9.2 Manometer
The manometer
This Davidson College page has a very good treatment of pressure measurement with a manometer, with simulations. And this manufacturer’s site surveys the many kinds of devices used to measure the pressure of gases in practical applications.
A modification of the barometer, the U-tube manometer, provides a simple device for measuring the pressure of any gas in a container. The U-tube is partially filled with mercury, one end is connected to container, while the other end can either be opened to the atmosphere. The pressure inside the container is found from the difference in height between the mercury in the two sides of the U-tube. The illustration below shows how the two kinds of manometer work.
Figure 9.16 Different Types of manometers
Ref: Wikimedia.org/
Ref: http://boomeria.org/physicslectures/atmospheric/atmospheric.html
The manometers ordinarily seen in the laboratory come in two flavors: closed-tube and open-tube. In the closed-tube unit shown at the left, the longer limb of the J-tube is evacuated by filling it with mercury and then inverting it. If the sample container is also evacuated, the mercury level will be the same in both limbs. When gas is let into the container, its pressure pushes the mercury down on one side and up on the other; the difference in levels is the pressure in torr.
In the open-tube manometer on the right, the atmosphere pushes the mercury column down in the open side, and again the pressure in torr is found from the difference in the levels. When using this method, the atmospheric pressure must be determined by means of a barometer.
For practical applications in engineering and industry, especially where higher pressures must be monitored, many types of mechanical and electrical pressure gauges are available.
Figure 9.17 gas Pressure gauge