Short Answer:

Instrumental errors in surveying are caused by imperfections, poor calibration, or misuse of instruments like levels, total stations, or tapes. These errors can lead to incorrect readings, which affect distances, angles, or elevations in the survey results.

The impact of instrumental errors can be serious—causing inaccurate maps, wrong construction layouts, and increased project costs. These errors must be minimized by using well-maintained, properly adjusted, and regularly checked instruments to ensure correct and reliable measurements in any civil engineering project.

Detailed Explanation:

Impact of instrumental errors in surveying

In surveying, instruments such as total stations, levels, theodolites, compasses, and measuring tapes are used to collect accurate data. However, if these tools are not in proper condition or used incorrectly, they can produce instrumental errors. These errors are systematic in nature, meaning they often follow a fixed pattern and affect all measurements in a predictable way.

Instrumental errors may arise from design defects, wear and tear, poor adjustment, or miscalibration. If not noticed or corrected, these errors can affect the entire survey, leading to incorrect outcomes.

Common causes of instrumental errors

Poor calibration – Instruments that are not calibrated may give slightly wrong readings every time. For example, a level bubble not set correctly will result in incorrect height measurements.
Manufacturing defects – Some instruments may have minor faults from the factory, such as a bent tape or a misaligned crosshair.
Wear and tear – Over time, instruments like measuring tapes can stretch or get damaged, and total stations may lose their alignment.
Improper use – Incorrect setup, like not leveling a theodolite or using a tape at an angle, leads to measurement errors.
Temperature effect – Steel tapes or instruments can expand or contract due to heat or cold, which affects the accuracy of readings.

Impact of these errors on surveying work

Wrong positioning: If distance or angle measurements are off, structures may be built in the wrong location.
Misalignment: In road or pipeline projects, small errors in angles or bearings can lead to misalignment over long distances.
Inaccurate elevations: Errors in leveling instruments can cause incorrect slopes, affecting drainage or foundation levels.
Poor quality maps or layouts: Instrumental errors result in incorrect plotting of points, leading to faulty designs or maps.
Increased rework: Errors often mean redoing surveys or correcting construction work, which delays the project and increases costs.
Safety issues: In serious cases, wrong measurements may lead to weak structures or unsafe conditions on-site.

How to prevent or reduce instrumental errors

Regular calibration: Instruments must be checked and calibrated before use to maintain accuracy.
Proper maintenance: Equipment should be cleaned, stored safely, and protected from dust, moisture, and damage.
Careful setup: Ensure the instrument is placed properly, leveled, and checked before taking any reading.
Use of standard tools: Certified and verified equipment helps reduce the chances of errors.
Routine checks and testing: Regular testing for known values can help verify the instrument’s accuracy.

Surveyors should always double-check instruments and perform field checks like back-sighting, double measurement, or reciprocal leveling to identify and correct any instrumental issues.

Conclusion:

Instrumental errors in surveying can have a strong negative impact on the accuracy of measurements, layout plans, and construction results. These errors arise from faults in the equipment or incorrect use. By understanding the causes and taking preventive steps like calibration and maintenance, surveyors can greatly reduce the effect of instrumental errors and ensure reliable, accurate survey data for successful project execution.