Total Station Electronic Tachometer and Its Use-EEWORLD

Collect

Total station type electronic tachometer and its use
Total station type electronic tachometer and its use Total station type electronic tachometer is referred to as total station. It is a measuring instrument composed of mechanical, optical and electronic components that can simultaneously measure angles (horizontal angle, vertical angle), distances (slant distance, horizontal distance, height difference) and process data. Since the instrument can complete all the measurement work on the measuring station with only one installation, it is called "total station". The
structural principle of the total station is shown in Figure 4-16. The upper part of the figure contains four major photoelectric systems for measurement, namely the horizontal angle measurement system, the vertical angle measurement system, the horizontal compensation system and the distance measurement system. Operation instructions, data and setting parameters can be input through the keyboard. The above systems are connected to the microprocessor through the I/O interface to the bus.
The microprocessor (CPU) is the core component of the total station, which mainly consists of a register series (buffer register, data register, instruction register), an operator and a controller. The main function of the microprocessor is to start the instrument to measure according to the keyboard instructions, perform verification and data transmission, processing, display, storage and other tasks during the measurement process, and ensure that the entire photoelectric measurement work is carried out in an orderly manner. Input and output devices are devices (interfaces) connected to external devices. Input and output devices enable the total station to communicate and transmit data with devices such as magnetic cards and microcomputers.
At present, many well-known surveying and mapping instrument manufacturers in the world produce various types of total stations.
2. Measurement function and principle of total station

Figure 4-18 Schematic diagram of photoelectric distance measurement (I) Overview Electromagnetic wave distance measurement is divided into short range (<3km), medium range (3-15km) and long range (>15km) according to the measurement range. According to the distance measurement accuracy, there are Class I (5mm), Class II (5mm-10mm) and Class III (>10mm). According to the carrier wave, the electromagnetic wave in the microwave band is used as the carrier wave, which is called a microwave rangefinder; the light wave is used as the cut wave, which is called a photoelectric rangefinder. The light sources used in photoelectric rangefinders include laser light sources and infrared light sources (ordinary light sources have been eliminated). The infrared rangefinder uses the infrared band as the carrier. Since the infrared rangefinder uses the fluorescence emitted by the gallium arsenide (GaAs) light-emitting diode as the carrier source, the intensity of the infrared light emitted can change with the intensity of the injected electrical signal, so it has the dual functions of a carrier source and a modulator. GaAs light-emitting diodes are small in size, high in brightness, low in power consumption, long in life, and can emit light continuously, so infrared rangefinders have developed more rapidly. This section discusses infrared photoelectric rangefinders. (II) Distance measurement principle To measure the distance D between points A and B, place the instrument at point A and the reflector at point B. The light beam emitted by the instrument goes from A to B, and then returns to the instrument after being reflected by the reflector. Assume that the speed of light c is known. If the time for the light beam to travel back and forth at the distance D to be measured is known, the distance D can be calculated by the following formula Where c = c. /n, c. is the speed of light in a vacuum, which is 299792458m/s, and n is the atmospheric refractive index, which is related to the wavelength of the light source used by the rangefinder, the temperature t on the measuring line, the air pressure P and the humidity e. The accuracy of measuring distance mainly depends on the accuracy of measuring time. For example, if the distance measurement accuracy is required to be ±1cm, the time measurement requires an accuracy of 6.7×10-11s, which is difficult to achieve. Therefore, most of them use indirect measurement methods to measure. There are two methods of indirect measurement: 1. Pulse ranging The light pulse is emitted by the transmitting system of the rangefinder, reflected by the measured target, and then received by the receiving system of the rangefinder. The number of clock pulses required for the round-trip time interval () of this light pulse is measured to obtain the distance D. Since the frequency of the counter is 300MHz (300×106Hz), the distance measurement accuracy is 0.5m, which is relatively low. 2. Phase distance measurement A continuous modulated light wave is emitted by the transmitting system of the rangefinder, and the phase shift caused by the modulated light wave propagating back and forth on the measuring line is measured to determine the distance D. Infrared photoelectric rangefinders generally use phase distance measurement. After an alternating voltage with a frequency of f is added to the GaAs light-emitting diode (i.e., an alternating current is injected), the light intensity it emits changes sinusoidally with the injected alternating current. This light is called modulated light. The modulated light emitted by the rangefinder at point A propagates at the distance to be measured, is reflected by the reflector and received by the receiver, and then the phase meter is used to compare the phase of the transmitted signal with the received signal, and the display shows the phase shift φ caused by the modulated light propagating back and forth at the distance to be measured. (III) Operation and use of total station The specific operation methods of different models of total stations will vary greatly. The following briefly introduces the basic operation and use of total stations. 1. Basic operation and use of total station 1) Horizontal angle measurement (1) Press the angle measurement key to put the total station in angle measurement mode and aim at the first target A. (2) Set the horizontal dial reading in direction A to 0°00′00″. (3) Aim at the second target B. The horizontal dial reading displayed at this time is the horizontal angle between the two directions. 2) Distance measurement (1) Set the prism constant Before measuring the distance, the prism constant must be entered into the instrument. The instrument will automatically correct the measured distance. (2) Set the atmospheric correction value or temperature and air pressure value The propagation speed of light in the atmosphere will change with the temperature and pressure of the atmosphere. 15℃ and 760mmHg are standard values set by the instrument. At this time, the atmospheric correction is 0ppm. During actual measurement, you can enter the temperature and air pressure values. The total station will automatically calculate the atmospheric correction value (you can also directly enter the atmospheric correction value) and correct the distance measurement result. (3) Measure the instrument height and prism height and enter them into the total station. (4) Distance measurement Aim at the center of the target prism and press the distance measurement key to start distance measurement. When the distance measurement is completed, the slope distance, horizontal distance and height difference are displayed. The total station has three distance measurement modes: fine measurement mode, tracking mode and coarse measurement mode. The fine measurement mode is the most commonly used distance measurement mode. The measurement time is about 2.5 seconds and the minimum display unit is 1mm. The tracking mode is often used to track moving targets or for continuous distance measurement during layout. The minimum display is generally 1cm and the distance measurement time is about 0.3 seconds each time. The coarse measurement mode takes about 0.7 seconds and the minimum display unit is 1cm or 1mm. When measuring distance or coordinates, you can press the distance measurement mode (MODE) key to select different distance measurement modes. It should be noted that some models of total stations cannot set the instrument height and prism height when measuring distance. The height difference displayed is the height difference between the center of the total station's horizontal axis and the center of the prism. 3) Coordinate measurement (1) Set the three-dimensional coordinates of the measuring station.

(2) Set the coordinates of the backsight point or set the horizontal dial reading in the backsight direction as its azimuth. When the coordinates of the backsight point are set, the total station will automatically calculate the azimuth in the backsight direction and set the horizontal dial reading in the backsight direction as its azimuth.
(3) Set the prism constant.
(4) Set the atmospheric correction value or the temperature and pressure value.
(5) Measure the instrument height and prism height and input them into the total station.
(6) Aim at the target prism and press the coordinate measurement key. The total station will start measuring distance and calculate and display the three-dimensional coordinates of the measuring point.

Reference address：Total Station Electronic Tachometer and Its Use

Previous article：Differential pair tube detection method
Next article：Emergency light circuit board schematic

Popular Resources
Popular amplifiers