EP1103038B1 - Circuit for recording, transmitting and evaluating measured values - Google Patents

Abstract

The invention relates to a circuit for recording, transmitting and evaluating measured values. Said circuit comprises a measured value recording part (1), a measured value evaluating part (2) and a connection (5) which is located between the measured value recording part (1) and the measured value evaluating part (2) and which consists of only a forward line (3) and a return line (4). The measured value recording part (1) comprises a measured value sensor (6), a measuring transducer circuit (7), a switching controller (8) connected in incoming circuit to said measuring transducer circuit (7), and a current regulator (9) connected in incoming circuit to said switching controller (8). The measured value evaluating part (2) has a voltage source (10) and an evaluating circuit (11), and the switching controller (8) supplies a constant operating voltage for the measuring transducer circuit (7). The current regulator (9), controlled by the measuring transducer circuit (7), adjusts a measured value current and supply current which represents the measured value and which flows through the forward line (3) and the return line (4). According to the invention, the power available to the measuring transducer circuit (7) is optimized by virtue of the fact that the current consumption of the measuring transducer circuit (7) can be controlled and is controlled such that the voltage drop via the current regulator (9) is as small as possible.

Description

The invention relates to a circuit arrangement for measured value acquisition, transmission and evaluation, comprising a Meßwerterfassungsteil, with a Meßwertauswertungsteil and with an existing only one outgoing line and a return line connection between the Meßwerterfassungsteil and Meßwertauswertungsteil, wherein the Meßwerterfassungsteil a transducer, a Meßwandlerschaltung, a switching regulator upstream of the switching regulator and a switching regulator upstream power controller, wherein the Meßwertauswertungsteil has a voltage source and an evaluation circuit and wherein the switching regulator provides a constant operating voltage for the Meßwandlerschaltung and the current controller, controlled by the Meßwandlerschaltung, representing the measured value, via the forward line and the return line sets flowing Meßwertund supply current, the current consumption of the transducer circuit is controllable and by a short itige reduction of the current consumption of the transducer circuit is controlled so that the voltage drop across the current controller is as small as possible and wherein parallel to the input of the switching regulator, a capacitor is connected.

Circuit arrangements of the type in question are widely known (cf., for example, the German patent 39 34 007 , the European disclosure 0 744 724 , the German publication 197 23 645 and especially the US 5,416,723 A ), For these circuits is essential that the connection between the Meßwerterfassungsteil and Meßwertauswertungsteil only consists of two lines and that flows through these two lines, a current that represents both the measured value and the power supply of the Meßwerterfassungsteils used; the current flowing through the two lines has consequently been referred to as the measurement and supply current.

Frequently, circuit arrangements of the type in question are designed and designed such that the voltage source located in the measured value evaluation part is a DC voltage source, that is to say the measured value and supply current is a direct current. These circuits are also often designed and designed so that the Meßwert- and supply current between a lower limit, namely 4 mA, and an upper limit, namely 20 mA, represents the measured value; the lower limit of 4 mA thus represents the smallest measured value, the upper limit of 20 mA the largest measured value (see the German Patent 39 34 007 , Page 2, lines 19 to 24).

In the following, it is always assumed that the circuit arrangement in question is one in which the voltage source provided in the measured value evaluation part is a DC voltage source, that is to say the measured value and supply current is a direct current. This is also the reason why the connection between the measured value detecting part and the measured value evaluating part has already been described as being composed of an outgoing line and a return line. Incidentally, the technical current direction is always assumed below; In a circuit connected to a DC voltage source, therefore, the DC current flows from the positive pole of the DC voltage source via the circuit to the negative pole of the DC voltage source.

The part of the circuit in question, which is previously and subsequently designated with Meßwerterfassungsteil is also known as a transmitting station (see, the German Patent 39 34 007 ) or as a donor agency (see European Published Application 0 744 724 and the German Offenlegungsschrift 197 23 645 ), while the part of the circuit in question referred to herein as Meßwertauswertungsteil also as a receiving station (see, the German Patent 39 34 007 ) or as the place of receipt (see European Published Application 0 744 724 and the German Offenlegungsschrift 197 23 645 ) referred to as. The connection between the measured value detection part and the measured value evaluation part, which is made according to the terminology used here, consisting of an outgoing line and a return line, is also referred to as a two-wire line (see German Patent Specification 39 34 007 , the European disclosure 0 744 724 and the German Offenlegungsschrift 197 23 645 ).

Since in the circuit arrangements in question - measured value representing - Meßwertstrom - as shown, usually lying between 4 mA and 20 mA - is also the supply current for the Meßwerterfassungsteil, which is the Meßwerterfassungsteil available electrical power through the lower Limit value of the measured value and supply current, so usually limited by 4 mA, - which is often problematic (see the German Patent 39 34 007 , Page 2. lines 25 to 42).

In the circuit arrangement in question, the Meßwandlerschaltung - with the associated transducer - actually the most functionally important part. In the case of the circuit arrangement in question, an operating state may occur in which the measured value and supply current can not be set proportionally to the measured value. The present invention is therefore based on the object to provide a circuit arrangement which does not have the problem described above.

Fig. 1

ein erstes Ausführungsbeispiel einer Schaltungsanordnung,

Fig. 2

ein zweites Ausführungsbeispiel einer erfindungsgemäßen Schaltungsanordnung,

Fig. 3 bis 6

graphische Darstellungen zur weiteren Erläuterung der Erfindung.

According to the above-mentioned object in a circuit arrangement of the type described initially and essentially solved in that one, controlled by the Meßwandlerschaltung, activated only when needed second power converter is provided and the second power controller with its input to the input of the first power controller and with its output connected to the return line. That and why with this measure the problem underlying the invention is achieved will be explained below with reference to a drawing in detail. In the drawing show

Fig. 1

a first embodiment of a circuit arrangement,

Fig. 2

A second embodiment of a circuit arrangement according to the invention,

Fig. 3 to 6

graphical representations for further explanation of the invention.

The in the Fig. 1 and 2 Circuit arrangements are determined and suitable for measured value acquisition, transmission and evaluation and consist in their basic structure of a Meßwerterfassungsteil 1, from a Meßwertauswertungsteil 2 and from a - consisting of only one forward line 3 and 4 from a return line - connection 5 between the Meßwerterfassungsteil 1 and the measured value evaluation part 2.

As the FIGS. 1 and 2 show, to the Meßwerterfassungsteil 1 an only indicated transducer 6, a transducer circuit 7, a the transducer circuit 7 upstream switching regulator 8 and the switching regulator 8 upstream Current controller 9. The measured value evaluation part 2 includes a voltage source 10 and an evaluation circuit 11. In the exemplary embodiments shown, two resistors 12, 13 are provided. The evaluation circuit 11 is parallel to the resistor 13; the evaluation circuit 11 is thus supplied to the resistor 13 resulting, the Meßwert- and supply current proportional voltage drop.

The switching regulator 8 supplies a - at least substantially - constant operating voltage for the transducer circuit 7. (For what is a switching regulator and how a switching regulator works, reference is made to the German patent 39 34 007 , Page 3, line 64, to page 4, line 45, and to the references Tietze. Schenk "Semiconductor Circuit Technology", 10th edition, Springer-Verlag, sections 18.5 "Switching power supplies", 18.6 "Secondary clocked switching regulator" and 18.7 "primary clocked switching regulator", pages 565-586 , and " Lexicon Electronics and Microelectronics ", VDI-Verlag, page 733 ). In the following, an ideal switching regulator is always assumed, ie a switching regulator which has no power loss and whose output voltage is constant.

The current controller 9 is controlled by the transducer circuit 7. By the current controller 9 a measuring value representing, on the forward line 3 and the return line 4 flowing Meßwert- and supply current is set. (The circuit part referred to here with current controller is also referred to as a controllable current source, so at least in the European published patent application 0 744 724 and in the German Offenlegungsschrift 127 23 645 , Instead of the term current controller, the term current controller is also used.)

In the illustrated and described circuit arrangements, the voltage source 10, the resistor 12, the forward line 3, the current regulator 9, the primary side of the switching regulator 8, the return line 4 and the resistor 13 are connected in series; they form a first circuit. The secondary side of the switching regulator 8 and the transducer circuit 7 form a second circuit.

In the Fig. 1 and 2 is still a resistance of the lead 3 embodying resistor 14 and a resistance of the return line 4 embodying resistor 15 is shown.

• mit U₁ die Spannung der Spannungsquelle 10,
• mit U₂ die Spannung am "Eingang" der aus der Hinleitung 3 und der Rückleitung 4 bestehenden Verbindung 5 zwischen dem Meßwertauswertungsteil 2 und dem Meßwerterfassungsteil 1,
• mit U₃ die Spannung am Eingang des Meßwerterfassungsteils 1,
• mit U₄ die Spannung am Eingang des Schaltreglers 8,
• mit U₅ die Spannung am Ausgang des Schaltreglers 8, die gleich der Spannung am Eingang der Meßwandlerschaltung 7 ist,
• mit I₁ der durch das Meßwertauswertungsteil 2 fließende Strom,
• mit I₂ der über die Hinleitung 3 und über die Rückleitung 4 fließende Strom,
• mit I₃ der durch das Meßwerterfassungsteil 1 fließende Strom,
• mit I₄ der primärseitig durch den Schaltregler 8 fließende Strom und
• mit I₅ der sekundärseitig durch den Schaltregler 8 und durch die Meßwandlerschaltung 7 fließende Strom.

Hereinafter referred to

• with U _1, the voltage of the voltage source 10,
• with U ₂ the voltage at the "input" of the connection 5 consisting of the forward line 3 and the return line 4 between the measured value evaluation part 2 and the measured value detection part 1,
• with U ₃ the voltage at the input of the measured value acquisition part 1,
• with U ₄ the voltage at the input of the switching regulator 8,
• with U _5, the voltage at the output of the switching regulator 8, which is equal to the voltage at the input of the transducer circuit 7,
• with I ₁ the current flowing through the measured value evaluation part 2,
• with I ₂ the current flowing via the forward line 3 and via the return line 4,
• with I ₃ the current flowing through the measured value detecting part 1,
• with I _{4 of} the primary side by the switching regulator 8 flowing current and
• with I _{5 of} the secondary side through the switching regulator 8 and through the transducer circuit 7 current flowing.

• Die Leistung P₁, die die Spannungsquelle 10 im Meßwertauswertungsteil 2 zur Verfügung stellt, ist gegeben durch folgende Gleichung: $${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{1}}\mathrm{=}{\mathrm{<figure-callout\; id="1"\; label="U"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{1}}$$
  
• Setzt man R₁₂ für den Wert des Widerstandes 12 und R₁₃ für den Wert des Widerstandes 13, so gilt dann für die Verlustleistung P_V,₁ innerhalb des Meßwertauswertungsteils 2: $${\mathrm{P}}_{\mathrm{V}\mathrm{,}\mathrm{1}}\mathrm{=}{{\mathrm{I}}_{\mathrm{1}}}^{\mathrm{2}}\mathrm{\cdot }\left({\mathrm{R}}_{\mathrm{12}}\mathrm{+}{\mathrm{<figure-callout\; id="13"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{13}}\right)$$
  
• Setzt man R₁₄ für den Wert des Widerstandes 14 der Hinleitung 3 und R₁₅ für den Wert des Widerstandes 15 der Rückleitung 4, so gilt für die Verlustleistung P_V,₂ auf der Verbindung 5 zwischen dem Meßwertauswertungsteil 2 und dem Meßwerterfassungsteil 1: $${\mathrm{P}}_{\mathrm{V}\mathrm{,}2}\mathrm{=}{{\mathrm{I}}_2}^{\mathrm{2}}\mathrm{\cdot }\left({\mathrm{<figure-callout\; id="14"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{14}}\mathrm{+}{\mathrm{<figure-callout\; id="15"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{15}}\right)$$
  
• Die Leistung P₃, die für das Meßwerterfassungsteil 1 zur Verfügung steht, ist durch die Spannung U₁ der Spannungsquelle 10, die Widerstände R₁₂, R₁₃, R₁₄ und R₁₅ sowie durch den aktuellen Meßwert- und Versorgungsstrom vorgegeben; für die Leistung P₃ gilt: $${\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{P}}_{\mathrm{1}}\mathrm{-}{\mathrm{P}}_{\mathrm{V}\mathrm{,}\mathrm{1}}\mathrm{-}{\mathrm{P}}_{\mathrm{V}\mathrm{,}\mathrm{2}}\mathrm{=}{\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="3"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{3}}$$
  
• Für die Spannung U₃ am Meßwerterfassungsteil 1 gilt: $${\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{U}}_{\mathrm{1}}\mathrm{-}{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{1}}\mathrm{\cdot }\left({\mathrm{R}}_{\mathrm{12}}\mathrm{+}{\mathrm{R}}_{\mathrm{13}}\right)\mathrm{-}{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{2}}\mathrm{\cdot }\left({\mathrm{<figure-callout\; id="14"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{14}}\mathrm{+}{\mathrm{<figure-callout\; id="15"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{15}}\right)$$
  
• Wie die Fig. 1 und 2 zeigen, gilt weiter für die Ströme I₃, I₂ und I₁: $${\mathrm{I}}_{\mathrm{3}}\mathrm{=}{\mathrm{I}}_{\mathrm{2}}\mathrm{=}{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{1}}$$
  
• Damit gilt für die Spannung U₃ am Meßwerterfassungsteil 1: $${\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{U}}_{\mathrm{1}}\mathrm{-}{\mathrm{<figure-callout\; id="3"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_3\mathrm{\cdot }\left({\mathrm{R}}_{\mathrm{12}}\mathrm{+}{\mathrm{<figure-callout\; id="13"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{13}}+{\mathrm{<figure-callout\; id="14"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{14}}\mathrm{+}{\mathrm{<figure-callout\; id="15"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{15}}\right)$$
  
• Für die Leistung P₃, die für das Meßwerterfassungsteil 1 zur Verfügung steht, gilt: $${\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{<figure-callout\; id="1"\; label="U"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{1}}\cdot {\mathrm{I}}_3-{{\mathrm{I}}_3}^2\mathrm{\cdot }\left({\mathrm{R}}_{\mathrm{12}}\mathrm{+}{\mathrm{<figure-callout\; id="13"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{13}}+{\mathrm{<figure-callout\; id="14"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{14}}\mathrm{+}{\mathrm{<figure-callout\; id="15"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{15}}\right)$$
  

With this definition, the following applies:

• The power P ₁ , which provides the voltage source 10 in the Meßwertauswertungsteil 2, is given by the following equation: $${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{1}}\mathrm{=}{\mathrm{<figure-callout\; id="1"\; label="U"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{1}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{1}}$$
  
• If one sets R ₁₂ for the value of the resistor 12 and R ₁₃ for the value of the resistor 13, the following applies for the power loss P _V , ₁ within the measured value evaluation part 2: $${\mathrm{P}}_{\mathrm{V}\mathrm{.}\mathrm{1}}\mathrm{=}{{\mathrm{I}}_{\mathrm{1}}}^{\mathrm{2}}\mathrm{\cdot }\left({\mathrm{R}}_{\mathrm{12}}\mathrm{+}{\mathrm{<figure-callout\; id="13"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{13}}\right)$$
  
• Substituting R ₁₄ for the value of the resistor 14 of the forward line 3 and R ₁₅ for the value of the resistor 15 of the return line 4, then applies to the power loss P _V , ₂ on the connection 5 between the Meßwertauswertungsteil 2 and the Meßwerterfassungsteil 1: $${\mathrm{P}}_{\mathrm{V}\mathrm{.}2}\mathrm{=}{{\mathrm{I}}_2}^{\mathrm{2}}\mathrm{\cdot }\left({\mathrm{<figure-callout\; id="14"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{14}}\mathrm{+}{\mathrm{<figure-callout\; id="15"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{15}}\right)$$
  
• The power P ₃ , which is available for the Meßwerterfassungsteil 1 is determined by the voltage U _{1 of} the voltage source 10, the resistors R ₁₂ , R ₁₃ , R ₁₄ and R ₁₅ and by the current Meßwert- and supply current; for the power P ₃ applies: $${\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{P}}_{\mathrm{1}}\mathrm{-}{\mathrm{P}}_{\mathrm{V}\mathrm{.}\mathrm{1}}\mathrm{-}{\mathrm{P}}_{\mathrm{V}\mathrm{.}\mathrm{2}}\mathrm{=}{\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="3"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{3}}$$
  
• For the voltage U ₃ on the measured value acquisition part 1, the following applies: $${\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{U}}_{\mathrm{1}}\mathrm{-}{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{1}}\mathrm{\cdot }\left({\mathrm{R}}_{\mathrm{12}}\mathrm{+}{\mathrm{R}}_{\mathrm{13}}\right)\mathrm{-}{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{2}}\mathrm{\cdot }\left({\mathrm{<figure-callout\; id="14"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{14}}\mathrm{+}{\mathrm{<figure-callout\; id="15"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{15}}\right)$$
  
• As the Fig. 1 and 2 show further applies to the currents I ₃ , I ₂ and I ₁ : $${\mathrm{I}}_{\mathrm{3}}\mathrm{=}{\mathrm{I}}_{\mathrm{2}}\mathrm{=}{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{1}}$$
  
• Thus applies to the voltage U ₃ at the measured value detecting part 1: $${\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{U}}_{\mathrm{1}}\mathrm{-}{\mathrm{<figure-callout\; id="3"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_3\mathrm{\cdot }\left({\mathrm{R}}_{\mathrm{12}}\mathrm{+}{\mathrm{<figure-callout\; id="13"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{13}}+{\mathrm{<figure-callout\; id="14"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{14}}\mathrm{+}{\mathrm{<figure-callout\; id="15"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{15}}\right)$$
  
• For the power P ₃ , which is available for the measured value acquisition part 1, the following applies: $${\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{3}}\mathrm{=}{\mathrm{<figure-callout\; id="1"\; label="U"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{1}}\cdot {\mathrm{I}}_3-{{\mathrm{I}}_3}^2\mathrm{\cdot }\left({\mathrm{R}}_{\mathrm{12}}\mathrm{+}{\mathrm{<figure-callout\; id="13"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{13}}+{\mathrm{<figure-callout\; id="14"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{14}}\mathrm{+}{\mathrm{<figure-callout\; id="15"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{15}}\right)$$
  

• Für den Stromsteller 9 gilt: $${\mathrm{I}}_{\mathrm{3}}\mathrm{=}{\mathrm{<figure-callout\; id="4"\; label="I"\; filenames="imgf0001.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{4}}$$
  
  
  und $${\mathrm{U}}_{}$$$${\mathrm{}}_{\mathrm{3}}>{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}$$
  
• Für die Verlustleistung P_V,₃ im Stromsteller 9 gilt: $${\mathrm{P}}_{\mathrm{V}\mathrm{,}\mathrm{3}}\mathrm{=}{\mathrm{I}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{U}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="4"\; label="I"\; filenames="imgf0001.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{4}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\mathrm{=}{\mathrm{I}}_{\mathrm{3}}\mathrm{\cdot }\left({\mathrm{U}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\right)$$
  
• Da vorausgesetzt ist, daß der Schaltregler 8 keine Verlustleistung hat, gilt am Schaltregler 8 für die eingangsseitige Leistung P₄ und für die ausgangsseitige Leistung P₅, die der Meßwandlerschaltung 7 zur Verfügung steht: $${\mathrm{<figure-callout\; id="4"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{4}}\mathrm{=}{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\mathrm{\cdot }{\mathrm{I}}_{\mathrm{4}}\mathrm{=}{\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{U}}_{\mathrm{5}}\mathrm{\cdot }{\mathrm{I}}_{\mathrm{5}}$$
  
• Betrachtet man die Leistung P₅, die der Meßwandlerschaltung 7 zur Verfügung steht, so gilt: $${\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{P}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="3"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{3}}\mathrm{\cdot }\left({\mathrm{U}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\right)\mathrm{=}{\mathrm{P}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="3"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}\mathrm{+}{\mathrm{I}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}$$
  

The available for the Meßwerterfassunasteil 1 power P ₃ is thus dependent on the measured value, namely the Meßwert- and supply current I ₃ . At a small measured value when the measured value and supply current I ₃ z. B. 4 mA, is therefore less power available than a large measured value when the Meßwert- and supply current I ₃ z. B. 20 mA. It is now ensured that as large a proportion of the transducer circuit 7 is available from the power P ₃ available to the measured value acquisition part 1, which results from the following:

• For the current controller 9 applies: $${\mathrm{I}}_{\mathrm{3}}\mathrm{=}{\mathrm{<figure-callout\; id="4"\; label="I"\; filenames="imgf0001.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{4}}$$
  
  
  and $${\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}>{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}$$
  
• For the power loss P _V , ₃ in the current controller 9 applies: $${\mathrm{P}}_{\mathrm{V}\mathrm{.}\mathrm{3}}\mathrm{=}{\mathrm{I}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{U}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="4"\; label="I"\; filenames="imgf0001.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{4}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\mathrm{=}{\mathrm{I}}_{\mathrm{3}}\mathrm{\cdot }\left({\mathrm{U}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\right)$$
  
• Since it is assumed that the switching regulator 8 has no power loss, applies to the switching regulator 8 for the input-side power P ₄ and for the output-side power P ₅ , the transducer circuit 7 is available: $${\mathrm{<figure-callout\; id="4"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{4}}\mathrm{=}{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\mathrm{\cdot }{\mathrm{I}}_{\mathrm{4}}\mathrm{=}{\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{U}}_{\mathrm{5}}\mathrm{\cdot }{\mathrm{I}}_{\mathrm{5}}$$
  
• Considering the power P _{5 available} to the transducer circuit 7, the following applies: $${\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{P}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="3"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{3}}\mathrm{\cdot }\left({\mathrm{U}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\right)\mathrm{=}{\mathrm{P}}_{\mathrm{3}}\mathrm{-}{\mathrm{<figure-callout\; id="3"\; label="I"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="3"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{3}}\mathrm{+}{\mathrm{I}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}$$
  

Equation 13 shows that the power P _{5 available} to the transducer circuit 7 can be optimized by the highest possible voltage U ₄ . Since the voltage U ₄ can not be greater than the voltage U ₃ , the difference between the voltage U ₃ and the voltage U _{4 must be} as small as possible. "As small as possible" - instead of "zero" - takes into account that the current controller 9 functionally necessary to, under the control of the transducer circuit 7, representing the measured value To be able to adjust the measured value and supply current I ₃ requires a minimum difference between the voltage U ₃ and the voltage U ₄ .

Since, according to the presupposition, the switching regulator 8 has no power loss, the primary-side power P ₄ is equal to the secondary-side power P ₅ , since the primary-side current I _{4 of} the switching regulator 8 is preset in the steady state, namely equal to the measured value and supply current predetermined by the transducer circuit 7 I ₃ , and since the secondary-side voltage U _{5 of} the switching regulator 8 is constant, a short-term reduction of the current consumption of the transducer circuit 7, ie a short-term reduction of the current flowing through the transducer circuit 7 and the secondary side through the switching regulator 8 current I ₅ , leading to an increase the voltage U ₄ on the primary side of the switching regulator 8, since the current I ₃ , now greater than the current I ₄ , can no longer be absorbed by the switching regulator 8. About the difference of the currents I ₃ and I ₄ - namely I ₃ - 14> 0 - a fictitious capacity is charged and the voltage U ₄ increases. Once the voltage U _{4 has} the desired size - "as large as possible" - has reached, the power consumption of the transducer circuit 7 must be increased again so that the current I _{3 is} equal to the current I ₄ , Since now the voltage U ₄ but larger is now than before, the power P ₄ = U ₄ - I ₄ is now greater than before. Since the voltage U ₅ at the output of the switching regulator 8 is constant, and the current I _{5 is} greater than before, and therefore the power converter circuit 7 available power P ₅ = U ₅ · I ₅ , Thus, it is shown that the measure, to control the current drawn by the transducer circuit 7 so that the voltage drop across the current controller 9, that is, the difference between the voltage U ₃ and the voltage U _4, is as small as possible, to an optimization of the transducer circuit 7 to the available power P ₅ leads.

In the in the Fig. 1 and 2 illustrated embodiments, it is indicated that the switching regulator 8 has a capacitor 16 on the input side. Such a switching regulator 8 is, for example, the switching regulator LT 1176-5 of the company Linea Technology. The capacitor 16 simplifies the control of the voltage U ₄ , as a result, the rate of change of the voltage U ₄ at a setting of I ₃ unlike I ₄ can be greatly reduced.

• Ausgehend von einem kleinen Meßwert und damit einem kleinen Meßwert- und Versorgungsstrom I₃ von z. B. 4 mA, stellt sich ein relativ großer Wert für die Spannung U₄ ein, da die Spannung U₃ auch relativ groß ist, - weil die Spannungsabfälle an den Widerständen 12, 13, 14 und 15 relativ gering sind. Ergibt sich nun sprunghaft ein relativ großer Meßwert und soll folglich ein relativ großer Meßwert- und Versorgungsstrom I₃ eingestellt werden, z. B. 20 mA, so ist das dann nicht möglich, wenn die durch den Kondensator 16 gepufferte Spannung U₄ größer ist als die Spannung U₃, die sich wegen der relativ großen Spannungsabfälle an den Widerständen 12, 13, ₁₄ und 15 einstellen müßte. Da der Stromsteller 9 nur arbeiten kann, wenn die Spannung U₃ größer ist als die Spannung U₄, kann der dem großen Meßwert entsprechende Meßwert- und Versorgungsstrom I₃ von 20 mA nicht eingestellt werden.

Is how that for those in the Fig. 1 and 2 illustrated embodiments, the switching regulator 8 provided on the input side with a capacitor 16, it may come to an operating state in which the Meßwert- and supply current I ₃ can not be set proportional to the measured value:

• Starting from a small reading and thus a small Meßwert- and supply current I ₃ of z. B. 4 mA, sets a relatively large value for the voltage U ₄ , since the voltage U _{3 is} also relatively large, - because the voltage drops across the resistors 12, 13, 14 and 15 are relatively low. Now results in a sudden relatively large measured value and should therefore be set a relatively large Meßwert- and supply current I ₃ , z. B. 20 mA, then that is not possible if the voltage buffered by the capacitor 16 U _{4 is} greater than the voltage U ₃ , which would have to adjust because of the relatively large voltage drops across the resistors 12, 13, ₁₄ and 15. Since the current controller 9 can only work when the voltage U _{3 is} greater than the voltage U ₄ , the large value corresponding Meßwert- and supply current I ₃ of 20 mA can not be adjusted.

To solve the above-mentioned problem is in the in Fig. 2 illustrated embodiment of a circuit arrangement according to the invention, a second, controlled by the transducer circuit 7, activated only when needed power controller 17 which is connected at its input to the input of the first power controller 9 and its output to the return line 4. In this embodiment, the Meßwert- and supply current I ₃ , which should be proportional to the measured value, composed of the current I ₄ via the first current regulator 9 and the current I ₆ via the second current controller 17. Consequently, can also be in the previously described Operating status Set the required measured value and supply current I ₃ .

In the previously described, in Fig. 2 illustrated embodiment of the circuit arrangement according to the invention, the current I ₆ does not contribute to the power P ₅ for the transducer circuit 7 via the second current controller 17; the current I ₆ via the second current controller 17 is therefore undesirable in principle. Consequently, in the embodiment after Fig. 2 additionally provided here second power controller 17 only activated "on demand", namely only and as long as the problem indicated above exists.

For the rest, what is in the Fig. 1 and 2 is not shown, the transducer circuit 7 to control their current consumption and / or to control the second current regulator 17 be parameterized, z. B. via the voltage U _{1 of} the voltage source 10 and / or via the resistors 12 and 13 in the Meßwertauswertungsteil 2 and / or via the resistors 14, 15 of the forward line 3 and / or the return line 4 and / or on the capacity of the input of the switching regulator 8 in parallel capacitor 16. It is also possible, the voltage drop across the first current controller 9, z. B. via an A / D converter, not shown, to control the current consumption of the transducer circuit 7 and / or to control the second current regulator 17 in the transducer circuit 7 introduce.

• Zunächst soll die Spannung U₃ am Eingang des Meßwerterfassungsteils 1, also die Spannung U₃ am Eingang des Stromreglers 9, betrachtet werden. Diese hängt von der Spannung U₁ der Spannungsquelle 10, der Summe der Widerstände 12, 13, 14 und 15 sowie dem durch das Meßwerterfassungsteil 1 fließenden Strom I₃ ab. In der Praxis können sich hier sehr unterschiedliche Charakteristiken durch unterschiedliche Meßwertauswertungsteile 2 und unterschiedliche Verbindungen 5 zwischen dem Meßwerterfassungsteil 1 und dem Meßwertauswertungsteil 2 ergeben. Diese sind bei der Auslieferung des Meßwerterfassungsteils 1 nicht bekannt; das Meßwerterfassungsteil 1 muß sich daher auf die vorgefundenen Verhältnisse automatisch adaptieren.

Now, the invention again with reference to the graphical representations in the Fig. 3 to 6 be explained:

• First, the voltage U ₃ at the input of the Meßwerterfassungsteils 1, so the voltage U ₃ at the input of the current controller 9, are considered. This depends on the voltage U _{1 of} the voltage source 10, the sum of the resistors 12, 13, 14 and 15 and the current flowing through the Meßwerterfassungsteil 1 current I ₃ . In practice, very different characteristics can result here through different measured value evaluation parts 2 and different connections 5 between the measured value acquisition part 1 and the measured value evaluation part 2. These are not known when the measured value acquisition part 1 is delivered; the measured value detecting part 1 must therefore adapt automatically to the conditions found.

In the Fig. 3 characteristic curves are shown which show the voltage U ₃ at the input of the current regulator 9 as a function of the current I ₃ flowing through the measured value acquisition part 1. This is the basis
the characteristic a is a voltage U ₁ of 24 V and a resistance of the connection 5 of 300 Ω,
the characteristic b is a voltage U ₁ of 24 V and a resistance of the compound 5 of 50 Ω and
the characteristic c has a voltage U ₁ of 17 V and a resistance of the connection 5 of 50 Ω.

The characteristic a - for a voltage U ₁ of 24 V and a resistance of the connection of 300 Ω - is particularly widespread, since this characteristic complies with the requirements of intrinsic safety in explosion protection.

Ideally, the voltage U ₄ at the output of the current regulator 9 is one volt below the voltage U ₃ at the input of the current regulator 9. The corresponding characteristic curve d is in Fig. 4 - together with the characteristic a off Fig. 3 - shown.

The current regulator 9 is also necessary because the current I ₅ flowing through the transducer circuit 7 can not be controlled as accurately as is necessary for the current I ₃ representing the measured value.

As already stated, the current controller 9 is controlled by the transducer circuit 7 so that it adjusts a measuring value representing, flowing through the connection 5 Meßwert- and supply current, the current I _3rd For this purpose, the transducer circuit 7 to a microcontroller 18, not shown in detail, which is also supplied by the current flowing through the Meßwerterfassungsteil 1 current I ₃ .

The circuit arrangement according to the invention can be used for a variety of very different transducers 6. The transducer 6 can, for. B. be designed for temperature, pressure, humidity, level or flow detection. In particular, the transducer 6 can be operated clocked, whereby the current consumption of the transducer circuit 7 can be influenced as a whole. Such a clockwise operation is z. B. in a magnetic-inductive flowmeter known (see U.S. Patent 4,766,770 ); also a microwave radar as a transducer 6 can be operated clocked.

If the current I ₅ flowing through the transducer circuit 7 has a pulse-like characteristic, then the current regulator 9 must provide smoothing; a pulse-like characteristic of the current I ₃ , that is, the measured value and supply current representing the measured value, namely, is not desirable. The extent of the necessary smoothing also determines the voltage drop across the current regulator 9 necessary for the operation, that is to say the voltage difference between the voltage U ₃ and the voltage U ₄ .

The present in the circuit arrangement according to the invention is particularly clear when considering two extreme cases, on the one hand the extreme case that the value changes abruptly from 100% to 0%, on the other hand, the extreme case that the measured value changes suddenly from 0% to 100% , Equal to these extreme cases are the so-called failure information, which is characterized by a current I ₃ , which is either less than 3.6 mA or greater than 21 mA. Reference is made to the NAMUR recommendation NE 43 "standardization of the signal level for the failure information of digital transducers with analog output signal", version: 18.01 1994, first edition: 18.01.1994, distributed by the NAMUR office, c / o Bayer AG, building K 9, 51368 Leverkusen.

For the first extreme case where the measured value suddenly changes from 100% to 0%, reference is made to the graph in FIG Fig. 5 , which first shows the characteristics a and d, in addition to the operating points 1, 2 and 3 are drawn.

Starting from the operating point 1. By the current controller 9, the current I _{3 can} change abruptly. Because of the capacitor 16, however, the voltage U ₄ can not change abruptly. This results in a shift from the operating point 1 to the operating point 2.

Assuming an ideal switching regulator 8, ie one which has no power loss, the power available to the transducer circuit 7 (see equation 12) results: $${\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{<figure-callout\; id="4"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{4}}\mathrm{=}{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\mathrm{\cdot }{\mathrm{I}}_{\mathrm{4}}\mathrm{=}\mathrm{17}\mathrm{V}\mathrm{,}\mathrm{4}\mathrm{mA}\mathrm{=}\mathrm{68}\mathrm{mW}\mathrm{,}$$

Desirable, however, is the operating point 3. There, the following performance would be available: $${\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{<figure-callout\; id="4"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\mathrm{4}}\mathrm{=}{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\mathrm{\cdot }{\mathrm{I}}_{\mathrm{4}}\mathrm{=}\mathrm{21}\mathrm{.}\mathrm{8th}\mathrm{V}\mathrm{,}\mathrm{4}\mathrm{mA}\mathrm{=}\mathrm{87}.2\mathrm{mW}\mathrm{,}$$

bzw. $${\mathrm{I}}_{\mathrm{5}}\mathrm{=}{\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{U}}_{\mathrm{5}}\mathrm{=}\mathrm{87},2\mathrm{mW}\mathrm{:}\mathrm{5}\mathrm{V}\mathrm{=}\mathrm{17}\mathrm{,}\mathrm{4}\mathrm{mA}\mathrm{.}$$

If one takes for the voltage U ₅ , so the voltage at the output of the switching regulator 8, which is equal to the voltage at the input of the transducer circuit 7, a constant value of z. B. 5 V, the following results for the two previously calculated power for the current I ₅ : $${\mathrm{I}}_{\mathrm{5}}\mathrm{=}{\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{U}}_{\mathrm{5}}\mathrm{=}\mathrm{68}\mathrm{mW}\mathrm{:}\mathrm{5}\mathrm{V}\mathrm{=}\mathrm{13}\mathrm{.}\mathrm{6}\mathrm{mA}$$

respectively. $${\mathrm{I}}_{\mathrm{5}}\mathrm{=}{\mathrm{P}}_{\mathrm{5}}\mathrm{=}{\mathrm{U}}_{\mathrm{5}}\mathrm{=}\mathrm{87}.2\mathrm{mW}\mathrm{:}\mathrm{5}\mathrm{V}\mathrm{=}\mathrm{17}\mathrm{.}\mathrm{4}\mathrm{mA}\mathrm{,}$$

It now reaches from the operating point 2 of the operating point 3, but not by increasing the current I ₅ . The current I ₄ would immediately greater than the current I ₃ , and it would take 16 charge from the capacitor. This in turn would lead to a reduction of the voltage U ₄ and thus to a shift of the operating point 2 in the undesired direction, namely to a smaller voltage U ₄ . The desired operating point 3 is reached when the current I _{5 is} reduced. The current I ₄ is immediately smaller than the current I ₃ . The capacitor 16 at the input of the switching regulator 8 is charged and the voltage U ₄ increases.

For the second extreme case where the measured value suddenly changes from 0% to 100%, reference is made to the graph in FIG Fig. 6 that, like the Fig. 5 , the characteristic curves a and d shows, in addition, operating points 1, 2 and 3 are located.

As in the first extreme case, even in the second extreme case, a sudden change in the voltage U ₄ , that is, a sudden change in the voltage at the input of the switching regulator 8 is not possible. The current controller 9 is now unable to set the measured value of the 100% current I ₃ , because even if the voltage U ₄ equal to the voltage U ₃ , the power controller 9 so no voltage drop would occur, the Meßwertauswertungsteil 2 via the connection 5 can not supply the corresponding electricity; the operating point 2 is therefore not a possible operating point.

In order to master the second extreme case, the in Fig. 2 illustrated second current controller 17 is required, which can set the corresponding current I ₃ , in this case 20 mA. With the additional power controller 17 so the operating point 3 is possible. The second current controller 17 is therefore not absolutely necessary, but only if the voltage U ₄ can not be reduced at the same rate of change as the measured value can change.

• Vorrangige Regelung: $${\mathrm{I}}_{\mathrm{3}}\mathrm{=}\mathrm{4}\mathrm{mA}\mathrm{+}\mathrm{M}\mathrm{\cdot }\mathrm{16}\mathrm{mA}\mathrm{,}$$
  
  
  wobei sich M als Faktor für den Meßwert von 0 bis 1 ändert.

For the control realized in the microcontroller 18 or with the microcontroller 18, the following now applies:

• Priority regulation: $${\mathrm{I}}_{\mathrm{3}}\mathrm{=}\mathrm{4}\mathrm{mA}\mathrm{+}\mathrm{M}\mathrm{\cdot }\mathrm{16}\mathrm{mA}\mathrm{.}$$
  
  
  where M changes as a factor for the measured value from 0 to 1.

When the voltage U ₄ becomes equal to the voltage U ₃ , the control automatically transitions from the current regulator 9 to the second current regulator 17. This can be done via the microcontroller 18 or by a corresponding hardware.

Subordinate regulation: $${\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{4}}\mathrm{=}{\mathrm{U}}_{\mathrm{3}}\mathrm{-}{\mathrm{U}}_{\mathrm{reserve}}\mathrm{;}$$

If the voltage U _reserve too large, the current I _{5 is} reduced, the voltage Ureserve is too small, the current I _{5 is} increased.

It should be noted that the circuit arrangement according to the invention has been described in connection with a voltage source 10 designed as a DC voltage source in Meßwertauswertungsteil 2, the Meßwert- and supply current I ₃ is thus present as DC. However, the teaching of the invention can be readily applied to embodiments in which as a voltage source an alternating voltage source is used and consequently the measured value and supply current I ₃ is present as alternating current.

Finally, it is expressly stated that what has been said previously in connection with the Fig. 3 to 6 has been explained, also belongs to the invention and is also essential to the invention. Unless the claims are complete or not contained, it remains reserved to supplement the claims accordingly.

Claims (8)

1. A circuit arrangement for measured value detection, transfer and analysis, with a measured value detection section (1), a measured value analyzing section (2) and a connection (5) consisting only of an outgoing conductor (3) and a return conductor (4) between the measured value detection section (1) and the measured value analyzing section (2), wherein the measured value detection section (1) has a measured value recorder (6), a measuring transformer circuit (7), a switch controller (8) connected upstream from the measuring transformer circuit (7) and a current regulator (9) connected upstream from the switch controller (8), wherein the measured value analyzing section (2) has a voltage source (10) and an analyzing circuit (11), and the switch controller (8) delivers a constant operating voltage for the measuring transformer circuit (7), and the first current regulator (9) - controlled by the measuring transformer circuit (7) - sets a measured value and power supply current flowing through the outgoing conductor (3) and the return conductor (4) and representing the measured value, wherein the current consumption of the measuring transformer circuit (7) is controllable and is controlled in such a way that the voltage drop via the current regulator (9) is as to small as possible and wherein a capacitor (16) is connected parallel to the input of the switch controller (8)
   characterized in
   a second current regulator (17) controlled by the measuring transformer circuit (7) and activated only when necessary is provided, and the second current regulator (17) is connected with its input to the input of the first current regulator (9) and with its output to return conductor (4).
2. The circuit arrangement according to claim 1, characterized in that the measuring transformer circuit (7) is programmable to control its current consumption and/or to control the second current regulator (17), e.g. via the voltage of the voltage source (10) and/or resistances (12, 13) in the measured value analyzing section (2) and/or via the resistances (14, 15) of the outgoing conductor (3) and/or of the return conductor (4) and/or the capacitance of the capacitor (16) connected parallel to the input of the switch controller (8).
3. The circuit arrangement according to claim 1 or 2, characterized in that the voltage drop is introduced into the measuring transformer circuit via the first current regulator (9), e.g. via an AD converter, to control current consumption of the measuring transformer circuit and/or to control the second current regulator.
4. The circuit arrangement according to one of claims 1 through 3, characterized in that the measuring transformer circuit (7) has a micro-controller (18) controlling the current regulator (9) and, where applicable, the second current regulator (17).
5. The circuit arrangement according to one of claims 1 through 4, characterized in that when the measured value drops "suddenly", e.g. decreases from 100% to 0%, the current (I₅) flowing through the measuring transformer circuit (7) is reduced in the short term.
6. The circuit arrangement according to one of claims I through 5, characterized in that when the measured value increases "suddenly", e.g. rises from 0% to 100%, the second current regulator (17) 'becomes connected'.
7. The circuit arrangement according to one of claims 1 through 6. characterized in that when the voltage (U₄) at the output of the first current regulator (9) attains the voltage (U₃) at the input of the first current regulator (9), the current control coming from the measuring transformer circuit (7) or from the micro-controller (18) in the measuring transformer circuit (7) is transferred from the current regulator (9) to the second current regulator (17).
8. The circuit arrangement according to one of claims 4 through 7, characterized in that by means of the micro-controller (18) provided in the measuring transformer circuit (7), the current (I₃) flowing through the measured value detection section (1) is controlled with priority and the voltage (U₄) at the output of the current regulator (9) is controlled with secondary importance.

Images