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FX Series Programmable Controllers Devices in Detail 4
4-46
4.15 Floating Point And Scientific Notation
PLC’s can use man
y
different s
y
stems and methods to store data.
The most common have alread
y
been discussed in previous sections e.
g
. BCD, Binar
y
,
Decimal, Hex. These are what is known as ‘inte
g
er’ formats or ‘whole number formats’.
As the titles su
gg
est these formats use onl
y
whole numbers with no representation of fractional
parts. However, there are two further formats which are becomin
g
increasin
g
l
y
important and
the
y
are:
a) Floatin
g
point and
b) Scientific notation
Both of these formats are in fact closel
y
related. The
y
both lend themselves to creatin
g
ver
y
lar
g
e or ver
y
small numbers which can describe both whole and fractional components.
General note:
• Sometimes the words ‘Format’, ‘Mode’ and ‘Notation’ are interchan
g
ed when descrip-
tions of these numerical processes are made. However, all of these words are providin
g
the same descriptive value and as such users should be aware of their existence.
Some useful constants
π
3.141 10
0
2
π
6.283 10
0
π
/4 7.853 10
-1
π
2
9.869 10
0
The speed of li
g
ht 2.997 10
8
m/s
Gravit
y
,
g
9.807 10
0
m/s
2
e 2.718 10
0
Fixed points:
Boilin
g
point of liquid ox
yg
en -1.8297 10
2
°
C
Meltin
g
point of ice 0.00 10
0
°
C
Triple point of water 1.00 10
-2
°
C
Boilin
g
point of water 1.00 10
2
°
C