Low-voltage communication buses are critical to networked automation systems and when they fail they are a pain to troubleshoot. We use them because the cables are cheap and you don’t need expensive switches, but what you save in parts you may pay in labor later. Ethernet/IP based communication is on the rise, but is still…
When installers build automation systems getting it working is their main focus. They see building automation security as an obstacle to overcome rather than the goal. If authentication is getting in the way, they disable it. When firewalls are blocking communication, they disable that too. Even more problematic is the fact that several popular automation…
I submitted a link to this site to AutomatedBuildings.com and Ken Sinclair got back to me with an interview request! You have find the interview in their April 2016 issue, here. In it we discuss in broad terms what this site is about and my plan for it going forward. Here’s a snippet: Sinclair: Is…
RS-485 bus grounding and termination seems like a magical ritual. Some people get lazy with the details of termination because buses often work even when termination is done incorrectly. I had some untwisted, shielded AWG22 lying around, so I used it to show a quick comparison between bus wiring in a controlled environment. I used…
Modbus is one of the simpliest protocols you’ll find in the field. It’s the closest protocol “to the metal” of the chip on a controller since it often just directly exposes the controller’s memory. There’s no point discovery here; there are no point names or descriptions to help you integrate. All you have are datasheets…
RS-485 grounding is frequently missing from commercial automation installations. It’s especially egregious when you are using your shield as your signal reference, because that reference is now noisy as heck. The shield’s job to collect interference. It’s up to you to make sure that interference goes somewhere. The Case Study I was looking at the…
I had the opportunity to troubleshoot an MS/TP BACnet bus using my Rigol DS1052E oscilloscope. Oscilloscopes are much more useful for bus diagnostics than a multimeter. Although they don’t tell you where the problem physically is, they can immediately confirm that you are in fact looking at a bus fault instead of a software problem…