| Full line catalog of Industrial controls including pressure gages, manometers, pressure-switches, transmitters, flowmeters, flow-switches, pitot tubes, anemometers, air velocity instruments, Level-Switches, temperature-controllers, thermocouples, RTDs, an Measurement of Pressurewith the Manometer Pressure is defined as a force per unit area - and the most accurate way to measure low air pressure is to balance a column of liquid of known weight against it and measure the height of the liquid column so balanced. The units of measure commonly used are inches of mercury (in. Hg), using mercury as the fluid and inches of water (in. w.c.), using water or oil as the fluid. Fig. 2-1. In its simplest form the manometer is a U-tube about half filled with liquid. With both ends of the tube open, the liquid is at the same height in each leg. Fig. 2-2. When positive pressure is applied to one leg, the liquid is forced down in that leg and up in the other. The difference in height, h, which is the sum of the readings above and below zero, indicates the pressure. Fig. 2-3. When a vacuum is applied to one leg, the liquid rises in that leg and falls in the other. The difference in height, h, which is the sum of the readings above and below zero, indicates the amount of vacuum. Instruments employing this principle are called manometers. The simplest form is the basic and well-known U-tube manometer. (Fig. 2-1). This device indicates...
|
