RedLion and AB 485 Network

[AlanSmith]

I have 4 machines each with an identicle PLC/HMi layout. Layout as follows...
AB SLC 503 cpu. The 485 port connects to a 1747 AIC.
The AIC then connects to a 1761 NET AIC via 485.
The NET AIC then connects to a PanelView Plus via RS232.
Each of the machines is the same and there is no connection between the machines.

I wish to modify the system so that a single RedLion DSP can collect and log a small amount of data from each plc.

As I see it, I have two options.
1) Connect all the AIC and NET AIC units together into a long Daisy Chain. Give each PLC a different "Address"
Add a new AIC (or NET AIC ?) and connect the DSP to this.

or

2) Connect the DSP to the "Serial" Port on the PLC's

Question for option 1... Will it work or will I get conflicts between the 4 x PanelViews and the RedLion DSP ?
Note, each PV would only need to access its own PLC. The DSP would need to access each PLC.

Question for option 2... Can a DSP be connected to 4 x PLC Serial ports at the same time ?
or... can I buy a DSP with 4 x separate RS232 ports on it.

I would also consider any other connection options instead of the above.

The DSP would "serve" the collected data to a PC via its ethernet port.

Thanks in advance for any advice
Alan

 

[JeremyH]

Hello,

Your first option will work as long as you make sure that all devices have unique addresses. This will probably be your easiest option. Option 2 is possible but you would need an expansion card for the DSP and an RS232/RS485 converter to have enough ports.

Thanks
Jeremy

 

[OkiePC]

With Option 1, you might run the risk of reducing the performance of the existing HMIs. Since DH485 is a token passing network, there can only be one master at a time. Right now, you have two devices on each isolated network, so they can take turns pretty fast.

When you have all 9 devices on a DH485 network, you may see performance degrade since it will take longer for the token to get all the way around the nodes. The amount of change in performance is going to depend greatly on the size and organization of the data being transferred by each device.

There are some fairly simple things you can do to help avoid issues like keeping all your node numbers together, so there are no gaps. And, keep the data used in each HMI in orderly blocks, so that a minimal number of reads and writes have to take place.