Converting Speed Rates - RS485 Modbus RTU

[sparkie]

So I'm working on an old project I did several years ago. It has 12 nodes on a modbus RTU network. I'm going back for an expansion.


I'm going to talk to the customer and see about just using Ethernet/IP for all of the new stuff, which I'm sure he will go for.


But the existing network is performing pretty slow. One of the nodes only supports 9600 baud. I'm looking to speed the network up. I want to increase the baud rate of the network and see how it performs.


In order to do this, I'm going to need to get that 9600 baud device isolated from the rest of the network so I can increase the baud rate.


Does anyone have any suggestions for a device that can take a higher modbus RTU baud rate and convert it to the 9600 the device needs, and vice versa?

 

[the_msp]

I've never heard of a device that can sit at say 19.2k baud and have a node on 9.6.

Might be worth talking to your local Moxa distributor and see if they have something.

If it were me and I was going for E/IP, I'd drop in a:

https://www.moxa.com/en/products/in...eways/mgate-5105-mb-eip-series#specifications

Two of, one for the higher baud-rate and one for the stand-alone, lower baud-rate.

 

[lfe]

I think you can ask the company in the link if that device can do the conversion . It specifies The Self-Tuner mode can support Multiple Baud Rate and Multiple Data Format

https://www.icpdas-usa.com/i_7514u.html

 

[Steve Bailey]

With 12 nodes on a Modbus RTU network, don't expect much of an improvement when going from 9600 to 19200. The overhead of sending out a command to a node and waiting for a response is a larger factor than the speed of the commands and responses.

 

[Ken Roach]

I think the ideal device is ICP-DAS TSH-700 series, probably the TSH-725.

https://www.icpdas-usa.com/tsh_700_serial_to_shared_device_servers.html

I have used a similar B&B RS-232 unit for a similar application years ago, but the ICP-DAS datasheets and technotes suggest that the TSH-725 will do exactly what you want: repeat the RS-485 serial data onto an isolated link at a different serial speed or framing setting.

 

[sparkie]

I think the ideal device is ICP-DAS TSH-700 series, probably the TSH-725.

https://www.icpdas-usa.com/tsh_700_serial_to_shared_device_servers.html

I have used a similar B&B RS-232 unit for a similar application years ago, but the ICP-DAS datasheets and technotes suggest that the TSH-725 will do exactly what you want: repeat the RS-485 serial data onto an isolated link at a different serial speed or framing setting.

Coming in clutch Ken.


Appreciate it.


Thinking I might be able to use this one to convert the controllers over to Modbus TCP as I have two PID controllers per box:
https://www.icpdas-usa.com/tsh_725i

With 12 nodes on a Modbus RTU network, don't expect much of an improvement when going from 9600 to 19200. The overhead of sending out a command to a node and waiting for a response is a larger factor than the speed of the commands and responses.

Yea, it takes a minute for everything to update, and I had to write a nice bit of hand-shaking and error-catching logic for it. I was misinformed by AD tech support. They told me that the controller would queue the traffic, but later I found it it only stores a couple messages and then dumps the rest, so you have to stagger the communications. That's why I'm not intending to expand on this network, but I do want to try and speed it up a bit while I'm out there working.


The new system will be dependent on the PLC, so I can migrate them away from this hand-control-backup strategy and to a strategy to protect and keep spares for the PLC.


The next thing I need to think of is a way to VPN in, as I'll be moving away and want to provide remote support for them.