Dual range pistons for pressure calibration

Dual piston deadweight testers can greatly enhance a lab?s capability to calibrate wide pressure ranges with the highest accuracy. With transducers and devices under test (DUTs) which have a broad measuring range, calibration could be a lengthy process, as you must change pistons among test points so that you can calibrate its entire range.
However, a dual piston deadweight tester has a high range piston and low range piston, that allows the technician more flexibility and efficiency in terms of calibration. This advancement comes from decades of innovation and customer interaction to find a solution for industry needs.
Formula for pressure calculations
Since 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 really a precisely manufactured piston-cylinder system, onto which a mass load is applied to be able to generate the individual test points in a calibration.
The mass load is proportional to the mark pressure, that is achieved through optimally graduated masses. The design 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 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 to be able to calibrate multiple or wide measuring ranges. This may become a cumbersome process, one that requires many resources. In 1953, the entity today referred to as DH-Budenberg pioneered the first dual range piston-cylinder technology with two pistons housed concentrically in a single unit. DH-Budenberg was later acquired by WIKA in 2011. The initial design included 1/8 in2 (low pressure) and 1/180 in2 (ruthless) pistons housed in one unit. Using a single mass-set it was now possible to create two points of equilibrium at 55 bar (low pressure) and 550 bar (high pressure) respectively. This is followed with the release of ruthless variant that could generate pressure upto 1100 bar.
Explanation dual piston design
The initial dual piston design was largely made of tool roll, and had an accuracy of 0.03 % of the pressure being measured in the standard model and 0.05 % in the high pressure model. In dual piston calibration, the load on the reduced pressure piston is used in 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 pressure gauge octa , the pressure is increased and the low pressure piston rises until a knife-edge on the bottom flange makes a seal against the low pressure cylinder and acts as the high pressure cylinder. Because the low pressure piston does not contribute to the overall weight of the piston and weight carrier, the weight carrier picks up 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 around 1,400 bar with accuracies right 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 ideal for calibrating a transducer with a broad measuring range, while maintaining the high accuracy for testing and calibration. With the use of just 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 are available on the WIKA website.