Analog Inputs and Outputs
ADwin
12
ADwin-Gold II
, Manual February 2013
18-bit measurements
Signals at the multiplexer outputs are converted with a 18-bit analog-to-digital-converter
(ADC), see Fig. 2 "
". The 18-bit ADC works fast (max. 2µs)
and very accurately (resolution 76µV).
There are two methods to convert measurement values, which are used alternatively:
–
single conversion: The conversion is started at a defined time and the value is
returned after the appropriate delay. The value can have a resolution of 16 bit or
18 bit.
–
continuous conversion: A sequential control continuously converts 16 bit values.
You can read the current value without waiting, but the exact time of conversion
is unknown.
Single conversion
The instruction
ADC
executes a complete measurement with one of the ADCs on the
analog input (see
) and returns a 16 bit value. The instruction considers for
instance the settling of the multiplexer and assures perfect measurements.
Measurement values with 18 bit resolution are available with the instruction
ADC24
(see
); the values are returned with 24 bit format (see
).
Both instructions run with the 18-bit ADC, only return values have different resolution.
Continuous conversion
with sequential control
ADwin-Gold II
provides a sequential control for each ADC, which can consecutively
read measurement values of several or all input channels of an ADC. Thus, the proces-
sor can be discharged a lot and only has to read completely converted values from the
sequential control’s buffer. The sequential controls work independently from each other.
Programming
Instructions to program analog inputs are described starting from
. The instruc-
tions are defined in the include file
<ADwinGoldII.inc>
and are described in the
online help, too.
Please pay attention to a low output resistance of the signal source (of the input sig-
nals), because it may have influence on the measuring accuracy. If this is not possible:
–
Depending on the output resistance a linear error is caused (about 1 digit per
10
Ω
).
You can compensate this by multiplying the measurement value with a corre-
sponding factor and get a sort of re-calibration.
–
From approx. 3k
Ω
upwards the multiplexer settling time extends.
The waiting time defined in the standard instruction
ADC
is then too short, so that
imprecise values are recalled. In this case please use the instructions described
in
Function
Instructions
do a complete measurement
ADC
,
ADC24
Do a measurement in steps
(see
SET_MUX1
,
SET_MUX2
Start_Conv
,
Wait_EOC
READ_ADC
initialize and start sequential control
SEQ_MODE
SEQ_SELECT
SEQ_SET_DELAY
SEQ_SET_GAIN
SEQ_START
Read data from sequential control
SEQ_READ
SEQ_STATUS
