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  This is a
  simplified block diagram of a single channel. 
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  The DSOS is an
  open loop system - send out a command and let it go to where it has to go. 
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  It is one of the
  only systems that adjusts the primary during observations.  Most radio telescopes are
  mechanically tuned to one zenith angle only. 
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  Starting on the
  left is the standoff assembly which consists of a mounting bracket, embedded
  thermistor, thermal electric cooler (TEC), and heat exchanger. 
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  DSOS computer
  gets the present ZA from the antenna computer, then gets the offset values
  for all 99 standoffs for the given ZA. 
  The D/As send out the desired voltage to the driver amps that drive
  the thermal electric coolers mounted to the standoffs.  The A/Ds monitor what the temperature
  is, in Volts.  As the difference
  between the desired setting and thermistor reading decreases, so does the
  drive level to the thermal electric coolers.  When the offset is close to 0 Volts, the standoff has
  acquired it's desired length change. 
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  ~Melanie Leong~ 
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