Archive for category Modbus
How do I read the Modbus fault code in my Honeywell RM7800 flame safety controller?
Posted by danstips in Burner Control, Combustion, Communications, Flame Safeguard Controls, Flame Safety, Modbus on June 26, 2014
More and more people are using Modbus to get data from their instruments and controllers back into their control systems for reporting, alarming and troubleshooting.
And while I can’t be there to help you set up your Modbus master, I can give you 13 rules and some general practice advice for communicating to any Modbus RTU device.
How do I get an RTD signal to two different devices?
Posted by danstips in API, Communications, Honeywell, Installation, Loop Controllers, Measurement, Modbus, Precision Digital, Recorders, RTDs, Siemens, Temperature, Temperature Transmitters, temperature transmitters, Transmitters on November 28, 2012
RTDs are great temperature sensors – accurate and easy to install. But they are not friendly when it comes to trying to get a single RTD to go to two places, like when an RTD temperature measurement has to go to both a controller and a recorder. People call and ask, “How do I split an RTD signal?” The short answer is, “You can’t.”
An RTD cannot be wired in parallel or in series to a second device. Any RTD input supplies a known, regulated ‘excitation’ current to the RTD. Mixing RTD inputs would mix currents and that’s a Big No-No.
There’s also a lead wire compensation circuit for 3- or 4-wire RTDs that would create problems if a single RTD were connected to two different RTD inputs. There’s just no feasible means of making two RTD analog inputs play nice together.
But all is not lost. There are several ways to achieve your goal.
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