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Wednesday, June 20, 2018
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Best method for this scenario

I have a situation where I want to use the MODBUS 485 option of a Gas Monitor Controller. I do not want to use the 4-20mA option as the analog input cards for the series of PLC are discontinued and cost thousands if you absolutely want one.

Currently the client has a CMM321 comms card on the rack that handles the HMI's on the network. This is done with the TCP port on the CMM321 card. The Ethernet cable is converted to Fiber and travels around 300 feet to another building. At this other building is where I will have the gas controller.

Would anyone agree that my best option is to utilize the fiber run and add a fiber to MODBUS 485 converter? What brand would you recommend?

Does anyone have any other suggestions?

Do that mean there are other spare TCP ports on the CCM321 comm card?

I would add an Ethernet switch to expand that Ethernet connection and use a Modbus 485 to Ethernet converter to add the gas controller to the network.

good luck

Is the gas monitor controller a Modbus master/client or a Modbus slave/server?

It warrants investigating which box plays which Modbus role and confirming that the respective functionality for that role resides in the box at each end.

Thank you for your reply. The Gas Detection Controller will act as a client.

Ethernet cards are no longer available for the 90-30 series PLC. I plan on using the existing Ethernet coming out of the CCM321 and splitting the Ethernet cord into a switch. From one of the ports on the new switch I will convert to Fiber that will end up 300 feet away and converted to RS485 to the Gas Detector that will be a slave.