Constant Current Hot-Wire Anemometer #2

Thread Starter


Joined Apr 26, 2021
I recognize that I am beating a dead horse, but I realized in retrospect that I could make tuning the loop filter easier if I could separate the heavy load of the wire from the filter itself. See attached.

I added R7 which makes selection of reasonable values of R6 and C1 far easier.

I am pretty sure that the chosen values for the filter are adequate for the task, if not maybe a little slower than it has to be. But without knowing the thermal characteristics of the wire, it'd be impossible to determine the fastest possible filter without potentially introducing instability.

Even if OP doesn't want this, maybe someone else would like to cobble it together and tell me if it works. I don't have the time!
Hi joeyd999,
I'm trying to build the circuit, seems to be working, however I managed to make a mistake and damaged the IC. Currently waiting on a new one. Meanwhile I'm now trying to understand the circuit better so I can change the parameters of Vin, Rwire etc..
I'm trying to supply the circuit with 12V and Rwire resistance to 4ohm.

Moderator edit: New thread created from old one.


Joined Aug 21, 2017
I had masterd my thesis zillion years ago, about 1980, over Pirani sensor using similar principle. There the tungsten wound coil, wire of 0.03 mm about 500 turns over 0.6 mm molibdenum wire into micro turner bench wound under the microscope by hands.... yes, I had a brilliant eyesight once :( Moly was only metal slippery enough be able to slipper the coil off when rady.

Pirani may be exploited in three regimes: constant voltage where current signalizes the wire temperature; constant current where voltage signalizes the temperature, or constant resistance regime where again voltage signalizes the vacuum under measurement. As the last regime gives about 10-50 fold shorter reaction time to the vacuum fluctuation but the aim was create the ultrafast vacuum gas-mixer with reaction in tens of microseconds, it was just very sophisticated job, taking in account that self adjusting circuit of course is readily prone for oscillation thus the Ziegler-Nichols later was frequent guest in my nightmares when awoke with wet forhead and cry halfmast on the lips :)


Joined Nov 6, 2012
What problem are you trying to solve ?
Are you just seeing if you can do it yourself ?
Mass Air Flow Sensors are installed on every Car since ~1995,
and they are easy to adapt to other projects.

MAF Installation Rules .PNG