Hello!
I have a problem regarding the time-stamp-interval.
I am measuring data with power monitoring devices (Sentron PAC4200) as well as pressure- and flow-sensors (via a S7-1200 PLC) and i'm reading data from the Sinumerik 840d (for example actual axis-speed).
In WinCC OA I am using MODBUS and S7 drivers and for all corresponding datapoints.
Polling is set to 100 ms and the Low-Level-comparision is set OFF for all datapoints.
I'm searching for a way to get data-points with the same starting point and the same timestamp-interval of optimally 100ms.
At the moment for most datapoints I only get a non-consistent resolution and the timestamps do not have the same starting point.
Here is an example of two datapoints (Axis-Speed and Power, Timestamp(ms)|Value(mm/s or Watt)):
Time(ms)|System1:actSpeed:
79|11,7187 104|11,7187 174|0 214|0 279|23,2817 309|23,2817 379|11,7187 419|11,7187 499|0 564|0 609|18,8789.
Time(ms)|System1:PAC8:
102|0,27217 199|0,27217 399|0,27289 600|0,27315 801|0,27302 999|0,27295 1201|0,27260 1399|0,27238 1600|0,27256 1800|0,27244 1999|0,27233.
As you can see the timestamps don't record at regular intervals and furthermore looking at the timespamps 79 and 104 or 279 and 309 i get the same data though i think there is a change in the value.
I am not entirely sure if it is caused by WinCC OA or my hardware.
Thank you in advance for any tipp!
Timestamp Problem
- Gertjan van Schijndel
- Posts:634
- Joined: Mon Aug 02, 2010 10:37 am
Re: Timestamp Problem
Maybe you are trying to poll too many values with this short interval.
How many s7 values are you trying to poll with this interval?
Do you get regular intervals, if you increase the interval to 500ms or 1000ms?
How many s7 values are you trying to poll with this interval?
Do you get regular intervals, if you increase the interval to 500ms or 1000ms?
- n_lev
- Posts:73
- Joined: Tue May 28, 2013 2:24 am
Re: Timestamp Problem
Generally speaking you can not rely on SCADA to get data with guaranteed time interval. This applies to any SCADA, not just WinCC OA.
The poll rate that you set is basically your "wish" but no SCADA will guarantee it. At the end of the day, SCADA is just a computer under Windows or Linux, hence the poll rate can be greatly affected by the PC performance, network performance and another 100 factors.
If you need to reliably log certain values at certain intervals, I'd use PLC. You can configure it to read inputs with time interval you need, then store the values to some datablock together with their respective timestamps. Then you can read all this infrom from SCADA with much slower interval at ignore the SCADA timestamps, use PLC timestamps instead.
Moreover, Siemens PLC's actually even have a special block that allows this kind of high speed reliable data logging. WinCC OA also allows you to use TSPP (I think that's the name) format of S7 driver to get timestamped values. But you can implement it with normal driver as well. You just have to do the data collection and timestamping in the PLC, not in SCADA.
The poll rate that you set is basically your "wish" but no SCADA will guarantee it. At the end of the day, SCADA is just a computer under Windows or Linux, hence the poll rate can be greatly affected by the PC performance, network performance and another 100 factors.
If you need to reliably log certain values at certain intervals, I'd use PLC. You can configure it to read inputs with time interval you need, then store the values to some datablock together with their respective timestamps. Then you can read all this infrom from SCADA with much slower interval at ignore the SCADA timestamps, use PLC timestamps instead.
Moreover, Siemens PLC's actually even have a special block that allows this kind of high speed reliable data logging. WinCC OA also allows you to use TSPP (I think that's the name) format of S7 driver to get timestamped values. But you can implement it with normal driver as well. You just have to do the data collection and timestamping in the PLC, not in SCADA.