15.1 Overview

The Helios AV model data acquisition circuit uses a 16-bit A/D converter. The full range of numerical values for a 16-bit number is 0 - 65535. However, the A/D converter uses two’s complement notation, so the A/D value is communicated as a signed integer, ranging from -32768 to +32767. Regardless of whether the A/D is configured for unipolar or bipolar input ranges, the value -32768 always refers to the bottom of the input range, and the value 32767 always refers to the top. 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 resolution is always 16 bits, but the value of 1 LSB will vary with the input range.