1) Due to the adoption of scanning technology, some structural errors of optical theodolite (such as eccentricity error of dial and marking error of dial) are eliminated.
2) Modern electronic theodolite has the function of three-axis automatic compensation, that is, it can automatically measure the horizontal axis error, vertical axis error and collimation axis error of the instrument and automatically correct the angle observation value.
3) The electronic theodolite can automatically store the observation results in the data recorder and display them directly on the display in digital mode, thus realizing the automation and digitization of angle measurement.
4) The electronic theodolite, photoelectric rangefinder and microcomputer are integrated to form the electronic velocimeter of the whole station, which can directly measure the three-dimensional coordinates of the measuring point. The combination of electronic speedometer and plotter in the whole station can realize the integration and automation of measurement, calculation and drawing.
The electronic theodolite is basically similar to the optical theodolite in structure and appearance, and its use method is basically the same as that of the optical theodolite, including three steps: placing instruments, aiming at targets and reading. Except that the reading is directly read on the display, the operation method of other steps is exactly the same as that of the optical theodolite.
The main difference between electronic theodolite and optical theodolite lies in the reading system. The optical theodolite adopts an optical dial with digital symbols and an optical reading system consisting of the dial and a series of optical prisms and lenses. Electronic theodolite adopts electronic dial and an angle measuring system composed of it, mechanical, electrical and optical devices. There are three kinds of angle measuring systems of electronic theodolite, namely dial coding method, incremental method and dynamic method. The angle measuring principles of various angle measuring systems are also different.
Figure 3-26 shows the appearance of T2000 electronic theodolite. The electronic theodolite adopts dynamic angle measuring system, which is mainly composed of dial, micro-motor, grating and photoelectric conversion device.
Figure 3-26 T2000 electronic theodolite
Figure 3-27t 2000 Dynamic Angle Measurement Principle
The dial of T2000 electronic theodolite is an optical glass ring with 1024 black and white stripes on it (Figure 3-27). Two pairs of gratings are installed on the dial, and each pair of gratings consists of a fixed grating LS and a movable grating LR. Among them, the fixed grating LS is installed on the outer edge of the scale, and its position is fixed, which is equivalent to the zero graduation of the optical scale, and the movable grating LR is installed on the inner edge of the scale, which rotates with the scope part, which is equivalent to the graduation of the optical scale. In order to eliminate the eccentricity difference of the dial, the grating with the same name is placed in the position with the opposite diameter.
When observing the angle, the direction value of the target is expressed as the angle between LS and LR. . Let the dividing value of the dial be? 0, with fractional value? 0 is a period, then? Value is equal to n whole periods (divisible value? 0) and the remainder δ is less than a whole period? The sum of, that is,
=N？ 0+Δ? (3- 14)
In order to determine the whole period number n, there are four special marks on the dial, one for every 90. When observing, the dial is driven by a micro motor and scanned by a grating. When one of LR or LS recognizes a special symbol for the first time, the counter starts counting the number of the whole period until the symbol reaches the other symbol. At this time, the value obtained by the counter is n.
To determine the remainder δ? The light emitting diode and photodiode mounted on the grating are located on the upper and lower sides of the dial respectively. The LED emits infrared light, which shines on the dial through the aperture of the grating. When the micro-motor drives the dial to rotate, the light transmittance changes constantly due to the bright and dark stripes on the dial, forming an optical signal. The signal is received by a photodiode arranged on the other side of the dial and converted into a sine wave electric signal. The sine wave electric signals output by LR and ls are shaped into square waves, and then the phase difference, δ? .
The above two parts of data are sent to the angle processor for processing and connected into a complete direction value, which is displayed by the display or recorded in the data recorder. This is the angle measuring principle of T2000 electronic theodolite.
Review exercises
1. What is the horizontal angle? What is a vertical angle? What are their ranges?
2.2 What are the parts? DJ6 optical theodolite?
3. What are the two contents of the theodolite? How to proceed? What's the purpose?
4. Please describe the operation steps, record calculation and tolerance rules of the back measurement method.
5. What is the function of the retest button (dial configuration device) on the theodolite? How to use it to configure the horizontal dial reading in the initial direction to 0 00' 00 "?
6. When measuring the vertical angle, why should the bubble in the vertical dial be centered before each reading, and then read?
7. When measuring the horizontal angle, why should we use the left and right position of the disc to observe it?
8. What is the vertical index difference? How to eliminate the difference of vertical index?
9. What are the spindles of theodolite? What conditions should they meet? Why?
10. When checking that the collimation axis is perpendicular to the horizontal axis, why do you choose a target as high as the instrument (that is, a horizontal target)? And when the horizontal axis is perpendicular to the vertical axis, why choose the goal higher? According to the method described in this book, can the order of these two tests be reversed?
1 1. What are the errors in angle observation? How to eliminate or weaken the influence of these mistakes?
12. aim at two points with different heights in the same vertical plane with theodolite. Are the readings on the horizontal dial the same? Is the difference between the two readings on the vertical dial a vertical angle? Why?
13. Observe the horizontal angle with DJ6 optical theodolite according to the measurement method, and sort out the calculation of horizontal angle observation in Table 3-4.
Table 3-4 Observation Record of Horizontal Angle
14. Observe the vertical angle with DJ6 optical theodolite according to the midline method, and sort out the vertical angle observation calculation in Table 3-5.
Table 3-5 Vertical Angle Observation Records
15. Observe a target with DJ6 optical theodolite. The reading of the left vertical disk is 7 1 45' 24 ".The vertical disk (left disk) of this instrument is marked as shown in Table 3-5 of14, and the measured vertical disk index difference is x =+24". What is the correct vertical angle α of this target?
16. What are the main errors in horizontal angle measurement? What problems should be paid attention to in observation in order to reduce the eccentricity error of station alignment?
17. What are the main features of electronic theodolite? What is the fundamental difference between it and optical theodolite?