Getting a quick measure cheap

Measuring on site can be a timely and costly affair. CW investigates the problems that occur when using traditional measuring techniques and learns how modern equipment can get more accurate results quicker and cheaper.

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By  Colin Foreman Published  October 30, 2004

Getting a quick measure cheap|~|Products Body.jpg|~||~|When it comes to measuring there are six basic tasks: Distance measuring; horizontal levelling or aligning; vertical levelling or aligning; slopes and inclines; 90 degree angles; and rebar detection. All of these tasks are necessary for many of the most common applications on a construction site. For example, measuring is necessary before formwork can be set. For distance measuring there are a number of traditional methods on offer, including the folding ruler, measuring tape, and roller tape. For horizontal levelling the most popular options are the water tube level, spirit levels and optical levels. For vertical levelling the plumb bob is the most popular method on offer, but chalk lines are also used. Slopes are measured using an optical level together with measuring staffs to set a level plane, from which the incline can be set. All these methods have inherent problems that stem from three general areas: The environment, human error, and the tools themselves. In this part of the world, temperature is a key factor when it comes to the environment. A steel measuring tape will not give the same reading at 45 degrees as it will at 21 degrees, because the tape will expand in the heat giving a lower reading. The same is true for water tubes as they also expand in the heat. Wind and gravity are other environmental factors. Plumb bobs can be greatly affected by the wind, as can measuring tapes that sag when measuring long distances, and if the tape is stretched to counter the sagging the reading will be less because the tape will be stretched. Perhaps the most significant source of error is the actual user of the tools themselves. Human error can involve the reading the wrong marking on a measuring tape, setting incorrect angles and using non-vertical measuring sticks when using an optical level, or actually being able to see whether the bubble in a spirit level is centred or not. The tools themselves may not be accurate. For example, a builders’ square is not accurate when the distance measured exceeds 1 m, this could be countered by using larger squares, but that would not be practical. Each of the traditional forms of measurement is affected by at least one of these factors. The graduations on a measuring tape may not be fully accurate and the angle may also be incorrect. In addition, any system that requires two people can lead to errors because the person who records the measurements may misinterpret what he is told by the person reading off the tape. Water tubes have a meniscus that can be read in a number of different ways, which leads to inconsistent results, especially when you consider the fact that two people are needed to make the readings. Spirit levels are only accurate to a point and do not work well for large surfaces which may only be level in places. The bubble is also not that sensitive, and fails to show slight variations clearly. optical levels In contrast, optical levels are very accurate tools but they are used as part of a system that includes another person holding a levelling staff, which can be fairly inaccurate. In essence the plumb bob is a perfect measuring device because it relies on gravity. However, when a plumb bob is used for setting the façade and cladding of a building it is not that accurate because the wind causes it to shake giving inaccurate results. Modern measuring products can be used to overcome these various flaws and at the same time offer a range of other benefits. Although the products may be more expensive than simple products like measuring tapes they can offer substantial saving in the long run. Unlike traditional systems that are slow and cumbersome, modern systems are quick and efficient. Another important factor for this market is that they are easy to use. “If a measuring system is not more convenient to use than the traditional methods on offer, nobody will want to use it,” says Charles Daher, market segment manager, Hilti. Accuracy together with safety and comfort is also improved. For example, if a distance across a ceiling is measured using traditional methods two people using ladders and measuring tape are needed, this may be unsafe, uncomfortable and unlikely to give accurate results. The final benefit is that, when compared to traditional methods, less people are needed to do the same task so staff are free to perform other duties. Modern measuring equipment use lasers, to perform a range of tasks including measuring distances, setting levels and right angles. The laser is basically a concentrated beam of light distributed in one direction. Instead of using all the colours of the spectrum just one colour is used so the light is focussed to give a small spot of light, like those used in common laser pointers. Like any laser, the spot increases in size the further it travels, but as long as it retains a good round shape it will still give accurate readings because the centre can be easily determined. The quality of the spot is a direct function of how good the laser is. Another important factor is visibility, which is affected by the colour of the laser. Although red is the most commonly used colour for lasers in the construction industry, green offers the best visibility, but they do not perform as well in other areas. Even different lasers of the same colour can vary when it comes to visibility. For example, a red laser with a wavelength of 435 nm is almost seven times more visible than a wavelength of 690 nm. Similarly, reflectivity and the colour of the target point is also important, white is best refection and black is the worst, in fact some products on the market struggle to register a reading against a black surface. The power of the beam used affects the accuracy, and also determines how safe the product is. There are three classes of laser that can be used, Class 3, Class 2 and Class 1. Class 1 semi visible or invisible and is eye safe but is not really powerful enough to generate accurate results. Class 2 is eye safe but in order to achieve accurate results a very good quality laser must be used to compensate for the lack of power. Class 3 is powerful enough to generate accurate results, but at the same time is also dangerous. “Some of the lasers that come from the Far East are extremely dangerous, and should be treated with caution,” says Colin Mackay, GM, HSS Hire Shops. Although modern measuring equipment may be more expensive than traditional tools and on first glance appear to be a complicated piece of kit, they have been well accepted across the region. “It is really just a case of explaining what the benefits are,” says Daher. “At first people just think they are ‘nice-to-have’ rather than essential tools, but once they realise how much time can be saved, cost is no longer is an issue because it can very quickly and easily be recovered,” he adds.||**||

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