SENSITIVITY OF LEVEL TUBE

A level tube or bubble tube is an important part of most of the surveying instruments. It consists of a glass tube partially filled with liquid. The space above the liquid surface is occupied by the vapours known as bubble.

• The sensitivity of the level tube is expressed in terms of the angle in seconds substanded at the centre of an arc of the level tube equal to one division of the tube.
• The radius of the upper surface of the tube is a measure of the sensitivity of the level tube. If the radius of level is quite large then even, a small movement of the level tube axis will cause a large displacement of the bubble and therefore, the tube would be very sensitive.
• Sensitivity is angular value per division (a).