10
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Technical Information
R1
R2
Duty cycle calculation
The RMS (root mean squared) value of a load is one
of the quantities often used to size PT components.
_____________________
L12t1 + L22t2 + ... + Ln2tn
LRMS = ––––––––––––––––––––
(11)
t1 + t2 + ... tn
where:
LRMS = RMS value of the load which can be in any
unit — hp, amp, etc.
L1
= Load during time period 1
L2
= Load during time period 2, etc.
t1
= Duration of time period 1
t2
= Duration of time period 2, etc.
Modulus of elasticity
PL
E = –––––
(12)
ADd
where:
E = Modulus of elasticity (lb/in2)
P = Axial load (lb)
L = Length of object (in)
A = Area of object (in2)
Dd = Increase in length resulting from axial load (in)
Hollow cylinder rotating about its own axis:
1
WK2 = ––– W(R12 + R22)
(8)
2
where:
WK2= Moment of inertia (lb•ft2)
W
= Weight of object (lb)
R1
= Outside radius (ft)
R2
= Inside radius (ft)
Material in linear motion with a continuous fixed
relation to a rotational speed, such as a conveyor
system:
V
WKL
2
= W(–––––)
2
(9)
2pN
where:
WKL2= Linear inertia (lb•ft2)
W
= Weight of material (lb)
V
= Linear velocity (fpm)
N
= Rotational speed of shaft (rpm)
Reflected inertia of a load through a speed
reduction means — gear, chain, or belt system:
WKL
2
WKR
2
= –––––
(10)
Rr
2
where:
WKR2= Reflected inertia (lb•ft2)
WKL2= Load inertia (lb•ft2)
Rr
= Reduction ratio
Time
L1
L2
L3
t1
––––––––––––––––– ––––––––––––
t3
––––– –––
––––––– –––––––
t2
•
•
•
Axial
Radial
Tangential
Circumferential
3
3
3
