It' s a SF800/2 miniature flowsensor from Swissflow and directly ordered from Swissflow BV in the Netherlands
Technical data (from the Swissflow website)
Data based on water at 20°C (68°F)
flow range : 0,5– 20
interchangeability : ± 2.25 %
accuracy : ± 1.00 %
reproducibility : ± 0.30 %
output : 50 to 2000 Hz, square wave on – off
sensitivity K : aprox. 6000 pulses
temperature range : -20°C
operating pressure : 16 bar
max. pressure : 40 bar at 20°C
excitation : 5 to 24 VDC, 12 to 24 mA
power consumption : 12 – 36 mA
liquid type : clear or translucent liquids capable of transmitting IR light
liquids : water, chemicals, oil (up to 1000 Cst) etc.
process connections : 3/8” hose barb or 3/8”BSP Male
electrical termination’s : 3-wire flat cable sealed in housing, 15 cm
wetted parts : PVDF, Vectra and Viton, or EPDM (mine is EDPM, don't ask me the differences...)
RS (560Ohm) is needed when supply voltage is higher than 13V. RL is 2k2 (the output of the SF800 is Open Collector type).
The output is identical to a RPM monitoring fan except for the frequency (should work on a mobo fan connector, although I never tried it...) and varies between 50Hz (0.5 liter/min or 30 liter/hour) and 2000Hz (20 liter/min or 1200 liter/hour)
A schematic of a digital frequencymeter to display the actual waterflow in liter/minute can be found here
SF800 in its original packing...
Close view with protective end caps on both ends...
Close view on input side. You can see the litlle rotor that rotates with the liquid flow. External threading is 3/8" BSP and internal diameter (ID) is about 10mm.
Connected to the output of my Eheim 1250...