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Author Topic: Anemometer Chris Hipp Phenomenal Film Handler Posts: 1462 From: Mesquite, Tx (east of Dallas) Registered: Jul 2003 posted 05-08-2004 12:13 AM                     Anyone have any recommendations on a good one that isn't oo expensive, under $100 would be good. Thanks  |  IP: Logged Brad Allen Jedi Master Film Handler Posts: 688 From: Evansville, IN, USA Registered: May 2000 posted 05-08-2004 12:51 AM                     Chris, I assume you'll be using this for it's normal purpose? Weather? If so, this is about as cheap as you can go and still have reliable equipment. Weather station  |  IP: Logged Chris Hipp Phenomenal Film Handler Posts: 1462 From: Mesquite, Tx (east of Dallas) Registered: Jul 2003 posted 05-08-2004 01:19 AM                     umm...I must be confused. I just need one to measure CFM for lamphouse exhaust and air ducts.  |  IP: Logged Josh Jones Redhat Posts: 1207 From: Plano, TX Registered: Apr 2000 posted 05-08-2004 02:27 AM                        Those I believe, are quite pricey. You could use the old stick trick. Ask Gord, he'll know.... Josh  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-08-2004 03:05 AM                     I don't know of any in the $100 and below category. Extech does have a selection that are not too pricey but definately over $100. http://www.extech.com/instrument/products/400_450/407114.html Steve  |  IP: Logged Carl Martin Phenomenal Film Handler Posts: 1424 From: Oakland, CA, USA Registered: Feb 2002 posted 05-08-2004 06:29 AM                        out of curiosity, what does cfm stand for, besides my name? carl  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 05-08-2004 07:56 AM                        cfm = cubic feet per minute (a measure of the VOLUME of air being drawn per minute)  |  IP: Logged John Anastasio Master Film Handler Posts: 325 From: Trenton, NJ, USA Registered: Sep 2000 posted 05-08-2004 07:57 AM                        Cubic feet per minute, and it's not a measure of air speed, which is what an anemometer will tell you. It's a measure of air volume over a given time interval. You also need to know the the diameter of the pipe to get the volume of air moved per minute. You could air moving through a BIG stack at the same speed as the air moving in a small stack, but you'll move more air through the larger one at that speed. There are some simple and cheap airspeed indicators used by ultralight pilots that consist of a pivoted indicator attached to a spring. You could probably build a cheap one from a small piece of sheet metal attached to a protractor and calibrated against a known air flow. Early pilots used a piece of cord tied to a strut. It told you not only speed, but direction of the relative wind.  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 05-08-2004 09:23 AM                     Extech makes one for $90: http://www.extech.com/instrument/products/451_499/45118.html But it doesn't read in cfm. The better one like Steve showed, is about $250. It the cheap ones do not measure in cfm, but you can use a converter to figure it out. You can get a cardboard 'slide rule' calculator or get the formula : http://www.nfsrps.com/airflow_formulas.html Be aware though, that the cheaper meters like the one above can be off by 40-50% if you don't hold it exactly right, and in the right place, etc. With any anemometer, the proper way to use it is to take several readings around the duct and average them out. If I just couldn't afford a better meter, I would try to borrow a good one and use to compare with cheap ones to get initial values.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 05-08-2004 09:33 AM                        Wouldn't the temperature of the hot air being pulled into the stack also be a good measure of how effective the ventilation was? The designers of the ventilation system need the CFM specification, but in reality, it's how hot the inside of the lamphouse gets that determines the required air flow.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 05-08-2004 09:58 AM                    Plus I don't know how accurate an air speed measurement coupled with stack diameter would be as it ignores laminar air flow.  |  IP: Logged John Anastasio Master Film Handler Posts: 325 From: Trenton, NJ, USA Registered: Sep 2000 posted 05-08-2004 06:25 PM                        I was just making the point that only knowing the speed of the air doesn't give you any indication of the actual flow in CFM, any more than knowing only the voltage alone in a circuit would give you the current...but if you know the speed and you know the area of the duct's cross section, you can certainly calculate the flow. Laminar flow is of course what you want in a duct if you want it to move air smoothly and be quiet. Turbulence only creates unwanted resistance and noise. Why do I have this sudden urge to watch "Brazil" now?  |  IP: Logged

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