Application of pressure transmitter
Application of pressure transmitter (differential pressure transmitter): Pressure is a basic measurement for measuring various process variables such as: pressure, differential pressure, flow, surface, density, etc.
Pressure transfer programs
1.1 Differential pressure
Differential pressure is the difference in magnitude between a certain pressure and a reference pressure. In a sense, absolute pressure can also be considered as a differential pressure, with a complete vacuum or absolute zero as the reference pressure. The barometer can also be considered a differential pressure, because in the barometer the atmospheric pressure is the reference pressure.
A common use of a pressure transmitter is to measure flow velocity. A mainstream element such as the one shown in Figure 4-1 has an internal constraint. This restriction reduces the cross-sectional area of the pipe through which it flows. This constraint increases the velocity of the fluid by crossing the constraint. Thus, liquids immediately upstream of the constraint have less kinetic energy (velocity) than fluid, which is immediately downstream of the constraint. This increase in kinetic energy during constraint is balanced by a decrease in potential energy (static pressure). Sealed valves on both sides of the constraint create a pressure difference in static pressure, which results in a reduction in the potential energy of the fluid. Example: Differential pressure transmitter lowers downstream pressure or pressure less than upstream pressure. This pressure difference is usually very small, typically from water column 1 to water column 750 (0). 24 to 186 KPa) depending on the amount of fluid and flow. An overview of differential pressure flow measurements is shown in Figure 2.
The calculation of the DP domain is as follows:
Low amplitude value = minimum back pressure High amplitude value = low amplitude value + H1 * Gl where mud = specific gravity of process fluid
1.4 Interface level measurement
Measuring the interface level, ie measuring the interface fluid level between two isolated liquids such as oil and water, can also be done using the differential pressure transmitter shown in Figure 7. Liquids 1 and 2 have different densities, and as long as the total surface of the tank is above the tap and as long as the distance h remains constant, the density changes and hence the hydrostatic pressure changes with the interface surface. change.
This measurement can be applied to open or closed tanks or clean or dirty liquids. Choosing the right type of instrument, including a capillary seal diaphragm, is like measuring a surface. While calculating the DP amplitude is as follows: Low amplitude value = H1 * (SG1 – SGc) High amplitude value = Low amplitude value + H1 * (SG2 – SGc) Where SG1 = Low specific gravity SGc = Liquid specific gravity in Capillary SG2 = higher specific gravitational fluid
1.5 Density measurement
The previous principle leads to the measurement of density in the tank. In this case, a homogeneous liquid with different density in the tank, depending on the change in density, puts different pressure on the transmitter. As long as the top level of the faucet remains and as long as h is constant, the transmitter responds to changes in density. Weight density is per unit unit, for example kilometers per cubic meter. If the density increases, the pressure on the lower faucet increases and so does the transmitter. Normally, like surface measurements, pressure difference transmitters are used because the openings are relatively small.
This measurement can be applied to open or closed tanks or clean or dirty liquids. Choosing the right type of instrument, including a capillary flood diaphragm, is like measuring a surface. While calculating the DP amplitude is as follows: Low amplitude value = H1 x (SGpl – SGc) High amplitude value = Low amplitude value + H1 x (SGph – SGpl) where SGpl = minimum process specific gravity SGc = specific gravity Fluid in capillary SGph = maximum specific gravity of process fluid
1.6 volume (product in the tank)
By determining the product level in a tank, the volume of process fluid can be calculated. If the relationship between
the volumesand the surface measured for tanks is linear with a cylindrical shape, this is not true for other shape
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