Calculation basis
ADwin
220
ADwin-Pro II
Hardware, manual Dec. 2018
6.2 Calculation basis
Voltage range
The standard voltage range of the analog inputs/outputs of the
ADwin
systems
is -10V … +10V (bipolar 20 Volt).
Allocating digits to
voltage
The 65536 (2
16
) digits are allocated to the corresponding voltage ranges of the
ADC and DAC in such a manner that the value for
– 0 (zero) digits corresponds to the maximum negative voltage.
– 65535 digits correspond to the maximum positive voltage.
The value for 65536 digits, exactly 10 Volt, is therefore just beyond the mea-
surement range, therefore you get for the 16-bit AD or DA conversion a max-
imum voltage value of 9.999695 Volt, and for the 18-bit AD conversion a value
of 9.999923706 Volt.
Zero offset
In bipolar settings, this results in a zero offset, called offset in the following text.
The offset has the value V
OFF
=-10V.
Least Significant bit
V
LSB
The value V
LSB
defines the voltage, which corresponds to the least significant
bit. The value in the standard setting is
– with 18-bit converters: 20V ./. 2
18
= 76.294µV
– with 16-bit converters: 20V ./. 2
16
= 305.175µV
– with 14-bit converters: 20V ./. 2
14
= 1220.7µV
Gain k
V
When using Pro-AIn modules with programmable gain arrays (PGA), you can
amplify the input voltage by factors 2, 4 and 8. Thus, the measurement range
gets smaller by the corresponding gain factor k
V
.
Please pay attention to the fact that also the interference signals are amplified
when using applications with k
V
> 1. These can be reduced by programming
digital filters in
ADbasic
.
Allocating the bits
In order to get the same allocation of bits during measurements with 14-bit
ADC as with a 16-bit ADC, the converted value is presented left-aligned in the
lower word (16 bit) with the 14-bit ADC. The least 2 significant bits are always
0.
The 16384 digits of a 14-bit ADC are mapped to the 65535 digits of a 16 bit
ADC. Therefore, 4 digits of the 16-bit ADC correspond to one digit of the 14 bit
ADC.
DAC
For DAC use the formula:
Bit no. 31…2
4
23…1
6
15…6
5…2
1…0
con-
tent
0
18-bit value in bits 6…23
0
0
0
0
16-bit value in bits 0…15
0
0
14-bit value in bits 2…15
0
upper word
lower word
Fig. 176 – Bit allocation with different resolutions
UOUT Digits ULSB UOFF
+
⋅
=
Digits
UOUT U
–
OFF
ULSB
-------------------------------------------
=
