Shaft Encoders

A shaft encoder is an electro-mechanical device used to convert the angular position of a shaft or axle to an analog or digital electrical signal. These devices are used in many applications including liquid level measurement. Part of the mechanical aspect of this device for level measurement utilizes a float and counter-weight attached to a line or tape placed around a pulley attached to the encoder’s shaft.

As the level changes, the float moves up and down and, thereby, rotating the pulley and the attached shaft – generating an electronic wave form for both rotating direction and amount. By converting shaft rotation into electronic signals, encoders are used to electronically monitor the position of a rotating shaft. There are two main types of encoders for liquid level measurements are absolute and incremental.

Advantages of Float-operated sensors for water level measurements:

• Since many older sites were designed for mechanical float operated measurement, encoders are easily adapted to existing float gear and gaging system.
• Float-operated systems are easy to understand and troubleshoot.
• Most encoders offer good temperature stability.
• Various electronic technologies can be used including digital incremental and digital absolute (encoders); analog absolute (potentiometers and Linear variable differential transformers); or digital absolute (synchros).
• Float is protected in a stilling well and sensor is not in direct contact with the water. Therefore the risk of damage is low from debris flow or fouling.
• Highly accurate with large sized floats.

Limitations of Float-operating sensors in water level measurement:

• Requires a stilling well to assure stability and reliability of the float-operating system.
• Rapid changes in water level may result in the cable / tape line becoming disengaged from the float-operating sensor’s pulley.