Vacuum (suction) monitoring

[Lagerhead]

Has anyone tinkered with real-time measurement of very light vacuum?

It happens that the suction level in my basement radon abatement system is a leading indicator of basement water infiltration. When the water table rises, the suction in the radon pipe increases. A rising suction level means I ought to take precautions, test the pumps, etc., and the earlier I know, the better. Having a trend line and/or a threshold trigger would be the objective.

The suction level in this system is very very low, from 0.5 to around 2.0 "inches of water," the entire range of which is about 0.1 PSI, minuscule relative to atmospheric pressure. If anyone has dealt with this challenge, I'd appreciate knowing your experiences.

Edit: Forgot to say that I can read the pressure manually with a venturi-type sight glass on the side of the pipe column.

Dave

[ If you are not familiar with this kind of basement radon abatement installation: A 4-inch plastic pipe runs tight into a hole in the basement slab. The other end of this pipe is outdoors, having an enclosed fan unit that pulls air from under the slab, which has the concentration of radon gas from the earth, and exhausts the gas safely into the air. Otherwise the radon gas would seep into the basement and from there concentrate in the house. This is a common problem in New England. ]

 

[sda]

I'm working on something similar to measure HVAC pressures. I picked up a couple of Dwyer 605-2 magnehelics and a dc power supply. These are 4-20ma current loop. The current measured accoss a 250ohm resistor will be 1-5vdc. Maybe some day I'll have the time to put it all together.

 

[BrettS]

I'm not terribly familiar with a system like that, but you mention that you have problems when the water table rises. Is there another way to monitor this? Maybe using a float switch in your sump pump well, or even monitoring how frequently your sump pump runs? Both of those would be pretty easy to do. Alternately you might be able rig up something to the sight glass that sends a beam through the glass and detects it on the other side... if the beam is blocked then it could send you a signal.

HTH,
Brett

 

[roussell]

Another option is to scavenge a vacuum sensor (MAP Sensor) from a fuel-injected car. Those sensors typically have a wide operating range and tend to have a high resolution. Usually they have three wires, Ground, +12V in and a 0-5 v output that is proportional with the amount of vacuum being produced. You should be able to find one on any late model car. I would think a 4 cylinder Honda or Toyota would make a good candidate.

Terry

 

[slipnfall]

Depends - do you have any means of aquiring an analog signal? If so, tap a connection into the 3-4" pipe, and measure with a low-ranged differential pressure transducer. This is expensive (lab grade) but they have very low/accurate ranges. I use them down to 0.25"WC at work and they're dead on. http://www.omega.com/ppt/pptsc.asp?ref=PX655&Nav=preb05

mid-tech solution would be to rig a photo transistor + circuit to the outside of your sight guage to provide a digital output.

Best/low-tech would be to call around to some of the RADON specialty services - I'm sure they have *some* sort of device intended to trigger an alarm for low vac condition (gasses not being vented, ie fan failure). I'm sure you could find the contacts inside and modify it for your usage.

Just a 'thought or two.
Jamie

Another option is to scavenge a vacuum sensor (MAP Sensor) from a fuel-injected car. Those sensors typically have a wide operating range and tend to have a high resolution. Usually they have three wires, Ground, +12V in and a 0-5 v output that is proportional with the amount of vacuum being produced. You should be able to find one on any late model car. I would think a 4 cylinder Honda or Toyota would make a good candidate.

Terry

 

[Lagerhead]

Thank you, gentlemen, for these excellent suggestions.

Price is a consideration, mainly because this is not a "must have" item for me, it is a convenience (at any time I can look at the glass in the basement, if I remember to do so). Also, an accuracy of +/- 10% is more than satisfactory.

I see that Dwyer has a non-indicating transducer in the right vacuum range, model MS-111, at less than $100 which is attractive.
http://www.grainger.com/Grainger/items/1AEW1

One question for me is whether and how the current loop output will interface with an Elk zone, a kind of connection that I have not done, but I am sure the expertise is here on the board (I remember an earlier thread about cutting the pull-up resistors; I am not inclined to do that). The automotive sensor is a great idea also and ought to be easily available, if they are in the right measurement range. Might mean supplementing the unit with an op amp and some parts?

My pumps have not run since the spring of last year, about 15 months ago, other than my dumping buckets of water occasionally. That is the nature of the underground water here on top of ledge rock -- sometimes water is present in quantity, sometime it disappears altogether. The radon vacuum level will give me literally a few days' notice of rising water levels. This is why I am so interested.

 

[slipnfall]

Yes you can wire an op-amp in comparator configuration as either a threshold detector, or window comparitor. The supply loops are 4-20mA. Pass this through a 275ohm resistor and you'll get a 1.1->5.5V range. Better yet just buy a sensor with 0-5Vdc output.

It would be nice to see a few analog inputs on the ELK, but I don't have much room to talk (it's not even installed yet!!)

That's an interesting link between the water level and radon... makes perfect sense, but I guess you 'got lucky in noticing it!

Jamie

Thank you, gentlemen, for these excellent suggestions.

Price is a consideration, mainly because this is not a "must have" item for me, it is a convenience (at any time I can look at the glass in the basement, if I remember to do so). Also, an accuracy of +/- 10% is more than satisfactory.

I see that Dwyer has a non-indicating transducer in the right vacuum range, model MS-111, at less than $100 which is attractive.
http://www.grainger.com/Grainger/items/1AEW1

One question for me is whether and how the current loop output will interface with an Elk zone, a kind of connection that I have not done, but I am sure the expertise is here on the board (I remember an earlier thread about cutting the pull-up resistors; I am not inclined to do that). The automotive sensor is a great idea also and ought to be easily available, if they are in the right measurement range. Might mean supplementing the unit with an op amp and some parts?

My pumps have not run since the spring of last year, about 15 months ago, other than my dumping buckets of water occasionally. That is the nature of the underground water here on top of ledge rock -- sometimes water is present in quantity, sometime it disappears altogether. The radon vacuum level will give me literally a few days' notice of rising water levels. This is why I am so interested.