BODC HEADED DOCUMENT NO.  34098                         
 Applies to BODC Series Ref. Nos.:   41066,  41091,  41110,  41134,  41158,     
                     41171,  41214,  41238,  41343,  41447,  41539              
    I.O.S. Off-Shore Pressure Recorder Mark III                                 
    The main part of the capsule is a forged aluminium sphere of 0.66m internal 
    diameter,  which  contains  the  data  logging system, acoustic command and 
    release units and all battery supplies.  Each half of the sphere is  bolted 
    to  a  central equatorial ring, a seal being provided by O rings. There are 
    twelve  outlets  through  this  ring  for  Marsh  Marine  type   electrical 
    connectors. The sphere is housed in a free flooding tubular aluminium alloy 
    frame. Also mounted on  this  frame  are  2  pressure  transducers,  a  sea 
    temperature   unit,   2  subsidary  platinum  resistance  thermometers  for 
    measuring sea temperature and 2 wound nickel scrolls that act  as  acoustic 
    pinger  beacons.  The  frame  and sphere, complete with attachments, have a 
    positive buoyancy, and in order to anchor them, they are mounted on a steel 
    tripod.  The tripod is attached to the main frame by a central pyro-release 
    The system incorporates a commercial data logger modified to operate in the 
    deep  sea  capsule.  The  logger  will  accept input from a total of twelve 
    separate sources or channels. The temperature  and  pressure  sensors  have 
    variable  frequency  outputs. The frequencies are counted over a 890 second 
    period and the total count for each channel is then recorded during a  scan 
    of  all  channels which lasts for 10 seconds.  Thus the averaged integrated 
    pressure and temperature values are logged every 15 minutes. Temperature is 
    measured  to  correct  for  the  temperature  coefficient  of  the pressure