READ_HEX  Reads SBE-Ascii-DataFiles with hexadecimal Values (HEX)

 [ Msg , Head , Data , Init ] = READ_HEX( FileName )

 Adjusted for SeaCat-SBE16plus-DataFiles, verify the Subfunctions
  which are listen below with the CalibrationSheets for correct formulas.
 
 Head =  HeaderStructure from READ_SBE

 Data = [ Day  T  C  P  S  [V0]  [V1]  [V2]  [V3]  [SBE38T] ]

 INIT = { VarID  Unit  Tag  Format }

            Variable           Unit    SubFunc    Coefficients from HEX-File

 Day        Matlab DATENUM    [day]    hex2time
 T          Temperature       [degC]   hex2temp   TA0, TA1, TA2, TA3
 C          Conductivity      [mS/cm]  hex2cond   G, H, I, J, CTCOR, CPCOR
 P          Pressure                   hex2pres   !!! not complete yet !!!
                                       hex2qres   !!! not complete yet !!!
 V0 .. V3   ExternalVoltages  [mV]     hex2volt   

 SBE38T     SBE38-Temperature [degC]   hex2sbe38  ???
 
 To convert the external voltages of additional Sensors, 
  add/edit the following Coefficients to the HEX-File before !!!

 Seapoint   Chl_a             [ug/l]   hex2chla   GAIN, SENS
 SBE43      Oxygen      [%] | [ml/l]   hex2oxyg   SOC, BOC, VOFFSET, TCOR, PCOR


 Use additional String-Inputs to specify the external Sensors 
  and their Order in the DataFile:

 READ_HEX( FileName , EXT1 , EXT2 , ... )

   SBE43:    'O' | 'X' | 'Oxygen'                   (PREF required, see below)
   Seapoint: 'F' | 'C' | 'Fluorometer | 'Chlorphyll'

 For not specified additional Sensors the Voltage [mV] of the Channel is returned.
 See also: READ_SBE, SBE_COND

 Valid Limits for the Data can be given by a Structure as last Input:

 READ_HEX( FileName , ... , LIM )

 Fields of Structure LIM:

    pres: [Pmin Pmax]  dbar
    temp: [Tmin Tmax]  degC
    cond: [Cmin Cmax]  mS/sm
    salt: [Smin Smax]  PSU
    chla: [Fmin Fmax]  ug/l  Seapoint Fluorecense
    oxyg: [Omin Omax]  %     Percent of OxygenSaturation

 Values outside this Limits are set to NaN.
 Check the begin of this M-File for the default Limits!!!

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 Compressibility Compensation of Sea-Bird Conductivity Sensors

 For Instruments without a build-in pressure sensor you can set
  the reference pressure for the compressibility compensation of
  the conductivity sensor:  READ_HEX( FileName , PREF , ... )

 By default the setup reference pressure from the header or ZERO is used.

 To correct the conductivity by a known pressure use the formula:

 C = C * ( 1 + CTCOR * T + CPCOR  * PREF ) / ( 1 + CTCOR * T + CPCOR  * P )

 defaults:  CTCOR = 3.25e-06;  CPCOR = -9.57e-08

 Reference:

 Seabird Electonics Application Note 10,
 "Compressibility Compensation of Sea-Bird Conductivity Sensors",
 http://www.seabird.com/application_notes/AN10.htm

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 A NONZERO IMAGinary part of PREF plots the TimeSeries!!!

 [ Msg , Header , Data , HeadINI , FIG ] = READ_HEX( FileName , PREF+i , ... )

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 Structure of HEX-DataLine (SeaCat SBE 16plus):

 tttttt    6  Temperature A/D-counts
 cccccc    6  CondFreq          = val / 256

 vvvv      4  PressTempCompVolt = val / 13.107  % PressureType 1 (StrainGauge)

 pppppp    6  PressFreq         = val / 256     % PressureType 3 (Quartz)
 vvvv      4  PressTempCompVolt = val / 13.107  % PressureType 3 (Quartz)

 vvvv      4  Ext0Volt          = val / 13.107  % [mV]
 vvvv      4  Ext1Volt          = val / 13.107
 vvvv      4  Ext2Volt          = val / 13.107
 vvvv      4  Ext3Volt          = val / 13.107

 tttttt    6  SBE38Temp         = val / 100 - 10

 ssssssss  8  seconds since 01.01.1980

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