Issues with Honeywell communicating with third parties?
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I am not a DCS technician; our plant’s DCS system communicates with third-party devices via S7-200. 1. The DCS system is fully configured without any issues; it has been used before as well. 2. The S7-200 was without power for approximately 1.5 years, and the voltage at the communication line was 3V. “The communication cables are not labeled, and the communication terminals are also unlabeled.” 3. There are two communication switches; none of the channels are numbered, so it’s not clear which channel was used previously. The communication twisted pair is in good condition, with a wire resistance of 2.6 ohms. Each channel was connected with the positive side on the left and the negative side on the right; none of the TX and RX lights on the switch lit up. When the wires were connected with the negative side on the left and the positive side on the right, only the RX light turned on for each channel. 4. DCS communication with third parties was attempted; when connected in the left-positive/right-negative configuration, no communication was established, and none of the lights on the switch lit up. Testing was not performed when the connection was reversed. 5. What are the main reasons why the TX and RX lights do not light up in the \"positive on the left, negative on the right\" connection method? “In a “left negative, right positive” communication cable, only one light is on – how does this situation arise? Reconnect the communication cable and then activate the DCS channel. Due to a lack of experience, I’m not sure if this method will work; could reconnecting the communication cable affect the switch ports?
Serial communication can be troublesome, as it’s sufficient to establish a connection at just one point; once that connection isn’t established, beginners will take a long time to figure things out. Here are some of my experiences and suggestions for working with communications: 1. What are the main reasons why the TX and RX lights do not light up? For communication, I don’t care whether the light is on or not; I only focus on whether data is being read from and written to by both sides. Communication successful, the indicator light flashes. Communication fails, and the indicator light does not flash. There’s no need to worry too much about this. 2. Will reversing the communication cable affect the switch port? Communication uses low-voltage signals, and frequent communication can lead to misconnection of the wires; therefore, it is advisable to try reversing the connection of those wires. If possible, it is recommended to use third-party serial communication devices, along with tools such as modscan and modsim, to test the communication between the two parties first, in order to determine which side has a communication issue. By establishing communication for one point first, it becomes easier to set up communication with the other points as well. Configure all the parameters for serial communication, such as the baud rate, parity, data bits, stop bits, etc., as well as the device address (many people I’ve worked with who were doing communication for the first time made this mistake). With Modbus communication, once all the parameters for the master and slave stations are set, the communication process isn’t that complicated.