Where does the delay come from.
If a 195 and a 150 rolled into a station at the same time. Where does the door opening process / times differ? Is it simply the 195 takes longer to respond to the button pressed? I presume there is software and processing involved on a 195 where its more relays and mechanical interlocking on a 150.
The answer to that question has many variables but let’s look at the slowest case scenario.
A multiple platform station (let’s say Oxford Road)
Northerns ASDO (Automatic selective door opening) system relies on input to tell it which platform it has arrived on. Only opening the correct amount of doors (length) and on the correct platform side.
This is done in two ways. Via a track beacon (you may have seen the yellow strips at the start and ends of platforms which TPE use) or via Driver input on arrival at the station.
Northern have chosen not to use track beacons. (Assuming down to costs for the number of stations we have) so the onus falls upon the driver to select the correct platform.
The problem then is Northern Drivers aren’t allowed to program the ASDO system once a journey has commenced.
So the 195/331s are fitted with a SDO/ASDO override switch at each door control panel for use by the guard.
So you arrive at the station and the guard has to use this switch, you’ll potentially hear 3 door releases and if your on the 3rd wave it’s going to seem like a long time.
Door release one is the guards local, which is reasonably slow. They have to then step onto the platform and check the train is accommodated and safe to open doors before stepping back onto the train to release. (Conventional units you can usually reach the door control from the platform and on a 150 your not fighting with commuters to get back on). Once the conductor gets back on they have to select ‘doors forward’ and release doors forward of their position before selecting ‘doors rear’ to open the doors rearward of their position (if applicable).
So if your to the rear of the guard your going to wait longer than those forward of the guard to get off/on.
This also explains why the door not in use symbols light up both sides on arrival at a multi platform station.
Hope that makes a bit of sense?