A simple traditional device used to measure the pressure has a piece of clear glass or plastic fluid-filled tube basically called a manometer.
A manometer indicates the difference between two pressures by a shift in liquid column height where the applied pressure causes the fluid height to shift proportionately. Thus, the pressure is measured in the terms of liquid height in this (inches of mercury or water) and is normally used as indicators, but they can also be provided with switches to detect the level of indicating fluid in the tubes.
In a manometer, liquid column height should always be interpreted at the centerline of the liquid column, regardless of the shape of the liquid’s meniscus (curved air/liquid interface).
Advantages:
- The simplicity and low cost are the main advantages of manometers.
- Available in different types of construction materials and designs as per the requirement.
Disadvantages:
- Because of density variation & light refraction, it is difficult to read out scale.
- Possible vaporization of the filling fluids at high vacuums or at high temperatures is another limitation.
- Due to the toxic nature of mercury, it is not suitable to use in all applications.
- It is necessary to compensate for capillary effects; variations in gravity by location; fluid compressibility; and temperature expansion of the filling fluid.
Different types of manometers:
Instrumentation Basics 