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alphapointe
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uC Boiler Sensing

I'm working on a project for my apartment building to build an interface from our HVAC system to the LAN (web interface for readings, SMS alerts for out-of-range, etc.)

I've got temperature and pressure figured out, along with outputs for compressor condensate drain and air dryer on/off. The only thing I'm having issues with is determining whether or not a boiler is firing.

We have 5 Munchkin boilers, and I would like to have the system indicate which ones are firing, but the boilers don't have any contacts that give me this indication...

The only thing I could come up with, would be determining whether the combustion blower was running, and giving a logic (5V) high or low (I can handle either) when it is. Any suggestions on how to do this (without cutting wires, which the guys don't want me to do)

Any ideas?
--
"When the hammer drops, the bullshit stops"

lutful
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said by alphapointe:

The only thing I could come up with, would be determining whether the combustion blower was running

You could use a piezo vibration sensor ... $2.95 at Sparkfun.
»www.sparkfun.com/products/9199

hardware bum

join:2004-01-26
State College, PA
reply to alphapointe
Yeah, piezo vibration sensor might work. A friend solved a similar problem sensing a tractor engine running by using a microphone.


cowboyro
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Shelton, CT
reply to alphapointe
I did something like that for my boiler. A doorbell transformer on the power circuit of the blower. 24V through optoinsulator for logic.


tschmidt
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Agree with cowboyro See Profile the easiest solution would bo to connect a LV transformer to each blower. Rectify the output and use it as an input to your system. Don't really need an opto since the transformer provides isolation.

The other option is to use split-core clip on current sensors if you are not allowed to connect directly.

»www.ghielectronics.com/downloads ··· 1%5D.pdf

You said you already have temperature figured out, but I'm a big fan of Dallas/Maxim 18B20 1-wire temp sensors. Digital output and you can hang multiple sensors on a single I/O.

/tom


cowboyro
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said by tschmidt:

Don't really need an opto since the transformer provides isolation.

I've seen failed LV transformers... Better safe than sorry...

lutful
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reply to alphapointe
said by alphapointe:

I've got temperature and pressure figured out ... only thing I'm having issues with is determining whether or not a boiler is firing.

Thought of an alternative (or complement) to vibration sensing of the blower. You could monitor temperature of the hot water pipe close to the boiler. My guess is that significant rise and fall in temp over a few minutes would be easily detectable.


alphapointe
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reply to tschmidt
Dallas 18B20's are what I'm using as well.

I think I have this figured out, as the guy who takes care of the boilers for us tells me that the circulation pump only runs when the boiler fires, and that its' wiring is accessible. He says "drop a 120v relay across it, and you got your closure"

Sounds good to me... He said he might even have some relays meant for this, he'd check and let me know.
--
"When the hammer drops, the bullshit stops"


shdesigns
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said by alphapointe:

I think I have this figured out, as the guy who takes care of the boilers for us tells me that the circulation pump only runs when the boiler fires, and that its' wiring is accessible. He says "drop a 120v relay across it, and you got your closure"

If it has zone valves they proably have contacts that turn on the pump. Some have aux contacts. You could use those or monitor the 24V signal to them. Would also give you info on what zone was calling for heat.

I would probably monitor the outputs of the thermostats through an opto..
--
Scott Henion

Embedded Systems Consultant,
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alphapointe
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reply to alphapointe
OK, I've got relays ordered, now I need to know what kind of connector this is so I can get the alarm pin (next to the orange wire of the middle connector) out... Anyone have any idea on what kind of terminal I need to shove in there/


--
"When the hammer drops, the bullshit stops"


tschmidt
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Molex .156 pin header perhaps.

/tom

lutful
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reply to alphapointe
Maybe the terminals from floppy/hdd power cables will fit.

»ca.mouser.com/ProductDetail/Mole ··· W6NNk%3d


alphapointe
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Tom is right, they're .156 Molex pins. I added them to my mouser order. (Jeff had a few bags on the truck, so I just copied down the part # and looked it up.)
--
"When the hammer drops, the bullshit stops"


alphapointe
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reply to alphapointe
It works. YAY!
Just waiting on the pins for the alarm signal now.


--
"When the hammer drops, the bullshit stops"

Kearnstd
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reply to alphapointe
what type of boiler is it fuel wise I mean.

Oil burners have a fire eye that looks for the flame, It is part of the safety system. no flame it instructs the control module to shut down the burner. If that is what you can tap on to than you will know more than if the blower fired up and know that there is actually fire.
--
[65 Arcanist]Filan(High Elf) Zone: Broadband Reports


tschmidt
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reply to alphapointe
said by alphapointe:

It works.

That's great. I love those ah-ha moments the first time a new project works.

Could you translate the graph you posted, not sure what I'm looking at.

/tom


alphapointe
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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)
--
"When the hammer drops, the bullshit stops"

Kearnstd
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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.
--
[65 Arcanist]Filan(High Elf) Zone: Broadband Reports


alphapointe
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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...)
--
"When the hammer drops, the bullshit stops"

Kearnstd
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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.)
--
[65 Arcanist]Filan(High Elf) Zone: Broadband Reports


alphapointe
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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...
--
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alphapointe
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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...
--
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alphapointe
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reply to alphapointe
Anyone have any ideas on a water level sensor that I can hook up to an arduino to get water level on the cooling tower? I've already got wireless serial radios so I can send the analog reading to the PLC (with another arduino)...

So far, the only thing I've been able to find are float switches, and while a low level float switch would do in a pinch, I would really like to see an actual depth (max 18", nominal 12") It doesn't need to be accurate within .001%, but accurate to 5-10% would be nice)
--
"When the hammer drops, the bullshit stops"


SparkChaser
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reply to alphapointe
There is eTape »www.milonetech.com/Home_Page.htm ··· age.html

OT what are you using for radio?

lutful
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reply to alphapointe
I agree eTape is most probably the best and simplest solution.

a) If you want something like etape, but want to stick it to outside surface of a glass/fiberglass/plastic container, there are capacitive tapes.

»www.molex.com/molex/products/fam ··· oduction

b) There are also radar-style RF sensors but a small antenna needs to be mounted to top inside surface of container. But won't measure accurately if liquid rises too close to the antenna.


alphapointe
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reply to SparkChaser
I'll do some reading on it when I get to work. The cooling tower is metal, so I'm not sure how well a capacitive sensor will work...

The radios I got are AP220 serial RF modules that I picked up off Ebay. They seem to work OK.
--
"When the hammer drops, the bullshit stops"

lutful
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Sorry, was not following the thread for some time. Capacitive sensing won't work at all through metal and the radio may not work reliably.


alphapointe
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I'm not worried about the radio. It and the arduino will be mounted to the top of the tower inside a plastic weatherproof box with a SLA battery and solar cell, and cabled to the sensor below. The receiver will be about 70' away line of sight, so that shouldn't be a problem.
--
"When the hammer drops, the bullshit stops"


alphapointe
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I'm going with the Etape that SparkChaser See Profile linked to. Reading the datasheet, it looks like this is the best option. Now its' time to start writing and testing code on both sides of the link.

YAY!
--
"When the hammer drops, the bullshit stops"