PC reads data slowly from PLC

Hi,

I've managed to write some dot net code and read data from temperature sensors via Allen Bradley PLC Micrologix 1400. Unfortunately the read action is pretty slow: 3 to 10 seconds each time. I know that sensor response times can be slow for (T and RH for example) but I don't suspect that to be the problem.
1.Can any one suggest a possible solution since my program is supposed to connect to at least 20 machines, each having 4 to 8 sensors for temperature and humidity (ie a total of 8 to 16 sensors per machine). At this slow data read speed, the system will fail.

2.Also, what is the typical PLC read data time by a PC (a few milliseconds or seconds)?

3.I'm using NI OPC server at present, but intend changing to Matrikon's OPC server for Allen Bradley. I'm not sure if I could use this or Matrikons Universal OPC server for PLCs with the Allen Bradley plug in.

Thanks in advance.

Hi,

OPC does slow it down a bit but you should get fast results.

You might want to give PeakHMI a try. It has a built in OPC server and can communicate with all the PLCs.

The update rate should be programmable.
I use RSLinx for my OPC server and an OPC client component from Kassl.
The update rate is set from the client.
3 to 10 seconds sounds like there is a communications issue though.

Thanks Mark & Steve. Any suggestions on which Matrikon OPC server is preferrable for use with AB Micrologix 1400?

I would put a protocol analyzer on the network (since it's Ethernet, it should be nearly trivial to run Wireshark on your PC) and see if it's the software polling slowly or the controller responding slowly.

My colleagues are of course correct; the OPC Client (in your case, the custom .NET application) determines the polling rate.

A MicroLogix 1400 can respond to a data request in then "tens of milliseconds" time range, so update times of 100 or 250 ms in OPC servers are not uncommon for fast applications.

Thanks Ken.