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Term 
Description 
Unit 
d 
Diameter 
m 
F 
Force 
N 
g 
Acceleration due to gravity 
ms^{2} 
J 
Total inertia 
kgm^{2} 
J_{L} 
Load inertia 
kgm^{2} 
J_{M} 
Motor inertia 
kgm^{2} 
m 
Mass 
kg 
M 
Motor torque 
Nm 
M_{a} 
Accelerating torque 
Nm 
M_{L} 
Load torque 
Nm 
n 
Rotational frequency 
rpm* 
n1 
 input 
rpm* 
n2 
 output 
rpm* 
Δn 
Change of rotational frequency 
rpm* 
p 
Pitch 
m 
P 
Motor power 
kW 
P_{a} 
Accelerating power 
kW 
P_{L} 
Load power absorbed 
kW 
r 
Radius 
m 
s 
Distance 
m 
t 
Acceleration time 
s 
Δt 
Acceleration period 
s 
v 
Linear velocity 
m/min* 
Δv 
Change of linear velocity 
m/min* 
V 
Traction capacity 
M^{3}s^{1} 
W 
Energy 
J (Joule) 
η 
Efficiency 
 
μ 
Coefficient of friction 
 
Note: For practical convenience, some of the units in the formulae following are not S1 units; for example, rotational
frequency is commonly measured in revolutions per minute, although the S1 unit is revolutions per second. In these servo drive formulae,
the terms used are as tabulated above.Those which are in nonS1 units are marked *.
Linear Motion
Fig. A
Consider a body mass m acted upon by a single force F, Fig A. The body accelerates in the direction in which the force
is acting, at a rate given by:
A = F/m
After a time t has elapsed, the body has achieved a velocity v, where:
v = u + at
(u is the initial velocity, before the force F was applied. If the body was initially at rest, u is zero)
The distance, s, travelled by the body during time t is
s = ut + at^{2}/2
Distance and velocity are related by the following equation, derived from the two previous ones:
v^{2}  u^{2} = 2as
The work done by the force in accelerating the body is the product of force and distance:
W = Fs
The kinetic energy of the body, ie the energy which it possesses by virtue of its motion, is the product of its mass
and the square of its velocity:
E_{k} = mv^{2}/2
Furthermore, since energy is conserved, the work done by the force is equal to the change in the body's kinetic
energy (neglecting losses):
W = m(v^{2}  u^{2})/2
Power is the rate at which work is done, therefore it is the product of force and velocity:
P = Fv




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Kubler Displays
The Measured Values of Inputs A and B are
associated mathematically. Thus the result can also be multiplied, divided or added to an offset
value, in order to obtain the desired display value. The user can consequently obtain up to three
display values with just one device: Display A, Display B and a display based on the calculation of
A and B. The analogue output ranges from 0/4 to 20 mA, +/10 V or 0 to 10 V.

Danfoss Drives
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