A differential pressure transmitter is a widely used instrument in industrial processes. As part of the process control system, it converts the differential pressure (pressure), flow, level, and other process parameters of liquids, gases, or steam into standardized output signals (such as 4-20mA current). These signals are used as input for display instruments, controllers, and regulators to ensure continuous monitoring and automatic control of production processes.
Dry and Wet Capillary Connections
Dry and wet capillary connections are two distinct installation methods for differential pressure transmitters when measuring liquid levels or pressures. The choice between these methods depends on the condensation behavior of the gas above the measured medium.
1. Dry Capillary Connection
In cases where the gas above the liquid does not condense, the capillary line on the low-pressure side of the transmitter remains dry. This setup is known as a dry capillary connection. The method of determining the transmitter’s measuring range in this case is similar to that of open-container liquid level measurement.
2. Wet Capillary Connection
If condensation occurs in the gas above the liquid, liquid will gradually accumulate in the capillary line on the low-pressure side of the transmitter, which can cause measurement errors. To eliminate this error, the capillary line on the low-pressure side is pre-filled with a specific liquid. This setup is known as a wet capillary connection. Wet capillary connections are ideal for complex conditions, such as gas condensation or large temperature fluctuations, as the filling liquid eliminates errors caused by the condensate. However, it is essential to ensure that the liquid used for filling remains stable.
Migration in Level Measurement with Single/Double Chamber Balancing Containers
Migration refers to the shifting of the transmitter’s measurement range without changing its overall span. Specifically, the measurement start point is moved below the reference point (zero), called negative migration, or moved above the reference point, called positive migration. The concept of migration is essential in ensuring accurate measurements across a wide range of conditions.