14.7 Convert the numerical data to a meaningful value

Once you have the A/D value, you need to convert it to a meaningful value. The first step is to convert it back to the actual measured voltage. Afterwards you may need to convert the voltage to some other engineering units (for example, the voltage may come from a temperature sensor, and then you would need to convert the voltage to the corresponding temperature according to the temperature sensor’s characteristics).

Since there are a large number of possible input devices, this secondary step is not included here; only conversion to input voltage is described. However you can combine both transformations into a single formula if desired.

To convert the A/D value to the corresponding input voltage, use the following formulas:

Conversion Formula for Bipolar Input Ranges

Input voltage = A/D value / 32768 * Full-scale input range

Example: Input range is ±5V and A/D value is 17761:

Input voltage = 17761 / 32768 * 5V = 2.710V

For a bipolar input range, 1 LSB = 1/32768 * Full-scale voltage.

Here is an illustration of the relationship between A/D code and input voltage for a bipolar input range (VFS = Full scale input voltage):

A/D Code

Input voltage symbolic formula

Input voltage for ±5V range

-32768

-VFS

-5.0000V

-32767

-VFS+ 1 LSB

-4.9998V

-1

-1 LSB

-0.00015V

0

0

0.0000V

1

+1 LSB

0.00015V

32767

VFS - 1 LSB

4.9998V

Conversion Formula for Unipolar Input Ranges

Input voltage = (A/D value + 32768) / 65536 * Full-scale input range

Example: Input range is 0-5V and A/D value is 17761:

Input voltage = (17761 + 32768) / 65536 * 5V = 3.855V

For a unipolar input range, 1 LSB = 1/65536 * Full-scale voltage.

Here is an illustration of the relationship between A/D code and input voltage for a unipolar input range (VFS = Full scale input voltage):

A/D Code

Input voltage symbolic formula

Input voltage for 0-5V range

-32768

0V

0.0000V

-32767

1 LSB (VFS / 65536)

0.000076V

-1

VFS / 2 - 1 LSB

2.4999V

0

VFS / 2

2.5000V

1

VFS / 2 + 1 LSB

2.5001V

32767

VFS - 1 LSB

4.9999V

Prometheus CPU User Manual V1.44

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Diamond Systems PR-Z32-EA-ST, PR-Z32-E-ST user manual Input voltage = A/D value / 32768 * Full-scale input range

PR-Z32-E-ST, PR-Z32-EA-ST specifications

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