@bogleg, you bring up a very important point regarding devices (appliances?) that we wish to connect to our control system.
When we select equipment for a grow room which will be controlled using typical timers, we don’t really need to be concerned with “interfacing” these devices, just whether they will do the job and we can afford them.
With an integrated control system (in our case using an industrial PLC) we must select devices which will be compatible with our design and the other equipment in the system.
One example is choosing a temperature/humidity transmitter. The transmitters that I am using are capable of sending a voltage signal or a current signal to the PLC. I have them set for voltage because the input modules that I selected accept 0 - 10 volts. The “current” devices would be a more appropriate choice if we had electrical/electromagnetic noise issues to deal with. If I had not been aware, it would be very easy to select a voltage input module and a current field device (or vice versa). This would not work.
When we are connecting analog devices such as temperature or humidity transmitters to our system it is crucial that we use appropriate cable (shielded) and that the shields are properly connected to ground at only one end of each cable (PLC end) and isolated at the other. If this is gibberish to you, we will clear this up over the next few discussions.
The choice to go with industrial automation imposes a set of constraints on most of the other equipment that can use. Are these constraints reasonable for your situation? The answers will likely fall in a wide spectrum.
It is best to come up with an overall system design before locking in on a specific set of equipment choices including the choice of whether or not to use industrial automation equipment at all.