Hercules III User Manual Rev A.2
www.diamondsystems.com
Page
66
13. ANALOG-TO-DIGITAL INPUT RANGES AND RESOLUTION
13.1
Overview
Hercules III uses a 16-bit A/D converter. The full range of numerical values for a 16-bit number is 0 - 65535.
Howeve
r, the A/D converter uses two’s complement notation, so the A/D value is interpreted as a signed integer,
ranging from
–32768 to +32767.
The smallest change in input voltage that can be detected is 1/(216), or 1/65536, of the full-scale input range.
This smallest change results in an increase or decrease of 1 in the A/D code, and is referred to as 1 LSB (1 Least
Significant Bit).
The analog inputs on Hercules III have three configuration options.
•
Single-ended or differential mode
•
Unipolar or bipolar mode
•
Input range (gain)
The single-ended/differential and unipolar/bipolar modes are configured using software.
13.1.1
Input Range Selection
You can select a gain setting for the inputs, which causes them to be amplified before they reach the A/D
converter. The gain setting is controlled in software, which allows it to be changed on a channel-by-channel
basis. In general, you should select the highest gain (smallest input range) that allows the A/D converter to read
the full range of voltages over which the input signals will vary. However, a gain that is too high causes the A/D
converter to clip at either the high end or low end, and you will not be able to read the full range of voltages on
your input signals.
13.1.2
Input Range Table
The table below indicates the analog input range for each possible configuration. The gain is set with the G1 and
G0 bits in the register at Base+3. The Gain value in the table is provided for clarity. Note that the single-ended
vs. differential setting has no impact on the input range or the resolution.
Polarity
G1
G0
Input Range
Resolution 1LSB
Bipolar
0
0
±10V
305µV
Bipolar
0
1
±5V
153µV
Bipolar
1
0
±2.5V
76µV
Bipolar
1
1
±1.25V
38µV
Unipolar
0
0
Invalid
Invalid
Unipolar
0
1
0 - 10V
153µV
Unipolar
1
0
0 - 5V
76µV
Unipolar
1
1
0 - 2.5V
38µV