There are many applications in which it is desirable to connect one or more flow sensors to a PLC (programmable logic controller), and the flow sensors are well suited for this. In many cases the digital pulse of a flow sensor can be connected directly, or with a minimum of components.
The flow sensors most commonly chosen for use with a PLC are USN series and USC series insertion flow sensors. These flow sensors, which have three wires, use Hall-effect technology. They need 5-24 Volts DC and up to 8 mA current, and they are current sinking (NPN) devices. The flow sensors can connect directly to the PLC if:
The flow sensor power on the PLC is 5 - 24 VDC (VDC is typical.)
The flow sensor power supply can provide at least 6 mA (100 mA is typical.)
The flow sensor input on the PLC can accept a current sinking device.