What I'm trying to do in my project is log 8 gas detectors off the GMI active 80 through a MODBUS connection on a Xenta 511 web server. In addition to this I want to pick up any high priority alarm signal from any one of the gas detectors and send that back to my project in the 511 to turn off a gas valve. A hard one to crack I know, but I would appreciate anyone who could help, thanks.

Best Regards
Lee

 

GMI does not publicly post documentation, so it's an unknown. The ZXenta 511 claims Modbus master functionality, so it's probably capable.

But, are these hazardous gas detectors?

Logging historical data from a gas detector via Modbus is probably acceptable, but doing a hazardous gas alarm via Modbus is very, very weak. I wouldn't buy into it.

Modbus is master-slave protocol, which means that a slave, a gas detector, cannot signal an alarm on its own. A Modbus slave is silent until spoken to by the master. The master has to poll the slave and then get a reply from the slave in order to get an alarm from the slave.

When you have multiple slaves, each slave requires its own poll and response. Polling time-outs can significantly delay sequential polling. Some masters deal poorly with time-outs or errors and leave stale data from earlier reads in their data table as though it is current data, with no obvious way of determining stale from new.

It's just not a good way to deal with hazardous gas alarms. Think hard wire.