Can a daisy chain of ION7330 Meters be configured for Modbus only Communications?

[Nicholas_Brown]

I have a customer that is using an ION7330 connected ethernet acting as a Ethergate gateway to a number of other serially connected ION7330s, all using ION protocol monitored by PME.

They now are looking to transition these devices to a 3rd party system that only uses Modbus protocol.

I know the ION7330 supports Modbus TCP and Modbus RTU individually, however, can the ION7330 also act at a gateway to the serially connection ION7330s using Modbus protocol?  Does the Ethergate funtionality support this?

[Charles_Murison]

Hello @Nicholas_Brown ,

First item to note, do not mix protocols on the serial line. Either ION only or Modbus only. 3rd Party system will replace PME and you will lose access to things like stored data and waveforms. Have you looked into PME feeding data to 3rd party system rather than from devices directly?

Ethergate is protocol agnostic, the Ethergate takes the data section of the Ethernet packet and sends this on the serial line, no preprocessing the packet. So in this regards, yes Etherget can support Modbus RTU over TCP. This would require that 3rd party system is able to send Modbus RTU message inside a TCP packet. Newer ION meters support Modbus gateway function. This supports Modbus TCP packets getting received by meter, processed, then sent on serial line as Modbus RTU message.

Note that modbus RTU over TCP with Ethergate has some inherit risks. There is no way to track requests to responses. Under some conditions it is possible to have a mismatch between the response received and request sent. 

Regards,
Charles

[Nicholas_Brown]

Thank you Charles, so are you then confirming that an ION7330 connected Ethernet could support a Modbus TCP connection (being polled for modbus data over port 502) and also simultaneously act as an Ethergate gateway for downstream Modbus requests to serially connected ION7330s (set for Modbus RTU on their comm ports) over port 7802? 

The scenerio is that PME is going away for this customer and we are helping them integrate the meter data to their new system, even though as you mention this will be a restricted subset of the overall available data.

[Charles_Murison · Accepted solution]

Hello @Nicholas_Brown 

ION 73XX meters are old and officially no longer supported. I do not have access to a meter to verify. From documents and FAQ I can see that meter does support Modbus TCP. https://www.se.com/ca/en/faqs/FA212335/
Meter would support 1 Modbus connection and 1 Ethergate connection.

Regards,

Charles

[Robert_Lee]

Just to clarify, the ION73xx series only supports Modbus TCP to the device itself.  Any software (replacing PME) would need to have the capability to send Modbus RTU encapsulated inside a TCP frame to port 7802 to talk to downstream devices.

This would require 2 separate connections using two different types of Modbus requests from the same software.  One connection to talk to the TCP connected 73xx device and a second different connection to communicate to the remaining serially connected 73xx devices.