictional force between the is sliding element 107 and the track 106 due to distortion of the track caused by the screw fixing. For the optimal operation of the apparatus 101, this distortion and increased frictional force should be minimised.) When the difference between the original measured force and the re-measured force is not greater than a predetermined force, the track is further fixed to the doorjamb using one or more additional screws. The fixing and measuring process continues, working along holes 108 in the apparatus 101 until all holes 108 have received a screw.

It may be noted that the wires 112 (shown in Figure 1) emerging from * S. * * * * ..

****eS * S the upper end of the apparatus 101 are typically routed up through a channel or hole in the ceiling or wall above the door and connected to terminals of a monitoring system.

Figure 12 With the apparatus 101 attached to the doorjamb 1101 a door is then attached to the door mounting plate 103 by means of screws screwed into the edge of the door through holes 105 in the door mounting plate.

The apparatus 101 is shown attached to the doorjamb 1101 with a door 1201 attached to the door mounting plate 103 in Figure 12.

Figure1 -A crosssectional view of the lower end of the apparatus 101 mounted to the doorjamb 1101 and with the door 1201 attached to the door mounting plate 103 is shown in Figure 13.

The lower end of the sliding element 107 rests on the protrusion 509 formed at the end of the support element 507, pushing downwards on the support element with a force primarily due to the weight of the door 1201. The shape of the track 106 and the sliding element 107 restricts movement of the sliding element to movement along the track and so the force exerted on the * support element 507 is generally downward. However, it has been found in testing that a small component of the force applied to the support element tends to push it towards the end portion 1301 of the track 106. Also, for the * ** * * 0 * S. *S*s0 * 0 correct operation of the apparatus, the necked portion of the support element 507, on which the strain gauges 511 B (and 51 IA not shown) are located, must support all of the weight of the door 1201. Consequently, the lower half of the supporting element 507, which includes the necked portion, must not be supported by the track. To ensure that this is the case, the tower end of the track 106 is recessed such that a gap 1302 exists between it and the support element 507.

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