Datasheet
m=
w
fs
c-c
fs zs
Weigh Scale Mode
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2.1 Display
Weigh scale mode can display mass in these units: μg (displayed as ug), g, kg, pounds (lb), stone (st),
and ounces (oz).
(2)
Internally, mass is measured in grams, and calibration factors are stored in grams. At display time, grams
are converted to the desired display unit using the conversion factors given in Table 1.
xxx
(2)
The avoirdupois units used by the ADS1x31REF are equal in the imperial and U. S. customary systems.
Table 1. Unit Conversion Factors and Display Formats
Unit Multiplier Format
micrograms (μg) 10
6
nnn.nnnug
milligrams (mg) 1000 nnn.nnnmg
grams (g) 1 nnn.nnng
kilograms (kg) 10
–3
nnn.nnnkg
ounces (oz) 0.035274 nnn.nnnoz
pounds (lb) 0.0022046 nnn.nnnlb
stone (st) 157.473 × 10
−6
nnstnn.nn
The display format for stone differs from the format used for the other units. One stone is equal to fourteen
pounds; weight in stone is commonly expressed as a number of stone followed by a number of pounds.
On the ADS1x31REF, two digits are shown for stone, followed by st, followed by pounds displayed to two
decimal places.
2.1.1 Calculation of Mass
Mass is calculated from ADC code using the formula:
w = m ● c + w
zs
– w
t
where:
• w = mass
• c = the ADC code
• w
t
= tare weight
• m, w
zs
, w
t
= values determined in the calibration process
m is a calibration constant, and is calculated using Equation 1:
(1)
where w
fs
is the user-specified calibration mass, c
fs
is the ADC code taken with the calibration mass
applied, and c
zs
is the ADC measurement taken with no load.
w
zs
, the zero-scale mass, is calculated from m and c
zs
using Equation 2:
w
zs
= –m ● c
zs
(2)
2.2 Button Functions
2.2.1 TARE
The tare function allows the mass of a substance to be measured separately from the mass of its
container. When the TARE button is pressed, the scale measures the mass and records it. This reading is
subtracted from each subsequent measurement.
The recorded tare value can be reset to zero by holding the TARE button down for at least one second.
When the tare value is to be reset, the display reads TARE OFF.
Tare is also reset following a calibration.
8
ADS1131REF and ADS1231REF SBAU175A–July 2010–Revised August 2011
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