Charts in Web VI not using current data - lag, delayed

[laserjet4200]

Hi, I'm using Labview to generate a "web portal" for viewing some realtime information coming from a number of machines.

The machines report power system frequency from a number of sites and display the current measurement as an ASCII readout on the Labview front panel, but I also have a chart showing the history of the measurements over the last 20 seconds.  When I look at the front panel on the computer hosting the VI (i.e. on its monitor) all is well and all the data is correct, current and up-to-date.

However, when I access via the web interface (using an Embedded VI) the ASCII readouts are all current, however, the chart is delayed by a variable amount.  I have seen it chart data 3 seconds behind the current samples, and sometimes nearly a minute behind.  i.e., the timestamp of the most recent value on the web chart is lagging the most recent time stamp at the server, even though the web interface is getting the most recent values on the ASCII readouts.

I'm guessing there is some sort of error in rendering the charts at the web client Labview Runtime Engine, but I've no idea how I might fix this.  Any advice would be much appreciated.

I am using Labview 7.1 for historical reasons, I can upgrade to 8.6, but would prefer not to.

Thanks 🙂

[GuenterMueller]

It is a good amount of time ago that I have been using remote panels with LabVIEW 7.0 but I have faced the same issue in 2003 (if I remember correctly). As far as I remember, the big difference between updating a numeric indicator and a chart is, that updating the chart requires the entire history needs to be send to the remote client.
You say "I also have a chart showing the history of the measurements over the last 20 seconds". I think that you expect too much from the remote panel in conjunction with charts. If you write to the chart at a slower rate you might get better behaviour.
Another apprach (I do not remember if this is a good tip): The behaviour might improve by decreasing the Chart History Length.
Hope this helps, Guenter

[laserjet4200]

Hi Guenter,

Thanks for your advise.  I've actually done a bit more investigation, and I have descovered that if I view the server in Remote Desktop alongside the web VI, the lag is actually several minutes long (currently 6 minutes) going by the time indexes on the chart.  The numeric indicators are up to date!  :s

Would you know if Labview 8 improves matters?

Thanks.

Message Edited by laserjet4200 on 01-08-2010 05:49 AM

[Owen.S]

Hi Laserjet4200,

How are your computers connected together? Are they networked? It seems like this lag issue has come up before and it has been the network problems.

Kind regards,