A DP Level Transmitter measures liquid level in a tank or vessel by detecting the difference in pressure between two points:
- High-pressure (HP) side – Located at the bottom of the tank (measures total pressure).
- Low-pressure (LP) side – Can be vented to the atmosphere (for open tanks) or connected to the top of the tank (for pressurized tanks).
The transmitter calculates the level based on hydrostatic or differential pressure, which is directly related to the liquid height.
Types of DP Level Measurements:
1. Open Tank Measurement (Vented to Atmosphere)
- LP side is open to the atmosphere, so it does not measure additional pressure.
- The DP transmitter directly measures the liquid level based on hydrostatic pressure.
✅ Application: Water tanks, open vessels, sumps.
2. Closed/Pressurized Tank Measurement
- LP side is connected to the top of the tank to compensate for gas/vapor pressure.
- The transmitter subtracts the gas pressure from the total pressure to measure only the liquid level.
✅ Application: Pressurized reactors, boilers, cryogenic tanks.
3. Interface Level Measurement (Two Liquids with Different Densities)
- Measures the level between two immiscible liquids (e.g., oil-water separation).
- Works by detecting the density difference between the two fluids.
✅ Application: Oil & gas separators, chemical reactors.
Limitations & Considerations:
⚠ Density variations – Accuracy depends on the liquid’s density, which may change with temperature.
⚠ Requires proper calibration – Must be set up based on liquid properties and process conditions.
⚠ Clogging risk – Impurities in the liquid can clog impulse lines (solution: use diaphragm seals).