I have a question regarding incorrect display of data in 485 communication

It’s hard to say. I can provide a direction for investigation, which is the scanning cycle of the communication signal. It is possible to investigate the issue step by step, starting from the root cause. First, identify which points are connected via the 485 interface; determine through which instruments and what signals these points are monitored on the DCS. If it is a 4–20mA current signal, there are usually no problems, as the scanning cycle for current signals on the AI cards of common DCS systems is quite short. If the DCS collects data through communication, the communication cycles between the incoming and outgoing transmissions are different, which may lead to communication errors. That is, when the upper-level system sends a query to the DCS, the DCS has not yet scanned for data from the lower-level devices, resulting in incorrect data and thus an alarm being triggered. I’m not sure about the other aspects either; let other experts answer them for you.

The latest checks show that there are no major issues with the data being sent from our end and received on the other end. However, alerts keep appearing on the website. Moreover, the trend charts in the backend show a straight line, indicating everything is normal, yet alerts still appear for no apparent reason. We believe that there is no problem with the data collection process; the issue must lie with the website or the network

If there are no issues with the source data or the transmission, then the problem lies in the monitoring software. The monitoring software’s polling cycle and alarm threshold may be quite close to each other, resulting in too little redundancy.

It’s probably the evil Internet of Things; most likely, there is an issue with the alarm settings on the host device of the Internet of Things, so the person in charge of setting up that device needs to adjust the alarm thresholds through the software

The tests confirm that there are no issues on our end; the 485 communication is working properly. When the 485 connection is interrupted, data retention is typically used, meaning that the data from before the interruption remains in use. The equipment used by the safety supervision agency needs to have a function for resuming communication. If alarms still occur, it might be a problem with the equipment or the software configuration used by that agency.

Check carefully the address through which the Safety Supervision Bureau communicates with you

The inspection schedule for the website was set incorrectly; the alert occurred at a time when inspections are not carried out. Making the necessary changes on the website side will resolve the issue

Have the safety supervision agency or the safety science institute determine exactly which point is triggering the alarm, and also have them check the alarm thresholds they have set. If they set the alarm lower limit to 0, it’s possible that certain parameters of our DCS are below 0 (when the liquid level is empty or there is no pressure, the 4–20mA signal may be 3.99mA or even lower); as a result, the value transmitted via 485 to the safety monitoring system becomes less than 0, triggering an alarm. They should adjust the alarm lower limit to a negative value or set it so that no alarm is triggered at that level.

It’s probably a website issue; last time they informed me that the data they received had noise, so I’m not sure how they handled it to fix it