Hubner TDP 1,2 Series, Operating And Assembly Instructions Manual

Page: 24 / 54

D.C. tachometer generator TDP 1,2
24
TDP1,2-MANUALen_R5(2018-12-19)ID74713 .doc
Description of the method of measurement used to determine linearity:
The tacho-generator to be tested is coupled to a prime mover fitted with a flywheel and operated
through a speed range of 100 to 3000 rpm. An incremental encoder (1000 pulses/rotation) is used to
measure the speed digitally to one decimal place. The tacho voltage is also measured digitally,
however, this is measured to three decimal places. A printer connected to both measuring devices
prints the voltage and speed. The measurements are taken at intervals of 100 rpm. At least 20
measured values are printed per measurement. The reference voltage at a speed of 1500 rpm is
selected as a reference point for all voltages and associated speeds.
The quotient obtained from the voltage at 1500 rpm and the speed of 1500 rpm is known as the
reference gradient. The voltages and speeds from 10 measured values respectively are
arithmetically averaged when evaluating the gradients and the gradient formed from these averaged
values.
Disturbance variables relative to linearity
Load current and armature reaction
If it is assumed that the speed-voltage curve at no load is a straight line at a particular angle, then
when load is applied (without taking account of armature reaction) the result is a straight line at a
less steep angle. The difference depends on
However, as the magnetic flux is distorted and weakened by the load current a further change
occurs to the voltage characteristic curve. The voltage drop resulting from the armature reaction
approximately follows the load current more or less according to a quadratic function and, therefore,
results in a slightly curved speed voltage curve when under load. Suitable design measures,
however, make it is possible to keep the field distortion caused by the armature reaction extremely
low. The max. permissible load current is provided for the respective machine type; however, the
linearity errors listed in the selection tables refer to the current resulting from termination with the
optimum load resistance. (F
rel
= 0.2‰, at max. permissible current 5‰.)