DE2556201A1 - ARRANGEMENT FOR DIGITAL DETERMINATION OF THE LEVEL VALUE OF AC VOLTAGES AND REGULATION OF A MEASURED VARIABLE WITH CONTROLLABLE TIME BEHAVIOR - Google Patents

Description

Dresden, February 12th, 1975

2556291

Arrangement for the digital determination of the level value of AC voltages as well as for regulating a measured variable with influenceable time behavior

The invention relates to an arrangement for the digital determination of the level value of alternating voltages or the regulation a measured variable with a time behavior that can be influenced, in which, in particular, for measuring or regulating the effective value alternating voltages of different waveforms over a very large amplitude range result in simple possibilities, to adapt the time behavior to almost any requirements.

In many areas of electronic measurement technology, the rms value is an existing or alternating variable supplied by transducers is the most important desired measured variable, for example when measuring disturbance variables and stochastic variables in control engineering, geophysics, acoustics and in vibration measurement and testing technology within the electronic The rms value generator represents one of the most problematic assemblies, due to the numerous, very different known technical solutions is sufficiently proven.

So are circuits using Therraocrosses entirely error-free with regard to the waveform of the alternating voltage, but only for a small amplitude range of the measured variable without switching (hereinafter called dynamic ura catch) suitable and very sluggish in setting.

In the case of simple electronic processes, a special time response is required for the respective task Settling to the measured value is considerably easier to implement; the dynamic range can also be expanded significantly * Circuits that have become known work, for example, with squaring, averaging and subsequent root extraction the measured variable, as in some cases also directly through

Standards is prescribed «, so-called rectifiers with a sliding Kniok characteristic are also frequently used long measurement times (registration and analysis of low-frequency processes j measurement and subsequent registration or calculation of long-term effects), for the processing of numerous and quickly accumulating data (aircraft noise monitoring, real-time analysis, test field tasks) or when a very defined working of the measuring chain (test systems with continuous Frequency and automatically kept constant level, recording of very wavy spectra, defined averaging of stochastically fluctuating levels). For these applications, the additional technical demands to rms-forming assemblies can be read t

- Very large dynamic range, since the levels that occur are considerable and not exactly predictable fluctuations «From this the almost exclusively desired output of measured variables on a logarithmic scale is inevitable, i.e. in level values, derivable

- Very different time behavior (sliding tent constant with continuous frequency, standardized acoustic Behavior in the event of aircraft noise monitoring, long-term · Averaging for stochastic quantities) ■>

- Digital output of measured values as directly as possible, since further data processing often takes place digitally.

Known circuits with improved properties use logarithmic circuits to form the logarithmic effective value, mostly using diodes or transistors, on which a squaring then only means a multiplication by two. With a suitable arrangement, the time constant formation can then be carried out independently of the level and the level value can be taken directly from the circuit _{or similar}

Numerous circuit arrangements that have become known use amplitude control in order to achieve the required dynamic range at least to limit the rectifier itself. The timing behavior is usually only of secondary importance measured.

For example, in analog recording level recorders the input alternating voltage is given to a measuring potentiometer Movable tap that is mechanically tightly coupled with a pen, removed The assemblies arranged below, ζ · Β. Amplifier, rectifier and comparator form a closed control loop if their output voltage, which corresponds to a control deviation, via an electromechanical Converter adjusts the tap of the measuring potentiometer until the rectifier is on the specified The measuring potentiometer usually contains a plurality of contacts along a contact path along which the above-mentioned tap can slide. To every contact is a point of a voltage divider consisting of ohmic resistors, depending on the dimensioning of this Resistors give you the desired dependency between input AC voltage and the position of the tap, which is a represents a direct measure of the measurand. A digital output of this position is only possible by means of an additional device for scanning possible.

Electrographic recorders use a Process on continuous recording paper a fixed arrangement of numerous electrodes, their electrical activation causes a marking on the recording paper that passes directly over the electrodes. The control the electrodes are done digitally. Known arrangements for recording DC voltages use this Process that follows the circuit technology of so-called trailing analog-to-digital converters for direct voltage measurements completely correspond. Characteristic assemblies are a pre-return meter, the meter reading of which is immediately immediate represents the digital J.Ießwertinformation and the at the same time digital-to-analog converted ^ n a comparator r; e filled and compared with the analog input signal.

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If these two signals deviate from each other, the the comparator once the counting direction of the counter is suitable, controlled and at the same time a gate circuit opened, the Allows counting impulses to reach the counter until the two input signals of the! Comparator are only sufficient show little difference. The time behavior is determined by the counting frequency, for which a fixed value is specified will.

Other known methods for measuring the effective value only allow amplitude changes on the rectifier itself that are the logarithm of the ratio of the input AC voltage to the smallest measurable input AC voltage, i.e. the level value, are proportional. For this purpose, the deviation of the rectifier voltage from a reference value is applied to a component given with exponential transfer characteristics and its output is used to vary the input amplitude of the array. Known designs have a time behavior this control loop is based on the formation of the rms value or its square on an inertia element corresponds to the first order.

Circuits of this type with digital were also published Feedback * which is a direct digital output of measured values with usually even greater dynamic range. No statements are made about the time behavior.

Also known is a broadband level meter that automatically adjusts _{to a constant level o} It serves as an upstream override protection for a selective level meter and contains digitally controllable attenuators _e Storage time is determined by dl · lowest occurring frequency of the level range and which in turn switches the attenuators.

A similar method that has become known uses a counter instead of the short-term memory and works with constant Counting frequencyβ

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Simple logarithmic circuits have a limited Dynamic range on. The time evaluation can correspond to a first-order inertia element, but it is difficult to configure it variably.

A defect on all analog recorders, the low reusability of reading turns into automatically operating measuring cells, as can be iueßsignal usually only technically or economically disadvantageous way into a digital signal converted _o The second major disadvantage is the very limited ability to influence the time response in the formation of the quantity as soon as one would like to fall below a characteristic mechanical response time determined by the moving masses.

Electrographic writers partially avoid these defects. The measuring signal is already available digitally and the writing process takes place without any movement of mechanical masses _o However, just like with digital voltmeters, only those arrangements have become known in which an applied direct voltage to be measured is compared to a comparator with the attenuated reference voltage controlled by a counter accordingly, only a linear relationship between the input and output variable is used. These circuit arrangements are therefore not yet suitable for a desired large dynamic range of an RMS value meter with only a slightly variable level at the rectifier itself. Methods with a time behavior that can be adapted to special measuring tasks are not known up to now. The above-mentioned electronically operating RMS meters with feedback from the rectifier to the input section represent a considerable step forward in terms of automation ·

The limits of the method are determined by the modulation limits of the transmission element in the feedback, which does not only have to process the entire measurement range in a logarithmic manner like the rectifier itself, but linearly, _{or the like}

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At this point, difficulties arise in terms of time behavior of the rectifier, since a desired time behavior can in principle be implemented electronically, but in many cases associated with an even greater required dynamic modulation of the return element is · At the same time, there are also noticeable level differences at the rectifier itself, which are also higher Requirements for accuracy and frequency range are not very compatible. Analog circuits need to be used for digital ones Further processing an additional downstream analog-digital converter

Circuit arrangements with digital conversion of the feedback signal avoid these deficiencies in part; especially can with an extended dynamic range compared to analog circuits. » Arrangements are not known for which, by means of additional measures, settling time or time behavior the arrangement designed variably and already standardized or technically particularly useful properties can be easily implemented »

The same applies to the broadband level meter mentioned, which is initially not a measuring device itself, but merely an auxiliary device for low-error and particularly clear detection of the measured variable. A display or output of the _{broadband Sffektivwertpegels is not equipped for the response time of the device to a new state is explicitly called a constant and determined by the lowest occurring in the measuring frequency settling time. For the effective valuation ζ · Β. Within the areas of measurement technology mentioned at the beginning, this arrangement, like the above-mentioned method, which operates with a counter and constant counting frequency, is therefore not always suitable

The purpose of the invention is to eliminate the shortcomings mentioned and to propose an arrangement for measuring and controlling alternating voltages which is completely suitable for automatically operating measuring stations _{or the like}

The invention is based on the object of creating an arrangement for measuring and regulating measured variables of alternating voltages over a very large dynamic range, in which the

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actual rectifier part to reduce sources of error is kept at a completely constant potential and in which the time behavior of the * vleßwertbildung comfortably meets the respective requirements is customizable.

According to the invention, in an arrangement with a time behavior that can be influenced, the jfleßwertbildung, consisting of a control loop with a digitally controllable voltage divider or amplifier, a rectifier, located behind the input, a summation element interconnecting a reference source with the rectifier output, one or more coraparators and an up / down counter, its input gate and whose counting direction is controlled by the comparator output and its counter outputs once with the control inputs of said digitally controllable voltage divider or amplifier and on the other hand connected to the output of the arrangement are, the object is achieved in that a source located in front of the input gate of the up / down counter for counting pulses that influence the frequency and / or the reference source Have voltage-influencing control inputs that connect to any points of the chain and / or the control circuit and / or external control variables, preferably via adjustment and correction elements. Here the individual switch Digits of the respective count value a voltage division or amplification that corresponds to the digit and place value on the assembly arranged between the input and the rectifier so that the rectifier level is the reference level and the number that appears on the counter in the balanced state is an immediate measure of the represents the level value to be determined. By controlling the frequency of the source for the counting pulses, it is possible to reduce the To vary the counting speed almost arbitrarily or to make it dependent on any controlling variable and thus that To design the timing behavior of the control loop almost arbitrarily. An arrangement according to the invention for narrow-band frequency analysis provides that either the output of a narrow band filter or the output of the digitally controlled voltage divider or Amplifier are also fed to inputs of a pulse shaper arranged as a counting pulse source, whose output pulse number with the number of Hull crossings of the input voltage of the pulse shaper is in a fixed numerical ratio and

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connected to the output of the Impuleformers on the Eingangstorung with dam counting input of the up-down counter · is thereby achieved is that the settling time of the control loop in inverse proportion to the filter center frequency is _o to control any physical quantity at a constant or programmed setpoint with an input side connected generator variable frequency, an arrangement according to the invention with a sliding time constant for the formation of the measured value is characterized in that the output of the generator is also fed to an input of the pulse shaper.

Another arrangement according to the invention, preferably with the time response of an inertia element of the first order in the formation of the measured value, provides that the source for counting pulses connected in front of the input interfering is designed as a voltage-frequency relay, the input of which is switched on either directly or via a switch controlled by the comparator arrangement a correction network that realizes the desired time behavior is connected on the input side to the output of the summation element, the second input of the controlled changeover switch being connected to a separate voltage source.The measurement of a long-term mean value of levels is carried out with a device according to the invention, in which the voltage-frequency converter has several simultaneously acting control inputs to achieve the desired timing, one of which is connected to the output of a correction network connected to the summation element on the input side and the other inputs to the outside Any effective control variables are switched, with control inputs of the correction network and of the voltage-frequency waidler preferably being able to be connected to the output of the up / down counter. According to the invention, an extension of the described arrangements is possible in that a control input of the reference source is connected to any point within the control loop or that the reference source is preferably implemented by a measuring rectifier, the input of which is connected to any, but not to the input of the digitally controllable voltage divider or amplifier is connected to the matching point of the measuring chain leading to the variable size, whereby a reference variable is additionally impressed on the control variable _{or the like}

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The invention is to be described in more detail below using a few exemplary embodiments, although not all possible ones Embodiments of the arrangement applied for according to the invention can be shown at this point, but to the person skilled in the art the basic direction for applying the invention is shown »In the accompanying drawing:

Fig. 1ί A block diagram of the basic principle of the invention arrangement

Fig. 2ϊ A measuring arrangement for narrow-band frequency analysis with sliding time constant

Fig. 3 * Hüne measuring arrangement for regulating a measured variable a constant or programmed A'ert with a sliding side constant

Fig. 4 A measuring arrangement for achieving a special transient behavior corresponding to a first-order tragic link

Fig. 51 A measuring arrangement for measuring long-term mean values

Fig "6: A measuring arrangement for measuring level differences"

In Fig. 1, the voltage to be measured comes from input E. the stepped controllable voltage divider or amplifier 1. The output voltage of the connected rectifier 2 is added in the summation element 4 of the voltage of a reference source 3 so that the voltage behind the summation element represents a hatred for the amount and sign of the control deviation and in the balanced state of the control loop it becomes Hull «This voltage is applied to one or more coraparators 5 supplied, which in turn controls the counting direction of the upstream counter 6 and control the input gate 7, at the input of which a variable counting frequency from a counting pulse source 8 is applied is. By changing the counting frequency, it is possible to change the settling time of the control loop and thus the Integrate measured variable over a shorter or longer period of time. The entrance gate is in the described mode of operation of the control loop is not absolutely necessary, but offers a number of practical advantages. So it is with two Comparators 5, the response thresholds of which are somewhat offset from one another, are possible at the point of derivation of the control loop

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to create a dead zone and thus influence small disturbances (r.ohaltstoße, Gleiohriohterwelligkeit) to make ineffective. -Furthermore, by blocking the counting pulses, an overflow of the Counter 6 can be prevented. So it is conceivable that Maxi— perform malwertepeioherungen by in the counting direction "backwards" the RLngangstor 7 is blocked for the counting pulses.

His Ließ device for low-band frequency analysis is shown in? i £. 2. Before the actual control loop, a duroh-timed low-band filter 10 that works with a constant relative band width is arranged, the output voltage of which has a sinusoidal curve with only slightly fluctuating frequency due to this narrow band. ^The derivation of the counting impulses z "r .. from the zero crossings of this voltage by means of a suitable pulse shaping stage 11 means that the oscillation time of the Hegel circuit is inversely proportional to the filter center frequency the measuring arrangement shown here has a time-optimal binso oscillation behavior and is ζ · Β _Ο particularly suitable for automatic measuring devices and for the frequency analysis of low-frequency or stoohastic processes In the controlled voltage part 1, there are practical advantages, since an essentially constant level is present at this point.

Another arrangement with sliding time constant is shown in Fig _y. 3 Here, a frequency generator 12 is used primarily for the production of any physical alternating quantity with output of sinusoidal voltage or narrow-band house voltage, in that a device 13 suitable for this is connected to the frequency generator 12 via the controllable voltage divider or amplifier 1. The level of the generated physical quantity should be kept constant or programmed according to given relationships. Such requirements arise, for example, in test field measurements on electroacoustic transmitters, in frequency response measurements of electrical and mechanical four-pole devices or in the vibration test

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physical size, whereby here often considerable, Unwanted fluctuations in the transmission properties in Depending on the frequency occur. About these fluctuations To regulate out, the device 13 additionally contains a converter for measuring the constant or to be programmed Size, the output of which with the rectifier 2 and the close- switched connected elements of the control loop already described is. The content of the counter controls the stepped voltage divider or amplifier 1, so that the physical quantity is constant adopts the desired pel value. The oscillation behavior of these Special attention must be paid to the arrangement, as there are often pronounced points of resonance in the transmission characteristic must be corrected and experience has shown that instabilities easily occur with a mismatched time constant, I'Jin suitable Single oscillation behavior is achieved in that the output of the frequency generator 12 is fed to the pulse shaper 11 is that a constant number of counting pulses z. B, at each hulldnrohgang the generator voltage to the input gate of the Counter outputs and thus siohert a slow settling to the desired value at low frequencies and a fast settling at high frequencies.

FIG. 4 shows how the counting frequency is obtained from the control loop itself is used to control a voltage-frequency converter 17 and, for this purpose, is carried out via an arbitrarily executable correction network 15, whose linear or nonlinear Transmission characteristics the respective desired sin oscillation behavior to ensure. Possible linear transfer functions they essentially result from combinations of in the control theory known transmission elements such. B. Inertia Integrating or differentiator,

The nonlinear properties are obtained, for example, when they are required Equalization of the amplitude characteristic, with two-way slide alignment the control deviation or when forming a potential function the control deviation.

For the often desired transient response corresponding to a first-order inertia element (simple RC low-pass element) lets sioh show that by taking the logarithm of the l'.eßp-size existing nonlinearities of the Hegel's circle when calculating

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tion of the time behavior can be mined. The usual transfer function F (p) of the closed control loop is ent ^ speaking of the default

P (p) » ^{"ΡΎ β} * ^{e, normalized} frequency of a transmission member (I)

From the known relationship between the frequency response of the transfer function F (p) and the frequency response of the transfer function of the open chain Fo £ p) in the case of a transfer behavior "One" of repatriation

one obtains the desired behavior (i) for

. (III)

This is precisely the behavior of the counter 6 in FIG. 4. Further elements in the transmission path must therefore cancel each other out in the frequency response. the connected correction network 19 mXQ then have the reciprocal frequency response of a lead element of the first order. In the event of a sudden drop in the input variable, an inertia element of the first order exhibits a linear decrease in the output variable for a logarithmic amplitude scale.During the counter reset it is therefore also possible to use a constant counting frequency of the voltage-frequency converter 17 independently of the output voltage of the correction network 19 zeitlioh linear change of the counter contents to force · of practical interest is the example _9, if the voltage-frequency converter 17 can process only one polarity or when up-and-discharge time should have different values, such as in the standardized display dynamic "pulse" of SohallpegelmeOteohnik In FIG. 4, this possibility is due to the insertion of a device arranged in front of the voltage-frequency converter 17! berüoksiohtigt of the capacitors 9 _f-controlled change-over switch 16, the 17 Aehlen the voltage-to-frequency converter when Vorwärtezähle to the Korrekturnetiwerk 19 and in reverse "switches to a separate adjustable Spannungequelle fourteenth

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^ 556201

In a further exemplary embodiment, by means of 71g. 5 the Measurement of a long-term mean value described. Such measurements take place near standardized methods, for example, for the detection of vibrations that act on the mensohliohen body or for measuring the equivalent continuous reverberation level Leq, the Long-term noise effects on the cafeteria recorded by a bin number. For this latter pail there is supposed to be a possibility are shown, at any point in time t the value of the equivalent continuous reverberation level added up to that point at the counter 6 can be read immediately. : loh definition results in the connection between the equi-

älenten continuous reverberation level Leq and the instantaneous value L * (t) des So reverberation level too

f O> 3 LaCO 1 J 10 q dtj

^{Le <} l -ICT ¹ SI i J ¹⁰ * dtj q - 2.5 ... 6 (IV)

Palis the described control loop with its counter 6 for each Point shows the value of the equivalent building reverberation level Leq (t) determined up to that point, this results in the current level from the sum of this display value and the current deviation of the Gleiohriohterausfrangssspannung üg from the reference voltage

(t)

ίο ψ

(ν)

From this one finds, using the relationship between the counter reading η (t), the smallest Fegelsohrltt Ö * L of the digital display, the output value Leq (t) and the counting frequency f _B (t) at the counter input

Leq (t) - η (t) ^ L - Γ f _B (t ·) dt »

Leq (t) - f _B (t) (VI)

a guide for the required control of the counting rate

¹ I.

2556291

(VII)

The term in braces is taken directly from the system deviation of the control loop by means of fciohtlinear transformations won; The pactor ^ arises from an additional high attitude a timer to the voltage-to-frequency converter 17.

Fig. 5 shows the basic arrangement for obtaining Long-term mean values · The correction network 15 processes the difference between that which has accumulated up to this point in time and output by the counter 6 Long-term mean value and the current level value of the measured variable, which are additionally connected to the voltage-frequency converter 17 External control variable 9 is the time for the present measurement task. Additional options for changing the Averaging as a function of the level of the level is shown in FIG. 5 by a connection of the output of the up / down counter 6 with control inputs of the correction network 15 and the Voltage-to-frequency converter 17 is shown. The function of voltage-frequency conversion the assembly 17 should include a suitable combination of all controlling input variables.

In all of the examples given so far, it is possible to use a variable reference source to create an additional control variable for the control loop .) or also to determine between unfiltered and filtered measured variable. Furthermore, it is possible to achieve special properties of a measured variable at this point, such as e.g. B ₀ simulating the so-called "acoustic reflex" when measuring the hearing impairment or programming an arbitrary response variable to be generated with a structure similar to FIG. 3,

Fig, 6 shows a simple measuring chain for determining the level. difference between the broadband at input E. Measuring signal and the sohraalbandigen component, IUe selected arrangement snrSunimlergli4ä 4

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causes a counter display of the level difference between the two Useful signal behind the narrowband filter 10 and the broadband level the broadband level at the Durohstiramen of the Sohmalbandfliters 10 does not experience any changes and therefore does not make any demands on time behavior. The counting pulses are derived in the same way as in Pig. 2.

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Claims (1)

Claims Arrangement for the digital determination of the level value of 'alternating voltages with influenceable time behavior of the Measurement value generation, consisting of a control circuit with a digitally controllable voltage divider located behind the input or an amplifier, a rectifier, a reference source that holds a reference source together with the connector output Summation element, one or more comparators and an up / down counter * its input gate and its Counting direction are controlled by the comparator output and its counter outputs once with the control inputs of the named digitally controllable voltage divider or amplifier and on the other hand connected to the output of the arrangement, daduroh marked that one in front of the entrance gate (7) of the up / down counter (6) located source for counting pulses (8) frequency-influencing and / or the reference source (3) have voltage-influencing control inputs that are marked with arbitrary points of the measuring chain and / or the sailing circle and / or external control variables, preferably via adaptation and Correction links (15) are connected " Arrangement naoh claim 1 with an additional input side Cohmal band filter, the output of which is connected to the input of the aforementioned control loop, daduroh marked, that either the output of the Sohmalbandfliters (10) or the output of the digitally controlled voltage divider or amplifier (1) are additionally led to inputs of a pulse shaper (11) arranged as a counting pulse source, the output pulse number of which with the number of zero continuous transitions of the input voltage of the pulse shaper (11) is in a fixed numerical ratio and that the output of the pulse shaper (11) via the input gate (7) is connected to the counting input of the up / down counter (6). - 17 - 609838/057 ^ Arrangement according to claims 1 and 2, preferably for amplitude control a measured variable, consisting of a generator of variable frequency, the output of which is connected to the input of the control loop connected and with an Ewisohen the exit of the controlled voltage divider or amplifier and the input of the rectifier switched device for generating and to measure any one on a given one Measurement location to be kept at a constant level or a level that can be changed according to a program, daduroh marked, that the output of the generator (12) is also led to an input of the pulse shaper (11), Arrangement naoh Anspruoh 1, daduroh characterized that the before the input interlock (7) source for counting pulses as Voltage-frequency converter (17) is carried out, the input of which either directly or via one of the comparator arrangement (5) controlled changeover switch (16) to an input-side with the output, which realizes the desired time behavior of the summation element (4) connected to the correction network (15), the second input of the controlled converter (16) is placed on a separate 8voltage source (14) is. Arrangement according to Claim 4, characterized in that the voltage-frequency converter (17) is used to achieve the desired Time behavior has several simultaneously acting control inputs, one of which is connected to the output of one on the input side with the summation element (4) connected Xor correction network— Plant (15) and the other inputs to any externally acting control variables (9) are contained, preferably Control inputs of the correction network, s (15) and des Voltage-frequency-tfasetEers (17) with the output of the up-down counter (6) can be connected. Arrangement according to claims 1 to 5, characterized in that a control input of the reference source (3) is connected to any point within the Hegel circle. - 18 - 609838 / 0S7Ö Arrangement according to requirements. 1 to 5, characterized in that the reference source (3) is preferably duroh realizes a L ^r eßgleiohriohter (18) whose Minpang leading to an arbitrary, jedooh nioht to the input of digitally controllable voltage divider or amplifier (1) the matching point of the weohselgröQen I. 'chain is connected. 809838 / 057Ö Blank page