DE2633136A1 - SIGNAL MEASUREMENT - Google Patents

Description

DipUr.fi. Pefcr-C. Sroka Dr.-Ing. Ernst Stratmann

4 Düsseldorf 1 Schadowplatz 9

Düsseldorf, July 21, 1976

46.11OA
766ο

Westinghouse Electric Corporation
Pittsburgh / PaY / V. StV Ά.

Signal measurement circuit

The invention relates to a signal measuring circuit, in particular a signal measuring circuit with a large measuring range.

Common signal measurement circuits that monitor an input signal should, the size of which fluctuates over time, are designed for a specific measuring range and based on this Measuring range limited. If the measurement requirements for a particular application are outside the working range of such Measuring circuit, auxiliary circuits are required. These additional circuits can be a switch for the measuring range (which can work manually or automatically) or also include a dynamic feedback circuit which has a function similar to that of a continuous circuit automatic gain control (AGC). The requirement of low noise, wide frequency range and good linearity make the construction of these auxiliary circuits complicated and expensive.

The object of the invention is to create a signal measuring circuit, which does not have the disadvantages mentioned above.

709809/0301

Telephone (0211) 32 0858 telegrams Custopat

ORIGINAL INSPECTBD

According to the invention, the object is provided by the main claim mentioned features solved, d. that is, it becomes a signal measurement circuit created with an extended measuring range, a measuring circuit device with a certain dynamic range, a the input of this measuring circuit device connected to the input circuit device and to the output of the Control circuit device connected to the measuring circuit device comprises in order to send a control signal to the input circuit device to place, to which the input circuit means responds in such a way that the magnitude of the signal to the signal measuring circuit applied input signal is adjusted so that its Level is within the specified measuring range. It is essential to the invention that the signal measuring circuit is an output circuit device which is connected to the output of the measuring circuit means, the output circuit means responds to the control signal in that the size of the output signal of the measuring circuit device to one of the Input signal brought corresponding level and an output signal is generated which corresponds to the input signal.

As already briefly stated above, uses the inventive Signal measuring circuit a relatively simple method for adapting the size of an input signal a level which is within the dynamic range of the signal measurement circuit. The dynamic range can be the effective value, the direct current value, the peak value etc. of the measured variable capture. Then the output signal of the measuring circuit set to a level comparable to the size of the input signal. This enables the most effective use of the measurement circuit to achieve the desired linear characteristic over an expanded range of input signals as well also to achieve an improved signal-to-noise ratio.

In the event that the input signal is of a magnitude which is below the lower limit of the dynamic range of the signal measuring circuit is a suitable amplifier circuit

709809/0301

used to increase the size of the input signal so that that it is within the dynamic range of the measuring circuit. Subsequently, a damping circuit reduces the output of the measuring circuit determines the magnitude of the output signal therefrom Measurement circuit to a level comparable to the original size of the input signal. In the event that the original size of the input signal is greater than the upper limit of the dynamic range of the measuring circuit would a damping circuit at the input of the measuring circuit and an amplifier is used at the output of the measuring circuit.

A particularly useful and simple implementation of this basic method is achieved by putting two together matched photoresistors are used. The resistance characteristics of the photoresistors, which are equally strong from a common light source are illuminated, change inversely proportional to the recorded light intensity. One the photoresistors will act as the input for the measuring circuit used to adjust the size of the input signal for the measuring circuit in a suitable manner, while the second photoresistor is connected to the output of the measuring circuit to compensate for the size of the output signal of the measuring circuit. An amplifier circuit for the light source, which continuously monitors the output signal of the measuring circuit and a dynamic drive for the Photoresistors supplies, serves as feedback control for the photoresistors and also sets the required area of the circuit for automatic gain control (AGC). Depending on the application requirements, the construction of the circuit can be such that the light output the common light source either directly proportional or inversely proportional to the output signal of the measuring circuit is.

The photo resistor provides a wide frequency range and low noise as the photoresistor is essentially a passive element and contains only resistive components.

709809/0301

Good linearity is achieved by using a matched pair of photoresistors since the error in the Implementation of input to output generated by the photoresistors, completely from the adjustment of the photoresistors depends. In the practical implementation, the adjustment can be made with great accuracy. The accuracy of the Adjustment is in no way limited by the type of photoresistors.

The invention is explained below on the basis of exemplary embodiments explained in more detail, which are shown in the drawings.

It shows:

Fig. 1 is a basic block diagram of the signal measurement circuit of the present invention;

Fig. 2 is a schematic representation of an embodiment of the invention according to FIG. 1, in which an adapted Pair of photo resistors is used;

Figures 3 and 4

schematic representations of modifications of the embodiment shown in FIG. 2;

5 shows a schematic representation of another embodiment of the invention shown in FIG. 1;

6 shows a schematic representation of a modification of the embodiment shown in FIG. 5; and

Figure 7 is a graphic representation of the dynamic range a signal measuring circuit according to the invention.

Referring to Fig. 1, there is a basic block diagram of a signal measuring circuit 10 shown, consisting of an input circuit 20 for the input signal adjustment, a measuring circuit 30 for

709809/03Ot

RMS-DC conversion, an output circuit 40 for output signal adjustment and a feedback control circuit 50. The RMS-DC converter 30 is responsive to an input voltage signal V- / supplied through the input signal conditioning circuit in such a way that a direct voltage output signal (DC) is generated which is indicative of the mean value (RMS value) of the input voltage signal V. (t) that fluctuates over time. Typical commercially available RMS-DC converters include the "Introniksschaltkreis R310" and the "Analog Devices Schaltkreis AD44O". The feedback control circuit 50 responds to the output signal V _{2 of} the RMS-DC converter 30 by supplying the control signal to the input signal adjustment circuit 20 in order to change the magnitude of the input signal V. (t) and thereby an output signal V- applied to the circuit 20 with a magnitude to generate which is within the defined dynamic range of the RMS-DC converter 30. The feedback control circuit 50 supplies a control signal in the same way to the output signal adaptation circuit 40, which also _{receives the output signal V 2 of} the RMS-DC converter 30 as an input signal. The output signal adjustment circuit 40 responds to the control signal by adjusting the magnitude of the signal V i by an amount corresponding to the adjustment made by the input signal adjustment circuit 20, but with an opposite polarity so that the output signal V _{0 is} a DC signal, which indicates the mean value of the input signal V _1n (t).

The defined dynamic range of the RMS-DC converter circuit 30 is _{plotted in FIG. 7 as a double logarithmic representation of V 0} over V. (t). From the graph of FIG. 7 it becomes clear that the optimum operation of the RMS-DC converter circuit 30 is achieved when the magnitude of the signal supplied to the RMS-DC converter circuit 30 is within the defined dynamic range. The function of the input signal conditioning circuit 20 is _{to adjust the magnitude of the actual input signal V in} (t) so that an input signal V ₁ for the RMS-DC converter

709809/0301

circuit 30 is achieved that is actually within the specified dynamic range of the RMS-DC converter circuit 30 lies.

At the same time, the feedback control circuit 50 provides the necessary control signals for the input signal adjustment circuit 20 to generate a signal within the specified dynamic range, while at the same time a control signal is supplied to the output signal adjustment circuit 40, which operates in the opposite manner to the input adjustment circuit 20, so that the output signal V _{Q of} the circuit is an accurate indication of the mean value of the input signal V. t (t). It can be seen that when the actual input signal V. The amplifier operates while the output signal adjustment circuit 40 is constructed to operate as an attenuator. When the magnitude of the actual input signal V. (t) is larger than the specified dynamic range of the RMS-DC converter 30, the input signal adjustment circuit 20 is constructed to function as an attenuator, while the output signal adjustment circuit 40 is constructed so as to that it acts as an amplifier.

This basic concept for expanding the measuring range of an RMS-DC converter circuit enables numerous circuit variations in realizing specific embodiments for this concept. E.g. in the circuits and 40 digitally controlled resistor networks are used with the feedback control circuit operating in the manner that it digitally increases the resistance in one circuit while at the same time increasing the resistance in the other circuit digitally decremented by the same value to obtain the desired combination of gain and attenuation. Below Referring to Figs. 2 to 4, a preferred embodiment is described which uses light actuated photoresistors.

709809/0301

It is assumed for the purposes of the following explanation that the input signal V _in (t) has a value which is less than the specified dynamic range of the RMS-DC converter circuit 30 corresponds. Therefore, the input signal adjustment circuit 20 increases the magnitude of the input signal V. (t), while the output signal adjustment circuit 40 _{decreases the magnitude of the output signal V 2 of} the RMS-DC converter circuit 30.

The variable electrical components in the circuits 20 and 40 of FIG. 2 consist, as shown, of the photoresistor R _pl and the photoresistor R _p2 · ° i ^e photoresistors Rp- and Rp ₂ are precisely matched to one another with regard to their operating characteristics and are typically made of Cadmium sulfide material (CdS) or cadmium selenium material (CdSe) produced, whereby they have a characteristic in such a way that the resistance changes inversely with the intensity of the incident light. The feedback control circuit 50 of FIG. 2 consists of a light source amplifier 52 and a light source 54, such as a light emitting diode, which serve as a common light source for illuminating the photoresistors R _p- and R _{p2 in a} similar manner.

For purposes of explanation, it is assumed that the photoresistor R _p1 provides a dynamic gain factor K for the input signal adaptation circuit 20. This then necessarily follows that the photoresistor R p2 provides a damping factor of 1 / K for the output signal _{matching circuit 40.} The K-factor can be made either linearly proportional or inversely proportional to the resistance value of the photoresistor.

The light source amplifier circuit 52 of the feedback control circuit 50 continuously monitors the output signal V _{2 of} the RMS-DC converter circuit 30 and provides a dynamic drive for the photoresistors Rp- and R _p2

709809/0301

of the light source 54 is either directly proportional or inversely proportional to the output of the RMS-DC converter circuit 30 be made. The feedback control circuit 50, like him 2, operates to provide the required automatic gain control (AGC) for the Determines the end of the circuit.

In the embodiment shown in Fig. 2, an input signal V. (t) with a relatively low value leads to a light output of the light source 54, which increases the factor K by reducing the amount of light incident until the value of the RMS-DC converter circuit 30 is supplied Signal V _{1 is} within the specified circuit dynamic range. As the magnitude of the input signal V. (t) increases, the light output of the light source 54 decreases, whereby the factor K decreases, since less amplification or attenuation by the circuits 20 and 40, respectively, is required. While the input signal V. (t) can fluctuate over a wide range, the change in the signal V- is limited to the specified dynamic range of the RMS-DC converter circuit 30. As a result, the usable operating range of the RMS-DC converter circuit 30 is expanded . It can also be seen that the magnitude of this range expansion obtained from circles 20, 40 and 50 depends on the dynamic range of the factor K. In practice, when using a single matched pair of photoresistors, the easily achievable dynamic range for the factor K is approximately 40 dB, which corresponds to a ratio of approximately 100: 1. This means that a range expansion of 40 dB results for a conventional RMS-DC converter circuit. The mode of operation of the embodiment shown in FIG. 2 for achieving an output signal V _Q , which is a direct current representation of the "mean value of the input signal V ^ _n Ct), can be expressed by the following equation:

709809/03Ot

V ₂ = κ

ν ₀ = V ₂ (1 / κ)

The embodiment of FIG. 2 is shown in greater detail in FIG. 3. The operational amplifiers A1, A2 and A3 provide the basic circuitry for the input signal adjustment circuit 20, the output signal adjustment circuit 40 and the feedback control circuit 50, respectively. In the embodiment shown in FIG Gain control, where the gain is determined by the fixed resistors R1 and R2 and the variable resistor formed _{by the photoresistor Rp 1.} The smallest amplification factor for the operational amplifier A1 is obtained at the maximum light output of the light source 54, which results in a smallest resistance for the photoresistor Rp-. The operational amplifier A1 has a maximum gain when the light output of the light source 54 is at its minimum value.

In the output signal matching _{circuit 40, the photoresistor R_ o is connected} in series with the input resistor R ₀ ^{1 of} the operational amplifier A2. The interconnection of the photo resistors R _n - and R_ _o in combination with the amplifiers A1 resp.

ir I ir &

A2 gives the dynamic gain factor K for the circuit 20 and the attenuation factor 1 / K for the circuit

The operational amplifier A3 of the feedback circuit 50 is connected to operate as a differential amplifier, one input _{responding to the output signal V 2} from the RMS-DC converter circuit 30 and its second input responding to a reference voltage level Vf supplied by a reference voltage source 56 . The amplifier A3 compares that of

709809/0301

_{The signal V 2} supplied to the RMS-DC converter circuit 30 with the reference voltage level V _f , which represents a signal quantity which is within the defined dynamic range of the RMS-DC converter circuit 30, as shown in FIG. Deviations of the signal V ₂ from the reference voltage level V _f produce a corresponding change in the light output of the light source 54 so as to produce a _{substantial correspondence between the value of the signal V 2} and the reference voltage Vf.

An input signal V. (t) with a value less than V _f reduces the light output of the light source 54 and thereby increases the resistance of the photoresistors R _p1 and R _p2 · This leads to an increase in the gain of the signal V. (t ), which is _{fed as signal V 1 to} the RMS-DC converter circuit 30 and to an increase in the attenuation of the signal V ₂ by the output signal adjustment circuit 40. Conversely, if the signal V _{2 of} the RMS-DC converter circuit is of a magnitude greater than of Vf, the light output of the light source is increased and the resistance of the photoresistors R _p1 and R _{p2 is} decreased.

The operation of the embodiment shown in FIG. 3 Signal measurement circuit 10 can be represented by the following equations:

V ₁ = -C (R ₀ + R _P1 ) Z]

V ₀ = [(R ₂ + Rp ₁ ) ZR ₁ ] * [R ₁ ¹ Z (R ₂ ¹ + R _p2 0

Since R _p1 = R _p2 and if R ₁ = R ₁ 'and R ₂ = R ₃ ¹ , we get:

703809/0301

If the operating range of the RMS-DC converter circuit 30 is to be expanded still further, additional mating pairs of photoresistors can be provided in the basic embodiment of FIG. An embodiment of this type is shown schematically in FIG. As can be seen, two input signal conditioning circuits 16 and 20 'are connected in cascade series arrangement, and so are two output signal conditioning circuits 40 and 40'. A first light source 54 reacts to the output of the light amplifier _{circuit 52 by illuminating the photo resistors RpI 1} and Rp _{12 of} ^the circuits 20 and 40, respectively, while a second light source 54 ' _{reacts to the output of the light amplifier circuit 52 by illuminating the photo resistors Rp 2} -I and Rp ₂₂ the circuits 20 'and 40' responds. In the embodiment shown in FIG. 3, it is only necessary that the working characteristic of the photoresistor R "-., Is the same as that of the photoresistor Rp-I ₂ / while the working characteristic of the photoresistor Rp ₂ -J must be the same, like that of the photo resistor Rp ₂₂

In Fig. 5 a further embodiment of the invention is shown, which differs from the embodiment of FIG. 2 in that that the output circuit has been replaced by a logarithmic ratio circuit with a Control circuit with automatically controlled gain is combined in such a way that both the usable area the signal measuring circuit is expanded and the signal-to-noise ratio of the measuring circuit is optimized.

The logarithmic ratio circuit 60 (log ratio circuit 60) consists of a reference signal circuit 61, a pair of logarithmic circuits 62 and 64 with identical logarithmic characteristic and a differential amplifier circuit 66.

Assuming that the log ratio circuit has the displacement characteristic D and the noise characteristic N.

709809/0301.

and that the magnitude of the input signal fed to the input matching circuit 20? changes with time and can be expressed by V. (t), the operation of the signal switch 10 can be represented by the following equations:

(DV ₁ = AV. _N (t)

(2) V ₂ = AV

(3) V ₃ = K log [AV + D + lf |

(4) V ₄ = K log AV _R

(5) V ₅ = K log [Av + D + N] - K log AV _R ; AV

₅ = K log AV_ = K log _V__
AV _R V _r

In these equations, K is a constant term and represents the scale factor for the logarithmic circuits 62 and 64, while the signal V _{1 is} the output of the circuit 20, the signal V _{2 is} the output of the measuring circuit 30, the signals V ₃ and Y. die Output signals of the logarithmic circuits 62 and 64 and the signal V ₅ denotes the output signal of the differential amplifier 66, while the signal V _{R is} a constant reference signal which is fed to the reference signal circuit 61. The magnitude of the signal V _R is selected according to the circuit design and the expected magnitude of the input signal V _in (t). The magnitude of the signal V _R is determined so that the term V / V- is neither too large nor too small so that the value of the output signal V _{5 is} within practical limits. Since the term AV is much larger than the term for circuit noise (D + N), the signal-to-noise ratio is significantly improved.

70980 3/0301

In the embodiment of Fig. _5f, in which the measuring circuit 30 was assumed to be a true RMS-DC converter, the term V in equations (2), (3), (4) and (5) represents the expression _Y V 1n ( t) ^A and the output signal Vr is a logarithmic representation of the real mean value (RMS value) of the input signal V _1n (t). Thus, log ratio circuit 60 operates to optimize the signal-to-noise performance of circuit 30 while also adjusting the magnitude of the output signal of measurement circuit 30 to a level identical to the initial input signal V. (t).

Referring to FIG. 6, there is shown a detailed schematic representation of an embodiment of the invention as shown in FIG. The embodiment further comprises a filter with maximum flat characteristic, which is typically a third of two filter sections order, namely a low-pass section of filter elements P1 and F1 ° and a high pass filter portion F2 is _0, the two filter sections the third order, which together meet the characteristics of a six-pole Butterworth filter , are important if the input signal V. (t) has a bandwidth that is on the other hand the bandwidth of the measuring circuit 30, in which case the filter sections operate in such a way that they make the measuring circuit 30 sensitive to the broadband input signals V . (t) ^β make ,,

χπ

Although filters are a maximum flat characteristic of particular value, depending on the application of the Signalmeß 1Ø ₁₇ and, therefore, these filters are discussed hereafter in greater detail, although the operation of the embodiment of the Signalmeßschaltung 10 β shown in detail in Fig ₀ is not of the filter sections F1, Fl 'and F2 dependent.

The control function with automatic gain adjustment of the embodiment shown in FIG. 5 is shown in FIG

7 09809/0301

a matched pair of photoresistors R _p1 and R _p2 and a common light source 54 is realized.

The feedback control circuit 50 of FIG. 6 is shown as consisting of an amplifier A2 which responds to the deviation of the output signal of the measuring circuit 30 with respect to the reference signal V _f to change the excitation signal for the light source 54. The change in the light level emitted by the light source 54 which _{impinges on the photoresistors R pl} and R _p2 changes the gain factor A of the circuits 20 and 61. The input signal adjustment circuit 20 reacts by adjusting the magnitude of the input signal ^v _in (t) to a level within of the dynamic range of the measuring circuit 30, so that it can be compared with the level represented _{by the reference signal V f.} The identical change in the resistance of the photoresistors R _p .j and R _p 2 changes the gain characteristics of the amplifiers A1 and A3 of the circuits 20 and 61, respectively. The reference signal circuit 61 operates to apply the gain A to the reference signal V "and supplies the resulting signal as an input to the logarithmic circuit. As explained in connection with FIG. 5, the output of the measuring circuit 30 is applied as an input to the logarithmic circuit 62 of the log ratio circuit 60. The logarithmic circuits 62 and 64 are shown schematically as consisting of operational amplifiers A4 and A5, respectively, with precisely matched transistors Q1 and Q2 which are connected to one another in a feedback arrangement. The function of the logarithmic circuits 14 and 64 can be realized using commercially available circuitry such as the analog device circuit AD755. The output of the logarithmic circuits 62 and 64 is fed to the differential amplifier 66 which, as shown, consists of an operational amplifier A6.

709809/0301

Assuming that the matched pair of photo resistors Rp ₁ and R ₂ and the light source 54 provide the amplification factor A, as described with respect to FIG. 5, that K _1, the scale factor of the logarithmic circuits 62 and 64 and that the measuring circuit 30 is a circuit that measures the mean value (RMS.), the operation of the embodiment shown in Fig. 6 can be represented by the following equations:

^ ₁ = C (Rp ₁ + R ₂ ) / R ₁ HYV ~ 7 (tP

_ln

V _R ;

V ₄ = K ₁

V ₅ = (K ₁ R ₈ ZR ₇ ) D- ⁰ S (V ₁ ZR ₅ ) - log

+ R ₂ ) + log "/ V _{± n} (t) ² - log R ₁ R ₅ - log (R _p2 + R ₂ ) - log (V ₁₄ ZR ₃ R

Since R _D1 and R _{0 are} exactly matched photoresistors and have a common light source, this means that R _D1 = R ₀₀ . Thus becomes

V ₅ = (K.

V ^V in ^{(t) 2} J

Since K ₁ and V_ are constant, the above equation can also be written in the following way:

V ₅ = K ₂ log K ₃ YV _1n (t) ²

whereby

K ₂ = K ₁ R ₈ ZR ₇ and

709809/0301

K ₃ - R ₃ E ₄ ZR ₁ R ₅ V _n .

As explained above, the third-order low-pass filter section consisting of the filter elements F1 and F1 'and the third-order high-pass filter section consisting of the filter element F2 are valuable additional devices for the signal measuring circuit 10 when an input signal V. (t) 'shows a bandwidth which is greater than the bandwidth which can be picked up by the measuring circuit 30. The splitting of the effective six-pole Butterworth filter, which is represented by the filter sections F1, Fl ¹ and F2, into a third-order low-pass filter section and a third-order high-pass filter section and the further splitting of the third-order low-pass filter section into two filter elements F1 and F1 'provides a new one Type of filtering which makes the measuring circuit both sensitive to broadband input signals V. (t) 'and also makes the effect of circuit noise that is generated by the circuit 20 as small as possible. The low pass filter section is split into two parts to improve broadband noise rejection. The combination of one half of the third-order low-pass filter section represented by the filter element F1 with the third-order high-pass filter section represented by the filter section F2 operates to limit the bandwidth of the input signal, thereby producing an input signal V. (t) 'which is within the bandwidth of the measuring circuit 20 is generated. The second half of the third order low-pass filter section, which is represented by the filter element F1 ', which is connected in series between the input signal matching circuit 20 and the measuring circuit 30, has the effect that the effect of the noise introduced by the input signal matching circuit 20 is made as small as possible. Although the filter sections are shown schematically as filters consisting of operational amplifiers OP and forming active filter elements, the function of bandwidth narrowing and noise filtering can also be achieved by using passive filter elements or a combination of passive and active filter elements.

703809/0301

elements can be achieved.

The third-order high-pass filter section F2 is shown to contain a variable resistor P in a feedback arrangement _{B to} enable an adjustable gain change, which can be used to normalize the input signal V. (t) " _o

Claim

709809/0301

Claims (1)

Claims; ι 1 .j signal measuring circuit with extended measuring range, with measuring circuit devices of a certain dynamic range, input circuit devices connected to the input of the measuring circuit devices and with control circuit devices connected to the output of the measuring circuit devices in order to deliver a control signal to the input circuit devices, the input circuit devices acting on this Control signal react in such a way that they adjust the magnitude of an input signal for the signal measuring circuit to a level within the defined dynamic range, characterized in that the signal measuring circuit (10) comprises output circuit devices (40) which are connected to the output of the measuring circuit devices (30) are connected so that the output circuit means (40) react to the control signal in such a way that the magnitude of the output signal (V- ^ of the measuring circuit means (30j is set to a level which corresponds to the input signal (7., _r> (fc}) and that they generate an output signal CVq) which corresponds to the input signal (V. Ct)) corresponds to 2c signal measuring circuit according to claim 1, characterized in that the input circuit means (20) _{contain a first photoresistor (Rp 1} ,) and that the output circuit means (40) contain a second photoresistor (Rp2 ^ and that the control circuit means (50) comprise a light source (54) _P to direct light energy to the photoresistors (E _p1 g R _p2 ) at the same time, the intensity of which is a function of the size of the output signal (Vp) of the measuring circuit devices (30) - whereby the first photoresistor (Rp ^) reacts to a change in the light energy thereby that it changes the electrical properties of the input circuit means (20) so that the magnitude of the input signal CV _in (t)) is adjusted by a predetermined value in a first direction, 709809/0301 while the second photo resistor (Rp-j) & uf the change to the light energy reacts by the fact that it reacts to the electrical. Characteristics of Output Circuit Devices (40) so changes that the magnitude of the output signal of the measuring circuit means (30) by the predetermined value in opposite Direction is changed. 3. Signalmeßschaltung according to claim 2 _t characterized in that the control circuit means (50) include a comparison = circuit (52) which is formed so as the Meßschaltkreiseinrichtungen (30) compares the output signal (V-) with a reference signal (56) which indicates the dynamic range of the measuring circuit means (30), in order in this way to place the magnitude of the set input signal in the dynamic range, the light source (54) being connected to the output of the comparison circuit (52). 4. Signal measuring circuit according to claim 2, characterized in that the first and the second photoresistor (R "^, Rp") form a pair of photoresistors that are matched to one another. 5. Signal measuring circuit according to claim 4 "characterized ^ that the input (20) and output _{circuit means (40) contain more than one matched pair of photoresistors (Rp 11} , Rp ₂ ^{-J / R} pi2 ' ^R P22 ^' 6. Signal measuring circuit according to claim 5, characterized in that that the control circuit devices (50) have a separate Light source (54 or 54 ') for each matched pair of photoresistors. 7. Signal measuring circuit according to claim 1, characterized in that the measuring circuit means (30) represent a circuit for measuring the mean value (mean square root, RMS) and that the output signal (V ₀ ) generated by the output circuit means (40) is the 7 09809/0301 Average value (RMS value) of the input signal (V. (t)) represents. 8. Signal measuring circuit according to claim 1, characterized in that that the output circuit means (40) comprise logarithmic circuit means (60) to a logarithmic To provide representation of the input signal (V. (t)). 9. Signal measuring circuit according to claim 8, characterized in that that the logarithmic circuit means (60) includes a reference signal circuit (61) so constructed is that it is the size of a predetermined reference signal (V-.) On the basis of the control signal sets that a first κ logarithmic circuit (62) is connected to the output of the measuring circuit means (30), that a second logarithmic circuit (64) is connected to the output of the reference signal circuit (61) to receive the set reference signal, and that a differential amplifier (66) is connected to the Output of the first and second logarithmic circuits (62 and 64, respectively) is connected to produce an output signal (V ₅ = V _Q ) which is a logarithmic representation of the input signal (V. (t)). 10. Signal measuring circuit according to claim 9, characterized in that the input circuit devices (20) contain a first photoresistor (Rp-), and that the reference signal circuit (61 _{) comprises a second photoresistor (Rp 2} ), that the control devices (50) have a light source ( 54) in order to simultaneously _{direct light energy to the photoresistors (Rp 1} , Rp ₂ ), which represents the control signal and the intensity of which is a function of the deviation of the output signal (V-) of the measuring circuit devices (30) from a predetermined point within the specified dynamic Area is. 709809/0301 11. Signal measuring circuit according to claim 10, characterized in that the first and the second photo resistor (R _p1 , R _p2 ) form a matched pair of photo resistors. 12. Signal measuring circuit according to claim 1, characterized in that the circuit further comprises a high-pass filter section (F2) and a first low-pass filter section (F1) at the input of the input circuit means (20) to receive input signals (V _in (t) ') whose bandwidth is larger is as the bandwidth of the measuring circuit means (30), as well as a second low pass filter section (F1 ¹ ) / connected between the input circuit means (20) and the measuring circuit means (30) to remove signal noise introduced by the input circuit means (20). 13. Signal measuring circuit according to claim 12, characterized in that the high-pass filter section (F2) is a third-order high-pass filter and that the first and second low-pass filter sections (F1 and F1 ¹ ) each represent one half of a third-order low-pass filter «, 14. Signal measuring circuit according to claim 13, characterized in that the filter sections (F1, F1 ', F2) as a maximum flat Butterworth filters working. ES / gl / jn 3 709809/0301