The ED-261-1 Transmitter uses an opto coupler for generating 2 pulses per revolution (optional 12 pulses per revolution). The signal from the opto coupler is supplied to a Schmitt-trigger for suppression of error pulses at low speed.
The output signal is switching from 0V to VCC –0,6V. The output signal is pulled up with a 10K resistor. Internal on-board there is a jumper which switch between the pull-up resistor and an open collector output.
Download datablad: ED-261-1.pdf