What Are The Difficulties Of Low Pressure Calibration?

Calibration is important regardless of what type of pressure you are monitoring.

Calibration is especially significant for low pressure requirements in critical applications such as vivariums, pharmaceutical manufacturing, cleanrooms and hospital isolation rooms. Other applications for low pressure include medical instrumentation, environmental pollution control, boiler combustion efficiency, air flow and research and development test stands.  

In all of these applications, it is not only important to use an accurate sensor for monitoring air pressure but also to ensure the sensor is working correctly and within specification. Calibration guarantees the sensor is reading pressure accurately, which is significant in these low pressure applications. For example, in an FDA regulated cleanroom environment, it is important to confirm the sensors accuracy to guarantee that the cleanroom is operating properly during the drug manufacturing process. Low pressure calibration is challenging and can pose the following difficulties:

Difficult to Generate a Stable Low Pressure (<1” W.C) During Calibration

With the cost of energy on the rise, building managers are forced to rethink how critical environments are pressurized while still complying with strict FDA guidelines. Differential pressure transducers provide critical feedback to an HVAC system to protect the space from contamination or to provide containment of particles from leaving the space. Decreasing the full span pressure ranges makes it exponentially more difficult to perform calibrations. Using traditional calibration technology, it is difficult to generate low pressure and to maintain a pressure stable enough to perform an accurate calibration. Open loop pressure generators can contribute up to 0.62% error based on pressure control stability alone.

Difficult To Obtain A Reference Standard Capable Of Maintaining Acceptable Test Uncertainty Ratios

Once a stable low pressure is generated, a reference standard accurate enough to validate that the sensor is being calibrated properly is required. A transducer that can measure low pressure ranges with a high enough accuracy to be suitable as a reference standard can be difficult to find. The ratio between the reference standard and the unit under test (UUT) is known as a “Test Uncertainty Ratio” (TUR). In order for a transducer to be used as a reference standard, it has to be accurate and stable over a given a period of time (typically a year) and provide a 4:1 TUR for the user.

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