DE102021108400B3 - Circuit arrangement and method for drift compensation - Google Patents

Abstract

A circuit arrangement 1 for drift compensation in resonant circuits for measured value acquisition is proposed, comprising a sensor resonant circuit 2 with a sensor circuit and a sensor element 3, which sensor element 3 is switched into the sensor circuit in series with a capacitive resistor C1, the sensor element 3 being connected to the negative Connection M of an astable multivibrator 5 is connected and generates a frequency change as a function of a variable measured variable. For the purpose of creating a circuit arrangement 1 which allows the measurement value acquisition, for example the temperature, the pressure, the brightness or the humidity, to be improved in its precision and at the same time effectively avoiding an age-related development of measurement inaccuracies, the circuit arrangement 1 Furthermore, a reference resonant circuit 4, which is constructed identically to the sensor resonant circuit 2, the reference resonant circuit 4 and the sensor resonant circuit 2 differ in that the reference resonant circuit 4 does not have a sensor element 3. The outputs 6 of the two astable flip-flops 5 are connected to an evaluation unit 7 for drift compensation.

Description

The present invention is based on a circuit arrangement designed according to the preamble of the main claim for drift compensation in resonant circuits for measured value acquisition. A method for drift compensation in resonant circuits for measured value acquisition is also described.

A large part of the sensor system is based on so-called sensor or measuring oscillating circuits, also called RC measuring oscillating circuits. Previously known circuit arrangements based on measuring oscillating circuits comprise, in addition to a resistor and a capacitance (capacitor), a comparator and a sensor element. A changing physical variable, for example the temperature, the pressure, the humidity, the brightness, the noise level or the like, changes the resistance or the capacitance of the sensor element, which changes the output frequency of the comparator of the measuring oscillating circuit. A circuit arrangement based on measuring oscillating circuits for temperature or pressure measurement is, for example, off JP S63-316 509 A known. In order to improve the accuracy of the measured value acquisition, this document proposes that the stability of the frequency of the oscillating circuit be determined by integrating a crystal oscillator so that aging effects of the other components of the oscillating circuit, which influence the output frequency of the comparator due to the change in the frequency of the oscillating circuit, are no longer so important.

The problem with previously known circuit arrangements based on measuring oscillating circuits is that the accuracy of the measured value acquisition suffers from a drift over time. Such a drift leads to a change in the output frequency of the comparator of the measuring oscillating circuit, for example as a result of the changing temperature or the aging of the oscillating circuit components, capacitor and / or resistor. This results in the disadvantage for the user that the measurement value acquisition, for example a temperature measurement in an installation module, in order to control the heating system or the blinds depending on the determined room temperature as a building technology actuator, is or becomes imprecise and undesired incorrect control of the heating system, the Blinds or the like are brought about. The circuit arrangement improved in this regard according to JP S63-316 509 A Although it represents a step in the right direction, it can ultimately not provide any elimination of the influences of aging of the components of the oscillating circuit, which is necessary for long-term precise measurement, despite the great design and cost-technical effort (use of a crystal oscillator). Rather, these influences of aging of the components of the measuring oscillating circuit are consciously accepted (albeit to a lesser extent).

A circuit and a method for determining the oscillation behavior for determining external influences are known from WO 2014/206 664 A1. The oscillation behavior is modified by changing external influences, the oscillation behavior being determined by sampling at a plurality of predetermined frequencies. This allows a particularly simple implementation.

EP 0 927 877 A2 discloses a measuring device and a method for measuring the fill level in a tank, the fill level signal being particularly precise and noise-free and the measuring device being inexpensive to manufacture.

In U.S. 4,590,575 A a dielectric compensated online measurement of substance levels is disclosed, which does not require any calibration effort. Inside the tank, the level of which is to be measured, there are two probes, a measuring probe and a reference probe.

CH 648 657 A5 discloses a method by means of which it is possible to precisely record measured values by means of frequency modulation on a measuring oscillator, without the need for a stabilized supply voltage and without additional cooling precautions having to be taken. For this purpose, a reference oscillator that is closely coupled to the measuring oscillator in terms of temperature and supply is used and the frequency of the measuring oscillator is related to that of the reference oscillator.

It is also off DE 10 2019 108 680 B3 an electrical installation module with a housing containing electrical / electronic components, with a support plate that covers the electrical / electronic components on the operator side and with an electrical sensor designed as a measuring resistor for precise and simple detection of a measured variable, such as temperature or humidity. For this purpose, the sensor is arranged on the operator-side side of the support plate, its electrical connections being led to the other side of the support plate and connected to the electrical / electronic components.

Proceeding from circuit arrangements based on measuring oscillating circuits embodied in this way, the present invention is based on the object of creating a circuit arrangement which allows the acquisition of measured values, for example the temperature, the pressure, the brightness or the air humidity, to improve its precision and at the same time to effectively avoid an aging-related development of measurement inaccuracies due to the ambient temperature.

According to the invention, this object is achieved by the features specified in the main claim and in the independent method claim.

The circuit arrangement according to the invention for drift compensation in resonant circuits for measured value acquisition comprises a sensor resonant circuit with a sensor circuit and a sensor element, which sensor element is connected in series with a capacitive resistor in the sensor circuit. The sensor element is connected in series with the capacitive resistor to the negative connection of an astable multivibrator. The sensor element, the resistance and / or capacitance of which changes due to a varying measured variable, brings about a change in frequency on the output line of the astable multivibrator.

To eliminate the drift influences of the sensor resonant circuit components, such as resistance and / or capacitance as a result of aging or a change in temperature, the circuit arrangement according to the invention cleverly has a reference resonant circuit constructed identically to the sensor resonant circuit. In the context of this invention, identically constructed means that the components are identical in construction, preferably even come from a production batch, in order to achieve perfect elimination of the effects of drift.

The only difference between the sensor oscillating circuit and the reference oscillating circuit is that the sensor oscillating circuit has the sensor element connected to the negative connection of the astable multivibrator, but the reference oscillating circuit does not have a sensor element.

For drift-adjusted measured value acquisition, the outputs of the two astable multivibrators are connected to an evaluation unit, preferably common with a view to cost savings. This advantageously enables the evaluation unit to separate the drift effect, which falsifies the measurement result over time, from the actual measurement result: This is based on the inventive approach that the drift effect caused, for example, by temperature changes or aging phenomena, is the same with regard to the identical oscillating circuit components in both oscillating circuits. The sensor oscillating circuit having the sensor element thus supplies a measured value, for example a temperature value, which can be adjusted by the evaluation unit by simple mathematical operations to remove the drift effect of the oscillating circuit components, which can be detected separately from the sensor oscillating circuit via the reference oscillating circuit, which is identical for both oscillating circuits.

In the circuit arrangement according to the invention, the sensor element particularly preferably has a resistance value that changes in response to a changing physical variable, such as temperature, air humidity and / or air pressure.

According to an embodiment of the circuit arrangement according to the invention that is particularly suitable for use in an installation module, the capacitive resistor is a capacitive series resistor for the sensor element, the capacitive series resistor being designed as a protective capacitor, for example of the Y class, in particular the Y1 class. It is also possible to use Y2 capacitors. By means of such a protective measure, the sensor can be arranged directly on or behind a surface, in particular a user interface, of an installation module, so that it is in direct contact with the environment from which it is to record the measured variable, such as temperature, humidity or the like, can be arranged.

According to a further developed embodiment of the circuit arrangement according to the invention, the astable multivibrators, both of the sensor circuit and of the reference resonant circuit, have a comparator and a comparator circuit provided by resistors. The comparator circuit comprises a voltage divider, from whose node located between the resistors of the voltage divider a partial voltage is branched off and applied to the non-inverting input of the comparator. A resistor is also used to connect the node to the output of the comparator. In addition to this partial voltage circuit branch, the comparator circuit has a circuit branch in which the capacitive resistor is integrated. This is connected to the inverting input of the comparator. This circuit branch also has a resistor which connects the inverting input of the comparator to its output. Since the sensor element is connected to this circuit branch in the sensor oscillating circuit, it can also be addressed as a sensor circuit. The resistance range of the sensor element can extend, for example, between 5 and 30 kΩ. The bandwidth of the frequency change caused by such a sensor element is correspondingly large. This means that such a sensor element, which is typically designed as a measuring resistor, is able to withstand the measured variable to be recorded, such as the temperature, very sensitive. The design of the capacitive resistor as a protective resistor ensures the necessary safety requirements, which is not the case with previously known flip-flops of this type.

According to a preferred development of the circuit arrangement according to the invention, the sensor element is arranged on the outside of the support plate of an installation module. This ensures that, in the event of a temperature measurement, the room temperature is recorded as precisely as possible and not a local temperature within the installation module that is not relevant for the user.

In a particularly preferred development of the circuit arrangement according to the invention, the material connecting the electronic components on the circuit board carrying the circuit arrangement has a conductivity at 0 ° C. of at least 20 S / m, in particular at least 40 S / m. The material connecting the electronic components is also made identical for both oscillating circuits. This ensures that there is no temperature distortion between the two oscillating circuits; consequently, both resonant circuits are subject to the same temperature-optimized boundary conditions in order to achieve optimal drift compensation.

The invention also relates to a method for drift compensation in resonant circuits for measured value acquisition, in which method an evaluation unit determines a directly compensated measured value on the basis of the output signals of a sensor resonant circuit having a sensor element and a reference resonant circuit, the reference resonant circuit being constructed identically to the sensor resonant circuit, but no sensor element having. Because of this configuration of the two oscillating circuits, the drift effects can be isolated from the actual measured value for determining the drift-compensated measured value. The advantage of this method is that as a result, with particularly simple means, an optimal, that is to say complete, drift compensation can be carried out in resonant circuits for measured value acquisition, which in particular is independent of aging processes. Such a method is preferably carried out particularly efficiently using the circuit arrangement according to the invention.

In a further development of the method according to the invention, the sensor circuit and the reference resonant circuit include an astable trigger stage that provides an output signal. The sensor element in the sensor oscillating circuit is connected to the negative connection of the astable multivibrator of the sensor oscillating circuit, so that the output signal of the sensor oscillating circuit is a frequency change as a function of a variable measured variable. Such a measured variable can be drift-adjusted by the evaluation unit and converted into a controlled variable - for example the current room temperature - and introduced into a control or regulating circuit, for example a heating system. In this way, it is possible to carry out a drift-compensated room temperature control.

According to one embodiment of the method according to the invention, the reference resonant circuit and / or the sensor resonant circuit are measured with regard to their frequency, the sensor element in the sensor resonant circuit being temporarily bridged so that the values of the capacitances in the sensor and reference resonant circuit can be inferred. The frequency obtained is then stored in a memory unit, the bridging of the sensor element being canceled. The drift-related change in the frequency of the reference oscillating circuit is then converted into a change in capacitance and the measured value determined by the sensor oscillating circuit is drift-compensated: The evaluation unit calculates the drift-related change in the capacitance of the reference oscillating circuit as a drift-related change in the capacitance of the sensor oscillating circuit from the determined measured value. This embodiment of the method according to the invention is a particularly practicable and simple solution for drift compensation, since the frequency measurements and the conversion into a change in capacitance are relatively simple and robust process steps and perfect drift compensation is permanently achieved. In a particularly simple case, the drift-related change in the capacitance of the sensor resonant circuit is calculated out by the evaluation unit by subtracting or adding the change in the capacitance of the reference resonant circuit from or to the change in the capacitance of the sensor resonant circuit.

• 1: eine schematische Darstellung der erfindungsgemäßen Schaltungsanordnung;
• 2: eine bevorzugte Ausführungsform der erfindungsgemäßen Schaltungsanordnung.

The invention will be explained in principle in more detail on the basis of several exemplary embodiments. Show:

• 1 : a schematic representation of the circuit arrangement according to the invention;
• 2 : a preferred embodiment of the circuit arrangement according to the invention.

In the various figures, the same parts are always provided with the same reference numerals and are therefore usually only named or mentioned once.

In 1 is the circuit arrangement according to the invention 1 for drift compensation in resonant circuits for measured value acquisition shown schematically. In essence, the circuit arrangement according to the invention comprises 1 a sensor oscillating circuit 2 with a sensor element 3 , which generates a frequency change as a function of a variable measured variable, as well as a reference resonant circuit 4th , which is identical to the sensor oscillating circuit 2 so built up is both resonant circuits 2.4 one capacitance C1 and an astable flip-flop 5 exhibit. The reference resonant circuit 4th and the sensor oscillating circuit 2 differ in that the reference resonant circuit 4th no sensor element 3 having. The components of the oscillating circuits 2, 4 are identical in construction, preferably even coming from one production batch, in order to achieve perfect elimination of the drift effects of the oscillating circuit components. The exits 6th of the two astable tilting stages 5 are connected to an evaluation unit 7th , for example a microcontroller or an FPGA (Field Programmable Gate Array) connected. This is the output signal of the sensor oscillating circuit 2 a frequency change as a function of a changeable measured variable, which measured variable by the evaluation unit 7th by comparing the output signal of the sensor oscillating circuit 2 and the reference resonant circuit 4th Adjusted for drift and preferably converted into a controlled variable and introduced into a control or regulating circuit, for example a heating system.

The detailed circuit arrangement according to the invention is particularly preferred 1 according to 2 . According to this embodiment, the astable flip-flops have 5 , both the sensor and the reference resonant circuit 2, 4, via a comparator K and one through resistances R1-R5 provided comparator circuit 8th . The comparator circuit 8th includes a voltage divider 9 , of which between the resistances R1-R5 of the voltage divider 9 located node 10 a partial voltage is branched off and to the non-inverting input 11 of the comparator K connected. In addition, a resistor is used to connect the node 10 with the exit 6th of the comparator K . In addition to this partial voltage circuit branch, the comparator circuit has 8th via a circuit branch in which the capacitive resistance C1 of the oscillating circuit is integrated. This is via a negative connection to the inverting input 12th of the comparator K connected. This circuit branch also has a resistor, which is the inverting input of the comparator K connects with its output. The reference resonant circuit 4th is identical to the sensor oscillating circuit 2 built, with the reference resonant circuit 4th and the sensor oscillating circuit 2 differ only in that the reference resonant circuit 4th no sensor element 3 having. The outputs are for final measurement value acquisition and drift compensation 6th of the two astable tilting stages 5 to an evaluation unit 7th connected. The exit 13th the evaluation unit 7th can then be introduced into a control or regulating circuit.

List of reference symbols

1

Circuit arrangement

2

Sensor oscillating circuit

3

Sensor element

4th

Reference resonant circuit

5

astable flip-flop

6th

exit

7th

Evaluation unit

8th

Comparator circuit

9

Voltage divider

10

Junction

11th

non-inverting input

12th

inverting input

13th

exit

C1

capacitive resistance

K

Comparator

R1-R5

resistance

M.

negative connection

Vpp

Operating voltage

Claims (8)

Circuit arrangement for drift compensation in resonant circuits for measured value acquisition, comprising a sensor resonant circuit (2) with a sensor circuit and a sensor element (3), which sensor element (3) is connected in series with a capacitive resistor (C1) in the sensor circuit, the sensor element ( 3) is connected to the negative connection (M) of an astable multivibrator (5) and generates a frequency change as a function of a variable measured variable, the circuit arrangement (1) also having a reference resonant circuit (4) which is constructed identically to the sensor resonant circuit (2) is, the reference resonant circuit (4) and the sensor resonant circuit (2) differ in that the reference resonant circuit (4) has no sensor element (3) and that the outputs (6) of the two astable multivibrators (5) to an evaluation unit (7) are connected, characterized in that the astable flip-flops (5) have a comparator (K) with a through resistance de provided comparator circuit (8), which comparator circuit (8) comprises a voltage divider (9), of which a partial voltage is applied to the non-inverting input (11) of the comparator (K) and with the interposition of a resistor also to the Output (6) of the comparator (5) is applied, as well as a capacitive circuit branch with the capacitive resistor (C1) connected to the inverting input (12) of the comparator (K) and an inverting input (12) of the comparator with its output (6 ) includes connecting resistance. Circuit arrangement according to Claim 1 , characterized in that the sensor element (3) has a resistance value that changes in response to a changing physical variable, such as temperature, air humidity and / or air pressure. Circuit arrangement according to one of the Claims 1 or 2 , characterized in that the capacitive resistor (C1) is a capacitive series resistor for the sensor element (3), the capacitive series resistor being designed as a protective capacitor, for example of the Y class. Circuit arrangement according to one of the Claims 1 until 3 , characterized in that the sensor element (3) is arranged on the outside of the support plate of an installation module. Circuit arrangement according to one of the Claims 1 until 4th , characterized in that the material connecting the electronic components on the circuit board carrying the circuit arrangement (1) has a conductivity at 0 ° C of at least 20 S / m, in particular at least 40 S / m. Method for drift compensation in oscillating circuits for recording measured values, in which method an evaluation unit (7) determines a drift-compensated measured value on the basis of the output signals of a sensor oscillating circuit (2) having a sensor element (3) and a reference oscillating circuit (4), the reference oscillating circuit (4) is constructed identically to the sensor oscillating circuit (2), but has no sensor element (3), characterized in that the reference oscillating circuit (4) and / or the sensor oscillating circuit (2) are measured with regard to their frequency, the sensor element (3) in the sensor oscillating circuit ( 2) is temporarily bridged so that conclusions can be drawn about the values of the capacitances (C1) in the sensor and reference oscillating circuit and these are stored in a memory unit, whereby the bridging of the sensor element (3) is canceled and the drift-related change in frequency of the reference resonant circuit (4) is converted into a change in capacitance and the measured value determined by the sensor oscillating circuit (2) is drift-compensated by the evaluation unit (7) calculating the drift-related change in the capacitance of the reference oscillating circuit (4) as a drift-related change in the capacitance of the sensor oscillating circuit (2) from the determined measured value. Procedure according to Claim 6 , characterized in that the sensor resonant circuit (2) and the reference resonant circuit (4) comprise an astable, output signal providing, flip-flop (5) and the sensor element (3) to the negative connection (M) of the astable flip-flop (5) of the sensor resonant circuit ( 2) is connected so that the output signal of the sensor oscillating circuit (2) is a frequency change depending on a variable measured variable. Procedure according to Claim 7 , characterized in that the H calculation of the drift-related change in the capacitance of the sensor oscillating circuit (2) is carried out by the evaluation unit (7) by subtracting or respectively subtracting the change in the capacitance of the reference oscillating circuit (4) from or to the change in the capacitance of the sensor oscillating circuit (2) is added.

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