--- title: "Vacuum Pressure: What is it & how do you measure it?" description: What is Vacuum Pressure and how do you measure pressure? image: https://www.setra.com/hs-fs/file-2786334973-jpg/blog-files/vacuum-measurements-range-1024x147.jpg --- ** ** ** - Website Pages - Products [![Setra Systems Logo](https://www.setra.com/hubfs/setra-logo.svg "Setra Systems Logo")](https://www.setra.com/) ![drop-down-pressure](https://www.setra.com/hs-fs/hubfs/angle-arrow-pointing-to-right.png?width=15&name=angle-arrow-pointing-to-right.png) **[Pressure Sensors](https://www.setra.com/product/pressure)** [Differential Pressure Sensors](https://www.setra.com/product/pressure/differential) [Absolute Pressure Sensors](https://www.setra.com/product/pressure/absolute) [Barometric Pressure Sensors](https://www.setra.com/product/pressure/barometric) [Compound Pressure Sensors](https://www.setra.com/product/pressure/compound) [Gauge Pressure Sensors](https://www.setra.com/product/pressure/gauge) [Submersible 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[Services & Calibration](https://www.setra.com/support/service) [New and Unused for Credit](https://www.setra.com/product-return) [Contact Us](https://www.setra.com/help-center) # Vacuum Pressure: What is it & how do you measure it? #### by [Tom Lish](https://www.setra.com/blog/author/tom-lish) - [Tweet](https://twitter.com/share) The term vacuum is often misunderstood. Consequently, it is commonly misapplied when discussing pressure measurements and choosing [pressure transducers](https://www.setra.com/product/pressure). Pressure is the exertion of force upon an object. However, pressure can be measured in many different ways, depending on the applications. - [Vacuum Pressure](https://www.setra.com/blog/vacuum-pressure-what-is-it-how-do-you-measure-it#VacuumPressure) - [Gauge Pressure](https://www.setra.com/blog/vacuum-pressure-what-is-it-how-do-you-measure-it#GaugePressure) - [Absolute Pressure](https://www.setra.com/blog/vacuum-pressure-what-is-it-how-do-you-measure-it#AbsolutePressure) - [Differential Pressure](https://www.setra.com/blog/vacuum-pressure-what-is-it-how-do-you-measure-it#DifferentialPressure) - [Setra's Vacuum Sensors](https://www.setra.com/blog/vacuum-pressure-what-is-it-how-do-you-measure-it#Setra) ## Vacuum Pressure By definition, vacuum is a space that is partially exhausted (as to the highest degree possible) by artificial means (such as an air pump). This definition is referring to a high or hard vacuum. Figure 1 illustrates that relationship of absolute and gauge pressure with 0 PSIA equal to a high or hard vacuum. **Figure 1:** ![Vacuum Measurements Range Setra](https://www.setra.com/hs-fs/file-2786334973-jpg/blog-files/vacuum-measurements-range-1024x147.jpg?width=600&height=86&name=vacuum-measurements-range-1024x147.jpg "Vacuum Measurements Range")       ## Gauge Pressure [Gauge pressure](https://www.setra.com/product/pressure/gauge) is pressure measured relative to ambient atmospheric pressure (approximately 14.7 PSIA). It is referred to as pounds per square inch (gauge) or PSIG. The electrical output of a gauge pressure transducer is 0 VDC at 0 PSIG (14.7 PSIA) and full scale output (typically 5 VDC) at full scale pressure (in PSIG).   ## Absolute Pressure [Absolute pressure](https://www.setra.com/blog/what-is-absolute-pressure) is measured relative to high vacuum (0 PSIA). It is referred to as pounds per square inch (absolute) or PSIA. The electrical output of an [absolute pressure transducer](https://www.setra.com/product/pressure/absolute) is 0 VDC at 0 PSIA and full scale output (typically 5 VDC) at full scale pressure (in PSIA). Vacuum can refer to any pressure between 0 PSIA and 14.7 PSIA and consequently must be further defined. For applications concerned with measuring vacuum pressures over this full range, two different approaches are often taken.   **Figure 2:** ![Relationship of absolute and vacuum pressures](https://www.setra.com/hs-fs/file-2786334983-jpg/blog-files/relationship-of-absolute-and-vacuum-pressures-1024x202.jpg?width=378&height=75&name=relationship-of-absolute-and-vacuum-pressures-1024x202.jpg "Relationship of absolute and vacuum pressures")     Vacuum pressure is measured relative to ambient atmospheric pressure. It is referred to as pounds per square inch (vacuum) or PSIV. The electrical output of a [vacuum pressure transducer ](https://www.setra.com/product/pressure/vacuum)is 0 VDC at 0 PSIV (14.7 PSIA) and full scale output (typically 5 VDC) at full scale vacuum, 14.7 (0 PSIA). The vacuum pressure transducer gives an increased positive voltage output proportional to decreasing pressure (increasing vacuum). The absolute pressure transducer gives an increased positive voltage output proportional to increasing pressure (decreasing vacuum). **Example** **             Vacuum Transducer** Range: 0 to 14.7 PSIV Output: 0 to 5 VDC **Absolute Transducer** Range: 0 to 14.7 PSIA Output: 0 to 5 VDC   ## Differential Pressure Vacuum also is often referred to as negative pressure (or soft vacuum). This occurs when the application requires monitoring both decreases in pressure below atmospheric pressure and increases in pressure above atmospheric bidirectional differential pressure.   **Figure 3:** ![Relationship between differential and absolute pressure](https://www.setra.com/hs-fs/file-2786334993-jpg/blog-files/relationship-between-differential-and-absolute-pressure-1024x99.jpg?width=540&height=52&name=relationship-between-differential-and-absolute-pressure-1024x99.jpg "Relationship between differential and absolute pressure")     Here [differential pressure](https://www.setra.com/product/pressure/differential) is pressure measured relative to a reference pressure. It is referred to as pounds per square inch (differential) or PSID. If the reference pressure is one atmosphere the differential pressure range is equal to gauge pressure range. The electrical output of a bidirectional differential pressure transducer is typically 0 VDC at one atmosphere with increased positive voltage output proportional to increased positive pressure and increased negative voltage output proportional to increased negative pressure. **Example** **             Bidirectional Differential Pressure Transducer** Range: 0 to ±5 PSID Output: 0 to ±2.4 VDC Bidirectional [differential pressure transducers](https://www.setra.com/product/pressure/differential) are used for soft or low vacuum measurements (typically greater than 5 PSIA) while low absolute pressure transducers are used for hard or high vacuum measurements (typically less than 5 PSIA). Figure 4 illustrates soft and hard vacuums. **Figure 4:** ![Soft and Hard Vacuums Diagram](https://www.setra.com/hs-fs/file-2786335003-jpg/blog-files/soft-and-hard-vacuums-1024x304.jpg?width=480&height=142&name=soft-and-hard-vacuums-1024x304.jpg "Soft and Hard Vacuums")           ## Setra's Vacuum Sensors Setra's vacuum pressure transducers are built with capacitive sensing technology and are used in a wide variety of applications. Accurate, reliable, and stable, Setra's Model [206](https://www.setra.com/products/pressure/model-206-industrial-pressure-transducer), [209](https://www.setra.com/products/pressure/model-209-gauge-pressure-transducer), and [210](https://www.setra.com/product/pressure/model-210) have been successfully integrated into applications from injection molding to semiconductor manufacturing. 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