RabbitCore eDisplay OP7200, Руководство пользователя

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User’s Manual 29
To get the best results form the A/D converter, it is necessary to calibrate each mode for
each of its gains. The following table provides a grid for each possible set of calibration
constants.
For the single-ended mode there are calibration constants for each channel and for each of
its gains, for a total of 64 sets of calibration constants. The milli-amp mode covers 4–20 mA
(actually 0–25 mA) currents. Separate calibration and read-back routines are provided for
this. Since only one range of current measurement is provided, these routines use only one
gain (4). One set of calibration constants is provided for each of the eight input channels.
The differential-mode routines use a pair of input channels to make measurements. In this
case, calibration constants are stored for each pair of channels and for each of the eight
gains, for a total of 32 sets of calibration constants.
When a calibration is performed, it fills in one of the squares in the table with a set of cal-
ibration constants representing the corresponding mode, channel, and gain. These con-
stants are stored in flash memory, and are thus maintained even when power is been
removed from the OP7200. Note that calibration constants are stored for each of the
modes. Since A/D converter read routines select the appropriate calibration constants based
on the mode, it is possible for software calls to move from one mode to another without
recalibration.
3.4.3.3 Calibration Recommendations
It is imperative that you calibrate each of the A/D converter inputs in the same manner as
they are to be used in the application. For example, if you will be performing floating dif-
ferential measurements or differential measurements using a common analog ground, then
calibrate the A/D converter in the corresponding manner. The calibration must be done
with the attenuator reference selection jumper in the desired position (see Figure 11). If a
Mode
Single-Ended mA Differential
Gain
Code
1 2 4 5 8 10 16 20 4 1 2 4 5 8 10 16 20
Inpu
t
0
1
2
3
4
5
6
7