Trying to figure out a way to benchtest Modbus RTU between several PLCs on the bench

Hey guys,

I've got a system I'm coded up, it is using three SCADAPack 357 controllers. Out in the field, they'll communicate via TeleDesign TS4000 radios with Modbus RTU (RS232) (one master, two slaves). The problem is, I won't have access to the radios on my bench, but I want to be able to do some testing of comms before I integrate onsite.

If it was Modbus TCP it would be easy, since it's just an ethernet connection. But with Modbus RTU via RS232 it's obviously a serial connection, not ethernet.

What I'm wondering is whether or not there's a straightforward way to test the serial connection between all three PLCs without having the actual radios at my disposal. Does anyone have any ideas on how you might go about this?

Thanks!

Humm... RS232 but there are two slaves? Maybe I'm confused, but don't you need two RS232 port on your master then?

I figure you can just wired directly from master to slaves on the bench and skip the radio to do the test.

you swap over to 485 or you can use a splitter.

we used to use these inthe past but I know there are probably some cheaper ones out there.

https://www.blackbox.com/en-us/store/Detail.aspx/3-Port-RS232-DB25-passive-splitter/TL073A-R4

I guess worst case you can hook up just one slave a time if you dont feel like spending any money.

harryting said:

Humm... RS232 but there are two slaves? Maybe I'm confused, but don't you need two RS232 port on your master then?

Click to expand...

Maybe I said something confusing? What I'm trying to describe is a master PLC that polls two remote pump stations via radio. The radio goes to the comm port of the SCADAPack, and each remote site has a radio as well.

diat150 said:

you swap over to 485 or you can use a splitter.

we used to use these inthe past but I know there are probably some cheaper ones out there.

https://www.blackbox.com/en-us/store/Detail.aspx/3-Port-RS232-DB25-passive-splitter/TL073A-R4

Click to expand...

That is exactly what I was trying to find, but didn't know what to call it. Thanks for the link! You can imagine the low quality google results of trying to describe a serial connection but in parallel.

I guess worst case you can hook up just one slave a time if you dont feel like spending any money.

Click to expand...

Yeah in theory I could do that. What I really want to test is that both pump stations act properly though, and they both rely on each other to run so testing one at a time would force me to miss out on a ton of functionality testing.

You can use a rs232 splitter from black box as well. But yeah if you don't have the radios I would do it hardwired.