In order not to lose itself in the untouchable nature, mankind has invented compasses, compasses, satellites, and other tools to solve the problem of “where am I?â€; as the safety requirements of large factories or mine workers improve, it is still necessary to solve “where are you? The personnel positioning problem.
The scale of production of factory enterprises has been continuously increasing, and production plants with thousands of mu of production have put forward higher requirements for the entire personnel management of safety production. In particular, electric power, refinery and chemical companies are high-temperature, high-pressure, flammable, explosive and toxic hazardous industries. Coupled with the characteristics of large-scale production equipment, dense, complex production processes, tight coupling of production processes, etc., compared with other industrial sectors have greater danger.
Fig. 1 Difficulties in positioning search and rescue due to equipment characteristics and industry specificity in large-scale factories
How to strengthen management and control, position the factory personnel in a timely manner, and reduce the probability of dangerous accidents have always been key issues in production. Industrial-grade technology requires higher positioning accuracy. It is necessary to differentiate individuals in the crowd and use it with special tags and sensors.
Figure 2 Different types of electronic tags and base stations
Today we come to understand the zigbee industrial-grade positioning program.
Figure 3 Two-dimensional map of the accuracy and development difficulty of various positioning solutions
TOF ranging function:
The ZM5168 module has a hardware Time-of-Flight (ToF) engine that has the capability to measure 2.4 GHz signal transmission time between two zigbee nodes. By measuring the transmission time of signals between nodes, the distance between the two zigbee nodes can be calculated. After measuring the distance between zigbee nodes, it can be used to develop application systems such as zigbee node positioning.
The operation mechanism for performing ToF between two zigbee nodes is: the local node sends a ToF message to the remote node, and the remote node automatically responds with a reply to the ToF message, as shown in FIG. 4 .
Figure 4 ToF operating mechanism
The local node measures the time from sending a ToF message to receiving a reply. This total time is T_TOT. At the same time, the remote node records the time T_TAT required to reply ACK. Subtracting the total time from the time spent by the remote node to reply ACK is the total time T_RTT between the two nodes. Assuming that the signal is equal between the two nodes, the signal transmission time between the two nodes is half of the total time, as shown in the formula.
ToF time calculation formula
Because ToF ranging depends on measuring the signal transmission time of the local and remote nodes, it will be affected by the clock frequency error of the two nodes. In order to reduce this effect, reverse measurement is needed, ie, the far-end node sends ToF packets. The local node responds to the reply and then averages the forward and reverse measurements to eliminate this frequency error effect. The ZF5168's ToF ranging command provides forward and reverse ranging.
Test example: (CMD is command, RSP is answer)
CMD: DE DF EF E1 20 01 00 08 AA
RSP:DE DF EF E1 20 01 00 07 00 01 54 28 2D FB 2D E6 00 01 42 50 2D FF 2E FA 00 01 36 7E 2D F2 2D F9 00 01 36 9E 2D E7 2D EE 00 01 4D 6B 2D F4 2E EC 00 01 3E E4 2D F5 2E F3 00 01 44 E6 2D EC 2D EF 00
The command requires forward ranging 8 times, and the returned response 7 times is successful ranging. The returned ranging data is as shown.
Multiply the measured ToF time by 0.03 to get the distance between two nodes in centimeters.
Table 1 Sample Test Data
Figure 5 Zhiyuan electronic zigbee wireless positioning scheme
Zigbee's transmission rate is low, the transmit power is only about 1mW, and the sleep mode is adopted, and the power consumption is low, so the zigbee configuration is very power-saving. Another star-shaped zigbee network under the polling mechanism theoretically has a capacity of up to 65,535 nodes, and the networking is flexible. Currently, zigbee wireless positioning solutions are widely used in field applications such as mine personnel positioning, factory personnel positioning, and tunnel personnel positioning.
The ZM516x is a series of low-power, high-performance zigbee modules developed by ZLG Zhiyuan Electronics based on the NXP JN5168 wireless microcontroller and provides a complete application integration solution based on the IEEE802.15.4 standard ISM band.
Figure 6 ZLG Zhiyuan Electronics ZM5168 Wireless Module
At the same time ZLG Zhiyuan Electronics R & D and production of a zigbee to Ethernet gateway device - ZBNET-300C-U industrial-grade standard design to achieve high-speed zigbee network and Ethernet transmission, without the need for secondary development can quickly zigbee LAN access Internet, for the purpose of remote zigbee control and data acquisition.
Figure 7 zigbee to Ethernet gateway device
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