National standard for small overpressure, underpressure and differential pressure in gaseous media

Name of Standard: National standard for low gauge pressure, negative gauge pressure and differential pressure in gaseous media

Code designation: ECM 170-5/02-022

Year of publication: 2002

Department: nr. 6013 CMI RI Brno

Guarantor: Ing. Zdeněk Krajíček, Ph.D., RNDr. Jiří Tesař, Ph.D (2002-2006)

Number of CMC lines provided: 2

Mode	Range	Uncertainty (k = 2)
Gauge pressure	1 Pa – 3,2 kPa	0,02 Pa + 8∙10^-5∙p
Negative gauge pressure	1 Pa – 3,2 kPa	0,02 Pa + 8∙10^-5∙p

(p is the value of the generated pressure in pascals)

CMC magnitudes are expressed in terms of expanded uncertainty using an expansion factor of k = 2 (coverage probability of approximately 95%).

This standard is based on the Furness Controls FRS4 digital piston pressure gauge. This instrument provides the low uncertainties and fundamental measurement principle of piston pressure gauges, but extends the range of these approaches to 1 Pa, and further provides a resolution of 0.001 Pa down to 1 kPa. This is made possible by two key elements of its design. Firstly, the weight of the piston is compensated by the dynamometer, allowing it to go down to zero pressures. And secondly, the 100cm² piston-cylinder, which is designed to guarantee high sensitivity, is centred in the housing using a special technology without a need of rotation. The measured pressure is fed to the upper end of the vertical piston in the housing. The pressure thus applied creates a vertical force on the piston, which is transmitted from the piston by means of a mechanical attachment to an electronic dynamometer whose digital output corresponds to the applied pressure. The design of the instruments allows the dynamometer to be recalibrated using a reference weight

The pressure generated by the national standard is calculated according to equation:

where stands for,

p .......…....	pressure,
k_N ........….	sensitivity constant of the instrument,
N .....….....	comparator indication during measurement,
N_K .....…....	comparator indication during zeroing,
T.....….....	temperature of the piston-cylinder,
α......…......	coefficient of thermal expansion of the gauge material,
g ......….....	local acceleration due to gravity,
g_N …….…	normal acceleration due to gravity,
T₀ ..............	reference temperature,
ρ_a ..............	the current density of the atmosphere,
ρ_N.............	the density of the atmosphere under normal conditions,
ρ_m ..............	density of the calibration weight.

Etalon has successfully participated in two published international comparisons.

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National standard for small overpressure, underpressure and differential pressure in gaseous media