Advice/learning about RS485 communication and a specific setup

[berry97]

Hey all, I'm a somewhat 'fresh' engineer so apologies if I say any profound nonsense.

I'm working on a project that involves using three Omron temperature controllers (Omron E5CN-HV2M-500 AC100-240) with RS485 compatible option modules in tandem with three high-current power supplies to heat some cathode setups. Currently, I have constructed an isolated electrical chassis that I can put in an electronics rack in the lab to help with noise problems, and am looking to set up some wiring that will help me to communicate with my temperature controllers from a computer.

Ideally, my setup will involve a single panel-mounted receptacle that will connect to each of the three temperature controllers within the chassis using a Daisy-Chain topology. (I also have an RS485 Opto-Isolator that has an Ethernet input and output, which leads me to want to use an Ethernet cable for the chassis receptacle.) However, if I do use Ethernet ports, at some point I will have to convert back to individual shielded wires, as my temperature controllers use screw-wire connections, and are not Ethernet-cable compatible.

Could someone with a bit more experience with RS485 communication verify that my thought process is correct on this, and perhaps enlighten me as to why so many guides recommend using Daisy-Chain setups in RS485 connections?

Thanks.

 

[KlausST]

Hi,

A picture could clarify your configuration.

To be true, I only know parallel bus RS485 configuration, not daisy chain.

Klaus

 

[FvM]

Are you actually referring to daisy chain (each node receiving and resending) the messages or simple party line? The latter is quite common for RS-485 networks, e.g. PROFIBUS. It can work with high speed when terminated at both ends of the party line.

 

[berry97]

This is the setup that I have in my head ATM. (sorry for mspaint quality)



The reason I mention "daisy-chain" in particular is because I have been reading a couple wiring guides on RS485 systems which specifically mention Daisy Chain as being the preferred method for organizing RS485 topology. Note that in my setup the Chassis is only about ~40x25cm, so the wire lengths won't be that long. I still plan on having coiled wires no matter what for noise reduction.

- - - Updated - - -

Also, here is a picture of the ports on the Omron temperature controller. I'm also holding up the small diagram of the option unit showing how it has two screw terminals designated for RS485 compatibility. However this raises the problem that clearly there is no Ethernet port on these controllers.

 

[FvM]

I conclude that the term "ethernet" in this thread actually means RJ45 connector, and that Omron sloppily designates a simple party line RS-485 topology "daisy chain".

Nevertheless the shown configuration should work.

 

[betwixt]

In colloquial terms, 'Daisy chain' refers to each node receiving and forwarding the information to the next so data passes through each one and on the the next like links in a chain. I agree with FvM, they are actually referring to the more normal topology where all modules is in parallel, sharing the same data wires and ideally ground connection.

The signaling is differential so in theory you can use twisted cable, including ethernet types as long as you correctly terminate at the ends. You do not and should not use a termination network anywhere other than the ends as it would serve no purpose but increase the load on the transmitting device.

You might find the modules have a switch to enable or disable the termination, if that is the case, only enable it on the end modules.

Brian.