Note: Descriptions are shown in the official language in which they were submitted.
133~
This invention relates to an arrangement for rotor- ~
frequency-dependent short~circuiting of rotor-series-resistances
for driving motors, more particularly in the case of hoist motors,
by means of a frequency-detecting and converter unit, a rated-
value factor, and a comparison circuit for producing a short-
circuitin~ command.
In one known arrangement of the above mentioned type,
the frequency is detected by char~ing a capacitor which has to be
charged at a specific voltage. In this case, the predetermined
voltage corresponds to the frequency to be measured, i.e. in this
case the rated value has to be adjusted by an expert, by means of
potentiometers and external voltmeters. The rotor-frequency to
be adjusted can not be reco~nized immediately from the ou-tside.
This requires an allocation list of the rotor-frequency for the
voltage to be measured. In addition to this,aspecific internal
resistance of the measurin~ instrument has to be maintained in
order to ensure the allocation. ~oreover, in the case of such
adjustments, the tolerances of the components in general must be
taken into account.
According to the invention, therefore, an arrangment
of the kind mentioned above is to be provided which will ensure
simple and reliable adjustment of the rated value and thus more
precise functioning of the arrangement as a whole. This is achieved
in a simple manner in that the frequency-detecting and converter
unit consists of a rotor-irequency-dependent gate-circuit which,
in the open condition,releases a fixed reference-frequency to a
counter which, in turn, passes the counted periods of the reference-
frequency, through a matrix-circuit as a digital actual rotor-fre-
quency value to the comparison circuit, rated-value pre-selection
being effected digitally by means of adjustable code-switches at
the comparison-circuit.
In order to be able to evaluate in the range of the
actual value also, and more or less independently of tolerances
in components such as capacitors and resistors, it is an advantage
for the fixed reference-frequency to be produced by a quartz
oscillator (reference-frequency generator). In order to be able
to construct the arrangement according to the invention with a
small number of components, especially as regards the matrix
circuit, it is an advantage for the matrix circuit to be in the
form of an EPROM (erasable programmable read only memory). The
use of an EPROM also makes it possible to increase the reference-
frequency. Increasing the reference-frequency permits more
accurate relaying of the rotor-frequency from the matrix circuit,
the EPROM having sufficient storage capacity available almost
without additional cost. Increasing the reference-frequency makes
it possible to obtain better resolution o-E the measurement results.
From the point of view of storage costs and the necessary accur-
acy in detecting rotor frequencies, a reference-frequency of 5 kHz
has been found advantageous. Since, when the driving motor is
started up, undefinable frequency-mixtures arise in the rotor,
which are unsuitable for evaluating the rotor frequency, it is an
advantage for the short-circuiting command from the comparison-
circuit (comparator) to be capable of being influenced by a delay-
circuit. ~n order not to exceed the addressing-range of the
-- 2
matrix, it is an advantage for the number of counted reference-
frequency periods to be limited to a m~i m~l value. Generally
speaking, this m~im~l value will correspond to the number of
reference-frequency periods during maximal openin~ of the gate
circuit.
In order to avoid additional switching means, i.e. to be
able to make use of already existing systems, it is an advantage
for the frequency-detecting and converter unit, and the rated value
pre-selector/ to be built up with the comparison-circuit as an
additional component, into a stored-programme control.
An example of an embodiment according to the invention
is described hereinafter in conjunction with the drawing attached
hereto, the method of operation being explained in greater detail.
The arrangement, represented in the drawing as a block-
wiring-dia~ram, ~or rotor-frequency-dependent short-circuiting of
rotor-resistances fox driving motors, which is of major interest
for hoists in particular, consists of a frequency-detecting unit 1
to which rotor-voltage 2 is fed. Converter unit 3 consists of a
counter 4, a re~erence-frequency generator 5 and, in the present
case, EMPROM 18. Digital rated-value pre-selector 6 consists, in
this case, of four two-digit code-switches 7. The code-switches
7 are BCB (binary-coded-decimal) coded and are connected, through
leads 8, to comparators 10. The actual value from EMPROM 18 is
connected, through lines 9, to comparators 10. As soon as the
actual value exceeds the rated value, comparators 10 release a
signal to a decodin~ circuit 11 for bus-system 12 of a freely
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programmable control such as that disclosed in the operating
instructions for the SIMATIC S5-110 A automating unit.
According to the exemplary embodiment one value from the
EMPROM 18 is compared with 4 values from the switches 7, e.g. the
value 10 is connected to the comparators 10 via the EMPROM 18 and
compared ~ith the values 41, 32, 05 and 99 given by the switches
7. When there is agreement, a signal is produced by the associated
comparator 10. The decoder 11 has a multiplexer output, i.e. the
outputs of the comparators 10 are interrogated one after the other
via the subsequent stored programmable control. The pointer in
the decoder 11 indicates which output, dependent on the stored
programmable control, is being interrogated via the bus system 12.
A delay-circuit 13 provides for a delay in the initial
command from decoding circuit 11, through the leads of bus-system
12 and through decoder 14, as a function of the switching state
of the driving-motor switching units.
The arrangement according to the invention functions
as follows: frequency-detecting unit 1 converts the line-voltage
into a s~uare wave voltage. Input-current limiting of frequency-
detecting unit 1 is effected by a choke 15. Voltage separation
between the rotor--voltage and the voltage fed to the arrangement
is effected by an optical coupler, not shown. In order to keep
measurement errors as low as possible, the duration of a rotor-
frequency period is measured from the beginning of one full wave
to the beginning of the next full wave. Through an input 16, the
rotor-voltage can be simulated by a frequency-generator, and this
input can therefore be provided as a test inputO The output from
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~97~33
frequency-detecting unit 1 is connected to the input to converter
unit 3. This input-signal releases output 15 from the reference-
frequency generator 5 in the manner of a gate-circuit, which makes
it possible to count the number of pulses from the reference-
frequency generator 5, by means of counter 4, according to one
period of the rotor-voltage, i.e, the number of pulses is propor-
tional to the period length. If the measurement results are to he
obtained in Hertz, the measured length of the period must be con-
verted into Hertz. In this examplary embodiment this is effected
by passing the period-length, as an address, to an EMPROM memory
18. This memory location contains, in BCD code, the value of the
frequency corresponding to the period length. Now this BCD-coded
frequency appears on leads 9 and is compared with the rated value
adjusted by code-switches 7 which is fed, through lines 8, to
comparators 10. The comparator results are fed as signals to
decoding circuit 11 which, in turn, passes them through bus-line 12
of the stored-programme control, possibly after a delay produced
by delay-circuit 13, to -the switching equipment handling the short-
circuiting of the rotor resistances.
The arrangement according to the invention makes it
possible to obtain measurements which are practically independent
of the tolerances of any capacitors or resistors. It also enables
the user to adjust the rated ~alue effortlessly, without special
knowledge, -training or difficulty. The assembly can be triggered
directly through the bus-systems of known stored programme controls
and may also be interrogated.
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