Calorimetric Flowswitch, Compact Version. Connection, 1/2" NPT. Output: NPN/PNP N/O; 4 - 20 maA.

 Calorimetric Meter/Switch KAL-A(K)
Brand: Kobold
MODELO: KAL-AK5-4-15-AS-PG
[KA-AK5]:
Operating principle, calorimetric
Mounting position: all directions
Indication: DUO-LED and LED-chain
Output, 4-20 mA (KAL-AK with contact output)
max. temperature, 80 °C
Power supply: 24 VDC
Protection class: IP 65
Connection thread, NPT
[4] Probe material: st.st. 1.4301
[15] Connection: 1/2"
[AS] Output: N/O NPN/PNP; 4-20 Ma
[PG] Electron. Connection: M16x1,5 PNP/NPN
Datasheet:
http://www.kobold.com/uploads/files/kal-k-gb-flow.pdf