About Pressure Calibrators

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LEARN MORE - About Pressure Calibrators

Like all measuring tools, Pressure gauges, sensors, transducers, and transmitters can drift and wear over time and lose their accuracy. Since accurate readings are critical to most industrial processes, an array of advanced technologies have been developed to calibrate these important measuring tools.

At its most basic, calibration compares two devices – the device to be calibrated, commonly called the unit under test, and a standard device with a known accuracy. Using the standard as a baseline, the unit under test is adjusted until both units display identical results, under identical pressure.

PRIMARY STANDARDS:  However, all standards are not equal. While all standards have a known accuracy, primary standards are fundamental measurement standards, meaning that their measurements are measured directly and are accurate enough that they stand alone to achieve their high accuracy.  They rely on such finite measurements as mass, length, and/or time, and are the most accurate calibration tools available.  

Example of Primary Standard for Measuring Pressure:  An example of a primary standard technology used for measuring pressure are dead weight gauges.  Although pressure is a calculated measurement (force divided by area) by the use of finite measurements such as a mass applied over an exact cross sectional area of a piston floating on a fluid such as water, oil or compressed gas it qualifies as a primary standard. 

SECONDARY STANDARDS:   They are usually calculated or derived measurements.  Secondary standards are inherantly less accurate than primary standards and are calibrated by primary standards.   However secondary standards can be very accurate, and are often referred to as working standards because they are considerably less expensive but much easier to use than primary standards. 

Example of Secondary Standard for Measuring Pressure:  An example would be a portable electronic calibrator, or a digital instrument, both of which use a pressure sensor internally that is calibrated against a primary pressure standard such as a deadweight gauge.  The pressure transducer has no idea what pressure is until it is calibrated against the known primary standard.Pressure is a calculated measurement (force over area) and calculated from fundamentals such as mass and cross sectional area.

Traceability

To achieve the best possible calibration, it is beneficial for the calibration and related measurements to comply with internationally-recognized standards. Establishing traceability can be accomplished by comparing it to a standard that is directly or indirectly related to national standards (e.g. NIST in the U.S.), international standards, or certified reference materials.

Pressure Calibrator Types

Deadweight Testers

Deadweight testers use established, traceable weights and a precision-machined piston and cylinder assembly to determine the accuracy of pressure gauges, sensors, transducers, and transmitters. The unit under test is positioned and the weights (which correspond to specific pressures) are added to the top of the piston assembly. At the same time, a pump generates pressure from the bottom, ultimately creating a balance between the force of the weights and pressure. Once balance has been achieved, the exact pressure is determined by the amount of weight used – the deadweight. The results are compared to the unit under test’s pressure, and corrections are made accordingly.

No other pressure calibration equipment can match the accuracy, repeatability, and stability of deadweight testers. Since they rely on weight to calculate pressure, they are considered primary standards and are globally accepted as the most accurate pressure measurement.

Calibration Pumps and Pressure Sources

Calibration pumps and similar pressure sources enable side-by-side readings from the unit under test and a traceable reference standard. Used as standalone devices or in tandem with multifunction calibrators, calibration pumps house mounts for both gauges. This enables the unit under test to be directly compared to the reference gauge as pressure is being generated; adjustments can then made accordingly.

Durable and portable, pressure pumps provide an easy way to field-test pressure gauge, sensor, transducer, and transmitter accuracy.

Multifunction Calibrators

Extremely versatile and able to accept input from a wide range of sensors, multifunction calibrators are also used to calibrate pressure equipment. In general, pressure calibration via a multifunction calibrator is similar to using just a hand pump and reference gauge. The multifunction calibrator provides the display and necessary electronics, while internal/external generation devices create pressure and pressure modules serve as the standard.

Multifunction calibrators, however, are much more sophisticated than hand pumps. Multifunction calibrators, for example, commonly have internal sensors that compensate for ambient pressure and temperature, thus mitigating two of the most common reasons for inaccurate calibration.

Pressure Calibration Kits/Systems

Pressure calibration kits and/or systems are generally built around multifunction calibrators or calibration pumps and include all the necessary items for pressure calibration performance. Often, multifunction calibrators or calibration pumps that are not part of a kit/system do not include all the adaptors, hoses, fittings, reference gauges, and the like that might be required. Purchasing full calibration kits/systems removes all the guesswork and provides all items needed, fully compatible and ready to perform.

Questions to Consider When Choosing a Pressure Calibrator: 

  1. What devices need to be calibrated?
  2. How accurate a measurement is needed?
  3. What measurement pressure range is required?
  4. Where will calibrations be performed? In the field? In a lab?
  5. Do calibrations need to be traceable to a nationally or internationally recognized standard?
  6. What additional accessories are required – adaptors, fittings, hoses, etc.?