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<H3><A NAME="SECTION003257200000000000000">
A modern single-channel photometer</A>
</H3>
Next, consider a more modern photometer that uses pulse-counting.
It has a ``neutral'' filter in addition to standard uvby filters.
The ``neutral'' filter is in series with the passband filters, and is used
to determine the dead-time correction.
The positions of these two filter mechanisms are recorded as two adjacent
digits in the data, so we can treat them as a single filter code; the second
digit is 1 when the ``neutral'' filter is in the beam.
<P>
There is also a shutter whose position is encoded separately in the data
stream: 0 means open, 1 means shut.
This can be treated as a second logical filter mechanism.
<P>
The photomultiplier in this modern instrument is in a thermoelectrically cooled
chamber, regulated to run at <IMG
WIDTH="26" HEIGHT="22" ALIGN="BOTTOM" BORDER="0"
SRC="img1159.gif"
ALT="$0^{\circ}$">
C (273 K).
Table <A HREF="node629.html#tbl:modern-example">I.14</A> shows what we get.
<P>
Again, there is only one detector, so we need not include the NDETUSED column.
<P>
<BR>
<DIV ALIGN="CENTER"><A NAME="30582"> </A>
<TABLE>
<CAPTION><STRONG>Table:</STRONG>
Instrument table file for a two-channel photometer</CAPTION>
<TR><TD>
Descriptor values:
<P>
<B>NFILTCAR</B> = 2
<P>
<B>NDETS</B> = 2
<P>
<B>FILTSTAT</B> = <TT>MEASURED</TT>
<P>
<B>FILTCAT</B> = <TT>' '</TT> (blank string)
<P>
<B>CONDITION</B> = <TT>AVERAGE</TT>
<P>
<P>
<DIV ALIGN="CENTER">
<P>
Passband sub-table<TABLE CELLPADDING=3 BORDER="1">
<TR><TD ALIGN="CENTER">NBAND</TD>
<TD ALIGN="LEFT">BAND</TD>
<TD ALIGN="LEFT">FILTCODE_1</TD>
<TD ALIGN="LEFT">FILTCODE_2</TD>
<TD ALIGN="LEFT">REDLEAK</TD>
<TD ALIGN="CENTER">NDETUSED</TD>
</TR>
<TR><TD ALIGN="CENTER">---</TD>
<TD ALIGN="LEFT">--</TD>
<TD ALIGN="LEFT">-----</TD>
<TD ALIGN="LEFT">-----</TD>
<TD ALIGN="LEFT">----</TD>
<TD ALIGN="CENTER">----</TD>
</TR>
<TR><TD ALIGN="CENTER">1</TD>
<TD ALIGN="LEFT">U</TD>
<TD ALIGN="LEFT">1</TD>
<TD ALIGN="LEFT">any</TD>
<TD ALIGN="LEFT">BLOCKED</TD>
<TD ALIGN="CENTER">1</TD>
</TR>
<TR><TD ALIGN="CENTER">2</TD>
<TD ALIGN="LEFT">B</TD>
<TD ALIGN="LEFT">2</TD>
<TD ALIGN="LEFT">any</TD>
<TD ALIGN="LEFT">BLOCKED</TD>
<TD ALIGN="CENTER">1</TD>
</TR>
<TR><TD ALIGN="CENTER">3</TD>
<TD ALIGN="LEFT">V</TD>
<TD ALIGN="LEFT">3</TD>
<TD ALIGN="LEFT">any</TD>
<TD ALIGN="LEFT">ABSENT</TD>
<TD ALIGN="CENTER">1</TD>
</TR>
<TR><TD ALIGN="CENTER">4</TD>
<TD ALIGN="LEFT">R</TD>
<TD ALIGN="LEFT">any</TD>
<TD ALIGN="LEFT">1</TD>
<TD ALIGN="LEFT">BLOCKED</TD>
<TD ALIGN="CENTER">2</TD>
</TR>
<TR><TD ALIGN="CENTER">5</TD>
<TD ALIGN="LEFT">I</TD>
<TD ALIGN="LEFT">any</TD>
<TD ALIGN="LEFT">2</TD>
<TD ALIGN="LEFT">ABSENT</TD>
<TD ALIGN="CENTER">2</TD>
</TR>
<TR><TD ALIGN="CENTER">6</TD>
<TD ALIGN="LEFT">DARK1</TD>
<TD ALIGN="LEFT">0</TD>
<TD ALIGN="LEFT">any</TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="CENTER">1</TD>
</TR>
<TR><TD ALIGN="CENTER">7</TD>
<TD ALIGN="LEFT">DARK2</TD>
<TD ALIGN="LEFT">any</TD>
<TD ALIGN="LEFT">0</TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="CENTER">2</TD>
</TR>
</TABLE>
<P>
<P>
Detector sub-table<TABLE CELLPADDING=3 BORDER="1">
<TR><TD ALIGN="CENTER">NDET</TD>
<TD ALIGN="CENTER">DET</TD>
<TD ALIGN="CENTER">SNUMBER</TD>
<TD ALIGN="CENTER">MODE</TD>
<TD ALIGN="LEFT">COOLING</TD>
</TR>
<TR><TD ALIGN="CENTER">--</TD>
<TD ALIGN="CENTER">--</TD>
<TD ALIGN="CENTER">----</TD>
<TD ALIGN="CENTER">--</TD>
<TD ALIGN="LEFT">----</TD>
</TR>
<TR><TD ALIGN="CENTER">1</TD>
<TD ALIGN="CENTER">PMT</TD>
<TD ALIGN="CENTER">S-13</TD>
<TD ALIGN="CENTER">CI</TD>
<TD ALIGN="LEFT">MEASURED</TD>
</TR>
<TR><TD ALIGN="CENTER">2</TD>
<TD ALIGN="CENTER">PMT</TD>
<TD ALIGN="CENTER">GAAS</TD>
<TD ALIGN="CENTER">CI</TD>
<TD ALIGN="LEFT">DRYICE</TD>
</TR>
</TABLE>
</DIV>
<A NAME="tbl:2-chan-example"> </A></TD></TR>
</TABLE>
</DIV>
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<I>Petra Nass</I>
<BR><I>1999-06-15</I>
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