Displacer Level Transmitter Simulator – Level & Interface Measurement
Process
Transmitter readings
| Actual level (mm) | |
| Wetted displacer length | |
| Buoyant force | |
| Apparent weight | |
| Measured (% of span) | |
| Measured level (mm) | |
| Output current | |
| Measurement error |
How Does a Displacer Level Transmitter Work?
A displacer level transmitter measures liquid level based on the principle of buoyancy. As the liquid level rises, a greater portion of the displacer becomes immersed in the liquid, increasing the buoyant force and reducing the displacer’s apparent weight. The transmitter converts this change into a level measurement signal.
1. Displacer Level Measurement
In level measurement mode, the transmitter measures the liquid level using the change in buoyant force acting on the displacer. The measured value can be converted into a standard 4–20 mA output, representing the configured level range.
- Low level: Lower buoyant force and higher apparent displacer weight.
- High level: Higher buoyant force and lower apparent displacer weight.
- 4 mA: Typically represents the configured lower range value.
- 20 mA: Typically represents the configured upper range value.
2. Interface Level Measurement
A displacer transmitter can also measure the interface between two liquids with different specific gravities, such as oil and water. The difference in liquid densities changes the buoyant force acting on the displacer, allowing the transmitter to detect the interface position.
Accurate interface measurement depends on the specific gravity of both liquids and the transmitter’s calibration settings.
3. Effect of Specific Gravity
Specific gravity directly affects buoyancy. If the actual liquid specific gravity differs from the value used during calibration, the transmitter may indicate an incorrect level. This simulator allows you to change the liquid specific gravity and observe its effect on apparent weight, measured level, and output current.
4. Try the Interactive Simulator
Use the simulator above to explore how the following parameters affect transmitter readings:
- Tank level and liquid interface position
- Heavy and light liquid specific gravity
- Buoyant force and apparent displacer weight
- Measured level and percentage of span
- Transmitter output in milliamps
- Measurement error caused by changes in specific gravity
Frequently Asked Questions
What is the working principle of a displacer level transmitter?
It works on Archimedes’ principle: an immersed object experiences an upward buoyant force equal to the weight of the fluid it displaces.
What is the difference between level and interface measurement?
Level measurement determines the height of a liquid, while interface measurement determines the boundary between two liquids of different densities.
Does specific gravity affect displacer level measurement?
Yes. A change in specific gravity changes the buoyant force and can cause measurement error if the transmitter is not calibrated for the actual process liquid.
Can a displacer transmitter measure oil–water interface?
Yes, provided the liquids have a sufficient density difference and the transmitter is correctly selected, installed, and calibrated.
Disclaimer: This simulator is intended for educational purposes. Actual transmitter behaviour depends on displacer dimensions, liquid density, operating conditions, mechanical design, and calibration configuration.
