On a long-distance transmission scheme for an AO signal
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Our facility needs to transmit a traffic signal to a chemical plant (which is 800 meters away from our control station). I have three options; please take a look: ① The signal sent from the field passes through a distributor (with one input and two outputs), and then is transmitted via cables to the machine cabinet at the other site； ②The signals from the site are output through the AO card in our control cabinet, and then sent via cables to the opposing party’s cabinet ； ③The signals from the site are sent to our cabinets, to the factory-level server database, and then transmitted over the Internet (in other words, the other party can access our database to retrieve this data) ； (This seems pretty cutting-edge; theoretically it’s feasible, as many such things exist in successful ERPs.)
I think the third option is better, as it allows for full utilization of ERP functions. Furthermore, it is also possible to eliminate a large number of cables; if the other party does not need the real-time data from this flow meter nor any control functions, the third method is the best choice.
See what the other party does with this signal; if control is involved, the third option is not suitable due to too many transmission steps and poor real-time performance. If management data is what’s needed, then it’s the preferred choice. 1 and 2 have the same effect, but the second one wastes card slots; the first one is the best.
I guess it’s due to measurement requirements; in fact, there’s absolutely no need to do this! For measuring instruments, you can use locks to prevent anyone from altering the data! If participating in control, then methods 1 and 2 must be adopted! The third one is just a data viewing function!
The first option is probably more practical – just need to add a safety barrier and a cable
First, determine the purpose of the flow rate signals collected by the plant. If they are used solely for monitoring purposes, and given that the distance is not great, the first approach can be adopted. The main goal of this approach is to prevent pipeline leaks; in other words, the instantaneous flow rate at the exit of the plant should be close to the instantaneous flow rate at the entrance. If the instantaneous flow rate at the entrance is lower than that at the exit, and the difference is significant, it indicates that there is a leak in the pipeline； Usually do not participate in control ； If the signals used include instantaneous flow rate and cumulative flow rate, the AO output method cannot be employed, because the total amount discharged equals the total amount incoming plus the amount within the pipeline. However, due to the multiple conversions involved with analog signals, it is inevitable that the discharged flow rate does not correspond to the incoming flow rate; in particular, there will be a difference in the cumulative flow rates on both sides. To ensure accurate measurement and reduce trade disputes, within a range of one kilometer, transmission is usually carried out directly using RS485-RTU along with a pair of RS485 fiber optic transceivers. In the projects I have worked on, both the instantaneous flow rate and the cumulative flow rate are always collected and transmitted to the other party. There are four methods: 1. Twisted pair (within 100 meters), 2. Fiber optic (multi-mode over several hundred meters or single-mode over several kilometers), 3. Radio waves (over ten kilometers), 4. GRPS (with no limit on transmission distance, but delays occur due to channel issues, especially during holidays). Due to confidentiality and security concerns, it is not possible to transmit data from ERP systems between different factories; in particular, making internal databases available to third parties is strictly prohibited
This post was last edited by bjdaydayup on 2012-5-14 at 13:36. My experience: the third method is the worst and practically unworkable； One issue is the large number of steps involved, and the other is that it involves data servers at different levels, which makes things complicated. Not to mention real-time performance and reliability, implementing this process is quite troublesome. The second method is also not good; wasting AO channels is a problem, and AO is generally quite expensive ； Additionally, using AO to drive the AI channel located 800 meters away is intended solely for data retrieval, and it doesn’t look good ； The first option is likely a more practical solution on-site. My recommendation is to use the first approach: either a 1-to-2 safety barrier or a signal distributor to transmit the sampling signals separately. Additionally, in ERP systems, data flow is usually unidirectional to a large extent; can such data be written to the production data server through ERP? I don’t dare to do that.
This post was last edited by huio1983 on 2012-5-14 at 15:22. I often shop on Taobao these days, and the shipping tracking section shows the progress in real time. By using the shipping order number to check on the logistics website, I realized that Taobao’s tracking system likely pulls information automatically from those websites (not necessarily through data transmission from a database), which is why I came up with this idea. Looking back, there is another significant flaw: the issue of time synchronization is not easy to resolve, and this has a considerable impact on traffic calculation.
If this traffic is just a set of data for the other party, the third option can be used
My understanding is that your unit needs to transmit a flow signal to other units; it’s simply a matter of instantaneous flow and cumulative flow, so there’s no need to consider how to control it. In that case, the first option is better: simply change your existing isolation gate to one that allows entry and exit at two points, and use signal cables to transmit the signals to the control cabinet of another manufacturer.