Voltage Display Ranges - Texas Instruments ADS1230REF User Manual

Analysis Mode
The voltage display is autoranging. All ranges are shown with six significant figures having three decimal
places. The ranges are given in
RMS noise: In this mode, a number of codes are read from the ADS1230, and an RMS noise calculation
is performed on them using the standard-deviation formula (given in
N
1
s =
(x x
N
å
N -
i
i =1
The result can be displayed as decimal codes, volts, or an effective number of bits (ENOB). For decimal
codes, s is displayed directly. (Hexadecimal is not available because s
N
is converted to a voltage as in raw mode.
ENOB: E is calculated using
24 log s :
-
2 N
E =
24 : s
The zero case is needed when a string of equal codes is read. This can happen when the converter is
clipping.
This measurement requires a number of codes to be read before a calculation can be made. Therefore,
during the first run, the display shows the word GOT followed by the number of samples collected. This
event happens when the mode is first entered, when the converter configuration changes, or when NEW
BLOCK is pressed.
The number of codes used in the calculation is selected in Configuration mode; 50 codes are used in
laboratory characterization, so this value is the default.
Peak-to-peak noise: In this mode, a number of codes are collected, and the absolute value of the
difference between the minimum and maximum is calculated. The result can be displayed in decimal or
hexadecimal codes, volts, or noise-free bits (ENOB). Volts are calculated as in raw mode; ENOB is
calculated in the same way as in RMS mode.
The number of codes used in the calculation is selectable in Configuration mode.
Averaged: In this mode, a number of codes are collected, and the average is calculated. The result can
be displayed in decimal codes or volts. (Hexadecimal is not available because the result may be
fractional.) Volts are calculated as in raw mode.
The number of codes used in the calculation is selectable in Configuration mode.
3.3 Progress Graph
The row of apostrophes at the top of the display are used to indicate measurement progress. In Raw
mode, the apostrophe moves across the display when data is being received from the converter. The
apostrophe moves once for every eight samples collected from the ADC.
In block collection modes, the apostrophes form a bar graph. As the collection of a block proceeds, the
bar graph increases. When the bar graph reaches all the way to the right, the new result is generated and
collection restarts.
12 ADS1230REF User's Guide
Table 4.
Table 4. Voltage Display Ranges
Nanovolts
Microvolts
Millivolts
Volts
2
)
Equation 5:
s 0
¹
N
0
=
N
VOLTAGE RANGE DISPLAY SUFFIX
< 1μV
< 1mV
< 1V
≥ 1V
Equation
SBAU125A – August 2007 – Revised September 2007
www.ti.com
n
u
m
V
4):
may be fractional.) For volts, s
N
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(4)
N
(5)