Can pressure sensors be used to measure liquid level?
Yes, it is ok to measure liquid level using a pressure sensor. A water level pressure sensor is a device that measures the water level in a container by detecting the pressure exerted by a column of water above the container. The water level is converted into a measurable pressure signal. These signals are then processed by a controller or computer for real-time water level monitoring and control. The higher the water level, the greater the pressure on the sensor. The water level can thus be calculated from this pressure reading.
Working principle of water level pressure sensors
The water level pressure sensor works by measuring the hydrostatic pressure exerted by the water column above. The pressure reading is converted to a corresponding water level. The higher the water level, the greater the pressure exerted on the sensor. The sensor is usually placed at the bottom of a tank or container. As the water level rises, the pressure on the sensor increases proportionally.
Hydrostatic pressure measurement
Hydrostatic pressure measurement uses the law of constant volume. That is, at normal temperature and pressure, the density and pressure of water are positively correlated. By measuring the pressure under water, the load-bearing capacity and water resistance of the test object can be reflected.
The measurement formula of hydrostatic pressure is: P = ρ*g*d.
Where:
- P represents hydrostatic pressure, in Pascal (Pa).
- ρ represents the density of the fluid, in kilograms per cubic meter (kg/m³).
- g represents the acceleration due to gravity, usually 9.8 m/s².
- h represents the height of the fluid, in meters (m).
Example calculation:
The hydrostatic pressure equation can be used to calculate the hydrostatic pressure at the bottom of a 10 m deep swimming pool. The pool is filled with water (density of water = 1000 kg/m³).
Solution:
- Given: • h = 10 m • ρ = 1000 kg/m³ • g = 9.81 m/s² (standard value of gravity)
- Calculate: • P = ρgh • P = (1000 kg/m³) * (9.81 m/s²) * (10 m) • P = 98,100 Pa (Pascals)
Points to Remember:
Units: Make sure all measurements are in consistent units before calculation (e.g. depth in meters, density in kg/m3).
Fluid Density: The density of a fluid is critical to accurately calculate pressure. This is especially true when dealing with fluids other than water.
Depth Measurement: The depth “h” should be measured from the free surface of the fluid to the point of measurement.
Types of water level pressure sensors
There are several types of water level sensors. Each type of sensor works differently, common ones include:
- Float-type water level sensor: This sensor uses the principle of buoyancy. The water level change is detected by the float floating up and down. The float-type water level sensor has a simple structure and is easy to debug. However, it is easily affected by liquid viscosity, impurities and magnetic substances, and the detection accuracy is low.
- Capacitive water level sensor: uses capacitance changes to reflect water level changes. Suitable for non-metallic water tanks. However, it may be disturbed when used in metal water tanks, affecting the accuracy and stability of the measurement.
- Ultrasonic water level sensor: Calculates water level by emitting ultrasonic waves and measuring the time difference of reflected waves. Ultrasonic sensors are not affected by the color or material of the liquid. Suitable for various media, but large in size and not suitable for small devices.
- Photoelectric water level sensor: It uses the principle of infrared light reflection for detection. It has the characteristics of high precision, high stability and long life. However, it is not suitable for use under direct sunlight. Environmental factors such as water vapor may affect the detection results.
- Pressure water level sensor: detects water level by measuring the pressure change caused by water level on the sensitive elements inside the sensor. Usually installed in a sealed container.
- Radar water level meter: Radar pulses are emitted through the radar water level sensor antenna. The antenna receives the pulses reflected from the water surface and records the time T. The measurement accuracy can reach ±3 mm. It is suitable for high-precision water level monitoring needs. It is a water level measuring instrument that uses electromagnetic waves to detect targets.
Using pressure sensors to measure water levels
Measuring water level with a pressure sensor uses the principle of hydrostatic pressure. Here the pressure exerted by a liquid column is proportional to its height. This means that the higher the water level, the greater the pressure measured by the sensor immersed in the liquid. The pressure sensor converts the pressure of the water column into an electrical signal that can be interpreted as the water level.
The form of measuring water level using pressure sensor:
- Submersible level gauge measures water level.
The probe of the submersible level gauge is actually a pressure sensor. The water level is calculated by measuring the static pressure of the liquid. When the level transmitter is immersed in a certain depth in the measured liquid, the pressure formula on the sensor’s liquid surface is: P = ρ × g × H + Po. Where P is the pressure on the transmitter’s liquid surface. ρ is the density of the measured liquid. g is the local gravitational acceleration. Po is the atmospheric pressure on the liquid surface. H is the depth of the transmitter immersed in the liquid. By measuring this pressure, the liquid level depth can be obtained.
- Pressure transmitter measures water level in open tanks.
For open tanks, a pressure transmitter can be installed at the bottom of the tank. By measuring the liquid pressure at the bottom of the container, the liquid level can be measured. In an open container, changes in atmospheric pressure will not affect the process fluid pressure in the tank. Therefore, only one pressure transmitter is needed to complete the measurement.
- Differential pressure transmitter measures the water level in a sealed tank.
For sealed tanks, a differential pressure transmitter is required. The water level is calculated by measuring the differential pressure between the top and bottom of the tank. The differential pressure transmitter works by measuring the pressure difference between the top and bottom of the sealed tank. The liquid level is determined. The pressure at the bottom of the container is equal to the liquid level multiplied by the specific gravity of the liquid plus the pressure of the container.
Application areas of water level sensors
Water level sensors are widely used in various fields. Mainly used in applications where monitoring and controlling water levels in tanks, reservoirs, rivers, lakes and irrigation systems is crucial. Basically anywhere where accurate measurement of water levels is required for efficient operation and safety purposes. To ensure smooth operation of production processes.
Specific application areas include:
- Water treatment plants:
Monitor water levels in water storage tanks, sedimentation tanks, and filtration units. To ensure the correct treatment process.
- Agricultural irrigation:
Water level sensors can detect soil moisture or water level in reservoirs. And automatically adjust irrigation volume based on data to achieve water-saving irrigation. Regulate water levels in wells, reservoirs, and irrigation canals. To optimize water use and crop yields.
- Home water supply:
In household appliances such as washing machines, coffee machines, and water dispensers, water level sensors are used to control water levels. Ensure that the equipment operates at the correct water level. Monitor the water level in roof water tanks to prevent overflow and ensure a stable water supply.
- Offshore operations:
Monitor water levels in ballast tanks and other ship compartments to ensure stability and safety.
- Wastewater management:
In the monitoring of water bodies such as rivers, lakes, and reservoirs, water level sensors help monitor water level changes. This is of great significance for flood warning and water resource management.
Advantages of using pressure sensors to measure liquid levels
Pressure sensors are not prone to wear and have no moving parts. This makes them a popular choice for water level applications in open or vented tanks. They are also well suited to foaming media, with measurements not affected by foam. They are cost-effective compared to some other level technologies. They are also generally a cost-effective choice. Key benefits of using pressure sensors for level measurement:
- Accuracy and Precision. Pressure sensors can provide very accurate measurements. This makes them ideal for applications that require high precision.
- No Moving Parts. Unlike some other level sensors, pressure sensors have no moving parts. This minimizes wear and tear and increases reliability.
- Insensitive to Foam. Pressure sensors are not affected by foam on the liquid surface, making them suitable for applications with foamy liquids.
- Wide Range of Applications. Pressure sensors can be used in a variety of environments. These include high temperatures, corrosive substances, and harsh conditions.
- Cost-Effective. Pressure sensors are a cost-effective option compared to some other level measurement technologies.
- Easy Installation. Pressure sensors are generally relatively easy to install and integrate into a system.
- Low Maintenance. Pressure sensors generally require very little maintenance due to their design.
Factors to consider when using pressure sensors for liquid level measurement
When using pressure sensors for level measurement, the pressure medium needs to be considered. The properties of the measured medium (e.g., viscosity, corrosiveness, etc.) will affect the choice and life of the sensor. For example, viscous liquids or corrosive media may require special sensor materials and processing. It is also important to ensure that the sensor is properly calibrated and can handle pressure spikes or pulsations.
Key points to consider:
- Liquid properties:
• Density. The density of a liquid directly affects the pressure exerted at a given depth, which affects the accuracy of the level measurement.
• Temperature. Changes in temperature will alter the density of the liquid, requiring temperature compensation to obtain accurate readings.
• Chemical compatibility. The sensor material must be compatible with the liquid to prevent corrosion or buildup. - Installation considerations:
• Tank geometry. The shape of the tank affects pressure distribution and measurement accuracy.
• Mounting location. The location of the sensor within the tank is critical to accurate level readings.
• Access. Consider the accessibility of the sensor for installation and maintenance. - Environmental factors:
• Pressure fluctuations. If the system experiences significant pressure changes, select a sensor designed to handle such conditions.
• Vibration. Consider the potential vibration in the environment and select a sensor that can withstand it.
• Moisture and humidity. If the sensor is exposed to moisture, ensure it has adequate protection.
Since water pressure sensors may come into contact with different kinds of water, you may need to consider whether they are suitable for different media. Such as drinking water, seawater, etc. Sino-Inst produces and supplies a full range of water level pressure sensors. They can be placed in the liquid, threaded, or flange mounted. Monitor the real-time liquid level and output signals to provide analytical data for water level changes.
If you would like to learn more about the media that water pressure sensors can measure, the applications for each type, and the different sensor options that are right for your design, feel free to contact us!
