Campbell Scientific PVS4100/4120/4150 Portable Automatic Samplers - Manual (Page 87)

A-1
Appendix A. Principles of Operation
Switching Methods (Sinking / NPN)
Sensor
LOAD
Sinking (NPN) Switch
The Sinking method connects or switches one side of the load to the negative
(-) side of the power supply. The positive (+) side is connected directly to the
other side of the load as shown. “NPN” refers to the type of transistor used to
act as a switch in this type of solid-state sensor.
Switching Methods (Sourcing / PNP)
Sensor
LOAD
Sourcing (PNP) Switch
The Sourcing method connects or switches one side of the load to the positive
(+) side of the power supply. The negative (-) side is connected directly to the
other side of the load as shown. “PNP” refers to the type of transistor used to
act as a switch in this type of solid-state sensor.