+Field notes / RS485
Nobody on the bus.
On a serial line, almost every fault looks the same: silence. Four call-outs, a scope, a label and a very slow scanner.
FIELD CALL / ON SITE
The new controller
The old controller died and was replaced with a spare from the shelf. It powers up fine. The temperature sensor on the line hasn’t answered since.
NOC gremlin: I’m the NOC gremlin. I don’t fix things. I watch.
- Polls
- 0
- Changes
- 0
- Hints
- 0/3
The line
Modbus RTU · half duplexLaptop connected to the controller’s service port.
Poll the sensor, look at the line, read the label.
A simplified model of a two-wire RS485 bus with one Modbus RTU slave. Frames and CRCs are real; timing, electrical levels and noise are stylised. Based on the kind of faults that actually show up on site.