
\documentclass[english,sanserif]{ptbposter}
%\documentclass[ngerman,sanserif]{ptbposter}
\usepackage[
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\phone{+49-30-3481-7262}
\fax{+49-30-3481-7503}
\email{Karl.Jousten@ptb.de}
\workingGroup{7.54 Vacuum Metrology}
\department{7.5 Heat and Vacuum}
\location{10587 Berlin}
\street{Abbestraße 2--12}
\QRcode{http://www.ptb.de/cms/fachabteilungen/abt7/fb-75/ag-754.html}

\title{\huge Continuous Expansion}

\begin{document}
\begin{multicols}{2}
\section{Method}

In the continuous expansion method, the pressure is reduced by a restriction. The gas flows continuously from a volume at relativ high pressure into the calibration chamber and thereafter to the vacuum pump.


  \includegraphics[width=0.9\columnwidth]{method-poster-en}
 %\caption{Korrekturen der Keithley}

The pressure in the calibration chamber is given by:

\begin{equation}
p= \frac{q_{pv}}{C} \qquad
	\begin{tabular}{@{}lll@{}} 
		$q_{pV}$& & Gas flow \\
		$C$ &  & Conductance \\ 
	\end{tabular} 
\end{equation}

\section{The Primary Standard CE-3}

\includegraphics[width=0.5\columnwidth]{CE_3}

At the PTB, pressures in the range $10^{-10}$ Pa to $10^{-2}$ Pa are generated by the primary standard CE-3, based on the continuous expansion method. This method was improved to enlarge the calibration range.
For these purposes two calibration chambers (UHV-chamber $V_1$ and XHV-chamber $V_2$ (Figure 3))and two cryo pumps were used. Between these chambers a flow divider channels about 99\% of the gas flow into $V_1$ and 1\% into $V_2$.
Thus the gas flow in $V_2$ will be about a factor 100 lower than in $V_1$. The gas flow $q_{pv}$ is produced and measured by the flowmeter FM-3.

\begin{center}
\includegraphics[width=0.9\columnwidth]{Skizze-poster-en}
\captionof{figure}{Scheme}
\end{center}

Cold surfaces at 2.6 K pump the gas molecules exiting from the two calibration chambers through the pump orifices. The high condensation probability of the gas molecules on these surfaces avoids backstreaming for most gas species into the calibration chamber. As a result the orifices act as a “black hole” for the gas molecules. If both cryo pumps operate, the gas flow $q_{pV}$ is subdivided into two gas flows into the respective chambers :
\begin{equation}
q_{pv}= q_{01}+q_{02} \qquad
\end{equation}
If only cryo pump KP1 operates, the calibration pressure in volume V 1 is given by:
\begin{equation}
p_1= \frac{q_{pv}}{\gamma_1 C_1}\cdot \frac{\sqrt{T_{CH_1}T_0}}{T_{FM}} \qquad
	\begin{tabular}{@{}lll@{}}
		$T_{CH1}$ & Temperatur of $V_1$  &  \\
		$T_{FM}$& Temperatur of flowmeter&  \\
		$\gamma_1$ & factor accounting back- &  \\ 
		         & streaming ($\approx1$) &  \\
		$q_{pV}$& Gas flow rate  &  \\  
		$T_{0}$& Reference &  \\ 
		& temperatur 23°C  &  \\
		$C_1$& Conductance of orifice  &  \\      
	\end{tabular} 
\end{equation}


\includegraphics[width=0.8\columnwidth]{uns-ce34evc}
\end{multicols}

\end{document}
