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• EIA/TIA-485 communication interface with low power requirements. 3. Armored twisted-pair shielded cable ASTP-120Ω (for RS485 & CAN) one pair 18 AWG, the outer diameter of the cable is about 12.3mm. It can be used in places with severe interference, frequent rodent damage, and lightning protection and explosion-proof requirements. Cable jacket: Made from high-quality PVC, the outermost jacket layer has high elasticity, helping to protect the cable from strong environmental impacts. RS485 is made for serial communication with high speeds, support for long distances, and support for multiple devices (slaves). The maximum slew rate also limits the maximum communication speed on the line. Noise is easily picked up and limits both the maximum distance and communication speed. We also see that there is a maximum slew rate defined for both RS232 and RS423. First of all we see that the speed of the differential interfaces RS422 and RS485 is far superior to the single ended versions RS232 and RS423. RS232, RS422, RS423 and RS485 are serial communication methods for computers and devices. The following debugging methods can be used according to the problems encountered. One of the main problems with RS232 is the lack of immunity for noise on the signal lines.

If high noise immunity is needed, often a combination of twisting and shielding is used as for example in STP, shielded twisted pair and FTP, foiled twisted pair networking cables. Therefore the trigger level of the RS232 interface is set relatively high at ±3 Volt. Because of this RS485 and the others can be used in situations with a severe ground level shift of several volts, where at the same time high bit rates are possible because the transition between logical 0 and logical 1 is only a few hundred millivolts. This means data can be transmitted in both directions to and fro devices one direction at a time. RS232 could only handle one at a time. One very common example in the automation world is remote control of VFDs or Variable Frequency Drives. RS485 is also commonly used for building automation as the simple wiring configuration and lengthy cable length are ideal for joining remote devices. All in all, RS485 really allowed full automation possible with its ability to connect so many devices at once. This allowed users in manufacturing facilities to connect larger applications and whole machines with one protocol.

There is no standard connector for the protocol. This is great for Supervisory Control and Data Acquisition (SCADA) systems where there are many devices and it also comes at a very low cost to implement. That is why RS485 is currently a widely used communication interface in data acquisition and control applications where multiple nodes communicate with each other. This works well and prevents the existence of ground loops, a common source of communication problems. They ground at main panel. Shifts in the ground level can have disastrous effects. Electric noise can cause all kinds of problems for electronics. Several volts difference in the ground level of the RS485 transmitter and receiver does not cause any problems. The transmitter and receiver compare the voltages of the data- and handshake lines with one common zero line. Sig- line. The RS485 receiver compares the voltage difference between both lines, instead of the absolute voltage level on a signal line.

The 485 communication line is composed of two twisted-pair lines. Ring topology arranges network nodes in a circular configuration where each node connects to two others, forming a closed loop. The flowmeter leverages RS485 for signal transmission and is connected in a serial configuration with the customer's central control system. If a star configuration is unavoidable, special RS-485 repeaters are available which bidirectionally listen for data on each span and then retransmit the data onto all other spans. The RS-485 bus network topology generally adopts a bus-type structure with terminal matching. You can also still simply use a terminal strip. Most manufacturers still utilize a DB-9 connector. So I need to find the 485 protocol the end points currently use? Are you saying only connect shield to ground at one end? RS232 referenced ground to decipher the data it was transmitting. Differential signals and twisting allows RS485 to communicate over much longer communication distances than achievable with RS232. This has been done to avoid reflections of signals. Twisted pairs in RS485 communication however adds immunity which is a much better way to fight noise.

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