How to Choose the Right RS485 Converter?
In the entire security industry, such as access control and attendance systems, parking systems, industrial control systems, industrial automation systems, etc., RS485 converters are widely used. Because the data of the system must be transmitted to the computer, and all the computers communicate with the 485 bus through the 232 serial port. With so many different types on the market, choosing a high-quality converter can be difficult. As we all know, if you want long-term and stable communication of the entire system, you must choose a high-quality RS485 converter, which can not only ensure stable communication, but also greatly reduce maintenance times and greatly reduce costs. So how can we choose high-quality products? The following are the points that need to be paid attention to in the 485 (RS232 to RS485) wiring specification:
The serial port is obtained through a converter and there are issues with quality and performance
Some computers, especially laptops, do not have serial ports. Need to buy USB-to-serial converters, PCI multi-serial cards and other equipment to expand the serial port, you need to pay attention to the purchase of branded equipment, because these equipments have similar functions, but the performance difference will be relatively large, and some conversion equipment has a larger lag Delays may affect normal communication.
Are you using a passive converter?
We believe that passive converters should be prohibited in access control/security systems. Passive converters have low cost, poor communication quality, short communication distance, poor load capacity, and almost no anti-interference ability. It is recommended that users use the 485 converter provided by the regular manufacturer. The manufacturer will do a lot of testing work on the RS485 converter, and carry out production and quality inspection with fixed performance parameters, so it has better compatibility with its access control equipment.
Is there a star join?
The 485 communication method requires each controller and converter to be connected hand in hand, and no bifurcation or star-shaped wiring is allowed in the middle. Because the interference generated by the line itself is very large, it is easy to cause unstable communication. The construction personnel can't take a chance, thinking that: the load is not much, the line is not long, it seems to be possible, and it is just a fluke and a fluke. Even if the communication can be normal during debugging, it is difficult to guarantee when the communication will not be normal during use.
Is there no twisted pair?
The 485 communication line adopts the principle of differential mode transmission, so it must be twisted pair (the network cable is composed of 4 pairs of twisted pairs, so choose one pair of the network cable, be careful not to be self-defeating, connect the network cable One-to-one, trying to thicken the lines to improve the communication quality is counterproductive.) For some construction workers, it is convenient to use ordinary power lines or parallel lines as 485 communication lines, because the distance between these parallel lines is very dangerous. The longer the line is, the greater the interference generated by the line itself, and the worse the anti-interference ability, until communication is impossible.
Is the communication line too long?
The nominal 485 communication line is 1200 meters. In fact, according to the line quality, installation environment, the performance of the controller communication chip, and the performance of the converter, the communication distance cannot be reached. Generally good equipment and environment can reach 500-800 meters, if the distance is too long, you can consider purchasing 485 repeaters from the converter manufacturer to extend the transmission distance.
485 bus can communicate with 128 devices?
In fact, not all 485 converters can carry 128 devices. It should be judged according to the model of the chip in the 485 converter and the model of the 485 device chip. Only the chip with a lower index can determine its load capacity. Generally, there are three levels of 485 chip load capacity - 32, 128 and 256. In addition, the theoretical nominal is often unattainable in practice. The longer the communication distance, the higher the baud rate, the thinner the wire diameter, the poorer the wire quality, and the stronger the lightning protection, all of which will reduce the number of real loads. When the load is not enough, the corresponding problems can be solved by adding 485 repeaters and 485 hubs.
The above introduces the key points of how to correctly choose a 485 converter. Users can choose different types of 485 converters according to different applications, and choose products that are cost-effective and suitable for use, so as to achieve twice the result with half the effort.
