【Weekly Question 20090601】Please discuss the applications of wireless technology based on your own understanding and practical experience.

Strictly speaking, wireless DCS or PLC systems are not entirely wireless; the use of wireless technology implies the presence of transmitting and receiving devices. There is a wireless connection between the transmitting and receiving devices, but a wired connection exists between those devices and the field instruments or actuators. Similarly, there is a wired connection between the receiving devices and the controller. I have used a control system that combines an AB company PLC with wireless controllers from German company HBC; it has 200 input points and is intended for use on multi-functional cranes ； Traditional control methods rely on cable connections; due to the large number of components that need to be operated and monitored, there are many cables connecting the cab to the controllers. Moreover, since the cab needs to rotate, cable failures occur frequently, resulting in substantial maintenance workload ； After technical upgrades carried out by our company, wireless remote control was adopted, as well as for ground-based operations. Following these upgrades, the system’s failure rate has significantly decreased, and it is now easier to operate. Now, many manufacturers are producing wireless devices, the transmission distance has **increased**, and there are more options available for selection.

I don’t know how the interference issues in wireless systems are resolved

It’s too expensive. Our company hasn’t used wireless technology before, so we’re not sure if there will be any interference

High-voltage testing line at a Xi’an factory of a Fortune 500 company. 100KV high-voltage testing. When a product breaks down, surges in the Ethernet circuit often cause damage to switches, the Ethernet ports of PLCs, and computer network cards. Even the hard drive is damaged. Use Moxa surge protectors with 4KV isolation. It doesn’t work; once it discharges or is broken down, the isolator is damaged. Weidmüller Ethernet surge protectors are used, with 45KV isolation. It still doesn’t work. Due to discharge or breakdown, the isolator may get damaged. Even if the isolator is damaged, it still cannot protect other Ethernet devices such as switches, PLC communication ports, network cards, etc. Finally, 2 wireless routers were added to serve as APs; the PLC is located close to one of the routers, so wired communication is used for connection. Computer wireless network cards are used as nodes. . That high-voltage equipment used in the experiment also uses wireless router 2 as an AP. The router uses an ASUS product from the computer market. It has been running for over half a year now, and there are no more instances of the PLC damaging the communication ports. . . There are no more cases of computer network cards burning out. . . The switch no longer overheats. Router 1 on the PLC side has never had any problems. Router 2 on the high-voltage testing equipment side “often occasionally” freezes. When operating at high voltages of over 60 KV and the product breaks down, the probability of a system crash is high, around 10%. (Previously, the odds were much higher than this – at least half a chance.) There was no penetration, no discharge, and no system crash. Of course, the proportion of products that experience breakdown is less than 1%. It’s acceptable. No damage has been found temporarily in the router on the high-voltage testing equipment side, but one spare unit has already been prepared. It’s only 260 yuan though, compared to computers, Moxa industrial switches, and PLC communication ports. 260 yuan is completely acceptable. And besides, it hasn’t been damaged yet. The control system is S7-300, with the CPU being the S7-315-2PN model that has a built-in Ethernet interface. The score is 80 points. No AO. AI, DI, and DO are all available. System communications are numerous and complex; the PLC is actually the least valuable component – it’s best for handling communications, but it also fails the fastest.

We have come across infinite meters, but we have not used them in practice. I’ve always wanted to find an opportunity to use it; this requires convincing the owners, and there should also be an appropriate environment for its use, such as in large facilities for oil depot management, sewage treatment, and similar applications. Personally, I think it has future potential, but it won’t replace any existing types of instruments; it simply adds another option to the instrument industry, which should be considered a blessing for those of us in this field.

Currently, ROSEMOUNT and HONEYWELL are both introducing their wireless smart transmitters, but the oil and chemical industry has doubts regarding their safety and reliability, such as: interference resistance? The attenuation of the signal is similar to that of mobile phone signals; blind spots and areas with no response are problematic. So my advice is that it would be more appropriate to apply them first in gathering and transportation facilities as well as integrated oil production stations; however, if their reliability were as high as that of military wireless equipment, it would undoubtedly save a great deal of cost and labor. Thank you, LZ; I will keep paying attention to this issue.