I am having hard time reading the fan RPM using NI 9205. The fan is powered with 12V, feed the tach signal to AI8. The voltage just slowly creep up to 11.75V and stopped, it does not respond to actual RPM. Is there anything I am missing here?
According to the spec sheet (page 530), the fan has a sensor that outputs two pulses per revolution and in order to see the pulses, you'll need a pull-up resistor. Once you can see the pulses, you'll need a way to count and convert them to RPM.