Thermal Mass Flow Measurement

how about asking vendor for more info

Thermal mass measurement is done with three units. Velocity of the air(gas) and the amount of energy required to keep the probe at the same temperature and time.

Velocity in a duct is measured at several points to get an average flow by calculation.

Temperature is usually considered static across the whole duct.

Doggoneit has it pretty close...Although I think in your average application a constant voltage is used. The resistance of the element either increases or decreases with temperature thus causing a change in current. This is what is measured. The amount of air (in this case) flowing across the element will determine how much cooling is affected on the element. The engineering that goes into the sensor takes care of the rest. You would never use the same sensor to measure air or liquid. Mass airflow sensor parameters would be specified as to cross sectional area of the conduit, ambient pressure etc. The temperature of the air is either taken with a different sensor and applied to the sensors output, or perhaps the thinning of the air with increasing temperature would be accounted for in the sensor's design. my2cents

If I am not mistaken, two resistors are used.One has a near-zero temperature/resistance curve.Resistance is steady regardless of temperature.The second resistor is a platinum type, very precise response to temperature.They are located in a very precise venturi with a known dimension.The resistors are placed in opposite legs of a wheatstone bridge.The amount current required to heat up the platinum resistor to an equal resistance as the fixed one is a measure of flow velocity.The velocity times the known area gives mass flow.An increase in velocity or an a decrease in temperature will reduce the resistance of the platiunum wire and more current is needed to balance the circuit.This is not the total picture for automotive functions, but it provides information that can be used to calculate fuel air mixture.The mass of the resistor is very miniscule compared to air volume, so it has almost zero effect on the incoming air temperature.

If you are speaking of mass air flow meters in general, there are many more types, including coriolis effect, vortex shedding,membrane type,vane type, turbine, wobble meters, and others.

HTRN