fan speed question (electronics)

[rb_at_the_zoo]

hi, noob here with ignorant question.

I'm just wondering if anyone can tell me the waveform output of the blue wire (supposedly tacho) on a Delta focussed flow fan (FFB1212EHE, 12VDC, 3A -FOO)? I'm trying to use this fan in another application - a small wind tunnel.

I've applied 12V and 3A but want to be able to reliably adjust the speed, or at least measure the rpm with different voltage inputs.
perhaps I need to apply a square wave to the blue wire?

Any suggestions? :think:
thanks, rb

[Greco101]

I don't know of anything that gives a even semi accurate rating of RPM but maybe you can hook up a fan speed controller and dial it in to w/e voltages you'd like using a voltage meter.