Rabbit OP7100 User Manual download pdf (Page 36)

30 eDisplay (OP7200)

calibration is performed and the jumper is subsequently moved, the corresponding input(s)

must be recalibrated. The calibration table only holds calibration constants based on

mode, channel, and gain. Other factors affecting the calibration must be taken into

account by calibrating using the same mode and gain setup as in the intended use.

It is not necessary to fill out the entire calibration table. Only the entries associated with

the modes, channels, and gains that you will be using are necessary. This fact can be used

to simplify and speed up the calibration process.

Each calibration is normally done at 10% less than the maximum and 10% more than the

minimum within a given voltage range defined by the mode, channel, and gain. However,

if an application is known to use only portion of a particular range, it is possible to obtain

improved accuracy by using calibration points that are 10% less than the expected maxi-

mum and 10% greater than the expected minimum.

3.4.3.4 Factory Calibration

Because of the large number of possible calibrations, the factory performs only a rudimen-

tary calibration on the unit. By default, all four of the attenuator reference selection jump-

ers are in the analog ground position. The factory performs a single-ended calibration on

each of the eight channels with a gain of 1 (0–20 V range). The remaining single-ended

calibration constants for the other seven gains are approximated and are filled in based on

the initial calibration. The milli-amp and differential portions of the table are filled in

using typical expected values. All read routines will work properly with these factory-ini-

tialized calibration constants, but only the single-ended mode should be expected to return

accurate results over a range of 0–20 V until you recalibrate the OP7200 for your use.

Sample programs are provided to illustrate how to read and calibrate the various A/D

inputs for the three operating modes.

These sample programs are found in the ADC subdirectory in SAMPLES\OP7200. See

Section 4.3, “Sample Programs,” for more information on these sample programs and how

to use them.

Mode Read Calibrate

Single-Ended, one channel

ADRD_SE_CH.C ADCAL_SE_CH.C

Single-Ended, all channels

ADRD_SE_ALL.C ADCAL_SE_ALL.C

Milli-Amp

ADRD_MA_CH.C ADCAL_MA_CH.C

Differential, analog ground

ADRD_DIFF_GND.C ADCAL_DIFF_GND.C

Differential, 2 V reference

ADRD_DIFF_2V.C ADCAL_DIFF_2V.C

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Rabbit OP7100 User Manual Page 36