I am working on a SCADA system that utilizes XTend-PKG radios; one base radio communicates with several remote sites and the base radio is connected to a PC workstation running National Instrument Lookout. The radio is connected through an RS232 to USB converter. In the existing system, the PC workstation and remote RTUs communicate with Modbus Serial. The comms statistics show very strong connection; ten sites are polled every five seconds and there have been no reported communications failures from the client (and there are comms statistics and each site shows >98% comms success).
My project is to replace the existing PC workstation with a SCADAPack PLC. I've copied all the Modbus serial settings (baud rate, parity, etc) from the existing workstation to the new PLC. What is happening is that when I plug the existing base radio into the new PLC, some of the remote sites will communicate but others simply will not; two or three remote sites will communicate with around 90% success rate, but others have literally never had a successful communication but as soon as I plug the radio back into the existing system, every site successfully polls within five seconds. The PLC indicates that checksum errors are occurring every time we have a communications failure. I've had tech support for the PLC check my code, and they say everything is configured correctly and that I should look at how the radios are configured.
On my laptop, I have a Modbus simulator program and when I connect to the existing base radio with an RS232-to-USB converter, I can poll all ten remote sites with no issue.
It seems like there is some sort of issue with the new hardware not going through an RS232-to-USB converter, as in the converter may be providing some sort of latency and now that I'm straight RS232 to RS232, there may be some sort of issue with timing (as in turnaround time, maybe)?
I've been able to pull all of the configuration settings off the existing radio through the XCTU terminal, and I'm working through them but was wondering if there was something I should specifically be looking for and if there is anything anyone can recommend for what to be checking.