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THE TECHNICAL PAGES
The DISTO Laser distance meter (by Guy Van Rentergem)


When I saw at a trade-show a leaflet of the world's first "handheld laser distance meter", I immediately thought of the possible use of this instrument for cave surveying purposes. Measuring distances, up to 100 m, with an amazing 0.3 cm precision. It seemed more like science-fiction to me!

So, put you old measuring-tapes away, here comes the Disto. As you can read in another article, the good old Suunto clinometer has also become redundant....

Working with the Disto is child's play. Press the button once and the laser is activated. Aim the laser beam (the red spot is very visible) and press the button a second time. After a few seconds, the distance is shown on the LCD-display. Could it be any easier?

The advantages of this device are numerous. Here are some examples, just use your imagination and you'll find a dozen more:

- In muddy conditions, you don't have to worry anymore about muddy measuring tapes.
- Tapes wear quickly: the digits fade away and in the cave, you'll risk mis-interpretation of the distances. With the Disto, this belongs to the past.
- Long distances are as precise as short ones. When using a tape, long distances will be over-estimated since the tape bends through.
- How high is this room, or aven? No problem. You know it within seconds.
- How deep is this pitch? No need to use two or more measuring tapes that are tied together, or Topofils that break while abseiling.
- Splendid white formations where you must try to pull your muddy tape in between without muddying them? From now on, just aim your Disto!
- How long is this lake? You'll know it without having to swim to the other side.
- My survey partner didn't show up... I'm alone. Thanks to the Disto, solo-surveying has become a lot easier.

BUT, there is one disadvantage too... the PRICE. This little beauty costed in 1996 some 45000 BEF (= 1200 USD) V.A.T. not included. Actually (1998), prices have dropped at least 20 % and let's hope that this trend continues.Disto Lasermeter !

The next step in surveying caves electronically, is combining the DISTO with the BOSCH electronic level. And then, why not, an electronic compass (and a computer perhaps?).

 

USING THE DISTO IN THE FIELD (Paul De Bie)

I had the pleasure to use the DISTO during several 6-hour survey sessions. The conditions were extremely muddy and using a normal tape, we surely would have been obliged to end the surveying after a couple of hours, because of a mud-covered tape. All advantages that Guy sums up in his article are true!

The DISTO allowed every time again a good and precise reading, even when aimed at muddy surfaces, cave walls or rocks. But we preferred to aim it at the back of my survey notebook. The DISTO will give you an immediate reply when aimed at a smooth surface. If you point it at a rough surface (rocks for instance), it will try to make an average by repeating the measurements during a few seconds.

Guy mentioned as the only disadvantage the high price of this thing. There are some other minor disadvantages.

- It is relatively big and heavy.
- It is robust and waterproof, but since it contains hi-tech electronics, you should be careful with it.
- The front lens has a special coating that can be easily scratched. I don't think you can cover it with a piece of plexi, since this would disturb the laser beam.

But, as a whole, this is good stuff and the future of it looks very promising indeed!

 

SOME TECHNICAL SPECIFICATIONS

This device uses an "amplitude modulated laser beam". The reflected laserlight that returns from the object that you are measuring to, is compared with a reference laser beam. The phase-shift is calculated and is directly proportional to the distance that was measured (thus permitting to calculate the distance).

It is powered by a build-in rechargeable battery.

History:
The first laser distance meter was already constructed in 1948 by a Swedish guy called Bergstrand. It could measure distance up to 40 kilometres. It took another 50 years before micro-electronics and small laserdiodes permitted to build small and handheld versions of this device.

Technical specifications:
Precision ▒ 3 millimetres
Maximal error ▒ 5 millimetres
Maximal reach: 100 metres
Dimensions (millimetres): 235 x 104 x 59 mm
Weight: 780 g
Number of measurements per battery charge: 400
Time to charge the battery: 1 hour (can be done though the cigarette-lighter of a car)
Working temperature range -10 C to + 50 C
Laser: 670 nanometre, 2 mW, laserclass 2 (IEC 825)

If you want to know more about the Disto lasermeters, then consult the site of Leica:
http://www.leica.com/surveying/product/disto.htm

The Disto exists in many models, even one that stores all readings and can be linked to a P.C. afterwards.
Meanwhile (april 1998) has BOSCH also a similar device, the DLE 30. It will probably be cheaper than the Leica.
 

 
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