Annual inspection of laboratory instruments by professional testing companies outside the school

Annual inspection of laboratory instruments by professional testing companies outside the school

Calibration Procedure for Total Station

1、 Purpose

Standardize the calibration work of total stations to ensure the accuracy and reliability of total station measurement data, meet the requirements for measurement accuracy in fields such as engineering surveying and topographic mapping, and ensure that the total station measurement results meet relevant standards and practical operational needs.

2、 Scope of application

Suitable for calibration of various optical and electronic total stations, including but not limited to total stations with angle measurement accuracy of 1 ", 2", 5 "levels, ranging accuracy of (1+1ppm × D) mm, (2+2ppm × D) mm, and other different precision specifications, covering newly purchased, in use, and repaired total stations.

3、 Reference standards

JJG 100-2003: "Verification Regulations for Total Station Electronic Speed Measuring Instruments" specifies the metrological performance requirements, general technical requirements, and control of measuring instruments for total stations, providing technical basis and operational specifications for calibration work.

2. GB/T 17159-2013: "Electronic Total Stations for Engineering Surveying" specifies the terminology and definitions, product classification, technical requirements, test methods, inspection rules, as well as requirements for marking, packaging, transportation, and storage of total stations.

4、 Terminology and definitions

1. Total Station: A high-tech measuring instrument that integrates optics, mechanics, and electronics. It can simultaneously measure angles (horizontal angle, vertical angle) and distances (slant distance, horizontal distance, elevation difference), and can calculate the three-dimensional coordinates of measurement points through internal programs.

2. Mean square error of angle measurement: an indicator that measures the accuracy of angle measurement with a total station. It refers to the mean square error of the observed value of a certain angle after multiple observations under the same observation conditions.

3. Mean square error in distance measurement: a parameter that reflects the accuracy of total station distance measurement, referring to the mean square error of the measured value after multiple measurements of a certain distance under the same observation conditions.

4. Constant addition: The fixed error of the total station ranging system is independent of the length of the measured distance.

5. Multiplying constant: The error coefficient proportional to the measured distance, measured in ppm (parts per million).

Annual inspection of laboratory instruments by professional testing companies outside the school

5、 Measurement characteristics

1. Angle measurement accuracy: The mean square error of the total station's angle measurement should not exceed its nominal accuracy. For example, for a total station with a nominal accuracy of 2 ", the mean square error of angle measurement should not exceed 2".

2. Distance measurement accuracy: The distance measurement error should follow the formula mD=\ \ pm (A+B × D), where mD is the distance measurement error, A is the fixed error (unit: mm), B is the proportional error coefficient (unit: ppm), and D is the distance measurement length (unit: km). For example, if the distance measurement accuracy of a total station is (2+2ppm × D) mm, then when the distance measurement length D=1km, the distance measurement error mD=\ \ pm (2+2 × 1) mm=\ \ pm 4mm.

3. Adding and multiplying constants: The error range of adding constants should be within the specified allowable error, generally ± (3-5) mm; The error of multiplying a constant should not exceed ± (1-2) ppm of its nominal value.

6、 Calibration conditions

1. Environmental conditions

• Temperature: (20 ± 5) ℃, with a temperature change rate not exceeding 1 ℃ per hour. Excessive or insufficient temperature, as well as drastic changes in temperature, can affect the refractive index of optical components inside the total station, the size of mechanical components, and the performance of electronic components, resulting in measurement errors.

Relative humidity: 35% -75%. Exceeding the humidity range may cause condensation inside the instrument, leading to mold growth in optical components, short circuits in circuits, and other issues that affect the normal operation of the instrument.

• Atmospheric pressure: (86-106) kPa. The change in atmospheric pressure can affect the density of air, which in turn affects the speed of light propagation in the air and affects the accuracy of distance measurement.

• Venue: The calibration site should be flat, solid, and free from obvious sources of vibration and electromagnetic interference. The site should have sufficient space to meet the calibration requirements of total station ranging and angle measurement. Generally, the length of the ranging calibration site should not be less than half of the maximum measuring range of the total station.

2. Calibration equipment

Standard baseline field: composed of several control points with known precise distances, with a distance accuracy better than one-third of the distance accuracy of the calibrated total station. Used for calibrating the distance measurement function of the total station, the distance measurement error of the total station is determined by comparing it with the distance values measured by the total station.

Multi tooth indexing table: The indexing accuracy is better than one-third of the angle measurement accuracy of the calibrated total station. If the angle measurement accuracy of the calibrated total station is 2 ", the indexing accuracy of the multi tooth indexing table should be better than 0.67". Used for calibrating the angle measurement function of the total station, by measuring the angle value of the multi tooth indexing table and comparing it with the angle value measured by the total station, the angle measurement error of the total station is calculated.

Standard reflective prism: High reflection efficiency, good stability, with known constants and accuracy that meets calibration requirements. As a reflection target during distance measurement calibration, it is used in conjunction with a total station.

Level: With an accuracy not lower than DS3 level, it is used to adjust the levelness of the calibration site and the installation base of the total station, ensuring that the total station is in a horizontal state and reducing measurement errors caused by instrument tilt.

• Temperature gauge and pressure gauge: The accuracy meets the measurement requirements of the calibration environment parameters, used to measure the temperature and atmospheric pressure of the calibration environment, in order to perform meteorological correction on the total station measurement data.

7、 Preparation before calibration

1. Appearance inspection

Check if the total station casing is damaged or deformed, if the display screen is damaged or abnormal, if the buttons can be operated normally, and if the battery compartment is clean and free of corrosion.

Check the telescope objective and eyepiece for dust, oil stains, scratches, smooth focusing, and clear crosshairs.

Confirm whether the operating components of the instrument, such as the foot screw, horizontal brake and micro screw, vertical brake and micro screw, are flexible and effective, and whether there is any looseness or jamming.

Check if the communication interface of the instrument is intact, if the connecting cables are damaged or aged, and if the plugs and sockets are in good contact.

2. Function check

Connect the power, turn on the total station, and check if the instrument can start normally and if all functional menus can be accessed normally.

Perform simple self testing functions, such as battery level detection, internal parameter checking of the instrument, etc., to check for error message prompts.

Test the angle measurement function of the total station, rotate the telescope, and observe whether the displayed values of horizontal and vertical angles change continuously and accurately.

Test the distance measurement function, measure the distance of known distance targets within a short distance (such as 5-10m), check whether the measurement results are reasonable, and whether the distance measurement time is normal.

3. Instrument placement: Place the total station on a stable tripod and adjust the height of the tripod legs using a level to make the base of the total station roughly horizontal. Accurately adjust the levelness of the total station through the foot screw to center the leveling bubble and ensure that the instrument is in a horizontal state. During the installation of the instrument, collision and vibration should be avoided.

4. Parameter setting: Set the corresponding meteorological correction parameters in the total station based on the temperature, atmospheric pressure, and other parameters of the calibration environment. At the same time, set the measurement mode of the total station to standard measurement mode, such as horizontal/vertical angle measurement mode for angle measurement and oblique distance measurement mode for distance measurement.

8、 Calibration Items and Methods

（1） Horizontal angle measurement error calibration

1. Connection and setting: Place the total station at the center of the multi tooth indexing table, accurately align and level it. Set the initial value for horizontal angle measurement in the total station to 0 ° 00 ′ 00 ″.

2. Measurement operation: Rotate the multi tooth indexing table and set the angles to 0 °, 30 °, 60 °, 90 °, 120 °, 150 °, 180 °, 210 °, 240 °, 270 °, 300 °, and 330 ° in sequence. Measure each angle position three times with a total station mirror (on the left side of the disc) and record the horizontal angle value measured each time; Then reverse the mirror (to the right) and repeat the above operation, recording the measurement values at each angle position again.

3. Calculation error: Calculate the average values of each angle position during the measurement of the front and back mirrors separately, and then calculate the difference between the average values of the front and back mirrors, which is twice the aiming deviation (2C). The formula is: 2C=\ \ text {front mirror average} - \ \ text {back mirror average} \ pm 180 °. Calculate the angle measurement error for each angle position, which is the difference between the average measurement of each angle position and the actual angle value of the multi tooth indexing table.

4. Result judgment: The angle measurement error and double sighting deviation (2C) at each angle position should not exceed the nominal angle measurement accuracy of the total station. If it exceeds the accuracy range, the horizontal and vertical axes of the total station need to be checked and adjusted, and then recalibrated.

（2） Calibration of vertical angle measurement error

1. Instrument placement and preparation: The total station is placed on a stable tripod, accurately aligned and leveled. Set the initial value for vertical angle measurement in the total station to 0 ° 00 ′ 00 ″. Choose a vertical target, such as the corner of a distant building or a dedicated vertical calibration target.

2. Measurement process: Aim at the target with the total station mirror (left side of the disc), measure the vertical angle, and record the measurement value; Then reverse the mirror (to the right of the disc) and aim at the same target again, measure the vertical angle and record it. Repeat the above operation for a total of 6 measurements.

3. Error calculation: Calculate the average vertical angle measured by the front and back mirrors separately, and calculate the difference between the average values of the front and back mirrors, that is, the index difference x. The formula is: x=\ frac {1} {2} (\ \ text {front mirror average} - \ \ text {back mirror average} \ pm 180 °). Calculate the vertical angle error of each measurement, which is the difference between the measured value and the theoretical vertical angle value (the target vertical angle is known or can be calculated by measuring other relevant parameters).

4. Judgment criteria: The vertical angle error and index difference of each measurement should not exceed the nominal angle measurement accuracy of the total station. If it exceeds the accuracy range, it is necessary to check whether the vertical disc index compensator of the total station is working properly, calibrate the compensator parameters or adjust the vertical axis perpendicularity of the total station.

（3） Distance measurement error calibration

1. Site layout and connection: Place the total station on the control point at one end of the standard baseline field, accurately align and level it. Place a standard reflective prism on the control point at the other end, ensuring that the center of the prism coincides with the control point.

2. Measurement operation: Set ranging parameters in the total station, such as meteorological correction parameters, prism constants, etc. Measure the known distance on the standard baseline field, from short distance to long distance, generally selecting no less than 5 points at different distances, measuring each point 3 times, and recording the slant distance value of each measurement. During the measurement process, the alignment accuracy of the total station and prism should be ensured to avoid displacement of the instrument and prism.

3. Data processing: Based on the slant distance value measured by the total station, combined with the meteorological conditions during the measurement and the parameters set by the total station, calculate the horizontal distance value. Compare the calculated horizontal distance value with the known horizontal distance value of the standard baseline field to calculate the distance measurement error. The formula for distance measurement error is: \ \ Delta D=D_x - D_n, where \ \ Delta D is the distance measurement error, D_x is the horizontal distance value calculated by the total station measurement, and D_n is the known horizontal distance value of the standard baseline field.

4. Calibration judgment: The calculated ranging error should meet the ranging accuracy requirements of the total station, that is, meet the error range specified in the formula mD=\ \ pm (A+B × D). If the distance measurement error exceeds the range, it is necessary to check the distance measurement system of the total station, such as whether the transmitting and receiving optical paths are normal, whether the distance measurement frequency is accurate, etc., and calibrate the additive and multiplicative constants of the total station.

（4） Calibration of addition and multiplication constants

1. Preparation: Select at least 3 known control points at different distances on the standard baseline field, with appropriate distance intervals such as 0.5km, 1km, and 1.5km. Place the total station in a suitable position, accurately align and level it.

2. Measurement operation: Measure the distance of 3 control points separately, measure each control point multiple times (usually 6-10 times), and record the slant distance value of each measurement. Simultaneously record the meteorological conditions during the measurement.

3. Data calculation: Based on the measured slant distance value and the known control point horizontal distance value, taking into account meteorological correction factors, the total station's additive constant K and multiplicative constant R are calculated by least squares fitting. The calculation process is relatively complex and is generally carried out with the help of professional calibration software or calculation tools.

4. Result determination: The calculated addition and multiplication constants should be within the allowable error range specified by the total station. If it exceeds the range, the distance measurement system of the total station needs to be adjusted or recalibrated. After calibration, perform distance measurement error calibration again to ensure that the distance measurement accuracy meets the requirements.

9、 Calibration result processing

1. Calibration records: During the calibration process, detailed records are kept of the calibration date, calibration personnel, total station model, number, calibration equipment information, measurement data for each calibration item, calculation results, etc. Calibration records should be accurate, clear, and complete, and should not be altered arbitrarily. The calibration record format can refer to Table 1:

|Calibration items | Measurement frequency | Measurement value | Average value | Error | Whether it is qualified|

|---|---|---|---|---|---|

|Horizontal angle measurement (0 °) | Mirror 1 | [Specific angle value] | ||

|Horizontal angle measurement (0 °) | Positive mirror 2 | [Specific angle value] | ||

|. ..|. ..|. ..|. ..|. ..|. ..|

|Vertical angle measurement (1st time) | Positive mirror | [Specific angle value] | ||

|Vertical angle measurement (1st time) | Inverted mirror | [Specific angle value] | ||

|. ..|. ..|. ..|. ..|. ..|. ..|

|Distance measurement (point 1) | First time | [slant distance value] | ||

|Distance measurement (point 1) | Second time | [slant distance value] | ||

|. ..|. ..|. ..|. ..|. ..|. ..|

|Constant calibration | [Calculation process and results] | | | ||

|Multiplication constant calibration | [Calculation process and results] | | | ||

2. Calibration certificate: A calibration certificate shall be issued for a qualified total station. The content of the calibration certificate includes basic information of the total station (name, model, number, manufacturer, etc.), calibration basis, calibration environmental conditions, calibration equipment, calibration items and results, calibration date, calibration personnel signature, calibration unit seal, etc. The calibration results should clearly provide the measurement values, error values, and conclusions on whether they meet the metrological characteristics requirements for each calibration item. The format of the calibration certificate can refer to the relevant metrological calibration certificate standard template.

3. Calibration report: For total stations that fail calibration, a calibration report shall be issued. The report should provide a detailed description of the non-conforming items and measurement results, analyze the reasons for the non-conforming items, such as damage to the optical components of the instrument, electronic component failures, mechanical component looseness, etc., and propose corresponding handling suggestions, such as repair, replacement of components, recalibration, etc. The format of the calibration report can be developed according to the actual situation, and should include basic information of the total station, an overview of the calibration situation, non-conforming items and analysis, and handling suggestions.

10、 Return time interval

1. Conventional situation: The interval for recalibration of the total station is generally 1 year. Under normal use, annual calibration can effectively ensure the measurement accuracy and reliability of the total station.

2. Special circumstances

• Frequency of use: If the total station is used very frequently, such as for multiple measurement projects every day or for continuous operations in large-scale engineering construction, the interval between rechecks can be appropriately shortened, and it is recommended to be 6 months. Frequent use will accelerate the wear of mechanical components and electronic components of the instrument, affecting measurement accuracy and requiring more frequent calibration.

• Operating environment: The total station is in harsh environments such as high temperature, high humidity, strong magnetic field, and high dust. The interval for recalibration should be shortened, usually 3-6 months. Adverse environments can have adverse effects on the optical, electronic, and mechanical performance of instruments, increasing the risk of measurement errors.

Equipment condition: After maintenance or replacement of key components (such as distance measuring heads, angle encoders, motherboards, etc.), the total station should be calibrated immediately. The interval for subsequent re calibration can be re evaluated and determined based on the stability and usage of the equipment after maintenance.