
\section{Gas Leakage Test}\label{sec:gas-leakage}

\subsection{Test Procedure}

After installing a new layer into the SM we want to test for leakages. This test will last two days.

\subsubsection{First day}

First connect both gas inputs at stack 4 with the Y-adapter to the flushline labeled outlet of the gassystem.

Leave both gas outputs at stack 0 open without connecting anything to them. This protects the layer from high
overpressure at high flow rates (reduced flow conductance at the layer output).

Secondly use the GUI or the commandline tool to set the flushline to 100 l/h CO2. This will create a slight
overpressure in the layer and in 10 hours you can be sure that there is CO2 almost everywhere in the layer.

You can then go on with the HV tests for the current installed layer safely after 5 hours flushing at 100 l/h CO2.

Continue flushing with this high rate over night to assure that there is no more air (with oxygen) inside the layer
the next day. Keep both gas outputs at stack 0 open!

\subsubsection{Second day}

The next day morning after the HV tests were successful continue with Ar/CO2 composition. 

Set the Ar/CO2 (83:17) gasflow for the flushline to 100 l/h and flush the layer for aprox. 5 hours. Then set the flow
to 25-50 l/h (lower setting over whole weekend, up to 50 l/h over night) and connect both gas outputs at stack 0 with
the orbisphere gas analyzer system (pressure sensor, bubbler and the oxygen sensor).

You will create an overpressure up to aprox. 2 mbar, therefore the measured oxygen content should drop to a few ppm within a hour (bottle offset).
The limit for CO2 4.5 is < 15 ppm, for Ar 4.6 < 10 ppm.

Wait until the oxygen content reaches a constant level.

When you have reached the even level switch the underpressure fan on (just press the power on switch, dont touch the adjusting knob). 

A slight underpressure of 0.5 up to 1 mbar will be created and in the flow you can measure oxygen which is eventually sucked
into the layer through gas leaks.

Regarding to 50 l/h flowrate you have to wait 5 hours to be sure that there are no leaks if the oxygen content keeps the level.
You can estimate the location of a gas leak by measuring the elapsed time since starting the underpressure until the oxygen level arised.

\subsection{Plot}

Start \inputcmd{orb510-viewer} from a shell on trd01. There will be shown a short
introduction how to use this program (please have start and stop flow dates/times handy - you will have to enter these as params).

