An equipment known as a dead weight tester is used to calibrate pressure by measuring the weight of force applied to a certain area and then dividing that figure by the area.
The equation for determining pressure in dead weight testers is force equals pressure divided by the region across which force is applied.
Range
The first consideration is the pressure range. One of the benefits of a DWT is that it may cover a broad variety of instruments. The DWT is an intrinsic percent-of-reading device, which means that its performance increases when lower pressures are applied. There is a lower breakpoint, often 10% of full scale, at which the specification ceases to be expressed as a percentage of reading.
When determining the range of a deadweight tester, the greatest pressure that must be created should be considered first. The whole scale should be bigger than this. Since the accuracy is a percentage of the reading standard, it is permissible to anticipate future growth and pick a DWT with a larger full scale than is now required.
Numerous pneumatic devices facilitate the measurement of gauge mode pressures below air pressure. This is sometimes referred to as vacuum mode or negative gauge. To help the calibration of these devices, a DWT may be fitted with a vacuum piston, where the piston is hanging with the weights below it.
Media
The next consideration when choosing a DWT is the media to be used. Frequently, the selection of the medium is determined by the needed pressure range. Pneumatic, or gas-powered, instruments are suited for use in low-pressure environments. When cleanliness is necessary, gas is preferable. Using gas also diminishes the effect of head height modifications. At greater pressures, however, water or oil must be used.
The effectiveness of gas as a medium is restricted to roughly 2000 psi. This is due to two factors. First, there is an increased chance of explosion at high gas pressures, and that is a safety problem. Second, the production of high gas pressure will need the use of costly intensifiers or gas boosters. Using oil or water removes these difficulties. Since water has poor lubrication, oil should be used wherever possible.
Pressure generation
A DWT is a full system that covers both the capacity to monitor the pressure as well as create the pressure.
To boost pressure in a mechanical dead-weight weight tester, a propelling pump is employed. The P3100 and P200 Series Deadweight Testers from Nagman contain a priming pump as a standard feature. The priming pump may also be used to remove gas from the system.
The generation of a minus gauge, or vacuum, is similar in principle to positive pressure. For lower suction pressures with modest quantities a built-in hand, the pump will be sufficient. For bigger quantities or greater vacuums, it may be beneficial to use an external vacuum pump.
Weight sets
Deadweight tests employ a precise piston-gauge system consisting of a vertically mounted, piston and cylinder assembly, and correctly calibrated weight masses that are put onto the piston. Weight sets are available in a number of units of measurement, including psi, inH2O, and MPa, and are calibrated to correspond with a particular deadweight tester. Additional weight sets, known as conversion weight sets, may be obtained in the necessary units and calibrated to match the same deadweight tester if more than one unit of measure is needed.
Accuracy
Like most measuring systems there are several elements that affect your accuracy. Potentially, the major element impacting accuracy in deadweight testing is local gravity. Gravity fluctuates significantly depending on the location. This has an effect on a deadweight tester’s minimum pressure increments. Nagman trims the weights throughout the manufacturing process to achieve the right nominal pressures at your location. Buying a new deadweight tester and having the manufacturer reduce the weights is advantageous in this regard.
Each Nagman DWT is available with either standard or enhanced accuracy. Standard on instruments with the increased accuracy option is software that facilitates the computation of the produced pressure.
For more precision, a piston gauge may be used. A piston gauge operates on the same premise as a DWT, but it is designed, constructed, and operated to give less uncertainty.
Conclusion
The ideal choice of deadweight tester should be made after careful consideration of the following criteria: the region of use, the range, and the accuracy class of the devices that are to be calibrated; the optimum pressure medium that is necessary; and the allowable basic starting pressure.
Deadweight testers provide highly flexible industrial and laboratory variants that may be tailored to the specific requirements of your application while maintaining an accuracy that is unrivaled.
