inductive analog Distance sensor:
inductive analog sensors are ideal for applications involving relatively short metal target travel They provide precision, non-contact position measurement by varying its electrical output in proportion to the position of a metal target within its working range.
linear potentiometer: 
Linear Potentiometers are well known displacement transducers. The working principle is voltage division on a hybride conductive film. It is possible to get different housing and mounting types, like versions for hydraulic cylinders, with spherical bearrings, clamping jaw mounting or sprung loaded.
ultrasonic sensor: 
work on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object.
This sensor is suitable for applications which require analog measurement of the distance between the sensor and the object. The sensor is capable of direct or scanning mode operation. Bright objects reflect transmitted light better than dark objects. Output voltage is dependent upon the brightness of the object to be measured.
