There are a large number of online equipment working in underground coal mines that do not have positioning function and the equipment installed with wireless positioning are susceptible to electromagnetic interference, resulting in low positioning accuracy. In order to solve the above problems, a distance measurement method between bus equipment based on RS485 data frame timing is proposed by combining the time domain reflectometry method of cable fault location and wireless single-sided-two-way-ranging time of flight method. The method uses the communication cable as a carrier to measure the distance between master and slave computers by using the flight time of communication data between a pair of master and slave computers. And the equipment along the bus measure the distance between themselves and slave computers by monitoring the data so as to realize the distance measurement between all equipment on the bus. Moreover, the one-dimensional distribution of equipment can be calculated based on the measurement results of 2 different reference slave computers. The factors affecting the distance measurement accuracy are analyzed from four aspects, clock frequency, master-slave computer clock deviation, circuit time delay and electromagnetic wave propagation speed. And the corresponding measures are proposed to improve the measurement accuracy. The method uses one mine intrinsically safe display as master computer and eight mine sensors as slave computers to establish the test platform so as to measure the distance between the bus equipment. The results show that this method does not need to change the hardware and only updates the software to measure the distance between all equipment on the RS485 bus, and a one-dimensional distribution with the master computer as the origin can be established. The distance measurement error within 5 km of the cable length does not exceed ±1.5 m, and the measurement result is not affected by transmission loss and electromagnetic interference.
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