EP0530072A1 - Method and device for control and regulation - Google Patents

Abstract

The invention relates to a device for control of a quantity x, by acting on a control quantity y with which the quantity x is in a one-to-one relationship when the value of a parameter h to which the quantity x is sensitive remains constant, the quantity x itself being, for each of the controlled values xp, a one-to-one function of the parameter h, the parameter h being capable of varying in an interval including a reference value hi, and for each of the values xp it is known to define a function yp = gp(h), yp being the value to be given to the quantity y to obtain the value xp when the parameter has the value h, the various functions gp(h) having the property that the value of a second function gp, (h) may be deduced from the value of a first function gp(h) for the same value of the parameter h by addition of a term known as a function of the difference between the real measured value hr of the parameter h and the reference value hi, the device being characterised in that the quantity x is represented by the output magnitude of an operational amplifier (10) having two inputs, a first (11) and a second (12) and in that to the first input (11) is applied, by means of a control 200, a voltage Ui representative of the control quantity yi to be applied in order to obtain the output quantity of value xi when h has the value hi, to the second input (12) a voltage Vc is applied which is the output quantity corrected by a correction device (40) of a sensor (30) of the parameter h, the output of the sensor (30) being corrected by the device (40) so that the corrected voltage Vc is equal to zero when h = hi and, in the opposite case equal to H(hr - hi). <IMAGE>

Description

The invention relates to methods and devices intended to control using a first quantity y a second quantity x this second quantity being itself for each of the values of the quantity x a known function of a parameter h that l 'we don't control. The method assumes that the quantity y is a one-to-one function of x: y = f (x) and that for each of the values of the quantity x such that x _p , x _p is a one-to-one function of a parameter h such that (x _p ) = f _p (h). It also follows that for a value of x _p , y is a function of h, y _p = g _p (h).

The method and the device according to the invention are applicable whenever a point of abscissa h of the curve representing a second value y₂ (h) can be deduced from the point of the same abscissa h of the curve representing a first value y₁ ( h) by adding a value which is a linear function of h. The invention can be extended to an initial control quantity Y one-to-one function of the quantity y, controlling a value X one-to-one function of the variable x. The functions Y _(y) , X _(x) and Y _{(X) are} not necessarily linear.

The invention relates in particular but not exclusively to a voltage control intended to polarize a diode with an intrinsic zone in current. In this application the first quantity y is a control voltage U, the controlled value x is the bias current I of the intrinsic zone diode and the parameter h influencing the value of the current is the temperature T of the diode. The need to strictly control the value of the direct bias current I of a PIN or PIN intrinsic zone diode is encountered each time in a circuit we want to control the value of the resistance R of this diode and in particular each time the diode has a controllable attenuator function.

The embodiments according to the known art do not make it possible to obtain commands for the bias current I of the intrinsically-zone diode that are well regulated in temperature and having switching times between two very short command values. In the embodiments according to the prior art, either the order is well temperature regulated but then the switching times are long, or the temperature regulation is ineffective.

The aim of the present invention is therefore to allow rapid control using a quantity y and effective regulation of a quantity x which for each of its values x _p is a known function f _p (h) d ' a parameter h, which implies that for each value x _p the quantity y is a function y _p = g _p (h), when the different functions g _p (h) have the property that the value of a second function g _p ′ (H) can be deduced from a value of a first function g _p (h) for the same value h by adding a constant term and a term proportional to the difference between the real value of h, h _r and a reference value h _i .

Another object of the invention is to be able to supply this command and this regulation over a wide range of values of the quantity x and over a wide range of variations of the parameter h.

Another object of the invention is to allow this command between a minimum value x _m and a maximum value x _M with a large number of control steps.

To carry out the invention, the properties of the operational amplifiers are used.

We know that the output voltage of an operational amplifier is proportional to the difference of the voltages applied to each of its two input terminals. It is this property which will be used in the method according to the invention. For this we will apply to one of the input terminals a voltage U _i equal to the voltage that should be applied to obtain, if the parameter h had a reference value h _i , the value x _i that we want get.

A zero value will be applied to the other input if the value of the parameter h is effectively equal to h _i and which will otherwise be equal to a value which is a function of the difference between the real value of the parameter h _r and the reference value h _i . The value applied to the other input will be equal to H _(hr-hi) , H _(hr-hi) being the value of the correction to be applied to U _i to obtain the value x _i when h is not equal to h _i but at h _r . To apply the process, it is therefore necessary to measure the parameter h at the place where this parameter influences the quantity x and to create by calculation or by any other means the correction necessary to take account of the real value h _r of the parameter h.

The method and the device according to the invention are particularly well suited when the change in the control voltage U _i results in self-regulation as a function of the parameter h of a part of the means ensuring the correction H _(hr-hi) .

The invention therefore relates to a method for controlling a quantity x between two values x _m and x _M , by action on a control quantity y with which the quantity x is in one-to-one relation when the value of a parameter h at which is sensitive, the quantity x remains constant, the quantity y having to vary between two values y _m and y _{M in} order to vary the quantity x from x _m to x _M when the parameter ha has a reference value h _i , the quantity x being itself for each of the values x _p ordered a one-to-one function of the parameter h, the parameter h being capable of varying within a predetermined interval including the reference value h _i , h _m h _M so that we can define for each of the values x _p of the variable x a function y _p = g _p (h), y _p being the value to be given to the quantity y to obtain the value x _p when the parameter has the value h, the different functions g _p (h) having the property that the value of a second function g _p , (h) can for any value of h included in the interval h _m h _M be deduced from the value of a first function g _p (h) for the same value of the parameter h, by addition of a known term as a function of the difference between the actual measured value h _r of the parameter h and the reference value h _i , process characterized in that the quantity x is represented by the output quantity of an operational amplifier having two inputs a first and a second and in that one applies to the first input a voltage U _i representative of the control quantity y _i to be applied to obtain the output quantity of value x _i when ha the reference value h _i , the voltage U _i varying from U _m to U _M when x _i varies from x _m to x _M ; a voltage V _c is applied to the second input which is the corrected output quantity of a sensor of parameter h, the output of the sensor being corrected so that the corrected voltage V _c is equal to 0 when h = h _i and otherwise equal to H (h _r -h _i ), the function H _(hr-hi) representing the value of the correction to be applied to the control quantity U _i to obtain the value commanded x _i when the parameter h changes from the reference value h _i to the measured value h _r

A particularly simple embodiment of the invention is obtained when the laws of variation of y as a function of the parameter h are linear. In this case, the sensor of the quantity h can be a linear sensor, the slope of the output quantity of the sensor as a function of h being of equal value and of sign opposite to one of the slopes of y _p as a function of h.

The invention is also well suited to the case where the different functions U _p (h) are arbitrary but deducible from one another by linear transformation.

In these two cases h _i designating a value of the interval h _m h _M a point of abscissa h of a second curve representative of y _p , as a function of h is deduced from the point of the same abscissa h of a first curve representative of y _p as a function of h by adding a constant term and a term proportional to the difference (hh _i ). The proportionality coefficient is when the curves are straight lines the ratio of the slopes of the second and the first line.

Preferably the reference value h _i is chosen in the middle of the variation range of h so that $${\text{h}}_{\text{i}}\text{=}\frac{{\text{h}}_{\text{m}}{\text{+ <figure-callout id="2" label="h M" filenames="imgf0003.png,imgf0004.png" state="{{state}}">h </figure-callout>}}_{\text{M}}}{\text{2}}$$

Preferably the reference function y _pr = g _pr (h) from which the other functions g _p (h) are deduced is chosen so that it corresponds to the function for which the quantity x _p ordered is located at center of the range of variation of the quantity x so that this value x _pr is equal to: $${\text{x}}_{\text{pr}}\text{=}\frac{{\text{x}}_{\text{m}}{\text{+ x}}_{\text{<figure-callout id="2" label="M" filenames="imgf0003.png,imgf0004.png" state="{{state}}">M</figure-callout>}}}{\text{2}}$$

In the particularly simple case where the laws of variation of y as a function of the parameter h are linear, the correction voltage can be applied by means of an operational amplifier, the gain of which is made proportional to the slope of the line representing the quantity y _p as a function of the parameter h, when the controlled quantity x has the value x _p . The gain variation is obtained by changing the value of a resistor placed in an amplifier feedback circuit.

par le nombre v de pas fins soit $$\frac{{\text{y}}_{\text{M}}{\text{-y}}_{\text{m}}}{\text{uv}}$$

If necessary, the correction voltage is the sum of two voltages, a so-called large step voltage obtained by dividing the total variation y _M -y _m by the number u of large steps and a so-called fine step voltage obtained by dividing the worth a big step either $$\frac{{\text{y}}_{\text{M}}{\text{-y}}_{\text{m}}}{\text{u}}$$

by the number v of fine steps be $$\frac{{\text{y}}_{\text{M}}{\text{-y}}_{\text{m}}}{\text{uv}}$$

The method and the device according to the invention will be described below in the case of application to the current control of a PIN diode.

• la figure 1 représente la variation de la résistance R d'une diode à zone intrinsèque PIN ou NIP lorsqu'elle est polarisée en direct par un courant I;
• la figure 2 représente la valeur de la tension U à appliquer à une diode ayant un courant de sortie constant lorsque la température varie pour différentes valeurs de courant ;
• la figure 3 représente un grossissement à des fins explicatives de courbes de la figure 2 ;
• la figure 4 représente des courbes de valeurs que doit prendre une grandeur de commande y pour garder constante une grandeur commandée x lorsqu'un paramètre auquel est sensible la grandeur x, varie ;
• la figure 5 représente un schéma de l'invention sous sa forme la plus générale ;
• la figure 6 représente des droites dites de correction de la valeur de la tension de commande en fonction du paramètre h ;
• la figure 7 représente la forme de réalisation de l'invention lorsque les fonctions y_p = g_p(h) sont linéaires ;
• la figure 8 représente une manière de réaliser l'invention lorsque la grandeur y est elle-même commandée par une grandeur Y et que la variable commandée en finale n'est pas la variable x mais une variable X fonction biunivoque de x ;
• la figure 9 représente le schéma synoptique d'ensemble de la réalisation particulière.
• la figure 10 illustre les résultats obtenus.

A general embodiment, a particular exemplary embodiment of the method and a device intended to apply the method for this particular exemplary embodiment will be described below with reference to the appended drawings in which:

• FIG. 1 represents the variation of the resistance R of a diode with an intrinsic zone PIN or NIP when it is directly biased by a current I;
• FIG. 2 represents the value of the voltage U to be applied to a diode having a constant output current when the temperature varies for different current values;
• Figure 3 shows a magnification for explanatory purposes of the curves of Figure 2;
• FIG. 4 represents curves of values which a control quantity y must take to keep a controlled quantity x constant when a parameter to which the quantity x is sensitive varies;
• FIG. 5 represents a diagram of the invention in its most general form;
• FIG. 6 represents so-called straight lines for correcting the value of the control voltage as a function of the parameter h;
• FIG. 7 represents the embodiment of the invention when the functions y _p = g _p (h) are linear;
• FIG. 8 represents a way of implementing the invention when the quantity y is itself controlled by a quantity Y and the variable ordered in the end is not the variable x but a variable X one-to-one function of x;
• FIG. 9 represents the overall block diagram of the particular embodiment.
• FIG. 10 illustrates the results obtained.

The particular example of application of the invention which follows relates to the control of a bias current of a PIN diode.

As explained above, it is known that the resistance of the diode is determined by the intensity I of the bias current. The curve representing the value of R as a function of I is represented in FIG. 1.

This curve shows that R is a one-to-one function of I so that the control of I leads to the control of R. In this example embodiment the control quantity "y" will be represented by the voltage U which should be applied to the input of an operational amplifier to obtain the value x represented here by the bias current of a diode connected to the output of the amplifier.

The parameter h is represented by the temperature T of the diode. It is known that when the temperature T of a PIN diode increases the bias voltage to be applied to the diode to obtain a constant output current I decreases.

The curves representing the voltage U which it is necessary to apply to the input of the amplifier to obtain a constant current when the temperature T varies are represented in FIG. 2 for values of I of 1uA, 1mA and 10mA.

These are straight lines with different slopes.

Two of these lines have been shown in FIG. 3, one of these lines, D _p represents the value of U as a function of T when the bias current is I _p the second D _i represents the value of U when the bias current is I _i (I _i > I _p ).

We see in this figure that the line D _i can be deduced from the line D _p as follows.

Let D₃ be the line passing through the point A of the line D _p , with coordinates T _i and U _i , and parallel to the line D _i A point on the line D _i is deduced from a point on the line D₃ thus constructed by addition to the value of U represented by the line D₃ for a value of T of a constant value equal to AA _i , A _i being the point of the line D _i of abscissa T _i .

The line D₃ thus constructed is deduced from the line D _p by addition to the value U _T given by the line D _p for an abscissa T of a magnitude (U - U _T ) proportional to the difference between T and T _i , the coefficient of proportionality being in this case the ratio of the slopes of the lines D _i and D _p .

It follows that the line D _i representing U as a function of T when I at the value I _i is deduced from the line D _p representing the value of U when I has the value I _p , except for an additive constant which is here AA _i by addition to the ordinate U _(T) obtained on the line D _p for the value T of a quantity K _ip (T - T _i ), the coefficient of proportionality K _ip being in this case equal to the ratio of the slopes of the lines D _i and D _p .

It follows that a point of a second straight line representing U as a function of T for a constant value I is deduced well from a point of abscissa T of a first straight line by addition to the ordinate of the point of abscissa T on the first line of a constant term, here AA _i and of a term proportional to the value of the abscissa difference (T - T _i ), T _i designating a value between the minimum temperature T _m and the maximum temperature T _M.

The different curves are not necessarily straight lines, thus FIG. 4 represents a set of three curves C₁, C₂, C₃, each of the curves representing the value to be given to the quantity y to keep the quantity x constant when the parameter h varies.

It also represents a point A on the curve C₁ of coordinates h _i y _i and a point A _i on the curve C₃ of abscissa h _i . The method is applicable if any point B of the curve C₃ of abscissa h is deduced from point C of abscissa h of the curve C₁ by addition to the ordinate of C of the value AA _i and of a term proportional to y _{(h - hi)} , the proportionality coefficient being the same for all the points C and B of the curves C₁ and C₃, or of the curves C₁ ′ C₃ ′ obtained by a first transformation of C₁ and C₃.

A device making it possible to carry out the invention in its most general form will now be described with reference to FIG. 5.

This figure represents a PIN1 diode whose resistance R is therefore to be controlled, therefore the current by means of a control voltage U. The command and control device is constituted by means 2. This means applies to the input of a operational amplifier of great internal resistance 10 having two inputs a first 11, a second 12 and an output 13, the control voltage U, as follows. The input 11 of this amplifier receives from a control circuit 200 a voltage U _i which would be the voltage to be applied to obtain a value I _i of the controlled current if the temperature of the diode had the reference value T _i .

The input 12 of this amplifier is supplied by the output of a temperature sensor 30, this output being corrected by means 40 which receives the value of the command from the control circuit 200. The sensor 30 is preferably located near the diode PIN 1 so that the temperature it senses is as close as possible to that of the diode.

As explained above, the method and the device according to the invention are particularly advantageous when the device for correcting the voltage delivered by the sensor 30 is self-regulating. It was seen above that when the functions y _(p) = g _p (h) are deductible from one another by linear transformation it is possible to obtain this result by using an operational amplifier. The curves representing U as a function of T for constant I are straight lines (see Figure 2). The corrections to be applied are shown in figure 6 in dotted lines.

In this figure, the reference value T _i is equal to 20 °, central value of the range -40 ° + 80 °.

The line B₁ of correction 1 has a slope opposite to the line I₁ representing U in function T for 1 equal to a first constant 1. The same is true for the lines B₂ B₃ of correction 2 and 3 and the lines I₂ and I₃, I = constant 2, I = constant 3.

The correction line B₁ crosses the line I₁ at a point on the abscissa T _i = 20 °. It is the same for the correction lines 2 and 3 and the lines I = constant 2 and I = constant 3. This means that for T = 20 °, the value to be applied to terminal 12 is equal to 0.

When T is different from 20 ° a correction should be applied, which for example if I = constant 1 is the desired value, must be proportional to the difference of ordinate between the line I = constant 1 and the line B droite of correction 1 for the abscissa T considered.

It has been seen that it is possible to produce a device using an operational amplifier. Such a device is shown in Figure 7. This figure is identical to Figure 5 but the device 40 has been detailed. It comprises an operational amplifier 41 comprising an output 12 and two inputs 43, 44. A feedback loop 47 brings the output voltage to the input 43 via a variable resistor 46, the input 43 also receives the output voltage of the sensor 30, the variable resistor 46 is controlled by the command 200. The value of the resistor 46 is such that the gain of the operational amplifier 41 is proportional to the value of the slope of the correction line used for the value ordered.

The operation is as follows:
When T = T _i the output voltage of the amplifier 41 is zero. It then varies in proportion to the difference between T and T _i , the value of the variation slope being fixed by the value of the gain of the operational amplifier itself controlled by the value displayed for the current I by the command 200.

The output 12 of the operational amplifier 41 is the second input of the operational amplifier 10.

The command 200 which controls the value of the voltage at the input of the amplifier 10 and the value of the resistor 46 placed in the counter loop reaction 47 has two parts 210 and 220 for performing each of these functions.

An embodiment of the control part 210 in connection with the input 11 will now be described with reference to FIG. 8.

In this embodiment the arrival of the command is made in decibel, that is to say in logarithmic value, a first linearization would therefore be necessary to return to the value of linear attenuation. The desired loss is a linear function of the value of the resistance entered to achieve the loss. The resistance introduced is the resistance of the PIN 1 diode, the variation curve of which as a function of I is shown in FIG. 1.

Since this curve is not a straight line, it would be necessary to introduce a second linearization transformation so that the means 40 works well in a linear fashion as indicated above with reference to the description of FIG. 7. These two linearizations are introduced in one. Finally in this embodiment, given the precision sought, a very fine pitch was required, this is obtained by splitting the control voltage into two steps, a large pitch and a fine pitch, the two voltages being added.

The control part 210 200 is produced in the following manner. The input command 201 coded on 6 parallel bits 201a to 201 f is supplied with a clock signal. It therefore makes it possible to obtain 2⁶, ie 64 attenuation steps distributed here between 0 and 64 decibels in steps of 1 decibel.

These signals are set to TTL 0.5 V standards by a D 202 flip-flop controlled by the clock signal.

The binary output word 203 of the flip-flop 202 which represents the input value to the TTL standards addresses two parallel circuits, one of these circuits whose reference numbers are simple represents the control of large pitch, the other whose Reference numbers are the same but with a prime sign represents the end pitch command. The description and operation of the large pitch control will now be described. The binary word 203 at the output of the flip-flop 202 addresses a programmable memory 204 whose boxes allow the storage of 8 bits. The values stored in the memories make it possible to carry out a transposition achieving the linearization mentioned above. We understand that because of the linearization the width of the steps at the output of the memory is variable and that one may need very fine steps which can only be achieved by coding on a larger number of bits.

It is also understood that such a transposition method makes it possible to linearize the relations of two quantities in one-to-one correspondence with one another.

The output information of the addressed box of the memory 204 are resynchronized by a flip-flop D 205 and sent to a digital analog converter (ADC) 206. The latter behaves like a resistor whose value changes according to the input values received .

The fine pitch command comprises the same elements having the same functions, ie a set of memory boxes 204 ′ a flip-flop 205 ′ and a digital analog converter 206 ′. The two resistors constituted by the two converters 206 and 206 ′ are connected in parallel between a reference voltage generator not shown and the input 207 of an operational amplifier 208.

The output 11 of this amplifier is the input of the adder amplifier 10 of FIG. 7.

The remainder 220 of the command 200 will now be made with reference to FIG. 9 which represents a simplified diagram giving a synoptic vision of the command and regulation assembly.

This figure shows that the attenuation control word 203 coming from the flip-flop 202 is sent not only to the transformation device represented in FIG. 8 by memories 204, flip-flops 205 (not represented in FIG. 9) and converters 206 but also towards an analog device 220 having an identical function constituted by a memory group 221 a flip-flop 222 and a digital analog converter 46 which plays the role of variable resistance as explained during the description of FIG. 7. The values displayed in the addressed memories by the control word 203 reproduce the image of a curve noted during preliminary tests on a diode PIN 1 mounted, under the same conditions. They represent the values of resistors 206 respectively 46 to be displayed to obtain the controlled loss.

Programming of the memories can be done manually using coding wheels remaining in the memories. One notes, in a table for T = T _i the decibel attenuations by decibel up to 64 and the corresponding word on each of the coding wheels. This information is then entered on the keyboard of a programmer for each of the memories

The programming of memories can also be computerized.

The output voltage of the temperature sensor 30 constitutes the reference voltage supplying the converter 46 and the input 43 of the operational amplifier 41. It is produced from a bare sensor and adapted for example by means of an amplifier operational so that its output voltage is equal to the supply voltage of the input 44 of the operational amplifier 41 when the temperature is equal to the reference temperature T _i .

In the case of implementation, the adaptation is particularly simple because the curves U as a function of T are straight lines and there are sensors on the market giving a linear voltage as a function of temperature. This is why it is possible to be satisfied in this case with an adaptation by operational amplifier. In the more general case where the variation curves of the quantity y as a function of h are arbitrary but deducible from one another by linear transformation, the adaptation may include a memory converter association to establish a corrected sensor output having the form of one of the functions y _p (h).

We therefore see that in this embodiment the input quantity Y which is here a decibel loss, controls a value y which is here the value of the voltage U applied to the input of the operational amplifier 10 which, in turn, -same, conditions the value of a quantity x which is here the value of the output current I of the amplifier 10 which itself conditions a quantity X which is the value of the resistance of the diode PIN 1.

The attenuation obtained is almost constant when the temperature T varies from -20 ° to + 80 °. The values obtained for a 16 dB and 37 dB command are shown in Figure 10.

The switching times between two commands are of the order of 200 nanoseconds.

Claims (15)

1 Method for controlling a quantity x between two values x _m and x _M , by action on a control quantity y with which the quantity x is in one-to-one relation when the value of a parameter h to which the quantity x is sensitive remains constant, the quantity y having to vary between two values y _m and y _M to vary the quantity x from x _m to x _M when the parameter ha has a reference value h _i , the quantity x being itself for each of the values x _p ordered a one-to-one function of the parameter h, the parameter h being capable of varying within a determined interval including the reference value h _i , h _m h _M so that we know how to define for each of the values x _p (h), of the variable x a function y _p = g _p (h), y _p being the value to be given to the quantity y to obtain the value x _p when the parameter has the value h. the different functions g _p (h) having the property that the value of a second function g _p (h) can for any value of h lying in the interval h _m , h _M be deduced from the value of a first function g _p (h) for the same value of the parameter h by adding a known term as a function of the difference between the actual measured value h _r of the parameter h and the reference value h _i , process, characterized in that the quantity x is represented by the output quantity of an operational amplifier having two inputs, a first and a second and in that one applies to the first input a voltage U _i representative of the control quantity y _i to be applied to obtain the quantity of value output x _i when ha the reference value h _i the voltage U _i varying from U _m to U _M when x _i varies from x _m to x _M ; a corrected voltage V _c is applied to the second input which is representative of the corrected output quantity of a sensor of the parameter h, the sensor output being corrected so that the corrected voltage V _c is zero when h = h _i and otherwise equal to H (h _r -h _i ), the function H (h _r -h _i ) representing the value of the correction to be applied to the control quantity U _i to obtain the commanded value x _i when the parameter h goes from the reference value h _i to the measured value h _r . 2. Method according to claim 1 applicable in the case where the functions y _p = g _p (h) are linear functions of h defined by their slopes a _p and where the sensor used gives a linear voltage as a function of h, characterized in this that the correction voltage applied to the second input of the operational amplifier is the output voltage of another operational amplifier having two inputs, a first and a second and which receives on the first of its inputs a reference voltage and on the second of its inputs the output voltage of the sensor, the gain of the amplifier being made proportional to a _p by action of the quantity y on a resistor placed in a feedback loop placed between the output and the second input of the other operational amplifier. 3. Method according to claim 1 applicable in the case where the functions y _p = g _p (h) are any functions deducible from each other by linear transformations, characterized in that the sensor used is adapted to reproduce l 'one of the curve y _p = g _p (h). 4. Method according to claim 1, characterized in that the reference value of the parameter h _i is located in the center of the range of variation of the parameter h. 5. Method according to one of claims 1 or 2, characterized in that the reference function y _pr = g _pr (h) from which the functions g _p (h) will be created is that which gives the quantity x its average value $$\frac{{\text{x}}_{\text{m}}{\text{+ x}}_{\text{M}}}{\text{2}}$$

6. Method according to claim 2 applicable in the case where the quantity y is itself a one-to-one function of another control quantity Y and where the variable x acts directly on the value of another variable X which is prefers to order by Y, Y and X being in these conditions in one-to-one relation, characterized in that the quantity Y is subjected to a transformation so that each value of the quantity Y corresponds to the value y which will ultimately give the magnitude X the desired value. 7. Control device for a quantity x between two values x _m and x _M , by action on a control quantity y with which the quantity x is in one-to-one relation when the value of a parameter h to which the quantity x is sensitive remains constant, the quantity y having to vary between two values y _m and y _M to vary the quantity x from x _m to x _M when the parameter ha has a reference value h _i , the quantity x being itself for each of the values x _p ordered a one-to-one function of the parameter h, the parameter h being likely to vary within a predetermined interval including the reference value h _i ,, h _m h _M so that we can define for each of the values x _p a function y _p = g _p (h), y _p being the value to give to quantity y to obtain the value x _p when the parameter has the value h, the different functions g _p (h) having the property that the value of a second function g _p , (h) can for any value of h included in the interval h _m h _M deduce from the value of a first function g _p (h) for the same value of the parameter h by adding a known term as a function of the difference between the actual measured value h _r of the parameter h and the reference value h _i , device characterized in that the quantity x is represented by the output quantity of an operational amplifier (10) having two inputs a first (11) and a second (12) and in that one applies to the first input (11) by means of a command 200 a e voltage U _i representative of the control quantity y _i to be applied to obtain the output quantity of value x _i when ha the reference value h _i , the voltage U _i varying from U _m to U _M when x _i varies from x _m to x _M , a voltage V _c is applied to the second input (12) which is the output quantity corrected by a correction device (40) of a sensor (30) of the parameter h the sensor output (30) being corrected by the device (40) so that the corrected voltage V _c is equal to 0 when h = h _i and otherwise equal to H _(hr-hi) , the function H _(hr-hi) representing the value of the correction to be applied to the control quantity U _i to obtain the commanded value x _i when the parameter h changes from the reference value h _i to the measured value h _r . 8. Device according to claim 7, characterized in that the control (200) comprises a first part (210) which controls the voltage U _i applied to the input U of the operational amplifier (10) and a second part 220 which controls the correction device (40). 9. Device according to claim 8 usable in the case where the functions y _p = g _p (h) are linear functions of h defined by their slope a _p , characterized in that the sensor (30) is a linear sensor and in that the correction device (40) consists of an operational amplifier (41) having two inputs a first (44) and a second (43) and an output (12) the first input (44) receiving a reference voltage and the second (43) receiving the voltage output of the sensor (30), the gain of the amplifier (41) being made proportional to a _p by a resistor (46) placed in a feedback loop (47) between the output (12) and the second input (43) the value of the resistance (46) being controlled by the part (220) of the control (200). 10. Device according to claim 8, characterized in that the control part (210) is constituted by a rocker D (202) having an input (201) and an output (203) the input (201) receiving the word control and the output (202) addressing a memory (204), the output of the memory (204) controlling an analog-digital converter (206) constituting a variable resistor connected to one of the inputs (207) of an operational amplifier ( 208) whose output (11) constitutes one of the inputs of the operational amplifier (10). 11. Device according to claim 10, characterized in that a flip-flop D (205) is interposed between the memory (204) and the converter (206). 12. Device according to claim 8, characterized in that the control part (210) is constituted by a rocker D (202) having an input (201) and an output (203) the input (201) receiving the word of control and the output (203) addressing two parallel lines, a first and a second, the first of these lines constituting a large pitch control and the second a fine pitch control, characterized in that each of the parallel lines has a memory (204, 204 ′) Addressed by the word at the output of the flip-flop D (203). controlling an analog to digital converter (206-206 ′) constituting a variable resistor connected to one of the inputs of an operational amplifier (208) whose output (11) constitutes one of the inputs of the operational amplifier (10) . 13. Device according to claim 12, characterized in that flip-flops D (205, 205 ′) are interposed between the memories (204, 204 ′) and the converters (206, 206 ′). 14. Device according to claim 9, characterized in that the control part (220) comprises a memory (221) addressed by the control word (203), the value contained in the addressed memory controlling the resistor (46) constituted by a digital to analog converter. 15. Device according to claim 14, characterized in that a flip-flop D (222) is interposed between the memory (221) and the converter (46).

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