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Version
08.2017
TERM
DESCRIPTION OF TERM
Peak force Peak force is the force produced when the peak current is applied to the forcer. It is the product of Force
constant (N/Apk) and Peak current (Apk). The forcer is not moving, there is no forced cooling and no
additional heat-sinking. The duration of the peak force is thermally limited and is therefore only allowable for
a period of 1second.
Continuous stall
force
Continuous stall force is the force produced when the continuous current is applied to the forcer. It is the
product : Force constant (N/Apk) x Continuous stall current (Apk) or : Force constant (N/Arms) x Continuous
stall current (Arms). The forcer is not moving and there is no forced cooling. It is quoted with and without the
addition of a 25 x 25 x 2.5 cm heatsink plate mounted with thermal grease to the mounting surface of the
forcer.
Peak current Peak current is the current required to heat the forcer phases to their maximum operating temperature
when the ambient temperature is 25°C, the forcer is not moving, there is no forced cooling and no additional
heat-sinking. It is the maximum allowable current before demagnetisation of the magnets occurs when the
magnet temperature is 100°C. The duration of the peak current is thermally limited and is therefore only
allowable for a period of 1 second.
Continuous stall
current
Continuous stall current is the current required to heat the forcer phases to their maximum operating
temperature when the ambient temperature is 25°C, the forcer is not moving and there is no forced cooling.
It is quoted with and without the addition of a 25 x 25 x 2.5 cm heatsink plate mounted with thermal grease
to the mounting surface of the forcer.
Force Constant
Force constant is the peak force produced when 1 ampere (peak) flows into one phase and 0.5 ampere
(peak) flows out of the remaining two phases (as in sinusoidal commutation) quoted in N/Apk. Alternatively,
it is the peak force produced when 0.707 ampere (rms) flows into one phase and 0.353 ampere (rms) flows
out of the remaining two phases (again as in sinusoidal commutation) quoted in N/Arms.
Back EMF Back EMF constant is the peak phase to phase voltage generated when the forcer is travelling at a velocity
of 1m/s.
Fundamental forcer
constant
Fundamental forcer constant is the continuous stall force divided by the square root of the power dissipated
in the forcer at that continuous stall force.
Eddy current loss Eddy current loss is the amount of opposing force produced by the forcer when it is travelling at a velocity of
1m/s.
Sleeve cogging force
Sleeve cogging force is the amount of force variation produced by having an iron sleeve. The variation is
independant of forcer current.
Resistance Resistance is measured phase to phase at temperatures of 25°C and 100°C.
Inductance Inductance is measured phase to phase at a frequency of 1 kHz. The actual value of inductance varies as
the forcer position varies so it is the minimum value that is quoted.
Electrical time
constant
Electrical time constant is the time taken for a step current input to the forcer to reach 63.2% of its value.
Continuous working
voltage
Continuous working voltage is the maximum allowable continuous voltage between any two forcer phases
or between any forcer phase and the forcer safety earth.
Pole pitch Pole pitch is the distance in millimetres for one complete electrical cycle (between like magnetic poles).
Power dissipation Power dissipation is the maximum power that can be dissipated by the forcer when the forcer phases are at
their maximum operating temperature, the ambient temperature is 25°C, the forcer is not moving and there is
no forced cooling. It is quoted with and without the addition of a 25 x 25 x 2.5cm heatsink plate mounted with
thermal grease to the mounting surface of the forcer.
8.3 TERMS AND ABBREVIATIONS
