INTEROFFICE MEMORANDUM                      JET PROPULSION LABORATORY

TO:        Dave Gruel                                S & I DFM 97-001
FROM:      Tim Schofield                              25th March 1997
SUBJECT:   ASI/MET Accelerometer - Data Conversion Expressions.
REFERENCE: (1). AIP data conversion expressions - Revision B, S & I
           DFM 96-014,   18th December 1996. From: Tim Schofield To:
           Distribution

This memo gives calibration expressions for the six ASI/MET science
and engineering accelerometers, based on the laboratory calibration
work of 2/96 and measurements taken in flight during spacecraft spin
down of 12/12/96.

A linear, temperature-dependent conversion from counts to acceleration
is used for each accelerometer head and gain setting, so that:

    Acceleration in g's = (Counts - A(T)) / B(T)

where: A(T) = A0 + A1T is the accelerometer bias in counts,
       B(T) = B0 + B1T is the accelerometer scale factor in counts/g,
       T is head temperature in centigrade,
       Counts lie in the range -8192 to +8191 (If counts > 8191,
               counts = counts -214).
       1 g = 9.795433 m.s-2,

The table below gives A0, A1, B0, and B1 for each head and gain
setting. The temperature sensor channel identifications associated
with each head are also given. Temperature sensor conversions are
given in reference (1).

Head                     Sx      Sy       Sz        Ex       E+yz      E-yz

Accelerometer Channel  W-2001  W-2002   W-2003    L-2001    L-2002    L-2003

Temperature Sensor     W-4001  W-4002   W-4003    L-4050    L-4051    L-4052

40  A0 Counts          2.75    -0.97     0.83      1.35     -0.02     -0.66
g   A1 Counts/degC    -0.023   -0.003   -0.003    -0.005    -0.000    -0.001
Range
    B0 Counts/g     -184.118  -185.581 -183.928  -182.776  -183.450  -183.924
    B1 Counts/g/degC  -0.028  -0.025    -0.030    -0.032    -0.032    -0.029

800 A0 Counts         -4.17    8.40     1.58      12.33     -4.93     -6.67
mg  A1 Counts/degC    -0.012   -0.011   -0.003     0.024     0.043     0.019
Range
    B0 Counts/g     -9008.76  -9031.40 -8978.62  -8938.97  -8933.65  -8976.08
    B1 Counts/g/degC  -0.805  -0.731    -0.822    -0.798    -0.697    -0.729

16  A0 Counts       -313.76   408.90     51.90    562.73    -336.07  -287.37
mg  A1 Counts/degC  -0.284    -0.512     0.095    -0.854     1.336     0.401
Range
    B0 Counts/g    -445743.0 -446319.0 -444297.0 -442228.0 -441730.0 -444094.0
    B1 Counts/g/degC   -34.0   -33.0     -37.0     -35.0     -38.0     -26.0

Notes on the Calibration Table.

 (1). Only A0 on the 16 mg range has been corrected for offset
      measurements in space, performed at temperatures in the
      11-12degC range. The combined effect of temperature differences
      and offset changes for the other gain settings was generally one
      count or less.

 (2). A(T) is represented quite poorly by a linear expression for the
      16 mg range. Errors can be as high as 2 or 3 counts. Offsets
      will therefore be most accurate at 11-12degC and will diverge
      slightly at other temperatures. For the other gain settings,
      errors are 1 count or less.

 (3). So far, 16 mg offsets have remained fairly stable in space. It
      is likely however that further small adjustments will have to be
      made.