THE DIFFERENCE BETWEEN A DEADWEIGHT TESTER AND A DIGITAL PRESSURE CALIBRATOR

THE DIFFERENCE BETWEEN A DEADWEIGHT TESTER AND A DIGITAL PRESSURE CALIBRATOR

The two most popular instruments used to calibrate pressure are deadweight testers and digital pressure calibrators. While deadweight testers have been the standard instrument used for as long as time, recent advancements in technology have led to development of digital pressure calibrators. Both instrument have advantages and disadvantages; therefore, it is important to know which instrument is best for you.

To help you get a better idea of if a deadweight tester is a better fit for you compared to a digital pressure calibrator or vice versa, we have mapped out advantages and disadvantages into the following categories:

ACCURACY

A deadweight tester is an instrument that acts as a physical generator for known pressure and also as a gauge that can accurately measure system pressure. Because the combination of masses are used to determine output pressure, a deadweight tester does not require a display. Operation of this instrument is under a simple formula – pressure is equal to pressure force applied to a known area. The output of this formula is known to be extremely accurate and consists of reading accuracies of ±0.015%.

Unlike a deadweight tester, a digital pressure calibrator must be combined with some form of a pressure source to generate a known pressure. Accuracies for a digital calibrator are typically full scale, e.g., ±0.050%.

SITE CORRECTIONS

An important factor to consider when comparing the accuracy and uncertainty of a deadweight tester and a digital calibrator is site correction.

GRAVITY

Deadweight testers are physical standards; therefore they are more likely to have effects that digital calibrators will not. For example, a deadweight tester will be affected by gravity. Depending on the location a deadweight tester is being used, pressure will vary. If a deadweight tester with the same mass is used in Salt Lake City, UT, it will have a different pressure than if it was used in Birmingham, AL. This is due to the force of gravity varying based on distance from the equator and elevation. If an output is altered due to gravity, users have two options to choose from for correction.

  • The digital tester can be calibrated to local gravity
  • The digital tester can be calibrated to the International Mean Gravity (980.665 gals) – a correction factor would then need to be calculated for the worksite.

This site correction only applies to a deadweight tester. Digital calibrators are not affected by gravity.

TEMPERATURE

Another site correction to consider when comparing a deadweight tester and a digital pressure calibrator is temperature. Temperature does not significantly affect a deadweight tester, uncertainty measurement should still be calculated and accounted for. Unlike a deadweight tester, digital pressure calibrators can be extremely vulnerable to temperature effects.

STANDARDS

The standards of a deadweight tester and a digital pressure calibrator also vary. Deadweight testers are primary standards, while digital pressure calibrators are secondary standards.

PRIMARY

A deadweight tester is considered a primary standard because it is based solely upon physical parameters and does not translate its measurements into an electronic or analog signal. Due to its physicality, a deadweight tester can cover a large range of pressures by using different masses and area components. While these are beneficial factors to have, a deadweight tester’s unit tends to be bulkier than a digital pressure calibrator’s. A deadweight tester is also more difficult to set up and requires a large sum of training to be able to be used properly.

SECONDARY

A digital pressure calibrator is considered a secondary standard because it translates pressure into an electronic signal via a transducer. A disadvantage of a digital pressure calibrator is that due to sensors used in its construction, it has limited ranges. If large pressure range needs to be covered, multiple units will need to be used. However, even if multiple units need to be used, a digital pressure calibrator will still be less bulky than that of a deadweight tester.

COST OF OWNERSHIP

Another factor to consider when comparing and contrasting a deadweight tester and a digital pressure calibrator is cost of ownership and long-term benefits.

Compared to a digital pressure calibrator, a deadweight tester typically costs more to purchase and to calibrate. However, a deadweight tester generally lasts longer than a digital pressure calibrator. It is also known to have a higher accuracy ratio, which eliminates errors throughout a system. With limited errors, chances of a higher monetary benefits are likely.

In conclusion, when considering whether you are in need of a deadweight tester or a digital pressure calibrator, it is important to consider the above advantages and disadvantages of each.

IN-HOUSE VS. OUTSOURCED CALIBRATION

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