Tilt-beams. Why use them?
With an abundance of wireless tilt-sensors on the market, and with their adoption increasing, what is the value of including tilt-beams in your monitoring system installation?
Mems based tilt-sensors provide a high level of accuracy measuring 2 axis rotation. However, their observation is limited to their own footprint of circa 100mm (dependent on the model installed). When converting the angleº of change they have recorded to mm/m, the assumption made is that the change in angle is not localised to the circa 100mm the sensor is able to measure.
Installing tllt-sensors mounted to tilt-beams expands the range over which the tilt-sensors measure the change in angle, and therefore significantly reduces the localisation of movement being extrapolated, when the tilt-sensors reading is used to calculate the change in verticality of the entire wall.
If we use the example of a 5m high wall, a tilt-sensor mounted half way up the wall, with a footprint of 100mm, is able to observe movement across 2% of the walls total height.
If the tilt-sensor observes a change in the vertical rotation of the wall of 0.01º, the calculation to convert this to mm of change results in 0.872mm over 5m. It is worth noting that the actual movement the sensor was able to observe 0.017mm over 100mm. We are therefore assuming the accuracy of 98% of the walls movement, and that the wall's movement is linear from top to bottom.
If the same tilt-sensor is installed on a 3m tilt-beam the sensor it is now able to measure the 0.01º change over 60% of the walls total height, significantly reducing the localisation of the tilt-sensor's measurements and the assumption of accuracy to 40%.
Installing two tilt-sensors on the 5m wall at 1.7m and 3.3m, we can now measure the wall in 2 sections and understand if the wall is moving as a whole. However, we are still only able to accurately measure 4% of the total height. Installing these two tilt-sensors on 2m tilt-beams increases our ability to measure 80% of the total height.
So what are the cons of using tilt-beams?
Our tilt-beams lengths are fabricated from aluminium, and as with all metals, the tilt-beams are susceptible to linear thermal expansion/contraction. If we assume the worst case scenario, the tilt-beam will increase in length by 24µm per 1ºC change in temperature. In the UK we see temperatures ranging from +40ºC to -20ºC.
So what impact does this have on the length of our tilt-beams. which would then translate to a risk of curvature of the beam?
The table below shows the minimum to maximum length of the tilt-beam based on an installation temperature of 15ºC and the effect of linear thermal expansion.
We can allow for a 0.5mm expansion at either end of the tilt-beam which will be absorbed by the available movement within the end fixing brackets. Therefore the risk of expansion translating into the curvature of the tilt-beam is reduced by 1mm. It should also be noted that as the tilt-sensor is mounted to the centre of the length of the tilt-beam, that, as any curvature in the beam has a high probability of being equal along its length, the only impact to the tilt-sensors rotation will be based on any offset of the sensor's position along the length of the beam.
With the risk of contraction from falling temperatures presenting no risk to the curvature of the beam, and the maximum expansion of a 3m beam at 40ºC being 1.8mm (1mm of which is absorbed by the fixings), the total expansion risk is 0.4mm at either end of the beam. For this to cause a curvature in the beam itself, the strength of the beam must be less than the strength of force of resistance. Based on the above, it is clear that thermal expansion of the tilt-beams impacting the accuracy of tilt-sensor readings is negligible
So what does this mean to the accuracy of our tilt-beams?
The maximum potential loss in accuracy from our tilt-beams is 0.013%. Based on the fact that by installing tilt-beams we decrease the assumption of angular change by 10x using a 1m tilt-beam, and 30x with a 3m tilt-beam, the pros of installing tilt-sensors on tilt-beams significantly outweighs the cons.
Our tilt-beams are available in bolt-fix and magnetic install options. Bolt-fix tilt-beams are available in 1m, 2m ,2.5m and 3m lengths as standard, and can be customised to any length up to 3m. Our magnetic tilt-beams are 1m as standard, and can be customised to any length up to this.
Customised installation fixings are also available, for specific sensors, prism mounting or any other requirements.
For information on wireless tilt-sensors please get in touch with our distribution partners.
For enquires or for more information about our tilt-beams, or any of our other systems, sensors and accessories please get in touch.