Site Refraction Issues
Number 1 Reason Customers Incorrectly Report Issues With Their Laser
99.9% of the Technical support calls we receive typically turn out to be Refraction and both the Laser Level and Detector are in fact working perfectly.
Not every User is aware that laser levels, both Rotary and Line lasers can be affected by reflective surfaces on the worksite. Customers report to the Service Centre that the detector (laser receiver) is faulty because it is picking up the laser beam in random positions. Terms like “incorrect levels”, “random positions”, “out-of-level” or “Detector not picking up the beam correctly” are used. Refraction is simply physics and will occur regardless of brand and how much money was spent.
“Refraction” is the phenomenon where light is transmitted but moves direction when it passes from one medium to another e.g. through air then glass or water. This is why when you shine a torch at a window the beam bounces off to another position. In the same way, this refraction can affect the correct setting out, when using laser beams. An easy example to understand is if, for example, a rotary laser is operated with a double-glazed window behind it. The true level position can be refracted and the deviation can be appreciable, even over small distances. In some instances, a double beam position can occur and the wrong level marked.
Another quick way to tell Refraction is happening (and not that the Laser or Detector is faulty) is if you are getting multiple positions on the Detector i.e. a datum above and below where you believe the true datum to be.
If hypothetically the Laser level was not self-levelling correctly, it would then obviously give a datum which is incorrect. However, the key to this is that the datum it projects will always be the same. For example always 2mm low. A Self-levelling laser (even if it was out of calibration) would never give multiple levels at the same time. The self-levelling mechanism just doesn't work that way.
It is also easy to forget that the laser has in many instances a 500m range with a 360-degree coverage. We routinely hear the statement "I am in the middle of nowhere - and there is nothing around me". To then find the Excavator or Van is parked 10m behind the user with a huge glass windscreen. The cause of the refraction also may not be on your site but the neighbouring property, across the street or in the next field.
It's too easy to conclude the laser is faulty rather than understanding what site conditions can cause this phenomenon.
To establish the cause of the issue and to troubleshoot the problem, your best option is to carry out a controlled test. This Data Sheet explains more about Refraction and then on page 3 explains how to check the calibration yourself.
Additionally, you can also do a quick check on-site by getting the Laser off the Tripod and putting it on a firm surface (paving slab or on a block) down at ground level. Typically in this position, you are below the position of any glazing, or shiny/reflective surfaces. Then go about 5-6m from the Laser and pick up the beam. You should then find the Detector is picking up the beam correctly. You can then continue to move further and further away. Again, you will typically find the Detector is operating normally. Don't be tempted at the start to go too close to Laser e.g. 30cm as all Detectors will struggle to give a true reading at this distance as they are intended to work at long range and going too close might seem like a good test, but is actually the opposite.
When you have established the Laser and Detector are operating correctly, you can eliminate the problem of Refraction by making sure that laser beam reflections cannot be bounced back to the detector. As an example, if your site has large glass windows, make sure you set-up the laser level so that when you hold the detector, the glass is behind you and the detector, so it cannot reflect on to it.
If it is not viable to temporarily re-locate the Laser you can try masking some of the Lasers output windows (so that the beam is only output in the direction you are working). Although each Laser Level is slightly different, most typically have a "light house" at the top which has 4 glass windows which are arranged Front, Back, Left & Right. If as an example, you are positioned directly in front of the window above the Lasers keypad you can use some brown cardboard to mask / block the Back, Left & Right windows allowing the laser beam to only be omitted from the Front glass directly to your location. This will then prevent the Laser beam from travelling out of the rear window, hitting an object behind and travelling back to your position but at a lower position.
Basically lookout for & position your laser, being aware of all reflective surfaces like glass and shiny wet surfaces.
