Confusion with meaning of low and high impedance sensor
The conversion from high impedance to low impedance is known as signal conditioning. It's necessary for most sensors in some way to match their output to the desired load.

For theses purposes, high and low impedance are a way of expressing how much load a source can handle while maintaining voltage (and therefore signal integrity.) 

A low impedance load draws lots of current, so it needs to be paired with a low impedance source that can sustain it. 

Some sensors generate a high signal voltage with very small current. This makes them a high impedance source. If connected to a low impedance load, there would be a significant drop in the source voltage. This is a bad thing because it's the voltage we usually want to measure. 

A buffer (and/or other conditioning method) is placed at the sensor output to measure the voltage and reproduce it from a high current (lower impedance) power source. This allows the sensor signal to drive longer runs and larger loads without distortion. 

National Instruments has a good tutorial and guide with theory and example circuits for the various methods of signal conditioning.