GB2486012A - Alarm for fall arrest system - Google Patents

Abstract

An alarm device for a fall protection system, the alarm device comprising a first connector 2 for connecting the device to a safety harness and a second connector 4 for connecting the device to a safety line, the device thereby being connected, in use, in series between the harness and the safety line, wherein the device includes load monitoring means 30 for monitoring the load between the connectors 2,4, and hence the load on the safety line, and for triggering an alarm 6 if the load exceeds a threshold. The load monitoring means 30 maybe an electrical load cell having a strain gauge.

Description

improvements in and relatingjp fall protection systems This invention relates to alarm devices for fall protection systems, and to fall protection systems having such alarm devices.

io The invention is particularly applicable to fall protection systems which provide personal fall protection to operatives, i.e. users, working at height. Such a system typically comprises a harness to be worn by the user and a safety line, also known as a lanyard, that connects the user to an anchoring point or member, for example a safety rail or eye fixture, on a supporting structure so that, if the user falls, the distance by which he or she drops is limited. The lanyard can incorporate or be connected in series with an energy absorbing device for reducing the acceleration experienced by the user in the period between falling and being stopped by the fall protection system.

Such a device typically comprises a block of webbing which is either woven or stitched together and which opens progressively in the event of a fall, and can limit the impact force (as the user is stopped by the taught lanyard) to 6 KN, whereas a user weighing 100 kg falling 4 metres before being stopped by a 2 metre long textile lanyard (without an energy absorbing element) could be as high as 20 lEN.

Various standards exist for energy absorbers globally.

In Europe energy absorbers must conform to standard EN355 which requires a minimum force of 2 lEN to initiate deployment and a maximum impact force of 6 KN during deployment and a minimum tensile strength of 15 KN afler deployment. Other standards apply to energy absorbers for use in other territories.

Energy absorbers are generally designed to be used in conjunction with a lanyard such that the combined length of both of the components is no more than 2 metres before deployment of the energy absorber. To ensure that the impact force is less than 6 KN in the event of a worst case fail with such a product (e.g. a fall of 4 metres), the energy absorber may need to extend by up to 1.75 metres in order to provide the necessary gentle braking effect.

FaIl protection systems having harnesses and lanyards (and sometimes energy absorbers) are worn daily by operatives globally and can be found in the petrochemical, power generation, utilities, construction, maintenance (for example window cleaning), industrial, commercial, emergency services and regulatory sectors, all of which can involve a user working at height. The protection systems do not i o eliminate the possibility of a fall, but are intended to mitigate the effects of any fall.

However, after a fall, a user may be held in a suspended state in the harness, possibly unconscious, until rescued. With the user in this state, the harness may significantly restrict the user's blood flow, giving rise to the risk of serious injury or death if the user is not recovered in a short period of time.

To that end, it is essential that a well considered and executable rescue plan is put in place by anybody responsible for people working at height and using fall protection systems. Indeed, there are codes of practice (for example British Standard 358454:2006 "Code of Practice for the Delivery of Training and Education for Work at Height and Rescue") that deal with this issue.

However, a thorough rescue plan may be of no benefit if a user's fall is not detected.

US 7,106,205 shows an alarm device for use with an energy absorbing lanyard. The device has an activation pin on the outside of the housing of the device. The pin is connected to a connecting member that is, in turn, attached to a portion of the shock absorbing lanyard which is spaced from the device and which will move away from the device when the lanyard is deployed, so that deployment of the lanyard extracts the pin which, in turn, triggers the alarm.

Because an essential portion of the trigger mechanism for the aIm-rn is external, it may be prone to damage, accidental dislodgement or snagging on structures/fixtures in the vicinity of the user. These problems could in turn lead to the triggering of the fall alarm or the failure of the alarm altogether. In addition, the alarm device forms part of a specially adapted shock absorbing lanyard which includes or can receive a suitable connecting member.

According to a first aspect of the invention, there is provided an alarm device for a fall protection system, the alarm device comprising a first connector for connecting the device to a safety harness and a second connector for connecting the device to a safety io line, the device thereby being connected, in use, in series between the harness and the safety line, wherein the device includes load monitoring means for monitoring the load between the connectors, and hence the load on the safety line, and for triggering an alarm if the load exceeds a threshold.

is Preferably said alarm is part of the alarm device.

Preferably, each connector comprises a respective eye.

It will be appreciated that the connectors may connect the device to the harness and safety line either directly or indirectly (for example via other connectors such as hooks or carabiners.

Accordingly, the connectors of the alarm device provide a means of connection for the device to the fall protection system and for connecting together the safety line and harness of such a system. In use, the connectors therefore will bear the load resulting from a fall.

The invention thus provides an alarm device that can readily be incorporated into an existing fall protection system, without the need to modify the latter, and that does not rely on an external element, such as a pin or additional webbing tail, for triggering the alarm.

Preferably, the first connector and the second connector are linked together via the load monitoring means in such a way that, in use, the load on the connectors is transmitted through the load monitoring means.

s Accordingly, if a user of a fall protection system fitted with the alarm device falls, the load monitoring means will bear substantially all of the load that is on the safety line.

This ensures that the load on the safety line is properly monitored by the load monitoring means.

Preferably, the load monitoring means comprises an electrical load cell, preferably having a strain gauge.

Such cells are robust and durable and can be subjected to considerable loads on multiple occasions, so that the device may be reused after a fall. In addition, the output of the cell is an electrical signal indicative of the magnitude of the load applied to the cell, and so can be readily analysed to determine whether the threshold has been exceeded.

The load cell and first and second connectors may be linked together in such a way that a tensile load applied to the connectors (to urge them away from each other) compresses the load cell. Alternatively, those components can be so linked that such a load applies a tensile force to the cell.

In these cases the cell may, in use, lie on the line of force exerted between the connectors.

Preferably however the cell is at least partially laterally spaced from at least one of the connectors. This enables the connectors to be situated closely adjacent to each other so as to reduce or minimise the increase in length of the fall protection system attributable to the alarm device. This will correspondingly reduce the distance that a user would fall before the safety line is pulled taught and/or before any energy absorber in the line is deployed.

Preferably, the cell is laterally spaced from both connectors and from said line of force.

In such a case, the load cell may to advantage frmnction as a shear detector.

Preferably, the device includes a source of electrical power, for example a battery, and a switch for automatically connecting the load cell to the source when the load between connectors is to be monitored. Preferably, the switch also automatically disconnects the load cell when the device is not in use. I0

The switch helps to preserve the power supply and avoids the problems, associated with a manual switch, of a user forgetting to switch the device on or off.

The switch may comprise a movement detector responsive to movement of the device.

Preferably, however, the connectors are linked together in such a way as to provide a lost motion connection which allows a small initial movement between the connectors, in response to the application of a small tensile load thereof, the switch being, operated to connect the load cell and power supply in response to said movement.

In this case, the link preferably includes biasing means, such as a compression spring, for urging the connectors towards each other over the range of said initial movements.

Preferably, the load monitoring means is operable to trigger the alarm if the load on the connector exceeds a lower threshold for a predetermined minimum period or if the load exceeds a second, higher threshold, regardless of duration.

The higher threshold may correspond to the load on the connectors caused by the initial force set up when the fall protection system arrests a fall. However, there may be other circumstances in which the user may require assistance, for example if the safety line becomes snagged on a building structure, or if the user has lost consciousness and is slumped in the harness. In such cases, the load being detected may not correspond to the load associated with a fall, but may exceed the lower threshold for at least predetermined period, thus triggering the alarm.

Preferably, the lower threshold corresponds to a load of at least approximately 500 N s (corresponding to the load applied by a 50 kilogram person slumped in the harness) and the predetermined period is 3 0-60 seconds.

Preferably, the higher threshold is approximately 2 KN.

io Preferably, the device is operable to emit both audio and visual alanns, and to that end preferably includes a loud speaker and a lamp, such as an LED based lamp or a xenon flash lamp.

The device may to advantage be operable to alter the nature of the alarm if the alarm is operating for more than a predetermined period.

This will serve to warn rescuers of the possible increased urgency of the need to recover the user.

In the case of an audio alarm, the change could be an alteration of the tone of the alarm, whilst a light emitting alarm could be made to change colour (if it uses a multicolour light source or sources) or the pattern of operation of a single colour source may be changed (for example by switching from continuous operation to flashing).

The device may to advantage also include a wireless transmitter, operable in response to the triggering of the alarm, to transmit a signal to a remote receiver having an onboard alarm.

Thus the device can warn another person, for example a supervisor or building site safety officer, who may be out of sight or earshot of the user.

The alarm device may conveniently include a test function for testing the alarm when there is no load on the connectors and a reset function for resetting the device after the alarm has been triggered, to enable reuse, each function conveniently being activated by means of a respective button on the device.

According to a second aspect of the invention, there is provided a fall protection system comprising a plurality of alarm devices, each having a wireless transmitter, and a common wireless receiver responsive to signals from any of said plurality of alarm devices, wherein each alarm device is operable to transmit to the receiver an alarm signal that includes an identification code for identifying the device, the receiver including a display for displaying an identification of which alarm device has been triggered.

Preferably, each alarm device is an alarm device in accordance with the first aspect of the invention.

The invention also lies in an alarm device for a fall protection system having a safety line for tethering a user to an anchoring point or member, the device having connectors for connecting the device to the line and load monitoring means for monitoring the tensile load on the line, the load monitoring means being operable to trigger an alarm if the load on the line exceeds a lower threshold for a predetermined minimum period of time or a higher threshold for any period of time.

According to a further aspect of the invention, there is provided an alarm device for a fall protection system having a safety line for tethering a user to an anchoring member, the alarm device having art internal alarm and load monitoring means for monitoring the tension on the safety line and triggering the alarm if the tension exceeds a threshold, wherein the load monitoring means comprises a load cell for producing an electrical output indicative of said tension.

The invention also lies in a fall protection system having a safety harness to be warn by the user, a safety line for tethering the harness and hence the user to an anchoring point or member and an alarm device as aforesaid.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:-Figure lisa front elevation of the exterior of a first embodiment of an alarm device in accordance with the invention; Figure 2 is a corresponding view of a slightly simplified version of the first io embodiment; Figure 3 is an elevational view showing two possible connectors for the alarm device; Figure 4 is a sectional front view of the alarm device of Figure 1; Figure 5 is a corresponding view of a second embodiment of alarm device in accordance with the invention; Figure 6 is a sectional side view of a third embodiment of alarm device in accordance with the invention; Figure 7 is a corresponding view of the fourth embodiment of alarm device in accordance with the invention; Figure 8 is an elevational view of a common wireless receiver unit for use with one or more alarm devices; Figure 9 shows the alarm device of Figure 5 when connected to a lanyard fitted with an energy absorber; and Figure 10 shows a fall protection system also in accordance with the invention, comprising the apparatus of Figure 9 connected to a worker's harness. [Please amend Figure 10 to show the harness and the upper anchoring pointlmember] With reference to Figure 1, an alarm device in accordance with the invention s comprises a housing 1 from one end of which projects a first connector 2 in the form of an eye for connecting the device to a safety harness. A second connector 4 for connecting the device to a safety line, such as a lanyard fitted with an energy absorber, projects from the opposite end of the housing 1 and also takes the form of an eye. The connectors 2 and 4 are linked together, in a way described below, so that if a io user of the device falls, the resultant tension in the safety line will be transmitted to the safety harness though the connectors 2 and 4 and can be measured by a load cell within the device. If the load cell detects a tension over a given threshold, then it activates an audible alarm using a loud speaker 6 and a visual alarm using flashing light emitting diodes 8 distributed around the sides of the housing 1. The device of is Figure 1 also includes an antenna 10 from which an RF alarm signal can be transmitted to be received by a remote receiver unit such as the unit shown in Figure 8. In the modified version of the first embodiment shown in Figure 2, the antenna (and the associated RF transmission circuitry) have been omitted, the device of Figure 2 being identical to that of Figure 1 in all other aspects. Accordingly, Figure 2 uses the same reference numerals as Figure 1 to denote corresponding features.

The connector 2 has an integral cross-piece 12 in which there is formed a circular aperture through which a rod 14 extends. The rod 14 is of a diameter slightly larger than that of the hole, but includes an annular indentation into which the portion of the piece 12 around the hole extends and a head 16 at its end; the connector 2 thus being rotatedly retained on the rod 14. Figure 3 shows an alternative arrangement in which the rod 14 is terminated in an integral eyelet 18 through which a carabiner 20 or hook extends.

On the front of the housing 1 there are provided a test button 22 for testing the alarm (prior to connection to a fall protection system), an adjustment button 24 which can be used to pair a device with the remote receiver and/or to turn off the radio transmitter (in situations in which radio transmissions would be perceived as hazardous). There is also a manual activation or reset button 26. The latter button can be used to trigger the alarm or, if the alarm is operating, to reset the device.

As can be seen from Figure 4, the rod 14 extends from the head 16 into an aperture in one end of the housing 1, and is terminated at its opposite end by a second head 28 which is situated within the housing 1 at a region opposite the opening through which the rod 14 extends.

io A compression load cell 30 is mounted on the rod 14 and sits on the head 28. The load cell 30 is of the type which includes a strain gauge that can be used to measure the compression on the load cell 30. Typically, such a gauge will have a serpentine track of a conductor applied to a substrate which flexes as a compressive load is applied to the cell, in such a way as to alter the electrical resistance of the track. This is alteration can be measured to provide an output indicative of the compressive load on the cell. It will be appreciated that other types of load cell could be used, for example load cells of the type incorporating piezoelectric elements.

A helical compression spring 32 sits on top of the cell 30 and acts between the cell 30 and a cross-piece 34 which is an integral part of the connector 4 and is similar to the cross-piece 12. Thus the cross-piece 34 also has a central circular aperture through which the rod 14 passes, but in this case the aperture is of a diameter slightly larger than that of the rod 14 so that the connector 4 is axially moveable along the rod 14.

The spring 32 acts as biasing means for urging the connector 4 upwards (when the device is orientated as shown in Figure 4) against a stop (not shown). In the event of a fall, the connector 4 will initially slide along the rod 14, against the biasing action of the spring 32, until the spring 32 is fully compressed. This sliding movement constitutes the lost motion in the link between the connector 2 and the connector 4 (the link in turn being constituted by the rod 14, heads 16 and 28 and load cell 30 and spring 32).

The alarm device includes a micro switch 35 which is closed by the sliding movement of the connector 4 away from the stop. The closing of the microswitch, in turn, connects the load cell 30 to a power supply in the form of a 9 volt lithium battery 36 via a printed circuit board 38.

The printed circuit board 38 includes electronic components for supplying power to s the load cell 30 and monitoring the signal received therefrom in a known fashion, and include suitable voltage and current regulators for ensuring that the current supplied to the load cell 30 is within the working tolerances of the latter, an amplifier for amplifying the output from the load cell 30, an analogue to digital converter for converting the output into a digital signal, and a microprocessor which is used for the io necessary control of the operation of the device, including the comparison of the digitised signal representative of the load on the cell 30 with a lower threshold of approximately 500 N and an upper threshold of approximately 2 KN, and timing means for determining whether the load exceeds the lower threshold of more than 30-60 seconds. The microprocessor is operable to activate the loudspeaker 6 and LEDs 8 if the upper threshold is exceeded (regardless of duration) or if the lower threshold is exceeded for more than 60 seconds. The microprocessor may also be operable to cause the tone of the audio alarm emitted by the speaker 6 to change after a predetermined period to indicate to potential rescuers the increased urgency of the need to reach the user.

The printed circuit board 38 also includes a driver for operating the loudspeaker 6 and a ftirther driver for operating each of the LEDs 8.

If the alarm device is triggered, then in addition to activating the loudspeaker 6 arid LEDs 8, the microprocessor will activate the RF transmitter to transmit an RF alarm signal via the antenna 10 to a receiver 40 of the type shown in Figure 8. The receiver shown in Figure 8 has an antenna 42 that is connected to RF receiver circuitry of a known type which will receive and demodulate the transmitted signal. The device also includes an LCD display screen 44 which can display an alarm message indicating the identity of the alarm device and the time that the alarm was triggered.

The receiver can also include a loudspeaker 46 for emitting an audible alarm. The alarm device and receiver can utilise frequency modulation or phase modulation and encoding techniques common to professional mobile radio or mobile telephone applications in order for the alarm device to transmit an alarm signal that carries an identification of that device to be decoded by the receiver. Alternatively, the alarm device and receiver may use a scheme more akin to walkie talkie radio in which case the necessary identification information can be carried by frequency modulating the s signal emitted by the device with a simple binary code.

The receiver can also be equipped with test, adjustment and manual activationireset buttons 48, 50 and 52 which can be operated to cause similar functions to those accessed by the buttons 22, 24 and 26 on the alarm device. I0

In use, the device is connected to a safety line in the way shown in Figure 9, in which reference numeral 54 denotes the lanyard and reference numeral 56 denotes an energy absorber in the form of a block of webbing which is woven or stitched together and which opens progressively in the event of a fall. The energy absorber 56 is shown as is an integral part of the lanyard 54, but can be an initially separate element which is attachable to an initially separate safety lanyard by means of an eye on one component and carabiner on the other. The end of the lanyard 54 remote from the energy absorber 56 is terminated in an eye 58 via which the lanyard can be attached to an anchoring or support member by any suitable means, for example by means of a carabiner attached to the member. At the opposite end of the lanyard 54 there is provided a carabiner 60 via which the lanyard 54 is attached to the alarm device.

An example of a carabiner attaching the lanyard 54 to an anchoring member (eye 61) is shown at 62 in Figure 10, from which it can be seen that a connector 2 of the alarm device is attached to another carabiner which is in turn attached to a user's safety harness 63. In the example shown in Figure 10, the user is climbing a structure which provides a series of steps/hand holds. If the user were to fall from the structure, the portion of the lanyard 54 between the energy absorber 56 and the eye 58 would extend until it is taught, during which period the user will be substantially in free fall.

However, once the lanyard 54 has been pulled taught, the webbing in the energy absorber 56 will be progressively unstitched and this unstitching will absorb the energy of the fall and gently decelerate the user until the webbing of the energy absorber has been fttlly extended. At this point, there will be an instantaneous increase in the tension in the lanyard 54 as the fall is finally anested. This instantaneous tension will be transmitted between the connectors 2 and 4, and so will be detected by means of the load cell 30. In addition, the instantaneous force will exceed the upper threshold mentioned above, and will therefore trigger the alarm. In another scenario, if the user passes out while on a supporting structure which prevents a full fall, the user may become slumped in the harness, as a result of which the tensile force tending to separate the connectors 2 and 4 may not exceed the upper threshold, but may be above the lower threshold while the user is in this state. If that situation persists for more than 60 seconds, the alarm will, again, be triggered.

It will be appreciated that the alarm device according to the invention can be inserted into a fall protection system in between a conventional lanyard (with or without an energy absorber) and a conventional harness without the need to modify either of these components. Alternatively, it is possible for the alarm device to be inserted between the end of the safety lanyard remote from the user and an anchoring member, although in this case the alarm will be sounding and/or emitting light at a position which may be at some distance from the user (i.e. at the top of the safety line).

With reference to Figure 5, the second embodiment of the alarm device in accordance with the invention shows many similar features with the first embodiment, and these are denoted by the reference numerals used in Figure 4, raised by 100. In this case, however, the connectors 102 and 104 are linked together via a tension cell, such as a strain gauge 200 in such a way that a tensile load between the two connectors would be detected as tension in the cell 200. To that end, the inboard end of the rod 114 is attached to the cell 200 at one end, whilst the connector 104 is attached to a lower rod 202, the inboard end of which is also attached to the cell 200. The means of attachment at the connector 104 to the rod 202 is the same as the means of attachment of the connector 102 to the rod I 14. Thus, the rod 202 is terminated in an outboard head 204, the connector 104 having an apertured cross-piece 134 through which the rod 202 passes and which sits on the head 204.

The relevant components on the board 138 are configured to function with the tension cell 200 to determine whether the tension detected by the latter exceeds either the two thresholds in the way described in relation to the compressive force on the cell 130 caused by the tension between the connectors 2 and 4 in the first embodiment.

The third embodiment of the device, as shown in Figure 6, also shows many common features with the first embodiment and these are therefore denoted by the reference numerals of Figure 4, raised by 300. As with the first embodiment, the embodiment shown in Figure 6 uses a compression cell 330 to monitor the tensile load between the connectors 302 and 304. In this case, however, the connectors 302 and 304 are laterally offset relative to each other, and are linked together in the following manner.

The connector 304 is connected to a second rod 370 in a similar fashion to the connection between the connector 302 and the rod 314. The rod 370 is offset from, but parallel to the rod 314 and extends up into the housing 1 into a region where the two rods overlap. The rod 370 is attached at its top region to an upper lug 372 which is is thus axially fixed to the rod 370. The lug 372 includes an aperture through which the rod 314 can, however, slide. The rod 314 is attached in the region of its lower end to a second lug 374 so that the lug 374 is axially fixed relative to the rod 314.

However, the lug 374 has an aperture through which the rod 370 passes so that the rod 370 can slide axially relative to the lug 374, but not the lug 372, whilst the rod 3 14 can slide axially relative to the lug 372 but not the lug 374. The load cell 330 sits on the lug 374 and provides a seat for the compression spring 332 which acts between the cell 330 and the upper lug 372 to urge the two lugs apart. Thus the link between the connectors 302 and 304 provides for lost motion which, in conjunction with a microswitch (not shown) can be used to provide automatic initial activation of the load cell 330 in response to initial movement of the connectors 302 and 304 away from each other. It will be appreciated that a tensile load between the two connectors will move the lugs 372 and 374 towards each other so that, when the spring 332 is fully compressed, the compression load detected by the cell 330 will be indicative of the tensile load between the two connectors.

Since the connectors 302 and 304 are offset relative to each other, this embodiment of device can be designed in such a way that the distance between the two connectors is reduced compared with the first and second embodiments. This is achieved because the load cell 330 is laterally offset relative to the connector 304.

In the embodiment of alarm device shown in Figure 7, the load detection means takes s the form of a shear detector 376 which links first and second connectors 378 a.nd 380 respectively. The shear detector takes the form of an internal bar 382 which carries a strain gauge 384, and which is laterally offset relative to both of the connector 378 and 380. The output from the strain gauge 384 is monitored in the same way as the output from the load cells of the other embodiments. If the user of the alarm device of [0 Figure 7 falls, the resultant tensile force on the connectors 378 and 380 acts along a line between those connectors, and laterally spaced from shear detector 376.

As can be seen from Figure 7, this configuration enables the connectors 378 and 380 to be located relatively close together.

It will be appreciated that the above embodiments are only some examples of devices in accordance with the invention, which includes within its scope many other variants.

For example, instead of having a load cell, a device according to the invention could simply have a spring or other compressive/elastic member (for example a rubber block) in conjunction with a switch which is activated when the first and second connectors of the device move apart (against the biasing force of the spring) beyond a predetermined distance. If the switch is closed as a result of either a fall or a slump of the user, the resulting applied load will most probably be present for longer than 30 seconds. On this basis, the switch could operate in conjunction with time delay circuitry so that if any load is applied (say above 50kg to avoid constant activation) and not relaxed after 30 seconds the device will activate the alarm. In this mode it will be preferable for the device to emit a single warning beep when the load reaches, say, 50kg. In this way an operative who is simply pulling against the device because he/she is. overstretching/reaching will be warned that, in effect, he/she has 30 seconds to back off and relieve the tension in the lines. Thus this variant in the device also can operate without the upper and lower thresholds of the previously described embodiments.

Claims (19)

1. CLAIMS1. An alarm device for a fall protection system, the alarm device comprising a first connector for connecting the device to a safety harness and a second connector for connecting the device to a safety line, the device thereby being connected, in use, in series between the harness and the safety line, wherein the device includes load monitoring means for monitoring the load between the connectors, and hence the load on the safety line, and for triggering an alarm if the load exceeds a threshold.
2. 2. The device of claim 1, wherein said alarm is part of the alarm device.
3. 3. The device of claim I or 2, wherein each connector comprises a respective eye. r

   0)
4. 4. The device of claims I to 3, wherein the first connector and the 0 second connector are linked together via the load monitoring means in such a way that, in use, the load on the connectors is transmitted through the load monitoring means.
5. 5. The device of claims I to 4, wherein the load monitoring means comprises an electrical load cell having a strain gauge.
6. 6. The device of claims I to 5, wherein the load cell and first and second connectors are linked together in such a way that a tensile load applied to the connectors compresses the load cell.
7. 7. The device of claims I to 5, wherein the first and second connectors are linked that such a load applies a tensile force to the cell.
8. 8. The device of claims 6 or 7, wherein the cell, in use, lies on the line of force exerted between connectors.
9. 9. The device of any preceding claim, wherein the cell is at least partially laterally spaced from at least one of the connectors.
10. 10. The device of claim 9, wherein the cell is laterally spaced from both connectors and from said line of force.
11. 11. The device of any preceding claim, wherein the device includes a source of electrical power and a switch for automatically connecting the load cell to the source when the load between connectors is to be monitored.
12. 12. The devices of claim 11, wherein the switch comprises a movement detector responsive to movement of the device.
13. 13. The device of claim 11, wherein the connectors are linked together in such a way as to provide a lost motion connection which allows a small initial movement between the connectors, in response to the application of a small 0) tensile load thereof, the switch being operated to connect the load cell and 0 power supply in response to said movement.N
14. 14. The device of any preceding claim wherein the load monitoring means is operable to trigger the alarm if the load on the connector exceeds a lower threshold for a predetermined minimum period or if the load exceeds a second, higher threshold, regardless of duration.
15. 15. The device of any preceding claim, operable to emit both audio and visual alarms.
16. 16. The device of any preceding claim operable to alter the nature of the alarm if the alarm is operating for more than a predetermined period.
17. 17. The device of any preceding claim, further comprises a wireless transmitter, operable in response to the triggering of the alarm, to transmit a signal to a remove receiver having an onboard alarm.
18. 18. The device of any preceding claim comprising a test component for testing the alarm when there is no load on the connectors and a reset function for resetting the device after the alarm has been triggered, to enable reuse, each function conveniently being activated by means of a respective button the device.
19. 19. A fall protection system comprising a plurality of alarm devices, according to any preceding claim each having a wireless transmitter, and a common wireless receiver responsive to signals from any of said plurality of alarm devices, wherein each alarm device is operable to transmit to the receiver an alarm signal that includes an identification code for identifying the device, the receiver including a display for displaying an identification of which alarm device has triggered. r a)N c\J