FR2533317A1 - Apparatus for measuring the instantaneous value of a current - Google Patents

Abstract

The apparatus measures currents and voltages. It consists of a current transformer 1 whose control secondary 3 is connected through a shaper 4 of the switching gate control signals to the control inputs 5, 6 of these switching gates 7, 8. The common point 15 of the switching gates 7, 8 is connected through the self inductance 17 to one of the terminals of the output secondary 16 of the current transformer 1. Another terminal of the winding 16 is connected to the common point 14 of the source of supply 13 of the switching gates through the resistor 18. The apparatus is used to generate reaction current signals in high-speed automatic regulating systems, e.g. in electrical feed controls of machine tools for metal cutting.

Description

The invention relates to measuring devices

  currents and voltages, and more specifically, a device

  Instantaneous current value measuring device Said device

  measurement reel is used to form the feedback signals

  rant in rapid automatic regulation systems,

  such as electric machine advance controls

tools for cutting machining.

  Instantaneous value measuring devices

  current, which currently exist, have unreliable

  sufficient, complicated construction and large dimensions

  sions. It is known an appae: idmesuredevaeur instantaneous current (see, for example, the Author's Certificate of

  U R S S N 194 162, cl N 03 F 9/00), including an amplifier

  magnetic push-pull inductor linker, a

  current derivative trainer made with a transformer

  current meter to air gap and an RC filter The control winding of the magnetic amplifier is inserted in

  the circuit of the current to be measured and in series with the primary

  re of the current transformer The secondary of the transformer

  current meter and the output of the magnetic push-pull amplifier are connected to the RC filter whose output serves as that of the instantaneous current value measuring device. RC filter ensures a low level of pulses at the output of the instantaneous value measuring device

current.

  The delay compensation for this filter is done

  using a signal taken from the secondary of the transformer

  current gauge to air gap The output signal from the

  same measurement corresponds to the current to be measured without

  amplitude and phase twists But in case of a variation

  rapid current measurement in the secondary to more

  several turns of the air-gap transformer arise from high voltages which can cause breakdown

  insulation of the winding Therefore, during measurements

  safe currents varying very quickly the cb roeste device of value

253331?

  instantaneous current has low reliability.

  It is still known a value-measuring device

  tane current comprising a current transformer whose primary is inserted in the circuit of the current to be measured, and the secondary control winding is electrically linked to the control inputs of two switching gates in series, the common point of those -this being electrically coupled to one of the terminals of the secondary output winding of the current transformer, the other terminal of this winding being linked to the midpoint of a power source of said doors via

  a resistor whose signal corresponds to the ins-

  of the current to be measured (see for example, the Certi-

  authorship of the TU R S S N 706787, cl G 01 RI 9/00).

  The measuring device also includes a block for

  the measurement of a current derivative using a transforma-

  gap current tester, the primary of which is set to

  rie with the primary of the first current transformer, and whose secondary and a resistor are connected to an RC filter The block also includes switching gates

which are transistorized.

  In the current measuring device in question around the switching time of the transistor switching gates the current transformer is saturated, and the transistor switching gates allow the saturation currents to pass substantially higher than the theoretical working values. brings an increase

  pulses of the output signal, loss of power

  this additional to the switching doors and a degra-

  reliability of the operation of the

current measurement.

  The operation of the

  instantaneous current value is characterized by a low

  ble switching frequency of transistor switching gates In order to have a low pulsation level of the device output signal, an RC filter is used

253331 Y

  exhibiting a large time constant, this resulting in an increase in dimensions The compensation for the delay due to the filter is done using a signal taken from the secondary of the air gap current transformer, the latter further increasing the space requirement In addition, in the event of a rapid change in the current to be measured,

  voltages arising at the secondary of the current transformer

  rant which cause the insulation breakdown of the winding.

  This factor makes the reliability of the measuring device worse.

instantaneous current value.

  The present invention relates to an instantaneous current value measuring device in which a decrease

  switching currents flowing through the doors

  mutation as well as the removal of overvoltages in the circuit would improve reliability, reduce

  dimensions and simplify the construction of this appa-

reil of measure.

  The problem posed is solved using an apparatus

  instantaneous current value measurement type

  comprising a current transformer by a primary of-

  which current to measure, a secondary control

  electrically connected to the control inputs of two doors

  Switching serial switches having their common electrical point

  three times coupled to one of the terminals of a secondary output

  tie of this current transformer, its other terminal being connected to the midpoint of a power source for the switching gates by means of a resistor, the voltage at this resistor corresponding to the instantaneous value of the current to be measured, said measuring device being according to the invention, characterized in that it has a choke having one of its terminals connected to the common point of the switching gates, and the second terminal; connected to one of the transformer secondary output terminals

  current, and a gate control signal trainer

  Switching tes having its inputs connected to the terminals of the secondary control of the current transformer, and its

253331?

  outputs, connected to the control inputs of the switching doors.

  It is helpful if the trainer

  control of switching gates has a block of different

  rentiation and a threshold element in series intended to compensate for the delay introduced by the choke at the self-oscillation frequency. It is useful that the primary transformer

  current embraces the magnetic circuit of the choke.

  It is helpful if the secondary exit from the trans-

  current trainer embraces the magnetic circuit of the inductor.

  The instantaneous value measuring device

  The proposed rant has high reliability thanks to the insertion

  Choke in the secondary transformer output circuit The presence of a choke limits the switching currents flowing through the doors

  switching at the supply current of the trans-

  current trainer The insertion of the self into a circuit

  low-voltage baking prevents high voltages from appearing on this inductor The use of the inductor and the signal generator for controlling the switching doors in a low-current circuit operating at high switching frequencies makes it possible to reduce the dimensions of the measurement device. -Even because in the above-mentioned operating modes a small self-inductor is used The delay due

  at the choke is compensated by the trainer of com-

  requires switching gates including a diff block

  ferentiation and a threshold element, The fact that the choke has an auxiliary winding inserted in the circuit of the current to be measured, the role of this auxiliary winding being played by the primary of the current transformer, makes it possible to limit the switching currents passing through the switching gates at the level of the choke supply current. The inverter control signal trainer represents in this

  case a scaling element.

  A further reduction in dimensions is obtained

  is due to the fact that as the main winding of the inductor the secondary output of the current transformer is used, embracing the magnetic circuits of the inductor and the current transformer.

  The invention will be explained in a description

  which will follow concrete versions of its implementation, with reference to the drawings, to which: FIG. 1 represents the diagram of an apparatus

  for measuring the instantaneous current value, according to the invention

  tion; FIG. 2 represents the diagram of a device for measuring the instantaneous current value, a second version of

  its implementation using a self winding auxi-

  liar, according to the invention; Figure 3 shows an arrangement diagram of the windings of the inductor and the current transformer

  on the magnetic circuits according to the invention.

  The device for measuring the instantaneous current value comprises a current transformer 1 (FIG. 1)

  a primary 2 of which is connected to the measured current circuit

  rer, and the terminals of a control secondary 3 are re-

  linked to the inputs of a trainer 4 of control signals for switching gates The outputs of trainer 4 are

  connected to the control inputs 5, 6 of the communication doors

tation 7 and 8 placed in series.

  The switching door 7 comprises a switching element 9 with unidirectional conduction, and a diode 10, while the switching door 8 comprises a switching element with unidirectional conduction 11 and a diode 12 The terminals of the circuit composed of the switching doors 7 , 8 are connected to a DC voltage supply source 13 having its midpoint 14. The common point 15 of the switching gates 7, 8 is linked to one of the terminals of an output secondary 16

  of the current transformer 1 through a choke 17.

  The other terminal of the secondary 16 is connected by the intermediary

  re of a resistance 18 at the midpoint 14 of the source

supply 13.

  In parallel with the resistor 18 is connected

  a voltmeter 19 whose voltage corresponds to the ins-

of the current to be measured.

  The formatter 4 for control signals of the switching gates comprises a differentiation block 20 and

  a threshold element 21 placed in series, the outputs of the element

  threshold 21 serving as outputs for the trainer 4.

  Another implementation version of the app

  same measurement of instantaneous current value is pos-

  sible when the primary 2 (figure 2) of the current transformer 1 embraces the magnetic circuit 22 of the inductor 17 and serves as an auxiliary winding / section 23 in the figure

  2 of choke 17 This avoids the need for compensation

  tion of the delay in the current circuit, and therefore

  the trainer 4 for control signals of the control doors

  mutation represents an element of scaling.

  As the main winding (section 24 in Figure 2) of the choke 17 serves the output secondary 16 of the current transformer 1, respectively embracing the magnetic circuits 22 (Figure 3), of the choke 17 and

of the current transformer 1.

  The operation of the

  instantaneous current value consists of the following.

  A current to be measured i 1 passes through the primary 2 (figure 1) of the current transformer 1 The switching gates 7, 8 together with the current transformer 1 and the inductor 17 constitute a multivibrator where the switching is done using the existence of a secondary current reaction i 2 whose circuit is closed by the inductor 17, the output secondary 16, the control secondary of the current transformer 1 and the formatter 4

  of control signals for switching gates.

  The oscillation frequency of said multivibrator is adopted high, and it is a function of the inductance value of the inductor 17, the time constant of the differentiation block 20 and the width of the hysteresis loop of the element threshold 21 produced in the form of a Schmidt flip-flop By measuring the currents varying at frequencies between 0 and 150 Hz, a switching reference of the switching gates 7, -8 is chosen

  in the tens of k Hz range, for example, 50 k Hz.

  During operation of the multivibrator it

  permanently produces the reversal of alternating magnetization

  native to the current transformer core, this allows

  both to transfer both direct and alternating current

  native from the current measurement circuit to the output secondary 16 The transformation of the current i 1

  to be measured in secondary current i 2 is done using the equalizer

  lity of the ampere-turn values of primary 2 and second-

  output area 16 of the current transformer 1 l The secondary current i 2 passes through the resistor 18 whose voltage corresponds to the instantaneous value of the

  current ia to measure The voltage drop on the resistance

  this 18 is adopted small compared to the voltage of

the power source 13.

  Let i 1 be the constant value current passing through the primary 2 of the current transformer 1 (indicated by an arrow in Figure 1); the secondary current i 2

  will then have the direction indicated by the arrow i 2.

  With the switching door 7 open, the

  current i 2 = ki 1, where k is the coefficient of proportion-

  nality, goes through the switching element 9 through the inductor 17, the output secondary 16 and the resistor 18 under the action of a positive voltage from the power source 13 Under the effect of this voltage

  a magnetization reversal of the magnetic circuit occurs

  tick 25 from the current transformer 1 to the positive values of the induction At a certain moment the saturation of this magnetic circuit 25 begins, the current i 2

then increasing.

  Thanks to the choke 17 the speed of variation of the current i 2 is limited, and when the saturation of the current transformer 1 begins, the tensioms are redistributed on the choke 17 and the winding

  16 so that the voltage rises to inductor 17 and decreases

  bare at windings 16 and 3 When the voltage drops to

  winding 3, it forms at the outlet of block 19 of diff

  ferentiation an alternating voltage, and at the moment of passage

  by zero of it the threshold element 21 elaborates a

  general controlling the blocking of the switching element 9.

  The element 9 being blocked, the current i 2 begins to pass through the diode 12 of the switching gate 8 At the winding 16 of the current transformer 1 applies from this moment a negative voltage, and begins the reversal d magnetization of the magnetic circuit 25 to

  negative induction values After a certain

  riode begins the saturation of the magnetic circuit 25 of the current transformer 1 in the field of induction

  negative The voltage at choke 17 then starts to rise

  worm, and at winding 3, to lower The block of differentia-

  tion 20 and the threshold element 21 form a com-

  command that unlocks element 9 and the process starts again.

  Thanks to the fact that the inductance of the self 17, the

  time constant of the differentiation block 20 and the lar-

  geur of the hysteresis loop of the threshold element 21 are adopted in a predetermined proportion, it becomes

  possible to obtain an operating regime without saturation

  tion of current transformer 1 Consequently, there are no pulses of current i 2 passing through the

resistance 18.

  The operation of the

  instantaneous value of the current together with the transforma-

  current generator 1 and choke 17 joined together constructively

tive resides in the following.

  The switching doors 7 (FIG. 2), 8 together with the current transformer 1 and the choke 17 constitute a multivibrator ensuring permanently

  alternating magnetization reversal of the magnetic circuit

  tick 25 of the current transformer 1 as well as a transformation of the current i 1 from the measurement circuit

  to the secondary circuit of current i 2 The ma-

  genetics 22 of the choke 17 is without air gap but it pre-

  feels a greater saturation induction by comparison

  sound with that of the magnetic circuit 25 of the transformer

  of current which is due to the use of materials

different genetics.

  Let, il and i 2 be the currents passing con-

  formally to the arrows in Figure 2, and element 9 is

  unlocked Under the action of a positive tension of the

  this feed 13 the magnet reversal occurs

  tation of the magnetic circuits 22, 25 of the choke 17 and

  from current transformer 1 to positive inductions

  ves, and at any time the magnetic circuit 25 of the current transformer 1 is saturated There is no magnetic saturation of the magnetic circuit

  22 of choke 17 because it has greater value

  their saturation induction that the transformer of

  current 1 Therefore at the time of saturation of the transformer

  current indicator I the value of i 2 will remain unchanged and

  will correspond to it 'the tension in its winding 3 tom-

  bera to 0, and then after changing signs will rise.

  Respectively, the voltage will vary at the output of the formatter 4 made in the form of scaling elements, and the element 9 will be blocked A negative voltage from

  the power source 13 then applies to the winding-

  ment 16, and begins the reversal of magnetization of

  magnetic circuits 22, 25 of the choke 17 and the transformer

  current dimmer 1 to negative inductions; After a certain period, the magnetic circuit 25 of the current transformer 1, the voltage in the winding 3 and at the output will occur.

  of the trainer 4 will change sign, and the switching door

  tion 7 will become conductive The saturation of the transformation

  current dimmer 1 will not then be accompanied in the negative induction zone by a variation of the current since the magnetic circuit 22 of the inductor 17 will remain unsaturated Thus, it is ensured in the measuring device

  of the current the shaping of a signal in the resistance

  ce 189 this signal being in proportion with the current to me-

  safe and not containing pulsations due to saturation

  ration of the magnetic circuit 25 of the current transformer. The present invention therefore makes it possible to simplify

  construction of the instantaneous value measurement device

  tane current thanks to the fact that the output signal at low pulsation level is obtained without recourse to a

  current transformer with air gap

  bent and unreliable in the circuit of the current to be measured

  nor to an RC filter with a large time constant.

Claims (4)

R E V E N D I C A T I 0 N S   1 Current value measuring device of the current type comprising a current transformer (1) by a   primary (2) from which the current to be measured flows, and a   control terminal (3) which is electrically connected to the control inputs (5, 6) of two series switching doors (7, 8), the common point (15) of which is electrically coupled to one of the terminals an output secondary (16) of the current transformer (1), another terminal of the output secondary (16) being connected to the midpoint (4) of a source (13) for supplying the switching gates by through a resistance (18) the   voltage at this resistor corresponding to the ins-   tantane of the current to be measured, characterized in that it comprises a choke (17), which has a terminal connected to the common point (15) of the switching gates (7, 8), and the other terminal connected to one terminals of the output secondary (16) of the current transformer (1), and a formatter (4) of control signals of the switching gates whose inputs are connected to the terminals of the secondary control (3) of the current transformer (1 ), and the outputs to   control inputs (5, 6) of the switching doors (7,8).   2 measuring device according to claim 1,   characterized in that the control signal formator (4)   of switching gates includes a differential block   tiation (20) and a threshold element (21) in series intended   to compensate for the delay due to the self at the frequency of oscillation- self-excited lations.   3 Measuring device according to claim 1, characterized in that the primary (2) of the transformer   current (1) embraces the magnetic circuit (22) of the choke 17.   4 Measuring device according to claim 3,   characterized in that the output secondary (16) of the trans-   current trainer (1) embraces the magnetic circuit (22) of the self (17).