The differential pressure sensor is a very versatile type of pressure measurement device and in addition to its main purpose of DP measurement, it is also used to measure other types of pressure, and other types of physical measurements that are not directly related to pressure.
Gauge Pressure
While differential pressure sensors are designed to handle pressure on both sides, you can also use them to measure gauge pressure. If you leave one side of the sensor open to the atmosphere, it will effectively function as a gauge pressure sensor, measuring the pressure of the system relative to the surrounding atmosphere.
Absolute Pressure
Differential pressure (DP) sensors offer a versatile solution for measuring absolute pressure. By applying and maintaining a vacuum on one port of the sensor, a reference point of absolute zero is established. This allows for measurement of pressure on the other port relative to true zero, effectively replicating the function of a dedicated absolute pressure sensor.
Barometric Pressure
Barometric pressure or atmospheric pressure can be measured using a differential pressure (DP) sensor. To achieve this, one side of the DP sensor must have a vacuum applied to create an absolute reference. The other side is exposed to the atmosphere. The DP sensor then measures the pressure difference between the atmosphere and the vacuum reference.
Many DP sensors allow for output signal rescaling, enabling them to provide higher-resolution measurements over a specific barometric pressure range.
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Vacuum Pressure (absolute)
The concept of vacuum pressure refers to any pressure below the current atmospheric pressure. One type of pressure sensor used to measure vacuum pressure are absolute pressure sensors, which measure the pressure relative to full vacuum.
To use a differential pressure sensor for absolute vacuum measurement, you must create a vacuum reference. This reference can be maintained with a continuous vacuum pump or by applying and then sealing full vacuum using a leak-tight valve. The sensor will then measure the partial vacuum pressure relative to this established full vacuum reference.
Vacuum Pressure (gauge)
Vacuum pressure refers to pressures below atmospheric levels. In industry, vacuum levels are often measured relative to atmospheric pressure using gauge reference sensors. Differential pressure (DP) sensors can also serve this purpose. By connecting the high side of the DP sensor to atmospheric pressure and the low side to the vacuum source, you can directly measure the vacuum as a gauge pressure.
Tank Liquid Level
Differential pressure sensors offer an effective and versatile method to measure liquid level in tanks. They work by sensing the pressure exerted by the submerged liquid’s weight. To account for pressure at the liquid surface (atmosphere for vented tanks, specific gas pressure for sealed tanks), the sensor uses two ports. One port connects to the tank bottom for total liquid pressure, while the other connects to the top (or vents directly for vented tanks) to access surface pressure. This setup cancels out the pressure acting on the top, leaving a reading that reflects only the liquid height.
Regular maintenance is needed to address potential calibration drift caused by liquid transfer from evaporation and condensation. To reduce the need for regular calibration checks, techniques like wet legs or remote seals can be employed. These techniques eliminate condensation issues in the low-side connection, but they do require factoring in the constant pressure from the reference liquid during level calculations.
Liquid Density
Measuring density directly can be challenging, as it requires simultaneously determining both the mass and volume of an object. However, when dealing with liquids, the process becomes significantly easier. Liquids conform to the shape of their container, allowing for a known, fixed volume.
Using the hydrostatic pressure formula (P = ρgh), we can relate the pressure within a liquid column to its density (ρ). Since gravity (g) and liquid height (h) remain constant in a tank, measuring the pressure is the key to determining density.
Differential pressure (DP) sensors exploit this principle by measuring the pressure difference between two fixed points within the liquid. This ensures that the pressure difference is measured for a fixed volume of liquid, allowing for a direct calculation of density using the hydrostatic pressure formula.
DP sensors enable several installation methods depending on factors like open vs. closed tanks, constant or varying liquid levels, and the risk of condensation.
Flow Measurement
Differential pressure (dp) flow measurement offers a versatile and adaptable solution for measuring flow rates in various applications. This technique relies on two key components: a primary element, which purposefully creates a pressure drop within the flow, and a differential pressure sensor, which measures the resulting pressure difference. By applying Bernoulli’s principle, the flow rate can be calculated as it is proportional to the square root of the pressure difference.
Advanced dp sensors often include features like square root extraction and measurements of static pressure and temperature, simplifying calculations and allowing for more precise flow measurements by compensating for density variations.
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