Dual range pistons for pressure calibration

Dual piston deadweight testers can greatly enhance a lab?s ability to calibrate wide pressure ranges with the best accuracy. With transducers and devices under test (DUTs) which have a broad measuring range, calibration could be a lengthy process, as you need to change pistons in between test points in order to calibrate its entire range.
However, a dual piston deadweight tester is equipped with a high range piston and low range piston, that allows the technician more flexibility and efficiency in terms of calibration. This advancement originates from decades of innovation and customer interaction to find a solution for industry needs.
Formula for pressure calculations
Because the Industrial Revolution, high accuracy pressure measurement has been a key requirement in process industries. Pressure measuring instruments like gauges were employed to measure and monitor pressure conditons. They must be calibrated against instruments of a higher amount of accuracy. Deadweight testers (also referred to as pressure balances) are high accuracy instruments used in the calibration of electronic or mechanical pressure instruments. The core component of a deadweight tester is a precisely manufactured piston-cylinder system, onto which a mass load is applied so as to generate the individual test points in a calibration.
The mass load is proportional to the prospective pressure, which is achieved through optimally graduated masses. The look of the entire calibration system, in addition to the precise manufacturing of the piston and cylinder, ensure quality performance with long free-rotation time and low sink rates of the piston. With measurement uncertainties right down to 0.002% of reading, deadweight testers are the golden standard in calibration.
A deadweight tester typically includes a single piston-cylinder system. This involves mass sets to be changed so as to calibrate multiple or wide measuring ranges. This could become a cumbersome process, one that requires many resources. In 1953, the entity today referred to as DH-Budenberg pioneered the initial dual range piston-cylinder technology with two pistons housed concentrically in one unit. DH-Budenberg was later acquired by WIKA in 2011. The first design included 1/8 in2 (low pressure) and 1/180 in2 (ruthless) pistons housed in a single unit. Using a single mass-set it was now possible to create two points of equilibrium at 55 bar (low pressure) and 550 bar (ruthless) respectively. This was followed with the release of ruthless variant which could generate pressure upto 1100 bar.
Explanation dual piston design
The first dual piston design was largely made of tool roll, and had an accuracy of 0.03 % of the pressure being measured in the typical model and 0.05 % in the high pressure model. In Track Record , the load on the low pressure piston is transferred to the auxiliary piston, that is directly linked to the weight carrier. When correct pressure is obtained, the piston head skirt floats within the reduced range or ?blue band.? To reach high pressure, the pressure is increased and the reduced pressure piston rises until a knife-edge on the bottom flange makes a seal against the low pressure cylinder and acts because the high pressure cylinder. Since the low pressure piston will not contribute to the entire weight of the piston and weight carrier, the weight carrier accumulates the auxiliary weight to pay. When correct pressure is achieved, the piston head skirt floats within the high range or ?red band.?
This iconic, patented DH-Budenberg red and blue band piston-cylinder system was re-engineered later with both piston and cylinder components made of tungsten carbide. With the refinements in pressure generation and piston manufacturing processes, dual ranges are actually available up to 1,400 bar with accuracies down to 0.006 % of reading.
These developments in dual piston technology made deadweight testers, such as for example DH-Budenberg?s CPB5800 Hydraulic Pressure Balance, the premier deadweight tester for industrial applications. It is especially useful for calibrating a transducer with a broad measuring range, while maintaining the high accuracy for testing and calibration. By using only a single mass set and calibrating instrument, this system can automatically switch between multiple test points of high and low pressure, making pressure calibration seamless, efficient and economical.
Note
More info on our pressure balances can be found on the WIKA website.

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