Introduction to Electronic Distance Measuring Instruments
Electronic distance measuring instruments (EDMIs) are surveying tools used to measure the distance between two points electronically via the use of electromagnetic waves. EDM is a method of determining the length between two points using the phase changes that occur with the propagation of electromagnetic energy waves.
Types of Distance Measurement Techniques
There are three main methods of measuring distance between two points: Direct Distance Measurement (DDM), Optical Distance Measurement (ODM) and Electromagnetic Distance Measurement (EDM). DDM is typically done by chaining or taping, while ODM is achieved through tacheometry, horizontal subtense method or telemetric method with optical wedge attachments. EDM has an accuracy of 1 in 105 and can measure distances of up to 100km.
Spectrum of an Electromagnetic Wave
Sunlight or artificially generated electromagnetic wave consists of waves of different lengths, forming a spectrum of an electromagnetic wave. This spectrum can be seen below.
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Distance Measurement Using Microwaves, Infrared Waves and Visible Light Waves
The use of microwaves, infrared waves, and visible light waves for distance measurement is quite common. In Electronic Distance Measurement (EDM) instruments, these waves are generated, modulated, and then propagated. Upon reflection at the point where the distance is to be measured from the instrument station, the waves are then received again by the instrument.
Measuring Time for Distance Estimation
Measuring the time taken for the waves to travel the two-times distance can be used to calculate the distance. However, the time taken is generally too short to measure accurately.
Phase Difference Method
The improved techniques used in EDM instruments employ the phase difference method. In this method, the number of completed waves and incomplete waves are measured. Knowing the length of the wave, distances are then calculated.
Built up microprocessors provided in the instrument calculate the distances and display it by liquid crystal display (LCD).
Origin of Electronic Distance Measurement
History of Electronic Distance Measurement
The use of Electronic Distance Measurement (EDM) devices to measure distances has been around since 1948 when the first instrument, called a geodimeter, was developed in Sweden. This instrument used modulated light beams to measure distances. In 1957, Africa developed the second instrument for EDM, called a tellurometer, which utilized modulated microwaves.
Advancement of Electronic Distance Measurement Technology
Since then, the technology of EDM has advanced drastically. Modern EDMs now display distances in digital form, and many contain microcomputers that can calculate the horizontal and vertical distances (DX and DY) as well as the sloped distance (DH). Some EDM devices are now incorporated into theodolites, which are called total stations or electronic tacheometers. These instruments can record both distances and angles simultaneously.
Benefits of Electronic Distance Measurement
The use of EDM devices has many benefits, such as increased accuracy and efficiency in distance measurement. It also reduces the need for manual surveying, allowing surveyors to cover larger areas in a shorter amount of time. EDM devices are also more cost-effective than traditional surveying equipment, making them a popular choice for surveyors.
Types of Electronic Distance Measurement Instrument
EDM instruments are classified based on the type of carrier wave as
- Microwave instruments
- Infrared wave instruments
- Light wave instruments.
Microwave Instruments
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These instruments make use of microwaves.
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Instruments Using Microwaves for Measuring Distances
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Such instruments were invented as early as 1950 in South Africa by Dr. T.L. Wadley and named them as Tellurometers.
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History of Tellurometers – Invention of Microwave Measurement Instruments
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The instrument needs only 12 to 24 V batteries. Hence they are light and highly portable.
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Portability and Easy Power Supply of Tellurometers
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Tellurometers can be used in day as well as in night. The range of these instruments is up to 100 km.
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Day and Night Usage of Tellurometers with Range of Up to 100 km
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It consists of two identical units. One unit is used as master unit and the other as remote unit.
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Design and Usage of Master and Remote Unit of Tellurometers
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Just by pressing a button, a master unit can be converted into a remote unit and a remote unit into a master unit.
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Converting Master and Remote Units of Tellurometers with a Button
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It needs two skilled persons to operate. A speech facility is provided to each operator to interact during measurements.
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Operation of Tellurometers with Speech Facility for Operators
Infrared Wave Instruments
Introduction to Distance Measuring Instruments
Distance Measuring Instruments (DMIs) are devices that use amplitude modulated infrared waves to measure the distance between two points. The accuracy achieved with these instruments is ± 10 mm and the range is up to 3 km. These instruments are light and economical, making them ideal for civil engineering works. Popular DMI brands include DISTOMAT DI 1000 and DISTOMAT DI 55.
How DMIs Work
DMIs work by using an optical prism reflector at the end of the line to be measured. This is then paired with a theodolite, which is a precision instrument that measures angles in the horizontal and vertical planes. The instrument then sends out a beam of modulated infrared waves, which bounces off the prism reflector and back to the instrument, providing a precise measurement of the distance between the two points.
Benefits of DMIs
DMIs are very accurate, with a precision of ± 10 mm, and they are also extremely lightweight and economical, making them ideal for civil engineering work. They can also measure distances of up to 3 km, making them suitable for a wide range of uses.
Conclusion
Distance Measuring Instruments are a versatile and accurate tool for measuring distances between
3. Visible Light Wave Instruments
What is Geodimeter?
Geodimeter is an instrument that relies on the propagation of modulated light waves to measure distances. It was developed in Sweden and is used in civil engineering projects. It has a range of up to 2.5 km at night, and up to 3 km during the day. The accuracy of the instrument varies from 0.5 mm to 5 mm/km.
How Does Geodimeter Work?
Geodimeter works by using modulated light waves to measure distances. The instrument works by sending out modulated light waves and then measuring the time it takes for the waves to return. From this, the distance between two points can be calculated.
Benefits of Geodimeter
Geodimeter provides accurate and reliable measurements of distances. Its range is up to 2.5 km at night and up to 3 km during the day. It has an accuracy of 0.5 mm to 5 mm/km, making it a good choice for civil engineering projects. Additionally, it is easy to use and cost-effective.
Operations of Electronic Distance Measurement Instruments
Understanding the Principle Behind EDM
Electromagnetic waves propagate through the atmosphere using a specific equation. This equation, known as the Electromagnetic Wave Equation, is used to determine the direction and intensity of the waves. By understanding the principles of this equation, one can work with EDM more effectively and accurately.
The Electromagnetic Wave Equation
The Electromagnetic Wave Equation is used to determine the direction and intensity of electromagnetic waves as they travel through the atmosphere. It is based on the principles of electricity and magnetism, which are essential for understanding how EDM works. The equation takes into account the effects of gravity, air temperature, and wind speed, among other factors, in order to accurately calculate the direction and intensity of the waves.
Explaining the Significance of EDM
EDM is an essential tool to accurately measure distances, angles, and other properties in a variety of contexts. It is commonly used in surveying and navigation, as well as in architecture and engineering. By understanding the principles of the Electromagnetic Wave Equation, one can work with EDM more effectively and obtain accurate, reliable results.
The Propagation of Electromagnetic Waves
Electromagnetic energy is propagated in the form of waves, and the velocity of these waves can be expressed using the equation “v = f x Wavelength”, where ‘v’ is the velocity of electromagnetic energy in meters per second (m/sec), ‘f’ is the modulated frequency in hertz (Hz), and ‘Wavelength’ is the wavelength measured in meters. Generally, these waves can be represented as a sine wave, as shown in the accompanying figure.
Phase of Wave – A Convenient Measurement for EDM
The phase of a wave is a very convenient method for measuring a small fraction of wavelength during EDM (electronic distance measurement). The points A, B, C, etc. represent various phase points.
- Introduction to the Survey Line:
AB is a survey line of length D that has been measured using EDM equipment. - Setup of the Equipment:
The equipment consists of a transmitter placed at point A, a receiver placed at point B and a timer. - Measurement Process:
When the electromagnetic wave is transmitted from point A, the timer at point B starts and stops when the incoming wave is received. This enables us to determine the transit time of the wave from A to B.
Solution to the Problem of Difficulty in Starting the Timer at B
In order to measure the distance between two points A and B, the transit time and velocity of the object must be known. From this information, the distance can be calculated. However, the problem arises when starting the timer at point B. In order to overcome this, a reflector can be placed at point B instead of a receiver, as shown in the figure below.
Solving the Timer Issue at B
The transit time can be used to measure the distance between two points, A and B, given the known velocity. However, difficulty arises when trying to start the timer at B. To solve this problem, a reflector can be placed instead of a receiver at point B. This will allow the timer to be started at point A and the signal will be reflected back to point B, allowing for the calculation of the distance between the two points.
Fig. Transit measurement arrangement with the help of a EDM and a reflector
Measurement of distance with EDM and a Reflector
Distance Measurement Using Out-of-Phase Signals
When two waves are sent from point A and reflected back from point B, the received signal can be out of phase by a measure of EDM (Electronic Distance Measurement). By measuring the phase difference between the transmitted and received signals, the equivalent distance can be determined. This technique is commonly used in surveying and navigation as it allows for the calculation of distances without any physical contact between the two points.
Advantages of EDM Distance Measurement
EDM distance measurement has several advantages over traditional methods of measuring distance. It is more accurate, cost-effective, and faster than other methods such as triangulation or optical distance measurement. Additionally, EDM is not affected by weather conditions as other methods may be.
Calculating Equivalent Distance from Out-of-Phase Signals
In order to calculate the equivalent distance from out-of-phase signals, the phase difference between the transmitted and received signals must be measured. This is typically done using a phase-shift measurement device, such as an oscilloscope. Once the phase difference is known, the equivalent distance can be calculated using a simple formula.
Conclusion
EDM distance measurement is a useful technique for measuring distances without physical contact between the two points. By measuring the phase difference between transmitted and received signals, the equivalent distance can be calculated. This method is accurate, cost-effective, and fast, making it a popular choice for many surveying and navigation applications.
Thus, the distance
where n is the integral number of wavelength,
in the double path
Error in Electronic Distance Measurement Instruments
Personal Errors
Errors in Initial Setup of EDMs and Reflectors
The accuracy of EDMs (electronic distance meters) and reflectors over the preferred stations is of utmost importance to ensure that all measurements are taken accurately. Inaccuracies in the initial setup of EDMs and reflectors can cause errors in the instrument and reflector measurements, leading to inaccurate data.
Errors in Instrument and Reflector Measurements
Instrument and reflector measurements are essential for accurately measuring distances in EDM and reflector surveys. Errors in these measurements can occur due to incorrect initial setup of EDMs and reflectors, improper calibration of the instruments, and other factors.
Errors in Atmospheric Pressure and Temperature Determination
Atmospheric pressure and temperature play a major role in the accuracy of EDM and reflector measurements. Errors in their determination can lead to inaccurate measurements and data. To ensure accuracy, atmospheric pressure and temperature must be frequently monitored and correctly measured.
Instrumental Errors
Calibration Errors:
What are the Chances of Getting Maladjusted Time Generating Frequent Errors?
Calibration errors can cause frequent maladjustments in time and lead to errors. Understanding the chances of calibration errors occurring and how to prevent them is essential for accurate timekeeping.
Errors Shown by the Reflectors
Understanding the Errors Shown by Reflectors for Accurate Timekeeping
Accurate timekeeping requires the use of reflectors to detect errors that can occur from calibration. Understanding the types of errors that reflectors can detect is important for maintaining the accuracy of timekeeping systems.
Natural Errors
- Atmospheric Variations Impacting EDM Instruments
- The use of EDM instruments is becoming increasingly popular due to their speed and accuracy in measurement. However, they can be more susceptible to atmospheric variations such as changes in temperature, pressure, and humidity. This can cause multiple refractions of the signals, making it more difficult to accurately measure distances. Understanding how the atmosphere can influence EDM instruments can help to improve the accuracy of their measurements.
- Advantages of Using EDM Instruments
- The main advantage of using EDM instruments is the speed and accuracy of their measurements. By automatically overcoming several obstacles that can be encountered when chaining, EDM instruments can quickly provide precise measurements that are reliable. This makes them an ideal choice for many surveying and mapping applications.