WO2014095474A1 - Appareil de champ à sortie analogique - Google Patents

Appareil de champ à sortie analogique Download PDF

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Publication number
WO2014095474A1
WO2014095474A1 PCT/EP2013/076019 EP2013076019W WO2014095474A1 WO 2014095474 A1 WO2014095474 A1 WO 2014095474A1 EP 2013076019 W EP2013076019 W EP 2013076019W WO 2014095474 A1 WO2014095474 A1 WO 2014095474A1
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WO
WIPO (PCT)
Prior art keywords
output
digital
pulse
analog
digital value
Prior art date
Application number
PCT/EP2013/076019
Other languages
German (de)
English (en)
Inventor
Patrick Balle
Eric Chemisky
Original Assignee
Siemens Aktiengesellschaft
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 Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Publication of WO2014095474A1 publication Critical patent/WO2014095474A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
    • G01D3/02—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups with provision for altering or correcting the law of variation
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/66—Digital/analogue converters
    • H03M1/661—Improving the reconstruction of the analogue output signal beyond the resolution of the digital input signal, e.g. by interpolation, by curve-fitting, by smoothing

Definitions

  • the invention relates to a field device with an analog output, in particular a transmitter for process instrumentation with a 4-20 mA interface as an analog output, according to the preamble of claim 1.
  • a transmitter for process instrumentation with a 4-20 mA interface as an analog output, according to the preamble of claim 1.
  • the process instrumentation transmitter with 4-20 mA interface are versatile to Measurement of physical or chemical quantities, for example, a pressure, a temperature or a pH used. These usually have a sensor whose sensor signal is amplified, digitized and then evaluated in a microcontroller and corrected for linearity and temperature behavior.
  • the thus processed sensor signal is converted in an output circuit with a digital / analog converter into an analog output signal, here an output current in the range of 4-20 mA, and transmitted via a two-wire line to an evaluation device, such as a programmable logic controller in an automation network.
  • a programmable logic controller as a field device may have an analog output, for example for the transfer of a manipulated variable to a control valve as an actuator with a corresponding analog input.
  • digital / analog converters with different modes of operation are known.
  • digital / analog converter with R2R network available.
  • a disadvantage of these components are the associated costs and also their high power consumption. This can be a significant disadvantage, especially for field devices that are supplied with their power required for operation via a 4-20 mA interface, since the available energy is very limited.
  • a field device with an analog output is known in which a microcontroller is used to generate a pulse width modulated signal, which is guided on a low-pass filter for signal smoothing.
  • the pulse-width-modulated signal is obtained by means of a timer integrated in the microcontroller and a buffer, on which a highly accurate reference voltage is guided for accurate level adjustment.
  • a compromise between the achievable dynamics and the setting accuracy of the analog signal must be concluded.
  • the frequency of the pulse width modulated signal which has a direct effect on the dynamics, results from the bit resolution of the digital / analog conversion and the clock frequency of the microcontroller and is proportional to the product of these two variables.
  • the timing of the microcontroller has a direct effect on its power consumption and can not be increased arbitrarily.
  • the frequency of the pulse width modulated signal can not be arbitrarily reduced in order to achieve a higher bit resolution, since this is decisive for the dynamics of the generated analog output signal.
  • a stepwise digital / analog conversion is carried out with a first stage in which first two analog signals with a lower resolution are generated, which are above and below the desired analog output signal lie, and with a downstream, second stage, in which the two analog signals generated in the first stage are used as the level of another pulse width modulated signal whose pulse-pause ratio must be set only with an accuracy that compared to the coarse resolution corresponds to the first stage still to be achieved further resolution.
  • the microcontroller can now be clocked at a lower frequency, so that the power consumption of the microcontroller As a result, more energy is available for the actual measuring task of the transmitter and, for example, for diagnostic functions. This can increase the measurement accuracy and reliability of the transmitter.
  • the invention has for its object to further improve the dynamics of an analog output for a field device with relatively little overhead.
  • the new field device of the type mentioned in the characterizing part of claim 1 features.
  • advantageous developments of the invention are described.
  • the invention is based on the finding that the dynamics of a high-resolution digital-to-analog converter can be increased in a particularly simple manner if, at times of otherwise insufficient dynamics, namely the occurrence of sudden changes in the analog signal to be converted Digital value, by applying a pulse to the output of a low-pass filter used for smoothing in the digital / analog converter, the change tracking is accelerated.
  • the PulsaufSclien In normal operation, that is, when no jumps in the measured value and thus the digital value occur in the stationary case, however, the PulsaufSclien is disabled so that it does not distort the output of the high-precision converter.
  • the invention thus has the advantage that the accuracy of the analog output signal can be maintained, but at the same time the reaction time is significantly increased at sudden changes.
  • highly accurate digital / analog converters of any type can be combined with the pulse-on circuit to increase the dynamics of the high-precision digital / analog converter.
  • a microcontroller for detecting a sudden change in the digital value is provided.
  • the same microcontroller generates a pulse-width-modulated signal as a function of the high-resolution digital value, which in a subsequent Switched RC second-order low-pass filter is smoothed. Furthermore, the microcontroller delivers the pulse for rapid change tracking on a tristate output.
  • Tristate output is activated for the predetermined period of the pulse immediately after the detection of sudden changes in the digital value and switched back into the high-impedance state after their expiration.
  • the charge state of a capacitor in an RC low-pass connected downstream of the tristate output is therefore changed only after the occurrence of discontinuous changes of the digital value by the pulse signal. Since both the first RC low-pass and the second at their output each have a capacitor and the two outputs of the low-pass filters are connected, there is a parallel connection of the two capacitors and it can be used to further reduce the manufacturing cost of the digital / analog converter the two capacitors are omitted.
  • a significant improvement in the dynamics is achieved even with different, strongly divergent jump heights of the detected changes in the digital value, if the respective duration of the pulse is predetermined in dependence of the respectively determined jump height.
  • the time duration is advantageously predetermined in such a way that after renewed deactivation of the tristate output, the signal level at the analog output corresponds at least approximately to the digital value. This can be done, for example, by calculating an analytical function which describes the relationship between detected jump height and suitable time duration, or by means of a characteristic curve or a characteristic field.
  • microcontroller Since a microcontroller is present in most field devices anyway, a particularly simple realization of the high-precision digital / analog converter with improved dynamics can be achieved if the microcontroller detects a sudden change in the digital value due to suitable programming, depending on the respective step.
  • height determines a suitably predetermined period of time for activating the tristate output of the pulse timer, using two integrated timer generates the pulse width modulated signal and the pulse for rapid change tracking and the
  • Tristate output of the second timer which provides the pulse, activated for the determined period of time after the detection of a step change.
  • Figure 2 is a functional block diagram for explaining the
  • a measuring transducer 1 for detecting a physical or chemical quantity X of a process has a pick-up 2, which converts this quantity into a measuring signal 3.
  • the measurement signal 3 is amplified and digitized.
  • the thus preprocessed measurement signal is fed to a microcontroller 5, which makes, for example, a compensation of non-linearities and temperature influences and calculates the measured value to be output.
  • the digital measured value ascertained by the microcontroller 5 is converted into an analog output signal which is transmitted via a 4-20 mA interface 7 for further use in a process plant in which the measuring transducer 1 is used. is issued.
  • the block diagram according to FIG. 2 shows the essential functional components which are connected to the digital / analogue Implementation are involved.
  • the digital value D is fed to a digital / analog converter whose essential components form a first timer 21 and a first RC low-pass filter 22.
  • a pulse width modulated signal Ul is generated in a known manner, the frequency of which is 16 hertz, for example, due to the high resolution and the clock frequency of the microcontroller 20.
  • the pulse-width-modulated signal U1 is smoothed and, in the stationary case, an analog output signal U0 is generated at the output, which is characterized by high accuracy due to the high resolution of the digital / analogue converter.
  • the first RC low-pass filter 22 consists of two first-order delay elements 23 and 24.
  • means for connecting a pulse to the output of the first RC low-pass filter 22 are additionally present essential components are a second timer 25 and a downstream, second RC low pass 26.
  • the second RC low-pass filter 26 consists in the embodiment shown only of a first-order delay element.
  • the first RC low-pass filter 22, like the second RC low-pass filter 26, has a capacitor at its output. Both capacitors are in a real circuit to reduce the
  • the analog output signal U0 is used to implement a 4-20 mA
  • Interface as an analog output of a field device, for example, as an analog voltage with a voltage level corresponding to the digital value on the basis of a field effect transistor. tor, which serves in a known manner for adjusting the loop current on the 4-20 mA interface.
  • any converter principles can be used.
  • the already known from the aforementioned DE 10 2007 046 560 AI known converter is used, which is characterized by high accuracy with already comparatively good dynamics.
  • the coarse fraction determined there can then be used simultaneously as a digital coarse part G for the second timer 25.
  • the second timer 25 has a tristate output 27, which in the stationary case, that is to say when no jumps of the digital value D occur which significantly exceed the resolution of the digital coarse part G, is switched to high-resistance state by programming the microcontroller 20.
  • the second timer does not have a tristate output
  • the tristate output can be implemented in a simple manner by means of a tristate buffer connected downstream of the second timer.
  • the stationary case in which the tristate output 27 of the second timer 25 is switched to high-impedance state.
  • the stepwise change of the digital value D from the initial voltage ul to the final voltage u2 is detected and, in order to achieve a rapid response to the change, the pulse lock is activated by activating the tristate output 27 and one of the End voltage u2 corresponding pulse signal U2 is generated with a high level on, for example, a reference voltage.
  • a possibly existing tristate output of the first timer 21 still remains in the active state, so that the pulse width modulated signal U1 is also generated corresponding to the new digital value for the final voltage u2.
  • the time period Atl is predetermined in such a way that, after its expiry, the signal level at the analog output corresponds approximately to the final voltage u2 and thus to the new digital value.
  • the microcontroller 20 calculates the time period Atl as a function of the respective jump height and in dependence on the position of the initial voltage ul and / or the final voltage u2 in such a way that the level accuracy reached at the time of the deactivation of the tristate output 27 is already approximately equal to the resolution of the digital coarse fraction G. of the digital value D corresponds.
  • the steady state case again sets in, in which the signal level at the analogue output is determined solely by the digital / analogue converter 21, 22.
  • the sequence controlled by the microcontroller 20 upon detection of a sudden change in the negative direction at the time t2 largely corresponds to that of the positive jump at the time t1. Only the time duration At2 and the level of the pulse signal U2, which is now switched to low level, for example GND, differ, since they correspond here to the sudden change from the voltage u2 to the voltage ul to be readjusted.
  • the invention was exemplified with a digital / analog converter, which based on
  • Pulse width modulation works. However, it is equally applicable to other types of converters. Depending on the requirements, in addition to the described embodiment, in which the digital coarse fraction G has half the bit width of the digital value D, any other bit width ratios can be selected.

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  • Engineering & Computer Science (AREA)
  • Technology Law (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Analogue/Digital Conversion (AREA)

Abstract

L'invention concerne un appareil de champ pourvu d'une sortie analogique, en particulier un convertisseur de mesure (1) permettant une instrumentation de processus au moyen d'une interface 4-20 mA en tant que sortie analogique (7). Un convertisseur numérique/analogique (21, 22) de très haute précision règle à lui-seul, dans le cas fixe, un niveau de signal lissé par un premier filtre passe-bas RC (22) sur la sortie analogique en fonction d'une valeur numérique (D). A l'apparition d'une brusque modification de la valeur numérique (D), une impulsion est affectée en plus à la sortie du premier filtre passe-bas RC (22). Après le changement de niveau, l'affectation d'impulsion (25, 26) est à nouveau désactivée. Un convertisseur numérique/analogique est donc obtenu avec une fabrication relativement simplifiée, et fournit un signal de sortie analogique à haute résolution et à dynamique améliorée.
PCT/EP2013/076019 2012-12-19 2013-12-10 Appareil de champ à sortie analogique WO2014095474A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102012223706.2A DE102012223706A1 (de) 2012-12-19 2012-12-19 Feldgerät mit einem Analogausgang
DE102012223706.2 2012-12-19

Publications (1)

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WO2014095474A1 true WO2014095474A1 (fr) 2014-06-26

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DE (1) DE102012223706A1 (fr)
WO (1) WO2014095474A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107218955B (zh) * 2016-03-22 2021-04-20 横河电机株式会社 现场设备以及检测器
DE102016207289B3 (de) * 2016-04-28 2017-05-04 Siemens Aktiengesellschaft Feldgerät zur Bestimmung einer Prozessgröße in der Prozessautomatisierung

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19728037A1 (de) * 1997-07-01 1999-01-07 Rexroth Mannesmann Gmbh Verfahren und Vorrichtung zur Umsetzung eines Digitalwertes in einen Analogwert
DE102007046560A1 (de) 2007-09-28 2009-04-02 Siemens Ag Feldgerät mit einem Analogausgang
DE102008054053A1 (de) * 2008-10-30 2010-05-06 Siemens Aktiengesellschaft Feldgerät für die Prozessautomatisierung
DE102009026785A1 (de) * 2009-01-30 2010-08-05 Endress + Hauser Gmbh + Co. Kg Feldgerät zur Bestimmung und/oder Überwachung einer physikalischen oder chemischen Prozessgröße

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10202028A1 (de) * 2002-01-18 2003-07-24 Endress & Hauser Gmbh & Co Kg Transmitter
DE10350100B4 (de) * 2003-10-27 2013-01-03 Kwl-Lighting Gmbh Steuervorrichtung und Verfahren zur Steuerung eines Leuchtelementes

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19728037A1 (de) * 1997-07-01 1999-01-07 Rexroth Mannesmann Gmbh Verfahren und Vorrichtung zur Umsetzung eines Digitalwertes in einen Analogwert
DE102007046560A1 (de) 2007-09-28 2009-04-02 Siemens Ag Feldgerät mit einem Analogausgang
DE102008054053A1 (de) * 2008-10-30 2010-05-06 Siemens Aktiengesellschaft Feldgerät für die Prozessautomatisierung
DE102009026785A1 (de) * 2009-01-30 2010-08-05 Endress + Hauser Gmbh + Co. Kg Feldgerät zur Bestimmung und/oder Überwachung einer physikalischen oder chemischen Prozessgröße

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