Development of calibration methods and resources in gas microflow measurement
Demand for accurate microflow measurement between 2 µg/s and 200 µg/s (0.1 ml/min and 10 ml/min) comes mainly from the automobile, gas and pharmaceutical industries, as well as from COFRAC-accredited laboratories that need traceability for their reference standards.
Manufacturers of flow meters and reference leaks in the microflow range also require calibration.
In view of the increased need for calibration in these industrial sectors, LNE decided to consolidate its position as a reference laboratory for this flow range by setting up a calibration bench based on the traced gas method.
The photo below shows LNE's microflow calibration bench (traced gas method).
LNE's microflow calibration bench (traced gas method).
The very low mass flow of the traced gas is generated and regulated with a high-stability device produced by the Swiss company LN Industries. The system consists of a heated, thermostat-controlled case (range 20°C to 40°C at ± 0.1°C) with a digital-display vacuum-gauge pressure regulator and gas feed through a filter and four sonic nozzles controlled by ultra-leakproof valves (leakage less than 0.5 µl/min). The nominal flow rate of the nozzles is 0.5, 1, 5 and 10 ml/min. The instrument's thermostat control and vacuum-referenced pressure regulator ensure that variations in atmospheric pressure or temperature in the laboratory need not be taken into account.
The mass flow of the vector gas is adjusted by means of a temperature controller and measured with great accuracy using a Molbloc laminar mass flow meter.
The analyser used to determine the traced gas content is a Varian CP-4900 micro-GC. For analysis of nitrogen, argon or helium, it has been fitted with two independent analytical channels, each consisting of a variable-volume micro-injector, a furnace, a 10-m molecular sieve column and a nano thermal conductivity detector (TCD).
The different phases of the study are as follows: