First, the transit system's composition and working principle
The use of towers, buildings or mountains and other high ground, set up large-scale transit station coverage. Transfer devices, including full-duplex radio, omni-directional antenna, feeder, duplexer, power supply.
Transit system components and working principle
System works and does not transit the same way, but the transit system needs a pair of frequency, such as the main station transceiver sub-station transceiver f1 and f2. Multipoint mode with polling (MODBUS communication protocol, etc.), the main station with the f1 through a sub-station transfer station to send commands, receive a transfer station that is used with the f1 f2 forward, with f2 a sub-station after receiving the command, f2 through the transfer station with the master sent to the response, with a transfer station that is received with f1 f2 forward, the master receives the sub-station with f1 response, to complete a point of polling.
Second, the system capacity calculations
Multipoint system, the system capacity (ie, the number of band RTU) depends on two premises:
A, the system requires much time, polling a (T s)
B, average number of polling each RTU data (D bytes) to send the system capacity (RTU number) = T / the time it takes for each RTU
C, polling command C (bytes)
Each RTU take the time = D × 10 (bits) / 9600 (rate) + transceiver conversion time (about 10ms) + C × 10 (bit) / 9600 (rate) + transceiver conversion time (about 10ms)
1, such as assuming 15 bytes per RTU transmission, polling command 10 bytes long, then take time for each RTU
15 × 10/9600 +0.01 +10 × 10/9600 +0.01 = 0.046 秒
If the system requires an update every 10 seconds, the system capacity
10/0.046 = 217 RTU
2, assuming the same transfer 50 bytes per RTU, RTU take time for each 50 × 10/9600 +0.01 +10 × 10/9600 +0.01 = 0.082 秒
If the system requires an update every 1 second, the system capacity
1/0.082 = 12 RTU
