Negative pressure reading

[Ca++]

Has anyone metered their negative pressure? I think my brain hurts. I want an inlet fan, sensitive to the rooms pressure. So I set about measuring said pressure, and things got a bit wrong.

First up, we know most of us have an atmospheric pressure sensor in our pockets, right? To use my old midrange samsung, I must dial *#0*# to open the service menu, them select sensors. My Barometer is there on the list, bouncing around the 1002.46 mark, near an open window. In my lounge 1002.39 and as I move up the stairs towards the room my extract is in, 1002.14 by the door, which has a 15mm crack. So into the room, I push the door to, and it barely makes a difference. 1002.11 or something. I thought my eyes should be bulging or something. That door makes less difference, then I ever expected. I know my full fan pressure is really upon the tent, who's pressure I wanted to control, and have not measured as it's dark. However, these are small fry numbers.

I don't want to use just a pressure differential switch, I want a couple of sensors with fan speed control. My goal is unloading the extract fan. My extraction isn't really about temp or rh primarily. It's about negative pressure for smell containment. before anything else. With that covered, RH only ever needs increasing, which can't be achieved by slowing the fan, who's already at the minimum for containment. I just increase the fan for temp in summer, but not by much. If I could instead control the fans based on pressure, it would allow me a bit more leeway. I could lower extract speed, or even let my typical vpd tracking controler, actual do something. Knowing my containment is in order. Which eases the extracts job. It all just comes together better.


Has anyone else done such atmospheric pressure testing? Perhaps they would like to, having found it on their phones. While writting this, that 1002.39 has moved to 1002.74 as the weather has changed. It seems to use the baro for altitude measurements. Blowing on the phone, finds it in the earpiece. Waterproof phone.


So little difference shutting the door. It's just not what I expected. Hence I'm reaching out. Though I suspect atmospheric pressure changes over the height of my stairs, may simply dwarf my fan. Then the room is simply not as sealed as it looks.

Next up, I have an air speed sensor to go in the ducting. That might shine some light on how sealed my room is.

 

[mudballs]

Has anyone else done such atmospheric pressure testing
yeah, but not to the degree you want i fear...i wanted negative pressure and used toilet paper pieces to see if inlet draft by intact ports/vents was strong enough to move the toilet paper.
Just for odor mostly, same as you. You'll burn motor off/on using a sensor trying to keep a steady state atmospheric pressure in a room not ISO Class 8 or above sealed i would think
Link to barometric lab shit

 

[Ca++]

Seen these? I'm guessing you may of. It's a diaphragm switch, with a hose attachment for each side of the diaphragm. A hose here, a hose there, it can offer a simple switching action, as low as 0.2 on the scale my phone talks. Though that online calc seems like it needs a second opinion.
Edit: This one isn't the best, they do a 20Pa one. This is 200Pa, but a better photo angle
I have access to these, and they are only $20 anyway. I might borrow one and see how it plays as a testing environment. As you say though, On/off isn't good. I guess I could translate that to high/low but I really want a variable fan speed. I find these sensors like the phone has, on boards, for 50c. That's basically free. I could look at a pair with a differential amplifier, and control my EC fans without too much effort. It just seems I will be responding more to cloud cover than room depressions though. That's not good control of an inlet fan.

On a different note, I would like one of these mechanical switches across my extractor. I could wire it to my flood alarm, which uses wifi to message my phone. The flood alarm was again, about 10$. However.. it uses a battery. I guess the battery compartment offers room for a power convertor, to run it off external power instead. It also has an audible alarm. Perhaps I won't do any better, concerning internet warnings of extract failure.

I wonder if I can contort myself around my pots, and shut the flap. Hmm..

 

[Ca++]

Oh.. my phone might be broke. The altitude reading was 80 meters, and having put it in my tent and the phone flashing green at me and vibrating, It now thinks 20 meters. 1010.50 which is very different. Like full scale different, on the image above. I need to learn my numbers, that calc must be wrong. 1000 hectopascal = 10 pascal it suggests. 100=centi surely, but hecto is off my scale of knowledge.
I think my phone could be off, but can the weather just be that different. I just know nothing of barometers. Except I need a weather station up my exhaust. Which is something I never thought I would say.

 

[Ca++]

This may be the droid I'm looking for
https://www.ali express.com/item/1005004668884481.html

It's like the one pictured before, except alloy, with a digital readout, and instead of a switch, it's 0-10v output. Just like an EC fan. £30 delivered.
No pressure difference, no inlet fan. More difference, more fan. All that's left is a little scaling.
This also suits my room inlet air scrubber. I would like to provide clean air. I can't supply more than the exhaust takes, or I go into positive pressure. Or jail. If Instead I supply less, the exhaust must work harder, and will find other gaps to bring air in from. Dirty air. With atmospheric pressure monitoring, I can have real time inlet air adjustments. Ones that track exhaust speed, and the opening and closing of doors.

I might pop it on the back burner for now, but it's interesting. I have also been looking at linear actuators for louver grills, so my exhaust fan still does all the work, but I make it's job easy (and quiet) as possible.