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[on:]

I work as a technician in a medical simulation lab (it's a fake hospital, with all the amenities, plus a central control room where we control and film everything), and one issue that we often run into is students will put oxygen on a patient or mannequin but won't verbalize the flow rate they've set it at.  Normally this isn't a problem because the scenario simply requires them to give the patient oxygen, and not how much, but occasionally we run scenarios that require a certain amount (either at least x liters/minute, or no more than x liters/minute).

So, what I want to do is build a flow meter that can plug directly into the christmas tree on the wall, not restrict the air flow at all, and allow the student to plug into a christmas tree on the device.  The device would then connect to a server (probably via the Wifi Shield board), and send the flow rate to a listening app in the control room.

Does that make sense?

So, I've been browsing the forums for a bit and I can't seem to find a reliable small airflow meter, and I was wondering if any of you know of one or how to build one.  Also, beside the mainboard, wifi, and the flow meter, is there anything else you would think I need?

[Reply #1 on:]

Doing this sort of measurement reliably and accurately enough to trust strikes me as very hard, unless you can take an existing solution. Presumably the people you're testing are expected to be able to find out what flow rate they're set up. This suggests that there may already be some flow monitoring equipment in use. Do you know what it is/how it works? Perhaps it would be possible to either duplicate that, or piggy-back some sort of monitoring on top of it. Otherwise the only sensible approach I can think of would be to put a small, known restriction in the supply and measure the pressure difference across it. Doing that safely when there is pressurised air involved may not be easy.

[Reply #2 on:]

Hi,

I googled and most medial flow meters are simple rotameters aka flow tubes aka a glass/plastic tube with a floating body in it and a scale printed on the tube, calibrated for a certain gas (accuracy ~ +/- 10%). Those simple and cheap devices do not have any digital or analog output.

I assume that the pressure through the "christams tree" is regulated elsewhere in the system and this is why you ask for a non-obstructive device.

Depending on the money you want to spend, your cheapest option may be a paddle-wheel flow meter with a hall effect sensor.
(http://www.omega.co.uk/shop/subsectionSC.asp?book=Green&subsection=F05) It essentially works like a bicycle speedometer but instead of speed you calculate volume per time from the spinning wheel that sits in our pipe. If you can find one that has a RS232 connection, you can interface with it (http://arduino.cc/en/Tutorial/ArduinoSoftwareRS232)...

Other options are vortex flowmeters and the above mentioned rotameters. The most precise and expensive you can buy is a coriolis effect flow meter, but this is way way to expensive for your application....

Prices will depend on the accuracy desired, flow range and so on. There are also industrial and laboratory devices that will send signals wireless or over LAN already (at more cost), so I am not sure an Arduino solution is the easiest to do for your case. Maybe a wireless device an be connected to an existing computer that is running in the control room anyway, but obviously I do not want to stop your DIY enthusiasm  

[Reply #3 on:]

If you put anything in the flow then you run the risk that when it fails it causes an obstruction.

students will put oxygen on a patient or mannequin but won't verbalize the flow rate they've set it at.

Your problem does not seem to be measuring the flow but rather knowing what the flow was set to.
How do the students set the flow?
Possibly you can just read the setting e.g. by using an encoder on the valve.

[Reply #4 on:]

and one issue that we often run into is students will put oxygen on a patient or mannequin but won't verbalize the flow rate they've set it at.

You have a lax training environment. If the student doesn't verbalize the flow rate, fail them on the session. If they are paying for the training they should quickly get the message. Medical environments require strict adherance to the rules.

[Reply #5 on:]

You have a lax training environment. If the student doesn't verbalize the flow rate,
fail them on the session.

I favour zoomkat's approach, you could still measure the valve setting though.
That would allow you to deduct points if they failed to verbalize and fail them if
they get the setting wrong (even if they did verbalize the correct value).

I hate written rules and procedures for two reasons;

• People forget them
• New people may not be aware of the correct procedure

If key actions are always verbalized then if a person forgets to do something others are much more likely to notice. Also new people immediately become aware that something is being done and so automatically learn to do it.

[Reply #6 on:]

I hate written rules and procedures for two reasons;

•People forget them
•New people may not be aware of the correct procedure

Think about that the next you or your family fly in an airliner.