Step 7 fast data access

Hi all,

I need to access PLC values using an external program that I am writing. I have tried OPC but it is not fast enough or reliable enough. Setting the OPC update rate to 50ms, I get data with 200-500ms gaps (tested using multiple clients). I need a constant stream of updates at least every 50ms.

Is it possible to get similar performance to monitoring values using the variable table (VAT) built into Simatic Manager?

This shows value changes pretty much instantly and is very consistent. It is exactly what I need, but is it possible to get this performance outside of the S7 product?

If not, do you have any other ideas?

Thanks for any help,
Gareth

Hi!
Something similar was discussed here:

http://www.plctalk.net/qanda/showthread.php?t=62960

Kalle

Thanks KalleOlsen, that was a great help.

I didn't realise that you could communicate directly via TCP/IP. From what I've done so far, it is much faster as well.

Thanks again,
Gareth

Vartab read functions

I've implemented the read functions, wich are used by the VarTab in my Library. (http://siemensplctoolboxlib.codeplex.com/). But I don't think that they are faster than the normal reading!

Depnds of S7 type and program scan-time. E.g. S7-315 uses MPI-bus betwwn CPU and CP, where MPI speed is 187.5kbit/s. That's why in HW-Config CP-Unit needs the Backplane Connection MPI-Address.
S7-400 series, S7-318 and up, there is not MPI Backplane.

I have done UDP-Server for PC and S7/CP sends data when data have changed. UDP-Server adds time-stamps to 1'st 2 CSV-file columns and data columns from PLC after that. UDP is faster than TCP/IP.

I tested it by 315CPU-->MPI-->CP-Lean-->PC. CPU's scanning time was about 10ms and PLC sends 26pcs 48char ASCII-data/second, where 1'st column was file-name without ".CSV". MPI spends about 3ms with 48char.
Can't use OB35 for speeding up, minimum interval is 10ms but maybe I can call SEND-block more than 1 time/scan in program. I have to test, can it send double qty.

Another thread where this topic was discussed