EP0979556A1 - Procede et dispositif pour la numerisation d'un signal de mesure analogique a dynamique elevee - Google Patents

Procede et dispositif pour la numerisation d'un signal de mesure analogique a dynamique elevee

Info

Publication number
EP0979556A1
EP0979556A1 EP98931923A EP98931923A EP0979556A1 EP 0979556 A1 EP0979556 A1 EP 0979556A1 EP 98931923 A EP98931923 A EP 98931923A EP 98931923 A EP98931923 A EP 98931923A EP 0979556 A1 EP0979556 A1 EP 0979556A1
Authority
EP
European Patent Office
Prior art keywords
analog
digital
data word
measurement signal
sampling time
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP98931923A
Other languages
German (de)
English (en)
Inventor
Stephan Mohr
Stefan Hain
Thomas Bosselmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP0979556A1 publication Critical patent/EP0979556A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/18—Automatic control for modifying the range of signals the converter can handle, e.g. gain ranging
    • H03M1/181—Automatic control for modifying the range of signals the converter can handle, e.g. gain ranging in feedback mode, i.e. by determining the range to be selected from one or more previous digital output values
    • H03M1/183—Automatic control for modifying the range of signals the converter can handle, e.g. gain ranging in feedback mode, i.e. by determining the range to be selected from one or more previous digital output values the feedback signal controlling the gain of an amplifier or attenuator preceding the analogue/digital converter
    • H03M1/185—Automatic control for modifying the range of signals the converter can handle, e.g. gain ranging in feedback mode, i.e. by determining the range to be selected from one or more previous digital output values the feedback signal controlling the gain of an amplifier or attenuator preceding the analogue/digital converter the determination of the range being based on more than one digital output value, e.g. on a running average, a power estimation or the rate of change

Definitions

  • the invention relates to a method and a device for digitizing an analog measurement signal.
  • An analog measurement signal is understood to mean a measurement signal whose amplitude is proportional to the measured size (amplitude-analog measurement signal).
  • analog measurement signals with high dynamics occur, which must be recorded and digitally transmitted to avoid interference, such as electromagnetic interference.
  • new types of inductive converters for measuring nominal currents and overcurrents in a high-voltage power conductor e.g. overhead line
  • analog current measurement signals with a dynamic range of 1: 2000 generate analog current measurement signals with a dynamic range of 1: 2000.
  • the analog measurement signals are first converted into a transmission data word of a word length (number of bits per word) predetermined by the digital resolution of the ADC, for example a 12-bit data word, in an analog-digital converter (ADC).
  • ADC analog-digital converter
  • the transmission data word is transmitted to an evaluation unit and further processed there, for example in a digital-to-analog converter (DAC) of the same digital resolution as the ADC, or converted back into an analog measurement signal also processed and / or output as a digital measured value.
  • DAC digital-to-analog converter
  • absolute errors in particular such as quantization errors in particular, limit the relative accuracy that can be achieved.
  • the relative over The smaller the quantization error on the one hand and the higher the transmission channel is controlled, the smaller the transmission error.
  • the upper limit control of the transmission channel, in particular the ADC limits the achievable dynamics for a given absolute error.
  • the dynamics of the digital measurement signal transmission can now be increased by reducing the absolute error of the transmission channel by using a higher-resolution ADC (with a larger number of bits of the data words). However, this increases the complexity of the circuitry and, above all, the energy consumption.
  • the relative accuracy of a described digital transmission channel is highest in the upper modulation range of the transmission channel, which corresponds to the upper measuring range of the analog measuring signal.
  • the situation is exactly the opposite when it comes to measuring current in energy technology.
  • the analog measurement signal can be scaled with a few discrete scaling factors, corresponding to a measurement range selection for an ampere / voltmeter, so that the transmission channel is controlled within predetermined limits.
  • analog-to-digital converters each with an upstream amplifier, can be connected in parallel, the amplifiers having different fixed gain factors in pairs.
  • the measurement signal is applied to the inputs of the amplifiers, and the output data word of the analog-digital converter that is processed by the associated , ß ß -.
  • the analog / digital converter in the system according to the invention can be optimally controlled at any time over a large dynamic range, regardless of the input signal.
  • FIG. 1 shows a device for digitizing and digitally transmitting an analog measurement signal in a basic structure
  • FIG. 2 shows a device for digitizing and digital
  • FIGS. 1 and 2 Transmission of analog measurement signals from a sensor head to a ground station and FIG. 3 a scaler with a multiplying digital-to-analog converter. Corresponding parts are provided with the same reference numerals in FIGS. 1 and 2.
  • the digital transmission system comprises a scaler 2, an analog-digital converter 3, a control device 4, a deskaler 5 and a digital-analog converter 6.
  • the analog measurement signal M to be transmitted is present at an input 21 of the scaler 2 .
  • This analog measurement signal M is a measure of a measurement variable measured by a sensor, for example an electrical current or an electrical voltage or a temperature or a pressure, and is in usually a band-limited and generally also continuous signal from a given measuring range. Even with a relatively wide measuring range for the measuring signal M and a correspondingly high signal dynamic, the measuring signal M should be digitized with a high relative accuracy and preferably be transmitted thereafter. This is achieved with the following measures.
  • Input 21 of the scaler 2 can be switched to suppress interference, an anti-aliasing filter, not shown.
  • the analog-digital converter 3 samples the scaled measurement signal M 'at sampling times ti with the natural number i as a counting index and forms the sampled ones
  • These transmission data words D (ti) are firstly supplied to the control device 4 via a data bus 11.
  • the control device 4 stores the transmission data words D (ti) with the associated sampling times ti in a memory 41 and forms a tten, current sampling time tn from a part and at least two of the last stored transmission data words D (ti) and the associated sampling times ti with i ⁇ n the scaling factor A (tn) at the current sampling time tn for the scaler 2.
  • the current scaling factor A (tn) can be calculated as the ratio of an extrapolated prospective transmission data word PD (tn) for the considered sampling time tn and a predetermined data word setpoint DS for the transmission data words D (ti) and D (tn ) be calculated.
  • the prospective transmission data word PD (tn) can be calculated by means of an extrapolation method known per se from at least two of the earlier stored value pairs (D (tn-1), tn-1), (D (tn-2), tn-2), in particular by linear extrapolation (eg gradient method) or also extrapolations with higher derivatives and also taking into account the differential equation of the anti-aliasing filter mentioned.
  • the signal amplitudes M (ti) of the analog measurement signal M at the previous sampling times ti with i ⁇ n are determined from the known associated scaling factors A (ti) and the known transmission data words D (ti) and it is determined from these signal amplitudes M (ti) predicts a prospective measurement signal PM (tn) at a current sampling time tn.
  • the current scaling factor A (tn) is now determined so that the product
  • a (tn) -PM (tn) is mapped by the analog-digital converter 3 to the data word setpoint DS.
  • the time profile of the measurement signal M or the scaled measurement signal M ' can also be tracked and evaluated via an analog circuit, for example a delay line (delay circuit).
  • Such an analog time evaluation can in particular also be used in combination with the described digital evaluation to protect the analog-digital converter 3 from being overloaded by transient interference signals.
  • the additional analog signal line 7 shown in FIG. 1 is then provided, via which the control device 4 is supplied with the analog measurement signal M.
  • the control device 4 then contains an analog differentiator for determining the signal change and a downstream comparator for comparing this signal change with a maximum permissible change and sets a predetermined maximum or minimum value for the prospective measurement signal PM or the prospective transmission data word D instead of the respectively calculated prospective value, if the predicted prospective value exceeds a predetermined limit due to the high signal gradient.
  • Transient interference signals in particular at higher frequencies (e.g. interference edges or other discontinuous signal changes) can also be suppressed by a band limitation by means of a low pass, for example the already mentioned anti-aliasing low pass, in front of the input 21 of the scaler 2.
  • a low pass for example the already mentioned anti-aliasing low pass
  • the data word setpoint DS is in the upper modulation range and preferably as close as possible to the outer limit (edge) of the modulation range (value range for the transmission data Words D (ti)) of the analog-digital converter 3 are selected, a small distance between the data word setpoint DS and this control limit being advantageous in order to take possible transients into account.
  • the data word setpoint DS is, for example, in a range between a corresponding numerical value 2 P ⁇ 1 and the numerical value 2 P -1 with maximum control of the analog-digital converter 3 for the transmission data words D (ti). A consistently high relative accuracy of the digitization is achieved over the entire measuring range of the analog measuring signal.
  • two data word setpoints for example + DS and -DS, can be taken into account, or with only one data word setpoint DS the amount or an effective value of an original measurement signal can be used as the measurement signal M or by selecting the sign of the scaling factor A ( ti) the scaled measurement signal M 'is always kept at one polarity (a sign).
  • the bit width (word length) of the transmission data words (D (ti)) determined by the digital resolution capacity of the analog-digital converter 3 is generally at least 10 bits, preferably at least 12 bits, and can also be higher, for example 16 bits.
  • the scaling factor A (ti) is preferably a binary data word.
  • the number of bits m of the digital scaling factor A (ti) determines the fineness of the scaling, since the number 2 m of the individual numerical values which the scaling factor A (ti) can assume naturally increases considerably with increasing number of bits m.
  • the bit number m of the scaling factor A (ti) is in generally not less than 8, in particular at least 10 bits and preferably at least 12 bits or 16 bits.
  • Such continuous control can also be achieved in an embodiment not shown with an analog scaling factor A and an associated analog controllable scaler, for example a controllable operational amplifier.
  • the transmission data words D (ti) at the sampling times ti, in particular the current transmission data word D (tn), can now be fed directly to signal processing or, as shown in FIG. 1, can be transmitted to the deskaler 5 via a digital transmission path 10.
  • the deskaler 5 multiplies each transmitted transmission data word D (ti) or D (tn) by the reciprocal value l / A (ti) or 1 / A (tn) of the scaling factor A (ti) or A (tn) and reconstructs it thereby the original measurement signal value M (tn) at the current sampling time tn in the form of a measurement data word (digital measurement signal value), which is denoted by E (ti) or E (tn).
  • This measurement data word E (ti) or E (tn) can now be converted with an (or more parallel-connected) digital-to-analog converter 6 into an analog evaluation signal M ′′ whose signal amplitude M ′′ (ti) Signal amplitude M (ti) of the original analog measurement signal M corresponds.
  • the device shows an embodiment of a device for digitally transmitting an analog electrical measurement signal for an electrical current or an electrical voltage in a high-voltage current conductor, not shown, for example an energy transmission network (overhead line or the like).
  • Such measurement signals generally have a limited bandwidth because of the properties of the network.
  • the device is partially integrated in a sensor head 30, which is at the high voltage potential and additionally a current sensor, not shown, for example an inductive converter, a shunt sensor or an optical Faraday sensor, or voltage converter, in particular an optical Pockels sensor.
  • Sensor which provides the measurement signal M, if necessary with the help of an optoelectric converter in electrical form.
  • the scaler 2 contains a multiplying digital-to-analog converter 20 with the measurement signal M as an analog input signal at an input 21.
  • the scaling factor A (ti) is converted with the analog measurement signal M as a multiplier into an output signal M 'as a scaled measurement signal which is present at the output 24 of the scaler 2.
  • An operational amplifier for further (fixed) amplification of the scaled measurement signal M ' is preferably connected between the multiplying digital-to-analog converter 20 and the output 24 of the scaler 2.
  • the scaled measurement signal M ' is fed from the output 24 of the scaler 2 to the input 31 of the analog-digital converter 3.
  • the analog-digital converter 3 scans (as in FIG. 1) the measurement signal M 'regularly at sampling times ti and converts the corresponding measurement signal amplitude M' (ti), which can be positive or negative, into a corresponding digital transmission data word D (ti) with a predetermined resolution.
  • a control device 8 is arranged in a ground station 40 which is at ground potential and is connected to the sensor head 30 via a bidirectional digital transmission path 12.
  • the digital transmission path 12 branches off in the sensor head 30 into a unidirectional digital transmission path 13 and a further, bidirectional digital transmission path 14.
  • the data word of the scaling factor A (ti) is transmitted from the control device 8 to the multiplying digital-to-analog converter 20 via the digital transmission path 12 and then the digital transmission path 13.
  • the sampling times ti in the form of digital values are transmitted from the control device 8 to the analog-digital converter 3 via the bidirectional digital transmission paths 12 and 14 and the transmission data words D (ti) are transmitted from the analog-digital converter 3 to the control device 8.
  • the downstream digital-to-analog converter 6, which receives the measurement data words E (ti) from the control device 8 via the data line 15, converts the measurement data words E (ti) back into the signal amplitudes M '' (ti) of an analog measurement signal M ''.
  • a higher resolution than the analog-digital converter 3 can also be provided for this conversion, for example have at least a 16-bit resolution to achieve greater accuracy.
  • a plurality of digital-to-analog converters can also be provided, for example a converter for the nominal current range and a converter for the protective range (overcurrents).
  • the measurement data words E (ti) can also be used directly as digital measurement signals without D / A conversion.
  • multiplying digital-to-analog converter 20 As a multiplying digital-to-analog converter 20, all known embodiments can be used, for example according to the book Tietze, Schenk, "semiconductor switching technology", 6th edition, Springer publishing house, 1983, Be th 742 and 743 and 750 and 751, the content of which is incorporated in the disclosure of the present application, or the commercially available components AD 7943 / AD7945 / AD7948 from the company Analog Devices, these known multiplying digital-to-analog converters comprise a digitally controllable current divider network, in particular an R-2R Resistor network, and a downstream operational amplifier.
  • FIG. 3 A particularly advantageous embodiment of a multiplying digital-to-analog converter is shown in FIG. 3 in an equivalent circuit diagram.
  • An operational amplifier 50 with an inverting input 54 and a non-inverting input 53 and an output 55 is provided.
  • a current divider network 57 is shown with an input resistor 56 and two digitally controllable subnetworks 51 and 52, which are shown in the equivalent circuit diagram as controllable resistors.
  • the subnetworks 51 and 52 can, for example, each comprise an R / 2R resistance network with assigned switches, the switch positions of which are determined by the individual bits of the digital control data word.
  • the output 55 of the operational amplifier 50 is via the sub-network 52 with the non-inverting input 53 and

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  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Analogue/Digital Conversion (AREA)
  • Measurement Of Current Or Voltage (AREA)

Abstract

L'invention concerne un procédé et un dispositif permettant de numériser un signal de mesure (M) analogique. A cet effet, le signal de mesure (M) est mis à l'échelle par multiplication par un facteur de mise à l'échelle (A(ti)), les amplitudes du signal de mesure ainsi mises à l'échelle (M'(ti)) sont, à des moments d'échantillonnage (ti) se succédant, chaque fois transformées en un mot de donnée (D(ti)) par un convertisseur analogique-numérique, et ce mot de donnée (D(ti)) est, par réglage du facteur de mise à l'échelle (A(ti)) à chaque moment d'échantillonnage (ti), régulé à une valeur de consigne de mot de donnée (DS) prédéterminée, en dehors de la plage de sortie du convertisseur analogique-numérique (3).
EP98931923A 1997-04-28 1998-04-15 Procede et dispositif pour la numerisation d'un signal de mesure analogique a dynamique elevee Withdrawn EP0979556A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE19717680 1997-04-28
DE19717680 1997-04-28
PCT/DE1998/001059 WO1998049776A1 (fr) 1997-04-28 1998-04-15 Procede et dispositif pour la numerisation d'un signal de mesure analogique a dynamique elevee

Publications (1)

Publication Number Publication Date
EP0979556A1 true EP0979556A1 (fr) 2000-02-16

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EP98931923A Withdrawn EP0979556A1 (fr) 1997-04-28 1998-04-15 Procede et dispositif pour la numerisation d'un signal de mesure analogique a dynamique elevee

Country Status (3)

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EP (1) EP0979556A1 (fr)
JP (1) JP2001522550A (fr)
WO (1) WO1998049776A1 (fr)

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Publication number Priority date Publication date Assignee Title
US6292120B1 (en) * 2000-03-02 2001-09-18 Adc Telecommunications, Inc. Automatic gain control for input to analog to digital converter
JP4432530B2 (ja) * 2004-02-23 2010-03-17 パナソニック株式会社 デジタル信号処理アンプ

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CH688459A5 (de) * 1992-02-04 1997-09-30 Ascom Audiosys Ag Verfahren zur Digitalisierung eines Signals, Verarbeitungseinheit zu dessen Ausfuehrung

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Title
See references of WO9849776A1 *

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WO1998049776A1 (fr) 1998-11-05
JP2001522550A (ja) 2001-11-13

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