UniData Communication Systems Starlog Prologger 7001, User Manual

Page: 55 / 73

9.4 PROLOGGER Linear Calibration Correction
The PROLOGGER uses the following linear correction formula:-
y = gx + o
Where: y = corrected value.
x = raw value (from A/D converter).
g = gain coefficient.
o = offset coefficient.
The gain coefficient (g) is made up of the gain coefficients from the
appropriate Gain Drive Table gain stage entry. The same applies to the offset
coefficient (o).
These coefficients represent decimal numbers (e.g. 0.15) which are stored in
the PROLOGGER in a normalised 16 bit form.
n
GAIN
The decimal gain coefficient is multiplied by 8192 to form the PROLOGGER
gain coefficient entry. That is, each bit is 1/8192 or 1.2207E-4.
g = 0.00610
g
= 0.00610 * 8192 = 50 (or 32 HEX)
Gain coefficients must be POSITIVE.
n
OFFSET
The decimal offset coefficient is multiplied by 8 to form the PROLOGGER
offset coefficient entry
in bits
. This offset must take into account the 16 bit
A/D conversion as each offset bit has a magnitude of 1/64516 of the input
signal range (155
µ
V/bit in the -5V to 5V range).
For example:
Gain stage = 1, input range -5 to 5V
each bit = 10,000,000/64516 = 155mV
therefore, if O (offset)= 1.55mV on a gain of 1
= 1.55/0.155 x 8 = 80 (50 HEX)
Offset coeffiecients may be POSITIVE or NEGATIVE.
PROLOGGER Hardware
PROLOGGER CONFIGURATION TABLE 49