Note: Descriptions are shown in the official language in which they were submitted.
DEVICE FOR CONVERTING ~GNETIC OR ELECTROMAGNETIC FIEL~ TEN-
SIT~' INl'O ELECTRIC SIGNAL
App]ication of the Invention
Tile present invention relates to electromecllanic tran-
sducer devices and in particular to devices for converting a
magnetic field intensity into an electric signal designed around
magnetically controlled contacts.
Background of the Invention
~ nown in the art are magnetically controlled contacts
made as ferromagnetic plates rigidly fixed in a support and over-
lapping each other at their free ends which will come cioser to
one another when the current flowing through a magnetizing coil
grows from zero to a certain value and diverge when it continues
growing. (see, for instance, US Patent No 3551860, Cl. 335-151,
published in 1969).
A variation of the magnetic field intensity will result
in a change of the gap between the ferromagnetic plates and, con-
sequently, of the intercontact capacitance. The teclmique based
on the use of the intercontact capacitance of the ferromagnetic
plates as a parameter specifying the magnitude of a magnetic
field intensity suffers from a number of drawbacks caused by the
fact that with shifts of the plates the intercontact capacitance
will vary in a non-linear way and at a low multiplicity factor.
Besides, the absolute values of this capacitance are quite small
(from 0.5 to 3.0 pF) and therefore their measurement re~uires
that high fre~iuencies should be used.
One of the known designs that is the closest to the
one proposed herein relates to a device for converting a magnetic
field intensity into an electric signal which comprises movable
elements made as ferromagnetic plates rigidly fixed in supports
so that their free ends overlap each other and an element for
sensing the relative displacement of the free ends of the
g
ferromagnetic platcs, the element being connected to a measuring
circuit. The displacement of the free ends of the ferromagnetic
plates is measured with the use of photodetector elements, such
as a photomultiplierand an illumination ]apm, mounted at opposite
sides of the gap between the overlapping ends of the ferromagnetic
plates. In such devices the magnetic field intensit~ is converted
into a current flowing through a photodetector element. ~see,
for instance, Zaretskas V.-S.S., Ragulskene V.L. "Mercury commuta-
tor elements for automatic devices". Energia, 1971, p. 51).
However, the use of such devices as a means for conver-
ting the intensity of a magnetic field into an electric value
requires a stable power supply, a dustless environment and precise
adjustment of the ferromagnetic plates Wit}l respect to the illu-
minator-photodetec~or axis. Negligence to these requirements
tends to reduce the reliability of such converters. sesides,
their conversion range is limited when the size of ferromagnetic
plates is increased.
srief Description of the Invention
The object of the present invention is to provide a
device for converting the intensity of a magnetic field into an
eiectric signal which would have high reliability and a wide
conversion range.
The essence of this invention consists in providing a
device for converting the intensit~ of a magnetic or electro-
magnetic field into an electric signal comprising movable elements
made as ferromagnetic plates rigidly fixed in supports so that
their free ends overlap each other, and an element sensing the
respective displacement of the free ends of the ferromagnetic
plates which is connected to a measuring circuit wherein, according
to the invention, the sensitive element is made as at least one
resistance strain gauge mounted at the deformation section in the
immediate vicinity to the point where the ferromagnetic plate is
- 3 -
.,.~, ~, .
17~
fixed in the support.
Conveniently the magnetic field source is made as a
current conduit while the device is provided with an assembly for
rotating the axis of the resistance strain gauge with respect to
the longitudinal axis of the current conduit, the assembly being
rigidly coupled with the supports.
Conveniently also the device is provided wlth a permanent
magnet mounted so that it can be shifted with respect to the
ferromagnetic plates in order to vary the resistance rating of the
strain gauge the value of which is used as an additional indication
of the permanent magnet position.
Preferably, the device should comprise a control mag-
netizing coil connected, via an amplifier-converter, to an a-c
voltage source of or periodic variations in the strain gauge
resistance.
Brief Description of the Drawings
The invention will be better understood from the following
description of its embodiments given by way of example and shown
in the accompanying drawings in which:
Fig. 1 presents a device for converting the intensity of
a magnetic field into an electric signal, the device being pro-
vided with one resistance strain gauge, according to the invention;
Fig. 2 presents the device as shown in Fig. 1, viewed
from above, according to the invention;
Fig. 3 presents a version of the proposed converter
~evice with two resistance strain gauges according to the inventlon;
Fig. 4 presents the proposed converter device with four
resistance strain gauges according to the invention;
Fig. 5 presents a version of the proposed converter
device with four resistance strain gauges installed on membranes
which are secured to the body of the device (longitudinal cross
section of the body and the membranes) according to the invention;
Fig. 6 presents a version of the proposed converter
device Witil a field source made as a current conduit (partial
longitudinal cross section) according to the invention;
Fig. 7 presents a version of the proposed converter
device wherein the field source is made as a permanent magnet
according to the invention;
Fig. 8 presents a diagram of connections between re-
sistance strain gauges and the measuring circuit in the proposed
converter device according to the invention;
Fig. 9 presents a version of the proposed converter
device wherein the resistance strain gauges are connected, via an
amplifier-converter, to a magnetizing control coil.
Detailed description of the Invention
The proposed device for converting the intensity of a
magnetic field into an electric signal comprises movable elements
made as ferromagnetic plates 1 (Fig. 1) and 2 rigidly fixed in
supports 3 and 4 so that their free ends overlap each other. The
device comprises also an element sensing the relative displacement
of the free ends of the ferromagnetic plates represented as at
least one resistance strain gau~e mounted at the deformation
section in the immediate vicinity to the point where the ferro-
magnetic plate is fixed in the support. The embodiment of the
inventlon described herein uses one resistance strain gauge 5
mounted on the ferromagnetic plate 1.
Terminals 6,7 of the resistance strain gauge 5 are
connected to a measuring circuit 8 (Fig. 2).
Fig. 3 presents another version of the embodiment of the
device for converting the intensity of a magnetic field into an
electric signal which, according to the invention, comprises an
additional resistance strain gauge 9 having terminals 10 and 11
mounted in a way similar to that of the resistance strain gauge
in the immediate vicinity to the point where the f~rromagnetic
- 5
,.. .
7~
plate 1 is fixed in the support 3 but on the opposite surface of
plate 1.
An additional resistance strain gauge 9 subjected to
deformation opposite to that of the resistance strain gauge 5
and located in the immediate vicinity to it makes it possible to
raise the magnitude of the useful signal (in the form of resistance
increment) and to reduce the temperature-dependent conversion
error caused by resistance temperature variations of the strain
gauge.
Fig. 4 presents another version of the embodiment of the
device for converting the intensity of a magnetic field into an
electric signal which, according to the invention, comprises,
in addition to those in the version of Fig. 3, still two more
resistance strain gauges 12 and 13 having terminals 14, 15, 16,
17 mounted on the ferromagnetic plate 2.
The use of the two more resistance strain gauges 12 and
13 makes it possible to raise the magnitude of the useful signal
still further though the displacement of the ferromagnetic plates
1 and 2 is the same.
The device for converting the intensity of a magnetic
field into an electric signal proposed herein and shown in Fig. 5
differs from the version presented in Fig. 4 in that it comprises
a casing 18 housin~ the ferromagnetic plates 1 and 2. The casing
18 is made of non-~erromagnetic material. The butt endsof the
caslr.g 18 are provided with broad sections carrying membranes 19
and 20 secured to them. The diameter of these membranes 19, 20
exceeds to a certain extent that of the casing 18 in its central
section. The membranes 19 and 20 have their edges rigidly fixed
(welded) to the casing 18. Connected rigidly to said membranes
19 and 20 at their centers are the ferromagnetic plates 1 and 2
respectively. The connection may be either sealed or unsealed.
In the version of the embodiment described herein the membranes 19
5J~ - 6 -
~o~o~
and 20 serve as resilient elements and perform the function of
supports for the ferromagnetic plates 1 and 2. Placed at the
outer surfaces of the membranes 19 and 20 are the resistance
strain gauges 5, 9 and 12, 13 respectively, which are secured
to deformation sections in the immediate vicinity to the points
where the ferromagnetic plates 1 and 2 are fixed.
The use of the casing 18 and the m~mbranes 19 and 20
which are connected rigidly to it makes it possible, firstly
to place the resistance strain gauges 5, 9, 12, 13 after the major
cornponents, including the ferromagnetic plates 1 and 2 have been
assembled; secondly, to arrange tne resistance strain gauges
5, 9, 12, 13 at the outer surfaces of the membranes 19, 20 r which
facilitates the connection of other components to the terminals
of the resistance strain gauges 5, 9, 12, 13, and thirdly, to
increase the number of resistance strain gauges in the s~stem
by means of securing them at the deformation sections of the mem-
branes 19, 20 Still another advantage of the version of the
embodiment of the proposed invention described herein consists in
that its design features allow to automate the procedure of its
production.
Fig. 6 pr~sents another version of the device according
to the invention wherein the field source is made as a current
conduit 2I. In addition the device is provided with an assembly
22 for rotating the axis of the resistance strain gauge 5 about
the longitudinal axis of the current conduit 21. The assembly
22 is rigidly coupled with the supports 3 and 4 through the casing
18. The supports 3 and 4 are made mainly of an isolation material
as washers. The casing 18 is made of non-ferromagnetic materials.
In order to increase the accuracy of converting the intensity of
a magnetic field into an electric signal the casing 18 is preferably
made of copper so as to form a short-circuited winding.
The use of the rotation assembly 22 allows to vary the
71
range and the sensitivity of converting the intensity of a magnetic
field generated by the current conduit 21 into an electric signal.
Fig. 7 presents a version of the device according to
the invention wherein the field source is made as a permanent
magnet 23 which serves as a complementary element of the proposed
device. Simultaneously the permanent magnet 23 performs the
function of a means for transferring the data on its position,
to which end it is mounted so that it can be shifted with respect
to the ferromagnetic plates 1 and 2 and hence, vary the resistance
of tlle strain gauge 5. The permanent magnet 5 is shifted with
the help of a holder 24 wherein the permanent magnet 23 is fixed
and by means of a rod 25 housed in guides 26 and rigidly coupled
with the holder.
The directions of the permanent magnet 23 shifts with
respect to the longitudinal axes of the Eerromagnetic plates
1, 2 as indicated by arrows in Fig. 7 are not the only possible.
The present version of the proposed device allows to consider the
shift and the position of the permanent magnet 23 in case of its
rotation as well as in case of its movement along the ferromagnetic
plates 1 and 2.
An index "X" indicates the effect caused by a sensor o~
the parameter to be measured (not shown in Fig. 7) on the rod 25
which shifts the permanent magnet 23. The functions of the sensor
of the parameter to be measured could be performed by a pressure
pic~-up, a temperature sensor, etc. which converts the parameter
to be measured into a displacement. The assembly described above
is especially suitable in transferring the results of measurements
to a remote user.
One of the possible embodiments of the converter version
hereinbefore described is a device for converting angular position
~- of the rod 25 of the permanent magnet 23 into variations of the
resistance of the strain gauge 25. Such a converter is used most
- 8 -
7:L
preferably in cases when the rotation rates of the rod 25 are about
zero. The above circumstance is due to the fact that the proposed
device for converting the intensity of a magnetic field into an
electric signal wherein ~he functions of a field source are per-
formed by the permanent magnet 23 combines in a most advantageous
way both a means allowing to determine the amount of displacement
of the permanent magnet and a means presenting the information on
the position (coordinate) of the permanent magnet 23. In par-
ticular the proposed design makes it possible to reliably and
accurately solve the problem of determining the position of
slowly rotating rotors in electric machines such as step-by-
step motors.
Fig. 8 presents a version of the device according to
the invention wherein the resistance strain gauges 5, 9, 12 and
13 are interconnected to one another and to the measuring circuit.
Shown in Fig. 8 in particular is the interconnection of said
resistance strain gauges 5, 9, 12, 13 into a bridge circuit one
diago~al of which is connected to a source of the supply voltage
U and the other, to the measuring circuit 8. The above method
of interconnecting the resistance strain gauges 5, 9, 12, 13
and the measuring circuit 8 makes it possible to obtain a large
electric signal in the form of an output current. This is due to
the fact that a variation of the magnetic field intensity will
cause a change of the resistance in all the four strain gauges 5,
9, 12, 13. Besides, the error introduced by ambient temperature
variations could be reduced drastically by means of selecting
resistance strain gauges having similar temperature responses.
The above device employing the proposed interconnection circuit
could be used to advantage as a remotely variable resistor, the
rating of which being varied either by means of changing the
current thatflows through the control magnetizing coil or by means
of shifting the p~rl,lanent magnet. An additional advantage of the
,, _ g _
. .:. ~.
7~
proposed method of interconnecting the resistance strain gauges
consists in that it allows to obtain an output in the form of a
current signal proportional to the product of the supply voltage
"U" by the current "I" which determines the intensity of the mag-
netic field being converted by the proposed device into an electric
signal. In case the supply voltage "U" is set equal to a voltage
drop across the ohmic-inductance load having the current "I"
flowing through it the output of the circuit will be proportional
to the power consumed by the load.
lG Fig. 9 presents a version of the device for converting
the intensity of a magnetic field into an electric signal accord-
ing to the invention which comprises a control magnetizing coil
27 connected, via an amplifier-converter 28, to the resistance
strain gauges 5, 9, 12, 13. This design of the proposed deviee
makes it possible to obtain a feedback loop using the position
of the ferromagnetic plates 1 and 2 as the source of a feedback
signal which can be either positive or negative, which allows
to vary the characteristics of convert:ing the intensity of a mag-
netie field into an eleetrie signal. In particular the deviee
ean operate as a null-indicator. However, in this case it is
re~uired that the electromagnetic field generated by the control
magnetizing coil 27 should compensate for the effect of the ex-
ternal magnetic field to be eonverted into an eleetric signal.
If there are several control magnetizing coils (not shown in Fig.
9) the displacement of the ferromagnetic plates 1 and 2 and their
resultant position will be determined by the sum (or difference)
effect of the coils.
In another version of the embodiment of Fig.-9, the
control magnetizing coil 27 is connected, via the amplifier-con-
verter 28, to an a-c voltage source, thereby providing for periodie
variations in the resistance of the strain gauges 5, 9, 12, 13 and
enabling a-c amplifiers to be used for hand~ing signals from the
- 10 - `
7~
strain gauges.
The device for converting the intensity of a magnetic
or an electromagnetic field into an electrlc signal shown in
Figs. 1 and 2 operates as follows.
As soon as a control signal in the form of a longitudinal
or a transverse magnetic or electromagnetic field is applied to
- a system of ferromagnetic plates 1 and 2 the latter will start
approaching each other and with the further increase of the control
signal they will diverge, provided that the initial gap and the
amount of overlapping between the ferromagnetic plates 1 and 2
exceed certain limiting values, i.e. the values at which the
ferromagnetic plates 1 and 2 still contact each other. In case
the above requirements are not met the proposed device will operate
within the time interval from the moment the ferromagnetic plates
1 and 2 start approaching each other till the moment when they
start moving with a jump to contact each other. In any case,
however, the above mutual approach of the ferromagnetic plates
1 and 2 is accompanied by their resilient bending strain since
~; they are rigidly fixed in the supports 3 and 4. The outer sur-
faces of the ferromagnetic plates 1 and 2 expand while the inner
ones contract. In the particular case of cantilever arrangement
of the ferromagnetic plates 1 and 2 the deformation section sub-
jected to the maximum strain will ~e located in the immediate
vicinity to the point where the ferromagnetic plate is fixed in
the support 3. It is at this section that the resistance strain
gauge should be located. A properly selected and mounted re-
sistance strain guage will vary its resistance in proportion to
the displacement of the free end of the ferromagnetic plate 1.
The variations of the resistance of the strain gauge 5 are sensed
by the measuring circuit 8 so that its output indicates the
intensity of the magnetic or electromagnetic field.
The operation of the version of the proposed device as
- 11 -
7~
shown in Fig. 3 is similar to that of the version presented in
Figs. l and 2. However, the use of complementary resistance
strain guage 9 makes it possible to compensate for temperature
errors and to raise the level of the useful signal in any of
the known ways.
The operation of the device for converting the intensi-
ty of a magnetic or electromagnetic field into an electric signal
arranged as shown in Fig. 4 is similar to that of the previous
version of the device. In order to raise the level of the output
still higher and to reduce the error to the minimum it is neces-
sary to select the resistance strain gauges 5, 9, 12 and 13 so
that they have similar responses and to install the ferromagnetic
plates 1 and 2 symmetrically so as their free ends bend to one and
the same extent while the resistances of the strain gauges 5, 13
and 9, 12 are equal.
The operation of the device arranged as shown in Fig. 5
is basically the same as that of the previous version. The fact
that the inside of the device is protected with a casing allows
to stabilize its response to a certain extent against variations
of the amount of dust, gas and other ingredients of the environ-
ment. The major difference, however, consists in-the use of the
deformation suffered by the membranes l9 and 20 performing the
functions of resilient elements. The ferromagnetic plates l and
2 and the membranes l9, 20 in the device are designed so that
the increase of the control signal represented by a longitudinal
or transverse magnetic or electromagnetic field will not result
in a resilient bending strain of the ferromagnetic plates l and 2
that are to approach each other, while the deformation of said
membranes will have the form of a waveshape bend. In this case
tne maximum strain sections in every membrane l9 and 20 will be
located at the points where they are fixed in the butt-ends of
the casing 18 and in the immediate vicinity to the place where the
f~2~ - 12 -
07~
ferromagnetic plates 1 and 2 are rigidly fixed in the membranes
19 and 20. It is at this sections that the resistance strain
gauges 5, 9, and 12, 13 are to be located. Properly selected
and mounted resistance strain gauges 5, 9, 12, 13 will vary their
resistances in proportion to the displacement of the free ends
of the ferromagne~ic plates 1 and 2.
The operation of the device designed according to the
invention as shown in Fig. 6 is basically similar to that of
the device versions presented in Figs. 1 and 2. The.only difference
however consists in that the control signal represented by a
longitudinal magneti.c field affecting the system of the ferro-
magnetic plates 1 and 2 is generated by a direct current flowing
through the current conduit 21. The use of copper to make the
casing 18 allows to reduce errors caused by expected var.iations
of the current I. The device will exhibit the maximum sensitivity
when the longitudinal axis of the ferromagnetic plates 1, 2 is
orthoc30nal to that of the current conduit 21, and the mimimum
sensitivity when the above axes are arranged parallel to each
other. In case the electromagnetic fields to be converted
sat~lrate the ferromagnetic plates 1 and 2 of the device the casing
18 shall be turned into a position where there-would be no
saturation of the ferromagnetic plates 1 and 2. The above version
of the device according to the invention permits to reliably
and accurately convert strong direct currents (tens and hundreds
of kiloampers) into electric signals as increments of the re-
sistance ratings of the strain gauge 5.
The operation of the device designed as shown in Fig. 7
is basically similar to that of its version presented in Figs. 1
and 2. The difference, however, consists in that the control
signal represented by a longitudinal (o~: transyerse) magnetic
field that affects the system of the ferromagnetic plates 1 and 2
is generated by the permanent magnet 23. The displacement of the
- 13 -
071
permanent magnet 23 will vary the intensity of the magnetic field
to be converted by the ferromagnetic plates 1 and 2 and the re-
sistance strain gauge 5 into an electric signal. In case it is
required to determine discrete displacements of the permanent mag-
net 23 when, for instance, the amount of the production is
counted piece by piece, tlle resistance strain gauge 5 will be
connected, via an amplifier-converter, to a counter of the dis-
cretely varying resistance of the strain gauge 5 (the amplifier-
converter and the counter are not shown in the drawing).
The circuit wherein the resistance strain gauges and
the measuring circuit are interconnected as sho~m in Fig. 8 will
operate in case the ferromagnetic plates 1 and 2 are being dls-
placed and the resistance ratings of the strain gauges 5, 9
and 12, 13 are changing.
Since the resistance strain gauges 5 and 9 as well as
12 and 13 are subjected to deformation effects caused by the dis-
placement of the ferromagnetic plates 1 and 2, the deformations
being of opposite signs, their arrangement in adjacent arms of the
bridge will ensure the maximum sensitivity of the circuit with
respect to the intensity of the magnetic or electromagnetic field
to be converted (the sensitivity of the circuit is the ratio
between the relative increment of the current àt the output of
the bridge to the relative variation of the intensity of the
magnetic or electromagnetic field). The initial adjustment of
the bridge requires that the resistance strain gauges 5, 9, 12,
13 snould be accurately selected. However this adjustment could
~e facilitated by means of adding a complementary balancing re-
sistor to the circuit of the device (not shown in the drawing).
The operation of the version of the device presented in
Fig. 9 depends on the mode of converting the intensity of a mag-
netic or electromagnetic field into an electric signal. This mode
can be eitller continuous or relay-like. In the continuous con-
- 14 -
version mode with negative feedback the output of the amplifier-
converter 28 is applied to the control magnetizing coil 27 which
forces the ferromagnetic plates 1 and 2 to return to their initial
positions since the electromagnetic field generated by the control
coil 27 will compensate for the effect of the magnetic or electro-
magnetic field to be converted. This mode of operation of the
device ensures high accuracy and sensitivity of the conversion
process. In the relay-like conversion mode with negative feed-
back the output of the amplifier-converter 28 is applied to the
control magnetizing coil 27 in a manner similar to that described
above. However the shape and the duration of the signal should
be different.
The operation of the device discussed herein is intended
to obtain a commutation mode that would be free from vibration and
ensure the optimum rate of commutation whereat the time required
for the ferromagnetic plates 1 and 2 to shift from one stable
position into another will be minimal. The proposed mode of
the operation of the device is based upon the theory and methods
of optimal control and a complement part of them which is known as
dynamic programming. In order to obtain the above effect the
control action represented by the number of ampere-turns should
be made as high as possible. The ferromagnetic plates 1 and 2 to
be closed are accelerated to the maximum speed and then the control
action is dropped in a jump to the zero level. Thus, the
ferromagnetic plates 1, 2 are "self-braked" and close at a zero
speed. After that the control action is generated again to
ensure that the ferromagnetic plates 1 and 2 remain in the closed
position. The value of the speed at which the ferromagnetic
plates 1,2 are displaced and their positions are determined with
the help of data provided by the resistance strain gauges 5, 9
12 and 13.
ThP embodiment in which the control magnetizing coil
- 15 -
LQ7~
27 is connected to an a-c voltage source via the amplifier- -
converter 28 operates as follows. The amplitude and frequency
of the supply a-c voltage are set in such a manner as to provide
for forced oscillations of the ferromagnetic plates 1 and 2 as
well as periodic variations in the resistance of the strain
gauges 5, 9, 12, 13. In the presence of an invariable or slowly
variable control action in the form of the magnetic (electromagne-
tic) field intensity, amplitude modulation of periodically varying
resistances of said strain gauges takes place.
- 16 -
