In applications like process control or robot control, for us, the deterministic behavior is mandatory while the speed of the communication is usually more than high enough. Communicating at lower speeds also has the advantage of being more resilient to the noise present in industrial environments. Forewarning : In standard applications where a Robotiq device is connected directly to a robot controller through the cable provided normally 5 or 10 m and where the Gripper is the only device on the communication bus, no special care is generally required to make the communication bus work.
But for people who intend to attach our product to a custom bus or use a longer cable than provided by Robotiq , you should pay attention to the following concept. RS is capable of up to 32 drivers and up to 32 receivers in a half-duplex multi drop configuration. Here's an example of a multi drop RS bus. RS can be transmitted at a distance of up to m feet when the data rate is below k bps. At higher data rates, the cable length must be reduced as shown in the chart below.
A long cable can act like a transmission line, in which case, care should be taken to properly connect the network. Let's look at the most important characteristics of the network that need to be accurately controlled. The network topology determines the way devices are connected together. The image below shows some common topologies. Among these possibilities, the best network topology for RS is a daisy chain or line , because this topology has the lowest impact on signal integrity.
A bus topology backbone using stubs is okay, but as the length of each stub increases, the maximum data rate that can be transmitted will decrease due to signal distortion on the communication line.
Using a twisted pair cable for RS helps to reduce electromagnetic interference. The twisted pair allows the noise that is on the line to be equivalent on both wires. The noise is still there, but because the receiver looks at the difference between the two signals, this difference is not affected by the noise and thus the receiver can accurately reestablish the original signal at the end.
Terminating a cable is the action of adding a resistor across the differential lines at both ends of the cable. The purpose of doing this is to reduce or eliminate the reflection coefficient on the line caused by an impedance mismatch. The resistance in the case of the RS standard is define as ohms. This reflection can lead to interference at the receiver input and then effect the signal integrity. This phenomenon is strongly correlated to the data rate and the length of the cable.
So in some circumstance where low data rates and short cables are used, a RS can work without a termination resistor. But as a precaution and to avoid any problems, resistors should always be used. Noise Resilience Factories are full of EMI Electro Magnetic Interference sources with long cable runs acting like antennas that pick up electrical noise easily. Contact Us. Email: [email protected]. Keep in touch. Stay up to date by joining our email newsletter.
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As RS networks become larger, the problem of data collisions becomes greater. This can be solved, at least in part by ensuring the hardware units converters, repeaters, micro-processor controls are designed to remain in a receive mode until they are ready to transmit data. Another approach is to design a 'single master' system. Here the master initiates a communications request to a "slave node" by addressing that unit.
The hardware detects the start-bit of the transmission and thereby enables the transmitter. Once a requested data is sent the hardware reverts back into a receive mode. RS was able to provide high speed data communications. Although many other formats have taken over, it was widely used and was able to meet the needs for a number of applications where data needed to be transmitted at high speeds for the time.
RS proved to be a robust standard and able to provide reliable data communications over extended distances.
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