Electronics > Beginners
Mass flow sensor
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Simon:
The thermistor measures incoming air temperature. The temperature of the wire will depend on the incomming air temperature and the speed of the air. So if you know the incoming air temperature when you measure the wire temperature you have the difference which allows you to extrapolate the air speed. now you know the air speed knowing the cross section area of the measuring duct you know the volume of air although techincally it is the mass as air pressure has to be taken into account. The latest MAF's have built in pressure sensors but previously these were seperate.
Benta:
Go to a wrecking yard and rip out the MAF sensor from a crashed car. The car car just needs to be younger than ~25 years. Easy.
james_s:
Older than that will work in many cases, Volvo started using air mass meters in 1983 with the first LH-Jetronic injection system. Turbo models followed in 1984 with the 760. By 1986 model year every car they sold in the USA was equipped with various versions of LH Jetronic across the range, many other European cars also used them.

American domestic cars were a bit slower to get fuel injection and quite a few older ones used flapper vane airflow sensors or MAP sensors that measure the absolute pressure in the intake manifold.

Salvage yard prices tend to be a bit on the high side though as the AMM is a relatively failure prone part so there is plenty of demand. I was surprised to find that some of the newer ones are actually cheaper, a friend of mine needed one for his Mercedes and it was only about $35 for a brand new one. A new one for my car is more than 5 times that price.
radiolistener:
You can use ultrasonic transducers in order to measure gas flow.

ZeroResistance:

--- Quote from: Simon on May 05, 2019, 07:40:17 pm ---The thermistor measures incoming air temperature. The temperature of the wire will depend on the incomming air temperature and the speed of the air. So if you know the incoming air temperature when you measure the wire temperature you have the difference which allows you to extrapolate the air speed. now you know the air speed knowing the cross section area of the measuring duct you know the volume of air although techincally it is the mass as air pressure has to be taken into account. The latest MAF's have built in pressure sensors but previously these were seperate.

--- End quote ---

I don't understand the following figure as attached.
Why is the thermistor arm also being corrected by the feedback?
Shouldn't the feedback only go to the hot wire platinum arm. and the thermistor arm be kept at a fixed voltage supply ?
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