Throttle position switch off-car

Testing the throttle position switch 

I connected to the ohm meter across the E and IDL pins and with the throttle shut, check for continuity.

then connected the ohm meter across the E and PSW pins and check for continuity when the throttle is wide open.

IDL = OL
PSW = 0.5 0hms
The results at both PSW and IDL pins were 0.5Ω showing continuity. This result is what we would expect to find on a working TPS.

Explain the internal operation of this sensor and why the resistance changes

when the throttle position switch is at idle, it shows 0.5ohm continuity. When the throttle at wide open, idle become open circuit and pwoer switch terminal become 0.5ohm.This send a signal to ECU to increase the duty cycle of injector to increase the engine speed.