Hello. I have a Digi One IAP successfully connected to a Caterpillar EMCP 3.3 Genset generator system.
2 wire setup. I have the exact same generator setup at another site and cannot get the Digi to poll modbus data. I can move the gateway to the working generator and it communicates fine. I can ping and get on the web gui fine. LED’s appear to be the same as the working unit.
Any ideas on what the issue may be or something I can try?
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Digi International Tech Support
I assume by 2-wire you mean RS-485? This sounds like a grounding issue to me (& I have 20 years experience with RS-485). Technically, all electrical circuits require a signal return (aka: the ‘third wire’ in a 2-wire RS-485). By only using 2 wires, you have 2 ‘current sources’ during transmit, and 2 ‘current sinks’ during receive. Don’t let the ‘+’ and ‘-’ labels fool you! Likely there is a grounding or power supply difference between the two sites. Do some research at web sites selling RS-485 isolators - they probably have white-papers on this topic.