Unit Conversion Factors And Display Formats - Texas Instruments ADS1232REF User Manual

Weigh Scale Mode
2.1 Display
Weigh scale mode can display mass in these uints: μg (displayed as ug), g, kg, pounds (lb), stone (st),
and ounces (oz).
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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
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The avoirdupois units used by the ADS1232REF are equal in the imperial and U. S. customary systems.
micrograms (μg)
milligrams (mg)
grams (g)
kilograms (kg)
ounces (oz)
pounds (lb)
stone (st)
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 ADS1232REF, 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
where:
• w = mass
• c = the ADC code
• w = tare weight
t
• m, w , w = values determined in the calibration process
zs t
m is a calibration constant, and is calculated using
w
fs
m =
c c
fs - zs
where w is the user-specified calibration mass, c
fs
applied, and c is the ADC measurement taken with no load.
zs
w , the zero-scale mass, is calculated from m and c
zs
w = –m ● c
zs zs
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 is also reset following a calibration.
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ADS1232REF User's Guide
Table 1. Unit Conversion Factors and Display Formats
UNIT
157.473 × 10
– w
t
Copyright © 2005–2011, Texas Instruments Incorporated
MULTIPLIER
6
10
1000
1
–3
10
0.035274
0.0022046
−6
Equation 1:
is the ADC code taken with the calibration mass
fs
using Equation
zs
.
TARE OFF
SBAU120B – November 2005 – Revised July 2011
Table 1.
FORMAT
nnn.nnnug
nnn.nnnmg
nnn.nnng
nnn.nnnkg
nnn.nnnoz
nnn.nnnlb
nnstnn.nn
2:
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