The accuracy of the total station is 2", which means that the error in the horizontal direction of a measurement round is no more than 2". The horizontal direction of a measurement round refers to the average value of the left and right direction values.
(1) Half-measurement regression zero-difference limit
Suppose there is a center error in the direction of the measurement, then the half-measurement regression zero-difference direction value = 4". 2C limit value takes the center error 2 times, that is, 2C=8”.
(2) The tolerance of the error in the measured return angle value and the difference in the angle value between the measured returns
The measured return angle value is the difference between the two direction values, measured with The horizontal angle is measured in two rounds using the back-to-back method, and twice the mean error is taken as the limit difference. Then the allowable error of the angle value difference between the measured rounds is 8".
(3) The mid-range of the half-measured back angle values The error and the tolerance of the difference between the upper and lower half-measured return angle values
The angle value of one measured return is the average of the upper and lower half-measured return angle values, so the error in the half-measured return angle value is 5.6", and the middle error is taken 2 times is the allowable error, and the allowable error is 11.2".
Extended information
Error analysis
The vertical scale consists of the main grating, the indicating grating, and the indicating grating It consists of a base, a shaft and a bushing. During the installation process of the vertical dial, the vertical dial index error and the horizontal axis tilt error will occur. The vertical dial index error is caused by incorrect installation of the fixed indicating grating. It refers to when the collimation axis is horizontal. , the vertical dial reading is not 90 degrees.
After installing the vertical dial, place the instrument on the instrument pier, aim at the target at infinity of the parallel light tube that is approximately the same height as the instrument, and use The zenith distance of the observation target on the left and right side is: α=90°-L+I; on the right side: α=R-270°-I, so I=1/2 (L+R-360°). If the index difference I exceeds the specified limit, correction is performed. There are two types of correction: one is mechanical correction, and the other is through software correction.
Loosen the indicating grating seat and bracket. Connect the 4 screws, rotate and adjust the indicator grating base, and measure the face left and face right again to calculate the index difference until the needs are met. Software calibration: Start the index difference correction program of the instrument, follow the prompts on the display, and take the face left and face right photos. Quasi-collimator, extract the index difference difference and store it. After the above correction, the angle displayed by the instrument is the value after correcting the index difference, that is, the value when the index is in the correct installation position.
The horizontal axis is tilted. The error is caused by the unequal heights of the two brackets supporting the horizontal axis. When the horizontal axis is tilted, it will have a great impact on the measurement of the horizontal angle. Under the premise that the vertical axis is vertical and the collimation axis is perpendicular to the horizontal axis: < /p>
① Take the center O of the horizontal axis as the center of the circle and any length as the radius. HH1 represents the horizontal position of the horizontal axis, H′H1′ represents the position when the horizontal axis is tilted, and the vertical angle is on the side of H1 , when the horizontal axis rotates around the vertical axis, the tilt angle β in each orientation is unchanged.
② When the horizontal axis is horizontal and the target T is sighted, the vertical sighting plane is OZTM′, It reads M′ on the horizontal dial. If the horizontal axis tilts at angle β, when the collimation axis points to the zenith, the collimation axis will not be at the correct OZ position, but will move to the OZ′ position. With such a sight When the alignment axis is aimed at the target T, the aiming surface is the inclined surface OZ′TM, and the reading on the horizontal dial is M. The chord length MM′=△β is the effect of the horizontal axis tilt error on the direction reading.
As the vertical surface of OZM, in the spherical triangle ZTM, ZT=Z, LZMT=β, TM≈α, LTZM=△β, then the spherical vertical angle formula is: sin△β=sinβ/sinz*sinα and because β and △β is a small angle, we can get △β=βtgα, which is the relationship between the influence of the horizontal axis tilt error on the horizontal angle.
The tilt error of the horizontal axis is verified using the flat and low (high) point method: two points are selected indoors, one is higher than the horizontal line of sight, the other is lower than the horizontal line of sight, and the vertical angle Satisfies α high = - α low, when observing the high point: (L-R) high = 2L/cosα high + 2β*tgα high When observing the low point: (L-R) low = 2L/cosα low + 2β*tgα low due to α High=∣αLow∣.
Then β=1/2 (C high-C low) cotα When using flat and high reading, just combine (L-R) flat = 2C and (L-R) low = 2L/ cosα low + 2β* The specific operation of tgα low is according to the software prompts. Sight the horizontal collimator light pipe with face down and face right respectively to solve the collimation axis error and indication difference β1. Then aim at the point parallel light pipe with face left and right face to solve the collimation axis error and index. The difference is β2. At this time, the horizontal axis tilt error can be obtained according to the above formula.
When the horizontal axis tilt error is too large, it can be corrected by adjusting the relative position of the indicator grating base on the vertical dial and the bracket, or it can be compensated according to the software.
Baidu Encyclopedia - Error in Angle Measurement
Baidu Encyclopedia - Total Station