Help to identify a Magnetic speed sensor

Hi.

Some time ago I salvaged this Magnetic speed sensor, don´t ask where it come. It was from a computer or audio devices.

It come with a shaft and a circular magnet on top of it, like in this example:

speed sensor

A close pic:

what I know so far:

pin 4 and 8 are connected to GND, before disassembling the device, I could identify the GND.
pin 2 and 6 are connected together.

just labelled M318 on the pcb.

Thanks for any clue.

PH_I_LN_magnetic.JPG