17-2000 C
2020-09-17
10(50)
ADQ8-8C Manual
17-2000 C 2020-09-17
10(50)
ACTUAL_ANALOG_RANGE
is the actual calibrated range of the device returned
from
SetInputRange
.
The maximum digital code 2^15 represents an analog signal with a level
ACTUAL_ANALOG_RANGE / 2
at the input. A specific analog signal
ANALOG_LEVEL
will then be represented by the following digital
code:
DIGITAL_CODE_LEVEL = ANALOG_LEVEL / ( ACTUAL_ANALOG_RANGE / 2 ) * 2^15
(3)
A specific code
DIGITAL_CODE_LEVEL
then represent the analog level as:
ANALOG_LEVEL = ( DIGITAL_CODE_LEVEL / 2^15 ) * ( ACTUAL_ANALOG_RANGE / 2)
(4)
2.4 Set analog DC-offset
A user-controlled DC-offset is available. The analog DC-offset is applied to the signal to better adopt to
the signal range of the digitizer. The analog range is by default set symmetrical around zero. If the sig-
nal is unipolar or heavily unsymmetrical, the DC-offset function can adjust the signal to an optimal verti-
cal position for the A/D converter. In this way, the full 10 bits can be used for representing the unipolar
pulse. The DC-offset is set with the command
SetAdjustableBias
.
The DC-offset is set in digital codes
DC_OFFSET_CODE
in the range [-2^15: 2^15-1], which correspond
to an analog signal level in the range:
[ –ACTUAL_ANALOG_RANGE / 2: ACTUAL_ANALOG_RANGE / 2 ].
(5)
To determine the parameter of
SetAdjustableBias
to get a DC-offset at the voltage level
DC_OFF-
SET_ANALOG
, use:
DC_OFFSET_CODE = round ( DC_OFFSET_ANALOG / ( ACTUAL_ANALOG_RANGE / 2 ) * 2^15 )
(6)
Since the digitizer has higher resolution than the intrinsic accuracy of the DC-offset generator, the
actual digital codes read out from the ADQ may differ from the expected level. For accurate baseline
measurements, the Digital Baseline Stabilizer (DBS) offers a digital correction of the baseline to an
accuracy of 22 bits,
2.5 Adjusting the digital gain and offset
The digital gain and offset block is primarily intended for factory calibration but it may also be accessed
by the user, and offers an efficient way of scaling the signal to suit processing in the PC.
The default setting is the calibration parameters
CAL_GAIN
and
CAL_OFFSET
. The raw data from the A/
D converter,
ADC_RAW_CODE
, is corrected with the calibrated values according to:
DIGITAL_OUTPUT_CODE = ADC_RAW_CODE * CAL_GAIN – CAL_OFFSET
(7)
The user can override these settings by using the software command
SetGainAndOffset
. The parameter
USER_GAIN
and
USER_OFFSET
can be applied in two ways; relative to the calibrated value or relative
to the raw code.
The normal mode of operation is to apply the gain and offset settings relative to the calibrated data as
DIGITAL_OUTPUT_CODE =
ADC_RAW_CODE * CAL_GAIN * USER_GAIN – CAL_OFFSET – USER_OFFSET.
(8)
By setting bit 7 in the channels parameter, the calibration data is overridden as:
DIGITAL_OUTPUT_CODE = ADC_RAW_CODE * USER_GAIN – USER_OFFSET
(9)
To get the raw code,
ADC_RAW_CODE
, use
SetGainAndOffset(128+CHANNEL,1024,0)
.
