SignalTraffic Forums

In a NEMA cabinet, what's the difference between a phase detector and a system detector? My P40 cabinet came with 23 loop amplifier cables hanging in the cabinet. I traced them out to the various terminals and noted the faint markings written on them. 12 of them are wired to the controller phase detector inputs in various combinations. These were all grouped on one terminal board on the side of the cabinet. The remaining 11 are on a second terminal board and are marked LS1/sys, LS2/sys, etc. thru LS8/sys. I can't find where they're connected to the controller at all. What function do they serve? The cabinet was wired for 8 phases, 4 overlaps and no peds. The cabinet came with 3 copies of the wiring diagram, but it was just the first page 3 times. It refers you to page 2 for the detector wiring. Go figure...

Well I've transitioned over to Highway Divides but I will come back here to answer your question

Phase detectors are those set up to simply place requests for vehicle calls. System detectors are essentially phase detectors that have been assigned as such through controller programming to operate traffic responsive coordination and/or gather reporting data. System detectors gather data based on the amount of calls within a given time to select coordination plans and adjust the timing of the controller in real time. System detectors also provide a report of various detector activity that is updated based on the controller program. Not sure why they'd be wired onto a separate board unless it was part of a custom set up by the municpality. In the EPACs, you just choose which detector input you want to function as a system detector.

In my cabinet I've assigned all the vehicle detector inputs I use to system detectors because the timing of my display is traffic (detector) responsive.

The basic NEMA controller spec has 8 inputs. Controller makers added more so the first 8 are vehicle detectors the next are system or auxiliary detectors. The LMD has 8 vehicle, 8 system and 8 auxiliary. On the 390 the system detectors can be mapped to the master which can track 16 of them coming from controllers on the system to determine cycle/split/offset selection. NEMA also didn't provide for timing features like delay or extension of the input call so that used to be handled by the detector.