Yes, this is correct. But that is why I added the qualifier that the unit could be recalibrated to measure speed and not mass. Regards, Jim > -------- Original Message -------- > Subject: Re: [TECH] Wind Speed/Direction 'sensor' source. > From: Kerry Wentworth > Date: Thu, March 24, 2011 11:08 am > To: "Microcontroller discussion list - Public." >=20 >=20 > Remember, it's not measuring air speed, but air mass, which is basically= =20 > speed*pressure. And I'm sure it measures the intake temperature. >=20 > Kerry >=20 >=20 > Adam Field wrote: > >> Michael, > >> > >> For a no moving part anneometer, you could use a piece of technology > >> from the automotive industry. > >> That would be the Hot Wire Mass Air Flow Sensor used on many cars and > >> trucks today. It is basically > >> two wires that are heated via an electric current. One of them is > >> shielded from the airflow. > >> The other is directly in the path of the airflow. The air moving pas= t > >> it cools it down. Circuitry > >> connected to the sensor then varies the current to bring it's > >> temperature back to where it was before > >> the air started cooling it down. This current then represents the ma= ss > >> of air flowing across the wire > >> and into the engine. > >> =20 > > > > Wandering slightly OT but still in the realm of measuring air propertie= s... > > > > That's interesting. The MAF on my newer model Nissan has a diode that > > can be plainly seen. It may have the wires you describe further into > > the sensor. The diode I assume is measuring the intake temperature. > > > > Is the two wire method assuming the reference wire is at the outside > > air ambient temperature? Otherwise, you have two unknowns cooling the > > wire, the air flow rate and the temperature (and pressure) of that > > air. > > > > =20 >=20 >=20 >=20 > --=20 > Internal Virus Database is out-of-date. > Checked by AVG Anti-Virus. > Version: 7.0.289 / Virus Database: 267.11.13 - Release Date: 10/6/05 >=20 > --=20 > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .