A level transmitter is a device used to measure and monitor the level of a substance, such as liquid or bulk material, in a container or vessel. It provides continuous or periodic level readings, which are crucial for process control and inventory management in various industries.
There are several types of level transmitters available, here we are going to discuss the working principle of “differential pressure level transmitter.”
- Principle: Differential pressure level transmitters work based on the principle of hydrostatic pressure. The pressure at a specific depth in a liquid is directly proportional to the height of the liquid column above that point.
- Installation: The level transmitter is typically mounted on the top of the vessel, and its sensing element extends down into the liquid or material being measured. The sensing element consists of a diaphragm or a similar mechanism that can sense the pressure exerted by the fluid.
- Reference Pressure: The level transmitter has two pressure ports: one is open to the atmosphere, and the other is connected to the vessel or tank. The pressure difference between these two ports is measured.
- Hydrostatic Pressure Calculation: The level transmitter measures the pressure difference caused by the liquid column above the sensing element. This pressure difference is converted into a level measurement using the hydrostatic pressure formula: P = ρgh, where P is the pressure, ρ is the density of the liquid, g is the acceleration due to gravity, and h is the height of the liquid column.
- Transmitter Output: The level transmitter converts the measured pressure difference into an electrical signal, which is typically in the form of a current (4-20 mA) or voltage. This signal is proportional to the level of the liquid in the vessel.
- Calibration: Before using the level transmitter, it needs to be calibrated to establish a relationship between the measured pressure difference and the corresponding level. Calibration involves applying known levels to the vessel and recording the corresponding output signal.
- Output Display or Transmission: The electrical output signal from the level transmitter can be displayed on a local indicator or transmitted to a control room for monitoring and control purposes. The signal can be further processed to trigger alarms, control pumps or valves, or integrate with other control systems.
It’s worth mentioning that there are other types of level transmitters, such as ultrasonic, radar, capacitance, and float-based transmitters, which operate on different principles but serve the same purpose of measuring and monitoring levels.