DE1006936B - Arrangement for electrical control devices, the control value of which is obtained by forming the difference between a setpoint and an actual value of electrical quantities - Google Patents

Description

GERMAN

The invention relates to electrical control devices in which the difference is formed between the setpoint and actual value electrical variables determines the size of the electrical control value. This is the case, for example when using magnetic amplifiers for any control or regulating purposes where there is a control error proportional differential voltage results in a control current.

In such control arrangements, the variable to be controlled is often converted by a transducer into a voltage Ui (actual value) proportional to this variable in accordance with the scheme according to FIG. 1 and compared with a fixed voltage U ₈ (nominal value). The difference between the actual value and the nominal value is then proportional to the absolute control error and serves as the input value of an amplifier device V, the output variable of which influences the variable to be controlled via an actuator. If a fixed voltage is not introduced as the setpoint, but an adjustable one by using a potentiometer P as shown in FIG . Known arrangements of this type for the input circuit of the amplifier have the disadvantage that a certain percentage change in the variable to be controlled corresponds to a control voltage of the amplifier which, in its absolute value, differs depending on the setpoint value set over its total adjustable range. This means that the percentage static control error of the arrangement, i.e. the accuracy of the control, varies with the size of the setpoint. This is particularly noticeable when, in order to avoid pendulum phenomena, which can occur, for example, with speed controls, feedbacks are required, the dimensioning and setting of which cause difficulties if the static accuracy and thus the sensitivity of the control changes within more or less wide limits .

According to the invention, these shortcomings of the known control arrangements, the control value of which by a Difference formation is obtained from a setpoint and an actual value, thereby avoiding inevitably with the setting of a new setpoint an additional device is adjusted or set in such a way that for a proportional control error that is the same in percentage terms and is the same for different ones Setpoint settings result in the same control value for the control device.

There are various possible solutions for this fundamental inventive concept. For example Inevitably with the setting of a new setpoint on the setpoint potentiometer, a series resistance is added

Arrangement for electrical

Control devices, their control value

by forming the difference from one

Setpoint and an actual value electrical

Sizes is gained

Applicant:

Siemens-Schuckertwerke

Corporation,

Berlin and Erlangen,

Erlangen, Werner-von-Siemens-Str. 50

Dipl.-Ing. Dr. Ing.Herbert Kind, Berlin-Mariendorf,

and Dipl.-Ing. Hans-Helmut Reuter, Berlin,

have been named as inventors

this can be changed or a tap on such a device can be adjusted. Should an exact observance of the condition can be achieved that with the same percentage deviation of the variable to be controlled in each case over the entire Range of the adjustable setpoint when the difference is calculated, the same control value results, see above If a series resistor is used, this must be effective, taking into account the values specified in the control arrangement Resistances, especially the resistors that can be set on the setpoint potentiometer, in their functional Dependency these can be adapted. In many cases, however, it can be sufficient, especially if it is only an approximate compliance with the specified condition that one is a linear functional dependency between the setting values on the series resistor and on the setpoint potentiometer used or complies with. To achieve this dependency, either a corresponding structure of the series resistance can be used can be selected, or such an adjusting device for the tap can also be used in connection therewith in the series resistance that they participate in the formation of the functional dependence is or brings about it alone.

For a more detailed explanation of the invention on the basis of an exemplary embodiment, reference is made to FIG. 3. In this Ui again denotes the actual value voltage and Uv the comparison voltage, while V denotes the amplifier to be controlled. P is again the setpoint potentiometer on which the desired

709 505/325

Setpoint is set. In series with the set part of the setpoint potentiometer P, the set part of the resistor R _{z is now via the tap P 1} via the tap R _zl . When a new setpoint is set on the setpoint potentiometer P, the tap R _Z1 is inevitably adjusted accordingly on the series resistor R _z , whereby the effect aimed for according to the invention is achieved.
For the effective explanation of the invention it follows

Rz = q> a (Xmin, Xmax, P, R ₁ , R ... R _n ) ■ (8)

The assumption according to formula (5) says that with a rigid coupling of the taps of the potentiometer and the additional resistor, ζ. B. in an embodiment of the arrangement with two rotary potentiometers on the same axis, the two resistors similar, z. B. both linear, is to identify the position of the potentiometer 10 can be wound. With a resistance R _z calculated according to equation (8) on the setpoint potentiometer P, the coordinate χ, a sufficient constancy of the input value of the amplifier is achieved over the entire setpoint setting range for many cases.

As an example, FIG. 4 shows in a qualitative representation the relationship between the change Δ I _s t in the control current and the position χ of the setpoint potentiometer

Λ DD

with constant relative change

introduced. It is defined by the ratio of the tapped nominal voltage U ₈ to the total reference voltage U _v on the potentiometer, i.e.

TT u _v

This means that 0; £ χ ; £ 1. x _min and x _max are the coordinates for the smallest and largest value of the range Ui

the actual voltage

by three characteristic curves, namely by the curve α for the target voltage, which can be set on the potentiometer for the operating conditions that govern the operation without additional resistance, using curve b. for operation at accurate Ab according to the invention

by creating the corresponding functional relationship between the potentiometer setting and the size of the additional resistance and by the curve c for an operation in accordance with the invention simple linear relationship between the potential

The coordinate y is also introduced. It is defined by

R _z tapped

y - .

R _z total

is true, u is Δ If the change in the control current is a percentage change p of the actual value, then the change in the control current is a function f of the other variables mentioned:

U _v denotes the entire comparison voltage lying on the setpoint potentiometer and the size of the additional resistor, as well as R ₁ to R _n further where for the potentiometer setting x _m i _n the DC resistances in the control circuit of the control arrangement (ζ. B. means of the three characteristic curve values The transverse resistance of the potentiometer P), the latter assumption in part, is justified if the requirements in the figures are not drawn, and if the assumption is made that in all three cases in the range

Xmin Si x S = Xmax should not fall below a certain static accuracy of the control arrangement and it is assumed that all other data of the control arrangement with the exception of the resistance R _z remain the same in all three cases.

In order to prevent the controlled amplifier from being damaged by excessive input values in the case of control arrangements, and / or to limit the output value 40 of the amplifier to one or both sides, it has been proposed to use a relay device comprising one or more relays at the input of the amplifier provide which responds above a certain control value, thereby switching off the amplifier and if the value for R _{z is} determined appropriately. 45 provides an equivalent voltage for the duration of this fault

AlSt ^ f ₁ [X, yRz, P, R ₁ ... R _n ). (2)

If Δ ist should remain constant as a function of χ , then it follows that

yRz = _Ψι (χ, Δ ist, p, R ₁ ... R _n ) (3)

is in general a nonlinear function of χ .

In most cases, however, a linear relationship between tap χ on the setpoint potentiometer and tap y on the additional resistor is sufficient

For example, if the following conditions are met:

For χ = x _m in let y = 0,

and (4)

for x = Xmax let y = 1,

this results in a linear relationship between y and χ

y =

Xmax Xmin

(5)

- / 2 \ X> Xmin, Xmax, R;

\ d (A ISt) dx

the input of the amplifier. An arrangement according to the invention can also be used in conjunction with such Protective devices are used. In the case of an arrangement according to the invention, however, when responding of the relay device with a constant difference between the setpoint and actual voltage increase at the terminals of the relay device because

x - Xmin , _, by switching off the parallel to the relay device

lying amplifier input the current through the additional resistor and thus the voltage drop across the latter is reduced. As a result, the The amplifier is only switched on again when the difference between the setpoint and actual value is significantly smaller and this would cause shocks to hit the amplifier input. This effect is further increased by that the dropout excitation at the relay is smaller than the response excitation.

Such a relay device can, however, then be used in conjunction with a device according to the invention use such a circuit or preparation if inevitably with a new setpoint setting

if Λ the relay device is made that despite the

dx J n \ action of the control device according to the invention and

^x ~ ^{Xmin despite the hold ratio} of the relay device das

= fs {xmin, Xmax, Rz, P, R ₁ ... R _n ) = 0. 7 ° drop of the relay device with almost the same

The most _{suitable condition for} determining R z is that at the point χ = x _min the change in AI _s t as a function of χ should be zero. So you do the math

yRz, p, R ₁ ... Rn),

(6a)

x-

-X,

min

Xmax

R _z> p, R ₁ ^ -R _n ), (6b)

P, R ₁ ... R _n ), (6c)

Difference value between the setpoint and actual voltage takes place like the response.

A solution according to the invention is z. B. achieved in that an additional series resistor on the relay device is provided, whose effective resistance value in the circuit inevitably in the setting of a new setpoint is also set in its value. This resistance is as long as the relay device has not responded as a protective device, short-circuited. If, however, the relay device speaks on, this resistor is switched on with its value in series with the relay device, so that In this way, the differential voltage between the actual and desired value is now applied to the series resistor according to the invention to the setpoint potentiometer, the resistance of the relay device and its additional resistance divides.

An example arrangement of this type is illustrated in FIG. 5 of the drawing. In this, Ut, U _v , P, R _z and V again designate the same parts with the same reference numerals as were already present in FIG.

In series in the connection line from the potentiometer P via the additional resistor R _z to the amplifier V are the switching contacts Kl and Ll of the polarized relays K and L, one of which responds when the actual voltage predominates and the other when the nominal voltage predominates. The windings of these relays are in the course of a line from the actual value line 1 via a resistor R _r , the additional _{resistor R z} to the potentiometer P. Parallel to the resistor R _r is a line in which the switching contacts K2 and L2 of the relays K and L are located . The switching elements Kl and Ll each belong to a changeover switch which, in the other switching position, is at the tap of a potentiometer Q , which is fed with the auxiliary voltage Uh. The arrangement is shown in the operating state in which it is working properly. If the difference between the setpoint voltage U _v and the actual value voltage Ut is too great, either the relay K or the relay L responds, depending on the direction of the current. The respective changeover contact Kl or Ll is then switched to the auxiliary voltage Uh , so that a corresponding voltage is then applied to the magnetic amplifier between this tap and the center tap of the potentiometer Q. At the same time, the contact K2 or L 2 of the relay K or L is opened, whereby the bridging of the resistor R _{r is} canceled and this is thus connected in series with the windings of the relays K and L. In this state, the voltage difference between line 1 and the potentiometer tap is divided up in the manner indicated, so that the relay drops out again if the same difference value between 1 and the potentiometer tap occurs again after the fault has ceased. A sufficient control of the conditions can often be achieved by maintaining a linear relationship between the resistance values of R _r and that of the resistance R _z according to the following relationship:

τ) ■ * Vmai Kz "

+ IAE - lAE, U AE - Uae

30th

35

* AE ΙΆΕ

in which Ivmax the maximum permissible current in the amplifier input (at which the relay responds), I _AE the relay response current, * _AE the relay waste current , UΆε the voltage between points A and E when the relay responds, "ae the corresponding voltage when An arrangement according to the invention can either be used in such a way that the control current supplied is fed directly to a regulating device or that only a corresponding proportional voltage value is fed to it, which is derived from a resistor over which the arrangement is located resulting control current flows.

If it is not intended with an arrangement according to the invention to eliminate the effect of the hold ratio of the relay on the dropout value, a simpler arrangement can be chosen in such a way that the resistor R _r according to the embodiment is omitted and instead one of the input resistance of the Amplifier corresponding parallel resistance to the relay windings with the separation of the connection line between the setpoint potentiometer and the amplifier is switched on. In this way, nothing changes in the electrical resistance ratio of the system before and after the relay device responds when the amplifier input is disconnected.

Claims (6)

PATENT CLAIMS: 1. Arrangement for electrical control devices whose control value is derived from the difference a setpoint and an actual value of electrical variables is obtained, characterized in that inevitably with the setting of a new setpoint, an additional device is set or adjusted in this way is that for a proportional control error that is the same in percentage terms when the difference is formed the same control value for the control device results in the case of different setpoint settings. 2. Arrangement according to claim 1, characterized in that inevitably with the setting of a Setpoint potentiometer a series resistance across the tap of the potentiometer in its value is changed. 3. Arrangement according to claim 1 and 2, characterized in that between the setting values of the Series resistance and the setting values of the setpoint potentiometer a linear functional Context is chosen. 4. Arrangement according to claim 1 or one of the following claims, wherein the input of the control amplifier a relay device is assigned, which responds to certain limit control values, in particular also as a protective device, and thereby the amplifier of the supplying the control current The device disconnects while simultaneously applying an equivalent voltage to the input of the amplifier, characterized in that with the setting of a new setpoint, the relay device is inevitably adapted in its mode of action that it is at any potentiometer setting drops practically at the same values at which it responds. 5. Arrangement according to claim 4, characterized in that in series with the windings of the Relay device is connected to a normally bridged resistance before it responds, the when the relay device responds, it is connected in series with it, and that this resistor with a new setting of the setpoint potentiometer inevitably such in its resistance value is changed for such a division between the setpoint potentiometer and the actual value connection standing voltage difference that the relay device with the same values of this voltage difference both drops and appeals. 6. Arrangement according to claim 1 or one of the following claims, wherein the input of the control amplifier a relay device is assigned, which responds to certain limit control values, especially as a protective device, and thereby separates the amplifier from the device supplying the control current while applying it at the same time an equivalent voltage to the input of the amplifier, characterized in that when responding the relay device for the switched off input of the amplifier a corresponding one Equivalent resistance of the excitation of the relay (s) is connected in parallel. 1 sheet of drawings © 709 506/325 4.57