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alphapointe
Don't Touch Me
MVM
join:2002-02-10
Columbia, MO

1 recommendation

alphapointe to tschmidt

MVM

to tschmidt

Re: uC Boiler Sensing

Stacked logic graph. Each boiler returns a 1 when it's running. For example, the very beginning of the graph where you see all 5 colors for quite a while was when I turned the circuit breakers for the boilers back on and they all fired like hell trying to bring the loop temperature back up...

It actually shows we have a programming error, and the boiler tech is going to have to fix it. They're short-cycling...
(BTW, Kearnstd, these are natural gas boilers)
Kearnstd
Space Elf
Premium Member
join:2002-01-22
Mullica Hill, NJ

Kearnstd

Premium Member

ahh okay if they are NG they likely use a thermalcouple for flame verification. NG does not burn brightly like oil so the photocells do not work.

Interesting thing about your graphing, Is that while it would be much more complex. You could in theory graph the whole cycle of the boiler.

Using an NG furnace for example, ours is controlled by a small circuit board and I know its process is on call for heat the draft inducer starts, the board waits for a completed circuit from the pressure switch indicating there is a draft, the glow plug turns on at the same time as the blower, when draft and heat are verified the gas comes on. And then a few seconds later the blower itself turns on. If any interm steps fail the whole unit shuts down.

no clue if it has a diag port to pull all that data from though.

alphapointe
Don't Touch Me
MVM
join:2002-02-10
Columbia, MO

alphapointe

MVM

There are serial ports on each boiler's control board, but they require proprietary software from HTP, and I don't need that kind of detail. The relays are working fine.

The real fun is going to be interfacing the chiller... (it has alarm relay contacts already, but it's 50 years old and scary to work on...)
Kearnstd
Space Elf
Premium Member
join:2002-01-22
Mullica Hill, NJ

Kearnstd

Premium Member

somehow I am not surprised it needs special software. All the better to milk money with. Of course that software may also allow computerized control and functions beyond diagnostics.

I can imagine the chiller being that old being kind of scary. Main thing to be aware of with alarm contacts on something that old is they might energize with line voltage when the unit needs to alarm. Verses a 24v control voltage.(keep in mind in some systems running 3ph and voltages higher than 240v, control voltage can simply mean single phase 120v.)

alphapointe
Don't Touch Me
MVM
join:2002-02-10
Columbia, MO

alphapointe

MVM

I've got the prints for it, it's just a dry contact closure on each of the three alarm relays.

The chiller is 480V 3ph, and when it starts, the contactor pulls in with a sound like a shotgun blast... it's one of those things where you press the start switch and nearly hit the deck anticipating an arc flash...

I'm considering putting a solid state relay across the 120V start/reset switch so we can start/reset the chiller remotely from the web interface to the PLC...
alphapointe

1 recommendation

alphapointe

MVM

Click for full size
I can't get back far enough for a full picture of this beast...

Everything is online and seems to be working fine. I think I'm going to need a third DA board, though, as each DA board only has 8 digital inputs, and the boilers take up 10 of the 16...