PROPOSED REDUCED DATA SET
                prepared by Oregon

The list of channels to be included in a reduced
data set will evolve considerably as we gain more
experience with the LIGO interferometers and PEM
systems.  Here we make a suggestion as to what
channels one might want to include in the initial reduced
data set.  This is a very useful exercise, because
it allows us to see what functionality the software
used to produce the reduced data set must have.

Above all, the software must be very flexible so that
the list of channels, as well as the methods of
compression and data reduction can be easily
changed.

Below we give a first suggestion as to what channels
might be included in the reduced data set.  Note that
the total rate of 200kB/s already exceeds our goal of
150kB/s.  However, this is before any ``non-destructive''
data compression.  For many channels, we expect a gain
of at least 3 or 4 from the simplest data non-destructive
data compression schemes.

Note that we plan to include simple trend-type information
about every channel in the system (min, max, mean and rms).
It may be useful to include some filtering before these
statistics are calculated.  For example, if the approximate
transfer function between a channel and the interferometer
is known, we may want to apply the transfer function to
the channel and then calculate the statistics.

As a first step we will need to implement software which
can properly decimate a list channels.   We will also
need the functionality to allow several channels to be
combined into a signal output (for example the quadrature
sums indicated below).  Something along the lines of the
current program  JDClient would be a good place to start.
 
 

  signal         | number | bytes  |  rate | Channel   | data rate
                                              number
 

GW strain signal
LHO 4K                 1      4      2kHz          0          8kB/s
LHO 2k                 1      4      2kHz      10000          8kB/s
LLO 4k                 1      4      2kHz      30000          8kB/s

Laser Power
LHO 4k                 1      2      2kHz          1          4kB/s
LHO 2k                 1      2      2kHz      10001          4kB/s
LLO 4k                 1      2      2kHz      30001          4kB/s
 
 

Control Signals
 various               12      2     2kHz        -           48kB/s
 
 

Max, Min, Mean,RMS
(all 1200 channels)  1200      8      1Hz        all        9.6kB/s
 

   PEM

Power Line Monitor
LHO                     1       2   0.5kHz        -           1kB/s
LLO                     1       2   0.5kHZ        -
 

LHO seismometers       15       2   0.25kHz     20000-      7.5kB/s
                                                20014

LLO seismometers        9       2   0.25kHz     40000       4.5kB/s
(9)                                             40008
 

LHO accelerometers      9       2     2kHz      20025...     36kB/s
(9  see note a)

LLO accelerometers      5       2     2kHz      40025...     20kB/s
(5  see note a)
 

Coarse FFTS:

LHO accelerometers     99       8      1Hz      20025      0.79kB/s
(see note b)                                    20123
 

LLO accelerometers     48       8      1Hz      40025      0.38kB/s
(see note b)                                    40072
 
 

LHO Microphones         5       2     2kHz      20124...    20kB/s
(see note c)

LLO Microphones         3       2     2kHz      40124...    12kB/s
(see note c)
 

LHO magnetometer        1       2     2kHZ      20171       4kB/s
(see note d)

LLO magnetometer        1       2     2kHZ      40171       4kB/s
(see note d)
 

total                                                      200kB/s
 

Notes:  (a) The stored signal will be the sum in quadrature for each
            of the x,y and z signals of a given accelerometer. At
            Hanford we keep 9 accelerometers, corresponding to
            the four test masses for each interferometer and
            the beam splitter.  At Livingston 5 accelerometers are
            kept. Eventually we may want to weight the x, y, and z
            signals according to the sensitivity of the interferometers
            to accelerations in different directions.

       (b)  For all accelerometers the power spectra in
            four bins of frequency is stored.

       (c)  One microphone readout should be kept for
            each building.

       (d)  Quadrature sum.