I have been given a project that involves using this bridge to communicate with a PLC via a repeater and polling remote radio. The project involves SCADA control of a multi-well system. The polling engine will make its requests for data via TCP/IP connection to the 174CEV30010 ethernet port. The modbus port will be connected to a polling remote radio (MDS 9790) via a RS-232 connection. The polling remote communicates with a repeater radio (same type) that communicates with the radio at the well (MDS 9710) that in turn communicates with the PLC (TSX Momentum).
Communications and configuration of the 174CEV30010 via the ethernet port has worked fine. The modbus communications via the radios to the PLC has not.
Is this a good application for the 174CEV30010 ?

 

I have had occasion to work with a Siemen SCADA system which is intended for use with Wastewater, Mining,Tranportation and other applications involving radio modems.

contact
Wayne King, SINAUT Marketing Manager

[email protected]

I work with Wayne as a contact to the Siemens Customer training department. In January I will be setting up the SINAUT system for an upcoming training class offer in February.

The PLC is the STEP7-300 PLC from Siemens. You add a TCP/IP card to the PLC rack and a TIM card for modem communications. You end up with a single rack that supports routing and the WAN network for communication to the RTUs and the PC workstations communicate tranparently. You are not required to engineer software drivers and write software to get multiple vendor products to work together.

The TIM card is part of the Siemens SINAUT subsystem for wide area communications.

hope this helps.
If you are interested in the SINAUT system check out www.sea.siemens.com/SITRAIN
and look for the new class on SINAUT


gary wrotnowski

 

Can you poll using Modbus/RTU only through the 2 radios - without CEV?

My first thought is it may not be a CEV issue - if the radio is adding gaps to the Modbus/RTU message, the PLC or CEV may be rejecting the messages. Some radios break data up into small packets (say 32 bytes each) and do retries internally. This can cause small timing gaps to appear on the serial port (in this case a potential pause after ever 32 chars). Some devices will incorrectly detect this as an EOM condition - which is why vendors of slave products worrying about enforcing the 3.5 char timeout are just cutting their own throats support-wise.

I'm not sure the setting on the Momentum, but the CEV has a "character timeout" which defaults to 50msec and you can set it up to 1000msec or more. As long as you're using standard Modbus commands, setting this high has no impact in performance as the CEV uses an "expectation" algorithm to estimate message size for published commands (and a few Modicon private ones). It only has impact when unknown commands are sent, in which case it must wait for the idle timeout.

If your radio requires RTS/CTS support, make sure you have the latest v1.6 firmware on the CEV and make sure you enable that in the firmware. It includes options to hold RTS active for a delay after sending etc.

Best Regards
- Lynn