Introduction of Prismatic Compass

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Introduction of Prismatic Compass

The prismatic compass is an essential tool used in the field of surveying and navigation. It has been in use for centuries and has undergone several changes and improvements over time. This article will provide an in-depth introduction to the prismatic compass, its history, construction, and uses. By understanding the fundamentals of this device, readers will gain a better understanding of its role in various fields and its importance in accurately determining direction. Whether you are a beginner or an experienced surveyor, this article will serve as a useful resource for comprehending the prismatic compass.

Instruments Used in Prismatic Compass Survey

Instruments Used in Prismatic Compass Survey

A prismatic compass is a traditional surveying tool that has been used by civil engineers for many years. It is a simple instrument that uses magnetic properties to determine the direction of magnetic north, which in turn is used to measure angles and directions in a surveying project. The prismatic compass is mainly used for small scale surveys, preliminary surveys, reconnaissance surveys, and mapping purposes. It is also commonly used for basic orientation and navigation in the field.

In this article, we will discuss the various instruments that are used in prismatic compass survey and their functions.

1. The Compass Needle
The compass needle is the main part of the prismatic compass. It is made of a lightweight magnetic material, such as steel or tungsten, which is magnetized and suspended on a pivot. The needle is aligned with the north-south direction, allowing the user to determine the direction of magnetic north. The needle is marked with a red and white arrow or line to indicate the north direction.

2. The Compass Box
The compass box is a circular container made of brass or aluminum that houses the compass needle. It is marked with degrees and minutes around its circumference, providing a scale for measuring directions.

3. The Prismatic Eyepiece
The prismatic eyepiece is a small glass prism that is attached to the top of the compass box. It allows the user to view the degrees and minutes on the compass box while sighting an object in the distance.

4. The Vanes and the Sight Aiming Screen
The vanes are two metal arms attached to the compass box that are used to sight objects in the field. The sight aiming screen is a small round sight that is attached to the top of one of the vanes. It is used to align the compass with the object being sighted.

5. The Tripod
The tripod is a three-legged stand that is used to support the prismatic compass. It allows for stable and accurate readings by keeping the compass box and needle in a fixed position.

6. The Plumb Bob
The plumb bob is a weight attached to a string that is used to determine vertical angles. It is used to make sure that the compass is held horizontally for accurate readings.

7. The Adjusting Screws
The adjusting screws are used to calibrate and adjust the prismatic compass for accurate readings. They are used to make small changes to the compass box and needle to ensure precise measurements.

In conclusion, prismatic compass surveying requires a combination of these instruments to measure angles and directions accurately. It is a simple and reliable method for basic surveying work, but it is not as accurate as modern surveying instruments. Therefore, it is mainly used for small scale surveys and preliminary work. However, certain engineering projects still require the use of a prismatic compass, and it remains an important tool in a civil engineer’s toolkit.

Uses of Prismatic Compass

Uses of Prismatic Compass

A prismatic compass is a traditional navigational instrument used by civil engineers for measuring direction, the angle of inclination, and slope. It consists of a circular box housing a magnetic needle that aligns with the Earth’s magnetic field, and a prism that reflects light onto the compass card. The compass card is marked with 360 degrees, allowing for easy measurement of bearings.

The prismatic compass has been used for centuries and is still widely used by civil engineers today, despite the availability of more advanced technology. Some of the common uses of prismatic compass are:

1. Mapping: One of the main uses of prismatic compass is for mapping purposes. Civil engineers use prismatic compass to determine bearings and angles which are essential for creating accurate topographical maps. This helps in identifying the layout of land, slopes, and elevation changes, which are crucial in planning the construction of roads, buildings, and other structures.

2. Surveying: Another important application of prismatic compass is in surveying. Civil engineers use prismatic compass to measure the magnetic bearings of the site. This helps in finding the direction of the site layout and in determining the position of existing structures or boundaries. It is also used to measure the angle of inclination or slope of the land, which is necessary for construction planning.

3. Construction: Prismatic compass is an essential tool for civil engineers during the construction phase. It is used to establish the orientation and alignment of structures, such as buildings, bridges, and roads. It helps to ensure that these structures are built in the right direction and at the correct angle, in accordance with the design and specifications.

4. Mineral Exploration: Another vital use of prismatic compass is in mineral exploration. This instrument is used to determine the strike and dip of mineral deposits, which helps in locating and extracting valuable resources. It is also used to map the topography of the area to identify potential mineral deposits.

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5. Navigation: Prismatic compass is a valuable tool for navigation, especially in remote and wilderness areas. Its compact size and simplicity make it easy to use while hiking, trekking, or camping. Civil engineers use the prismatic compass to navigate through rough terrains, dense forests, and other natural obstacles to reach their construction sites.

In conclusion, the prismatic compass is an essential tool for civil engineers, especially in the fieldwork. It helps in accurate mapping, surveying, construction, mineral exploration, and navigation, making it an indispensable instrument for civil engineering projects. Despite the advent of modern technology, prismatic compass is still extensively used by civil engineers due to its reliability, durability, and simplicity.

Parts of Prismatic Compass

Parts of Prismatic Compass

A prismatic compass is a traditional surveying tool that has been used for centuries by civil engineers and other professionals to determine the direction, angle, and distance of different points on the land. It consists of several parts that work together to provide accurate measurements and readings. In this article, we will discuss the main parts of a prismatic compass and their functions.

1. Housing or Base Plate:

The housing or base plate is the main structure of the prismatic compass. It is usually made of metal or plastic and has a circular or rectangular shape. The housing is designed to protect the internal components of the compass and provide a stable platform for the compass to rest on during measurements.

2. Magnetic Needle:

The magnetic needle is the most crucial part of a prismatic compass. It is a lightweight, magnetized needle that is suspended by a pivot at its center. The needle is usually marked with N (North) and S (South) to indicate the direction of the Earth’s magnetic field. The needle always points towards the Earth’s magnetic poles, making it an essential tool for determining direction.

3. Compass Dial:

The compass dial is a circular disc that is attached to the housing of the compass. It is marked with 360 degrees and divided into four cardinal directions (North, East, South, and West). The compass dial rotates with the magnetic needle and allows the user to read angles and directions accurately.

4. Prism:

The prism is a small glass or plastic prism that is mounted at the center of the compass’s housing. The prism’s purpose is to focus the image of the compass dial onto the eyepiece, making it easier for the user to read the measurements.

5. Eyepiece:

The eyepiece is a small opening on the top of the housing that allows the user to look through and read the compass dial. The eyepiece is usually attached to a magnifying glass, which helps to increase the visibility of the compass readings.

6. Index Pin:

The index pin is a small pin or marker on the compass dial that is used to read the angle or direction of a specific point. It is usually located on the edge or rim of the compass dial and moves along with the magnetic needle.

7. Tripod Socket:

The tripod socket is a threaded opening at the base of the housing that is used to attach the compass to a tripod or other mounting device. It helps to stabilize the compass and allows for more accurate measurements.

8. Leveling Screws:

The leveling screws are small screws located under the compass housing that allows the user to adjust the compass’s level. They help to ensure that the compass is positioned and held at a perfect 90-degree angle, which is essential for accurate measurements.

9. Sight:

The sight is a small opening or notch on the top of the prism that is used to align the compass with a specific point. It is usually used in conjunction with the index pin to take accurate measurements.

10. Lid:

The lid is a protective cover that is used to protect the compass’s internal components when it is not in use. It is usually made of metal or plastic and can be easily opened and closed.

In conclusion, a prismatic compass is a simple yet powerful tool that is used by civil engineers and surveyors worldwide. Its various parts work together to provide accurate readings and measurements, making it an essential instrument for any construction project. By understanding the different components of a prismatic compass, one can make the

Least Count and Bearing

Least Count and Bearing

Least Count:
In the field of engineering, Least Count refers to the smallest measurement that can be accurately read from a measuring device. It is an important concept as it determines the precision and accuracy of any measurement. The smaller the least count value, the more precise the measurement can be. It is typically expressed in units of length, such as millimeters, inches, or centimeters.

In order to determine the least count of a measuring device, the divisions on its scale are divided by the total number of divisions on the scale. For example, if a ruler has divisions of 1 millimeter and total length of 10 centimeters, the least count would be 0.1 millimeters. This means that the smallest length that can be accurately measured using this ruler is 0.1 millimeters.

In engineering, different measuring devices have different least counts depending on their application. For instance, a vernier caliper has a least count of 0.01 millimeters, making it suitable for precise measurements in manufacturing and machining processes. On the other hand, a measuring tape used in the construction industry has a least count of 1 centimeter, which is sufficient for general measurements on site.

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Bearing:
Bearing is the direction in which a particular point or object is located relative to another point. It is used in civil engineering for various purposes, such as surveying and geotechnical engineering. The most common types of bearings used in engineering are magnetic bearing and true bearing.

Magnetic bearing is based on the magnetic north, which constantly changes its position due to variations in the Earth’s magnetic field. It is usually measured using a magnetic compass and is expressed in degrees, minutes, and seconds. This type of bearing is commonly used in navigation, geology, and archaeology.

On the other hand, true bearing is based on true north, which is the direction towards the geographic North Pole. It is considered a more accurate type of bearing as it is not affected by the Earth’s magnetic field. It is usually measured using a theodolite or a total station and is also expressed in degrees, minutes, and seconds. True bearing is commonly used in surveying and civil engineering for precise positioning and layout of structures and infrastructure.

In civil engineering, bearing is an essential aspect in the design and construction process. It helps determine the direction and orientation of structures, roads, and other elements in relation to the surrounding environment. Precise measurement of bearing is crucial to ensure the overall functionality and safety of any project.

Handling of Prismatic Compass

Handling of Prismatic Compass

A prismatic compass is a measuring instrument commonly used for surveying and navigation purposes. It consists of a magnetic needle enclosed in a glass window, with a graduated circular scale around it. The compass is designed to provide accurate measurements of direction and angle, making it a valuable tool for civil engineers in planning and design.

Here are the steps for handling a prismatic compass:

1. Familiarize yourself with the compass: Before using the prismatic compass, it is important to understand its various parts and their functions. The needle inside the compass is magnetized and points towards the earth’s north pole. The graduated circle surrounding the needle is divided into 360 degrees, with cardinal and intercardinal directions marked (N, NE, NW, etc.). The prismatic glass window allows for easy reading of both the needle and the scale.

2. Set up the compass: To use the prismatic compass, it must be placed on a stable surface, such as a tripod or a level ground. Make sure that the compass is level, and the direction of north is aligned with the needle. This can be done by rotating the compass until the needle points to the north and adjusting the tripod if needed.

3. Take a reading: Once the compass is set up, the next step is to take a reading of the direction or angle of the object you want to measure. Look through the prism window and align the object with the hairline on the compass scale. The direction of the object can be read directly from the compass scale in degrees.

4. Correct for magnetic declination: The earth’s magnetic north is not always aligned with the true north, and this difference is known as magnetic declination. It is essential to correct for declination to ensure accurate measurements. Consult the compass manual or a map to determine the magnetic declination for your location, and adjust the reading accordingly.

5. Move the compass with caution: While taking measurements, it is essential to handle the compass with care. Any sudden movement or impact can disturb the alignment of the needle and result in inaccurate readings. It is also crucial to avoid placing the compass near any magnetic objects, such as smartphones, metal objects, or power lines, as they can interfere with the compass’s magnetic field.

6. Store the compass properly: After using the prismatic compass, it is essential to store it correctly. The magnetic needle of the compass is sensitive and can lose its magnetization if stored near magnetic objects. The compass should be kept in a dry and dust-free place, away from any heat or moisture.

In conclusion, prismatic compasses are valuable tools for civil engineers, providing accurate and reliable measurements of direction and angle. By following the steps mentioned above, one can handle a prismatic compass with ease and ensure precise measurements in various surveying and navigation tasks.

Adjustment of Prismatic Compass

Adjustment of Prismatic Compass

Adjustment of Prismatic Compass
A prismatic compass is an instrument used by civil engineers for measuring the direction and angle of a line in the field. It consists of a circular compass and a sighting mechanism with a prism on top, allowing the user to accurately aim and read the direction of the line. As with any measuring instruments, it is essential to ensure that a prismatic compass is properly adjusted before using it for any surveying work. In this article, we will discuss the various aspects of adjusting a prismatic compass.

Types of Adjustment:
There are two types of adjustments that are usually performed on a prismatic compass: permanent adjustment and temporary adjustment. Permanent adjustment involves aligning the compass with the magnetic meridian, while temporary adjustment deals with eliminating any errors due to inclinations or eccentricity in the compass needle. Both adjustments are important and must be done correctly for accurate readings.

Permanent Adjustment:
Permanent adjustment is done to align the compass with the magnetic meridian, which is the direction of the Earth’s magnetic field. This process is essential for accurate and consistent readings. Follow the steps below for permanent adjustment:

Step 1: Place the compass on a level surface and make sure it is kept away from any magnetic or metallic objects.

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Step 2: Set the index ring to zero degrees by aligning it with the north-south marked line on the case of the compass.

Step 3: Rotate the compass in the horizontal plane until the magnetic needle comes to rest in the north-south position.

Step 4: Make a mark on the ground at the base of the compass. This is known as the reference mark.

Step 5: Rotate the compass by 180 degrees, so the index ring now points to 180 degrees and make another mark on the ground at the base of the compass. This is known as the reverse mark.

Step 6: Find the mid-point between the two marks and place a stake at that point. This is known as the mean point.

Step 7: Move the compass towards the mean point. As you do this, the magnetic needle should remain in the north-south position. If it doesn’t, adjust the index ring until it does.

Step 8: When the compass is moved to the mean point, the reference mark, the reverse mark, and the mean point should be in a straight line. If they are not, the compass needs to be adjusted further.

Step 9: Repeat the process until the reference mark, the reverse mark, and the mean point are in a straight line.

Temporary Adjustment:
Temporary adjustment is usually done after the permanent adjustment process and is necessary to eliminate any errors due to inclinations or eccentricity in the compass. It is a less precise adjustment and is done before taking each reading. Follow the steps below for temporary adjustment:

Step 1: Place the compass on a level surface and make sure it is kept away from any magnetic or metallic objects.

Step 2: Set the index ring to 360 degrees by aligning it with the north-south marked line on the case of the compass.

Step 3: Rotate the compass in the horizontal plane until the magnetic needle comes to rest in the north-south position.

Step 4: If the magnetic needle does not point to the reference mark, rotate the compass until the needle points to the reference mark.

Step 5: Take the reading by looking through the sighting mechanism.

Step 6: Reverse the compass and take another

Sources of Errors in Prismatic Compass

Prismatic compass is a type of surveying instrument used to measure horizontal angles. It consists of a magnetic needle or attraction needle, a prism, a graduated circle, and a sighting mechanism. It is widely used in land surveys, construction projects, and various other applications.

However, like any other instrument, prismatic compasses are prone to errors. These errors can occur due to various factors, and it is essential for a civil engineer to understand these sources of errors to obtain accurate measurements.

1. Variations in magnetic declination: The magnetic needle of a prismatic compass is affected by the Earth’s magnetic field. However, the strength and direction of this field can change depending on the location and time. This leads to variations in magnetic declination, which can cause errors in the readings of the compass. Civil engineers must take into account the local magnetic declination and make necessary adjustments to ensure accurate measurements.

2. Magnetic interference: The prismatic compass should be kept away from any magnetic objects, such as steel rods, pipes, or nearby electrical equipment. These objects can create magnetic fields that can interfere with the compass needle and affect its readings. It is crucial to keep the compass away from such sources of magnetic interference to avoid errors.

3. Inclination: Prismatic compasses are designed to measure horizontal angles. Therefore, any inclination or tilting of the compass can lead to errors in the readings. It is essential to keep the compass leveled and perpendicular to the ground to obtain accurate measurements.

4. Parallax error: Parallax error is a common source of error in prismatic compass readings. This error occurs when the user’s eye is not at the correct position while reading the compass. It leads to a shift in the apparent position of the needle, resulting in inaccurate measurements. Proper care and training must be given to the surveyors to avoid this error.

5. Graduation errors: The graduated circle of a prismatic compass is used to measure angles. However, if the circle is not accurately graduated, it can lead to errors in the readings. These errors can be caused by manufacturing defects or wear and tear of the instrument. Regular calibration and maintenance of the instrument can help minimize the impact of these errors.

6. Human error: The accuracy of prismatic compass readings is highly dependent on the user. Any misalignment, misinterpretation, or incorrect handling of the instrument by the operator can result in errors. Therefore, proper training and experience are crucial to obtain accurate readings.

In conclusion, prismatic compass errors can arise due to a multitude of factors. It is essential to identify and understand these sources of errors to obtain precise measurements. Regular maintenance and calibration of the instrument, along with proper training of the surveyors, can help minimize the impact of these errors on surveying accuracy.

Conclusion

In conclusion, the prismatic compass has revolutionized the field of navigation and surveying. Its ability to measure bearings, angles, and directions accurately has made it an essential tool for various industries such as construction, mining, and military. The compact and lightweight design of the prismatic compass has made it a convenient and reliable device for on-field use. With advancements in modern technology, the prismatic compass has been further improved with features such as magnifying lenses, luminous dials, and built-in clinometers. Overall, the introduction of prismatic compass has greatly aided in the precision and efficiency of various navigation and surveying tasks, making it an invaluable asset for professionals in these industries.

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