anemometer using thermistors

[naz83]

hi

i did rig up a circuit witht thermistors for air flow sensing it seemed to work fine until i realised i had connected -10v instead of ground but after i connected to ground it stopped working, donno why?

is there a way of testing it on software if so can any1 plz tell me how? and how do i measure air velocity in software

Thanks

 

[KMoffett]

naz83,

I know your question is about simulation software, but it would help a great deal in solving your problem in your first sentence if you posted a schematic.

Or...keep your question in your original post, not starting a new one. https://www.electro-tech-online.com/threads/air-flow-monitor-using-thermal-sensing.108845/

Ken

 

[3v0]

EDIT: Ignore this post


I expect when you ran it with -10V instead of gnd it was working at a higher voltage. Are you using dual supply op amps. A schematic would help.

Does it still work if you move it to -10V.

 

[naz83]

I am using 741 as my opamp and in the schematic i am using 100k thermistor instead of 50k and 1k thermistor instead of 2k.

could any1 plz explain to me the relation between thermistor resistance and temperature as i need to measure the temperatures of both thermistors. one of them was really hot, which should be and the other was at normal temp.

The initial current in the ma showed 10ma and when i blew air over the circuit it increased to 60ma. the output voltage at point U was 1.7v initially with a dc offset and when air blew over the circuit it increased to 2.1v.

can any1 plz verify if this circuit is correct to work as an air flow sensor, it did work for me whn i connected it to -10 instead of ground. but however the power supply dint read 10v after i switched it on, it dropped from showing 10v to 3v or so i dont know the reason.

Thanks for all the help

 

[naz83]

hi

the circuit works with -10v instead of ground, but does not work with ground. one of the thermistors gets heated and d other is at room temp, how do i measure the temperatures and what is the relation between thermistor resistance and temperature?

 

[ericgibbs]

hi

the circuit works with -10v instead of ground, but does not work with ground. one of the thermistors gets heated and d other is at room temp, how do i measure the temperatures and what is the relation between thermistor resistance and temperature?

hi,
This link gives the formula and other info.
All temperatures in Kelvin

**broken link removed**