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Pressure gauge accuracy?
#1
I purchased a cpap manometer to check my machine while it is new just because I like to tinker with things. (small round plastic piece with floating ball)

I tried it on my machine and it read lower than the pressure was set to on the machine.

Is it suppose to be super accurate or just used as a guide to monitor long term performance.
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#2
I bought a digital manometer from Amazon. It's in inches-H2O -- but, conversion to cm-H2O is just a factor of 2.54 cm/inch.
I used it to check my ResMed VPAP-S. On the lower (exhilation) pressure, it's dead on.
I cannot get a good reading on inhilation pressure as the meter does not slew quickly enough to follow the pressure curve.

I would suggest that that a floating ball in plastic is an approximate device.

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#3
peels,

Plastic thing with a floating ball? Sounds like a flow meter to me. This would measure the air flow through the hose. If it says something like lpm on the side (liters per minute), it definetly is. If it's a piston/spring type manometer, you're right, it is about as accurate as measuring your battery electrolyte specific gravity with the 99 cent glass tube with colored beads from the auto parts place.

You can find several posts on this forum on how to build a manometer (pressure, or more precisely, differential pressure) from some cheap plastic tubing, likely less than $5. Ignoring the incredibly small variations that you likely don't have access to pure water and probably don't want to do the temperature compensation calcuations, it will be spot on to check the pressures. It can't be wrong, it's what metrologists call a primary standard.

Have fun with it. As long as we're tied to this therapy we might as well entertain ourselves.
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#4
I could have gone all geeky and made a water manometer but i just wanted to get a baseline and check it once in awhile to make sure the machine isn't going off or leaks in the hose etc.

I'll mark my setting as reference.

I wish I had it a few days ago when I traded my noisy machine for a quieter one. The comparison would have been nice.
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#5
Just get some tygon hose ,colored water,mm/cm ruler and you have an accurate meter. Had to do this to set propane regulator on a gas ceramic kiln --not a big deal . Neat to know how to do it . Cheap too.
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#6
If you think about it, you can use a homemade u-tube manometer as a pressure source to test a manometer. Or hook up a hose to the manometer, and stick the end into a glass of water, and measure the depth of the air column.
Get the free SleepyHead software here.
Useful links.
Click here for information on the main alternative to CPAP.
If it's midnight and a DME tells you it's dark outside, go and check it yourself.
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