Help ID this sensor from CPAP machine

[mishima]

I was taking apart a CPAP (continuous positive airway pressure) humidifier earlier and found 2 of these sensors spaced around 5 cm apart from each other. They were in an air conduit leading from a filter material on the outside of the device to the pump intake. The points of the sensors were more or less in the center of the conduit. Any ideas?

 

[jim hardy]

They sure look like temperature sensors.
http://sensing.honeywell.com/honeyw...nea-machines-application-note-008155-9-en.pdf
scroll down to thermistors.

Why two of them? if one is heated they could infer flow...

 

[mishima]

Thanks for that perfect reference, and it makes sense. I was guessing it was related to air quality. I will put it on an instrumentation amp later.

Edit: actually just an ohmmeter would reveal its character

 

[Mike_In_Plano]

Yep, classic mass flow meter.
Sometimes one is used to find baseline temperature while the other is driven hard to heat, such as in an anemometer. Other times, both are heated, but their orientation in the air stream gives preferred heat transfer to one or the other depending upon flow direction.