We have hosted a Factory PMI/SQL application on a server. We are not able to see the real-time trends over the WAN. The whole trend window is blank, no lines, however the time keeps changing. If a pen is checked/unchecked, a part of the trend lines appears for a few seconds (2-3) but then again disappears. However this problem is not reported over another machine on the local LAN where the server is hosted. We had even seen this problem when viewing the Factory PMI Dairy Plant Demo Application hosted on your web-site.
Few more light on the above topic:
What I noticed was that while plotting the trend the time on the x-axis is based on the system time of the machine where the trend is being plotted. So if we say Last 5 mins and the current system time on the client machine is 6:50:00 PM, the trend will be plotted from 6:45:00 PM (on extreme left) to 6:50:00 (on extreme right). However the data which is plotted inside the trend is fetched from the server machine.
So for e.g. if the server machine is lagging the client machine in time by 15 minutes i.e. server machine shows time 6:30:00 PM. Then in this case since the client machine is plotting data between 6:40:00 PM and 6:45:00 PM, but there is no data yet stored on the server for this time interval hence the client window will show blank.
Question:Shouldnt the trend time plotted on the x-axis on the client machine be taken from the server? Otherwise this system will have a problem when the client and the server are in different time zones (which may be the reason why we in India are not able to see the trends from your dairy plant demo hosted in the US)
Though this is one of the reason, this does not seem to be the only reason. Even in the case where the lag between the server and client machine is less than the time interval of the time trend window, the trends are not to be seen.
Yep, this is a timezone issue. Your timezone is making your realtime chart ask for data that the server thinks is in the future, which is why you’re not seeing any data. The easy chart should compensate for the gateway’s timezone. Thanks for the careful analysis of the problem, we’ll resolve it in the next release, either by adding a timezone adjustment feature onto the easy chart or by making the queries timezone-independent (normalized to GMT)