User guide

5
2.3 Units of measure
CPR
Cycles per
Revolution
Denes the number of
electrical cycles that an
encoder provides in a
single revolution.
CPR = 2π x LPmm x Rop
LPI Lines per Inch
Denes the number of
window-bar pairs in a
length of 1inch
LPmm Lines per mm
Denes the number of
window-bar pairs in a
length of 1mm. Note that
LPmm=LPI/25.4
Rop Optical Radius
The distance from the
center of the codewheel
to the middle of the data
track
°e Electrical Degree
Denes the electrical
angle of an encoder
signal. 1 cycle is equal to
360 °e
°
Mechanical
Degree
Mechanical angle. One
revolution is equal to 360°
’ Arc Minute Mechanical angle. 1° = 60’
” Arc Second
Mechanical angle. 1° = 60’
= 3600”
Bit Binary Digit
Denes the smallest
resolution, usually used
for absolute encoder
Rev. Revolution
Dene the full complete
rotation of a shaft or
codewheel. 1 Revolution
= 360°
f Frequency
Encoder count frequency.
Expressed in Hertz (Hz).
f = CPR x RPM/60
RPM
Revolution per
Minute
Angular speed that is
commonly used to dene
motor turning speed
RPS
Revolution per
Second
1RPS = 60RPM
°C Degree Celcius Denes the temperature
3.0 Main Characteristics
Typically there are many characteristics that designers
look at before deciding which encoder will best suit
their applications. Most engineers base their selection
primarily on six main characteristics: resolutions, operating
temperature, output signals, shaft sizes, motor speed and
motor diameter.
3.1 Resolutions
Cycles Per Revolution
Lines Per Inch
Encoder resolution denes the smallest measurement
unit that the encoder signal can provide. For a linear
application, the resolution is typically dened by the pitch
length (one pair of window and bar) or the count density.
WindowBar
1 Count (x)
The pitch length is specied in millimeters or inches. The
count density is referred to as the Lines per mm (LPmm) or
Lines per inch (LPI).
Length
Number of Window and Bar Pairs
Count Density =
x
1
=
x(mm)
1
LPmm =
x(in)
1
LPI =
Where x = pitch length (length of 1 pair of window and bar)