A laser rangefinder is an indispensable assistant for quickly and accurately measuring the length and area of rooms, and the distances between individual objects. Let’s understand the principle of operation of the device, its main characteristics and functions that you should pay attention to when purchasing.
Types of rangefinders
All rangefinders are divided into two types – ultrasonic and laser.
Ultrasonic rangefinders use the principle of echolocation – the property of a sound wave to be reflected from various objects. The transmitter of these devices produces a sound wave in the frequency range inaudible to the human ear – 40–45 kHz.
The sound wave reflected from the measurement object is captured by the rangefinder’s sensitive microphone. The rangefinder controller calculates the time that has passed from the moment the ultrasonic wave is generated to its reception and, taking into account the known value of the speed of sound, calculates the measured distance.
A laser rangefinder uses a laser beam with a specific wavelength to measure distances.
The laser beam travels at a much higher speed and is less susceptible to attenuation. Accordingly, the measurement range of laser rangefinders is much greater than that of ultrasonic ones. Therefore, most of the devices used today are laser rangefinders.
Operating principle of a laser rangefinder
According to the principle of operation, laser rangefinders are divided into pulse and phase.
In pulse rangefinders, a high-power pulsed laser sends a short-lasting beam at the target. The reflected beam is caught by the device’s radiation detector, and an ultra-precise timer measures the time it takes the laser beam to travel to the target and back. Knowing the speed of light and the measured time, the device calculates the distance to the target.
The high power of a pulsed laser and the high cost of a timer limit their use. They are mainly used in military scopes.
Unlike pulse lasers, safer low-power lasers of phase rangefinders operate continuously. The phase method used in them is based on determining the phase difference between the sent and received modulated signals.
The signal reflected from the target is received by the photodetector of the device, and its phase is compared with the phase of the laser reference signal. Then the rangefinder changes the modulation frequency and repeats the measurement. Knowing the magnitude of phase shifts, the speed of light and the laser modulation frequency, the device processor solves a system of linear equations and calculates the distance to the target.
The color of a laser beam is determined by its wavelength. Two types of lasers are commonly used: green with a wavelength of 515–535 nm and red with a wavelength of 620–690 nm. The human eye distinguishes these colors best. However, the green spot of the laser beam is often lost in the background surrounding the measurement target. Therefore, most modern rangefinders are equipped with red lasers.
In terms of safety level, most lasers used in entry-level and mid-level rangefinders belong to the second safety class. The low power of their laser beam can damage the retina only when directly exposed to it for a long time. Which, in principle, should not be done at all.
The maximum measuring distance is the main characteristic of the rangefinder. It defines the maximum distance available for indoor measurements and distances between buildings and other objects.
The maximum range directly depends on the power of the laser emitter and the sensitivity of the rangefinder photodetector. To measure longer distances, more powerful radiation and better photodetector optics are required.
The maximum range of devices determines their areas of application.
The maximum measuring distance range of the most popular models is 21–40 and 41–100 meters. Simple entry-level models have a maximum range of up to 20 meters. The most powerful laser rangefinders can measure distances of up to 500 meters or more.
The minimum measurement distance is the closest distance from the rangefinder to the object being measured. The laser beam moves from the emitter to the target at a very small angle, and, having been reflected from the target, must hit the photodetector lens. At very short distances, the angle of reflection from the target is not enough – the beam simply does not hit the photodetector lens.
Minimizing the dimensions of the emitter and photodetector made it possible to bring their axes closer together. For the vast majority of modern laser rangefinders, this figure does not exceed 10 centimeters.
Error is the deviation in the accuracy of measurements of the distance to an object from the actual value. The smaller the measurement error of the rangefinder, the more accurate the measurement will be. Since phase rangefinders operate with very small phase shift values, their error is very small. For most modern devices it is 1.5-3 mm.
Number of points to start from. The reference point for rangefinders is the place from which the device begins measuring.
By default, the reference point for all laser rangefinders is on the back of the device. The device automatically adds the length of its body to the measured distance.
A very small number of rangefinders have one reference point. Many more instruments have two reference points. The second is on the front of the rangefinder.
Rangefinders that can be mounted on a tripod have a third reference point – from the mounting point on the tripod. In this case, the device automatically adds the distance from the front to the mounting point to the measurement result.
Models with a folding (retractable) bracket have a fourth reference point – at the end of the bracket folded 180°. The bracket allows you to measure distances from corners where the entire rangefinder body does not fit.
The bracket tilted 90° (for measuring from external corners) duplicates the first reference point.
Units. Laser rangefinders display measurement results in both the metric (meter, centimeter) system and the inch (inch, foot, yard) system. Select models use both metric systems.
Storage of measurements in the built-in memory. The capabilities of rangefinders are not limited to displaying the measurement result on the display. Previous measurement results are stored in the internal memory of the device.
Number of saved measurements. Most rangefinders store up to 20 measurements. If necessary, you can choose a model for yourself that stores up to 50 measurements.
Display backlight. The presence of a backlight on the display built into the device makes it more convenient to use the device at night and in poor lighting conditions.
Built-in sight. With a built-in sight, many issues related to determining the measuring point at long distances are resolved. Some rangefinders are equipped with a video camera that displays an image of the object being measured. The device measures to the point at which the crosshair is aimed, even if the laser point is not visible (for example, in bright sunlight).
To more accurately aim the sight at the measuring point, the camera allows you to zoom in on the image, usually up to three times.
Possibility of installation on a tripod. For more accurate measurements of large distances, it is necessary to firmly fix the rangefinder. For this purpose, the body of many devices has a mounting point for a tripod. As a rule, the mount is universal, which allows the use of various types and models of tripods.
Liquid level. The water level allows you to position the rangefinder on a tripod as level as possible. The need to use a water level arises during engineering and construction work that requires high measurement accuracy.
Type of food. A rangefinder is a self-contained measuring device. The main types of power supply for rangefinders are from batteries or from rechargeable batteries. For large volumes of on-site measurements, a spare set of batteries is preferable to built-in batteries – charging the batteries requires time and a source of electricity.
Sound indication is a very useful rangefinder option that can inform the user about the operating modes of the device and the degree of battery discharge. Sound indication is necessary in marking mode when approaching the planned point.
Protection class – type of rangefinder protection applied. Most devices have a protection class of IP54, which means that dust entering the housing does not affect the operation of the device, and its housing itself only protects the device from splashes and drops of water.
Point to point/distance
With this function you can easily measure, for example, the length and width of objects on the roof. After aiming and measuring the start and end points of the distance to be measured, the display will show the desired result. The function is available on rangefinders equipped with an inclinometer and the ability to mount on a tripod.
The main function of the rangefinder is realized by pointing the laser beam at the measurement point and pressing the single (single/continuous) measurement key.
The area of the floor, walls or ceiling is determined using two dimensions – length and width. The result is calculated automatically and displayed. After the third measurement – height, the device will calculate the volume of the room.
Calculation using the Pythagorean theorem
Calculations using the Pythagorean theorem are available in four options.
In the first option , the hypotenuse c of the hypothetical triangle and the nearest leg a are determined . The required height ( leg b ) is calculated automatically.
In the second option, the hypotenuse c is calculated . We rarely use this option, since the length of the hypotenuse can be determined by direct measurement. Measurement in this option is used when there are objects that prevent direct measurement.
In the third option, it is enough to measure the distances from 1 , a , from 2 (hypotenuse of the large triangle, common leg, hypotenuse of the small triangle). And the device will calculate the desired result as the difference between the calculated legs b 1 and b 2 .
In the fourth option, it is enough to measure the distances from 1 , from 2 and a (the hypotenuses of the triangles and the common leg). The device will give the desired result (the sum of the calculated legs b 1 and b 2 ).
Changing the reference point
If there are two or more reference points, you can select the most appropriate point for each specific measurement.
Measuring minimum and maximum
By slightly swaying the device, you can determine the diagonal of the room (maximum distance) and the perpendicular to the wall (minimum distance).
Another name for the function is Triangle and Room Angle Function . It is used when calculating the area of polygonal rooms and areas.
By dividing the room into imaginary right triangles, using three measurements you can determine their areas and then add them up. In this case, the device will calculate and display the angle of the room.
If it is not possible to achieve a normal result by direct measurement, one of the indirect measurement methods available on the rangefinder is used. The function is available on rangefinders equipped with an inclinometer.
This function is used when horizontal aiming is obstructed by any obstacle. When measuring the hypotenuse AB, the length of the leg AC is calculated automatically taking into account a certain angle of inclination of the device.
Using this function, the height of buildings or trees that do not have suitable landmarks is determined. When measuring the distance to the top and bottom points of an object, the device will automatically determine its height. The function is available on rangefinders equipped with an inclinometer.
Continuous measurement function
This function is usually combined with the Markup function .
The function can be used to find the required distance from a particular object. To activate the function, you must switch the rangefinder from single to continuous measurement mode.
The function allows you to add and subtract the results of several measurements. An example of a subtraction function is to compare ceiling heights in different corners of a room.
The function allows you to calculate the area of two or more walls of a room. Often used by painters to determine consumables during repairs.
If you plan to use the rangefinder only indoors, then it will be enough to purchase a device with a maximum measuring distance from 21 to 40 meters .
When measuring long distances, the right choice would be to purchase a rangefinder with a long range and the ability to mount on a tripod and a built-in sight .
For measurements indoors or in an area with large interference for measurements, you will need a rangefinder with an inclinometer function and indirect measurement .
Laser rangefinder or regular tape measure? What is the best way to measure distance? Why are they so convenient in measurements, how to use them in practice? This is discussed in a short video.