oxygen meters

tirsdag den 16. februar 2021 kl. 23.28.13 UTC+1 skrev RichD:

afaik it measures how much of the light from a red LED and an IR LED gets through the finger, the two wavelengths get absorbed differently by oxygenated and deoxygenated blood

So am I. Given that they only ever seem to read 99% all the time, they're an attractive target product for Chinese fakers. Who's ever going to find out? If the customer is someone buying it for their own personal use, I mean; not talking about hospitals where there's a lot of moribund patients lying about to test them on.

--

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

You can alter the "fit" and notice a change in displayed SpO2. They also show pulse rate -- which is relatively easy to verify.

I suspect they are a highly integrated device so not much to save by "hardwiring" the display.

They aren't particularly accurate, though. Perhaps +-2%. So, 95 may be ~93 or ~97. But, there is a wide range of "normal" and if you're experiencing related problems, then you're likely to encounter readings closer to 90 (or lower!) than 100.

Because they are so simple to affix, there's little cost to monitoring the value for a few seconds... then, removing and reseating the device to see if anything has changed.

Yes. And "pulse" can be seen as amplitude modulation.

HP Journal Oct 1976 describes an early ear clip machine using filtered tungsten light source and HP Journal Feb 1997 describes a fingertip unit using LED/IRED sources. Both articles explain the various confounding factors and principles.

piglet

All you have to do is hold your breath for a minute or two to depress the reading and then hyperventilate!

Here is some background, The early patents explain things.

Joe Gwinn

Ran into some test equipment that's just scrap now as the specialty instrument bulbs are no longer made and supply dried up ages ago. Anyone else affected by this before?

Sure; everyone who uses firebottles for electronic purposes has had that experience. My old tuning-eye FM tuner is kinda weak nowadays...

Some of the halogen bulbs should remain in production for a while, but the supply chain seems to include lots of counterfeits (inexpensive, but NOT long-life bulbs; probably not really halogen chemistry). When an Osram 64425 lamp burned out...that part number is no longer produced, so I got some made-in-China unlabeled parts... that don't perform.

I was on hospital Oxygen therapy for a while and I got me one when they released me. I compared it with the ones at the hospital. There probably calibration labs around for checking medical stuff.

I've hard you can use toes and ear lobes too.

Yup. You're looking for Peripheral Saturation (the 'S' and 'p' in "SpO2") -- contrasted with Arterial, Venous or Tissue (a/v/t).

On infants they use the bulk of the foot.

(monitoring this is important during surgery -- anesthesia)

IIRC, they use a reflective technology to monitor SpO2 on your forehead for sleep studies.