When looking to calibrate your equipment, there are several approaches to get it done properly. One type includes pressure calibration, which is also becoming even more popular because of the many advantages of this process. Below discusses some of the pros and cons associated with pressure calibration.
Compressed gasses are found to be more constant and stable when compared to hydraulic fluid. This is because gasses are highly capable of getting compressed while hydraulic fluids do not have this distinctiveness. This means that if there are any temperature or volume variances, the pressure with hydraulic fluid could get affected immensely, whereas with gasses, due to its ability to cope with compression, it is likely to just expand and behave with respect to any changes due to volume and temperature. This is typically prevalent in pressures applied due to leakage which affects the pressure in the machine.
- In relation to the stability of compressed gases, these allow better pressure manipulation compared to use of hydraulic fluids. In addition, it also allows a wider range of testing breakpoints such as 0.1 inch pressure to 3,000 psi.
- Using compressed gas provides a tidier and cleaner process when compared to hydraulic fluid because it does not leave residues that could contaminate the gas system as well as eliminating the issues of freezing fluids in machine corners. On top of this, there will be no liquid spillage after conducting calibrations.
- Some limitations of pressured gas calibration may include not being able to provide good results beyond 3,000 psi. In this regard, however, people have the option to use hydraulic fluids to conduct calibrations.
Conditions to consider before conducting calibrations
Once a decision is made about utilizing pressure calibrations, the following points have to be taken into account first before calibration:
- Master equipment's accuracy. Following the requisites of the European Standard EN837-1, the direct drive pneumo gauge must undergo at least ten constant increments of rising and falling pressures. This process requires that the gauge be lightly tapped before reading the meter.
- Identify SC/SG. Particularly the SG or the specific gravity of the sea water varies in the different parts of the world. This is particularly important if one is using sea water scale.
- Temperature. The initial temperature setting for and when doing calibrations is typically at 20C +/-2C. While this component could get affected by the materials used to construct the equipment and other manufacturer specific components, the accepted inaccuracy indexes can be between 0.3% up to 0.5% Full Scale Deflection (FSD) per +/-10 Kelvin.
In addition, if the equipment has to be transported from the facility to a shop, it is imperative that the machine be allowed sometime to settle for at least 24 hours. This is due to the possible change in environment conditions which could affect the temperature and other components that may provide incorrect results. This is specifically imposed for equipments that are sensitive to temperature changes.
- Correct mounting of the equipment during testing. This is specifically monitored when the equipment has to be transferred to another shop for calibration. If the machine has to be in an upright position, the testers should check to see whether it is in the proper upright position, which includes checking whether the base is at the correct level at all foot.
- Calibration media to use. For example if a machine goes through a process of degreasing when it was built, then calibrations should include certain mediums that do not contain oil. These include using pressured gasses such as Nitrogen.
In conclusion, when running calibrations on any equipment, it is important to also check if the company or the specialists that will conduct the process is knowledgeable about the process. This is to ensure that your machine will continue to provide optimized performance in the longest way possible. In this way, you get more value for your money when you purchase the equipment and for the calibration processes that have to be performed. In addition, you also get better yield when your equipment is at its best conditions.
Published on behalf of Ms. Joanna Smith. She is an expert in pressured gas calibration and a long-time collaborator with Zenith Sales and Calibration.
