Frequently Asked Questions Back to Main FAQ Page General - Laser Distance Meter
What is a laser distance meter?
How does it work?
How does it differ from a range finder?
How does it differ from ultrasonic/sonar devices?
Who uses laser measuring devices?
What are the advantages of a laser distance meter?
What different kinds of laser measuring devices are available?
Is there any change in the accuracy as the distance increases?
What is a Direct measurement?
What is an Indirect measurement (triangulation)?
What models have the Indirect (Triangulation, Pythagorean) capability?
How does the Indirect (also called Triangulation or Pythagorean) method work?
Which Leica DISTOs offer an interface for communicating with a computer or PDA?
What is the difference between typical and maximum measuring accuracy?
What is measuring accuracy?
How can I monitor my measuring equipment on my own?
What is a laser distance meter?
A handheld device that uses a laser for measuring distances between two objects. The best models are accurate within (+/-) 1 mm and have a range of up to 650 ft. The original, and most popular laser distance meter is the Disto by Leica Geosystems. Many competitor''s models are manufactured by Leica and sold under private label, including the Stanley, CST/ Berger, Pacific Laser Systems, Stabila and Apache brands.Back to top How does a laser distance meter work?
The user aims a red laser dot at an object, such as a wall, pole, cabinet or board. The user then triggers the unit to measure and the distance to the red dot is displayed on the screen. Normally, the unit is placed where the user would hold a tape measure and the dot is aimed at the point to which the tape would be extended. Precision optics and laser physics are used to quickly and accurately determine the distance to the object.
The most accurate devices use the phase shift method. They are accurate within +/- 1/16th inch and have a range of up to 600 ft. The most common of these is the Disto by Leica.
For a scientific explanation of what a laser is and how it works, see these articles from :
How Stuff Works
WiseGeek
rp-photonics
For articles explaining how lasers are used to obtain measurements, go to:
Phase Shift Method
Time of flight method Back to top How does it differ from a range finder?
Laser range finders are generally used for longer distances and when accuracy is not as critical. They are commonly used for hunting, golf and forestry applications. They often use the time of flight method for determining distance. The measuring ranges vary, but can be as great as 1000 yards and typically have an accuracy of +/- 1 yard. Bushnell, Leica, Nikon and Optonics are a few of the range finder manufacturers.
Back to top How does it differ from ultrasonic/sonar devices?
The mass market devices commonly found at home improvement stores such as the Strait Line laser tape, Stanley Intellemeasure, Ryobi and Black and Decker are actually not laser measuring devices, but sonar or ultrasonic devices with a laser pointer used only for aiming the device. They emit a sound wave and measure the time it takes for the sound to come back to the unit. They then calculate how far the sound traveled before it was reflected back. There is no guarantee that the sound was reflected from the same item at which the laser was pointed, thus often providing the user with false readings, especially in rooms with furniture or cabinets on the wall. The range on ultrasonic devices is normally limited to 50 feet, they do not work well outdoors and they are normally accurate within +/- 6 inches over a 50 foot range. They are useful in applications where accuracy is not required and there are no obstructions in the measuring environment. Back to top Who uses laser measuring devices?
Common users are Insurance Adjusters, Real Estate Appraisers, Contractors, Architects, Real Estate Agents, Stage Technicians, Painters, Plumbers, Surveyors, Estimators, A/C Installers, Phone Linemen, Window Installers, Window Covering Installers, Carpet Installers and Flooring Salesmen. Back to top What are the advantages of a laser distance meter?
Time savings: It is normally much faster to turn the laser on, hold it against a wall, for example, aim at the opposite wall and press the button than to extend a tape measure to the far wall take the reading, and retract the tape. This is true in small rooms, and even more so on larger areas. The more crowded the area being measured, whether with furniture, equipment, trees, etc, the greater the time savings. Typical measuring jobs can be completed in about 1/3 the time required to use a tape measure. Time savings increase as the distances get longer.
Accuracy: Laser devices measure the true, straight line distance between two points, without the bend or sag that commonly occurs in tape measures.
Prevention of Errors: It is much easier to read the digital display on a laser measuring device, which can be held in a convenient position, than to read a tape measure that needs to be held in the measuring position. Most laser devices allow the user to select the units of measure, eliminating the need for conversion of units, a common source of measurement error. Laser devices display the measured value, preventing the user from misreading the dash marks on a tape.
One Person Can Take Most Measurements: Tape measures often require a 2nd person to hold the end of the tape. Lasers are simply aimed at a target, such as a wall, pole, door, stake or post.
Difficult to Reach Measurements: High ceiling measurements are as easy as setting the laser on the floor and aiming at the ceiling. Tall buildings, 2nd floor extensions, measurements across water, measurements in tight quarters, are all easier with a laser measuring device. Some models are able to triangulate measurements that are otherwise inaccessible.
Data Interface: Some lasers are capable of sending the measurements directly to a computer for further processing. The Disto A6, Disto Plus and the new Disto D8 will transmit measured dimensions to ANY Windows software using a Bluetooth data interface. Many software vendors are incorporating the ability to import measurements directly from the these devices into their programs, including Xactware, Apex, Symbility, Simsol, PowerClaim, PowerCAD, ZipCad and others.
Safety: There is significant risk involved when using a tape measure at extreme heights or on steep inclines. And, many times more than one person is required for such measurements. Now, with the Disto D8''s new indirect measurement capabilities combined with the 360 degree tilt sensor, measurements can be taken from the ground AND by a single person.
See also: 12 Reasons to Buy a Disto Back to top What different kinds of laser measuring devices are available?
Laser Distance Meters: These are handheld devices and are used for distances up to 650 feet with accuracy up to +/- 1 mm. The Disto brand by Leica is the market leader and has 7 models, the Disto A5, Disto A6, Disto A8, Disto D2, Disto D3, Disto D5 and Disto D8.
Laser Range Finders: These are handheld devices. Rangefinder manufacturers include Bushnell, Leica, Nikon and Optonics. A few of the applications include hunting, archery and golf. They generally measure a longer range than Laser distance meters; up to 1000 yards, with accuracy to within +/- 1 yard.
Laser Sensors: Laser sensors are commonly used in manufacturing, quality control, and processing applications. They are more appropriate for shorter ranges; from under an inch to several yards. But commonly laser sensors are much more accurate -- in the thousandths of an inch. Keyence is a leading manufacturer of laser sensors. Back to top Is there any change in the accuracy as the distance increases?
The tolerance does not improve at shorter distances. It is essentially the same over the entire range (up to 200m or 650 ft.) of distances being measured. However, at distances over 100m (300 ft), additional errors of +/-5 ppm (parts per million) (+/-0.5mm/100m) come into play. Back to top What is a direct measurement ?
A direct measurement is one where the operator positions the measuring device at one end of the object being measured and points the red laser dot to the other end of the object to obtain a measurement. Direct measurements are commonly used indoors to determine the width of a room. The user holds the base of the device against a wall, and aims to laser dot at the wall across the room. Direct measurements are very accurate. WIth the use of the addition and subtraction keys, and creative selection of targets, most objects can be measured using the direct method. For situations where it is difficult to use the direct method, some laser distance meters have an indirect measurement, or triangulation feature.
Click here to view an animated tutorial Back to top What is an indirect measurement (triangulation)?
Indirect measurements allow the user to measure objects that don''t have easy targets. A common use of this feature is measuring the width of a house from the street. The easiest method requires the user to stand in front of the house, in line with (perpendicular to) one end of the wall being measured. The user takes one measurement to the far end of the wall, and a second measurement to the near end of the wall. Both measurements must be taken from exactly the same point. The length of the wall is calculated and shown on the display. This method is the first triangulation option on the Disto.
A more accurate method uses 3 measurements. The user is able to stand anywhere in front of the house, between the ends. The first measurement is taken to the left end, a second measurement is taken perpendicular to the house, directly in front of the user, and the third measurement is taken to the right end of the house. All three measurements must be taken from exactly the same point. The Disto calculcates the length of the house. This is the second triangulation option on the Disto.
The third triangulation option on the Disto allows the user to measure the height of a second story window (or similar feature) from the ground. The user measures the distance to the top of the window, then to the bottom of the window, and then the distance they are standing away from the house. Again, all three measurements must be taken from exactly the same position. The Disto returns the height of the window.
To access these features, press the triangulation key on the disto. Toggle through to select the method preferred, and follow the prompts on the screen that show the order and location of each measurement. Note: Indirect measurements are not as accurate as direct measurements, and the accuracy specs do not apply. Typical accuracy on a 40 foot indirect measurement, using proper methods is (+/-) 1 foot. Distagage recommends practicing indoors to hone your skills prior to using this method outdoors. Back to top What models have the Indirect (Triangulation, Pythagorean) capability?
The Disto A5, Disto A6, Disto A8, Disto D2, Disto D3, Disto D5, Disto D8, as well as the Disto Plus have the triangulation features. The Trimble HD150 will triangulate using the two point method. The Disto A3 and Disto A2 models do not triangulate. Older Disto Classic and Disto Pro models all feature the triangulation capability, but the Disto Lite and Tape models did not offer this feature. Back to top How does the indirect (also called Triangulation or Pythagorean) method work?
Laser measuring devices use a process called triangulation to calculate indirect measurements. Triangulation involves measuring two sides of a right triangle and mathematically determining the missing (3rd) side using the Pythagorean Theorem ? ?the sum of the squares of the two sides (shortest legs) of a right triangle is equal to the square of the hypotenuse (longest side).? For example, if you were able to position yourself at the southwest corner of a house (facing north) so that you can see the complete south side of the house (off to your right) and also at a position perfectly in line with the west side of the house, you have created a right triangle. One leg of the right triangle is the distance from you to the southwest corner of the house. The diagonal measurement from you to the southeast corner of the house is the hypotenuse (longest side). The third side (missing leg) is the distance from the southwest corner to the southeast corner of the house. With indirect measurements, the Disto takes these two measurements and mathematically determines the missing side for you; no mathematical computations are required of the operator. In this example, if the first measurement taken for the perpendicular distance from you to the southwest corner was 60 feet and the second measurement from you to the southeast corner is 100 feet, you could use the Pythagorean theorem to determine the missing leg. To mathematically compute this, you would do the following:
(60 x 60) + (Missing Leg x Missing Leg) = (100 x 100)
3,600 + (Missing Leg x Missing Leg) = 10,000
3,600 ?3,600 + (Missing Leg x Missing Leg) = 10,000 ?3600 (subtract 3600 from both sides)
(Missing Leg x Missing Leg) = 6,400
Missing Leg = 80 ft (square root of 6,400) Back to top Which Leica DISTOs offer an interface for communicating with a computer?
The Leica DISTO� A6, Disto Plus and Disto D8 utilize BLUETOOTH� technology for commuication with bluetooth compatible computers and Pocket PCs. Measurements and directions (up, down, left right, etc.) can be transferred wirelessly. The Leica DISTO� memo, Leica DISTO� pro of the 2nd generation, Leica DISTO� pro4 and Leica DISTO� pro4a have a RS232 interface for connecting directly to a computer. .
Back to top What is measuring accuracy?
Measuring accuracy is specified in accordance with ISO-recommendation ISO/R 1938-1971, with a statistical safety of 95% (2s, i.e. two-fold standard deviation). Typical measuring accuracy is based on average measuring conditions within the specified measurement range. It is not valid for special application functions and calculations, such as Pythagoras and is not valid in tracking mode (continuous tracking). Back to top How can I monitor or calibrate my Disto?
Measure an easily accessible distance of 2m to 10m with a distance measuring instrument approved by your national bureau of standards. Make 10 measurements over the same distance with the Leica DISTO�. Determine the deviation of your measurements from the actual distance and calculate the standard deviation from the results. Record the value and set the time for the next series of measurements. Repeat these check measurements regularly, especially before and after important measuring tasks. Mark the Leica DISTO� with an?inspected? sticker and protocol the entire monitoring process. Your Leica DISTO� meets the specified accuracy, if the standard deviation is equal to or less than the value stated as the typical standard deviation. A Leica DISTO� checked on the test distance works with the specified accuracy over the entire specified measuring and temperature ranges.
Back to top
|
|
|
