A primary standard for the calibration of sniffer test leak devices

Abstract

Test leaks with a gas flow to atmospheric pressure are often called sniffer test leaks. They are used to calibrate leak detectors for sniffing applications. Sniffer test leaks need calibration against a standard. A primary standard for the calibration of sniffer test leaks with relatively low measurement uncertainties is described. It is assured that the measurement result is traceable to the relevant SI units and that there is a well-known and complete measurement uncertainty budget. The measurement range of the system is from 4 × 10−11 mol s−1 (corresponding to 10−4 Pa l s−1 at 23 °C) to 4 × 10−9 mol s−1 (10−2 Pa l s−1 at 23 °C), which is the most often needed range in industry of around 1 g loss per year of the cooling agent R134a. The temperature where the calibration can be carried out may vary from 18 °C to 30 °C. The flow rate of any test gas not condensing in this temperature range can be measured.

Development of a gas micro-flow transfer standard

“…(4) and (13)). Deviations of -0.9% for capillary 1, 2.5% for capillary 2 and -4.9% for capillary 3 have been observed with the primary constant pressure flowmeter.…”

“…More recently, this principle has been shown to be suitable for calibrating leak rates flowing at atmospheric pressure [4,5]. The measured quantity is the so-called throughput q pV , in Pa m 3 s -1 , given by the following definition:…”

Leak rate metrology for the society and industry

“…They are essentially based on constant pressure-variable volume method. The best relative standard uncertainties of NMIs flow-meters [22][23][24][25][26][27][28][29] are ranging from 2% to 0.3% for molar flow between 10 À11 mol/s and 10 À8 mol/s and referred to atmospheric pressure. When the gas flow has to be delivered to vacuum the standard uncertainty lies in the range from 1.4% (at 4 Â 10 À13 mol/s) to 0.14% (at 10 À6 mol/s).…”

Perspectives of atmospheric reference leaks calibration by gravimetric method

“…The primary leak standards working at the atmospheric pressure can be divided into those being sensitive [1] and being insensitive [2][3][4][5][6][7][8] to a detected gas species. The problem of the first group is that they can work only with a limited number of gases, the problem of the second group is that they measure depleted amount of gas, i.e.…”