An injector for injecting fluids from a syringe into an animal subject comprising: a housing； a 5 drive ram bidirectionally movable along a longitudinal axis of said drive ram； a magnet disposed on a surface of said drive ram； a motor drivingly coupled to said drive ram to selectively advance and retract said drive ram along said longitudinal axis； and a magnetic sensor disposed within said housing for determining whether an end of said drive ram is in a home position proximal to a forward end of said housing of said injector, wherein said 10 magnetic sensor operates in concert with said magnet disposed on said drive ram to detect magnetic field emitted from said magnet.
